--> Abstract: Sedimentary Provenance Using Nd Isotopes: Application To Sedimentary Basins In Australia, by D. J. Whitford and J. Hamilton; #90987 (1993).

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WHITFORD, D. J., and P. JOE HAMILTON, CSIRO, North Ryde, New South Wales, Australia

ABSTRACT: Sedimentary Provenance Using Nd Isotopes: Application To Sedimentary Basins In Australia

The Sm-Nd geochronometer can be used for determining sedimentary provenance. The derivation of provenance information from a sediment involves estimating when its crustal precursors were fractionated from the earth's mantle. The Sm/Nd ratio of crustal rocks is largely unaffected by intracrustal processes and thus, Sm-Nd isotope measurements can be used to calculate an "age" when the Nd departed from a mantle source. The calculated age may not have direct time significance but can be used to make inferences about sediment sources and has potential application as a correlation tool.

A number of sedimentary basins in Australia have been sampled for such provenance studies. One such example is of the Jurassic sandstones of the petroliferous Eromanga Basin of onshore Australia. The play concept is one of a lithic sand seal of the Birkhead Formation to quartzose reservoir sandstones of the Hutton Formation on structural closures. Neodymium model ages have been calculated from isotopic measurements on rocks spanning the Hutton-Birkhead transition from several wells. There is a marked decrease in ages from a range of 1.2-1.7 Ga in the Hutton Sandstone to a range of 0.88-0.96 Ga for the Birkhead Formation. The old Nd model ages for the Hutton Sandstone are consistent with their

derivation from old cratonic rocks whereas the younger ages from the Birkhead Formation imply a provenance change with the sediments derived from an admixture of cratonically-derived sediments with younger crustal material possibly derived from a contemporary volcanic arc.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.