Facies analysis and depositional environments of Permian carbonates of the Venezuelan Andes: Palaeogeographic implications for Northern Gondwana

Upper Palaeozoic strata in South America were deposited over cratonic areas and in intracratonic basins (e.g. Solimoes, Amazonas, Parana); however in many areas such as Venezuela and Colombia they are rarely exposed through dense vegetation and the nature of the terrain, so that the strata are poorly documented. However, these strata do have significant implications for the palaeogeography of the time. This article reports on a study of the Permian carbonates of the Palmarito Formation, exposed throughout the Venezuelan Andes, and discusses the succession of palaeoenvironments and the palaeogeography resulting from detailed field and lab work. Deposition took place on an extensive ramp which probably dipped gently northwards towards the open ocean. Much of the Palmarito succession shows a general transgressive trend, with a few thinner, more-regressive intervals, likely a response to glaciation–deglaciation cycles. Towards the end of the Permian in the Venezuelan Andes region, a major sea-level fall led to extensive uplift and erosion, resulting in a major disconformity between the Upper Guadalupian carbonates and overlying Jurassic red beds. The early Palmarito tidal-flat facies are noteworthy for their sub-metre-scale mud-to-sand cycles with incipient palaeosoil fabrics. Overlying mid-outer ramp carbonate facies are characterised by thin storm beds and bioclastic lenses, arranged into metre-scale coarsening-upward cycles. Succeeding shallow-marine inner-mid ramp, bioclastic grain–wacke-stones are dominated by an open-marine fauna of fusulinids, calcareous algae, crinoids, bryozoans and brachiopods. Outer-ramp facies are wacke–mud-stones with sponge spicules, radiolarians and brachiopod fragments. There are similarities between the Permian deposits of Venezuela and those recorded from Guatemala and Mexico to the north, and from Colombia and Peru–Bolivia to the west and southwest, where carbonate systems also dominate. These facies were all part of a tropical foreland basin setting, the Mucuchachi Basin, which contrasts with the other Late Palaeozoic intracratonic basins in South America. Evidence provided here demonstrates that a seaway existed between Laurentia and Gondwana from the Early Permian through to the late Early Permian.