Date of Award
Fall 2024
Project Type
Thesis
Program or Major
Oceanography
Degree Name
Master of Science
First Advisor
Joel E Johnson
Second Advisor
Stephen C Phillips
Third Advisor
Robert Letscher
Abstract
The UT-GOM2-2 Deepwater Hydrate Coring Expedition collected continuous conventional and pressure cores in the Terrebonne Basin, Gulf of Mexico (GOM) to 155 mbsf to investigate the physical, chemical, and biological properties of sediments within, bounding, and overlying methane hydrates. Calcareous nannofossil biostratigraphy constrains the age of the upper 145 mbsf to the Pleistocene (<0.66 Ma) to recent. Description of UT-GOM2-2 Hole H003 revealed a lithologic unit from 4.5 to 152 mbsf, defined by bimodal sedimentation of carbonate oozes and interbedded muds. In this thesis, we examine the shallowest mud-to-carbonate ooze transition to investigate the processes driving this bimodal sedimentation through measurements of biogenic silica (BSi), total carbon (TC), total nitrogen (TN), total sulfur (TS), total organic carbon (TOC), and δ13C of total organic carbon (δ13C-TOC) from 4.62 to 37.83 mbsf. Mixed planktonic foraminifers were picked for radiocarbon dates through 14.39 mbsf, constraining the last ~42,000 years. Our results are integrated with additional existing shipboard and post-cruise data sets, including XRF core scanning data, calcareous nannofossil biostratigraphy, reworked calcareous nannofossil abundance, smear slide analyses, and magnetic susceptibility data. Our integrated results suggest that the BSi record represents reworked (RW) Cretaceous radiolarians delivered fluvially to the site, rather than Pleistocene to recent radiolarians produced via in situ productivity. Evidence of greater terrigenous flux by RW Cretaceous microfossils (both calcareous nannofossils and radiolarians) during Marine Isotope Stage (MIS) 2 is consistent with a closer distance of the site to the shoreline during a sea-level low stand. Increased grain size and sand delivery during the last deglacial (16 to 8.9 ka) are consistent with meltwater pulse-driven sedimentation documented elsewhere in the Gulf of Mexico (e.g. Emiliani et al., 1975; Aharon, 2003). Below the radiocarbon constrained interval, two biostratigraphic age datums from 70 to 290 ka nearly constrain a full glacial-interglacial cycle (most of MIS 4-8), where coarse turbidite delivery is greatly increased during a glacial period, consistent with sea level low stands, and reworked sediment delivery greatly increases towards the interglacial period, consistent with meltwater pulses and higher sea level. Though stadial/interstadial processes are evident in our datasets, it appears that the bimodal sedimentation represents a systematic shift in the proximity of the site to the Mississippi River mouth. Low and relatively consistent CaCO3 content, depleted δ13C values, and high TOC:TN values within the carbonate ooze interval suggest that in situ productivity does not increase, but rather dilution by terrigenous sediment decreases. These findings have implications for the deposition of coarse- and fine-grained lithologies on the northern Gulf of Mexico, which may ultimately influence gas hydrate distribution along continental margins. Additionally, these findings suggest that BSi can be measured in GOM sediments as a proxy for the Mississippi River flux.
Recommended Citation
Tozier, Kayla, "Investigating Late Pleistocene To Recent Bimodal Sedimentation in the Terrebonne Basin, Gulf of Mexico" (2024). Master's Theses and Capstones. 1902.
https://scholars.unh.edu/thesis/1902