Master of Science (MS)
Geology and Geophysics
Extensive studies have examined the syn- and post-rift sediments in the South China Sea and surrounding margins, but pre-rift, Eocene deposits are rare. Here we examine organic-walled microfossils from the South China Sea, recovered at Site U1435 of IODP Expedition 349 to provide palynostratigraphic control and characterize the environmental setting before, and in response to, the initiation of seafloor spreading in the basin ~33 Ma. The well preserved palynological assemblage recovered allow dating of sediments sampled at Site U1435. Units II and III are now subdivided in 4 subzones; Zone 1 is essentially barren, Zones 2 and 3A are assigned an age of 50.5 to 40.6 Ma, Zone 3B likely ranges from 40.6 to 33.9 Ma (Unit II is thus Eocene in age), and Zone 4 (Unit IB) is likely ranging from 33.9 to 30.72 Ma (early Oligocene in age). The lack of palynomorphs and the extreme thermal maturity of the palynomorphs recovered in Zone 1 is believed to be associated to intense volcanism in proximity to site U1435. A decrease in terrestrial palynomorphs and the first appearance of Homotryblium plectilum at 40.6 Ma, both indicative of sea level rise, permits the integration of our biostratigraphic data into a sequence stratigraphic framework. This event is believed to be associated with the TA3.5 sequence cycle highstand in the lower Bartonian with the TA3.5 maximum flooding surface (41.2 Ma) marking the Lutetian/Bartonian boundary (middle Eocene). The palynological assemblage also provided valuable information on the environmental evolution in the northern South China Sea. The Eocene time interval sampled is characterized by abundant spores and Homotryblium spp. dinoflagellates, both indicative of a nearshore setting, with abundant palms and Spinizonocolpites spp. mangroves characteristic of a warm everwet environment. The lower Oligocene is characterized by decreasing abundance in spores, palms, and mangroves along with increasing conifers, thus indicating that the early Oligocene cooling was felt in the South China Sea as well. An acme of a new dinoflagellate, referred to herein as Spiniferites cf. pseudofurcatus is a new marker of the Eocene/Oligocene boundary, of potential regional value as characteristic of the newly opening South China Sea.
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Gregory, Mitchell Clifford, "Palynostratigraphy and Environmental Implication of Organic-walled Microfossils Recovered from IODP Site U1435" (2017). LSU Master's Theses. 4563.
Available for download on Saturday, February 23, 2019