Paleoambientes sedimentarios de la Formacion Apeleg, Cretacico Inferior de la Cuenca de Aisen, Region XI, Chile

Abstract

ABSTRACT. Sedimentary paleoenvironments of the Apeleg Formation, Lower Cretaceous of the Aisen basin, Region XI, Chile. Lower Cretaceous marine and terrestrial sandstones, and subordinate shales, crop out in southern Chile, between Cerro Kalterfeld and Coihaique (45°-46°S). These beds are equivalent in age and facies with strata in the Apeleg Formation defined in neighbouring Argentina. In Chile, the Apeleg Formation conforms a coarsening upwards succession divisible into a Lower Member, mostly composed of marine deposits, and an Upper Member with mainly terrestrial beds; the contact between these members is sharp but not markedly erosional in the studied exposures. Beds in the lower member represent the following major sedimentary environments: shelf or prodelta, delta front and coastal to sublittoral. Strata in the upper member represent sandy tidal flat and alluvial and deltaic plain deposits; the latter are recognized through wave and tidal reworking of fluvial beds. The Apeleg Formation terminates a transgressive-regressive cycle that begins with Berriasian coquinae and oyster beds (Cotidiano Formation), mantling a volcanic relief (Ibanez Formation), and follows with euxinic shales (Katterfeld Formation). Progradation of the sandy Apeleg depositional systems may have been controlled by an eustatic stillstand in the Hauterivian-Barremian.