Study on a fossil nautiloid – surprising insights

Seuß B (2012)


Publication Language: English

Publication Type: Conference contribution, Abstract of lecture

Publication year: 2012

Event location: Berlin

Abstract

The Buckhorn Asphalt Quarry in Oklahoma, USA, yields a Desmoinesian (Upper Carboniferous) faunal assemblage of outstanding preservation caused by synsedimentary or contemporary impregnation of sediments and fauna with hydrocarbons. These hydrocarbons prevented diagenetic processes to a high degree. The faunal assemblage evolved in a (sub)tropical shallow marine setting and is, with more that 160 reported species, one of the most diverse Paleozoic faunas known to date. The succession is strongly dominated by molluscs, i.e., gastropods, cephalopods, and bivalves, accompanied by e.g., fusulinids, ostracods, echinoderms, and bryozoans. The sediments are mainly mixed siliciclastic-carbonatic and exhibit a single cycle of trans- and regression, with cephalopod-dominated sediments ("cephalopod coquina") representing the deepest marine deposits. Two cephalopod shell remains from the cephalopod coquina were selected for a detailed isotope study (O, C). One shell remain derives from a so far unidentified specimen, the second one from an orthoconic nautiloid which was tentatively assigned to Hebetorthoceras unicamera. Hebetorthoceras is characterized by preservation of two chambers of the phragmocone with nicely preserved cameral and siphuncular deposits. Before samples were prepared the shell remains were intensively studied by using SEM, EDX, XRD-GADDS, and by a series of thin sections. As expected, original shell microstructure and material were still preserved accompanied by parts influenced by diagenetic alteration. Anyhow, both altered and unaltered shell material and both, cameral deposits and shells were sampled with high resolution. Primary isotope signals were used to recalculate local paleotemperatures (unidentified remain: 28-31°C; Hebetorthoceras: 14-15°C) for the sea covering the area of the Buckhorn Asphalt Quarry. Samples exhibiting diagenetic alteration were used to reconstruct diagenetic pathways within the cephalopod remains. So far so good, if there weren't two distinct oval marks on the outside of Hebetorthoceras and the rather abnormal formation and mineralogy of the cameral deposits of this specific specimen. In a subsequent study both, the oval marks and the cameral deposits were examined and it turned out, that a) Hebetorthoceras was victim of a predator, b) this attack was sublethal, c) the specimen was able to precipitate further cameral deposits after the assault, d) it precipitated high magnesium-calcitic cameral deposits during lifetime, and e) the HMC was not a reaction to the heavy injury caused by the attack, but was even formed before. Please download the supplementary material for details on this presented study.

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How to cite

APA:

Seuß, B. (2012). Study on a fossil nautiloid – surprising insights. Paper presentation at Annual Meeting of the Paläontologische Gesellschaft, Berlin.

MLA:

Seuß, Barbara. "Study on a fossil nautiloid – surprising insights." Presented at Annual Meeting of the Paläontologische Gesellschaft, Berlin 2012.

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