Structural Architecture of the Southern Orange Basin, Block 5/6, Offshore South Africa

Abstract

The Orange Basin is a passive margin recording the continental break-up of Gondwana by tectonic processes involving rifting and drifting of the South Atlantic Ocean. The northern part of the Orange basin preserves the main depocentre where the remarkable Ibhubesi Gas field is located. Based on exploratory results the tectonostratigraphy of the Orange basin is characterised by syn-rift grabens and half-grabens, as well as thick Barremian-Lower Aptian post-rift sequences ranging in thickness from 7 km in the north to 3 km in the south. The post-rift sedimentary succession in the south is thinner resulting in potential for oil-prone source rocks compared to the northern side of the Orange basin which is gas prone. In this study the subsurface stratigraphy and structural architecture of the southern part of the basin is delineated through the interpretation of 2D reflection seismic data from Block 5/6. The structural deformation revealed by the southern Orange Basin records the compressional domain - transitional domain – extensional domain; marked by the presence of grabens, toe thrust structures and listric faults respectively. Transform faults act as conduits for gas seepage which is a positive indication for an existence of an active petroleum system. The transitional crust is characterised by seawards dipping reflectors, volcanics interbedded with siliclastic sediments and volcanic intrusions. Investigation of the southern segment of the Orange basin presents an opportunity to examine the under-explored ultra-deep waters where there is potential for deep seated slope fans (canyon fill and slumped blocks) and basin floor fans (turbidites and channelized facies).

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016