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Christoph Lehmann1, Timothy J. Bralower2, Isabel P. Montañez3, David A. Osleger3
(1) BP Amoco, Houston, TX
(2) University of North Carolina, Chapel Hill, NC
(3) University of California, Davis, CA

Abstract: Applying sequence stratigraphic concepts between shallow- and deep-water carbonates, Lower Cretaceous, northeastern Mexico

Lower Cretaceous shallow- and deep-water carbonates are superbly exposed in mountain ranges of the Sierra Madre foldbelt of northeastern Mexico. A detailed sequence stratigraphic model for the shallow-water Cupido (Barremian-Aptian) and Coahuila (Albian) platform carbonates was constructed and constrained by available biostratigraphy and C and Sr isotope stratigraphies. Through correlation of vertical cycle stacking patterns, five composite sequences (Cu1, Cu2, Cu-Co3, Co4, and Co5) were recognized. Extensive folding and faulting have resulted in a lack of laterally continuous outcrops, making translation of sequence stratigraphic events into deep-water sections difficult. However, some correlations can be made using the available biostratigraphic control. Three abrupt peaks in Corg content correlate with globally recognized oceanic anoxic events OAE1a (early Aptian) and OAE1b (early Albian) and a significant, gulf-wide event in the late Aptian Globigerinelloides algerianus foraminiferal Zone. All three events exhibit short-term decreases followed by increases in C-isotope values (0.5-3 per mil). In the shallow-water sections, only the late Aptian event was recognized as a shale separating the two platform episodes and interpreted as a maximum flooding interval within Cu-Co3, which spans the time between the Cupido platform backstep and Coahuila platform initiation. The OAE1a event most likely coincides with flooding above the early Aptian sequence boundary on top of Cu2 and marks the beginning of the Cupido platform backstep during the early TST of Cu-Co3. The early Albian OAE1b event falls within the early HST and establishment of the Coahuila platform. Therefore, all significant oceanic anoxic events seem to be correlative with relatively high sea level in the region, although they formed at different positions on the relative sea-level curve.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana