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Architecture of Channel levee Build Up in Unidirectional Migrating Turbidite Channel Complexes in Plio-Pleistocene Channel Levee System of Indus Offshore Basin, Pakistan

Abstract

The Plio-Pleistocene channel levee system of Indus Offshore Basin, Pakistan shows tremendous Turbidite channel levee complexes in the deep-water environment. The Plio-Pleistocene channel levee system is present at a shallow depth from the sea floor. High sinuosity to low gradient Plio-Pleistocene channel levee system is highly confined to partially confined showing significant unidirectional movement. As a consequence of unidirectional movement the architecture of the channel levee complexes are modified. The levee build up in this study is distributed to two categories i.e. symmetrical and asymmetrical levees. Unidirectional migrating Plio-Pliestocene channels show significant asymmetrical levee build up as smaller levees deposit in the direction of migration while a broader and thicker levee is deposited in the opposite direction. The Plio-Pleistocene channels show that the successive channels eroded the smaller levee on the outer bend of the channel complexes and deposited another set of levee with similar characteristics as the previously built channel levee. This continuous unidirectional migration resulted in the progressive growth of compound levee on inner bend of the channel complex with each flow. The levees in direction of migration are steeper as compared to the levees on the inner bend which show gentle and downlapping reflections. The analytical calculations of at least 10 channel levee complexes also show a similar trend where the average thickness of inner bend levee is 810 m while the average thickness of opposite levee is 500 m. Contrary to unidirectional migrating channel levee complexes the vertically aggrading confined channel levee complexes show symmetrical channel levee growth. The study suggest that the levee initially built up by the unidirectional migration of the channel also impacts the subsequent channel buildup. Such levee accumulations hinder the swaying of the channel and further force the lateral migration of the channel, particularly transforming the channel behavior and architecture. The successive erosion of levee and deposition of channel fill stack to form potential zone for hydrocarbon accumulation. Keywords: Indus Offshore; Unidirectional Migration; Channel Levee; Petroleum Play