AAPG Europe Regional Conference, Global Analogues of the Atlantic Margin

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Reconstructed Cretaceous Palaeosurface Geology Maps for South America and Africa

Abstract

A new generation of palaeosurface maps, which show deposition and bedrock types and associated drainage networks, have been compiled for South America and Africa for the 12 time stages of the Cretaceous. The reconstructions represent maximum erosive surface for each map and are compiled at a scale of 1:5,000,000; they also indicate the type of bedrock being eroded in the hinterlands and its bulk transport pathway. The intention is to assist geologists and explorationists by feeding these data sets into source to sink reconstructions, with the aim of understanding reservoir qualities. Generating the continental-scale palaeosurface geology for each timeslice involves the use of a lengthy, complex and robust workflow that involves several iterations, during which the geology of the palaeoland surface is fully understood and each stage of the procedure is subjected to a rigorous quality control process. Initial data collation was from 87 published geological maps, with compilation scales ranging from 1:500,000 to 1:2,000,000; these maps were then comprehensively attributed, standardised and correlated against the literature. Anything younger than the Cretaceous was removed for this study; therefore, only relevant geology would be rotated back to the palaeoposition. This produced an initial understanding of Cretaceous and older surface geology; however, there were large gaps in the data. Using our latest release Digital Atlas of Global Palaeogeography: Mega-regional Explorer Map Series, which was drawn at a scale of 1:5,000,000, together with the 1:1,000,000 structural data set, we were able to extrapolate the extent of sediments that have been either subsequently eroded or buried. Any remaining gaps indicate that there was no deposition during the Cretaceous. The palaeogeographies also record the tectonic histories; these, in conjunction with literature, are used to help understand the types of pre-Cretaceous sediments. During this whole process, the effects of Cenozoic uplift and erosion are considered, as is the likely amount of uplift and erosion of sediments during each timeslice. The drainage networks are also from the Mega-regional Explorer Map Series, although with modified attribution that is more compatible with the palaeosurface maps. The maps are good visual representations of the interactions between surface geology, transport pathways and influencing structures. They enable users to understand basin sediment source regions and lithologies. Moreover, the results can and have been used in source to sink studies that have combined results from Getech’s climate, ocean, tide and lithofacies prediction (including sediment flux) models to better understand the character, quality and distribution of potential reservoirs. The maps therefore give insights vital for future hydrocarbon exploration. We present reconstructed palaeosurface geology maps for South America and Africa, including the South Atlantic and East African margins as these are key areas for hydrocarbon exploration.