Doctor of Philosophy (PhD)
Geology and Geophysics
Sedimentary fabrics preserved in the rock record provide some of the best evidence for interpreting paleo-depositional conditions. Muddy sediments in particular are important paleoenvironmental archives, preserving the most complete stratigraphic record of any rock type in basinal settings. However, the full range of mechanisms responsible for the deposition of muddy sediments, particularly in high-energy settings, remains poorly understood. Although frequently observed in modern settings, muddy prodeltaic deposits are rarely identified in the rock record, in part because no catalogue of easily distinguishable recognition criteria exists for this class of mudstones. In order to help overcome this deficiency, this dissertation project employs a combination of oceanographic techniques including shallow seismic surveying, radioisotope geochemistry, sedimentary fabric analyses, and a rock record study to investigate (1) the mechanisms of sediment dispersal and accumulation on the muddy Southwest Louisiana (SWLA) Chenier Plain shelf, where current-wave-enhanced sediment gravity flows (CWESGFs) are understood to play a key role in progradation; (2) the characteristics of the muddy sedimentary fabrics deposited in response to site-specific hydrodynamic conditions on the SWLA shelf; and (3) how muddy sedimentary fabrics deposited in a shallow shelf environment are preserved in the rock record, and how post-depositional changes (e.g., bioturbation, compaction, and diagenesis) alter these fabrics by examining the Ordovician Power Steps Formation, Bell Island, Newfoundland. The results of these investigations show that (1) CWESGFs are effective mechanisms for the offshore transport of muds on the SWLA Chenier Plain shelf. In addition to simply transporting sediment, CWESGFs contribute to the development of unstable seabed conditions where mass-failures can develop, even on extremely low gradients. (2) CWESGF microstratigraphy reflects the site-specific flow development in response to the combined effects of waves, wave period, currents, and gravity and thusly these sediments can be studied in terms of a semi-quantitative framework. (3) The Lower Ordovician Power Steps formation contains sedimentary structures that record evidence of storm-driven muddy transport in a high-energy prodeltaic setting. The high-energy setting likely inhibited bioturbation, while an abundance of highly reactive mafic minerals sourced from a Palaeozoic hinterland led to early cementation that inhibited compaction, preserving diagnostic sedimentary fabrics.
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Denommee, Kathryn Christine, "Developing Recognition Criteria for Current-Wave-Enhanced Sediment Gravity Flows" (2015). LSU Doctoral Dissertations. 563.
Bentley, Samuel J.