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Transforming the Transform: Insights Into the Tectonostratigraphic Development of the Ghanaian Transform Margin From Newly Acquired Long-Offset Reflection Seismic Data

Abstract

Transforming the Transform: Insights into the Tectonostratigraphic Development of the Ghanaian Transform Margin From Newly Acquired Long-offset Reflection Seismic Data

The Ghanaian Transform margin consists of three major basins that have been explored to varying degrees. The structurally complex margin is a mixed transform-rift margin, with a strong compressional overprint that is evident throughout. To date exploration has largely focused in the mid – nearshore areas of the Tano Basin and nearshore of the Salt Ponds Basin yielding numerous discoveries and producing fields, proving a significant working petroleum system on the margin. Through exploration efforts thus far the proximal Tano (post-Albian) Basin is reasonably well understood the remainder of the margin is less so.

To facilitate a greater understanding of the margin as a whole ION acquired ~5500km of long-offset 2D reflection seismic during the summer of 2018. These data were imaged to a depth of 40km, tie key wells, cross numerous fields and successfully image the entire sediment pile and crustal thickness. These new data allow a fully integrated tectonostratigraphic model for the development of the Ghanaian margin to be constructed, which we present here.

We show the presence of significant sediment thicknesses below current well penetrations allowing for the creation of new petroleum plays in addition to those already known. The crustal structure is observed in striking detail and the distribution of crustal domains and thicknesses accurately mapped throughout. Strong evidence for magma-poor hyper-extension is presented with some potential for localized mantle exhumation within the Tano Basin with indications (potential SDRs) of elevated magmatic activity within the Romanche Fracture Zone.

The highly attenuated crust is resultant from at least three rift episodes; a Palaeozoic event, largely within the Salt Ponds Basin, and two Cretaceous rift events seen across the margin. The new data reveal two episodes of NW-SE directed compressional strain that are partitioned across the margin. Spectacular examples of margin inversion are observed along the length of Ghana Ridge/Romanche FZ and fault reactivation occurs throughout the Tano Basin, providing additional play potential.

The tectonostratigraphic model (updated structural elements, crustal and stratigraphic distribution maps) resulting from the newly acquired seismic data enhance our understanding of the mega-regional petroleum system, and reduce risk exploring the underexplored/frontier areas of the Ghanaian offshore and providing new play potential in the more explored areas.