--> Abstract: Multidisciplinary Interpretation of Deep-water Salt Tectonics in the South Atlantic Sedimentary Basins, by W. U. Mohriak, M. Bassetto, and I. S. Vieira; #90937 (1998).

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Abstract: Multidisciplinary Interpretation of Deep-water Salt Tectonics in the South Atlantic Sedimentary Basins

MOHRIAK, W. U., M. BASSETTO, I.S. VIEIRA, Petroleo Brasileiro S.A. - E&P - Gerex / Geinof, Rio de Janeiro, RJ

An integrated, multidisciplinary study of the salt tectonics styles in deep-water frontier regions of the South Atlantic (with main emphasis on the northeastern Brazilian margin) was carried out. The methodology was based on regional integration of geological and geophysical data, particularly deep seismic reflection profiles and potential field data (gravity and magnetics), results of exploratory drilling, detailed paleontologic analysis of the pre- and post-salt sedimentary succession, physical models, and analogs with other sedimentary basins.

The South Atlantic salt basins are associated with Late Jurassic / Early Cretaceous extensional processes that formed a rift system within the South American and African plates. Deep-penetration multichannel seismic profiles recently acquired in the northeastern Brazilian margin have advanced the interpretation towards ultra-deep water provinces, including the characterization of seaward-dipping reflectors near the continental / oceanic crust boundary, the extremely rapid transition to oceanic crust, and elusive features probably related to salt tectonics near the crustal limit, and foldbelts associated with downdip compression of post-salt sedimentary layers.

Some earlier models for salt deposition assumed that evaporites in the northeastern region of Brazil were restricted to the onshore and to the platform, which constituted preferential sites for salt accumulation in elongated gulfs during the Aptian transitional phase. However, the regional deep seismic profiles have provided evidence for diapiric features located near the boundary between continental and oceanic crust. The integration of gravity and magnetic with seismic reflection data resulted in the alternative interpretations for some of these features. Most of them have been interpreted either as volcanic mounds, outer basement highs, basement horsts, tilted rift blocks, transpressional structures along fracture zones, salt and mud diapirs, reefs, channels, or even correspond to seismic processing artifacts. The integration between different methods allowed a consistent differentiation between end-member structures such as salt and igneous intrusions. However, some elusive features may require refinements in seismic processing and a smaller grid of potential field data.