Use Of One-Scale Stratigraphy And Chemostratigraphy To Evaluate Conditions Of Deposition And Preservation Of A Triassic Lagerstatte, South-Central Virginia

ASU Author/Contributor (non-ASU co-authors, if there are any, appear on document)
Dr.. Cynthia Liutkus-Pierce, Assistant Professor (Creator)
Institution
Appalachian State University (ASU )
Web Site: https://library.appstate.edu/

Abstract: The rich, fossiliferous Triassic sediments exposed in the Virginia Solite Quarry include a 34-mm-thick ‘‘insect layer’’ that is notable for detailed preservation of soft-bodied invertebrate and vertebrate remains. We describe this unique Konservat-Lagerstatte and use sedimentologic and geochemical analyses to interpret the environmental conditions necessary to preserve such delicate fossils. This work is among the first attempts to apply detailed geochemical/stratigraphic analysis to the study of Lagerstatten and we report on a 332-mm-thick section that includes the insect layer and the rocks immediately below and above it. Our analysis successfully constrains various aspects of the depositional and diagenetic history of the Lagerstatte and permits a detailed analysis of changing conditions prior to, during, and after deposition. Geochemical and sedimentologic analyses of the insect layer and surrounding lithologies reveal a change from siliciclastic-dominated layers (Unit 1) to dolomite-silici- clastic laminites above (Unit 2 and the insect layer), separated by a boundary dolostone layer that is traceable for over 200 m. We interpret this sedimentary shift as the initial stages in the transgression of a shallow, saline, alkaline rift-basin lake over lake margin deposits. The absence of bioturbation by plants and benthic organisms, as well as a lack of predation on the insects, is not explained by significant water depth, but is instead more reasonably considered a result of the chemistry of the water at the lake margin, affected by groundwater seeps, which provided F-, Mg-, and Ca-rich fluids. Although the initial conditions of preservation are remarkable, it is equally impressive that the fossils survived extensive diagenesis, e.g. dissolution of quartz and coarsening of dolomite.

Additional Information

Publication
C. M. Liutkus, J. S. Beard, N. C. Fraser, P. C. Ragland. (2010). "Use Of One-Scale Stratigraphy And Chemostratigraphy To Evaluate Conditions Of Deposition And Preservation Of A Triassic Lagerstatte, South-Central Virginia," Journal of Paleolimnology, v. 44, p. 645- 666. [DOI 10.1007/s10933-010-9445-1]. Version of Record Available @ (http://0-link.springer.com.wncln.wncln.org/article/10.1007/ s10933-010-9445-1).
Language: English
Date: 2010
Keywords
Rift basin, Lacustrine, Newark Supergroup, Insects, Danville-Dan River Basin

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