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.
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.
Boulders on the back of the quarried ledge at Winspit contain fossils and trace fossils. A recent discovery of mine when I last visited were numerous very small worm tubes, frequently amassed in discrete areas or layers, around and below black chert nodules in the Portland Stone Cherty series rocks. It is difficult to be certain of the identification of these worm tubes (maybe someone can look at these pictures and tell me) but it is known that serpulid worms called Glomerula gordialis are found in this particuar geological and geographical location, and I am assuming for the time being that these are the same species.
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.
This marks the final post in the series about the rocks at Ferriters Cove. I had spent a happy few hours on the beach and reached the limit of accessible shore at Ferriters Cove. Time to call it a day. At this northernmost part of the shore, the steeply sloping strata in the cliff, with the bedding planes facing outwards as a continuous sheet, at first seem to be buckling under their own weight, as seen in images 55a and 56 in the previous post. Then, just a few metres further on, the strata can be viewed side-on across the bedding planes with the sequence of individual layers revealed. The strata are curved concavely so that the cliff face is like the under-side of a huge wave, the crest of which is curving over and about to crash down and break. You can see this best in images 60 and 61.
There are also some enigmatic markings on that part of the bedrock on the beach which is covered each day by the tide. I wonder if these are fossils. Photo 73 has a number of rounded shapes that look like they might be gastropods; and Bembexia is a marine snail that is recorded in this locality.
More problematic are the plant-like patterns which occur on a number of rocks (see images 79 – 81). They seem to have a central stem with numerous branchlets along the length. I am not at all certain that these are fossils although they seem to be integral with the surface of the rock and to have a slightly different composition which is reflected in the fact that there is no black biofilm (maybe lichen) growing on them. I am fairly sure that the ‘plants’ are not grazing trails left by the feeding activities of the adjacent limpets and periwinkles. Plants are in fact recorded from the Silurian but I cannot find any illustrations that resemble these Ferriters Cove ‘plants’.
In an article about the Silurian Period on the website of the University of California Museum of Paleontology it says:
Perhaps the most striking of all biological events in the Silurian was the evolution of vascular plants, which have been the basis of terrestrial ecology since their appearance. Most Silurian plant fossils have been assigned to the genus Cocksonia, a collection of branching-stemmed plants that produce sporangia at their tips.
However, drawings of that particular genus show a very different branching system to that exhibited by the Ferriters Cove ‘plants’. Maybe I will get a clearer understanding when I have tracked down some of the specialist research papers on the fossils of this area such as those written by C. H. Holland:
Holland, C. H. (1969) Irish counterpart of the Silurian of Newfoundland. Memoir of the association of Petroleum Geologists 12, 298-308.
Holland, C. H. (1987) Stratigraphical and structural relationships of the Dingle Group (Silurian), County Kerry, Ireland. Geological Magazine 124, 33-42.
Holland, C. H. (1988) The fossiliferous Silurian rocks of the Dunquin inlier, Dingle Peninsula, County Kerry, Ireland. Transactions of the Royal Society of Edinburgh: Earth Sciences 79, 347-360.
By the time I had reached the northernmost edge of the beach at Ferriters Cove, the Silurian rocks had changed their appearance again. The cliff here is higher and composed of a wonderful patchwork of mainly yellow slabs with purple-grey markings. Many of these slabs have fallen to the shore in a thick loose layer. Among these pieces of stone I found some more fossils, internal casts and impressions of brachiopods, including different species to the one I found earlier (I thought that might be Leptaena sp.). Two particular brachiopods are mentioned on the sign at the entrance to the beach, Holcospirifer (bigugosus?) and Rhipidium (hibernicum?), and it is likely that the fossils in images 57b,c,& d belong to one or both of those species. I am wondering if the much larger regular rounded fossil in image 57a is a species of Atrypa.
Bassett, M. G., Cocks, L. R. M., and Holland C.H. (1976) The affinities of two endemic Silurian brachiopods from the Dingle Peninsula, Ireland, Palaeontology, Vol. 19, Part 4, pp. 615 – 625, pls. 93-95.
I thought you would all enjoy this posting by the Geological Society of London. Be sure to click on all the links – especially the delightful Dinosaur Song and the 10 Most Mind-blowing Landscapes. Wonderful.
According to the world of Feng Shui, rose quartz attracts and keeps love. If you want to get all scientific about it, that pink colour is thought to be caused by trace amounts of titanium, iron or manganese.
Location. Romantic, but not too romantic. Something to stir the hearts of even the most heart-heardened geologist. One of these ten most mind blowing landscapes should do the trick.
Menu. Rock cakes are just a bit obvious, aren’t they? We’ve taken our menu plan from the Geologic and Paleontologic Cookbook. How…
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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:
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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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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Trace fossils are geological records of biological activity. The rocks at Winspit in Dorset have preserved evidence of the burrowing habits of invertebrate animals that once lived in the soft wet sediments on the seabed and seashore of shallow seas over 135 million years ago in the Upper Jurassic period.
These trace fossils include burrows and tunnels made by crabs and worms. In some instances, the holes made by the creatures remain visible – as pictured in the first three photographs below. They look remarkably similar to the holes made by boring bivalved molluscs and by mud-tube dwelling marine polychaetes that occur in present day calcareous stones and mollusc shells (see the earlier posts on these subjects). As I am not a palaeontologist, I concede that this may not actually be a parallel causation – just a coincidence.
In most of the examples illustrated by the photographs below, the spaces enclosed by the burrows have been infilled by other sediments so that instead of the original hollow tubes and tunnels remaining in the hardened rock, the burrows have become roughly cylindrical solids. The infill substance seems to be harder than the matrix surrounding it. This means that the softer rock has weathered more readily and the burrows stand out like cords.
A pile of large angular boulders, between one and two metres across, rests on the rocky ledge at the foot of the cliffs where the valley meets the sea at Winspit. On the flat surfaces of some of the rocks are intricate patterns made up of horizontally branching networks of solid tubes about a centimetres or so in diameter. These are similar to the burrows made by decapod crustaceans (crabs) called Thalassinoides.
Large fossilised remains are found in these strata as well as the trace fossils. One of the best known, because of its large size, is the ammonite Titanites giganteus as shown in the picture above. It is about 40 centimetres in diameter. Although well embedded in the massive boulder, and a feature of the location for as long as anyone remembers, someone has recently tried unsuccessfully to hack it out of the rock. It is a shame because it has left the wonderful fossil damaged and defaced.
Some of the burrows, particularly the larger ones that may have been made by crabs, seem from these trace fossils to have passed through a series of layers in the sediments. Sediments from different layers are mixed up, and older sediments brought to the surface and deposited above more recent ones, as animals excavate their tunnels. This process is called bioturbation. Geologists, palaeontologists, and archaeologists are all aware of the implications of bioturbation for the interpretation of results from their research and excavations.
Another name for trace fossil is ichnofossil. To read some more about ichnofossils click here.
Revision of a post first published 9 December 2009
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