Cretaceous extensional systems of the Golfo San Jorge basin: Insights from the analysis of fault length and displacement data

Abstract

Displacement profiles and maps were used in the subsurface of the Golfo San Jorge basin in the Manantiales Behr region to analyze factors affecting the geometric and kinematic evolution of an extensional system and its relationship with the migration and trapping of hydrocarbons. Two fault types were recognized: faults affecting both the basement and the sedimentary cover, and faults restricted to the sedimentary cover. The vertical growth of the faults within the sedimentary cover was constrained by vertical lithologic variations and by intersection with the free surface. Faults involving the basement are synsedimentary and show Dmax/L relationships and aspect ratios that allow their distinction from the shallower fault planes. The geometric coherence shown in the aggregated displacement profile and map suggests a synchronous kinematic evolution for the faults developed inside the sedimentary cover. Observed fault trace lengths and throw values distributions may indicate that those faults grew by the early linkage of isolated fault segments followed by the progressive building of displacement. Reactivation of pre-existent basement fabric had little influence on faulting across overlying sedimentary cover probably because the fine-grained beds of Pozo D-129 Formation acted as a structural decoupling level. The low degree of connection between the shallow and deep portions of the faults disregards the hypothesis of vertical migration from a local source pod. The mapping of fault segments with higher values of displacement and the recognition of transfer zones may help to locate and delineate footwall hydrocarbon traps. Comparison and integration with other studies show that Cretaceous fault systems in the eastern Golfo San Jorge basin have grown mainly by rapid length establishment and subsequent displacement accumulation. Also, most of the basement-involved structures do not connect significantly with overlying fault arrays.