--> ABSTRACT: Tectonically Forced Backstepping and Drowning of Foreland Carbonate Platforms and Reefs, by Steven L. Dorobek; #91020 (1995).

Datapages, Inc.Print this page

Tectonically Forced Backstepping and Drowning of Foreland Carbonate Platforms and Reefs

Steven L. Dorobek

Carbonate platforms and reefs commonly form on the distal side of a foreland basin during active stages of basin development and may provide an excellent record of basin evolution and relative sea level change. Synorogenic foreland carbonate platforms typically have ramp profiles that mimic the flexural profile produced by tectonic loading. Exceptions to this occur where non-flexural deformation across the foreland produces local structural highs that affect carbonate platform morphology. Ramp morphologies develop because flexure controls depositional gradient, subsidence rate, and water depth along the profile.

During active convergence, the flexural profile migrates cratonward in unison with the advancing orogenic wedge. Synorogenic carbonate ramps are forced to backstep cratonward. Basinward parts of some foreland carbonate ramps may be drowned (sensu stricto) during active convergence, especially when: 1) the underling lithosphere has low rigidity; 2) the orogenic wedge advances rapidly; 3) a eustatic sea level rise occurs at the same time as migration of the flexural profile; or 4) some other environmental stress affects carbonate-producing benthos. Two-dimensional forward models show that flexural drowning of some Phanerozoic carbonate platforms, even without a coeval eustatic sea level rise or other environmental stress, is possible in less than 250,000 yr.

Reefs located downslope from the forebulge crest may develop into pinnacles during active stages of convergence. Pinnacle morphologies might develop even without true eustatic rise because as the flexural profile migrates cratonward, reef-building organisms must keep pace with ever increasing subsidence rates. These pinnacle reefs will have "catch-up" fabrics before final drowning or termination by prograding siliciclastic sediments.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995