MS, University of Cincinnati, 2016, Arts and Sciences: Geology

Studies of Precambrian life on Earth have been dominated by those of shallow marine deposits, and in order to gain a more complete picture of life's early evolution it is important to consider a wider range of inhabited environments, including deep marine and terrestrial ecosystems. Evidence for early microbial life comes primarily from fossil microorganisms (microfossils), microbial sedimentary structures (e.g., stromatolites), and sedimentary organic matter (e.g., kerogen). The diversity and preservation of these different forms of fossil evidence introduces several challenges to their interpretation, requiring thorough analysis for accurately determining their biological origins. Investigating the paleobiology, organic geochemistry, and thermal maturity of such deposits provides a holistic approach to exploring the Precambrian biosphere in unfamiliar paleoenvironments. This thesis presents two studies of unique Precambrian ecosystems: a diverse microfossil assemblage from a 2.52-billion-year-old (Ga) deep marine deposit, and thermally altered stromatolites from a 1.4-billion-year-old evaporitic lacustrine deposit. Black cherts from the upper Gamohaan Formation (2.52 Ga) contain a consortium of organic-walled large and small coccoids, tubular filaments, and mat-like biofilm structures. Geochemical analyses of stromatolitic chert-carbonate from the Middlebrun Bay Member (1.4 Ga) in contact with a mafic sill show a trend in organic carbon isotopes relative to thermal maturity that is contrary to theoretical predictions. Findings from these studies reveal, for the first time, microfossil evidence of a diverse microbial community in the open Archean ocean prior to the Great Oxidation Event (GOE) ~2.4 billion years ago, and provide insight on the relationship between thermal maturity and organic carbon isotopes within a set of terrestrial stromatolites. Together, these studies help capture the enigmatic nature of the Precambrian fossil record and expand our full unders (open full item for complete abstract)

Committee: Andrew Czaja Ph.D. (Committee Chair); Julie K. Bartley Ph.D. (Committee Member); Carlton Brett Ph.D. (Committee Member); Aaron Diefendorf Ph.D. (Committee Member) Subjects: Planetology

Master of Science, University of Akron, 2009, Geology-Environmental Geology

The field of paleotempestology has gained more awareness in the past decade as a result of increased hurricane intensity, quantity, and duration within the late Holocene. One of the best localities to find records of hurricane overwash deposits is in the Bahamian islands. San Salvador Island, Bahamas (SSI) is a small (150km2), isolated carbonate platform, that contains shallow (0.5-3m) saline lakes that occur in between interdune areas of arcuate dune ridges. Due to San Salvador Island's location within the Bahamian archipelago and the Atlantic Ocean, the island is poised to record hurricane strikes and the record of these events can be found in coastal lakes. Clear Pond is a shallow (~1m), variably saline (16-30 ppt) lake in the southwestern edge of the island, that is separated from the Atlantic Ocean by Holocene dunes. It was a previously uncharacterized pond, but like many other depositional environments on San Salvador, it is constantly recording climatic and anthropogenic changes on the island. This study addresses the following questions: 1) Is there a seasonal salinity variation within the pond and what is the general limnology of the pond, 2) Can we identify large storm events in the sedimentary record of Clear Pond, and 3) What is the depositional history for Clear Pond for the past 4000 years? Nine sediment cores, ranging in length from 50 to 150 cm, were recovered from Clear Pond. The cores were analyzed for organic and carbonate content, dry bulk density, grain size, sediment fabric, and mollusk and ostracode composition. Additionally, x-ray fluorescence, spectrophotometry, and x-radiography were carried out on sediment cores. Salinity varied from brackish conditions in the summer and fall to more marine during the winter and spring seasons. It was also influenced by a previously uncharacterized karst conduit. Large storm events were identified through an increase in grain size and dry bulk density, and additionally by x-radiographs. A catastrophic hurr (open full item for complete abstract)

Committee: Lisa Park PhD (Advisor) Subjects: Geology; Paleoecology