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Stable Isotope Evidence for Depositional Cycles and Diagenetic Patterns in Brushy Canyon and Cherry Canyon Formations, Delaware Basin, West Texas

David A. Mucciarone, Douglas F. Williams, Arnold H. Bouma

A stable isotope study on two cores from the Brushy Canyon Formation and three cores from the Cherry Canyon Formation of the Delaware basin reveal distinct ^dgr18O isotopic differences in the carbonate matrix of these two clastic facies. The ^dgr18O isotopic values in the two Brushy Canyon cores are similar, regardless of whether the cores are from an overbank or channel part of the deep-water fan complex. The three Cherry Canyon cores are considerably more enriched in ^dgr18O than the Brushy Canyon cores, i.e., some values exceed +100 per mil relative to PDB. The ^dgr18O record of the three cores appears to correlate regionally with both isotopic composition and the geophysical logs. The extremely enriched ^dgr18O va ues (> +30 per mil) in the Cherry Canyon directly correspond to the fine to medium siltstones. The fine to medium sandstones represent a relatively depleted ^dgr18O isotopic signal of less than +30 per mil. The large ^dgr18O contrast between the Brushy Canyon and Cherry Canyon basinal clastics suggests that changes in sea level, combined with possible wind-blown clastic and evaporitic materials from back-reef lagoonal environments, could enhance the distinct isotopic differences of the two clastic facies. Although diagenesis is part of the isotopic signal of the carbonate matrix of both basinal clastic facies, the effects of diagenesis have not totally eliminated the primary isotopic signal due to the depositional processes of the two clastic facies.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.