Cretaceous black shales of Venezuelan Andes: preliminary results on stratigraphy and paleoenvironmental interpretations

Abstract

This paper deals mainly with the Late Cretaceous La Luna Formation on the Venezuelan Andean Platform. The studied area (the so-called Transversale de Barquisimeto) is located at the contact zone between the Andes of Merida and allochthonous slabs thrusted from the Caribbean Domain and is crosscut by a major active transform fault (the Bocono Fault), which is part of the contact zone between the Caribbean and South-American plates. The La Luna Formation is made of dark, organic-rich, laminated limestones and shales and, though always appearing with black shale facies, is different in the areas located in the north or in the south of the Bocono Fault. We provide here some new information about the biostratigraphic frame of the La Luna Formation and of the overlying Colon Formation. In the studied area, the depositional environment of the La Luna Formation was certainly rather shallow (near storm wave base) and stratified. During deposition of La Luna Formation, dysaerobic to anoxic conditions prevailed, which may be linked with a regional anoxic event, perhaps related to seasonal upwelling along the northern coast of South America during Late Cretaceous time.