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

The application of high‐resolution seismic geomorphology, integrated with lithological data from the continental margin offshore The Gambia, northwest Africa, documents a complex tectono‐stratigraphic history through the Cretaceous. This reveals the spatial‐temporal evolution of submarine canyons by quantifying the related basin depositional elements and providing an estimate of intra‐ versus extra‐basinal sediment budget. The margin developed from the Jurassic to Aptian as a carbonate escarpment. Followed by, an Albian‐aged wave‐dominated delta system that prograded to the palaeo‐shelf edge. This is the first major delivery of siliciclastic sediment into the basin during the evolution of the continental margin, with increased sediment input linked to exhumation events of the hinterland. Subaqueous channel systems (up to 320 m wide) meandered through the pro‐delta region reaching the palaeo‐shelf edge, where it is postulated they initiated early submarine canyonisation of the margin. The canyonisation was long‐lived (ca. 28 Myr) dissecting the inherited seascape topography. Thirteen submarine canyons can be mapped, associated with a Late Cretaceous‐aged regional composite unconformity (RCU), classified as shelf incised or slope confined. Major knickpoints within the canyons and the sharp inflection point along the margin are controlled by the lithological contrast between carbonate and siliciclastic subcrop lithologies. Analysis of the base‐of‐slope deposits at the terminus of the canyons identifies two end‐member lobe styles, debris‐rich and debris‐poor, reflecting the amount of carbonate detritus eroded and redeposited from the escarpment margin (blocks up to ca. 1 km3). The vast majority of canyon‐derived sediment (97%) in the base‐of‐slope is interpreted as locally derived intra‐basinal material. The average volume of sediment bypassed through shelf‐incised canyons is an order of magnitude higher than the slope‐confined systems. These results document a complex mixed‐margin evolution, with seascape evolution, sedimentation style and volume controlled by shelf‐margin collapse, far‐field tectonic activity and the effects of hinterland rejuvenation of the siliciclastic source.

Mixed siliciclastic‐carbonate deep‐marine systems (mixed systems) are less documented in the geological record than pure siliciclastic systems. The similarities and differences between these systems are, therefore, poorly understood. A well‐exposed Late Cretaceous mixed system on the northern side of the Eastern Greater Caucasus, Azerbaijan, provides an opportunity to study the interaction between contemporaneous siliciclastic and carbonate deep‐marine deposition. Facies analysis reveals a Cenomanian–early Turonian siliciclastic submarine channel complex that abruptly transitions into a Mid Turonian–Maastrichtian mixed lobe‐dominated succession. The channels are entrenched in lows on the palaeo‐seafloor but are absent 10 km towards the west where an Early Cretaceous submarine landslide complex acted as a topographic barrier to deposition. By the Campanian, this topography was largely healed allowing extensive deposition of the mixed lobe‐dominated succession. Evidence for irregular bathymetry is recorded by opposing palaeoflow indicators and frequent submarine landslides. The overall sequence is interpreted to represent the abrupt transition from Cenomanian–early Turonian siliciclastic progradation to c. Mid Turonian retrogradation, followed by a gradual return to progradation in the Santonian–Maastrichtian. The siliciclastic systems periodically punctuate a more widely extensive calcareous system from the Mid Turonian onwards, resulting in a mixed deep‐marine system. Mixed lobes differ from their siliciclastic counterparts in that they contain both siliciclastic and calcareous depositional elements making determining distal and proximal environments challenging using conventional terminology and complicate palaeogeographic interpretations. Modulation and remobilisation also occur between the two contemporaneous systems making stacking patterns difficult to decipher. The results provide insight into the behaviour of multiple contemporaneous deep‐marine fans, an aspect that is challenging to decipher in non‐mixed systems. The study area is comparable in terms of facies, architectures and the presence of widespread instability to offshore The Gambia, NW Africa, and could form a suitable analogue for mixed deep‐marine systems observed elsewhere.

Mixed siliciclastic-carbonate deep-marine systems, herein termed ‘mixed systems’, are less well documented than their siliciclastic-dominated counterparts, but may be common globally and misinterpreted as transient transition zones between carbonate and siliciclastic deposition. The well-exposed Upper Cretaceous mixed-system of the Buduq Trough, Eastern Greater Caucasus (EGC), Azerbaijan, provides an opportunity to study the interaction between contemporaneous siliciclastic and carbonate deep-marine deposition. The Buduq Trough represents a sub-basin formed within the larger unstable post-rift margin of the EGC. Qualitative and quantitative facies analysis reveals that Upper Cretaceous stratigraphy of the Buduq Trough comprises a Cenomanian-Turonian siliciclastic submarine channel complex, which abruptly transitions into a Coniacian-Maastrichtian mixed-lobe succession. The Cenomanian – Turonian channels are shown to be entrenched in lows on the palaeo-seafloor, with the sequence entirely absent 10 km toward the west, where a Lower Cretaceous submarine landslide complex is suggested to have acted as a topographic barrier to deposition. By the Campanian this topography was largely healed, allowing deposition of the mixed-lobe succession across the Buduq Trough. Evidence for topography remains recorded through opposing palaeocurrents and frequent submarine landslides. The overall sequence is interpreted to represent abrupt Cenomanian-Turonian siliciclastic progradation, followed by ~Coniacian retrogradation, before a more gradual progradation in the Santonian-Maastrichtian. This deep-marine siliciclastic system interfingers with a calcareous system from the Coniacian onwards. These mixed lobe systems are different to siliciclastic-dominated systems in that they contain both siliciclastic and calcareous depositional elements, making classification of distal and proximal difficult using conventional terminology and complicating palaeogeographic interpretations. Modulation and remobilisation also occurs between the two contemporaneous systems, making stacking patterns difficult to decipher. The Buduq Trough is analogous in many ways to offshore The Gambia, NW Africa, and could be a suitable analogue for mixed deep-marine systems globally.

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