Segmentation of the Guyanas continental margin of South America is inherited from the dual-phase Mesozoic rifting history controlling the first-order post-rift sedimentary architecture. The margin is divided into two segments by a transform marginal plateau (TMP), the Demerara Rise, into the Central and Equatorial Atlantic domains. This paper investigates the heterogeneities in the post-rift sedimentary systems at a mega-regional scale (>1000 km). Re-sampling seven key exploration wells and scientific boreholes provides new data (189 analysed samples) that have been used to build a high-resolution stratigraphic framework using multiple biostratigraphic techniques integrated with organic geochemistry to refine the timing of 10 key stratigraphic surfaces and three megasequences. The results have been used to calibrate the interpretation of a margin-scale two-dimensional seismic reflection dataset and build megasequence isochore maps, structural restorations and gross depositional environment maps at key time intervals of the margin evolution.Our findings revise the dating of the basal succession drilled by the A2-1 well, indicating that the oldest post-rift sequence penetrated along the margin is late Tithonian age (previously Callovian). Early Central Atlantic carbonate platform sediments passively infilled subcircular-shaped basement topography controlled by underlying basement structure of thinned continental crust. Barremian-Aptian rifting in the Equatorial Atlantic folding and thrusting the Demerara Rise resulting in major uplift, gravitational margin collapse, transpressional structures, and peneplanation of up to 1 km of sediment capped by the regional angular base Albian unconformity. Equatorial Atlantic rifting led to margin segmentation and the formation of the TMP, where two major unconformities developed during the intra Late Albian and base Cenomanian. These two unconformities are time synchronous with oceanic crust accretion offshore French Guiana and in the Demerara-Guinea transform, respectively. A marine connection between the Central and Equatorial Atlantic is demonstrated by middle Late Albian times, coinciding with deposition of the organic-rich source rock of the Canje Formation) (average TOC 4.21 %). The succession is variably truncated by the middle Campanian unconformity. Refining the stratigraphic framework within the context of the structural evolution and segmentation of the Guyanas margin impacts the understanding of key petroleum system elements.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5280490

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International audienceLarge acritarchs were recovered from the Awaynat Wanin II Formation in the A1-69 borehole, western Libya at 394.4 m. This sample has been dated by acritarchs and spores as Givetian (Middle Devonian). Two species of acanthomorph acritarchs were recovered that are unusually large for the Paleozoic. The first type, represented by a single specimen, is a new occurrence of a previously described but unnamed form from the Middle Devonian of the Sahara. The second type, which is more abundant, is named as Vanguestainidium cucurbitulum gen. et sp. nov. Biogeochemical analysis using infrared microspectroscopy shows that the wall composition of this new taxon is close to algaenans isolated from the green alga Botryococcus braunii Kützing 1849 although these forms are not morphologically similar. The presence of well-preserved fragile palynomorphs, abundant terrestrially-derived palynomorphs including large megaspores, and rare marine palynomorphs suggests deposition in a low-energy nearshore environment such as a coastal swamp

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