Journal of Conference Abstracts

ODP Leg 182: Great Australia Bight ­ The Mineralogical and Diageneic Interpretation of Cool-Water Carbonates from the Analysis of Wireline Log Data Using Mineralogical Inversion Software

Guy Spence (ghs2@le.ac.uk)¹, Mads Huuse², Peter Harvey¹, Maurice Tucker³ & ODP Leg 182 Shipboard Scientific Party

¹ Dept. of Geology, Leicester University, England

² Dept. of Earth, Sciences, Aarhus, Universitet, Denmark

³ Dept. of Geological, Sciences, Durham, University, England

Ocean Drilling Program Leg 182 investigated the Cenozoic cool-water carbonates in the western Great Australian Bight deposited in a mid to high latitude setting in water temperatures of less than 20 degrees Celcius. Carbonate accumulation on the southern Australian divergent passive margin began in the Eocene and continued throughout the Cenozoic. Wireline logging tools were used to gather continuous in situ down hole geophysical data from eigth of the boreholes drilled through the carbonate succession. The acquired logs include spectral gamma-ray, porosity, density, resistivity PEF (photoelectric effect), FMS (Formation MicroScanner-resistivity images), sonic velocity and magnetic susceptibility. Mineral inversion analysis of the log data has been used to attempt to determine quantitative stratigraphic variations in sediment mineralogical composition at all the logged sites. The minerals included in the inversion models were: high Mg-calcite, low Mg-calcite, aragonite, dolomite, glauconite, phosphate, quartz and clay minerals. Mineralogical and diagenetic trends identified by transform analysis are interpreted within the context of oceanographic changes and relative sea-level and climatic fluctuations during deposition. A significant advantage of using wireline log data to investigate stratigraphic changes in mineralogy is that it provides continuous coverage of the entire open hole interval of each borehole and is not dependent on good core recovery for XRD analysis. During Leg 182 interbedding of hard chert horizons and soft calcareous sediments was the cause of poor core recovery in many intervals.

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