12 May 2015

Offshore Gabon

A regional interpretation of western Offshore Gabon was based on an IGC interpretation of satellite-derived gravity data offshore and a compilation of published data offshore and onshore. The Regional Geologic Features map featured in this report shows a series of basins and high blocks trending sub parallel to and subnormal to the coastline. Numerous fault/fracture zones extend northeast from oceanic crust areas of the South Atlantic onto the offshore shelf and the onshore coastal areas of Gabon. One major fault/fracture zone, the N’Komi, divides coastal Gabon into two main structural provinces: the south and the north.

The coastal plain widens northward from the Gabon-Congo border to the Gabon-Equatorial Guinea border and is bounded to the east by basement outcrop. It contains five named basins (two of which extend into the offshore) and five named high blocks (one of which extends into the offshore).

The offshore shelf contains five significant basins and five major high blocks. Those closest to the coastline are poorly defined by satellite-derived gravity because the satellite data lose resolution close to shore. Northeast-trending gravity anomalies or anomaly offsets confirm and/or further define the fault/fracture zones noted in much of the literature, although location of some features has been modified from the literature on the basis of IGC’s gravity interpretation. A major hinge zone and the ocean-continent crust boundary have been interpreted based on the gravity data. Six high amplitude gravity maxima in northern Gabon are interpreted as volcanic plugs, two of which are named.

In the offshore and coastal province of Gabon as in most basins, basement deformation has strongly influenced basin sedimentary structure and stratigraphy. Major geologic features critical to the formation of oil and gas fields, such as fault zones, structural highs, and depocenters, are seen as basement-related and are present onshore and offshore Gabon. IGC’s interpretation of the Isostatic gravity residual, Bouguer gravity, and data enhancement maps, integrated with published maps and data, has made possible a viable offshore extension of three distinctive onshore basement provinces: South Gabon, N’Komi Fault Zone and North Gabon.

In summary, the interpretation presented is a qualitative analysis of the structural trends and features onshore and offshore Gabon. Geologic features discussed in the literature have been correlated with, and similar features interpreted from, the IGC generated gravity residuals and data enhancement maps.