Geochemical Correlation of Sedimentary Rocks: ABSTRACT

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A geochemical method has been developed that can provide effective regional or local correlations in sedimentary sections. This method depends on careful selection and processing of well samples followed by quantitative spectrochemical analysis for both major and trace elements. It has been used successfully in numerous field studies involving sand/shale and carbonate sections of nearly every geologic age from Cambrian to Holocene. The method relies primarily on compositional variables in the clay component of sediments because these have the best long-range continuity in a basin. Ratios of related elements such as V/Cr and Cu/Ni are useful because they minimize the effects of lateral changes in lithology or environment. Ratios that reflect primarily basinal changes in water composition are particularly useful, although environmental or provenance influences can be used as well. Abrupt changes in element ratios commonly record the locations of unconformities that are useful in correlation, whether or not they represent a major hiatus. This geochmical method has proved to be especially well suited to defining correlation points within late Paleozoic strata of Devonian to Leonardian age in west Texas. Spectrochemical analyses of shale drill cuttings from wells covering much of the Delaware and Juno-Val Verde basins defined regional geochemical units. They extend throughout the Delaware basin, into the Juno-Val Verde basin to the southeast, and onto the Carlsbad shelf to the northwest. Individual correlation points were identified over distances of up to 300 mi (483 km). Data from later seismic surveys support the stratigraphic concepts developed from the geochemical correlations. End_of_Article - Last_Page 993------------