Identifier

etd-04072011-121327

Degree

Master of Science (MS)

Department

Geology and Geophysics

Document Type

Thesis

Abstract

The Antarctic Drilling Program (ANDRILL) recovered 1138.54 m of sub-seafloor marine sediments with 98% core recovery at the AND2-2A drill site in South McMurdo Sound. Biostratigraphy, magnetostratigraphy, and isotopic dating (Acton et al., 2008) indicated that an Early to Middle Miocene section (223-1138.54 mbsf) was recovered. This study focuses on an interval with high concentrations of palynomorphs, located between 460.57 and 403.48 mbsf and dated to 16.7 Ma to 16.2 Ma according to the updated Acton et al. (2008) ANDRILL SMS age model. Palynological results show a pronounced increase in organic microfossils between 434.01 and 431.91 mbsf, compared to levels recorded in underlying lower Miocene samples. In addition to the rich pollen and dinoflagellate cysts recovered within this 4-m interval, a single grain of the freshwater algae belonging to the family of Zygnemataceae was recovered at 431.91 mbsf, indicating that some fresh-water was pooling on the surface. The unusually rich samples are mainly characterized by a pronounced increase in pollen of Nothofagidites spp. and Podocarpidites spp., and spores of the mosses Coptospora sp. and Rhoipites sp. This assemblage is coincident with an increase in relative abundance of various dinoflagellate cysts, mainly Operculodinium centrocarpum and Labyrinthodinium truncatum, and the acritarchs Leiosphaeridia, Mecsekia sp, and Cymatiosphera sp. These marine and terrestrial palynomorphs indicate a peak warming period for the first phase of the Mid Miocene Climatic Optimum at 16.5 Ma only matched in intensity by younger AND2-2A sediments at 312 – 310 mbsf, dated to 15.7 – 15.5 Ma (Warny et al., 2009). However, the terrestrial signal is significantly higher at 434 – 431 mbsf compared to the marine dominated assemblages at 310 mbsf implying that the climatic changes were more strongly felt on land than in the surface waters. We propose that this palynological signal reflects the amelioration of the paleoclimate in Antarctica during the first peak of the Middle Miocene Climatic Optimum as recorded in the Zachos et al. (2008) oxygen isotope curve.

Date

2011

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Warny, Sophie

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