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2018 AAPG International Conference and Exhibition

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Towards the Development of an Integrated Central Atlantic Tectono-Stratigraphic Framework

Abstract

During the late Mesozoic, the Central Atlantic region was a large enclosed basin; this offers the potential to compare the conjugate margins to provide a comprehensive assessment of basin evolution. This paper presents results from an ongoing multi-disciplinary project that aims to define a new stratigraphic framework for the Mesozoic in the Central Atlantic by integrating a suite of geoscience data from outcrop and subsurface wells. The results are already identifying pan-Atlantic sequence stratigraphic surfaces, improving stratigraphic resolution and realising existing source rock development models. Cumulatively, over 400 samples have been collected and analysed using multiple biostratigraphical techniques. New data includes detailed logging and sampling of the exposed Mesozoic stratigraphy of Maio, Cape Verde, a re-evaluation of 7 IODP sites, integration of data from available exploration wells. This extensive dataset covers a broad geographical area along the African and conjugate margin. Initial work is heavily basin-focused, new work re-sampling Senegal exploration wells aims to extend this framework onto the shelf and further onshore to cover the full depositional system. Early results include a new interpretation from DSDP 41-367 that highlights a previously unreported Lower Berriasian unconformity (LBU) which removes much of the late Tithonian sediments. Anoxia appears more widespread stratigraphically than previously defined, supported by new TOC and pyrolysis data, which is being integrated to better understand the hydrocarbon generating potential of these rich source rock intervals. High core recovery in DSDP 76-534a has permitted a new interpretation of the Base Albian unconformity (BAU), recognised elsewhere across the Atlantic region, suggesting there is a significant super-regional event at this time. This is associated with a major progradational phase of deltaic systems on both sides of the conjugate during the Albian, delivering plant debris-rich sediment to the deep basin and forming prolific reservoirs on the shelf (i.e. SNE field, Senegal). Further work by NARG, defining exhumation rates from low-T thermochronology data in northwest Africa, suggests a pulse of source area uplift around 120Ma. Hence at this time, it is postulated sediment loading of the shelf and continental crust by active Albian delta systems supplied by hinterland uplift triggered a tectonic/isostatic rebound of the oceanic crust forming the BAU.