Abstract The Miocene channel play of offshore Angola contains the recent giant discoveries of Girassol, Dahlia, etc. From recent 3D surveys that extend across the salt front onto the abyssal plain in the Outer Congo Fan, it can be seen that this play can now be continued out into theultra-deep water into a new highly prospective frontier area. This presentation covers this area’s prospectivity and the use of the models generated here in the salt province. The Congo Fan of Angola shows evidence of extensive sand deposition from the Oligocene onwards. This sand deposition extends beyond the current exploration targets in the salt diapir province onto the abyssal plain, an area that has been covered by recent 3D seismic data sets. By using these data, the morphology of differing styles of sand deposition can be shown in a variety of ways including amplitude extraction, timeslices, opacity, and 3D visualisation. All these methods work well in this area because the strong amplitude/acoustic impedance contrast between sand and shale is combined with the approximately flat-lying nature of the abyssal plain. These factors allow the depositional morphologies to be shown without the influence or bias of interpretation. In this province of offshore Angola, it can be also demonstrated that the Cretaceous and early Tertiary on the abyssal plain shows little or no seismic evidence of sand deposition. However, this section is a prime candidate to contain mature source rocks, the evidence for which can be demonstrated by the clear ‘DHIs’ seen in the overlying sands. Micro-faults that act as hydrocarbon migration conduits can be seen on the data. The abyssal plain is at first sight the ultimate location for the ‘subtle’( i.e. , stratigraphic) trap; however, closures can also be shown to exist as drapes over basement features and allochthonous salt bodies. The models generated on the abyssal plain can be applied in the far more heavily structured salt diapir province, to provide an understanding of the channel and fan systems in this area. The multiple DHIs here, combined with numerous sands and four-way dip closures suggest that this is a highly prospective area.

Abstract The Congo deep-sea fan was surveyed recently by a unique set of data that includes as of today more than 30 piston cores and 25,000 km of 2D high resolution seismic acquisition. During the different cruises, the following tools were used simultaneously: an EM12 dual Simrad swath bathymetric and sonar system, a 3.5 kHz mud penetrator, an oceanographic seismic system (6 traces), and a multichannel seismic streamer (96 traces) with G.I. air gun source. The data set covers an area in excess of 200,000 km 2 from the canyon head to the most recent depositional lobes 700 km downslope. In this four year project cosponsored by ELF and IFREMER, the prime objective was to gain comprehension of the construction and the lateral evolution of the recent fan. As a result, we were able to build a chronostratigraphic and architectural model at the fan scale. The Congo Canyon geometry has been enhanced and has confirmed the lack of any tributaries downdip from the continental shelf. Furthermore, no real large scale slumped blocks have observed at the base of the steep submarine canyon slopes. Therefore, widening of the canyon seems to have occurred through progressive sliding and creeping of the bordering Congolese and Angola platform into the canyon valley. The recent Congo fan growth results from the stacking and overlapping of at least 3 main stratigraphic units. Each unit is composed of numerous channel-levee complexes laterally switching path through time by avulsion. Previous interpretation of “distributaries” at the toe of the Congo submarine canyon is invalidated as this surveys shows that they are in fact abandoned channel-levee complexes. It has also been confirmed that in this particular mud-rich submarine fan setting, only one channel is active at a time. The present day “active” fan channel as well as the canyon are eroding into previously deposited sediments. In the levees, individual sub-kilometer scale morphological features have been mapped, and sedimentary and/ or structural processes responsible for such geometries have been reviewed. The present day depositional lobe is more than 700 km away from the Congo River mouth. It occupies an area of around 300 km 2 and shows clustered lobes, 20 km long, prograding down slope. It is now clear that multibeam coverage of the lower part of the canyon, over complex lobe, and channel avulsion zones shows strong similarities with seismic attribute maps of West Africa’s structurally controlled turbiditic channel complexes.

Abstract A wide variety of proxies has been applied to study the terrestrial input in the Congo deep-sea fan area, the composition of its overlying waters, and the land–ocean interactions of the past 1 to 2 million years. These proxies include stable isotopes of foraminifers, total organic carbon (TOC), alkenone-derived sea-surface temperatures (SST), biomarker content and compound-specific stable isotopes, element composition, clay minerals, pollen and spores, dinoflagellate cysts, diatom valves, and opal. Not only the sedimentation in the deep-sea fan but also the productivity of the overlying waters is strongly influenced by the Congo River discharge and its fluctuations depending on the strength of the monsoon. SST and marine productivity are further affected by wind- and river-induced upwelling. A direct relation between SST, precipitation in the Congo Basin, vegetation cover, chemical weathering, and runoff could be established for the past 200 thousand years. Increase of mean global ice volume between 1000 and 500 ka suppressed the precession forcing of trade-wind zonality and monsoonal river runoff, leading to a higher production of nonsilica marine organisms compared to diatoms, and increased eolian transport of terrigenous material.

Abstract Records of organic matter accumulation, organic carbon isotopic composition and iron content covering the last 1.7 Ma are presented for the Congo Fan Ocean Drilling Program (ODP) Site 1075, and are compared with their counterparts from ODP Site 663 in the equatorial upwelling region. They are discussed with regard to variations in African precipitation and Congo River discharge and in the context of changes in trade-wind-driven marine productivity for the tropical Atlantic at periodicities typical of Milankovitch forcing. On the Congo Fan, elevated total organic carbon mass accumulation rates (TOC MAR) and Fe intensities occur predominantly during interglacial periods when the African monsoon was most intense. Band-pass filtering applied to TOC MAR shows distinct precessional variations, indicating that the African climate was largely controlled by low-latitude insolation changes. Only for the last 0.6 Ma, an interval of enhanced glacial-interglacial climate changes, is the precessional TOC MAR signal superimposed by a strong 100 ka oscillation. In contrast, variations in terrestrial iron input to the Congo Fan indicate pronounced 100 ka variance already well before global glacial-interglacial cycles increased in amplitude between 0.9 and 0.6 Ma. Obliquity cycles in the Fe signal are strongly expressed for the last 0.9 Ma. The highest amplitudes in the precessional variance of fluvial Fe input occur when amplitudes in the 100 ka oscillation were at intermediate levels and reveal a 800 ka cycle in phase shift with respect to precessional forcing. Together with a pronounced 800 ka signal in the 100 ka amplitude variations during the last 1.7 Ma, the Congo Fan iron record therefore suggests that eccentricity modulation of the low-latitude insolation directly influenced the equatorial African monsoon system and probably the weathering conditions on land. It further suggests that low-latitude precessional forcing and monsoonal response in the tropics might have played an important role for 100 ka cycles in global climate well before huge continental ice sheets existed.

Africa's major rivers are associated with some of the largest deep-water petroleum systems in the world. The most successful of these in terms of hydrocarbon discoveries, the Congo, Niger and Nile, are currently sites of intense exploration activity, while others (such as the Kwanza, Zambezi, and Rufiji-Ruvuma) have yet to yield a significant number of finds and remain under explored. The theme of this paper is to review examples of these systems, attempt to show why this has occurred and where some of the future offshore hydrocarbon provinces of Africa will be. Seismic data will be used to review the deep water plays and prospectivity associated with each major river system. The deep-water systems reviewed include the Congo, Niger, Nile, Kwanza, Zambezi, and Rufiji-Ruvuma. The more mature deep-water hydrocarbon provinces will be compared with the less explored areas. Suggestions as to the reasons for limited exploration of some areas will be made, concluding that visible structuring is as least as important as the perceived presence of source rock in the initial decision to explore in a basin. Visible structuring in the form of salt or mud diapirs, anticlines, etc., undoubtedly makes exploration “easier” in choosing locations and “selling” prospects in the early stages of basin exploration. Seeking stratigraphic traps when there are few or no structures is very difficult in an unexplored basin. The future exploration potential of the deep water provinces will be reviewed with particular reference to the currently less explored or less mature areas to show their untested prospectivity. As exploration has moved into deeper water in known hydrocarbon provinces such as Niger and Congo deltas, then the targets have been the deeper water analogies of existing plays; i.e., Niger delta mud supported anticlines and Congo fan channelized sands. In areas in which there are few or no existing working plays, extension by analogy into deep water breaks down or does not exist. So often in these areas new plays and source rock postulations have to be developed. Examples of new untested plays that do not exist in shallower water are shown from Tanzania Rufiji-Ruvuma and Mozambique deep water systems where there has been no drilling. Many of these involve structuring that does not exist in the shallower explored areas and are beginning to attract interest. In areas such the Kwanza Basin where there is a very structured sedimentary section the (correct) perception that the play type is not the same as farther north in the Congo Fan has caused the area to be downgraded, despite the fact that hydrocarbons have been found here. This downgrading is partially due to recent wells targeting the same play as farther north and failing to find oil. In this case, the primary reservoir targets are not highly visible Tertiary channel sands but Cretaceous sands having a more subtle seismic expression, a play that has proven to work by the Semba-1. The potential of the ultra deep water (i.e., water depths >3km) and abyssal areas beyond the Congo and Niger fans will be examined to demonstrate that as yet untested plays and prospectivity exist in these future exploration provinces.

Abstract The Lower Congo Basin and Congo Fan of Angola contain giant oil discoveries in Oligocene & Miocene deep-water sands; the Late Cretaceous and Tertiary fans in the Campos Basin of Brazil contain some 90% of Brazil’s reserves. Petroleum exploration in these vast, deep-water regions is resource-hungry, increasing the value of techniques that facilitate quick and inexpensive extrapolation from discoveries into undrilled areas. Our work demonstrates a strong correlation in these basins between reservoir fairways and various attributes of the gravity signature. We provide comparisons between published interpretations based on well and seismic data and our interpretations of gravity attribute images. We demonstrate the use of geographic information systems (GIS) techniques to facilitate the comparisons, discuss the possible basis for these correlations and speculate on their application to other basins. We conclude with notes on current research to improve the resolution of the gravity data and future refinements to our processing and interpretation methods.