--> Abstract: Present-Day Stress Orientations Across a Delta-Deepwater Fold-Thrust Belt System, NW Borneo, by Rosalind C. King, Richard Hillis, and Mark Tingay; #90078 (2008)

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Present-Day Stress Orientations Across a Delta-Deepwater Fold-Thrust Belt System, NW Borneo

Rosalind C. King, Richard Hillis, and Mark Tingay
Australian School of Petroleum, University of Adelaide, Adelaide, SA, Australia

Delta toe fold-thrust belts are widely considered to be caused by margin-normal compressional stresses generated by margin-normal gravitational extension of the delta top. However, this coupled extension and compression hypothesis has never been tested using in-situ stress measurements. We use observations of borehole breakout and drilling-induced fractures in 56 wells over the Baram Delta-Deepwater Fold-Thrust Belt System, NW Borneo, to reveal three distinct neotectonic provinces; an inverted province, an extension province and a compression province. The extension and compression provinces are situated on the outer shelf and slope to basin floor and are defined by active gravity driven deltaic tectonics. The extension province exhibits NE-SW striking, active normal faults that reflect the NE-SW, margin-parallel maximum horizontal stress orientation. The compression province exhibits NE-SW striking thrusts, which are consistent with a NW-SE, margin-normal maximum horizontal stress orientation. The inverted province is situated onshore to inner shelf, and is defined by inverted ancient extensional delta structures and a NW-SE, margin-normal maximum horizontal stress orientation. This first documentation of stress orientations across a delta-deepwater fold-thrust belt system witnesses two 90° maximum horizontal stress rotations: 1) from NW-SE, margin-normal in the inverted province to NE-SE, margin-parallel in the extension province, and; 2) from NE-SW, margin-parallel in the extension province to NW-SE, margin-normal in the compression province. The latter is consistent with the contemporary stresses generated by updip gravity driven extension of the delta and subsequent compression in the deepwater fold-thrust belt.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas