West, Ian M. 2016. Cheddar Gorge - Geological field guide. Supplement to Geology of the Wessex Coast. Internet site: www.southampton.ac.uk/~imw/Mendip-Hills.htm. By Ian West, Romsey, and School of Ocean and Earth Science, Southampton University. Version: Revised 23rd January 2016.

Geology of Cheddar Gorge, Mendip Hills

Ian West ,
Romsey, and
Faculty of Natural and Environmental Sciences,
Southampton University,
Webpage hosted by iSolutions, Southampton University

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Cheddar Gorge, is a classic gorge or canyon, geological exposure of Carboniferous Limestone, and it is most famous for its caves. The thick limestone is varied and fossiliferous in parts, but much of the rock is very hard, non-porous limestone, the details of which are obscured by a dark grey surface. However, the geological details have long been studied. This webpage is intended by means of photographs, text, maps and diagrams to place the gorge and its caves into geological perspective.

Click on images for larger, higher resolution versions!

Cheddar Gorge, Mendip Hills, Somerset, introductory view down the gorge, just up from The Horseshoe, 29th July 2015

A general view of the cliffs seen to the south of Landslip Quarry, Cheddar Gorge, including the grassy Amphitheatre and the high, vertical cliff, on the right, frequently used for rock-climbing

MENDIP CARBONIFEROUS WEBPAGES:
Cheddar Gorge - Geology
- (this webpage)
Mendip Hills - Geology (other than Cheddar Gorge)
Carboniferous Geology Bibliography

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1 - INTRODUCTION TO CHEDDAR GORGE
1-INT-1. 1-INTRODUCTION - General
1-INT-2. 1-INTRODUCTION - Safety
1-INT-3. 1-INTRODUCTION - Topographic
1-INT-4. 1-INTRODUCTION - Geological Maps
1-INT-5. 1-INTRODUCTION - Geology - Introduction
1-INT-6. 1-INTRODUCTION - Geology - Introduction continued

1 - INTRODUCTION - 6

Carboniferous Limestone - General Introduction

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2 - STRATIGRAPHY OF CHEDDAR GORGE
2-STRAT-1. 2-STRATIGRAPHY - Stratal Succession ]
2-STRAT-1a. 2-STRATIGRAPHY - Stratal Succession - Hypersaline Lagoonal Phases (Modiola Phases)
2-STRAT-2. 2-STRATIGRAPHY - Cheddar Oolite Formation
2-STRAT-3a. 2-STRATIGRAPHY - Clifton Down Limestone Formation (1) Introduction
2-STRAT-3b. 2-STRATIGRAPHY - Clifton Down Limestone Formation (2) Sequence
2-STRAT-4. 2-STRATIGRAPHY - Triassic, Dolomitic Conglomerate Formation
2-STRAT-5. 2-STRATIGRAPHY - Pleistocene Head
2-STRAT-6. 2-STRATIGRAPHY - Cave Deposits
2-STRAT-7. 2-STRATIGRAPHY - Alluvium

2a - STRUCTURE AND TECTONICS OF CHEDDAR GORGE
2a-STRUCTURE-1 Structure and Tectonics - Introduction
2a-STRUCTURE-2 Structure and Tectonics - Strike-Slip-Faulting-
2a-STRUCTURE-3 Structure and Tectonics - Extensional Fractures -
2a-STRUCTURE-4 Structure and Tectonics - Other Tectonism-

3 - GEOMORPHOLOGY AND HYDROGEOLOGY OF CHEDDAR GORGE
3-GEOMORPH-1. Geomorphology - Introduction
3-GEOMORPH-2. Geomorphology - The Origin of Cheddar Gorge (section to be added)
3-GEOMORPH-3. Geomorphology - Quaternary Erosion.
3-GEOMORPH-4. Hydrogeology - Origin of Cave Systems.

4 - LOCATIONS IN CHEDDAR GORGE
(Up-gorge to Down-Gorge and then high south cliffs)

4-LOCAT-1. Location - Black Rock Gate
4-LOCAT-2. Location - Black Rock Gate to the old Reservoir
4-LOCAT-3. Location - Old Reservoir
4-LOCAT-4. Location - Above Horseshoe Bend
4-LOCAT-5. Location - Horseshoe Bend
4-LOCAT-5a. Location - Horseshoe Bend - Brachiopod Beds
4-LOCAT-5b. Location - Horseshoe Bend - Stromatolites
4-LOCAT-5c. Location - Horseshoe Bend - [other]
4-LOCAT-6. Location - Between Horseshoe Bend and Landslip Quarry
4-LOCAT-7. Location - Landslip Quarry
4-LOCAT-7a. Location - Amphitheatre and High Climbing Wall(almost opposite Landslip Quarry)
4-LOCAT-8. Location - Cooper's Hole Area
4-LOCAT-9. Location - Strike-Slip Fault Area
4-LOCAT-10. Location - Gough's Cave Entrance and Cliffs
4-LOCAT-11. Location - Resurgence
4-LOCAT-12. Location - Cox's Cave area
4-LOCAT-13. Location - Lion Rock
4-LOCAT-14. Location - Pond Area
4-LOCAT-15. Location - Cheddar Village
4-LOCAT-16. Location - Jacob's Ladder and Lookout Tower
4-LOCAT-17. Location - High Rock Viewpoint (top cliffs)
4-LOCAT-18. Location - Pinnacles Area (top cliffs)
4-LOCAT-19. Location - Top Cliffs (up-gorge)
4-LOCAT-20. Location - Batts Coombe Quarry (NW of Cheddar Gorge)

5 - FOSSILS IN CHEDDAR GORGE
5-FOSSILS-1. Fossils - Corals of the Lower Clifton Down Limestone.
5-FOSSILS-2. Fossils - Brachiopods of the Lower Clifton Down Limestone

5-FOSSILS-3. Other Fossils

6 - CAVES IN CHEDDAR GORGE
6-SHOWCAVES-1. Caves - Introduction - Show-Caves Location
6-SHOWCAVES-2. Caves - Introduction - Cave Systems

6a - SHOW CAVES IN CHEDDAR GORGE - GOUGH'S CAVE
6a-GOUGHS-1. Gough's Cave - Introduction
6a-GOUGHS-2. Gough's Cave -
6a-GOUGHS-3. Gough's Cave - Stanton's Survey
6a-GOUGHS-4. Gough's Cave -
6a-GOUGHS-5. Gough's Cave -

6b - SHOW CAVES IN CHEDDAR GORGE - COX'S CAVE
6b-COX-2. Cox's Cave - Introduction
6b-COX-2. Cox's Cave -

7 - OTHER CAVES IN CHEDDAR GORGE
7-OTHERCAVES-1. Other Caves -
7-OTHERCAVES-2. Water Input above Horseshoe Bend
7-OTHERCAVES-3. Other Caves -
7-OTHERCAVES-4. Great Oones Hole -
7-OTHERCAVES-5. Pride Evans Hole -
7-OTHERCAVES-6. Caves -
7-OTHERCAVES-7. Caves -

8 - MISCELLANEOUS IN CHEDDAR GORGE
8-MISC-1. Red Staining, probably Triassic
8-MISC-2. Miscellaneous -
8-MISC-3. Miscellaneous -
8-MISC-4. Miscellaneous -

9 - ACKNOWLEDGEMENTS
9-ACKNOW-1. Acknowledgements -

10 - REFERENCES
10-REFERENCES-1. References -
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1 - INTRODUCTION - 1

General

Cheddar Gorge is a famous locality in southern England. It is notable as a canyon-like feature, unusual in this part of the world, and with extensive cave systems. These are in Carboniferous Limestone of about 350 million years old. The gorge is visited by vast numbers of people. There are many car parks, often completely or nearly filled. It is a busy place, particularly in the lower, western part, where people go to visit Gough' Cave and Cox's Cave, both of them being well-known show-caves with entry fees. In geological terms the gorge is interesting in terms of geological structure, and it has a consistent dip of about 20 degrees in a direction towards the south-south west. The Carboniferous Limestone here is unusually thick, about a kilometre in total, although only a part, high in the succession is exposed in the gorge. The place is rather disappointing in terms of visible fossils and not many are at all conspicuous. However, the limestones are at certain levels full of brachiopods and corals. The hard lithification of the limestone and the peculiar dark, almost black, weathering, makes them very difficult to see. The origin of the gorge is particularly interesting and usually attributed to erosion by the outflow of melt-water in the late Pleistocene ice age. This topic will be discussed further, in a part of the webpage yet to be added.

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2 - INTRODUCTION - SAFETY

Respect private property; both sides and the base of Cheddar Gorge is on private land, and abide by safety rules, regulations and official notices. Do not enter caves, other than show-caves, without permission and the necessary expertise and equipment. Do not climb the cliffs to get to promontories or caves, without proper equipment and necessary expertise. To the casual visitor the road traffic is the greatest hazard.

Many of the exposures in this area are in quarries, either working or abandoned. Please abide strictly by the rules of working quarries. In abandoned quarries take care not approach from above unstable cliff edges.

In the old quarry, and particularly in the road or road-side footpaths, take care with regard to risk of falling rock. There is risk at various places and there are small signs on the cliff-base rocks, indicating the danger. In some places, as at Horsehoe Bend, some blocks of fallen rock can be seen at the foot of cliffs.

Do not hammer chert, which occurs in the Carboniferous Limestone, and which, when struck, can give off very dangerous splinters that can cause loss of eye sight. Take the usual precautions of using sturdy footware and take suitable clothing when walking on upland areas. Be particularly careful with the steep walls of Cheddar Gorge. Do not climb these, and do not ascend other than by using proper footpaths. Take car on irregular and/or slippery rocks in and around Cheddar Gorge and other localities. Beware of the risk of occasional falling rocks in the gorge. Do not enter caves, other than commercially operated ones, and do not undertake caving without proper equipment and without the assistance of experienced people and knowledge of the cave systems.

When making geological studies in Cheddar Gorge, Burrington Coombe or other places, take care not to ignore road traffic. Fast-moving cars and other vehicles can be a significant risk, to individual geologists or students and particularly to parties walking on the roads. Note that there is no roadside pavement in Cheddar Gorge, there are many bends and vehicles, particularly cars can pass close by and at some speed. It is easy to be involved in geological study or geological photography and to accidently walk backwards onto the busy and rather narrow road.

Take care on irregular or loose blocks, as in Landslip Quarry, Cheddar Gorge and other places. It is easy to slip and to put a foot down a fissure.

In the coastal extension of the Mendip Hills in the Weston-super-Mare area, there are risks from rising tide and from walking into soft mud at low tide. This webpage is purely descriptive and it does not recommend that any particular activity takes place. It is not an itinerary and not a climbing guide, collecting guide, caving guide or even a walking route guide.

You do not have to go anywhere and if you do go to a particular place, you go at your own risk. You are not advised or encouraged here to rock-climb, enter caves or take risks with traffic; you are not advised to hammer anything, remove anything or make yourself a nuisance to tourists. It is your own responsibility to avoid falling down rocks, and if a rock falls on you, it is the result of risk which you take.

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1 - INTRODUCTION - 3

Introductory Topographic Maps

An introductory and simplified contour map of Cheddar Gorge, Mendip Hills, Somerset

. A map showing local detail of parts of Cheddar Gorge, Mendip Hills, Somerset

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A simple map of part of Cheddar Gorge, Mendip Hills, Somerset, based an old notice board, showing some location names that are not present on other maps.

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Cheddar Cliffs in lower Cheddar Gorge with diagrams relating topographic features and geological outcrops, Mendip Hills, Somerset

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1 - INTRODUCTION - 4

Geological Maps

Purchase of Available BGS Geological Maps of the Mendips and Cheddar Gorge is, of course, recommended. They are usually available from the BGS (British Geological Survey) Bookshop online, and at low cost. They are well-worth buying if you are interested in the geology of the area.

A special Geological Sheet ST 45 Cheddar, scale 1:25,000 covers the Cheddar area in detail. This map really should be obtained by anyone interested in the geology of this area. It is very clear and easy to read and it explains the Cheddar area in its structural perspective.

For the eastern Mendips in broader terms, see the British Geological Survey, Wells Sheet, No. 280, Solid and Drift and the the Frome Sheet, No. 281, Solid and Drift, 1:50,000 of the British Geological Survey. These maps can be purchased from the BGS bookshop, online.

Example part of the BGS Geological Map, 1:25,000, Sheet 45, and which includes Cheddar Gorge, Mendip Hills, Somerset

See also the following:
Institute of Geological Sciences [now the British Geological Survey], Bristol District, Solid and Drift, One Inch Series, parts of sheets 250, 251, 264, 265, 280 and 281. The old 1946 edition, with additions in 1956, is largely the basis for the redrawn map below (which not a direct copy and not a photocopy), but other maps have also been used. See the latest version of the Bristol District geological map from BGS.

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A simplified, redrawn, general geological map of part of the Mendip Hills area, to show the structure and its relationship to Cheddar Gorge, Somerset, based mainly on old geological maps, and with topography not shown

Above is the very simplified geological map of the Mendips and the area around Cheddar Gorge. It has been completely redrawn largely based on old maps, but with some updating of nomenclature. No topography is shown.

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A completely redrawn, geological map of Cheddar Gorge, Mendip Hills, Somerset, with various modifications but based on Green and Welch, 1965, with minor additions from the BGS 1966 map and other sources

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The following are some brief comments on the simplified geological map, provided above. This map has been completely manually redrawn, pixel by pixel, with basic geological information and no topographic data. Colours are different. It is based, without geological revision (except some nomenclatural changes) on the two British Geological Survey maps of the area of interest around Cheddar Gorge, and these are referred to below. It is merely introductory and for general educational purposes and is not at all intended as any substitute for obtaining and studying the appropriate British Geological Survey Maps. Indeed, this effectively advertises them. The British Geological Survey Maps also show topographic data and place names (which are not on the simplified map provided here.

Various editions exist of the following relevant maps and purchase of appropriate available versions is strongly recommended from the BGS Bookshop Online. They are both very good and very interesting maps and have been available in various editions at different years [the specialist will notice terminological differences]:

BGS. Geological Sheet ST 45 (Solid and Drift Edition) Cheddar, Scale 1: 25,000, [About 2 and a half inches to one mile}. Institute of Geological Science or British Geological Survey. Classical Areas of British Geology Series. 1959; 1969. There is a new edition of 1983. Six Inch Sheets are also available from BGS.

BGS. Geological Sheet - Bristol District, Special Sheet, (Solid and Drift Edition). Parts of BGS Geological Maps - sheets 250, 251, 264, 265, 280 and 281. (These specific sheets may also be relevant, if available).

BGS. Geological Sheet - Bristol 264. [not to be confused with the Bristol District Sheet]. 1:50,000 edition. This does not include Cheddar Gorge or the nearby Mendip Hills. It deals with an area to the northwest, including Bristol, Avonmouth, Filton, Clevedon, Yatton, Flax Bourton and Keynsham.

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1 - INTRODUCTION - 5

Geology General Introduction

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Thickness of Carboniferous Limestone

The thickness of the Carboniferous Limestone in the Mendip area and in relation to South Wales has been given by George (1972), fig. 1. The thickness is very great in the Mendips, being between 900 metres in the northwestern part and increasing to 1100 metres in the southeastern part of the range of hills. At Cheddar Gorge the thickness is roughly about 1 kilometre. Compared to other areas, this great thickness is similar to that in the Gower Peninsula, South Wales. The thickness is less to the north, and is soon zero, as St. George's Land is approached (i.e. now central Wales). The increase in thickness towards the south is greatest at Bosherton in the Pembrokeshire area, where the Lower Carboniferous or Dinantian (Avonian in old terminology) reaches almost 1500 metres. Thus the Mendip sequence is a very thick carbonate facies. It is also near the southern limit of the limestone facies. Further to the south, in Devon, the non-carbonate Culm facies occurs. Note that in spite of the great thickness of Carboniferous Limestone, there, only the uppermost part is seen in the lower, much publicly visited, part of Cheddar Gorge

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The Carboniferous Limestone of the Mendips is of shelf facies. It has several oolite horizons which are clear indicators of high-energy, clear shallow water. Fossil coral remains are common, again indicating shallow, marine water. So, it is a major and very thick, carbonate shelf facies, showing only minor oscillations in depth and of specific type of carbonate rock. It is quite surprising that carbonate shelf facies could be maintained in fairly uniform conditions for such a long interval of time.

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Lion Rock of Clifton Down Limestone and at the entrance to Cheddar Gorge, Mendip Hills, Somerset, 6th August 2015

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Rectilinear jointing and bedding are structures controlling the topography of the cliffs of Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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From near Gough's Cave, looking up Cheddar Gorge, Mendip Hills, Somerset, in stormy conditions, with approaching rain

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A Southampton University student field trip to Cheddar Gorge, Mendip Hills, Somerset, in April 1998

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A composite image for location purposes, the bus turning area, up Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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1 - INTRODUCTION - 6

Carboniferous Limestone - Introduction continued.

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Mineral Composition

The Carboniferous Limestone is a thick, hard, old limestone. dominantly composed of the calcium carbonate (CaCO3) in the form of the hexagonal (rhombohedral) mineral calcite [low-Mg calcite]. This is mostly as anhedral crystals, forming both the bioclasts and the matrix (either finer micrite or a coarser calcite cement).

The less stable, calcium carbonate mineral, aragonite (also CaCO3 but orthorhombic and often with some fairly high, strontium carbonate content) was almost certainly originally present here within shells. It was probably common in Carboniferous ammonoids, nautiloids and bivalve etc., as in Jurassic strata. The situations were not drastically different. However, aragonite has mainly been lost by diagenesis in this older strata, and only preserved in exceptional circumstances (particularly bituminous shales-. See the papers of Stehli and of Yochelson for more information on this topic.

Aragonite is not stable in meteoric water (i.e. fresh land water, not seawater), except when sometimes protected by clays and/or organic matter. It is not usually found in the old, hard Carboniferous limestone of southern England, but it can survive quite easily in younger geological carbonate sediments if they are within clay or shale. The general lack of aragonite would be expected in such old carbonate rocks that have been subject to tectonic action, deep burial and subsequent uplift and a long time phase. Aragonite is known from oil shales in Scotland, where the Carboniferous is not thermally mature and there is preserving organic matter. It is also in natural asphalt deposits. Elsewhere it is usually rare or absent, or replaced by calcite. See the papers mentioned above and also Hallam and O'Hara for more information. Aragonite would not generally be expected in the old, hard and rather massive limestones of Cheddar Gorge, only abundant low-Mg calcite, but exceptional occurrences are not impossible.

Porosity and Permeability

The Clifton Down Limestone Formation of Cheddar Gorge is hard, dark micritic rock that seems to be of very low porosity. In contrast the Cheddar oolite etc, further down in the sequence is likely to have much higher porosity and permeability in places. A very low porosity is common for certain parts of the Carboniferous sequence at certain localities . Some Irish Carboniferous Limestone has less than 1 percent porosity. A Buxton Carboniferous limestone was found to have only 2.9 percent porosity and a dry density of 2.71. This accords with the theoretical figure for 100 percent calcite which is 2.71 (i.e. the specific gravity of calcite). The permeability of the Buxton rocks was as low as 0.3. Some poroperm data on a small number of Carboniferous Limestone samples, but not specifically for Cheddar Gorge is given in : Bell (2013), p. 570..

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2 - STRATIGRAPHY - 1

Stratal Succession - Introduction

A correlation diagram for the Lower Carboniferous strata from the Avon Gorge to Burrington Coombe to Cheddar Gorge, Mendip Hills, Somerset

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2 - STRATIGRAPHY - 1a

Stratal Succession

Regressive Hypersaline Lagoonal Phases
("Modiola Phases" with stromatolites)

[Go also to related subject matter -
Stromatolites at Horseshoe Bend, Cheddar Gorge.]

While most of the Carboniferous Limestone is of shallow marine facies with crinoidal limestones, coral-rich limestones, etc, some parts of it are of carbonate lagoon type, sometimes with raised salinities and environments just approaching those suitable for evaporite deposition. This has been recognised since the beginning of the 20th century. More recently the transgressions and regressions were discussed more specicifically by Ramsbottom (1973). In summary, the transgressive phases on the shelf areas are represented by bioclastic limestones. However, the regressive phases are characterised by oolitic limestones and calcite mudstones, the latter often containing stromatolites. These are interpreted as the early stages of evaporite deposition. There may be dolomitisation beneath these regressive phases, according to Ramsbottom (1973). Above the base of D1 the minor cyclicity affects the whole area of England and Wales and was the result of eustatic changes in sea level.

The regressive phases are of special interest and easily recognised by the presence of stromatolites. It is also likely some minor evaporites in the Mendip area might be associated with these. Within the Carboniferous Limestone of South Wales, the Avon Gorge and the Mendip Hills there are three sequences of limestone with evidence of raised palaeosalinity. These broad regressive phases were known in the past as the "Modiola Phases". They have always been regarded as calcareous lagoon phases and the higher salinity has long been recognised. They were described back long ago by Dixon (1907) and Dixon and Vaughan (1911). The old discussion was mainly in relation to the coastal exposures of the Gower Peninsula, South Wales, where the exposure is particularly good. They are also of broader application to Bristol, Bath and Mendip area. The authors, mentioned above, discussed the following (based with modifications on their Table 3, p. 514). The occurrence of stromatolites at Cheddar Gorge has been reported by Green and Welch (1965). They found them in the upper 55m. of the Clifton Down Limestone, 47m from the top, and about 13m. above the Lithostrotion Beds. The examples seen at Cooper's Hole, mentioned below might be closer to the Lithostrotion beds than that but distance has not been measured. It is quite likely that there are move stromatolite horizons than are clearly exposed. Green and Welch (1965), p. 31, referred to "algal limestone" (i.e. stromatolites), including Ortonella sp. The present writer has not seen the Ortonella and they may well be referring to a different horizon but still within the high Clifton Down Limestone. The matter of finding particular features is not at all easy because of very high cliffs and most exposures being of dark limestone, hard and oscure and not showing details. Cheddar Gorge is not easy for geological study and it is almost certain that much is missed by the casual geological visitor and, perhaps, even by the experienced surveyor working in detail in difficult places.

This present website on Cheddar Gorge, reports then only two occurrences, which seem to be from the upper two of these lagoonal phases (and both are easily accessible).

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1. Lowest Modiola Phase.

(not seen at Cheddar Gorge - beneath the lowest strata)

The hypersaline sequence at the base of K [i.e. basal Tournasian]. "Some beds yield little, except: - lamellibranchs [bivalves] such as Modiola and Sanguinolites [bivalve - Cardiidea], Spirobis (?);abundant ostracods such as Cytherella.".. "Some beds show brecciation in which the fragments are but slightly separated. Beds with fragments [clasts] of contemporaneous sediments. Presence of pure oolites of fine grain [c.f. Basal Purbeck, hypersaline, lagoonal, fine-grained oolites (see West, 1975)]... "Packing of ostracods within one another by long-continued drifting". Fotenote says "First noticed in [lagoonal] Purbeck limestone by Mr. F. Chapman, 1906 ". Purple and green shales and fine conglomerate are sometimes present. Some plant remains from nearby land have been found in this regressive phase, but not in Cheddar Gorge.

2. Middle Modiola Phase.

(the Horseshoe Bend Stromatolite Bed at Cheddar Gorge)

This at the base of C2 + S1 [i.e. below the Seminula Pisolite and the Fluorite Bed]. The presence of some stromatolites is described: "calcite mudstones [micrite] and dolomite-mudstones to finely lamined; a little of the latter crumpled as in landscape marble". Almost all the beds are unfossiliferous or yield only particular bivalves, such as the high-salinity tolerant Sanguinolites. Generally there is an absence of normal marine beds to within this particular hypersaline Modiola phase (Dixon and Vaughan, 1911). [but with a minor exception of a thin crinoid parting at Caswell Bay, Gower]. Some plant remains from nearby land have been found in this regressive phase, but not in Cheddar Gorge.

[For more information on this bivalve, see the following website descriptive summary; note the reference to tolerance of hypersaline water.
"Sanguinolites variabilis
Description: Specimen of a fossil bivalve, Sanguinolites variabilis, collected from the Scremerston Coal Group, Redesdale Ironstone of Early Carboniferous, Dinantian, Visean, Asbian age from Comb (?), Northumberland (NE England). Collected by John Dunn. This bivalve burrowed into the surface of shallow tropical sea floor. It fed on small food particles that it filtered out of the sea water. The bivalve probably died in its burrow because its two shells have remained joined together. Sanguinolites is usually found in a specialised high density - low diversity fauna that could tolerate extremely salty (hypersaline) sea water such as that found in coastal lagoons. It is often found with another bivalve Modiolus after which this specialised community is named. The specimen was found in Northumberland. It is from the Carboniferous period (362 - 290 million years ago)"]
[From the website: Sanguinolites variabilis.]

3. Highest Modiola Phase

(the Cooper's Hole Stromatolite Beds, and possibly others, not seen)

The Modiola Phase at the top of S2, the uppermost Clifton Down Limestone Formation, and present, amongst other places at Cheddar Gorge. It includes pisolites (in Gower) and stromatolites or thrombolites (sometimes referred to in old literature as "Landscape Marble") at the Avon Gorge, Chipping Sodbury and Cheddar Gorge. According to Dixon and Vaughan Spirorbis - like annelids occur in places [These ancient, small coiled forms with a shell are now not considered to be Spirorbis but actually microconchid "worm" tubes.]. A "Mitcheldeania - type alga" [Ortonella]has been reported from southwestern Gower. This Modiola phase is not a simple and continuous unit derived from hypersaline conditions. There has been frequent oscillation of salinity with brachiopod and crinoidal beds. At Cooper's Hole, Cheddar Gorge some scattered brachiopods are present between stromatolite beds. Plant remains are not know from this highest lagoonal phase.

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Modiola Phases - Palaeoenvironments

The three Modiola Phases in the Lower Carboniferous of the southern England and south Wales area are to some extent also discussed a little later by (Reynolds, 1921).

With regard to the Modiola Phases, the interesting problem is that of the salinity tolerance of the Carboniferous mussel-like bivalve, Modiola. In the Carboniferous of the region, it characterises lagoonal facies, ofen with stromatolites and therefore probably sometimes hypersaline. Minor evaporites are present in the Carboniferous Limestone of this region. This apparently euryhaline bivalve also occurs in parts of the Tournasian evaporitic sequence from the Tweed Borehole, from near Berwick-on-Tweed. There it is under investigation by the British Geological Survey and several researchers. There is a possible modern analogue. The modern mussel-like bivalve Brachidontes pharaonis has a salinity tolerance from 35 to 53 psu [practical salinity units]. Brachidontes lives in the waters of Qatar and theoretically could approach the gypsum-precipitating sabkhas. Some of the Arabian Gulf facies have obvious similarities to those of the British Lower Carboniferous.

A significant comment made in the old but thoughtful paper of Dixon and Vaughan (1911) is that the occurrence of the Modiola Phases indicates a very limited tidal range. This may be true but there are also factors of the extent of restriction of water-flow and of scale of the lagoons which have also to be considered. This is a general problem, not restricted to the Carboniferous of southern Britain.

Another factor to be considered, but not discussed by those authors, is that there may be evidence (at least at Cheddar Gorge)of fairly rapid change in salinity. Thus the stromatolite beds at Cooper's Hole, Cheddar Gorge have some brachiopods between them. If comparison is made with the basal Lulworth Formation, (late Jurassic) Purbeck Group of southern England then it will seen that in that case the truely marine water almost never impinge on the lagoonal evaporite facies. The palaeosalinities certainly changed, but open marine influence is not seen there. Rapid marine transgression is seen in the Carboniferous Limestone Modiola Phases. We now leave this topic and consider other aspects of the Lower Carboniferous of Cheddar Gorge.

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2 - STRATIGRAPHY - 2

Stratal Succession.

The Cheddar Oolite Formation

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The Cheddar Oolite Formation is not well exposed in the main part of Cheddar Gorge. On the geological map a small inlier is shown at the Horseshoe Bend. This is not obvious at the surface but road material, a small car park and grass may have covered it.

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2 - STRATIGRAPHY - 3a

Stratal Succession

The Clifton Down Limestone Formation (1) - Introduction

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Clifton Down Limestone, the lower splintery part, above the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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The part of the Carboniferous Limestone Group into which Cheddar Gorge is cut is the Clifton Down Limestone Formation. See the BGS Lexicon of Named Rock Units (just Google - "Clifton Down Limestone Formation"). This is from a higher part of the Carboniferous Limestone Group. It is Arundian to Holkerian in age [about middle Visean, about 340 million years old, in simple terms].

Its main characteristics can be summarised as follows:
This formation consists of splintery dark grey calcite and dolomite mudstones, pale grey oolitic, dark grey bioclastic and oncolitic limestones and some mudstones (after BGS). Scattered cherts and silicified fossils occur within part of it. In Cheddar Gorge it is not easy to see the details because of dark joint surface, which rarely shows much detail. A favourable exposure with good weathering is needed.

The Clifton Down Limestone Formation is 266m. in the Avon Gorge but thins to 150 to 200m in the Mendips (BGS Lexicon).

This is carbonate sediment from shallow water in a hot, nearly equatorial environment. Cheddar Gorge area was just south of the equator at the time. The sea was shallow and clear and suitable for the growth of corals. The limestone was deposited in a variety of settings, from shallow carbonate shelf to barrier or back barrier (or even lagoon).

The fauna of the Clifton Down Limestone is marked by an abundance of individuals in places. In Cheddar Gorge a rich fauna will not easily be found because of the type of exposure, as mentioned above. In reality there is an abundance of individuals but a paucity of species (Green and Welch, 1965). It includes the coral Lithostrotion martini (this has groups of corals which are circular in cross-section). Basaltiform (i.e hexagonal) Lithostrotion corals also occur. In practice, in the field the species cannot be identified but lithostrotion is quite easily found, particularly at Landslip Quarry. Composita ficoidea ["Seminula ficoidea" in old literature] is a smooth-shelled brachiopod that is apparently common, but not easy to see. A large productid brachiopod Productus corrugatohemisphericus has been found in this limestone, although not necessarily in Cheddar Gorge. In summary, you are most likely to see colonies of Lithostrotion, usually of a non-basaltiform type. Some photographs of rather poor specimens are shown in this webpage.

Some obvious palaeoenvironmental conclusions can be drawn from the Lithostrotion corals. Water salinity could not have exceeded about 50 ppt (parts per thousand). Condition in much of the Arabian Gulf are broadly similar today, but close inshore to UAE the salinity rises above 50 and it is too hypersaline to compare to this Carboniferous Limestone of Cheddar Gorge. This is compatible with the rarity of evaporites in the limestone sequence here. Carboniferous Limestone evaporites do occur in the Mendips but are not abundant here (elsewhere Lower Carboniferous evaporites are well-developed; the climate was appropriate for their precipitation, but the environments were not always appropriate.).

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2 - STRATIGRAPHY - 3b

Stratal Succession

The Clifton Down Limestone Formation (2) - Sequence

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For details of the Clifton Down Limestone succession at Cheddar Gorge see particularly:
Green and Welch (1965), p. 19 and p. 31. This formation is very thick but there is easy access to it in the area of the Horseshoe Bend (lower part of the Lower Clifton Down Limestone Formation), the cliffs just west of Horseshoe Bend (chert beds, with a single continuous chert bed at the base), and at the lower part of Landslip Quarry (Lithostrotion Beds). The upper part of the old quarry, with the stepped, quarried exposure in the calcite mudstone above the Lithostrotion Beds.

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2 - STRATIGRAPHY-4

Stratal Succession.

The Triassic Dolomitic Conglomerate Formation

The Dolomitic Conglomerate is a breccia or conglomerate consisting of blocks or fragments of Carboniferous Limestone in a matrix of sandy marl or fine-grained limestone debris (Green and Welch, 1965). The clasts range in size from about a centimetre or smaller up to more than a metre. The cemented rock is hard and can form crags like those of the Carboniferous Limestone. Although widely developed at the margins of the Mendip Hills and in former wadis or valleys (such as at Burrington Coombe) it is not a significant component within the main cliffs of Cheddar Gorge. They are almost entirely Carboniferous Limestone. As the name suggests, it is extensively dolomitised, although not necessarily fully. Dolomitisation can be accompanied by hydration or partial hydration of the original hematite to limonite (or goethite) so that the colour can change from red to yellow to yellowish brown (Green and Welch, 1965).

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2 - STRATIGRAPHY - 5

Stratal Succession.

Pleistocene Head

Head is poorly sorted, stony, gravelly loam and clay on top of the older deposits. It is of Pleistocene age and is considered to have been formed by solifluction in periglacial conditions.

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2 - STRATIGRAPHY - 6

Stratal Succession.

Cave Deposits

Cave deposits range from water-laid sand, silt and gravel, to frost breccias and brown and reddish brown cave earths (Green and Welch, 1965). They are important deposits which may in some places contain human remains and artefacts. [This section will be expanded later.]

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2 - STRATIGRAPHY-7

Stratal Succession.

Alluvium

Alluvial gravel occurs on the lower ground, normally in stream valleys. [Further details will be added.]

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2a - STRUCTURE AND TECTONICS OF CHEDDAR GORGE

2a-STRUCTURE-1

Structure and Tectonics - Introduction

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2a - STRUCTURE 2

Strike-Slip-Faulting

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2a - STRUCTURE 3

Extensional Fractures

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The local opening up and collapse of an extensional fracture system just up-gorge from the Horseshoe Bend, and opposite the Pinnacles, Cheddar Gorge, Mendip Hills, Somerset

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2a - STRUCTURE 4

[ready for use]

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3 - GEOMORPHOLOGY OF CHEDDAR GORGE

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3 - GEOMORPHOLOGY - 1.

Introduction

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3 - GEOMORPHOLOGY - 2.

The Origin of Cheddar Gorge

(a new section to be added)

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3 - GEOMORPHOLOGY AND HYDROGEOLOGY - 3.

Quaternary Erosion

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A broad view of Cheddar Gorge and the Cheddar Reservoir, Somerset, from the high cliffs above the south side of the gorge

Cheddar Gorge is very youthful, probably almost entirely of Pleistocene origin and it lacks river terraces. Most stream and river valleys in the south of England have had a progressively downcutting development, leaving terraces as indicators of their history. There are usually recent river or stream valleys within older valleys. In the Mendip Hills some of the valley systems are very old. Burrington Coombe, for example, has a precursor of Triassic age, now partly filled with Triassic debris, the Dolomitic Conglomerate. There was a desert wadi there about 250 million years ago. This is not the case in the lower and main part of Cheddar Gorge. As the photograph above shows, there is no trace of a pre-existing valley here.

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4 - GEOMORPHOLOGY - HYDROGEOLOGY - ORIGIN OF CAVE SYSTEMS

Origin of Caves - Hydrogeology

The Carboniferous Limestone of the Mendip Hills is an important aquifer. It is the most important in the region (Green and Welch, 1965). It is, of course, well known that the water table is deep beneath the surface under the Mendips. The situation is not simple, though. The Clifton Down Limestone of the area, in which the major cave systems occur has in terms of individual blocks of rock low porosities. However, it is characterised by many joints, fissure and caves.

Of course the caves and the hydrogeology of the Cheddar Gorge region has long been studied, and in various ways. It is not necessarily easy to understand, partly because the gorge has a long history in human terms (very short in geological terms) during which the water table was in various different positions and the climate was varied from periglacial to temperate and relative warm at present. In addition there has long been a special emphasise on particular caves, in addition to overview studies.

A particularly useful and recommended paper that explains to some extent the Cheddar Gorge aquifer and the development of the caves is that of Worthington and Ford, 2009, Self-Organised Permeability in Carbonate Aquifers. It is relevant to Cheddar Gorge (see p. 330). It is quantitative and moderately technical, but the general geological reader can understand the formulae in general with a little guesswork, if they are not experienced in hydrogeology. The general themes can be easily understood by the general (geological) reader anyway, and the paper is conveniently available online. It is recommended as a background to discussion of Cheddar Gorge cave and hydrogeological problems. Some points relevant to Cheddar Gorge and its caves are given in some notes below that are based on the paper. You are strongly advised to obtain the paper and study it in full, though.

Worthington and Ford, 2009 - Carbonate Aquifers - Some summary notes.

Some major points, mainly from Worthington and Ford, 2009 () relevant to the limestones of Cheddar Gorge, are summarised here in simplified form. Carbonate rocks, i.e. limestones etc, are unusual in being moderately soluble in infiltrating water, with dissolved solids (i.e. calcium bicarbonate). Typical dissolved solid concentrations are 100 to 300 milligrams per litre [milligram - thousanth of a gram). At Cheddar the emerging water will be "hard water" with high calcium carbonate (dissolved as bicarbonate). The high carbonate content is not a health problem and may be beneficial.
Carbonate aquifers can have groundwater velocities on average, faster than in other rock types. Sampling in wells shows that are commonly contaminated by microbes Worthington and Ford, 2009 ()(referring to Embrey and Runkle, 2006). In other words, water from rain, acquiring bacteria etc. at the surface, travels relatively quickly through fissures and joints and caves in some hard limestone rocks. In contrast it may filter very slowly through beds of siltstone (or the special case of fine-grained Chalk), spending a long time underground and away from surface organisms. Perhaps, as expected, the stream at Cheddar is able to rise quite fast after a spell of heavy rain. If this is the case then transport of microbes may be faster than elsewhere, although this does not imply that there is any real health hazard in this clean natural environment. [However, in the unlikely case of some sudden pollution affecting the Mendip Hills, nuclear for example, the relatively quick-response water system of Cheddar Gorge would soon carry polluted waters to the outflowing resurgence. In contrast, deep boreholes in Chalk, further east would long continue to yield uncontaminated water.]

Practical and theoretical models have used to understand dissolution in carbonate aquifers; that is to say the natural underground dissolving of limestone rock so as to form natural underground reservoirs of water. The pattern of the natural processes that takes place, including the enlargement of joints, fissures and caves has been much researched and largely determined. Therefore there is a theoretical model for the formation of solution features in limestone.

Worthington and Ford, 2009 explain these natural processes in theory. They only mention Cheddar Gorge, almost in passing, on p. 330. However, the principles that they recognise are important.

In theory rainwater should start to dissolve the first limestone which it first encounters at the surface. If the water can become saturated for calcium carbonate, it will not,of course, dissolve any more carbonate. However, it reality, the dissolution of calcium carbonate does not take place quickly and completely near the surface. The descending water is not fully saturated. Thus it still has the capacity to dissolve more limestone underground. Fast-moving water, that is not saturated, flows through natural fractures, dissolving limestone and enlarging them. Of course that would be expected. It should be noted, though, that the faster the water flows, the more the limestone is dissolved.

When the cavity is sufficiently wide the water becomes turbulent and then enlarges rapidly. The critical turbulent phase is known as "breakthrough". As this rapid enlargement along the channels takes place there is then a drop in the head of water. This causes a reorientation of the flow field so that flow is towards the main channels. Tributary channels then form. There are also many very small channels formed, and these may be only one to ten millimetres in width. Some but not all carbonate aquifers develop large cavities, i.e. caves, large enough for people to walk in. The relatively fast-flowing water can develop a system with channels and tributaries heading towards a spring or outflow. In other words, with turbulent flow, the underground water can organise itself in a manner that resembles a surface river system [see Fig. 1 of Washington and Ford, 2009].

In Britain the Chalk, accounting for 55 percent of total groundwater production in England and Wales is very different from the Carboniferous Limestone. The Chalk has traditionally been thought of as a porous medium and it actually has a high porosity. However, the most of the actual water-flow is not straight through the bulk of the Chalk, but in channels with apertures (i.e. joints, fissures etc) of a few millimetres up to a few centimetres. These small apertures are relatively numerous but large apertures (i.e. caves) are rare.

Carboniferous Limestone Channel Aquifers (Caves)

The Carboniferous Limestone is considered to be a well-developed, karst aquifer Worthington and Ford, 2009. In the Carboniferous Limestone of the Yorkshire Dales stream passages form a dendritic (tree-like) pattern, like a surface river system. There can be one main spring or outflow, but others slightly higher and liable to operate in flood conditions. The larger channels are caves. Worthington and Ford, 2009. The caves, however, only represent a very small fraction of the volume of the aquifer. The Carboniferous Limestone has fewer larger channels and these are the caves. However, the actual percentage volume of caves (channels) in the saturated zone, that is below the water table, at Cheddar Gorge is only 0.02 percent Atkinson (1977). It seems to be proven that the cave channels represent only a very small proportion of the overall pore space for water within the Carboniferous Limestone at Cheddar.

Triple Porosity Types in Carbonate Aquifers (i.e. Cheddar limestones)

Much of the underground water is in joints, small fissures and matrix pores. In carbonate rocks in general the matrix [small pores] provides almost all storage but has very long residence times (Worthington, 2007). It will not change fast or become polluted quickly. Channels, i.e. caves etc, provide little storage, account for most of the flow and have very short residence times. The Worthington paper confirms the view that the water of the Cheddar Caves comes in and out fast. Thus it is, in theory, liable to pollution from above, should the land surface be polluted. The fractures, numerous in the Clifton Down Limestone, have an intermediate role between matrix and channels and have low storage and moderate residence times. The author makes the point that the carbonate aquifers are not so much marked by ranging from conduit [cave] flow to diffuse flow [through the small pores of the matrix] but rather have triple porosity with contrasting properties of matrix, fractures and channels.

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4 - LOCATIONS IN CHEDDAR GORGE


(From the high ground in the south and in a dowwn-gorge direction. Then with some additional comment on the high cliff tops of the south side. )

4 - LOCATIONS - 1

Black Rock Gate

Black Rock Gate is near the highest end of the gorge, really just a valley at this point. The bedrock is the Cheddar Limestone Formation of probable Chadian age. This is the basal unit of the Visean.

There is an old limekiln nearby. This is shown in the National Trust website:
Cheddar Gorge - Black Rock Limekiln Walk. The bedrock is the Cheddar Limestone Formation

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4 - LOCATIONS - 2

Black Rock Gate to Old Reservoir

In the upper part of Cheddar Gorge, before the main cliffs are reached there are small cliffs approaching the road side and some minor slopes of scree. Some of this scree is fossiliferous, with remains of brachiopods, mostly broken

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4 - LOCATIONS - 3

The Old Reservoir

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The old reservoir in the higher part of Cheddar Gorge, Mendip Hills, Somerset, a useful landmark

The old reservoir in the higher part of Cheddar Gorge is a useful indicator of position. It is further up than the bus-turning layby. The top of the Cheddar Oolite Formation is in contact with the higher Clifton Down Limestone Formation, beneath the reservoir. The cliffs at the back only show the Clifton Down Limestone, and Cheddar Oolite exposure have to be sought further up the gorge above the position of the reservoir. Incidently, notice the gorge is fairly wide at this point, thus giving space for the reservoir. There is a major, circular, open reservoir now on lower ground near Cheddar village.

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4 - LOCATIONS - 4

Above Horseshoe Bend
(i.e. up-gorge from Horseshoe Bend - Below The Pinnacles)

(Cheddar Oolite to Lower Clifton Down Limestone Formation)

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The Pinnacles at Cheddar Gorge, Mendip Hills, here viewed upwards, are located on a major zone of jointing which crosses the gorge

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At the cliff top, above Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, with a view of Cheddar Reservoir in the distance

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The two Pinnacles of Cheddar Gorge, Mendip Hills, seen from the hilltop above

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Extensional jointing in the Carboniferous Limestone of Cheddar Gorge, Mendip Hills, Somerset, perhaps of Jurassic date

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Extensional fissuring in the Carboniferous strata of the Mendip Hills has been described and discussed by Wall and Jenkyns (2004) [ Wall, and Jenkyns, 2004. The age, origin and tectonic significance of Mesozoic sediment-filled fissures in the Mendip Hills (SW England): implications for extension models and Jurassic sea-level curves.Geol. Mag.]. They reported that in the eastern Mendip Hills, on the northern margin of the Wessex Basin, SW England, the Carboniferous Limestone is cut by numerous fissures that are filled with Mesozoic sediments (sedimentary dykes, neptunian dykes)... The vast majority of the Mendip fissures are interpreted as having formed as a response of the Carboniferous Limestone, north of major basin-bounding faults, to pulses of tectonic extension during Ladinian-Norian/Rhaetian, late Hettangian-early Sinemurian, late Sinemurian-early Pliensbachian, mid-Pliensbachian, late Pliensbachian and Bajocian times.

In Cheddar Gorge, particularly in the area of the Pinnacles and the Horseshoe Bend, there are numerous, well-developed, open joints or fissures. These trend NE to SW. They do not usually show slickensides nor obvious sediment fills, although it does not mean that they are not necessarily present somewhere in the area.

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Looking down Cheddar Gorge to Horseshoe Bend, showing some geomorphological features, Mendip Hills, Somerset

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4 - LOCATIONS - 5

5. Horseshoe Bend - General
(introductory)

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Modified and labelled aerial and map views of the Horseshoe Bend area, Cheddar Gorge, Mendip Hills, Somerset, with scales

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The up-gorge side of Horseshoe Bend, central promontory, Cheddar Gorge, Mendip Hills, Somerset-unlabelled photograph

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The basal Clifton Down Limestone Formation sequence, with approximate vertical scale, at Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset

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The above diagrams are provided as introductory maps or aerial photographs or sections of the Horseshoe Bend area of Cheddar Gorge with a scale. They are given as a simple basis for future more detailed work, including, so it is intended, vertical cliff and stratal measurements.

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At Horseshoe Bend Road, Cheddar Gorge, Mendip Hills, Somerset, 6th August 2015

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Some labelled individual beds of the lowest part of the Lower Clifton Down Limestone Formation at Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset

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4 - LOCATIONS - 5a

5. Horseshoe Bend - Brachiopod Beds

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A medium-distance view of the location of the articulated brachiopod bed, Lower Clifton Down Limestone Formation, constriction end of Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, 2015

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The location in the inner part of Horseshoe Bend of the articulated brachiopod bed, Cheddar Gorge, Mendip Hills, Somerset

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A biocoenosis of paired brachiopod valves, the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, 9th September 2015

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More brachiopod and some coral remains in a slightly lower part of the biomicrite, the inner part of the Horseshoe Bend, near the constriction, Cheddar Gorge, Mendip Hills, Somerset

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A view of the inner, down-gorge cliff of Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, to show the proven and suspected locations of the articulated brachiopod bed

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At Horseshoe Bend, the stromatolite bed and the articulated brachiopod bed, a biocoenosis, can be seen at certain points but they are not immediately obvious. There also seem to be finely laminated beds that might be of microbial mat origin. Note that at the bottom of the cliff there is the apparent junction, based on the BGS map, between the Cheddar Oolite Formation (below) and the Lower Clifton Down Limestone Formation (above and forming most of the cliff). The images above should facilitate finding the units, but it may be difficult to trace them laterally. Study is not helped by the busy road traffic at this rather hazardous bend, and great care must be taken when visiting as a geologist. Note that it would not be easy to lead a large field party here because of the traffic and this is not recommended as a very safe place. One or two people can examine the cliff here but it is necessary to listen for and to watch for approaching road traffic. It is a little safer on the roadside footpath, on the inside of the bend.

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Brachiopods in the East Cliff of Horseshoe Bend

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A thin bed of bioclastic limestone with brachiopods, inner cliff of the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset

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Brachiopod beds can also be seen in the eastern, inner cliff of Horseshoe Bend. They are also present in the lower part of the Lower Clifton Down Limestone. The example shown above is of a brachiopod shell debris bed, not a biocoenosis

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4 - LOCATIONS - 5b

5b. Horseshoe Bend -
Stromatolite Mounds and Mats in the Lower Clifton Down Limestone.

(The Lower S2 stromatolites already known from Avon Gorge, Burrington Coombe and Chipping Sodbury etc. continue through to Cheddar Gorge.)

[Addtional Notes: With regard to Carboniferous stromatolites in general see also the relevant part of the stratigraphical introduction. Go to: Cheddar Gorge - Stratigraphical Introduction - Modiola Phases]

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Description - Laterally-Linked Hemispherical Mounds (LLH)

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The approximate position of the stromatolite bed of the Lower Clifton Down Limestone, at Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset

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A general photograph, for positioning purposes, showing the stromatolite bed of the Lower Clifton Down Limestone at Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, 9th September 2015

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The general position of the stromatolite bed in the Clifton Down Limestone at the roadside at Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset

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Stromatolite mounds in the lower part of the Lower Clifton Down Limestone Formation, the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, 9th September 2015

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Details of stromatolites in the Lower Clifton Down Limestone Formation at Cheddar Gorge, Mendip Hills, showing lamination above and below the main bed

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Details of stromatolites in the Lower Clifton Down Limestone Formation at Cheddar Gorge, wet surface after acid etching

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Details of stromatolite mounds at the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, an enhanced field photograph

Compare these Carboniferous stromatolites with the almost identical modern (LLH - laterally linked hemisphaeroid), algal stromatolites of Marion Lake, South Australia, particularly as shown by Von der Borch (1977) in Fig. 4E (p.699). The modern examples from Marion Lake are aragonite, with blue-green algal fibres, and with much associated gypsum as lenticular crystals.

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[the following is from a higher stromatolite horizon at Cooper's Hole, and shown here again for comparison]

Laterally-linked stromatolites at Cooper's Hole, Cheddar Gorge, from the upper of the two main stromatolite horizons of the Clifton Down Limestone; compare with the lower ones at Horseshoe Bend

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Obvious hemispherical stromatolite structures, of microbial mat or "algal mat" origin, are visible in the Lower Clifton Down Limestone Formation at the outer curve of Horseshoe Bend. They are present very low in the Clifton Down Limestone, beneath the Chert Beds and just above the brachiopod beds that are a notable feature of this locality.

The bed can be traced, to some extent, round the Horseshoe Bend cliffs, although it is mostly high and out of reach. Just round the upper corner, where there is a major joint and a partially collapsed block, the bed can be seen again. Here the lamination is obvious, but laterally-linked hemispheroids can not be proven.

The exact stratigraphical position this Lower stromatolite Bed has not been measured, but they may be about 10 metres or less from the base of the Clifton Down Limestone Formation (lower part). The location is shown in photographs, but no accurate surveying has been undertaken.

The boundaries of the stromatolite at Horseshoe Bend, Cheddar Gorge, are not clearly seen, and the overall size and shape is not known. The bedding is broadly parallel though, it is unlikely the stromatolite structure is very thick. Since stromatolites are obvious adjacent to road, where people walk past, there are probably many more in the less accessible, high, cliffs of Cheddar Gorge.

Particularly note that this small exposure of stromatolites suggests that there is a bed of stromatolites at this horizon, resembling the superb surface shown by the Avon RIGS group in Barnhill Quarry, Chipping Sodbury. Go to:
Outcrop, the blog of the Avon RIGS group, 19th March 2012. See the photograph here, part-way down the page. The photograph credit is to: WYG Environment, Barnhill Quarry Geoconservation Assessment

Stromatolites have already been recorded from the Clifton Down Limestone Formation in the general Bristol-Mendips region by Kirkham (2005), although his paper is mainly concerned with Ortonella and with thrombolites, rather than typical, laminated stromatolites. There appears to be some thrombolitic fabric within the Horseshoe Bend stromatolite, but it has not yet been studied in detail. The thrombolites discussed by Kirkham are mainly concentrated in the "Concretionary Beds" of the Bristol area. The strata he discussed are at the top of the Clifton Down Limestone (and top of the Holkerian) and thus significantly higher then the stromatolite shown here.

Rather further north, in the Clifton Down Limestone Formation at Chipping Sodbury and Wick Murray and Wright (1971) recorded "algal mats" or microbial mats. These intertidal features were found at the bottom and top of a cycle of sedimentation. The sequence, which they studied at Chipping Sodbury is much thinner than the thick sequence at Cheddar Gorge. At Cheddar the intertidal stromatolite occurs near the bottom of the Clifton Down Limestone but, as noted, is not exactly at the base.

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In the Avon Gorge the basal part of the Clifton Down Limestone (S2) contains stromatolites. They are smaller than those at Cheddar Gorge, but may be from near the same horizon. They have been reported as "Algal Limestone, Concretionary Beds, S2(d), Observatory Hill, Clifton." (Reynolds, S.H. (1921) re Avon section, Bristol. Reynolds described and photographed what are in effect stromatolites. (As at Cheddar Gorge they occur some way below the beds with abundant Lithostrotion corals, i.e. at the Landslip Quarry).
On p. 232 "Massive limestone, occasionally oolitic, alternating with 'Concretionary' (algal) and Seminula Bands. Upper Beds with shaley partings. 125ft. [38m] - The 'Concretionary Beds' are [were] ill-exposed in the southern part of the wooded slope south of the Great Quarry." They are referred to as part of the Third 'Modiola' Phase.

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Another occurrence of stromatolites is at Burrington Coombe, not far to the north of Cheddar Gorge. Stromatolites have been recorded in S2, i.e. the Holkerian Stage and broadly equivalent to the Clifton Down Limestone. However, the particular records seem to apply to higher parts of the S2 sequence than is seen at Horseshoe Bend, where the stromatolites occur near the base of the Clifton Down Limestone Formation and below the limestones rich in Lithostrotion. It is quite reasonable that more than one horizon of stromatolite may occur, as at Chipping Sodbury (mentioned above). It is just a very shallow, hypersaline facies.

The reference to the Burrington Coombe stromatolites is as follows:
See:
Reynolds and Vaughan (1911), p. 345:
The "concretionary beds" which are best seen at about the middle of the quarry, are essentially the same as those of the Avon section, and the account given in the paper already referred to of the peculiar 'Landscape' or 'Cotham Marble' [stromatolite in modern terminology] is applicable to the Burrington rocks. Section (see Plate XXVIII, fig. 1) show that this type of rock is to a large extent made up of a mass of small interlacing tubules, which Dr. Bather suggests may be calcareous algae. Dr. G.H. Hinde has .. [to be continued]

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Elsewhere, further afield, Carboniferous stromatolites are associated, as would be expected, with evaporites: e.g. West, Brandon and Smith (1968). A stromatolite bed from Bellavally Gap in Ireland is shown above, but it does not show the mound-like or laterally-linked hemispheroid form. The example in Cheddar Gorge clearly show the mound-like development of the stromatolite structure. It is similar to the Barnhill Quarry stromatolites. It is much like the classic Shark Bay stromatolites, which are in hypersaline water and in proximity to gypsum deposits.

It is also of interest that Kirkam found, in the Bristol area, calcitised evaporite horizons including enterolithic anhydrite of sabkha type Kirkham (2005). Incidently this is very abundant in non-calcitised condition, still as anhydrite, in the Lower Carboniferous Tweed Borehole of BGS, near Berwick-on-Tweed [at present, 2015, this is being studied in detail, and the writer has seen some thin-sections].

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(1)Description - Microbial Mat Limestone(?)

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A location photograph to show the position of the finely laminated limestone at Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, 1st October 2015

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Finely laminated limestone, that may be of microbial mat origin in the central spur of Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, rather lower than the hemispheroidal stromatolites

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A closer view of finely laminated limestone, probably of microbial mat origin in the central spur of the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset

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A very finely laminated limestone sequence, slightly reddish (on the exposed surface, but without domal stromatolites occurs a little lower in the same sequence at the same locality of Horseshoe Bend, Cheddar Gorge. This has not been investigated in thin-section. It is likely to be, but not proven to be, also of microbial mat origin. The evidence is the very fine lamination, the absence of ripple-bedding or cross-bedding and the apparent absence of brachiopods, corals or other fossils.

The bed can be clearly seen in the cliff of the spur, just across the road from the domal stromatolites. It is stratigraphically lower by a few metres but the vertical separation has not been measured.

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(2) Analogues - Other Carboniferous Microbial Mats and Stromatolites

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Stromatolites or microbial mat limestones [i.e. algal limestones] are well-known features, both of the Planet Earth and the related planet Mars (although hummocky and dome-shaped thrombolites are more conspicuous there than are the laminated stromatolites; but of course the thrombolites are more easily seen and photographed by a Mars rover machine). It is not clear which planet they first originated on, before being transported by meteorites, but this is a sideline, not relevant to the present study.

Stromatolites common in the Lower Carboniferous limestones at many places. They are well-developed, for example, in the Visean of Leitrim in Ireland ( West et al., 1968) where they are associated with evaporites. They are undoubtedly of hypersaline origin, at least on this planet.

Similar occurrences microbial mats associated with sabkha, nodular gypsum or anhydrite occur repetitively in the Tweed Borehole of early Carboniferous Limestone, near Berwick-upon-Tweed. Of course this stromatolite -evaporite associated is very familiar in other Formations such as the Purbeck Group in Dorset (West (1964) and West (1975) , etc.)

At no great distance from Cheddar Gorge, at Chipping Sodbury outlier to the north, [and at the Avon Gorge and Burrington Coombe], stromatolites are well-developed in thin stratal units within the Clifton Down Limestone Formation. the same formation at which they occur at Cheddar Gorge (and elsewhere). The Clifton Down Limestone, is the Visean unit in which they mainly occur. They are also known from the older Tournasian strata elsewhere in the region. The stromatolites occur in fairly thin units within a thicker limestone sequence and represent temporary increases in salinity to hypersaline. For details of the Chipping Sodbury occurrence see: Murray and Wright (1971). A very good surface of stromatolites has been preserved in the area in more recent times.

The stromatolite bed in Cheddar Gorge roadside section is not unusual for the Carboniferous of Britain and Ireland. Dolomitisation can occur in associated beds, but this is not always the case and there seems not to be a close relationship at Cheddar Gore. Evaporites, can occur with stromatolies but and this is the normal situation for a sabkha cycle. Precipitation of calcium sulphate often occurs in the sequence directly above microbial mats or stromatolites, and the loss of calcium from the waters increases the local Mg/Ca ratio. A possible implication of the Horseshoe Bend stromatolite bed is that evaporites might have been present above. The strata immediately above need examining. Consideration might also be given to the major bedding plane a short distance above, which causes one of the "steps" in the Cheddar Gorge cliffs. Find traces of evaporites in the thick and hard Clifton Down Limestone Formation is not easy.

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The Horseshoe Bend occurrence is not a first discovery of stromatolites in the Mendips; it is just a conveniently accessible occurrence at a well-known locality. Indeed, the British Geological Survey in a webpage on Mendip rocks has already mentioned the occurrence of stromatolites in the highest part of the Clifton Down Limestone Formation. They are also present, as shown in photographs below in the lower part of the Clifton Down Limestone at Horseshoe Bend, Cheddar Gorge. Here, for comparison, is a brief extract from the BGS descriptions of the strata, with reference to the Clifton Down Limestone. Go to the following webpage, a small relevant extract from which is given below:

The Rocks of Mendip.
"Clifton Down Limestone Formation
The lithology is dominated by calcite mudstones with a locally abundant but low diversity fossil assemblage. At Burrington Combe the formation is about 170 m thick, and three subdivisions can generally be recognised across the Mendip area. The lowest unit comprises a mixture of calcite mudstones, white oolitic limestones and dark splintery limestones. This interval is relatively expanded in the Cheddar area, where a 38 m thick dark limestone ('Cheddar Limestone Member') is overlain by a 58 m thick white oolitic limestone ('Cheddar Oolite Member'). The middle part of the succession is dominated by fine-grained, grey-black limestone with nodules and bands of chert and abundant remains of the coral Siphonodendron ['Lithostrotion'] martini ('Lithostrotion Limestone'). Porcellaneous calcite mudstones dominate the highest part of the formation, including locally developed algal mudstones and stromatolites, indicating deposition in a very shallow-water, near-shore or lagoonal environment."

The small stromatolite mounds shown here are present at Horseshoe Bend in Cheddar Gorge. They are in the lower part of the Clifton Down Limestone Formation, underneath the fine-grained, grey-black limestone mentioned by BGS. They are stratigraphically above some well-developed brachiopod shell beds at this locality. Their precise stratigraphical position has not been measured as yet, but they may be about only 10 or 20 metres above the base of the formation (judging from the geological map, which shows some Cheddar Oolite Formation at the bend, although not seen by the writer, as yet).

The stromatolites are predominantly mounds with an internal structure of fine lamination and thus true stromatolites. There are, on a small scale, some thrombolitic parts within them, though, but insufficient to list them as thrombolites. Their lateral distribution is unknown and, of course there might be others at high horizons (this seems very likely). The problem of seeing these clearly in Cheddar Gorge is the usual one. The limestones, long exposed to weathering, even since Pleistocene days, have a dark surface which obscures much fossil detail. You can only see lithological or faunal detail at certain places where the limestone has been fairly recently broken. The lateral distribution of this particular bed is so-far unknown. Not only is there the exposure problem, but in addition, to see the bed elsewhere would need rock climbing

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Modern Analogues - Shark Bay, Australia etc.

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Below is an illustration of the well-known modern stromatolites at Shark Bay, Western Austalia, which is provided for comparison.

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A Jurassic, Purbeck, thrombolite seen northeast of Portland Bill, Dorset, and similar to modern stromatolites at Shark Bay, Western Australia, left photograph courtesy of Dr. Geoff Townson

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More information on Shark Bay analogues will be added here.

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4 - LOCATIONS - 5c

5c. Horseshoe Bend -
[Additional - for future use]

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4 - LOCATIONS - 6

Between Horseshoe Bend and Landslip Quarry (Chert Member Cliffs)

Introduction:

From Horseshoe Bend in a down-gorge direction, but just before Landslip Quarry is encounted there are good cliff exposures with chert on the south (steep) side of the gorge. Immediately before the picnic area of Landslip Quarry is reached the exposures are seen near the base of a high vertical cliff (used by rock climbers). The place can be recognised by the fact that it is a car park (there are many) but with a metre high bank and a footpath on the top.

The notable feature in this vertical cliff is the Chert Member of the Lower Clifton Down Limestone. The most conspicuous part is a thin continuous bed of chert within two half-metre thick limestones. There is more chert above discontinuous or semi-continuous. This chert-bearing unit is fossiliferous and cross-sections of brachiopods can be seen. Probably, like the Portland Chert Member of the Portland Stone in Dorset it once contained abundant siliceous sponge spicules. These are of opaline silica when deposited but the silica enters into solution and is redeposited locally as chert. This is the probable origin, but the writer is not aware that this chert topic has been investigated in the rocks of Cheddar Gorge [if it has, a note will be added in due course].

The Chert Member can be followed up-gorge to some extent and it passes above the Brachiopod Member of the Lower Clifton Down Limestone at Horseshoe Bend. It is very easy to recognise at road level, but it is not conspicuous at a distance higher in the cliffs. The limestone is too dark for the black chert to make a good, clearly-visible contrast.

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Long composite photograph showing the cliffs between the Landslip area and Horseshoe Bend, with correlation of major partings (bedding-parallel) in the Clifton Down Limestone, Cheddar Gorge, Mendip Hills, Somerset

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A broad view of the south side of the Landslip Quarry Bend, Cheddar Gorge, Mendip Hills, showing the location of the Chert Beds cliff exposure

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A medium distance view of the Chert Beds of Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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Continuous chert bed and discontinuous chert in the Chert Beds, or lower cherty part of the Clifton Down Limestone, Cheddar Gorge, Mendip Hills, Somerset

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A conspicuous, continous band of chert from the Chert Beds, or lower cherty part of the Clifton Down Limestone, Cheddar Gorge, Mendip Hills, Somerset, with rule

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A rock climber at the overhang above the Chert Member of the Lower Clifton Down Limestone Formation, Cheddar Gorge, Mendip Hills, Somerset, 9th September 2015

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As shown in a photograph above, with a rule present, note that the bed above the continuous chert (the supra-chert bed) is almost exactly 50cm thick. This is useful in determining the thickness of beds above and below as seen in photographs.

The Chert Member at Landslip Quarry Bend

Opposite Landslip Quarry, but a little up-gorge (i.e. partly towards the Horseshoe Bend) on the south (steep) side of Cheddar Gorge is the Chert Chert Member of the Lower Clifton Down Limestone. The most conspicuous part is a thin continuous bed of chert within two half-metre thick limestones. There is more chert above discontinuous or semi-continuous. This chert-bearing unit is fossiliferous and cross-sections of brachiopods can be seen. Probably, like the Portland Chert Member of the Portland Stone in Dorset it once contained abundant siliceous sponge spicules. These are of opaline silica when deposited but the silica enters into solution and is redeposited locally as chert. This is the probable origin, but the writer is not aware that this chert topic has been investigated in the rocks of Cheddar Gorge [if it has, a note will be added in due course].

The Chert Member can be followed up-gorge to some extent and it passes above the Brachiopod Member of the Lower Clifton Down Limestone at Horseshoe Bend. It is very easy to recognise at road level, but it is not conspicuous at a distance higher in the cliffs. The limestone is too dark for the black chert to make a good, clearly-visible contrast.

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4 - LOCATIONS -7

Landslip Quarry (a good location for study) Note: The landslide here is downdip at relatively low angle on a bedding plane. This may be, according to the defination of Bromhead (2013) an SPH - a "slide-prone horizon" but, unusually in a hard rock, the lower part of the Clifton Down Limestone. They are commonly seen in the Eocene Barton Clay of the cliffs of Hampshire (go to my Barton Erosion website and to references by Professor Max Barton).

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A general view from the cliff top of the upper part of the Landslip Quarry area, Cheddar Gorge, Mendip Hills, Somerset, 2015

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A view obliquely downwards towards Landslip Quarry in Cheddar Gorge, Mendip Hills, Somerset, taken from near High Rock

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Photograph of landslip area, Cheddar Gorge, Mendip Hills, taken from the high clifftop on the south side and showing labelled details

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A general view of Landslip Quarry, Cheddar Gorge, Mendip Hills, Somerset, 20th July 2015

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The fallen slabs at Landslip Quarry, Cheddar Gorge, Mendip Hills, Somerset, seen from close up on the adjacent path

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A former working face of Landslip Quarry, Cheddar Gorge, Mendip Hills, Somerset, showing massive bedding and some old drill holes

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A general, labelled, introductory view of the Landslip Quarry area, showing both sides of the road, Cheddar Gorge, Mendip Hills, Somerset

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Part of an old map showing the quarry in Cheddar Gorge, Mendip Hills, Somerset, in about 1902

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The Landslip Quarry area of Cheddar Gorge is conspicuous, easily found and with easy car parking. It is quite easy to scramble up to the old quarry. The place is a major tourist site, with an old quarry in the cliffs of the north side, and a picnic area with large square rocks near the road. It is a good site geologically with many features of interest, including fossils. It also provides an opportunity to get away from the busy road traffic. It is recommended, but take care and only go to higher parts if you consider it safe to do so with regard to your ability and the conditions at the time. There is risk of slipping or falling on rocks or into crevices or joints.

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At Landslip Quarry there was major quarrying which destroyed the near-vertical on the northern side of the gorge and has seriously damaged its natural beauty. The quarry was worked by John Wainwright and Company from 1902. The main worked stretch is a substantial rock face trending NE to SW. This is shown in photographs below, and the holes made by steam drilling machines (after the landslip) can be seen. The informal name, Landslip Quarry, originated because of a landslide or landslip in February 1906. It is interesting to see where this occurred and why it happened. A visiting field party may wish to look at the old quarry and students might be asked to explain the specific reason for the landslide.

It will be clear that the main working quarry face trends from NE to SW. This is broadly at right angles to the dip of about 20 degrees in a direction towards the south-southeast. There are major, partially open, bedding planes at intervals (two in particular) which are a potential weakness. The main quarrying face was into almost the strike direction. Where the step-like quarrying has taken place and where there are drill-holes the risk of a landslide would have been very low. Landslides are not expected in hard rock without clay. The east-northeasterm end of the quarry (up-gorge) is differently situated. Here, for a short stretch the quarrying was against the dip. It was foolish to quarry up-dip even with an angle of only about 20 degrees. This is particularly the case in view of the existence of two major, open bedding planes (one of these originated a still-stand with growth of corals over the temporarily static sea-floor - see photo.)

Actual landsliding, as opposed to rock-fall is abnormal in this massive limestone and there is probably little, if any, elsewhere in Cheddar Gorge. By working up-dip in this corner and effectively cutting giant, downward-sloping steps, the quarriers weakened the cliff and caused a major rock slide and also a small rotational landslide down towards the SSW (i.e. down-dip). The local rotation was sufficient to turn a small stratal sequence of limestone onto its side (see photograph below). This type of rock failure is fairly common in limestone-clay sequences in sea cliff, with the clay being the slipping weakness. It would not be expected in a gorge of solid Carboniferous Limestone [although note that it is difficult to see whether there is any clay in the major open bedding planes; coral preservation features suggest that there might be]. However, although the rotational feature is of interest, it is minor, and rock sliding was almost certainly the major factor. The separated, moved rocks are obvious in the photographs below.

The landslip or landslide does not seem large now, but apparently it did block the gorge for a time. The back-rotated strata can be seen but are not conspicuous. More limestone has just slid down-dip. The sloping slabs are obvious in this corner, near the picnic area.
The BGS website - Detailed Site Information - West Mendip Quarries should be consulted for more information. They mention that there were minor slippages from time to time prior to the landslide and, that in addition, the quarrying operations involved blasting. It was obviously unsafe at this east-northeastern end. Now, long after the landslide and rock fall there is some very irregular rock there, but no specific problem.

Not yet mentioned is an additional factor that was probably responsible for the failure, ie. the rockfall and landslide. back of the quarry, in the landslide area, has a southwesterly trending strike-slip fault. This is a major fault of sinistral type and with former movement almost parallel to bedding. It is a very obvious feature and it overhangs to some extent. It is probably the best-exposed strike-slip fault in Cheddar Gorge and so it is a feature that visiting geologists should see. It is interesting in that it is partially reddened, hinting, of course, at a Triassic date. This fault is a plane of separation of the limestone that was closer to the gorge from that which is more distant and firmly in place.

The major quarrying of the limestone of the natural feature of Cheddar Gorge should not have taken place. It does not seem to have destroyed cave systems. However, now the Landslip Quarry is quite a convenient location for visitors to the gorge and it has a picnic site. It is good for geologists and geological parties because it provides easy access, with just a bit of scrambling, to a strike-slip fault, abundant fossil corals, and to rock fall and landslide features. It also shows the remains of drilling and blasting limestone. The upper and east-southeastern part (landslip part) does require care because there are rocks sloping towards a small but dangerous cliff. in addition it is easy to slip between the edges of the rocks or into small fissures. The sensible and cautious adult can generally avoid problems or major risks, but this upper part has sloping slabs and deep fissures and is likely to be unsafe for children, especially if they are too adventurous and approach the cliff edges. Other parts of the old quarry may not necessarily pose the same risks, and obviously, some sensible judgement at the site is needed. No specific activity here or elsewhere is recommended in this webpage, which is just descriptive and not an itinerary. Rock climbers and cavers will, of course, probably know about routes and hazards.

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John Wainwright and Co. were quarrying limestone here, opposite High Rock, in 1902. There was stone crushing machinery and steam drilling machines. In February 1906 a major landslide blocked the gorge here ( Carter, 2014). There is a photograph of the landslide area, apparently matching the eastern part of the quarry, in the book by Pickering and Foster (2011) Cheddar through Time.

The rock fall was was blamed on the quarrying operations. The National Trust at about this time purchased the north side of Cheddar Gorge (the south side belongs to the Longleat Estate). The Trust objected to quarrying operations here and they ceased.

For more information go to: British Geological Survey - History, West Mendip Quarries.

The back boundary fissures of the landslide are vertical to overhanging (particularly overhanging in the case of the lower plane). They are red-stained, suggesting that they were joints (or faults) in existence in Triassic times. Travertine has been been formed much more recently. This has vertical stripes, resulting from downward water seepage. Notice that the blocks of the landslide are much larger than normal quarrying blocks. These angular blocks are at various angles in the eastern part of the old quarry area. Some of them are tilted down towards the road.

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Branching corals, Lithostrotion, on a Carboniferous sea floor at Landslip Quarry, Cheddar Gorge, Mendip Hills, Somerset

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At Landslip Quarry, Cheddar Gorge, Mendip Hills, looking across to High Rock, 29th July 2015

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Looking southwest from the Landslip Quarry, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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4 - LOCATIONS -7a

Amphitheatre and High Climbing Wall or High Climbing Rock
(This is a vertical cliff, just west of the Amphitheate, and almost opposite Landslip Quarry; it is not the official "High Rock" on the top of the gorge hill, i.e. a little higher and reached by the top footpath)

This is a good area to see the succession of the Upper Clifton Down Limestone. Unfortunately, though, direct access, however,is impossible for the most part except to expert rock-climbers. The cliffs can be viewed and photographed easily from the base. There is a lack of named members or other subdivisions in the Upper Clifton Down Limestone and some informal (temporary?) names are used here for the practical purposes of identifying rock units.

The "striped limestone" unit of 2.75m. thick is a convenient unit to recognise use for positioning. It is not know whether this is stromatolitic limestone or whether the neat parallel-bedding is of some other origin. It is not accessible to the non-climber. Notices in a photograph below, that at least two of the beds within this member have a thin "double" parting (with one or two centimetres between bedding planes).

With regard to the larger scale, note that there are at least three major and conspicuous partings that are parallel to bedding in this big cliff section. In at least one case (MP - 3) there is an indication (not proof) they are the result of bed-over-bed sliding during tectonic processes. An interesting aspect is that there are small overhangs (probably well-known to rock-climbers) at these parting, and, furthemore, there seem to be slickensides present at at least the uppermost one. Parting MP-3 is at the base of the "striped limestone" and has one conspicuous limestone (with a thin division at the base) just beneath it.

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The Amphitheatre and the high climbing cliff at Cheddar Gorge, Mendip Hills, Somerset, all being Upper Clifton Down Limestone, but with some artificial lightening of the striped beds and some darkening of the major partings

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An enlarged view of the striped beds in the high climbing cliff adjacent to the Amphitheatre, Cheddar Gorge, Mendip Hills, Somerset

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Cheddar Gorge, Mendip Hills, Somerset

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A bedding-parallel, shear plane, MP-3, in the Upper Clifton Down Limestone Formation, just beneath the striped beds, in the high climbing cliff, near the Amphitheatre, Cheddar Gorge, Mendip Hills, Somerset

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There is a remarkable, vertical cliff face, about 450ft. or 135m. high, on the south side of Cheddar Gorge, almost opposite to Landslip Quarry. It is frequently used by rock climbers. (Initially, I mistakenly thought that this was "High Rock", but that seems to be not this vertical cliff but it is a high viewpoint on the cliff top, slightly east of here. The name relates to a cliff-top footpath location. If any photographs are mis-labelled as a result of this, they will be progressively corrected as work on this website proceeds. Apologies for any confusion caused!)

The vertical character of the cliff face is mainly because it is almost a strike section (but not exactly) with the limestone dipping into the cliff at about 20 degrees (almost but not exactly normal to the cliff face). Thus this is a very stable situation (like Gad Cliff in the Portland Stone of Dorset). Any potential slippage of the beds is towards the cliff, not away from it. Thus landslipping at this southern side is almost impossible (unlike the north side). Presumably the Cheddar Gorge stream, when in flood in the Pleistocene periglacial conditions, cut into the base of this face and removed most of the directly fallen rock. The stream channel flowing near the strike direction has moved sideways in a down-dip direction, that is uniclinal shift, thus progressively having moved towards the face of High Rock. This has presumably kept the face vertical, clean and free of debris.

The vertical cliff face seen in the above photographs (and used by rock climbers) consists of Upper Clifton Down Limestone, largely hard, grey micrite. The next unit above, the Oxwich Head Limestone Formation is mapped at above this cliff face in the uppermost and isolated rock exposures in the grassy summit area. The mapping by the British Geological Survey does not indicate a junction within this continuous and vertical rock face.

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4 - LOCATIONS - 8

Cooper's Hole Area

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Cooper's Hole cave in a car park in Cheddar Gorge, Mendip Hills, Somerset

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Cooper's Hole and enlarged bedding planes in the Clifton Down Limestone Formation, general view, Cheddar Gorge, Mendip Hills, Somerset

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A closer view of the entrance to Cooper's Hole, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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This is an easily-seen cave entrance in a car park, about 200 metres up the gorge from Gough's Cave (a little further up from the coach park). It is almost opposite Pride Evans Hole on the other bank of the gorge. It is an asphalted area, not picturesque (even with some graffiti), in the corner of the car park. Normally no entry is allowed and it is controlled by Cheddar Caves Ltd. A low level area beyond the railings was dug by MCG in 1959-1962. The southwestern passage sloped down 40 degrees in muddy scree, with a stalagmitic travertine layer, but is now largely flooded by road drainage and is largely choked (Barrington and Stanton, 1977). There is a south passage sloping up to a tight squeeze (Thynne Squeeze) and into a small muddy chamber. Some old steps were found to have been cut into the stalagmite slope (Barrington and Stanton, 1977).

The roof of the cave is evenly-bedded limestone, dipping at about 20 degrees in a direction southwest. This limestone is in the lower part of the (upper unit) of Clifton Down Limestone of calcite mudstone (i.e. micrite) type. Presumably the rather rectangular cave results from flow of water from the gorge into the rock at this small bend. The undissolved roof at the entrance is bedding-parallel, and is almost certainly the result of failure along a bedding plane (i.e. a bed of limestone has fallen). Like some other water-entry caves in the gorge, the cave is roungly rectangular in cross-section at the entrance and wider than higher.

Incidently the cave has been in use since the Iron Age (archaeological dig, 1931-32). There is also four feet of clay with charcoal beds, probably of lead smelting origin (Barrington and Stanton, 1977).

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Laterally-linked stromatolites at Cooper's Hole, Cheddar Gorge, from the upper of the two main stromatolite horizons of the Clifton Down Limestone; compare with the lower ones at Horseshoe Bend

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Some laterally-linked stromatolites in the upper part of the Clifton Down Limestone are very accessible here, and adjacent to parked cars. However, some experience with stromatolites is needed to identify them quickly. If you look for a reddened area of limestone surface, under the overhang at the left hand side of the cave, you can see them. Some brachiopods are associated. There may be many other examples in the huge cliffs of Cheddar Gorge, but these are very accessible. They are from a higher horizon than the laterally-linked stromatolites at the narrow, lower part of Horseshoe Bend (go to that section of this webpage). Unfortunately, some fossil or sedimentological features like this can only be seen at certain places in the hard, blocky grey or black cliffs of Cheddar Gorge. There may well be others in rather inaccessible places.

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4 - LOCATIONS - 9

Strike-Slip Fault Area

Strike-Slip Fault Car Park (lower gorge)

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This place is not far down-gorge from Landslip Quarry. It is a small projection from the south side of the gorge, separating two fairly small car parks. It is notable for obvious slickensides. A slab of limestone projects towards the road, appearing like a step.

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The location of the slickenside and downbulge section in a car park, lower Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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A slickensided fault surface and a tectonic downbulge at a car park in the lower Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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A tectonised zone of Clifton Down Limestone, adjacent to strike-slip faults, lower part of Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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Strike-slip faulting in the lower part of Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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A strike-slip fault seen in the vicinity of the Landslip Quarry, but south cliffs, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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A good and easy place to see the effects of Variscan tectonic activity is a short distance up the Gorge from Gough's Cave (at a small car park on the south side). At first sight two slickensided surfaces can be seen at the eastern end of the car park. Looking up it will soon be noticed that the bedded limestone passess laterally into a cemented limestone breccia. There does not seem to be significant vertical displacement. The brecciation is quite major and thus the tectonic movement was on quite a significant scale. The fault planes does not seem to have been open to Trias because of lack of red material. Obviously, for this region, a dolomitic conglomerate origin must be considered, but the association with strike-slip faulting makes this more likely to be of tectonic origin. Notice that on the large scale geological map of Cheddar Gorge by the British Geological Survey, "disturbed strata" is recorded in the top cliffs, approximately above this area.

(Incidently, beware of busy car traffic at the sharp curve in the road here; it is easy to step back into traffic).

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4 - LOCATIONS - 10

Gough's Cave Entrance and Cliffs.

[photographs of this are shown elsewhere in the webpage, and more will be added]

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4 - LOCATIONS - 11

Resurgence Water

A heavy flow of water at the resurgence, Cheddar Gorge, Mendip Hills, Somerset, on a rainy day, 29th July 2015

[section to be added]

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4 - LOCATIONS - 12

Cox's Cave Entrance

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4 - LOCATIONS - 13

Lion Rock

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4 - LOCATIONS - 14

Pond Area

[section to be added]

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4 - LOCATIONS - 15

Cheddar Village

[section to be added]

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4 - LOCATIONS - 16

Jacob's Ladder and the Lookout Tower

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Jabobs Ladder, steps up one part of Cheddar Gorge, Mendip Hills, Somerset

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Jacob's Ladder is a set of 274 steps up to the upper part (but not the highest part) of the gorge from Cox's Cave. There is a fee at the Cox's Cave entrance for using the steps. There is also a separate public footpath to the same upper part. This is the top of the specific area near Cox's and Gough's Cave, but the highest part of the Cheddar Gorge Cliffs is not here but further to the northeast. So Jacob's Ladder does not take you to the top of the main part of the gorge. It gives quick access to the steel Lookout Tower. From the top of Jacob's Ladder you can begin a steady and undemanding ascent to High Rock and the other high parts of the gorge. The path is at a moderate and steady slope and not difficult. Most of the public crowd, however, only seem to go to the Lookout Tower and as you walk on up from here the number of people around decreases substantially. Beyond High Rock you may be the only person walking into the upper woodlands. This is a peaceful contrast to the upward, rushing people of Jacob's Ladder or to the human blockages that now arise in the Lookout Tower (built before plump people were commonplace in England).

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Cheddar Village and Cheddar Reservoir seen from the Lookout Tower at the top of Jacob's Ladder, Cheddar Gorge, Mendip Hills, Somerset, 6th August 2015

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4 - LOCATIONS - 17

High Rock Area (top cliffs)

[photographs to be added]

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4 - LOCATIONS - 18

Pinnacles Area (top cliffs)

There is an easy footpath from the top of Jacob's Ladder, that slopes up to this high area. The height here above sea-level is about 850 feet or about 260 metres. The village of Cheddar is on quite low ground so you will be walking up most of this height. [details to be added]

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4 - LOCATIONS - 19

Top Cliffs in the Upper (Eastern) Part of the Gorge.

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4 - LOCATIONS - 20

Batt's Coombe Quarry, Northwest of Cheddar Gorge.

A distant view of Batts Coombe Quarry in Carboniferous Limestone, as photographed from near High Rock, above Cheddar Gorge, Mendip Hills, Somerset, August 2015

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Batts Coombe, or Batts Combe or Batt's Combe, Quarry (and adjacent Chelm's Grove Quarry) are the names which have been used for limestone quarries quite close to Cheddar Gorge. It can be seen in the distance from the path above the high cliffs on the south side of the Gorge, although it does not particularly spoil the view. It is not visible from within Cheddar Gorge (except possibly to climbers).

This major limestone aggregrate quarry of Batts Coombe is only about one kilometre northwest of Cheddar Gorge (see the maps at the beginning of this webpage). Developed from the older and smaller Chelmsgrove Quarry, it has in recent years appreciably expanded in the direction of the gorge. In theory, it might begin to destroy Cheddar Gorge in about fifty or a hundred years, although it does not pose a direct threat at the moment. Small-scale quarrying has already been stopped in the gorge so it seems unlikely the major destruction would be permitted, although of course, the future point of view is unknown.

The limestone used is mainly Clifton Down Limestone Formation. Hanson Aggregates produce the crushed limestone and export it a relatively short distance to South Wales as lime for the manufacturing of steel.

The quarry may not be popular to all. Some years ago, the speleologist and author (Stanton, 1966) was concerned about the proximity Chelm's Combe and Batts' Combe Quarries to Cheddar Gorge. An extract of his disapproving comments is given below:

"Second only to Fairy Cave Quarry in unsuitable location is Chelm's Combe Quarry (8, not working at present) and the concession belonging to Batt's Combe Quarry (7) adjoining it on the south east. The quarry is close to the complex of springs at Cheddar, the largest in Mendip and a major source for the Water Undertaking. As at Fairy Cave it is cutting into the hillside between the springs and their feeder swallets to the north, and is sure to intersect a complicated passage system above the underground streams. Already two caves with 400 ft. of passages have been exposed. A possible connexion between the area and the springs was established in 1962 when, a few hours after loud nocturnal underground rumblings were heard below a house roughly half-way between the springs and the quarry, the water began to flow very muddy and continued thus for several days. There had been no heavy rainfall. It may be inferred that there was a major collapse of rocks and mud into the underground streamway, conceivably triggered by the heavy blasting that regularly takes place in Batt's Combe Quarry."

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5 - FOSSILS OF CHEDDAR GORGE - 1

Corals of the Lower Clifton Down Limestone

Ian West points out the coral Lithostrotion in the Clifton Down Limestone, lower part of Cheddar Gorge, Mendip Hills, Somerset, in April 1998

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The fossil coral Lithostrotion, seen on a bedding plane, Clifton Down Limestone, Landslip Quarry area, Cheddar Gorge, Mendip Hills, Somerset, April 1998

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Fossiliferous, reddish limestone beds in the Clifton Down Limestone, lower part, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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Fossil corals and brachiopods seen in cross-section in a cliff face of the lower part of the Clifton Down Limestone, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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Red-stained branching corals, Lithostrotion, Clifton Down Limestone, Landslip Quarry, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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The branching coral Lithostrotion is abundant in the lower part (with chert) of the Clifton Down Limestone of Cheddar Gorge. It is most easily found in the vicinity of Landslip Quarry. Various photographs of this are shown above.

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5 - FOSSILS OF CHEDDAR GORGE - 2

Brachiopods of the Lower Clifton Down Limestone

A brachiopod-coral shell bed at Cheddar Gorge, Mendip Hills, Somerset, showing some shell fragmentation by wave action, but only limited compaction

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A thin bed of bioclastic limestone with brachiopods, inner cliff of the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset

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A biocoenosis of pair brachiopod valves, the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, 9th September 2015

The photograph above shows some palaeoenvironment changes in a short vertical distance. The main fossil bed is biocoenosis with paired valves of brachiopods, more or less in the place they were living. Higher up the bed has been reworked by wave or current action and contains separate valves that have been washed around by the waves in shallow water. At the top of the bed is a re-activation surface, where there was probably some erosion. Here there are traces of ripple marks in cross-section, although the exposure is not sufficiently good to firmly prove this.

The bed sequence resembles a typical shallowing-up cycle. In general in this area the Clifton Down Limestone Formation appears to show cyclical sequences on something like a metre scale. They probably, as is common elsewhere, the result of small marine transgressions, shallowing upward to a reworked bed with ripple marks. The possibly reworked beds are not perfectly laminated but have a wavy appearance probably resulting from ripple marks.

With the regard to the fossils present in the Clifton Down Limestone, the British Geological Survey (BGS) have provided relevant summary information in a webpage on The Fossils of Mendip

They commented:

"The Clifton Down Limestone has a rich but low diversity fauna. The most notable feature is the abundant, partly silicified remains of the coral Siphonodendron ['Lithostrotion'] martini in the middle part of the formation. This coral-rich interval, named the 'Lithostrotion Beds', forms a conspicuous marker-interval that can be traced across the Mendip region. Axophyllum 'Carcinophyllum' vaughani is another widely occurring coral in this unit, and the brachiopod fauna includes Composita, which are concentrated at horizons throughout the formation. Megachonetes and Linoprotonia also occur, and Davidsonina is common in the lower part of the Clifton Down Limestone."

Arriving in the field at Cheddar Gorge, some fossils can be seen in the Clifton Down Limestone Formation but they are not immediately obvious. They are not often well-preserved or separable from the formation rock. Higher up the gorge small brachiopod fossils can be found quite easily in the scree, but these are from the older Cheddar Limestone Formation.

In the main part of the gorge at Horseshoe Bend there is a very fossiliferous unit, although it would be almost impossible to extract them. A thin bed at about the base of the Clifton Down Limestone Formation, and about 30cm or so in thickness, can be seen to contain abundant fossils at the inner cliff of the Horseshoe Bend, northeastern side. The fossil are not perfectly exposed but are obvioulsy sections through brachiopods and some corals. Some small parts of the rock face are shown above.

Although the rock is very firmly lithified at the present it was at one time not very different from the porous, low-density, Portland Roach or shell bed. It is a type of shell beach deposit which has not been highly compacted. It differs from the well-known, Jurassic Portland Stone, shell bed in the abundance of corals. This is because the Carboniferous palaeolatitude of southern England was near equitorial, whereas the Portland palaeolatitude was Mediterranean. The other difference from a Jurassic shell bed is the very hard lithification. This may be because of the Variscan orogeny and the major thrusts nearby. A question arises as to what was its state of lithification at the time of formation of the Triassic dolomitic conglomerate. These are petrographic matters not investigated here though.

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5 - FOSSILS OF CHEDDAR GORGE - 3

Fossils in Other Formations

The Cheddar Limestone Formation is particularly fossiliferous in parts. Remains of brachiopods can be found in scree in the higher parts of Cheddar Gorge.

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6 - SHOW CAVES - 1

Cheddar Show Caves - Introduction - Location

Gough's Cave and Cox's Cave are the two showcaves at the southwestern end of Cheddar Gorge. They are the main reason that many people visit the gorge. Cox's Cave has special stalactite and stalagmite feature but is a smaller cave. Gough's Cave is much larger and probably more well-known. It has extensions that are not accessible to the public, and its origin is complex. The next few images which follow set the scene outside the cave on a summer's day.

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A down-gorge view to the Gough's show-caves entry area and shop and cafe at Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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The tourist area near the entrance to Gough's Cave, Cheddar Gorge, Mendip Hills, Somerset

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At the coffee cafe above the entrance to Gough's Cave, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015, Ian West

Above the entrance to Gough's Cave, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

The entrance to Gough's Cave, Cheddar Gorge, Mendip Hills, Somerset, with a picture of Richard Gough

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Cheddar is famous for its show caves - Gough's Cave and Cox's Cave. It is not feasible in a geological webpage to discuss them in full speleological detail, although some relevant notes and diagrams will be added from time to time. Although very important for tourism, the caves are considered here as dissolution structures with an interesting history. The caves are in tourist area near the downslope end of the gorge. It is difficult to park close by but there are several car parks a little further up the gorge, and it is easy to walk back to the cave entrances. There are cafes, shops and toilets in the cave entrance area and this is a useful place for visitors and can be quite crowded in dry summer conditions.

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A photograph, Mirror Pool, Cheddar Caves, Cheddar Gorge, Mendip Hills, by Andrew Stawarz on flickr

Gough's Cave and Cox's Cave are the two showcaves at the southwestern end of Cheddar Gorge. They are the main reason that many people visit the gorge.

[Summary from Barrington and Stanton (1977)]

"Gough's Cave is an abandoned upper level of the Cheddar underground river. Water rose through the Boulder Chamber floor, first forming the Great Oones Hole via King Solomons Temple, then Long Hole via the Fonts, finally emerging to daylight via the present entrance.

The cave, originally a low tunnel extending to a choke just short of the Fonts, was dug open to the public by R.C. Gough and his sons, 1890-1898 and was opened to the public in the latter year. Gough had to wait many years, until the death of an old woman who lived in the entrance passage, before he could start digging. Flints and bones were found during deepening of the entrance passage, and the "Cheddar Man" skeleton appeared in 1903 when the entrance to Skeleton Pit was being cleared. An archaeological dig by SANHS (R.F. Parry), 1927-30, proved a rich Cheddarian (Latest Palaeolithic, old "Magdalanian" or "Cresswellian") deposit with hundreds of flints in cave earth and scree, overlying stream-borne sand and pebble-beds and underlying cave earth with signs of Iron Age and Romano-British occupation. WCC dug 6 sites in the Boulder Chamber, 1960-65, in search of ancient upstream passage. The final shaft was abandoned when 30 feet deep and only 8 feet above resurgence level, due to frequent flooding.

For more detailed information on later exploration see:
Farrant, A.E. 1991. The Gough's Cave System: Exploration since 1985 and a reappraisal of the geomorphology. This paper is available in full online. Please go to the reference list here, below, to obtain the online details.

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6 - SHOW-CAVES - Introduction (Gough's etc.)

Cave Systems of the main showcave - Gough's Cave

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Introductory comparison of locations of caves in Cheddar Gorge, Mendip Hills, Somerset, and of geological outcrops

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A long profile of Cheddar Gorge, Mendip Hills, Somerset, with great vertical exaggeration, but with locations of cave systems, the present thalweg and postulated former thalwegs, redrawn, with modifications, after Stanton, 1985

Details to be added.

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The show caves are at the western end of the gorge, in an area popular with tourists. There are shops and facilities there. These are shown in photographs in other parts of this webpage.

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6a - 3 - GOUGH'S CAVE - CONTINUED

The Stanton Survey and Interpretation

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Hydrogeological interpretation of the Cheddar Gorge, Mendip Hills, Somerset, following a survey by Dr. W.I. Stanton, 1985, section redrawn with minor additions

[notes to be added]

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6a - 4 - GOUGH'S CAVE - CONTINUED

Blank for futue use

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6a - 5 - GOUGH'S CAVE - CONTINUED

The ........

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6a - 6 - GOUGH'S CAVE - CONTINUED

The ........

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6a - 7 - GOUGH'S CAVE - CONTINUED

The ........

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6b - COX'S CAVE - 1

[for future use]

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6b - COX'S CAVE - 2

[for future use]

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7 - OTHER CAVES IN CHEDDAR GORGE

(7) Introduction
[to be added]

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(7/2 and 3 ) Water Input above Horseshoe Bend

A water input location with stratal-related, rectangular caves, above the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, 6th August 2015

Temporary water flow at the road near two rectangular swallet caves, above the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

Up the gorge, a short distance above Horseshoe Bend, there are two small rectangular caves on the south side of the gorge. They are obviously stratal related and they are associated with clear evidence of water input along widened bedding planes in the limestone (probably Cheddar Oolite Formation). There is little doubt that this is a former input are into the major cave systems of Gough's Cave and Cox's Cave further down the gorge and also on this south side.

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(7/4). Great Oone's Hole ( or Great Oones Hole)
The entrance to this case is at about 93m., quite high in the cliffs of the lower part of Cheddar Gorge. It is further down the gorge than the conspicuous Cooper's Hole (in a car park) but higher in forested cliffs. In geological terms it is at about the base of the outcrop of the Oxwich Head Limestone Formation. As mentioned below, stalagmite from within it has been dated, and this is of geological interest.
This cave is in Cheddar Gorge, inconspicuous amongst trees on the left bank at the head of the slope, 49m or 160 feet above the coach park beside Cooper's Hole. The coach park and Cooper's Hole are well-known to the public, but they are not generally aware of Great Oones Hole, up the cliff and inconspicuous from below. It is owned by Cheddar Caves Ltd., and there is occasional access. The entrance to the cave is a 5 metre wide arch. It is within the Longleat Estate, which owns most of the south side of Cheddar Gorge. There was once, in 1956, a locked gate but this was later removed (Mullan and Moody, 2014).
Stalagmite samples were taken in the early 1980s for radiometric dating. The material was reanalysed using modern techniques in 2013, according to Mullan and Moody (2014). A re-examination of a flowstone fragment from the lower part of Great Oone's Hole has yielded a Marine Isotope Stage 9 [MIS 9] age (about 280,000 years to 330,000 years). That is about the middle of the British Wolstonian Stage (the long glacial phase before the Ipswichian Interglacial). It was from the lower part of the cave. Dr. Joyce Lundberg wrote that "Great Oone's Hole is a palaeoresurgence cave for Cheddar River that is currently accessible from Gough's Cave". Mullan and Moody (2014) noted that "As such, ages on Great Oone's flowstone potentially provide minimum ages for stream abandonment and can be used to refine estimates of Gorge downcutting rate, work pioneered by Andy Farrant".

Historic Note re Great Oones Hole
In the Second World War (1939-1945) there was, at one stage, fear of invasion by German forces. A British Resistance Organisation was set up with men of the Auxiliary Units. This highly secret organisation had explosives and booby-traps to retard any German advance. For an account of the secret operations in the Mendips from 1939-1945 see the book, "Somerset v. Hitler" 256 pages, by Donald Brown (2014) . The high and inconspicuous cave of Great Oone's Hole was a secret underground Operational Base for the Cheddar region, although it seems to have been rather primitive in type. The following is a short, relevant extract from (Brown, 2014, (2014), p.84).
"In Cheddar, Arthur Parsons says.
Then we got a place up the gorge [Cheddar Gorge], Great Oone's Hole. Its all grown over now, but then there were only a few trees on the top. You had to go up and then over this ledge to get into the cave..." .. "This cave, Great Oone's, marvellous place, just what we wanted. We built the front of the cave up with stones and ivy and a trapdoor with grass on, to lift up. We did it ourselves at nights. We built some bunks in there with wire netting and made a cupboard with galvanised iron for airing wet clothes. Then we planned what would happen if we got cut off, how we would live. We'd go up on the hill, get some swedes and turnips, catch a few rabbits and have a stew-up like. We had an oil stove and an oven like a biscuit tin to go on top of the stove." [There was also a water tank, catching dripping water and a pipe with a tap.]
"We went up every night, usually two of us, to make sure everything was alright, and probably stay the night and the next night somebody else would go up. Once a week all the lot would stay. We had a telephone from inside the cave and buried the wire all up to the top of the gorge and in case of emergency we did send a man up on top. Our orders were, when the church bells started ringing we had to disappear. No code-word. You didn't go home you went straight to the base. [i.e. Great Oone's Hole]"

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5 - Pride Evans' Hole
(and Pride Evans' Locker)

A view of Pride Evans' Hole, a short cave in Cheddar Gorge, Mendip Hills, Somerset, 6th August 2015

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An oblique view of Pride Evans' Hole, Cheddar Gorge, Mendip Hills, Somerset, showing some minor seepage in an almost downdip direction

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A view down Cheddar Gorge at the cave of Pride Evans Hole, Mendip Hills, Somerset, 6th August 2015

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This cave is in the cliff, 50ft or about 15 metres in the cliff above the road, and opposite Cooper's Hole (in the coach car park). It is obvious if you look up a bit and across the road from the coach car park. It is a short roomy cave that does not extend in for any significant distance. It was occupied by Mr. Pride Evans, the Welsh keeper of the Cheddar Pound, and his family in about 1810.

[A rather unlikely event occurred in this cave much later, according to the press. In 2013, a one kilogram, Second World War, German, cylindrical steel, incendiary device, dropped from a plane, was found in Pride Evans Hole by a ten year old girl, Lilymay Barnett. Lilymay and her father Steve took the rusted metal object into Derrick's Tea Room so as to enquire as what to do with it. A caver at nearby Gough's Cave then placed it for safety in a bucket of water. Fortunately no-one was harmed by the discovery of this historic device.]
[This story was reported in the Western Daily Press Online for 2013, item-18747295. http://www.westerndailypress.co.uk/Girl-10-finds-????-Cheddar-Gorge/story-18747295-detail/story.html]

Elongate solution cave just southwest of Pride Evans Cave, Cheddar Gorge, Mendip Hills, Somerset

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8 - MISCELLANEOUS

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8 - Miscellaneous.

Triassic Red Staining

A vein of red-stained, fibrous calcite in the Clifton Down Limestone, northeast of Gough's Cave, Cheddar Gorge, Mendip Hills, Somerset

It is very common in the Mendip Hills to find patches of reddish limestone, in amongst the generally grey Carboniferous Limestone. This is usually the result of Triassic red sediments, which originally occurred above the Carbonferous strata over much of the Mendip Hills. Veins of red-stained, fibrous calcite can be seen in places, and some photographs are shown above.

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2 - Misc.

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3 - Misc.

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4 - Misc.

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9. ACKNOWLEDGEMENTS

Acknowledgements

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. 10. REFERENCES

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References

Please go to:
Carboniferous Geology Bibliography (this mainly related to the Mendip Hills, including Cheddar Gorge, but also includes some references regarding the Tweed Borehole, north of England).

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