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Definition of a fault permeability predictor from outcrop studies of a faulted turbidite sequence, Taranaki, New Zealand

Lookup NU author(s): Professor Andrew Aplin

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Abstract

Post-depositional normal faults within the turbidite sequence of the Late Miocene Mount Messenger Formation of the Taranaki Basin, New Zealand are characterized by granulation and cataclasis of sands and by the smearing of clay beds. Clay smears maintain continuity for high ratios of fault throw to clay source bed thickness (c. 8), but are highly variable in thickness, and gaps occur at any point between the clay source bed cut-offs at higher ratios. Although cataclastic fault rock permeabilities may be appreciably lower (c. two orders of magnitude) than host rock sandstone permeabilities, the occurrence of continuous clay smears, combined with low clay permeabilities (10s to 100s nD) means that the primary control on fault rock permeability is clay smear continuity. A new permeability predictor, the Probabilistic Shale Smear Factor (PSSF), is developed which incorporates the main characteristics of clay smearing from the Taranaki Basin. The PSSF method calculates fault permeabilities from a simple model of multiple clay smears within fault zones, predicting a more heterogeneous and realistic fault rock structure than other approaches (e.g. Shale Gouge Ratio, SGR). Nevertheless, its averaging effects at higher ratios of fault throw to bed thickness provide a rationale for the application of other fault rock mixing models, e.g. SGR, at appropriate scales. © The Geological Society of London 2007.

Publication metadata

Author(s): Childs C, Walsh J, Manzocchi T, Strand J, Nicol A, Tomasso M, Schöpfer M, Aplin AC

Publication type: Article

Publication status: Published

Journal: Geological Society Special Publication

Year: 2007

Volume: 292

Pages: 235-258

Print publication date: 01/01/2007

ISSN (print): 0305-8719

ISSN (electronic):

Publisher: Geological Society Publishing House

URL: http://dx.doi.org/10.1144/SP292.14

DOI: 10.1144/SP292.14

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