Natural Radioactive Series Dating of Pleistocene Oceanic Materials

Thomson, John (1971) Natural Radioactive Series Dating of Pleistocene Oceanic Materials. PhD thesis, University of Glasgow.

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Abstract

Long sediment cores from the deep ocean can provide a continuous record of sedimentation from the present hack in time, in contrast to the fragmentary record available from the continents. Prom such cores, micropaleontological analysis has established "paleoclimatic" and ''paleotemperature" curves for the Pleistocene epoch, the most recent period of geological time. Elevated fossil coral reefs provide useful cross-correlations for the deep sea stratigraphy, because they may represent warm periods and corresponding high sea stands. Natural series disequilibrium dating is one of the few chronological methods available to define an absolute time scale for the marine record over the past 500,000 years. Most previous dating work has been performed on cores taken from the Caribbean Sea, because of the uniformity of sedimentation in that area. In this study, a time scale is estimated back to 400,000 years B.P. for a long globigerina ooze core from the equatorial Atlantic Ocean. Experimental data from the core indicate that the clay component of sedimentation has been uniform over this period in respect of the natural series parents U238 and Th232. While there is evidence that Ra migrates in the core, and that U234 possibly does, the Th 230/U234 activity ratio shows a regular logarithmic decrease with depth. Sedimentation rates of 2.20+/-0.16 cm./10e3 yr. and 2.32+/-0.17 cm./10e3 yr. are obtained from the (Th230 excess) and (Th230 excess/Th232) methods respectively over the depth interval 25-927 cm. These rates yield ages of 136,000 and 129,000 yr. B.P., and 423,000 and 401,000 yr. B.P. for the important W/X and U/V paleoclimatic boundaries. This is in good agreement with one of the two chronologies presently pronosed. (Pa231 excess) rates of sedimentation over the depth interval 5-185 cm, are consistently higher that (Th230 excess) rates over the same range. While the components of sedimentation fluctuate in this denth interval, calculation shows that (Pa231 excess) is consistently lacking in the core. Ages obtained by the Th230/U234 method for unrecrystallised fossil corals from the Upper Terrace of Aldabra Atoll lie in the range 127,000+/-9,000 yr, B.P., which is synchronous with the last high sea stand. Stratigraphic evidence suggests that the entire present atoll was formed at that time, implying that the fauna and flora have been established in less than 120,000 years.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Sedimentary geology, Paleontology, Marine geology, Geochemistry, Paleoclimate science
Date of Award: 1971
Depositing User: Enlighten Team
Unique ID: glathesis:1971-78580
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:09
Last Modified: 30 Jan 2020 15:09
URI: http://theses.gla.ac.uk/id/eprint/78580

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