Granton Shrimp Bed

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The Granton Shrimp Bed is a fossil-bearing deposit exposed on the southern shore of the Firth of Forth near Edinburgh, in Scotland. It is classified as a Konservat-Lagerstätten because of the exceptional quality of preservation of the fossils and is dominated by crustaceans; the deposit dates back to the Lower Carboniferous, some 359 to 323 million years ago. [1]

Fossil Preserved remains or traces of organisms from a past geological age

A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood, oil, coal, and DNA remnants. The totality of fossils is known as the fossil record.

Firth of Forth estuary or firth of Scotlands River Forth

The Firth of Forth is the estuary (firth) of several Scottish rivers including the River Forth. It meets the North Sea with Fife on the north coast and Lothian on the south. It was known as Bodotria in Roman times. In the Norse sagas it was known as the Myrkvifiörd.

Edinburgh City and council area in Scotland

Edinburgh is the capital city of Scotland and one of its 32 council areas. Historically part of the county of Midlothian, it is located in Lothian on the Firth of Forth's southern shore.

Contents

Location and geological setting

The Granton Shrimp Bed is located on the south shore of the Firth of Forth about 3 km (2 mi) from the centre of Edinburgh. It consists of a layer of dolomitic limestone surrounded by Dinantian mud shales which were formed as a result of the deposit of material in either a delta plain setting or in an inter-distributary bay, where sedimentation occurred because of flood-generated incursions. [1]

Dolostone Sedimentary carbonate rock that contains a high percentage of the mineral dolomite

Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite, CaMg(CO3)2. In old USGS publications, it was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolostones or magnesium-rich limestones. Technically, dolostone has a stoichiometric ratio of nearly equal amounts of magnesium and calcium. Most dolostones formed as a magnesium replacement of limestone or lime mud prior to lithification. It is resistant to erosion and can either contain bedded layers or be unbedded. It is less soluble than limestone in weakly acidic groundwater, but it can still develop solution features over time. Dolostone can act as an oil and natural gas reservoir.

Dinantian is the name of a series or epoch from the Lower Carboniferous system in Europe. It can stand for a series of rocks in Europe or the time span in which they were deposited.

River delta Silt deposition landform at the mouth of a river

A river delta is a landform that forms from deposition of sediment that is carried by a river as the flow leaves its mouth and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or another river that cannot carry away the supplied sediment. The size and shape of a delta is controlled by the balance between watershed processes that supply sediment, and receiving basin processes that redistribute, sequester, and export that sediment. The size, geometry, and location of the receiving basin also plays an important role in delta evolution. River deltas are important in human civilization, as they are major agricultural production centers and population centers. They can provide coastline defense and can impact drinking water supply. They are also ecologically important, with different species' assemblages depending on their landscape position.

The shrimp bed resulted from the periodic inundations of marine water into stagnant lagoons, each incursion leaving a lamina of limestone rich in the fossils of soft-bodied marine invertebrates and other animals. These conditions of fluctuating salinity seem to have created a suitable habitat for an assemblage of shrimp-like crustaceans, fish, bellerophonts, conchostracans and ostracods. The sudden changes in salinity caused mass mortalities of this fauna, and also brought marine species such as orthocone cephalopods, polychaete worms and conodonts, which are also found fossilised here. [2]

Lagoon A shallow body of water separated from a larger body of water by barrier islands or reefs

A lagoon is a shallow body of water separated from a larger body of water by barrier islands or reefs. Lagoons are commonly divided into coastal lagoons and atoll lagoons. They have also been identified as occurring on mixed-sand and gravel coastlines. There is an overlap between bodies of water classified as coastal lagoons and bodies of water classified as estuaries. Lagoons are common coastal features around many parts of the world.

Bellerophontoidea superfamily of molluscs

Bellerophontoidea,, common name "bellerophonts", is a superfamily of extinct planospirally-coiled globose molluscs. This superfamily is generally included within the Gastropoda, but may instead be a group of monoplacophorans. The taxon first appeared late in the Cambrian and continued until late in the Triassic.

Clam shrimp suborder of arthropods

Clam shrimp are a taxon of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant, and known from the fossil record, from at least the Devonian period and perhaps before. They were originally classified in a single order Conchostraca, which later proved to be paraphyletic, being separated into three different orders: Cyclestherida, Laevicaudata, and Spinicaudata.

Fauna

The Granton Shrimp Bed was first brought to the attention of the scientific community by D Tait in 1923. [3] He stated that a common crustacean fossilised in the bed was Tealliocaris , but that there were other species there new to science. One of these, the commonest shrimp in this community, was subsequently described by F.R. Schram in 1979 as Waterstonella grantonensis , named for Dr. Charles Waterstone, keeper of geology at the Royal Scottish Museum, and the location where it was found. [4] The shrimp bed is also important because it was the first place to provide evidence of the structure of conodonts; this is because these animals were soft-bodied, and only their teeth were suited for preservation under normal conditions. [5] Other unique soft-bodied animals were also found in the bed. The small number of fossils with shells were not decalcified, and the lack of bioturbation suggests that the sediment was largely lacking in oxygen. The exceptional state of preservation suggests that the assemblage of fossils is likely to represent the original community and not just some elements of it. [1]

Tealliocaris is an extinct genus of pygocephalomorphans from the Carboniferous.

Waterstonella grantonensis is a species of fossil crustacean so distinct from other crustaceans that it has been placed in its own genus, Waterstonella, family, Waterstonellidae, and order, Waterstonellidea. It is named after Dr. Charles Waterstone, keeper of geology at the Royal Scottish Museum, while the specific epithet commemorates the location where the fossil was found, the Granton shrimp beds, near Edinburgh.

Conodont Extinct agnathan chordates resembling eels

Conodonts are extinct agnathan chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils found in isolation and now called conodont elements. Knowledge about soft tissues remains limited. The animals are also called Conodontophora to avoid ambiguity.

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Prioniodontida, also known as the "complex conodonts", is a large clade of conodonts that includes two major evolutionary grades; the Prioniodinina and the Ozarkodinina. It includes many of the more famous conodonts, such as the giant ordovician Promissum (Prioniodinina) from the Soom Shale and the Carboniferous specimens from the Granton Shrimp bed (Ozarkodinina). They are euconodonts, in that their elements are composed of two layers; the crown and the basal body, and are assumed to be a clade.

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References

  1. 1 2 3 Briggs, D.E.G.; Clark, N.D.L.; Clarkson, E.N.K. (1991). "The Granton 'shrimp-bed', Edinburgh--a Lower Carboniferous Konservat-Lagerstätten". Transactions of the Royal Society of Edinburgh: Earth Sciences. 82: 65–85. doi:10.1017/S0263593300007525.CS1 maint: Multiple names: authors list (link)
  2. Cater, John M.L. (1987). "Sedimentology of part of the Lower Oil-Shale Group (Dinantian) sequence at Granton, Edinburgh, including the Granton "shrimp-bed"". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 78 (1): 29–40. doi:10.1017/S0263593300010932.
  3. Tait, D. (1923). "Notice of a shrimp-bearing limestone in the Calciferous Sandstone Series at Granton, near Edinburgh". Transactions of the Edinburgh Geological Society. 11 (2): 131–134. doi:10.1144/transed.11.2.131.
  4. Clarkson, E.N.K. (1985). "Carboniferous crustaceans". Geology Today . 1 (1): 11–15. doi:10.1111/j.1365-2451.1985.tb00277.x.
  5. Briggs, D. E. G.; Clarkson, E. N. K.; Aldridge, R. J. (1983). "The conodont animal". Lethaia. 16 (1): 1–14. doi:10.1111/j.1502-3931.1983.tb01993.x.