Tectonic Controls on the Mesozoic Development of Stratigraphic Pinch-Out in the Exmouth Plateau – North West Shelf, Australia

Abstract

Multiple phases of extension resulted in the formation of the Northern Carnarvon Basin, and Exmouth Plateau. The extensional history has created regional uplift, as well as the uplift of individual footwall fault blocks. Superimposed on this are variations in sediment supply that affect the extent to which rift-related structures are filled, resulting in the formation of stratigraphic pinch-outs. This study aims to uncover the detailed timing of fault activity and the fill history of Mesozoic fault blocks on the Exmouth Plateau and to consider the implications of this for the formation of stratigraphic traps. Fault-block rotation and uplift began during the latest Triassic across the central plateau and continued into the early Cretaceous. Fault block rotation was more limited to the east of the plateau. Sediment supply from the latest Triassic to middle Jurassic was mainly sourced from the east, resulting in under filled half-grabens, eroded fault block crests and onlap of sediment onto rotated fault blocks in the central part of the plateau. Fault block crests remain emergent in the central area from the latest Triassic to early Cretaceous. Near to the start of the Cretaceous, there was a major change in sediment supply with input of large volumes of sediment from the south. Lowermost Cretaceous sediments onlap onto existing emergent fault blocks, while all but the largest blocks are drowned during the latter part of the early Cretaceous deposition. Driven by rift-related activity, stratigraphic traps become a likely option in the central plateau. The syn-kinematic strata onlap the earlier deposition, creating stratigraphic architecture that has result in the formation of pinch-out traps in the latest Triassic, Jurassic and earliest Cretaceous sequences. Understanding the syn-extensional fault and deposition dynamics has implications for syn-rift plays in the outboard Exmouth Plateau.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018