Seatown Ammonites

Lots of serious fossil hunters go to Seatown in Dorset to find fossil ammonites that have fallen to the beach from the cliffs. The cliffs for the most part are composed of Green Ammonite Member which is part of the Charmouth Mudstone Formation laid down in the Jurassic Period. The ammonites that are most commonly found in this type of rock are Aegoceras, Androgynoceras, Liparoceras, and Oistoceras. I haven’t found any decent fossils of the type I could pick up and take home, but there are plenty of fossils and ammonite impressions to be seen lying in pieces of rock on the shingle beach where people with hammers have broken them open. These pictures show some of the specimens that I found on my last visit. I am not sure which species they represent but maybe some local geologist may be able to look at these images and tell me what they are.

Belemnites at Seatown

Belemnite fossil in situ in Belemnite Marl at Seatown, Dorset, England.

The most common fossils at Seatown on the Dorset coast are belemnites. These are bullet-shaped internal hard parts of a type of extinct cephalopod (think cuttlefish, squid and octopus). For a great deal of the length of the beach, the rock strata are hidden by debris falling down from layers above. There are lots of minor mudslides and landslips. However, as you get nearer to the western extremity of the beach, approaching Golden Cap, a continuous kerb-like, harder, and more calcareous stone layer makes an appearance. This is the Belemnite Stone that has been raised to view by a small anticlinal flexure. Below it are many layers of Belemnite Marl that can be seen in cross-section in the vertical face at the base of the cliff; and also extending out horizontally beneath the gravelly beach and exposed at low tide. They alternate light and dark layers. Fossils are abundant with belemnites predominating but ammonites are also common. The huge numbers of belemnites are thought to have resulted from mass die-offs following mating frenzies.

Plant Fossils at Cape Enrage

Plant fossils are abundant in the Ward Point Member rocks at Cape Enrage in New Brunswick. You do not need to be an expert to find them in beach stones beneath the cliffs. You do need to be an expert to identify all the fragments accurately. I am not an expert. However, as far as I can make out, most of the fossils that I saw were the strap-like leaves of Cordaites, a primitive conifer from upland regions which according to the guide books resemble Amaryllis leaves or corn husks. There were also fragments of Calamites stems; this was a tree-like plant that could grow up to 10 m tall and is related to the much smaller present day horsetails or Equisetum plants (see images below). The stem is ribbed and jointed like bamboo with a diameter of about 10 cm and it would have had narrow whorled leaves at intervals along the stem. It formed dense thick undergrowth in lowland wetter areas. The diverse fossil flora at Cape Enrage represents dead vegetation washed downstream by rivers and stacked up in piles on the banks of many river channels about 320 million years ago in the late Carboniferous Period. The plant debris would become covered in successive layers of sediment brought down by the rivers as they wandered across the flood plain to the sea, and eventually preserved in sandstones and mudstones.

The Cape Enrage Visitor Centre has some excellent examples of fossils on display, and education officers are available to give advice and help with identifications. They are very helpful and friendly. I am sure that, time permitting, a professional guided tour would reveal many more in situ fossils of different types than those illustrated here.

Friendly guide at Cape Enrage

Friendly guide at Cape Enrage

Fossils at Prissen’s Tor

Coral fossils in High Tor Limestone at Prissen's Tor on the Gower Peninsula

I was sitting on a rock ledge at Prissen’s Tor eating my picnic lunch when I noticed that I was sitting on lots of small fossils. Prissen’s Tor is one of a number of rock outcrops at Broughton Bay on the north shore of the Gower Peninsula. The rocks are all made of Carboniferous Limestone but each outcrop was laid down at a different stage during that period and has its own characteristic composition, texture, fossils, and name.

This post is about Prissen’s Tor on the north side of the beach at Broughton (Grid Ref. SN 425937) – to the right as you face the sea. It is composed of that part of the Carboniferous Limestone known as High Tor Limestone (HTL) which was laid down after the Black Rock Limestone, and after the Gully Oolite, but before the Hunts Bay Oolite that outcrops at Twlc Point on the south side of Broughton Bay (Grid Ref. SN 415931).

The spectacular cliffs along the south shore of Gower, featured in earlier posts about Mewslade Bay, are also comprised of High Tor Limestone. HTL additionally includes the Caswell Bay Mudstones found in their type exposure at Caswell Bay on the south shore of the Gower Peninsula.

High Tor Limestone strata vary in thickness from place to place in South Wales – between 100 and 150 feet thick – and make up a massive cliff-forming unit of Arundian age. Based on a study of 44 localities within the HTL in South Wales, Beus (1984) says that invertebrate marine fossils within it occur mainly in distinct mollusc or coral-brachiopod associations reflecting the original habitat communities and particular environmental conditions.

Beus says that of the two recognised lithofacies in the HTL, the main one is known as the “standard” facies and is composed of crinoidal bioclastic limestone. This richly fossiliferous crinoidal limestone is anything from thin to thick bedded and generally forms blocky and resistant ledges or massive cliffs. These bioclastic limestones are composed mainly of whole shells or shell fragments of brachiopods, bryozoans, corals, molluscs, foraminifera and crinoidal plates together with limestone pellets set in starry calcite or in some cases micrite matrix. The “standard” facies seems to compare with the character of the rock at Prissen’s Tor.

In this post, photographs 1 – 6 show longitudinal- and cross-sections through fossilised solitary corals, with the internal divisions clearly visible. Photograph 7 shows a cross-section through the two valves of a shell which is probably a brachiopod but could possibly be a bivalve mollusc. Photographs 8 – 12 mostly show fossilised pieces of crinoid stems. These are made up of numerous articulating segments in life, and here occur both as individual plates or segments, or chains of segments. Crinoids, also known as Sea Lilies, are related to the Echinoderms like Brittle Stars, Sea Urchins, and Starfish. They are a group that has survived to the present day, and though rare, live on deep sea beds.

The remaining images 13 – 16 give views across Broughton Bay to indicate the location of Prissen’s Tor.

REFERENCES

Beus, S. S. (1984) Fossil Associations of the High Tor Limestone (Lower Carboniferous) of South Wales, Journal of Palaeontology, Volume 58, No. 3, pp 651-667.

Howells, M. F. (2007) British Regional Geology: Wales, British Geological Survey, Natural Environment Research Council, Chapter 7, p 112-153, ISBN 978-085272584-9.

Coral fossils in High Tor Limestone at Prissen's Tor on the Gower Peninsula

Coral fossils in High Tor Limestone at Prissen's Tor on the Gower Peninsula

Coral fossils in High Tor Limestone at Prissen's Tor on the Gower Peninsula

Coral fossils in High Tor Limestone at Prissen's Tor on the Gower Peninsula

Coral fossils in High Tor Limestone at Prissen's Tor on the Gower Peninsula

Fossil seashell (either brachiopod or bivalve) in High Tor Limestone at Prissen's Tor on the Gower Peninsula

Fossil crinoid stem segments in High Tor Limestone at Prissen's Tor on the Gower Peninsula

Fossil crinoid stem segments in High Tor Limestone at Prissen's Tor on the Gower Peninsula

Fossil crinoid stem segments in High Tor Limestone at Prissen's Tor on the Gower Peninsula

Fossil crinoid stem segments in High Tor Limestone at Prissen's Tor on the Gower Peninsula

Fossil crinoid stem segments in High Tor Limestone at Prissen's Tor on the Gower Peninsula

View of Prissen's Tor on the Gower Peninsula

View looking north-east across Broughton Bay towards Prissen's Tor on the Gower Peninsula

View looking north-east across Broughton Bay towards Prissen's Tor on the Gower Peninsula

View looking north-east across Broughton Bay towards Prissen's Tor on the Gower Peninsula

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Trilobites

Trilobite fossils in a slab of mid-Cambrian Rock from British Columbia, Canada

Trilobites are probably the best known fossils after the dinosaurs. These photographs show details of Ogygopsis and Paradoxides trilobites in a slab of mid-Cambrian Rock from British Columbia that was collected by T. H. Clark in 1924 and is now on show in the History of Life Displays in the Dawson Gallery at the Redpath Museum, McGill University, Montreal in Canada.

The Redpath Museum is a delightful place with traditional style displays. The fossil exhibits in the Dawson Gallery are arranged in a sequence that makes it easy to understand their role in describing the history and evolution of life on earth. A beautifully illustrated guide book accompanies the displays, and I can do no better than quote about the trilobites from this source as a taster of the guide which is an up to date and easy to understand reference on the role of fossils in unravelling the history of life on earth.

Trilobites are the most diverse group of extinct animals with about 15,000 known fossilised species described so far and new species are still being discovered. They ranged in length from less than 1 mm to over 70 cm, and occupied many habitats and adopted many modes of life. They included predators, scavengers, grazers, filter feeders, and swimming plankton feeders. Their diversity reached its peak in the Late Cambrian and Early Ordovician periods (they represented as much as 60 per cent of animal life in the Cambrian), but afterwards they quickly declined, suffering heavy losses in both the Late Ordovician and Late Devonian mass extinctions. They surviving species finally became extinct at the end of the Permian.

The Fossils’ Tale – A  Gallery Guide – The History of Life Displays in the Dawson Gallery by Torsten Bernhardt (2010), RedpathMuseum, ISBN -978-0-7717-0700-1.

Redpath Museum online at http://www.mcgill.ca/redpath

Trilobite fossils in a slab of mid-Cambrian rock from British Columbia, Canada

Trilobite fossils in a slab of mid-Cambrian Rock from British Columbia, Canada

Trilobite fossils in a slab of mid-Cambrian Rock from British Columbia, Canada

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Storm Beach Boulders & Coral Fossils at Broughton [4]

Close-up detail of coral fossils in Carboniferous Limestone boulder on the Gower Peninsula

This is the fourth in a series of photographs documenting boulders with colonial coral fossils seen on the beach at Broughton Bay on the Gower Peninsula in South Wales. See the earlier posts:

Fossil Coral at Broughton Bay

Storm Beach Boulders & Coral Fossils at Broughton Bay [2]

Storm Beach Boulders & Coral Fossils at Broughton Bay [3]

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Storm Beach Boulders & Coral Fossils at Broughton [3]

Storm beach boulder with coral at Broughton Bay

This is the third in a series of posts documenting boulders with colonial coral fossils seen on the beach at Broughton Bay on the Gower Peninsula in South Wales. See the earlier posts:

Fossil Coral at Broughton Bay

Storm Beach Boulders & Coral Fossils at Broughton Bay [2]

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Storm Beach Boulders & Coral Fossils at Broughton [2]

Close-up detail of coral fossils in Carboniferous Limestone boulder on the Gower Peninsula

This is the second in a series of posts about coral fossils in Carboniferous Limestone at Broughton Bay on the Gower Peninsula.  See the earlier post Fossil Coral at Broughton Bay for more details.

These fossils belong to a group of colonial corals of the lithostrotionid type, probably Lithostrotion junceum.

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Brachiopod Fossils in Hunts Bay Oolite at Broughton Bay

Brachiopod fossils embedded in the Hunts Bay Oolite Subgroup strata of the Carboniferous Limestone

The rocks higher up the exposed face on the west side of Broughton Bay are characterised by their churned up and complex structure that could be evidence for storm events breaking up newly-formed sediments in the deep past. I was unable to recognise any fossils embedded in those particular rocks. See the earlier posts:

Rocks on the west side of Broughton Bay – Part 1

Rocks on the west side of Broughton Bay – Part 2

Rocks on the west side of Broughton Bay – Part 3

However, the lower levels of the exposed Hunts Bay Oolite Subgroup rocks on the west side of Broughton Bay have an entirely different appearance, being a great deal more uniform in colour, texture, and structure. They represent a distinct phase of rock formation. Fossils are present. These fossils represent shoreline accumulations of empty shells on the edge of a shallow lagoon where calcareous deposits gradually built up around them without disturbance by extreme weather events.

The fossils are those of large brachiopods, which are similar to bivalved molluscs but differ from them in possessing a form of internal skeleton. The shells are a couple of inches in diameter and are most often seen side-on in groups that have settled one within the other. The shells frequently occur in layers. In the photographs shown here, the curved edges of the shells are clearly visible. Sometimes the shells themselves have been preserved (perhaps by permineralisation) and in other places it may be just the moulds of the shells or the casts of the moulds. From the angles visible, I have not been able to specifically identify them and put a Latin name to them yet.

In nearby caves, and elsewhere among storm boulders on the beach, fossil corals can also be found. These were featured in the earlier post Fossil coral at Broughton Bay.

The whole of Broughton Bay has a fascinating geological history which I am gradually getting to understand. Relatively recent aspects of this geology include the emergent tree stumps of a Submerged forest at Broughton Bay and also the recent exposures of an iron pan derived from decomposition of old peat beds.

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Rock around Chillagoe Part 5 – Silurian fossils

Fossil corals, brachiopods, bivalves, and crinoids, from ancient seas 400 million years ago, survive in the limestone of the Chillagoe District, Queensland, Australia. An abundance of these Silurian marine invertebrate fossils are preserved in the rocky outcrops in the area and easy to spot.  You can see them on the natural rough surfaces of the cliff-like sides to the karst towers or bluffs. You can also see them in the cut sections of adjacent boulders where the marble quarrymen have been exploring the commercial potential of new sites.

I didn’t see all the types of fossil known to occur here; neither can I now put a scientific name on the specimens I discovered. I noted cross and longitudinal sections of solitary corals – some quite large. There seemed to be a lot of colonial pipe corals – transverse sections of them en masse and lengthwise views of individual pipes. There were crinoid or sea lily stems too. In life, these resemble flowers but are really multi-armed animals of the starfish family which attach to the sea bed by a long jointed, flexible stalk. It is mostly small pieces, or a series of pieces, of the articulated stalk that have been preserved in the rock.

Large bivalved mollusc shells, some still joined together in the pair, were the most numerous fossils – and there were many brachiopods as well. These occurred as distinct shelly layers in the way they had been deposited in the sea-bed sediments so long ago. However, major upheavals and folding of the compacted deposits during later geological periods has resulted in these layers of fossils being re-oriented from the original horizontal to an almost vertical alignment.

Rocks and Landscapes of the Chillagoe District by W. F. Wilmott and D. L. Trezise, 1989, Queensland Department of Mines, Queensland Department of Natural Resources, Mines and Energy, ISBN 0 7345 2486 2, QNRME04050, pp 3-7, gives details of the sediment deposition off the edge of the continent between the Silurian and Devonian Periods – when the Chillagoe fossils were formed.


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