Lacustrine and paleontological records from the middle Norian of the Eastern Cordillera of Colombia: Paleoenvironmental and paleobiogeographic implications of western paleo-equatorial Pangea

Abstract

The Bocas and Montebel formations in the Eastern Cordillera of Colombia, North Andes, contain a Late Triassic (middle Norian) lacustrine sedimentary record accumulated at low paleolatitudes. We provide here a detailed study of these units as well as new data on the paleobiogeographic affinities and paleoenvironmental the western paleo-equatorial belt of Pangea. A comprehensive stratigraphic, sedimentological, and paleontological analysis of these formations revealed lake-level fluctuations. Facies analysis demonstrates the presence of deep lake, open-water shallow lake, small-scale littoral deltas, marsh/swamp, and marginal lake subenvironments, indicating periods of lacustrine expansion and contraction. These sedimentary features are consistent with the Richmond-type lacustrine complex, defined for low paleolatitude lacustrine records of the early Mesozoic basins of the central and north Atlantic margins. Furthermore, we report the occurrence of fossil assemblages of plants in the Bocas and Montebel formations, including Podozamites sp., Pagiophyllum sp., Brachyphyllumsp., Otozamites sp., Zamites sp., Pecopteris sp. and Coniopteris sp. In addition, fossils of clam shrimps (Shipingia hebaozhaiensis, Shipingia olseni, Euestheria winterpockensis, and Gregoriusella sp.), and vertebrates (actinopterygian fishes and possible phytosaurs) that are typical of the Upper Triassic successions in North America and Europe, are identified. The presence of these flora and fauna provides compelling evidence of strong paleobiogeographic affinities, suggesting a Laurasian faunal influence in northwestern Gondwana and the absence of a typical southern Gondwana fauna and flora for this paleo-equatorial region of Pangea.