Abstract: Gravity-Driven Compressional Structural Closures in Brazi1ian Deep-Waters - a New Frontier Play

ZALAN, PEDRO VICTOR, Petrobras/E & P

Summary

As the exploration in the Brazilian continental margin moved into deep waters and the predominantly stratigraphic traps containing immense volumes of turbidite sands started to be successfully tested, all the attentions were focused towards syn-depositional lows, seismic facies analysis, pinch-outs and amplitude anomalies. Classical structural closures, namely anticlines, were temporarily put aside; with the exception of some roll-over structures.

Meanwhile, the deep-water seismic sections gradually unfolded a new structural style, that was not so prominent in the continental shelves. Huge, multiple, stacked gravitational slides, presenting extensional listric fault provinces below the continental slope and frontal compressional provinces in the continental rises were detected in practically all basins, with or without salt beds.

Some of these compressional provinces display horizontal and vertical dimensions of typical foreland fold-and-thrust belts. The structural styles present within them, such as extensive decollement levels, intense folding (detachment-, fault-propagation and fault-bend folding), duplexes and growth-folding; so typical of convergent margin overthrust belts, were conspicuously recognized in many of such gravitational slides.

Some anticlines, especially of the fault-bend and fault-propagation (snake head anticlines) folding mode, exhibit very large dimensions and reasonable integrity, pointing to the possibility of the existence of classical anticlinal closures in the range of several tens of square kilometers. Internal seismic facies indicate the occurrence of interlayered sandstones and shales. None of such gravity-driven compressional anticlines have been drilled up to now and they constitute a very tempting frontier play in the Brazilian deep waters.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah