Seismic stratigraphy of the Eocene–lower Oligocene in the uruguayan continental margin

Abstract

The uruguayan continental margin was generated following the fragmentation of the Gondwana supercontinent and the subsequent opening of South Atlantic Ocean. It constitutes an extensive sedimentation area in which three sedimentary basins can be found: the Punta del Este Basin, the southernmost portion of the Pelotas Basin, and the poorly defined Oriental del Plata Basin. The aim of this work was the identification and characterization of the different seismic units (seismic facies, systems tracts, depositional sequences) for the sedimentary interval assigned to the Eocene in the Uruguayan continental margin. Sequence stratigraphy was used as a basin analysis method for this purpose, using a database that consisted of approximately 10,000 kilometers of 2D seismic sections, acquired in exploratory surveys in 2007 and 2008. The workflow included the recognition of stacking patterns and/or stratal terminations, the definition of genetically significant stratigraphic surfaces and, based on these, the identification of systems tracts and depositional sequences. Three depositional sequences were identified in the studied sedimentary interval. The basal sequence is composed of four depositional systems tracts, including falling stage, normal regression (lowstand and highstand) and transgressive deposits. The intermediate sequence only preserves lowstand normal regression deposits. The third sequence is composed by three depositional systems tracts, including lowstand, transgressive and falling stage deposits.