PATTERNS AND PROCESSES INFLUENCING UPPER CRETACEOUS REEFS

Abstract

Upper Cretaceous reefs wereconcentrated inlow to mid latitude regions in theNorthern Hemisphere between the Americas and the Arabian Peninsula Rudist bivalves scleractinian corals sponges stromatoporoids and algae were the dominant biota. Most Late Cenomanian through Santonian reefs occurred in low paleolatitudes 0-30°N and were dominated by rudist bivalves North of 30° reefs constructed of corals stromatoporoids and siliceous sponges outnumbered those of bivalves Campanian through Maastrichtian reefs occurred between the equator and 30° N and were also dominated by bivalves whereas corals and bryozoans dominated the northern occurrences The distribution of Upper Cretaceous reefs was analyzed with respect to paleogeography surface current circulation patterns sea level and sea water chemistry. Considering the paleogeographic setting of the Late Cretaceous westward flowing surface currents accounted for the low to mid latitude distribution patterns of reefs whereas northward surface currents could account for northern occurrences in the European and North American regions especially during sea level highstands when shelfal areas were flooded. There is a global correspondence between the development of Upper Cretaceous reefs and the first-order sea-level highstand of Haq et al. (1987) but there is only a regional not global correlation between reefs and second order sea level fluctuations some reefs were associated with third order and fourth order fluctuations. We found no direct correspondence between the global distribution of Upper Cretaceous reefs and oceanic anoxic events salinity, aragonite-calcite seas or sea-surface temperature, although links still need to beinvestigated for geographic regions and subdivisions of the Late Cretaceous. Numerical analyses of the PaleoReef database allowed for an assessmentof the biological and physical attributes of reefs. From this database Upper Cretaceous reefs representing the Upper Zuni III supersequence. Late Cenomanian Santonian can be characterized by rudists of theconstructor guild. Other biota are also prominent. Biostromes and reef mounds in shallow intraplatform or platform-margin settings have large amounts of micrite and amoderate debris potential. Reefs representing the Upper ZuniIV supersequence Campanian Maastrichtian can be characterized by rudists and oysters of the constructor guild. Other biota are prominent Biostromes and reef mounds in a marginal marine setting have large to moderate amounts of micriteand a moderate debris potential.