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Abstract: Use of Strontium Isotopes in the Interpretation of Thrust Structures in Carbonates of Papua New Guinea

L. I. Eisenberg, J. C. Phelps, C. F. Kluth

The Miocene age shallow water platform Darai Limestone makes up most of the surface exposures in the Papua New Guinea Fold Belt. The stratigraphy of the Darai can be broken into several units, based on fossils, and in some cases, subtle lithologic changes. In general, however, the units cannot be readily recognized in the heavily forested, rugged karst topography of the New Guinea Fold Belt. The ratio of Sr 87 to Sr 86 has been shown to vary with the age and therefore the stratigraphic level of the Darai. We have used this relationship to constrain the position of surface exposures and well data in the Darai on the Mananda Anticline, a large hydrocarbon bearing surface structure, within the Papuan Fold Belt. In turn, we have used the information about stratigraphic level n the Darai to constrain our interpretations of structural geometry at depth at Mananda. Specifically, the information was used to estimate depth to the base of the Darai in the construction of a series of structural cross sections. In addition, the Sr isotope data gathered from surface traverses suggested the presence of repetition of units of the Darai by numerous small-scale faults on the southwestern flank of the structure. Reexamination of radar images and surface data revealed subtle indications of the faults, previously unrecognized by mapping focused on large scale exploration problems.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France