OffshoreFozdoAmazonas

Brazil Offshore

Amazonas Mouth Geographic Basin

This manual autotrace of a regional seismic line of the Amazonas mouth geographic basin illustrate the small fold belt developed, in the distal part of the Atlantic-type divergent margin, mainly, during the deposition of the Neogene Amazonas cone in association with a listric fault complex. In fact, the shortened structures (anticlines and thrust faults) are the counterpart of the up-dip extension materialize by the normal growth faults. The basement correspond, probably, to the volcanic crust, in which sub-aerial lava-flows, i.e., SDRs cannot be excluded, as suggested on the next autotrace.

As for the previous tentative interpretation, we must take into account the seismic pitfall introduced by the abrupt changing in water water, as well as, its progressive seaward increasing. Actually, before starting a tentative geological interpretation of an offshore seismic line (conventional and deepwater) it is, highly, recommended to do, even mentally, a roughly depth conversion. As illustrated, the distal part of the Atlantic-type divergent margin, i.e., SDRs and the post-Pangea continental encroachment stratigraphic cycle, deposited above the oceanic crust, which uppermost layer seems to be formed by pillow lava effusing from immersed sheeted dykes. The SDRs ("sub-aerial" lava-flows) are associated with outcropping sheeted dykes as suggested in the geological model proposed by K. Hinz, in 1981 (see Page 5A).