Aplicação de biomarcadores no estudo paleoambiental das formações geológicas atravessadas pelo Furo Mecupa-1

Abstract

This study applies organic geochemistry analyses, with emphasis on molecular biomarkers, to reconstruct the paleoenvironmental conditions of the geological formations crossed by the Mecupa-1 hole, located in the Rovuma Basin, northern Mozambique. Four formations were analyzed: Mifume (Late Cretaceous), Upper Jingone (Paleocene-Eocene), Quissanga (Eocene) and Chinda (Neogene). The interpretation of the biomarkers revealed that the Pristano/Phytane (Pr/Ph) ratios suggest deposition under predominantly reducing to anoxic conditions, typical of restricted marine environments, while the Pr/n-C17 and Ph/n-C18 ratios show preservation of n-alkanes in Mifume and Alto Jingone, contrasting with signs of more intense biodegradation in the Quissanga Formation. The diasterane/esteranes ratio and the distribution of C27–C29 sternanes indicate variations in the contribution of marine and continental organic matter, distinguishing intervals with predominance of phytoplankton algae and others with a higher contribution of terrestrial plants. Among hopanes, the C29/C30 ratio and the distribution of C31–C35 homohopanes point to carbonate and hypersaline environments at certain levels, while the Ts/Tm ratio served as an additional indicator of maturity and type of lithofacies. In general, the results demonstrate that the studied sediments were deposited in marine to coastal environments, under reducing conditions, but with variations in salinity, oxygenation and contribution of terrestrial versus marine organic matter, confirming the relevance of the meso-Cenozoic sequences of the Rovuma Basin as potential source rocks