The role of the Rio de la Plata transfer system on the offshore petroleum systems of Uruguay

Abstract

The Uruguayan continental margin, covering an approximate area of 125,000 km2 up to the 200 nautic mile limit), continues to be an underexplored region with significant hydrocarbon potential. Within this area two major basins are recognized: the Punta del Este Basin and the southernmost part of the Pelotas Basin. Both basins were formed as a consequence of the fragmentation of Gondwana and subsequent opening of the Atlantic Ocean, sharing a common genesis with the Orange Basin (offshore Namibia), located in its conjugate margin. From an exploratory standpoint, this is even more important in the light of recent and significant hydrocarbons discoveries made in the Orange Basin (e.g. Venus,and Graff-1). The Rio de la Plata Transfer System (RPTS), with a WNW orientation, separates the Punta del Este and Pelotas basins, located to the south and north respectively and, by itself, defines the central sector of the Uruguayan continental margin with very particular characteristics. This WNW trending fault system dissected the Uruguayan continental margin, resulting in crustal attenuation, faulting, and sinistral displacement of different features, including SDR wedges and the associated magnetic anomalies. This tectonic process significantly influenced sediment deposition from Aptian to at least Turonian times in the transition area between Punta del Este and Pelotas basins, exerting a substantial impact on petroleum systems. The unique configuration fostered the development of a significant depocenter in the central offshore region of Uruguay, creating a restricted area within the newly formed Aptian Sea. This environment potentially facilitated the accumulation of thicker and higher TOC shales compared to adjacent areas. The increased sediment overburden of this region, coupled with crustal attenuation, likely led to source rock maturation, coinciding with previous models. Sedimentation during this period was profoundly shaped by this distinctive configuration, characterized by a fault-bounded depocenter spanning 10,000 km2, flanked to the WSW and ENE by the Punta del Este and Pelotas SDR wedges, respectively, and to the north by the Polonio High. Consequently, whereas the Pelotas Basin sector of the Uruguayan continental margin experienced sediment starvation, the Punta del Este basin and its central depocenter received high-rate sedimentation, predominantly sourced from the NW, facilitating the development of several potential reservoirs and formation of stratigraphic traps. This depocenter stands out as the region with the highest concentration of faults along the entire Uruguayan continental margin, serving as potential migration pathways, further influencing the dynamics of the petroleum systems.