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The Taphonomy, Paleoecology and Depositional Environment of Vertebrate Microfossil Bonebeds from the Late Cretaceous Hell Creek Formation in Garfield County, Montana
Moran, Sean Michael
Moran, Sean Michael
Abstract
Vertebrate micro fossil bone beds (VMBs) have been used as a source of paleoecological data for decades, but the processes by which they form are poorly understood. Scatological, lacustrine, and fluvial channel lag processes have all been offered as potential mechanisms by which fossil elements are concentrated. This project tests the recent hypothesis that small lacustrine environments are the first stage in the development of VMBs with fluvial VMBs representing reworked samples of previously deposited lacustrine VMBs. Additionally, this study tested the reliability of reconstructing paleoecology using surface collected bulk samples as opposed to in situ quarrying. Three bulk samples, representing one lacustrine and one fluvial VMB, collected from the Late Cretaceous Hell Creek Formation of Garfield County, Montana were used to compile taxonomic and taphonomic data. In order to reconstruct paleoecology, specimens were identified to the lowest possible taxonomic level. To examine taphonomic features from each site, anatomy, wear, shape, and maximum dimension were measured and/ or noted for each specimen. Rarefaction curves were used to examine taxon richness across the three samples while controlling for sampling size. Detrended correspondence analyses made it possible to compare the three samples according to taxon richness and abundance. The ShannonWiener Diversity Index was calculated as a proxy for taxo evenness across the three VMB samples. Finally, taphonomic data were plotted and statistically analyzed to look for significant differences in size and wear across the fluvial and lacustrine samples. Paleoecological data from this study do not support the hypothesis of a solely lacustrine source for the fluvial VMB. Taphonomic comparisons show fluvial samples had significantly more wear than samples collected from the lacustrine VMB. Rarefaction and detrended correspondence analyses show that surface collected samples may provide a fairly accurate representation of taxon richness measured from the quarried samples, but a poor representation of species composition and abundance.
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2011-01-01
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Geology