La serie Triasica de Los Pastores (Algeciras)

Abstract

Seven superimposed lithostratigraphic units have been distinguished in the Upper Trias of Los Pastores (Algeciras). The four lower units (1 to 4) show clayey-sandy-evaporitic Keuper facies. Pollen associations obtained from dark pelitic levels, and bivalves sampled from carbonate intercalations within these four lower units allow to date them as Carnian. These lower units can be correlated with the K1 to K3 units of the Keuper of the Subbetic and of other regions of the Iberian Peninsula. Concerning the three higher units, the unit 6 is pelitic-carbonatic and evaporitic and it also bears Carnian pollen associations. The units 5 and 7, however, are carbonatic and show clearly marine facies and organisms (Involutinidae and dasycladacean algae) of the same type than those shown by the Upper Triassic of Alpine Facies of the Internal Zones of the Chain (Alpujarrides and Rondaides). The Trias of Los Pastores belongs to an arid ecuatorial phytogeographical province, whose the vegetation was dominated by xerophytic elements. It was deposited in a wide coastal flat with marginal terrigenuos influence and close to a carbonate platform, in peritidal and shallow marine depositional environments, very sensitive to sea-level fluctuations. The marine carbonate intercalations bear low-diversity, dwarf and opportunistic marine faunal associations, typical of shallow, restricted, unstable and ecologicaUy inmature environments, as it has been confirmed independently by facies analysis.