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Structural Styles associated with Fault-Propagation Folds in Salt-Influenced Rift Basins: Halten Terrace, Offshore Norway

Author(s): Alexander J. Coleman Basins Research Group (BRG), Department of Earth Science and Engineering, Imperial College, Prince Consort Road, London, SW7 2BP, United Kingdom
Christopher A.-L. Jackson Basins Research Group (BRG), Department of Earth Science and Engineering, Imperial College, Prince Consort Road, London, SW7 2BP, United Kingdom
Oliver B. Duffy Bureau of Economic Geology, University of Texas at Austin, University Station, Box X, Austin, TX 78713-8924, U.S.A.

Normal fault growth is typically associated with the development of fault-propagation folds; especially in evolving salt-influenced rift basins, whereby the presence of a ductile, evaporite-rich unit in a brittle succession may decouple folded supra-salt (cover) and faulted sub-salt (basement) strata. Cover structures and the underlying fault blocks may form hydrocarbon traps, although imaging can be poor. This study examines the along-strike variability and controls on structural styles associated with a salt-influenced fault-related fold underlain and controlled by a series of down- stepping fault blocks.

A 2000 km², high quality, 3D seismic reflection survey of Hallen Terrace, offshore Norway, has been used to understand how normal fault growth in the presence of salt controls fault-linkage, fold development, basin physiography and syn-rift stratigraphic response. Moreover, we relate fold geometry, and cover-restricted fault strike variations to salt thickness, sub-salt fault throw and polarity. Hallen Terrace forms an ideal setting as the pre-rift Triassic salt lacks the effects of extensive diapirism and is well imaged. This permits detailed mapping of salt thickness variations and deconvolution of the spatial relationship between supra- and sub-salt faults and folds.

Quantitative analysis and 3D mapping of fault geometry shows salt strongly influences fault-linkage i.e. the propagation of sub-salt faults to higher stratigraphic levels and development of fold amplitude along-strike. We have identified a series of <15 km long, <400 ms throw, N-S- to NE-SW-striking basement-restricted faults below an 18 km long, >15 km wide, NW-facing, S-plunging monocline. At the southern extent of the fault-fold system, cover-restricted faults show similar strikes and polarity to their W-dipping, NE-SW striking sub-salt counterparts and are soft- linked. In the centre, throw is focused along W-dipping, N-S hard-linked faults to the east, and fold amplitude increases with greater salt thicknesses atop ·steeper sub-salt topography. Northwards, total throw decreases and greater fault polarity and strike disparity occurs between sub- and supra-salt faults associated with cover gravity- gliding and folding over increasingly flat, wider spaced, lesser-throw fault blocks.

We illustrate how basement-involved deformation can influence the fold structural style at different stratigraphic levels producing an extensive range of structural geometries and trapping styles. These are controlled by sub- and supra-salt fault coupling, salt thickness and fault throw.


Title:
Structural Styles associated with Fault-Propagation Folds in Salt-Influenced Rift Basins: Halten Terrace, Offshore Norway
Type:
Poster (Student)
Origin:
Mixed
Day:
1
Session:
0
Daily sequence no.:
07
Lead author last name:
Coleman
Lead author first name:
Alexander J.
Affiliation(s):
Basins Research Group (BRG), Department of Earth Science and Engineering, Imperial College, Prince Consort Road, London, SW7 2BP
Country:
United Kingdom
Abstract status:
All ok
UID:
54