PROTO-OCEANIC CRUST: TYPES, EMPLACEMENT MECHANISMS, AND RELATIONSHIPS TO HYDROCARBON MATURATION

Over the past three years we have conducted two projects, SAMBA and NAMBA, which have analyzed the development of continental margin basins in the South and North Atlantic oceans respectively. One consistent feature that has been observed at nearly all continental margins in this area is that of proto-oceanic crust or POC. The POC is a transitional zone between the extended continental crust and pure oceanic crust. Several authors have observed this type of crustal material at continental ocean boundaries (COB). The correlation and extent of these materials has not been well documented.

As part of our projects we have integrated seismic, well, gravity, magnetic and topographic data into a Geological Information System (GIS) project. This integration has allowed us to observe that the POC has a distinctive gravity and/or magnetic signature. On seismic sections POC typically shows an architecture of tilted fault blocks and on lapping fill. In some areas the POC appears to have been derived from the emplacement of volcanic material at or near sea level during the final stages of continental separation. In these areas the POC was then buried by a mixture of volcanic material and clastics in regions of restricted lacustrine to oceanic circulation. In other areas POC appears to be composed of abducted material possibly mixed with continental fragments. These may have been emplaced in a deeper, possibly open marine environment. Other types POC emplacements are also observed. These will be illustrated in a variety of Atlantic locations

The type, mechanism and emplacement environment of POC become important as hydrocarbon exploration proceeds into deeper and deeper water, beyond normal continental crust. Hydrocarbon maturation is dependent upon the age of emplacement, type and thickness of covering sediments, availability of higher heat flows from volcanic and possibly from abducted material. The type of material is also important in the production and/or conduction of heat, which may produce higher heat flows. We present an assessment of these factors on hydrocarbon prospectivity.