PENNSYLVANIAN MICROBIAL CARBONATE PLATFORMS OF THE CANTABRIAN ZONE (NW SPAIN): THE DEVELOPMENT OF NUMEROUS HIGH-RELIEF PLATFORMS IN AN ACTIVE FORELAND BASIN

A wide spectrum of high-relief and steep-fronted microbial-dominated carbonate platforms nucleated nearly synchronously during Early Bashkirian times in the distal margin of the foreland basin of the Cantabrian Zone (NW... [ view full abstract ]

A wide spectrum of high-relief and steep-fronted microbial-dominated carbonate platforms nucleated nearly synchronously during Early Bashkirian times in the distal margin of the foreland basin of the Cantabrian Zone (NW Spain), a basin that developed in the eastern embayment of the Palaeotethys Ocean during the collision between Laurentia and Gondwana. These carbonate platform crop out in numerous nearly vertically-rotated thrust sheets providing good seismic-scale transects. Detailed geological mapping and available biostratigraphic data allow investigating outcrop platform size, growth styles, and platform evolution based on stratal patterns as well as the age of platform demise. This study reveals that the stacking patterns, growth styles and evolution of these carbonate platforms vary depending on their location within the foreland basin, which controlled the rates of accommodation, terrigenous input and, most probably, sea-water chemistry and trophic levels.
Close to the foredeep of the basin, carbonate platforms consisted of isolated depositional systems of moderate size (from a few kilometres up to a few tens of kilometres in width, and 500-1500 m in thickness) buried by orogen-derived siliciclastics during Late Bashkirian to Early Moscovian. In most of the cases, these carbonate systems show aggradational growth styles and limited progradation of the foreland-oriented platform margin. Due to their size and growth styles, they could be considered good outcrop analogues of the subsurface reservoirs of the Pricaspian Basin (e.g., Tengiz, Korolev, Karachaganak).