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AAPG Bulletin

Abstract

AAPG Bulletin, V. 90, No. 8 (August 2006), P. 1227-1249.

Copyright copy2006. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/03280604014

Evolution of fracture and fault-controlled fluid pathways in carbonates of the Albanides fold-thrust belt

Brita R. Graham Wall,1 Radu Girbacea,2 Agim Mesonjesi,3 Atilla Aydin4

1Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115; present address: U.S. Geological Survey, 345 Middlefield Road MS 910, Menlo Park, California 94025; [email protected]
2Occidental Oil and Gas Corporation, Houston, Texas 77046
3Occidental Oil and Gas Corporation of Albania, Tirana, Albania
4Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115

ABSTRACT

The process of fracture and fault formation in carbonates of the Albanides fold-thrust belt has been systematically documented using hierarchical development of structural elements from hand sample, outcrop, and geologic-map scales. The function of fractures and faults in fluid migration was elucidated using calcite cement and bitumen in these structures as a paleoflow indicator. Two prefolding pressure-solution and vein assemblages were identified: an overburden assemblage and a remote tectonic stress assemblage. Sheared layer-parallel pressure-solution surfaces of the overburden assemblage define mechanical layers. Shearing of mechanical layers associated with folding resulted in the formation of a series of folding assemblage fractures at different orientations, depending on the slip direction of individual mechanical layers. Prefolding- and folding-related fracture assemblages together formed fragmentation zones in mechanical layers and are the sites of incipient fault localization. Further deformation along these sites was accommodated by rotation and translation of fragmented rock, which formed breccia and facilitated fault offset across multiple mechanical layers. Strike-slip faults formed by this process are organized in two sets in an apparent conjugate pattern. Calcite cement and bitumen that accumulated along fractures and faults are evidence of localized fluid flow along fault zones. By systematic identification of fractures and faults, their evolution, and their fluid and bitumen contents, along with subsurface core and well-log data, we identify northeast-southwest–trending strike-slip faults and the associated structures as dominant fluid pathways in the Albanides fold-thrust belt.

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