Stratigraphy and paleoenvironments of the Lumbrera Formation, Salta Group, northwestern Argentina

Abstract

In northwestern Argentina, the Lumbrera Formation represents the uppermost unit of the Salta Group (Cretaceous - Paleogene). Two sections are recognized in this unit based on the facies associations, recognized from bottom to top as Lumbrera Inferior and Lumbrera Superior. The basal section consists of gravel-sand and sandy permanent fluvial systems and a perennial fresh-water lake (Faja Verde). The upper section is characterized by clastic fine-grained sedimentation and locally, by conglomeratic sandstones deposited in ephemeral fluvial and ephemeral lake systems. Based on the sedimentary features and the fossil record of both sections, an abrupt climate change is interpreted, which varies from temperate humid in the base to warm/hot and dry in the upper part. The sedimentary and stratigraphic features allow interpreting two main depositional cycles for the Lumbrera Formation, divided by a major unconformity. These differences are not only the result of climatic changes but also represent variations in the basin configuration like subsidence rate changes and depocenters location that indicates the beginning of the foreland basin in Northwestern Argentina.