High-resolution sequence tracking in Metán-Alemania Sub-basin (Salta Basin Maastrichtian – Argentina): detailed stratigraphic anatomy of a lacustrine system under the influence of microbial processes

Abstract

The large oil discoveries of the past few years in the Brazilian “pre-salt” province have led to the necessity of conducting studies into the outcrops of sedimentary systems analogous to the reservoir rocks present in Brazil. In this context, the Salta Basin and Yacoraite Formation have a remarkable importance because of the similarities to the “pre-salt” sedimentary deposits. Located in northwest-ern Argentina, the Salta Basin evolved from an intracontinental tectonic rift context during the Cretaceous and early Paleogene periods, forming sub-basins that were filled by sediments from the Pirgua (syn-rift), Balbuena and Santa Barbara (both sag deposits) Sub-groups. In particular, the sag development in Metán-Alemania Sub-basin during the Maastrichtian (Yacoraite Formation) allowed the deposition of carbonate rocks in a typical lacustrine environment, where climatic factors – associated with Milankovitch cycles – played strong controls. The carbonate facies present in the studied area consist mainly of stromatolites and oolitic grain-stones, which are related to periods of dry weather during a progressive decrease of lake-water depth. By applying high-resolution stratigraphy techniques, individualized elementary sequences were ranked into medium and low frequency sequences and cor-related over tens of kilometers in the basin. Thus, high-resolution stratigraphy applied to lacustrine carbonate successions allowed a better understand-ing of their depositional evolution and stacking pat-tern, becoming an important tool for predictability and facies mapping. It is, therefore, a methodology with applicability in the oil industry, where rocks of the same nature constitute productive reservoirs.