Abstract: Improved Age Correlation in Shallow Water Carbonate Sequences with Carbon Isotope Stratigraphy: The Aptian Shuaiba Formation. Oman and United Arab Emirates

Volker Vahrenkamp

Carbon isotope profiles in cored wells have been used to significantly improve age control and lateral correlation in an Early Cretaceous shallow water carbonate platform in Oman and the UAE.

Good time control is a prerequisite for stratigraphic correlation aimed at predicting reservoir heterogeneity and stratigraphic traps. On a field and regional scale, however, shallow-water carbonates often lack sufficient time control. Biostratigraphy usually provides a coarse stratigraphic frame only, leaving a high potential for miscorrelation.

Secular variations of carbon isotope ratios in the Early Cretaceous ocean have been documented in great detail from pelagic limestone sequences and have been correlated with open-ocean bio zones (Weissert & Lini 1991). Carbon isotope profiles in cores from the shallow water Aptian Shuaiba Formation in Oman and the UAE can be correlated with these open-ocean secular variations. The absolute magnitude of the variations of carbon isotope ratios by more then 2^pmil and the overall direction of trends are identical between the deep and shallow marine carbonate profiles within a biostratigraphically constrained time interval. Thus, secular variations can be used to significantly improve the time-stratigraphic constraints on the deposition of the Shuaiba Formation.

Previously, carbon isotope signatures of the Shuaiba Formation have been used to indicate subaerial exposure and related diagenesis in these shallow water sequences. However, our results suggest that the carbon isotope variations in the investigated sequences are largely of depositional origin without apparent diagenetic overprint.

Carbon isotope stratigraphy has significant potential for application in many carbonate sequences and reservoirs in time intervals where secular isotope variations can be well constrained from pelagic limestone sequences.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994