LITOFACIES, PALEOAMBIENTES y PALEONTOLOGÍA DE LA FORMACIÓN MELO (PÉRMICO INFERIOR) EN ARROYO SECO, DEPTO. RIVERA, REPÚBLICA ORIENTAL DEL URUGUAY. PARTES I Y II

Abstract

A detailed description ofthe lithofacies, the stratification properties, and the palaeocurrent distribution, in the lower part of the Melo Formation (46 m thick) is given. Considered as the parastratotype, the succession is divided into three sections. The lower section is interpreted as deposited on proximal platforms, with frequent storm generated structures, and represents a low stand system. The middle and upper sections represent a distal platform environment, related to a transgresive system which appears as four successive coarsening up parasequences disposed in a retrogradational seto The palynological analysis allowed to define five levels which do not correlate exactly with the three-fold stratigraphic division mentioned above. The lower half of the studied succession bears a typical continental association (3 levels, nominated VG, L and C), while the upper half has a strong marine influence as shown by the presence of acritharcs (2 Ievels, named Mt and Me). Comparison with palynofloras from other outcrops ofthe Melo Formation in Uruguay, and time-equivalent units of the Chaco-Paranense Basin (Argentina) and Paraná Basin (Brazil) is included. According to this analysis, it is concluded that the age of the Arroyo Seco succession is restricted to the Sakmarian-Artinskian interval. AIso a list of all the presently known species is given.