MIDDLE CRETACEOUS CARIBBEAN CARBONATE SHELF CRISES REVISITED

During the Barremian through Early Cenomanian interval Caribbean shelf and platform margin paleocommunities changed from coral-algal-rudist to rudist dominated and locally colonial corals were accessory organisms. Two hypotheses have been proposed to explain this change. Rudists out competed corals in a superheated, hypersaline Supertethyan climate zone (Kauffman and Johnson, 1988). The alternative “Strangelove pump” with niche exclusion hypothesis proposed that shelf-margin paleocommunities were stressed by a complex of environmental factors driven by increased frequency of shelf flooding by dysaerobic to aerobic water masses (Scott, 1995).

New data on Albian strata in drill holes, outcrops and climate modeling test these hypotheses. Low oxygen water masses developed in Albian oceans numerous times resulting in six widespread organic-rich black shale deposits cyclically interbedded with limestone and marl. OAE 1b @ 113.57-110.17 is recorded in Lower Albian slope deposits below the Comanchean shelf margin. OAE 1c @ 102.35-101.39 is recorded in the lower Upper Albian shelf deposits. OAE 1d @ 97.38-96.98 is identified in uppermost Upper Albian nearshore shale and limestone. Early Albian sea level flooded the Comanche shelf and the two Late Albian sea-level rises flooded the Western Interior of North America.

Rare Upper Albian rudist-coral paleocommunities occupied local shelf margin fault blocks. Late Albian rudist buildups occur no farther north than about paleolatitude 30°N, about 10° less than predicted by the “Supertethys” model. Climate modeling suggests that small eddies formed in Cretaceous oceans and that the Caribbean was arid but not extremely hot. Interior shelf buildups were composed principally of rudists, and fore-reef slopes hosted thrombolitic buildups, and their species composition did not change