Global ETD Search

1	Quantitative Estimates of Time-Averaging in Brachiopod Shell Accumulations from a Holocene Tropical Shelf (SW Brazil) Carroll, Monica 06 August 2001 (has links) Time-averaging, the mixing of fossils of different ages within a single bed, defines the limit of temporal resolution of the fossil record. Quantitative estimates of this resolution threshold have not been acquired for any group other than mollusks. This study provides the first quantitative estimates of time-averaging for brachiopods, extending our understanding of intrinsic, or group specific controls on this process. Estimates were obtained by direct dating of individual terebratulid brachiopod shells Bouchardia rosea (Mawe) collected from modern surficial shelly accumulations in the Southeast Brazilian Bight (SW Atlantic). Using amino acid racemization dating calibrated with radiocarbon, 82 individual brachiopod shells, collected from four nearshore localities, were dated. The shells vary in age from modern to 3000 years, standard deviation = 680 years. The age distribution is significantly right-skewed (K3=2.48). At 50-year resolution, the temporal completeness is 75% for the last 1000 years and declines to 20% completeness for 1000-2000 yr. BP. Preservational quality (taphonomy) of modern (<50 yr.) shells is statistically indistinguishable from that of older shells, demonstrating that shell taphonomy is not a good predictor of within-assemblage relative age. These results conform to previously published results for mollusks. Therefore, brachiopods can show considerable time-averaging and this time-averaging can be on a scale similar to aragonitic mollusks despite the apparent lack of robustness of calcitic brachiopod shells. This suggests that the brachiopod fossil record can be notably time-averaged, but estimates of this mixing cannot be reliably deciphered from the taphonomic condition of shells. / Master of Science Bouchardia rosea Terebratulid Brachiopods Fossil record Amino Acid Racemization Dating Taphonomy
2	Quantitative Ecological and Taphonomic Patterns in Late Cenozoic Mollusk-Dominated Marine Fossil Assemblages Barbour Wood, Susan L. 27 June 2006 (has links) Applications in paleontological research are far from being limited to taxonomic collection and identification. Nor is such research limited to working solely on fossil data. Actualistic paleontology is the study of modern or recent organisms and processes to better understand those of the past. The bulk of this body of research falls under the category of actualistic paleontology, and examines geochronological methods and error biases in dating biological specimens ranging in age from modern to thousands of years old. Although such methods are arguably not perfect, error rates of ± a few hundred to few thousand years can be extremely important when considering ecological relationships among both Holocene taxa and time-averaged paleocommunities, but quite diminished when considering implications on more traditional dating techniques for ancient strata. Regardless, understanding implications of time resolution is important in analyses of and comparisons between any biological dataset. The following chapters are united by quantitative and statistical management of data with varying levels of temporal resolution, and represent four manuscripts that either are in press or soon to be submitted for publication. / Ph. D. radiocarbon dating brachiopods Bouchardia mollusks Semele Holocene Quaternary Brazil Ubatuba Bay reservoir age taphonomy time averaging Atlantic Coastal Plain Miocene Pliocene Eastover Cobham Bay Yorktown Sunken Meadow aspartic Amino acid racemization paleoecology gradient ordination

Search results

Quantitative Estimates of Time-Averaging in Brachiopod Shell Accumulations from a Holocene Tropical Shelf (SW Brazil)

Quantitative Ecological and Taphonomic Patterns in Late Cenozoic Mollusk-Dominated Marine Fossil Assemblages