Zambeze

Mozambique Offshore

Zambeze Offshore

On this tentative geological interpretation of a time Canvas autotrace, the reader must take into account the pitfall introduced by the abrupt change in the water depth (never forget the seismic waves travel slower in the water than through the sediments, i.e., in a time seismic line the horizons under a large water depth are too much deep than in a depth seismic line, which is closer to the geological reality). One of the more important geological events recognized on this autotrace is the presence of SDRs, i.e., sub-aerial lava-flows (sorry by the tautology, lava cannot flows in the water), which oblige geoscientists to assume the Beira High as a buried hill of the thinned Gondwana lithosphere and the breakup unconformity as the interface between the continental crust and the SDRs (see Page 36). On the other hand, there is a possibility of development of rift-type basins within the thinned continental crust as hypothesized on the tentative interpretation. Above the breakup unconformity the Atlantic-type divergent margin sediments deposited in two major sedimentary packages (see details in next plates).

As said previously take into account the seismic pitfall induced by the abrupt change in water depth. Two high of the basement (Benguera and Beira) and contingent rift-type basins form the infrastructure of the Atlantic-type divergent margin in which two sedimentary phase are, easily, recognized since they exhibit quite different internal configuration. The transgressive phase has a retrogradation geometry, while the regressive phase has progradational geometry. The limit between these two phase is the Cenomanian-Turonian downlap surface, along which or in association which organic rich sediments can be deposited (potential source-rocks). In the regressive phase and particularly in the Tertiary package, the seaward movement of the shelf break can be, easily, followed, as well as, the procession of associated turbidite depositional systems.