Pleistocene Rapid Sea Level Change in Western Australia

April 6th, 2010

Climate change affects sea level causing sea level fluctuations, which are correlated to glacial and interglacial periods. During glacial intervals water is stored as ice on the continents; therefore, sea level drops. When temperatures increase during interglacial periods, the melting ice sheets return the water to the ocean basins thereby raising sea level. These intervals of higher sea level occur while the Earth’s climate is relatively warm. Hence, coral growth is particularly widespread.

The sea level high stand during the Last Interglacial of Pleistocene time is of interest because it was initially thought to be particularly long and stable, lasting between 131-119 ka (thousand years ago). Coral reefs thrived in tropical regions across the globe including the Bahamas, Belize, Hawaii and Australia, and now are exposed several meters above present sea level. In the last 10 years, a bipartite rapid sea level fluctuation termed the Devil’s Point Event was discovered in the Bahamas. Geological evidence suggests that sea level fell 4 m and then rose 6 m. U-Th dates indicate this event lasted less than 1500 years between 125 and 123.5 ka, thus suggesting that climate and sea level during the Last Interglacial were not as stable as had been thought previously. Very recent work has interpreted the Devil’s Point Event from exposures in tropical Western Australia; however, the timing of the event in that region is unknown.

The purpose of this study is to provide initial radiometric dates from corals associated with the Devil’s Point Event in Western Australia. Fossil corals were collected from Point Maxwell and Sandalwood Peninsula in Western Australia. X-ray crystallography was completed to determine the percent aragonite present in the corals. Corals with greater than 72% aragonite were chemically separated for uranium and thorium to obtain radiometric dates by alpha spectrometry. Dates obtained from below the erosional surface range from 122,722 ± 6,194 years to 173,365 ± 9,287 years. A date from above the surface occurs at 63,243 ± 5,342. These results suggest that the surface in Western Australia may be contemporaneous with the Devil’s Point Event in the Bahamas. Thus the rapid sea level fluctuation documented for the Bahamas was a global event.

Kristyn Rodzinyak, ’10 Trenton, Ontario
Majors: Geology, Chemistry

Sponsor: Benjamin Greenstein

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