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Upper Cretaceous reefs were concentrated in low- to mid-latitude regions in the Northern 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 be investigated for geographic regions and subdivisions of the Late Cretaceous.

Numerical analyses of the PaleoReef database allowed for an assessment of the biological and physical attributes of reefs. From this database, Upper Cretaceous reefs representing the Upper Zuni 111 supersequence (Late Cenomanian-Santonian) can be characterized by rudists of the constructor guild. Other biota are also prominent. Biostromes and reef mounds in shallow intraplatform or platform-margin settings have large amounts of micrite and a moderate debris potential. Reefs representing the Upper Zuni IV supersequence (Campanian-Maastrichtian) can be characterized by rudists and oysters of the constructor guild. Other biota areprominent. Biostromes and reef mounds in a marginal marine setting have large to moderate amounts of micrite and a moderate debris potential.

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