Abstract: Initiation and Maintenance of Carbonate Escarpments

John M. Hurst, Gregor P. Eberli

Modern and ancient carbonate platform escarpments are common, but their origin and maintenance are enigmatic. However, structural evidence from embryonic systems (Miocene, Gulf of Suez; Oligocene-Miocene, Burma; Permian, East Greenland; Devonian, Australia) indicates that escarpments originated along the crest of extensional fault blocks, growing vertically with subsidence and precluded from prograding by fault-controlled slope height. Compelling stratigraphic (lower Palaeozoic, North Greenland; Cretaceous Maiella, Italy) and seismic evidence (Cretaceous southern Gulf of Mexico and western North Africa) suggests fault-controlled initiation of these mature escarpments. In contrast, the origin of some Aptian-Albian escarpments (Gulf of Mexico; Adriatic) cannot be related to underlying e tensional faults.

Following localisation, vertical aggradation is primarily controlled by subsidence and sedimentation rate. Seismic and outcrop information suggests primarily flat aggradation with some low-angle internal relief. Margin facies are commonly similar to the bank interior; specific reef or biostromes are often lacking. Platform aggradation alone may maintain the escarpment. In other cases, slope height and declivity relates to sediment spalling and slope failure, due to oversteepening or dissolution. Escarpment height also relates to basinal sedimentation rate. In the Maiella and other Mesozoic-Tertiary platforms, sedimentation of pelagic and periplatform ooze constantly masks the margin, significantly reducing its height. In contrast, Palaeozoic escarpments (and some middle Cretaceous) ma maintain relief in the order of several kilometres due in part to low productivity. Independent of slope height, the escarpment is a bypass zone. As a result, the sedimentary sequences are detached into genetically but not geometrically related platform top and basin units.

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