Mud Layers and Oxygen Isotopic Ratios in Late Glacial Stalagmites from Coastal Western Australia

April 14th, 2012

Mud layers trapped within stalagmites from caves in a variety of environmental settings have been interpreted as flood deposits.  Here we present a combined petrographic and isotopic analysis of one glacial-age stalagmite, AUS-118 from Cape Range, coastal Western Australia.  Stalagmite AUS-118 was thin sectioned and visually inspected and 121 mud layers were identified.  The distance of each layer was measured from the bottom of the stalagmite.  Dates for each mud layer were calculated using a growth model based on four uranium-thorium dates.  The mud layers date from 15,310 to 25,720 years ago and they were bundled into 100 year-long growth intervals to calculate flood frequency. In addition, stable isotope samples were drilled and then analyzed at the University of Nevada Stable Isotope Laboratory and were assigned an age using the same model.  Because of recent studies from northern Australia and the West Pacific Warm Pool that reveal a climatic teleconnection to the North Atlantic, we compared the general trend of mud layer ages with that of Greenland ice core oxygen isotopic ratio data.  Our preliminary results suggest an intriguing (but statistically untested) similarity at centennial-to millennial-scales.  We also found a visual similarity between the trends of mud layer ages and the oxygen isotopic ratios. Because rainwater oxygen isotopes in this region are strongly influenced by tropical cyclones and lower stalagmite oxygen isotopic ratios coincide with periods of more frequent mud layers, it is possible that these layers record changes in tropical cyclone frequency.  However, many other explanations must also be explored.

Ni An, ’14
Chengdu, China
Majors: Geology, Environmental Studies

Sponsor: Rhawn Denniston

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