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Geochemical Analysis Of Eolian Fluxes During The Transition From Greenhouse To Icehouse Conditions In Equatorial Pacific., Daniel Nicholas Miller
Geochemical Analysis Of Eolian Fluxes During The Transition From Greenhouse To Icehouse Conditions In Equatorial Pacific., Daniel Nicholas Miller
Theses and Dissertations
To assess the atmospheric conditions during times of differing pole to equator thermal gradients through the middle Eocene to early Oligocene, 42 to 30 Ma, samples from deep-sea sediment cores U1331, U1332, U1333 from IODP Expedition 320/321 in the eastern equatorial Pacific (EEP) have been chemically leached to isolate the operationally defined eolian dust (ODED; <63 μm fraction). The ODED was analyzed for neodymium (Nd) isotopic compositions and rare earth element (REE) concentrations in order to determine the provenance of the ODED fraction and to elucidate the environmental conditions (e.g. predominant wind patterns) during deposition over the interval of study. The variations in the ODED fraction are expected to be controlled by changes in sources delivered via eolian input. However, negative cerium anomalies in the Post Achaean Australian Shale (PAAS) normalized rare earth element profiles of the ODED show a biasing geochemical seawater phase to the ODED signature. It is found that εNd values and cerium anomalies (Ce/Ce*) of ODED are consistent with fossil fish teeth values that record bottom water signatures from the same location and time period until ~36-37 Ma; around the Priabonian/Bartonian boundary marked by increased thermal gradients due to the emplacement of high elevation glaciers on Antarctica (Scher et. al., 2014). Moreover, the more negative cerium anomalies correlate to more radiogenic εNd values. The geochemical seawater signature in the ODED samples is believed to be caused by a change in sedimentary phase regulated by the spatial paleoposition of the sites relative to the biological high productivity zone and/or the depth of the CCD. Subsequently these regulators on the sedimentary phases of the ODED were investigated for biasing the geochemical signatures of the ODED, assumed to be changes in sources thereby provenance. Together, the Nd and REE results from the study temporally indicate that the ODED fraction may be a mixing between two sources, that of a biasing biogenic and/or authigenic source that records seawater conditions, and that of an older, less radiogenic continental source, inferred as Asian loess, as an increased thermal gradient prevails over the course of the study. Further research needs to be performed to make more robust and conclusive linkages between sources, mixing of sources, and atmospheric eolian delivery patterns, highlighting the necessity for a better understanding of atmospheric conditions during important climatic events throughout the history of the Earth.
Geochemical Source Components In Seafloor Lavas In The Aleutian Back-Arc, Max Thomas Siegrist
Geochemical Source Components In Seafloor Lavas In The Aleutian Back-Arc, Max Thomas Siegrist
Theses and Dissertations
Whole-rock compositions of seafloor lavas are used to constrain the processes and source characteristics contributing to the formation of geochemically distinctive, primitive magma types located in the Aleutian back-arc. Samples were dredged primarily from small volcanic cones on the seafloor, located between the emergent volcanoes and in the back-arc up to 60 km from the volcanic front. Compositions vary from basalt to dacite, with 48-70 % SiO2 and 4-13 % MgO. Nearly 30% of the samples are primitive, with Mg/Mg+Fe >0.60. Most primitive samples are basalts, which fall into two groups, based on minor and trace element abundances. Low/med-K …