From Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.

Bureau Seminar, April 20, 2007

Syndepositional Fracture Patterns of the Devonian Reef Complexes, Canning Basin, Western Australia


Ned Frost

Jackson School of Geosciences, University of Texas at Austin.

Abstract:

Syndepositional fractures, an important feature of high-relief reef-rimmed carbonate systems, exert profound control on many facets of platform evolution, including timing and frequency of platform-margin collapse, generation of an early diagenetic fluid-flow system, and subsequent karst-enhanced permeability development. On the basis of fracture data collected from the Devonian reef complexes of Western Australia’s Canning Basin, I assert that development of large-scale syndepositional fracture networks is controlled primarily by (1) stratigraphic architecture and (2) structural setting.

My data reveal that attributes and spatial arrangement of syndepositional fractures vary significantly with depositional facies and stratigraphic setting. This study also demonstrates that syndepositional fracture intensity follows a strong linear relationship with platform-margin trajectory (P/A ratio) in the Devonian reef complexes. Fracture intensity is highest in strongly progradational platform margins and diminishes in aggradational and retrogradational margins regardless of proximity to regional structure, whereas, in the platform interior, structurally controlled settings consistently display fracture intensities higher than predicted by platform-margin trajectory.

These results indicate that syndepositional fracture development in the platform margin (regardless of trajectory) and in the platform interior of prograding platforms requires no external drivers and can be explained solely by stratigraphic architecture. While in the interior of low P/A ratio platforms, stratigraphic controls on syndepositional fracture development decreases in effectiveness, and an external driver (i.e., syndepositional tectonics) is required to generate extensive fracturing.

This study provides a tool for potentially predicting syndepositional fracture characteristics (e.g., orientation, intensity, and location) in the subsurface and provides a method of characterizing syndepositional deformation in carbonate systems.