Tectonic Evolution of the Durban/Zululand Basin: Implications for Exploration in a Poorly Understood Frontier Margin

Abstract

The Durban-Zululand Basin provides an exceptional example of a transform margin that developed during Gondwana break-up and subsequent evolution of the Falklands-Aghulas Fracture Zone. The area remains an untested frontier basin with substantial potential for hydrocarbon exploration in particular following recent discoveries in East Africa. Recent acquisition of high fidelity 2D reflection data from offshore Durban and Zululand Basin, in SE South Africa, has provided unparalleled new insights into the basin evolution, its crustal architecture and structural development.

As there is limited well data we undertake an integrated frontier exploration approach in this area, integrating potential field data, seismic mega-sequence analysis, geodynamic modelling and basin analysis to predict the hydrocarbon potential. Not only does this allow us to consider the temporal development of accommodation, hence assess the role of sediment supply and distribution, it also provides invaluable information on heat flow that is used to constrain potential source rock maturation and migration.

The Durban/Zululand Basin represents an interplay between continental rifting, break-up and an intra-plate transform system; any play concepts have to reflect this interplay. As a consequence, the observed proximity of highly-extended continental margin with volcanic, results in the juxtaposition of both rift plays and volcanic plays as well as subsidence and thermal histories that may not match existing models. Furthermore, the subsequent overprinting of the transform margin leads to the disaggregation of these crustal terrains and the development of long lived axial sediment supply providing possible clastic reservoir separated from bathymetric highs that may be more carbonate prone.

The structural framework mapping of the newly acquired reflection data, coupled with potential field data modelling, illustrates the highly variable nature of the crust in the Durban basin that incorporates a range of crustal types from highly extended crust, allochthonous basement highs to magmatic crust. Understanding the spatial distribution of crustal type provides a fundamentally new insight into both the heat flow prediction for source maturation but also the controls on sediment supply and transport that will influence reservoir distribution. Furthermore, the study highlights the importance of applying an integrated approach to basin analysis and petroleum system modelling in complex, frontier basins.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018