CRETACEOUS REEF ECOSYSTEMS AND ENVIRONMENTAL ASSOCIATIONS

Cretaceous reef ecosystems were global in their geographic extent and were concentrated in northern hemisphere, low and middle latitude regions between the Americas and the Arabian Peninsula for the duration of the period. Numerical data for reef ecosystems provided an assessment of the biological and physical attributes of reefs through time. Rudists and other bivalves dominated the reefs. Corals, sponges, stromatoporoids, gastropods, echinoids, arthropods, bryozoans, brachiopods, hydrozoans, algae, and foraminifers were associated with Upper Cretaceous shallow-water carbonate and/or mixed carbonate-siliciclastic platforms. These associated biota occurred in various concentrations within and/or adjacent to reefs and were involved in the constructor, baffler, binder, dweller and/or destroyer guilds. A positive association occurs between the development of Upper Cretaceous reef ecosystems and first-order sea-level highstands, but regional correlations exist between reefs and second-order sea-level fluctuations. Some reefs were associated with third- and fourth-order fluctuations. Reef distribution is linked strongly to paleogeography and surface currents, for the configuration of landmasses, ocean basins, and surface currents provided the conduit for the northern-hemisphere distribution of reefs. The global link between Cretaceous reefs and oceanic anoxic events is still unknown, although regional correlations have been proposed. Likewise a global correspondence between reefs and hypersaline conditions, and between reefs and elevated surface water temperatures does not exist, but local and regional studies show reefs associated with superheated, and hypersaline to normal marine waters.