Architectural complexities and morphological variations of the indus fan and its elements: Understanding of the turbidite system through seismic characterization

Abstract

The investigations of the processes occurring in submarine fans improve the understanding of intricacies of deepwater turbidity system and their associated developed architectural elements. The seismic patterns and depositional geometries of the channel levee complexes of the Indus fan have been studied using 2D/3D seismic and well data. The Indus fan is the second largest submarine fan in the world, with a horizontal extent of some 1500 km and a thickness of approx. 9 km. The development source of the Indus fan is divided into two units primarily based on their stratigraphic architecture and depositional characteristics. Firstly, the Eocene-Oligocene to Miocene lower unit that is built of channel lobes, and regionally developed large mass-transport deposits including megaturbidites. The other unit is Miocene and the Quaternary upper part that constitute major channel levee complexes with minor intercalations of locally developed mass transport deposits. The former progressively increase in thickness and width upwards the Eocene-Oligocene to Quaternary. This gave rise to symmetrical and asymmetrical growth patterns as a result of multiple phases of erosion and deposition. Such an architecture is present at an extensive scale primarily in the Plio-Pleistocene channels where the vertical to lateral growth ratio is higher than the channels. A single episode of thick MTDs is recognized by seismic reflection geometries suggesting sea level fluctuations that occurred between the Eocene-Oligocene and the Miocene, and from the Pliocene and the Quaternary channels. Regional confinements drastically affected the development of the Indus fan from the Eocene-Oligocene to Miocene, diminishing from the Pliocene-Quaternary. Sediment zonation occurred owing to the presence of structural confinements that controlled the growth of channel levee complexes and in general the entire Indus fan. Our results based on seismic reflection data of channel levee complexes suggest that increasing but alternating sediment supply from Eocene till Plio-Pleistocene, assisted the active channels and levee growth. Continuous increase in turbidity current size and energy along with sedimentation rates modified (i.e., increased the channel aspect ratio) the channel architecture of the Indus Fan.