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Open Access Dissertation
Doctor of Philosophy (PhD)
Year Degree Awarded
Month Degree Awarded
R. Mark Leckie
Climate | Geology | Oceanography | Paleobiology | Paleontology | Sedimentology | Stratigraphy
Ocean gateway changes, once the best mechanism for driving abrupt climatic change, have fallen from favor. They have been largely replaced within the literature by changes in CO2 concentration and orbital forcing. This dissertation looks at three intervals of relative stability (Oligocene), prolonged change (Plio-Pleistocene), or transient events (Oligocene/Miocene boundary) in order to better understand the oceanographic circumstances which govern ‘events’ in the paleoceanographic record.
Chapter 1 discusses the chronostratigraphy of Integrated Ocean Drilling Program (IODP) Site U1396 (Expedition 340) in the Caribbean Sea. A combination of paleomagnetostratigraphy, biostratigraphy, astrochronology, and correlation to Marine Isotope Stages (MIS) allows a high-resolution age model to be constructed. Sedimentation rates are calculated for the paleomagnetic and MIS age models, and with and without volcanic sediments. The findings agree with shipboard determination of slowing sedimentation toward the present, and suggest either increased winnowing due to bottom-water flow or changes in productivity altering the biotic flux at the site.
Chapter 2 reexamines the Oligocene at Ocean Drilling Project (ODP) Sites 803 and 628 with revised taxonomic concepts. There are disagreements between the global compilations of macroevolutionary rates and the rates calculated at Site 803, though several hypotheses are discussed to explain the findings. A series of illustrations are presented to aid in taxonomic identification through this difficult interval.
Chapter 3 focuses on the Mi-1 event, discussing several new records: Deep Sea Drilling Program Site 78, ODP Site 803 (both equatorial Pacific Ocean), and ODP Site 744 (southern Kerguelen Plateau). After reviewing the leading hypotheses for Mi-1, the three new sites are used to test the paleoproductivity hypothesis, and use those records to investigate the importance of different orbital parameters. Lastly, the foram fragmentation index is employed to examine changes in the lysocline at the sites, demonstrating that there are dramatic global changes in the lysocline throughout the leadup to Mi-1. While carbonate sequestering carbon through the lysocline changes (or infact deepening Calcite Compensation Depth) cannot explain abrupt cooling events on their own (e.g., Coxall et al., 2005), a narrative discussion of the leadup to Mi-1 puts the lysocline changes in context with findings at other sites.
Fraass, Andrew J., "Ocean Gateways and Glaciation: Planktic Foraminiferal Records from the Southern Ocean, Equatorial Pacific, and Caribbean" (2016). Doctoral Dissertations. 659.