About This Item
- Full TextFull Text(subscription required)
- Pay-Per-View PurchasePay-Per-View
Purchase Options Explain
Share This Item
The AAPG/Datapages Combined Publications Database
AAPG Special Volumes
Abstract
Zalan, Pedro Victor,
DOI:10.1306/13251344M943089
2011 by The American Association of Petroleum Geologists.
Fault-related Folding in the Deep Waters of the Equatorial Margin of Brazil
Pedro Victor Zalan1
1Petrobras/EP/E
P-EXP/GPE/NNE, Rio de Janeiro, RJ, Brazil
ACKNOWLEDGMENTS
The author thanks Petrobras for the permission to publish this manuscript and to geophysicists Walter Leitzke, Carlos Alves C. Filho, Tereza Cristina F. Ramos, and Adriana Perpetuo S. da Silva; to geologist Marcos Domingues; and to technician Haroldo M. Ramos, all from Petrobras, for their help in the processing and conversion to depth of the seismic sections, in the elaboration of maps, and in the drawing of the figures. Also, two reviewers, Ian Davison and Jose de Vera, presented thoughtful analyses on the first draft and stimulated a more profound discussion of the mechanisms involved in the folding, thus greatly improving the original manuscript.
ABSTRACT
Two gravitational fold and thrust belts (GFTBs) from the deep waters of the Para-Maranhao and Barreirinhas basins were interpreted in two-dimensional seismic sections and analyzed using the concepts of fault-related folding and taper-wedge mechanics. These basins lie in the equatorial Atlantic Ocean margin of Brazil, a classic example of transform to oblique (transtensional) continental margin. There, deep-water anoxic shales of probably Turonian age served as decollement zones to Late Cretaceous and Paleogene predominantly siliciclastic wedges to slide down from upper slope (extension) to lower slope (contraction) realms. The structural style of both fold belts is typical thin-skinned tectonics with imbricate thrust faults branching upward from the detachment level with associated fault-related folding. The direction of tectonic transport is from the coast to offshore (southwest to northeast). The similarities and differences between the GFTBs were highlighted. The most striking difference regards the distribution of contractional strain throughout the fold belt. In the Para-Maranhao GFTB, a single major contraction event was achieved via eight regularly spaced imbricate thrust faults. Intervening slices present all types of classic fault-related folding (fault-bend, fault-propagation, and detachment folds). In the Barreirinhas GFTB, an earlier minor contraction was also spread over regularly spaced faults; however, a major late contraction was achieved by one main thrust fault with one major fault-related fold associated to it. This fold is predominantly a shear fault-bend fold whose geometry varies slightly along strike. Their main similarities regard the discrete nature of the detachment level, their structural coherence
and narrowness, their low to moderate wedge taper, and their noncritical nature of the taper wedge. Both present syntectonic growth strata that record variations in the balance between the rates of sedimentation and structural uplift of the fold, and folding by limb rotation. The fault-related folding thus determined and the parameters established for wedge taper are slightly different from those presented by active submarine fold and thrust belts at convergent margins and passive margins throughout the world. The decollement dip of the GFTBs is significantly lower, and the bathymetric slope is somewhat higher than elsewhere around the globe.
Pay-Per-View Purchase Options
The article is available through a document delivery service. Explain these Purchase Options.
Watermarked PDF Document: $14 | |
Open PDF Document: $24 |