SURFACE AREA CONTROL OF SHALLOW CRATONIC TO DEEP MARINE CARBONATE ACCUMULATION

Sites of calcium-magnesium carbonate accumulation have been shifting from shallow shelf to deep marine settings since the late Cretaceous. During this time, total area of flooded epicratonic shelf has decreased about 50%, and areas of shelf carbonate deposition have declined from 27 x 10(6) km(2) to present areas of 1.4 x 10(6) km(2) while the maximum extent of platform carbonate accumulation has decreased from about 50 degrees to 28 degrees north latitude. In terms of cratonic carbonate, this decrease in tropical shelf area has resulted in a sixfold reduction in shoal-water limestone accumulation from a Cretaceous rate of 0.6 x km(3)/m.y. to a present value of about 0.1 x 10(6) km(3)/m.y. Over the same time period, the global carbonate compensation depth has deepened by about 1.5 km, attendant with a threefold areal increase of calcite ooze depositionn (40 to 130 x 10(6) km(2)). This expansion has resulted in an eightfold increase in pelagic limestone accumulation from a Cretaceous rate of 0.05 x 10(6) km(3)/m.y. to a present rate of about 0.4 x 10(6) km(3)/m.y. Transfer of accumulation from shallow cratonic to deep marine depositional settings records the central role of sedimentary environment surface area in predicating the differential partitioning of finite carbonate fluxes to Phanerozoic global oceans.