The Tectono-Sedimentary Evolution of NW Madagascar: Application in Frontier Exploration of Deep Water Basins

Watkinson, Matthew P.¹, Edward P. Blunt², Mark A. Enfield³ (1) PDF Fellowship, University of Plymouth, Plymouth, United Kingdom (2) Sterling Energy plc, Harpenden, United Kingdom (3) PDF Ltd, Streatley, United Kingdom

The offshore basins of NW Madagascar present a significant frontier exploration challenge as a result of their complex geological evolution and a relative paucity of subsurface data. Exploration risk is being constrained through the integration of analyses of onshore geology and seismic sequence stratigraphy with an evaluation of the tectonic evolution of the southern Indian Ocean region. The resulting tectono-stratigraphic framework is being applied in offshore subsurface exploration.

The tectono-stratigraphy of NW Madagascar comprises seven megasequences. These can be related to Karoo extensional tectonics, Early Jurassic rifting between East Africa and Madagascar, opening of the Somali Basin-Mozambique Channel, mid-Cretaceous strike-slip tectonics, Late Cretaceous rifting between India/Seychelles and NE Madagascar and subsequently changes in the location and vectors of ocean spreading in the Indian Ocean during latest Cretaceous/Paleocene and the Cenozoic. The presence and distribution of these megasquences and the structural styles associated with them have been confirmed through a detailed evaluation of the onshore geology of NW Madagascar, including fieldwork.

The application of the tectono-stratigraphic framework to exploration offshore has been facilitated through analysis of a seismic database which has been significantly improved by reprocessing and new acquisition. And the sequence stratigraphic and structural interpretation of seismic data has provided new insights into the link between tectonics, salt behaviour and the nature and distribution of key play elements of the basins.