Structural evolution and sediment depositional system along the transform margin- Palar–Pennar basin, Indian east coast

Abstract

Continental transform margins are characterized by sub-vertical strike-slip faults and rapid change in thermal gradient across the margin from continental to oceanic crust. The continental crust terminates abruptly along such sheared margins. Tectonic evolution associated with sedimentation in continental slope of the Palar–Pennar transform margin is inadequately understood due to limited seismic data and/or poor imaging with few well controls. Exploratory drilling attempts for hydrocarbon presence have resulted in some promising outcomes in the Palar–Pennar basin.The Palar–Pennar graben in onland is bound by steep normal rift faults, which reactivated by strike-slip movement during late syn-rift time as Antarctica separated along the NNW to ∼ N-trending Coromandal transform margin in the offshore part. The pre-existing Precambrian shear zones and lineaments in the basement have played a governing role in the basin development. The onland drainage pattern is structurally controlled as observed from its rectangular drainage pattern, tectonic index and sinuosity index. In offshore area of the basin, seismic interpretation identifies distinct pull-apart rift basin along the Coromandal transform margin with syn-rift deposits in the lower continental slope portion. Strike-slip movement uplifted the fault blocks in the southern part of the pull-apart basin. This has also reactivated some of the rift faults in the syn-rift section. Such reactivation results in early post-rift seal breach. This tectonic event has implication in the depositional sequences, which has been portrayed by seismic stratigraphic analysis and construction of chronostratigraphic section across the transform margin in this work. Thickening of post-rift deposition towards E -SE, major hiatus, large scale mass transport complexes and erosional events have been identified from such analysis. On this basis, seven distinct tectonic sequences, M1 to M5 in Mesozoic and T1 and T2 in Tertiary, have been identified. The chronostratigraphic section can help in deciphering the relative sea level changes based on the nature of stratal terminations, extent of erosion and non-deposition. This study emphasizes the tectonic-controlled drainage system and geometry as well as sedimentation pattern in onland and offshore deepwater area of Palar – Pennar basin alongside the Coromondal transform margin.