Integrated Analysis of the Geological Controls on the Lacustrine Source Rocks of the Cuyana Rift Basin, Argentina

Abstract

Successful exploration depends on the construction of a petroleum system model based on a comprehensive dynamic basin study. Depositional sequences are the result of a complex interaction between sediment supply, the availability of accommodation space (both involving tectonic components), sea level variations (which also may have a significant tectonic influence) and climate variations. The first-order control on basin geometry is the deformation field resulting from the tectonic activity, and it represents a fundamental control on sedimentation and the location of the resulting environments. In any basin, the geometry of the main faults should provide the final morphology of the trough and the resulting subsidence, and will therefore control the sedimentation rate, grain size, channel migration, avulsion episodes and the development of lakes. The Cuyana Basin is a Triassic continental rift developed during differential intraplate stresses derived from a backarc extension. The basin was filled with a tectonically induced second-order thick pile of continental deposits arranged into three third-order sequences composed of alluvial-fluvial to lacustrine facies which evolved in mostly isolated depocenters. This non-marine record showed that sea level was not a factor influencing depositional patterns; instead it seemed to have been the interaction between tectonics (subsidence-uplift, propagation, interaction and linking) and climate influencing the accommodation space, sedimentation rate, water input and the biological evolution of lakes that are presently significant hydrocarbon source rock and possible unconventional reservoirs. From outcrops to subsurface data the source rocks of the Cuyana Basin could be characterized as deposited in underfilled to balanced- filled lacustrine environments. These lakes were located close to the faults and subjected to climatic base-level fall-to-rise turnarounds and thus show a marked cyclicity. Total organic content may reach 14 % and corresponds to macro and micro floral remains, freshwater invertebrates and kerogen types I and II. Lacustrine facies are vertically stacked in patterns that can be related to the basin extensional cycles. Fourth order parasequences could be also characterized based on detailed information about mineralogy and fossil content. This contribution helps to understand the possible controls on the insertion and evolution of the lacustrine source rocks.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018