Anatomy of a basin-controlled foreland fold-thrust belt curve: The Tres Marias salient, Sao Francisco basin, Brazil

作者：Reis Humberto L S^*; Alkmim Fernando F

来源：Marine and Petroleum Geology, 2015, 66: 711-731.

DOI：10.1016/j.marpetgeo.2015.07.013

• Tres Marias salient
• Sao Francisco basin
• Ediacaran
• Basin-controlled curve
• Low friction detachment
• Hydrocarbon exploration
• Brazil

Salients, as common features of fold-thrust belts, correspond to convex-to-foreland map-view curves. Hosting sedimentary sequences younger than 1,8 Ga., the intracratonic Ski Francisco basin of southeastern Brazil encompasses two foreland fold-thrust belts of opposite vergences: the Brasilia, on the west, and the Aracuai, on the east. These belts culminate in the central portion of the basin in form of two almost touching antitaxial curves developed in response to diachronic orogenic events affecting the basin fill-units during the Ediacaran Brasiliano/Pan-African assembly of West Gondwana. Located in the external sector of the thin-skinned Brasilia foreland fold-thrust belt, the ca. 130 km long and 80 km wide Tres Marias salient involves the up to 2500 m-thick Ediacaran Bambui sequence. In order to characterize the overall architecture and processes involved in the generation of the Tres Marias salient, we conducted a detailed structural investigation of the southern segment of the Brasilia foreland fold-thrust belt, based on surface, seismic, well and aerogeophysical data interpretation. The salient is frankly dominated by monotonous trains of upright chevron folds, bounded by a small number west-dipping thrust faults. The structural traces of thrusts and fold hinges on maps trend preferentially NS in the central portion of the salient, curving progressively toward NE and NW in its southern and northern limbs, respectively. The entire system is linked to a spoon-shaped detachment zone located near the base of the Ediacaran Bambui strata, whose maximum thickness roughly coincides with the salient culmination. Our analysis led to the conclusion that the Tres Marias salient corresponds to a basin-controlled curve, generated during a single and progressive deformational episode. Its fold-dominated character and the high symmetry of its internal fabrics can be explained by the low friction of the associated detachment (located along a lower Bambui sequence black shale) and the mechanical behavior of the pelite-dominated deposits incorporated in the fold-thrust wedge. The occurrence of seepages and recent gas discoveries in the Tres Marias salient area point toward its potential for unconventional hydrocarbon resources. Our investigation suggests that the main basin controls that led to the development of the salient might have controlled the quality and distribution of Proterozoic petroleum system elements.

• 出版日期2015-9