Controls on Contrasting Sandbody Architectures in Resedimented Oolitic Units from Rift Systems of the Mediterranean Jurassic

Frances Vivien Abbots

Jurassic facies over much of southern Europe record the infill of major rift systems created by the breakup of Tethys in response to the opening Atlantic Ocean. The modeling of resedimented carbonate sands deposited in rifts, with potential for facies association with basinal source rocks and pelagic seals, is discussed with reference to three resedimented oolitic sandbodies of contrasting architectures and their application to fan and recently developed apron models. In rift environments subject to active tectonism, sandbody architecture and depositional style are controlled by the size and paleogeography of the source platform and the interplay between tectonism and eustatic changes in sea level.

Localized development of a small, prograding, sand-rich oolitic fan occurs in the deep-water Brenha Formation (Toarcian-Bajocian) of western Portugal. Controlled by prefan tectonism and a limited source area, its fan characteristics are contrasted with two radically different contemporary oolitic aprons.

The Cutri Formation (Bathonian), a minor apron system from Mallorca, is characterized by infrequently initiated, high-density oolitic turbidites related to phases of tectonic activity on platform bounding faults. Affected by minor tectonism and subsidence, this apron was short lived because the source platform was drowned. This contrasts with the Vajont oolite formation (Bajocian-lower Oxfordian), northern Italy, a major resedimented oolitic sandbody interpreted as a tectonically aggraded faulted-slope apron. Predominantly sheet-like oolitic turbidites were fed via a line source from a gullied margin into a deep, narrow rift basin. The resulting wedge-shape sandbody formed from overlapping turbidites stacked into poorly developed, mainly fining-upward cycles aggraded by major fault-re ated subsidence.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.