Abstract: Cretaceous Carbonate Platforms: Controls and Questions

R. W. Scott, J. A. Simo, J. P. Masse, Paul Enos

For about 80 million years during the Cretaceous, carbonate platforms covered vast areas within the Tethyan Realm and fixed great amounts of calcium carbonate. Study of the global history of environmental and biotic processes was one of the main goals of the Global Sedimentary Geology Program. The Cretaceous Resources, Events, and Rhythms (CRER) Project resulted from GSGP and it comprised five working groups. WG-4 has focused research on carbonate platforms.

Thirty-two case studies provide maps and cross sections on the stratigraphy, geometry, facies, sequence stratigraphy, thickness, areal extent, depositional setting, paleoclimate, platform type, facies types, and rock-forming organisms. A few conclusions are that Cretaceous platforms: (1) are wedge-shaped sedimentary prisms thickest at the shelf margin, but at escarpments they are tabular subparallel units; (2) aggrade and prograde into the basin except at faulted escarpment margins; (3) formed upon both passive and active continental margins, in island arcs, and upon seamounts; (4) platforms rimming cratons reflect the interaction of terrigenous runoff and marine transgressions; (5) generally began as ramps and accreted into rimmed platforms; (6) were terminated by the affects of temp rature and/or the interaction of turbidity, nutrients, anoxic water masses, and tectonics; (7) exhibit coastal encroachment that may be coeval with progradation.

Sequence stratigraphic models of Cretaceous platforms tend to differ in important ways from those of solely terrigenous clastic shelves. These platforms consist mainly of transgressive and highstand systems tracts bounded by regional drowning unconformities that may have also been subaerially exposed to fresh waters. Strata onlapping the platform slope are generally deep-water transgressive systems tracts rather than lowstand tracts.

Some of the important research areas yet to be fully addressed are: (1) rates of carbonate production and accumulation and platform accretion; (2) history of growth, exposure and drowning of platforms in different tectonic settings; (3) community successions and facies changes during platform drowning and recovery; (4) relationships between biotic crises and platform demise on a global scale; (5) paleobiogeographic implications of platform biota for global palinspastic reconstructions; (6) denudation rates in karstic terrains; (7) relation of platform processes and sediments to prevailing winds, temperature, evaporation and precipitation rates, among others; and (8) affects of platform development upon global CO₂ balance and the greenhouse model.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994