Entrained sand generates fault-plane reflections on a deep-water thrust zone.

Thrust zones in a deep-water fold-thrust belt, offshore northwestern Borneo, display prominent reflections that can be mapped through a three-dimensional seismic volume. Unlike faultplane reflections obtained from thrusts in other systems, these have positive polarity. Well data show that the reflections in the Borneo data set originate from fault-bound sandstone slices, with porosity-occluding calcite cement, entrained along the thrust zone. The thrust zone can support elevated fluid pressures beneath the fault with the cemented sandstones. Multiple sandstone slices indicate complex patterns of thrust zone localization, perhaps a common feature for deformation in sedimentary multilayers typical of many deep-water depositional successions. [ABSTRACT FROM AUTHOR]