ABSTRACT: A Mixed Carbonate/Clastic Example in a Restricted Bay in a Temperate Carbonate Shelf (Cala Fornells, northern Minorca Spain)

J. J. Fornos, V. Forteza, C. Jaume, A. Martinez-Taberner

Cala Fornells is a restricted bay located in the northern section of the island Minorca. Cala Fornells has a surface area of 4 km² and a maximum depth of 25 m at the mouth, which connects with the northern Minorca platform. Due to ephemeral streams with very fine textural inflow, the sedimentary facies present in the floor of the bay are primarily controlled by the bioclastic carbonate ecosystem production and the terrigenous input. The distribution of the facies is related to three major factors: (1) bathymetry, which controls the ecosystem distribution (Cymodocea

nodosa-Caulerpa prolifera, Posidonia oceanica, and maerl communities, from shallowest to deepest); (2) hydrodynamic conditions due to northern winds (locally called Tramuntana), which control the grain size distribution; and (3) local ephemeral streams, which control the terrigenous input. In the coarser fractions of the sediment (gravel and sand), the main components in the deepest zones are skeletal fragments of red algae. The shallowest zones contain fragments of the green alga Halimeda tuna, which may represent up to 50% of the total bioclastic fraction. The terrigenous components are mostly shales and only locally do we find a sand fragment of limestone and quartz grains. The organic matter content is very high (over 6% in the finest fractions), whereas in the more hydrodynamic a d deeper facies (25 m) where the bioclastic fractions are predominant, the organic carbon content is below 0.5%.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990