--> Abstract: Sequence Stratigraphy and the Demise of Carbonate Platforms, by W. Schlager; #91004 (1991)

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Sequence Stratigraphy and the Demise of Carbonate Platforms

SCHLAGER, WOLFGANG, Free University/Earth Sciences, Amsterdam, The Netherlands

The termination of carbonate platforms and the change to siliciclastic deposition produce pronounced unconformities because carbonates and siliciclastics develop different sea-floor morphology and follow different patterns of sediment input and dispersal. Geometrically, these unconformities resemble lowstand unconformities but platform termination by exposure is rare in settings with continued sedimentation. With a lag time of only a few thousand years, the platform will resume growth when reflooded under the same environmental conditions. Most platforms are terminated by drowning--they become submerged to below the photic zone or they drown in a flood of siliciclastic sediment.

The high growth potential of healthy platforms severely limits the possibility of drowning by sea-level pulse. During the rapid Holocene transgression, many reefs and platforms grew at rates of 10(3) Bubnoffs (= microns per year), some in excess of 10(4) Bubnoffs. Scleractinian corals, the key element in the growth of platform rims, can grow at over 10(3) Bubnoffs and similar growth rates have been observed on fossil frame builders. The rates of long-term subsidence as well as third-order sea-level cycles are 10(1)-10(2) Bubnoffs. Platform drowning is, therefore, more often controlled by changes in the marine environment and reduction in growth potential than by sea-level pulses. The coincidence of oceanic anoxia and mass drowning of platforms in the mid-Cretaceous, the Early Jurassic and the Late Devonian illustrate the environmental dimension of drowning.

Drowning unconformities demonstrate the importance of environmental change as an autonomous control on sequences, independent of sea-level fluctuations.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)