Date of Award
Doctor of Philosophy (PhD)
Dena M. Smith
The late Eocene Florissant lake shales are host to the most diverse early freshwater diatom flora known in the fossil record. These 34.05 ± 0.08 Ma deposits also yield well-preserved terrestrial and aquatic fossils that represent life during the approach to the final phase of cooling that followed the thermal maximum of the early middle Paleogene. This study begins with a synthesis of the earliest (pre-Neogene) records of non-marine diatom genera from the Florissant and 8 other fossil localities. Nearly all pre-Neogene diatom genera are extant genera, and genus richness increased through time. Cumulative richness for the Florissant diatoms is 33 genera, 14 of which are first-time recorded occurrences. Florissant has 18 more genera than any of the 6 older floras examined.
The next component of the study is a detailed floristics assessment of the Florissant diatoms conducted at the Clare's Quarry site. A total of 20 freshwater diatom genera are described and imaged, 8 of which are first occurrences in the geologic record. Among these 20 genera, 4 new species and 2 new varieties are named. As many as 48 taxa show affinities for known modern species. In total, 55 taxa are described and illustrated. The study concludes with an integrated examination of the paleolimnology of Florissant lake at Clare's Quarry from sedimentological characteristics of host lithologies, autecological preferences of the most similar modern diatom taxa (modern analogs), and the occurrences of associated macrofossils. Evidence is found in support of an anoxic hypolimnion and a deep bathymetry for the depocenter. The interpreted diatom paleoecology places this plankton-rich, open-water lake site within range of major stream outflow that introduced lake marginal and non-lake-dwelling diatoms, and plant and insect macrofossils into the lake. Slow suspension settling of diatoms, fine clays, and airfall tuffs characteristic of deep lake sedimentation is interrupted by fines of episodic distal turbidites. This investigation demonstrates the power of integrating data from allied sub-disciplines to better characterize paleoenvironments and their inhabitants.
Benson, Mary Ellen, "Freshwater Diatom Paleontology and Paleolimnology of the Late Eocene Florissant Formation, Teller County, Colorado" (2011). Geological Sciences Graduate Theses & Dissertations. 21.