Figure 7

The stratigraphy of the Jurassic rift basins is poorly known in Suriname, since no penetrations by the wells are available. However, from the Takutu graben in Guyana an estimate of the early basin fill can be made. Lacustrine source rocks, alluvial fans and fluviatile deposits, together with volcano-clastics, make-up the lower stratigraphy, while salts herald the ensuing marine development of clastics and carbonates. The regional unconformity of Albian/Aptian age (marking he break-up of Africa and South America) is overlain by a prograding sequence of clastic sediments, with only short periods of carbonate deposition. The sedimentary environment ranges from terrestrial to deep marine, roughly paralleling the modern day situation. Numerous onshore and 22 offshore wells provide a reasonable data set to evaluate the stratigraphy. An excellent Cenomanian-Turonian marine source rock overlies the Aptian/Albian unconformity. This source rock has been deposited over large parts of the basin, and has a documented gross thickness of 50-500m and total organic carbon contents up to 14%. Biomarker data from Abary-1 suggest a marine source rock to be present in the Lower Tertiary over part of the basin. Biomarker data from a Cretaceous oil sample from a well west of the Tambaredjo field indicates the presence of an active Jurassic oil system, probably related to the well developed syn-rift grabens offshore. Reservoir-seal pairs can be found in just about any age bracket. Oil and gas have been encountered in Upper Cretaceous and Tertiary reservoirs as diverse as valley-fills, point bars, shallow marine sands and turbidites.
Structuration is intense in the pre-Albian section, with extensional faulting during basin formation, and reverse faulting and folding during the inversion phase. During the Upper Cretaceous and Tertiary structuration is very mild, and the sequence is largely a monocline. However, new detailed inspection of seismic data have revealed that large domal structures exist along the palaeo-shelf edge, which were probably formed as result of strike-slip movements.