Exceptional Preservation of Molluscs in the Buckhorn Asphalt
Seuß B, Nützel A, Schulbert C (2007)
Publication Language: English
Publication Type: Conference contribution, Abstract of a poster
Publication year: 2007
Event location: Freiberg
Abstract
The Late Carboniferous Buckhorn Asphalt Quarry contains the best preserved Palaeozoic molluscs known world wide. The molluscs are commonly present in their original aragonitic preservation. Shell microstructures, larval shells, and colour patterns are commonly preserved. The good preservation of the fossil molluscs from the Buckhorn Asphalt was caused by Ordovician oil intruding the sediments simultaneously to or short after deposition, sealing pore space and preventing recrystallisation. The oil transformed into asphalt loosing its volatiles. The fauna of the Buckhorn Asphalt Quarry is dominated by molluscs, especially by cephalopods and small gastropods. The great abundance of molluscs and the unique preservation make the Buckhorn Asphalt one of the most important fossil Lagerstätten for Palaeozoic molluscs. The Buckhorn Asphalt Quarry is located near Sulphur, Oklahoma (USA), in the Arbuckle Mountains. It exposes a suite of clastic Carboniferous sediments including siliciclastic limestones, mollusc coquinas, conglomerates, and sandstones. The mollusc bearing sediments from the Buckhorn Asphalt Quarry are of Late Carboniferous (Desmoinesian, ~308 - 306.5 Ma) age. Deposition of the sediments took place near the palaeoequator during that time. For documentation from which facies the fossils derive thin section were prepared. The high asphalt amount made is necessary to impregnate the rock samples with synthetic resin before preparing the thin section. To remove the asphalt of the samples and dissolve them a Soxhlet apparatus had to be used. Dissolved sediments were further disaggregated with tensides to remove hydrophobic matter, and then the material was wet-sieved. The fossils of the Buckhorn Asphalt Quarry allowed us to study a unique Palaeozoic assemblage of microborers which were studied in thin sections, casts and etchings. It turned out, that the detected ichno-fossils represent the most diverse Palaeozoic assemblage of micro-bioeroders proved yet. The Buckhorn Asphalt Quarry is an outstanding source of information, as it is one of the very few Palaeozoic deposits in which mollusc shells are preserved in almost unaltered composition. Original shell structures and mineralogy, protoconchs or prodissoconchs are commonly preserved. Colour preservation of naticopsids is present. Gastropods (~50 species) are the most diverse group in the faunal assemblage. Ammonites and nautiloids are very abundant, bivalves are common. Moreover, a rich marine invertebrate fauna including e.g. brachiopods, echinoderms, bryozoans, ostracods, foraminifera is present. Vertebrate remains are rare, remains of land plants are up to several decimetres in size. The exceptional preservation mollusc shells provides a “preservational window“ for studying a Late Palaeozoic microboring assemblage revealing a total of 18 known ichnospecies and the new ichnotaxon Aurimorpha varia – the most diverse Palaeozoic microboring assemblage known to date. First results suggest that most fossils including the gastropods lived in shallow water as is indicated by the diverse assemblage of bioeroders within the mollusc shells as well as by the presence of large plant remains. The fossil material was mixed with siliciclastic sediment, some of them conglomeratic, and transported over a relatively steep slope or in channels by mass flow events. Data about early ontogenetic mollusc shells and shell microstructure provide important information for phylogeny and taxonomy. We can also study heterochronic processes and compare larval and adult shell morphologies. The fact that shells are commonly unaltered by diagenesis and are present in their original mineralogical composition allows the study of original isotope signals in order to reconstruct palaeo-environmental conditions.
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Germany (DE)How to cite
APA:
Seuß, B., Nützel, A., & Schulbert, C. (2007). Exceptional Preservation of Molluscs in the Buckhorn Asphalt. Poster presentation at Annual Meeting of the Paläontologische Gesellschaft, Freiberg.
MLA:
Seuß, Barbara, Alexander Nützel, and Christian Schulbert. "Exceptional Preservation of Molluscs in the Buckhorn Asphalt." Presented at Annual Meeting of the Paläontologische Gesellschaft, Freiberg 2007.
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