ABSTRACT: Marine Carbonate Sequences from Foreland Area

DOROBEK, S. L., Texas A&M University, College Station, TX

Marine carbonate deposition in shallow water foreland settings typically is limited to distal foreland areas during periods of thrust advancement. Synorogenic siliciclastic sedimentation in the proximal foredeep and foreland basin asymmetry are obvious first-order controls on the distribution of synorogenic marine carbonate strata. Foreland carbonate platforms that overlie antecedent passive margin sequences typically extend farthest basinward during initial stages of convergence. During this time, the orogenic wedge is thrust onto attenuated continental lithosphere, producing an underfilled proximal foredeep. During subsequent advancement of the orogenic wedge and progressive loading of continental lithosphere with higher flexural rigidity, the foredeep widens and shallows. The basin may become overfilled and siliciclastics terminate carbonate platforms in distal foreland areas. Sequence stacking patterns in distal foreland carbonates may be controlled largely by episodic thrusting events and concomitant changes in flexure of the distal foreland. Examples include the Middle Ordovician of the Central Appalachians, Upper Cretaceous platforms in northern Spain, and the Tertiary of southwestern Papua New Guinea.

Foreland carbonates typically develop ramp profiles, possibly mimicking the form of the flexural profile. Rimmed shelves may develop where an antecedent rimmed shelf existed prior to convergence. The rimmed shelf profile is maintained if the foredeep remains underfilled or flexure and/or eustatic sea level rise do not drown the rim. Complex platforms may develop where anisotropies exist in foreland lithosphere. Vertical uplift of crustal blocks may produce isolated carbonate platforms close to an orogenic wedge. Examples include the Diablo and Central Basin platforms in the Marathon foreland of west Texas. Uplift of these platforms was great enough that siliciclastics derived from the adjacent Marathon orogenic wedge were diverted into adjacent basinal areas and did not affect carbona e sedimentation on the platforms. Complex differential subsidence in distal foreland areas also can influence facies tracts, platform evolution, and parasequence stacking patterns. Examples include Devonian-Mississippian foreland carbonates of the North American Cordillera.

During periods of relative tectonic quiescence, carbonate units may prograde from both cratonic and hinterland sides of a foreland basin. These carbonates accumulate in underfilled depocenters inherited from earlier phases of thrust loading. Basin subsidence rates and siliciclastic influx are low; sequence geometries and stacking patterns may be controlled largely by eustasy. Platform profiles have very low dips, and progradation rates of shoal water facies are very high. Examples include Silurian-Devonian carbonates of the Central Appalachians.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)