Paleostress analysis and rift kinematics of the petroliferous Barmer rift basin, western Rajasthan, India

Abstract

The NW-trending Barmer rift in western Rajasthan is one of the major petroliferous Indian basins. The basin rifted twice: (i) NW – SE extension in Early Cretaceous, and (ii) NE – SW extension during Late Maastrichtian to Early Paleogene. We performed structural fieldwork mainly along the rift margins to decipher the rift kinematics through geologic time. We collected ∼500 fault-slip data from limited outcrops along the basin's western and eastern margins. Paleostress analysis was performed for the first time in this basin using Win_Tensor, T-Tecto and FaultKin software. The outcome of this analyses shows that a strike-slip stress regime was prevalent in the western rift margin whereas the eastern margin experienced extension to transtension. Four paleostress regimes, DΔ, Dα, DΦ, and Dβ, were identified by inverting the fault-slip data. The two separate extensional regimes, during the Early Cretaceous and in the Late Maastrichtian to Early Paleogene, are confirmed. These are Dα (NW – SE extension) and Dβ (NE – SW extension). The analysis also presents two strike-slip regimes with varying maximum horizontal stress (SHMax) orientation, viz. DΔ and DΦ. Exact age correlation for these strike-slip regimes remains indeterminate. However, we deduced DΔ and DΦ were associated with the first extensional phase (Dα) during Early Cretaceous linked to India – Madagascar oblique separation. The Barmer rift extended obliquely guided by pre-existing structures. Remote sensing image analysis indicates that part of the western margin is neotectonically active as inferred from the drainage morphometry. The stress inversion analysis of earthquake focal mechanism data depicts a strike-slip transpressive regime prevailing at present in the NW India along with ∼ N-trending SHMax. This is mainly responsible for the neotectonic activities in the basin. We documented several fault gouge zones along moderately-dipping faults in the Cretaceous outcrops at the eastern margin. The lower the fault dips, the thicker the gouge zones associated with the faults. Such thick fault gouge of around 100 cm or more may act as a structural fault bound trap for Cretaceous reservoirs at depth. (Words: 324).