Sedimentology and paleogeography of an Upper Cretaceous turbidite basin in the South-Central Pyrenees, Spain

The present study deals with the primary lithology, sedimentary structures, depositional history and paleogeography of an Upper Cretaceous turbidite basin in the south-central Pyrenees, and presents a brief review of the lithology and depositional environment of surrounding contemporaneous deposits. During Coniacian to lower Maastrichtian, over a longitudinal distance of about 80 km along the present strike of the Pyrenees, thick series of calcareous turbidites, pebbly mudflows, slumps, sedimentary limestone breccias and marls accumulated, constituting what is termed the Vallcarga Formation. Sedimentary structures occurring in this formation indicate a relatively proximal site of deposition. A close study of the primary lithology of the Vallcarga sediments shows that they are largely composed of calcareous material derived from a shallow shelf, such as fossils, limestone rock fragments, intraclasts, pellets and micrite, with an additional admixture of terrigenous quartz and muscovite grains. A brief study was carried out in areas surrounding the Vallcarga Formation in which sediments of the same age are cropping out. Terrigenous material was supplied in areas to the NW and NE of the Upper Cretaceous basin, derived from granodioritic massifs exposed there, whereas in the southern part of the basin limestones were deposited, largely composed of reefal detritus. It is concluded that the turbidite basin was a small trough, and was brought about by increased local subsidence. In the westernmost part, this subsidence led to the formation of a fault-controlled submarine canyon, filled up with sedimentary breccias,possibly derived from the collapse and submarine erosion of an uprising diapire-like anticlinal structure. Field observations as well as measurements of current directions show that the basin was composed of three parts, separated partially or entirely by submarine swells. Each of these parts was filled up by currents flowing in a different direction, thus resembling the present basins off the coast of southern California.