Foramol Carbonate Shelves as Depositional Site and Source Area: Recent and Ancient Examples from the Mediterranean Region

G. Carannante, L. Simone

In recent environments, only limited carbonate depositional areas are dominated by coral reefs. Such platforms frequently develop rimmed margins and are characterized by chlorozoan facies with large contributions of nonskeletal grains. They are practically limited to warm tropical seas. In temperate seas as well as anomalous tropical zones, large areas of the middle-outer shelf are covered by skeletal debris with variable amounts of mollusks, foraminifers, coralline algae, bryozoans, etc (foramol facies). Apart from the skeletal fragments derived from the shallow inner shelf and the contribution from local endobiota and epibiota, the source of the bioclastic sediments may be found in limited and scattered areas supporting active carbonate-producing assemblages. These shelves do not develop organized rimmed margins. As a consequence, an open carbonate shelf is produced, sedimentation rate is very low, and the micritic fraction is pumped away to the slope. Seaward, the bioclastic sediments gradually pass to relic deposits of the outermost shelf where phosphatization and glauconitization phenomena may occur.

Fossil counterparts of similar deposits are present in the Mediterranean region (e.g., Spain, Italy, Malta, Libya), locally showing good reservoir properties. Examples are described from the Miocene of the Southern Apennines (Italy) where a variety rich in encrusting coralline algae is present, as well as from the Upper Cretaceous of the Southern Apennines and northwest Sardinia (Italy) where scattered rudistid buildups are associated with bioclastic sediments rich in coralline algae and bryozoans.

From the foramol open shelves, essentially during low sea level stands, large quantities of sediments reach the slope by means of gravity flows. Evidence of this may be found in foramol bioclastic beds intercalated with slope-to-basin deposits in the Mesozoic-Cenozoic sequences of Sardinia and the Southern Apennines.

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