Testing Global Synchroneity of Lower Cretaceous (Albian) Depositional Sequences: The Coahulia Carbonate Ramp, NE Mexico and the Gavrovo Platform, NW Greece

Christoph Lehmann, Jurgen Grotsch, Isabel P. Montanez, and David A. Osleger

Albian pelagic carbonate productivity cycles and redox cycles have been positively linked to changes in the Earth's orbital parameters. However, the mechanism(s) controlling the deposition of peritidal cycles during Cretaceous Greenhouse time remains controversial. Two Albian carbonate platforms, the Coahuila carbonate ramp of NE Mexico and the Gavrovo platform of NW Greece, were studied in order to compare the depositional and accommodation history of the two platforms.

The Coahuila carbonate platform developed as a distally steepened ramp attached to a basement block. Outcrop sections consist of up to 140 peritidal cycles with an average cycle thickness of 4.5 m. Peritidal cycles shallow upward from subtidal bases of peloidal-packstones/grainstones with rudists and bioturbated wackestones, to fenestral mudstones and tidal-flat laminites. In contrast, the Gavrovo platform developed as an isolated carbonate platform composed of Barremian to late Albian peritidal cycles. At Mt. Kanala, 272 m of Albian peritidal carbonates are exposed with an average cycle thickness of 2.7 m. Meter-scale cycles shallow upward from foraminifera-packstones, rudist floatstones and gastropod floatstones to birdseye mudstones.

Cycle stacking patterns for both platforms define a long-term decrease in accommodation space (Lower Albian), followed by a long-term increase (Upper Albian). This trend is independent of the differing accumulation and subsidence rates, and paleogeographic setting of both platforms. The accommodation history is consistent with published Albian sea level curves, suggesting that high-frequency cycles have formed from allocyclic processes which appear to be of global extent. Furthermore, the carbon isotope stratigraphy defined for Lower Cretaceous carbonates in Greece suggests a causal relationship between the accommodation history of the platform and seawater carbon isotope composition which is being evaluated in deep and shallow water Albian carbonates of Mexico.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California