Evidence of currents in outcrops of Pliocene Ayeyarwaddy River and Implication for sands distribution in Deep waters West of the Myanmar Coast

Abstract

Recently announced gas discoveries in the Plio-Pleistocene of the south-western offshore of Myanmar between 2012, when MPRL E&P's Pyi Thar-1 discovery opened a new gas play, and 2015-2017 when three more wells discovered gas in deep waters, showed significant sands development. These relatively abundant sands, definitely not from the Bengal Fan, prompt the question of their provenance, timing and mode of deposition. Publicly available data, announcements and literature, as well as extensive field work by MPRL E&P, indicate intermittent detachment episodes of the semi-rigid Myanmar Platelet from the India Plate during its continuous translational subduction below the Sunda Plate. These episodes are marked by catastrophic regional slumps exceeding 1,500 km2 in area and several hundred meters in thickness in two distinct periods, Lower Pliocene and Upper Pleistocene. The absence of mega-slumps during Middle to Late Pliocene and early Pleistocene suggests that the Myanmar Platelet was locked to the India Plate during these times, which were therefore favourable to connect the terrestrial fluvial system of the Ayeyarwaddy River with deep water deposition through the Watthe slump scar area. Paleo-current data from onshore, Southern Central Myanmar basin Plio-Pleistocene formation indicates a W or SSW directed trend, consistent with a paleo-Ayeyarwaddy fluvial system reaching the sea in the Chaungtha-Ngwe Saung area. The Watthe Lower Pliocene mega-slump opened a breach through which the paleo-Ayeyarwaddy River (paleo-Pathein River), brought massive sands into the Bengal Bay during the Pliocene and Lower Pleistocene, filling a section of the trench between the India Plate and the Myanmar Platelet. This area was therefore part of the submarine Ayeyarwaddy Delta during the Plio-Pleistocene, and distinct from the Rakhine Offshore Basin fed by the Ganges-Brahmaputra River system.

AAPG Datapages/Search and Discovery Article #90336 ©2018 AAPG Asia Pacific Region, The 4th AAPG/EAGE/MGS Myanmar Oil and Gas Conference, Myanmar: A Global Oil and Gas Hotspot: Unleashing the Petroleum Systems Potential, Yangon, Myanmar, November 13-15, 2018