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Abstract: Rollover Development and Resulting Geometry with Applications to Rapid Stratigraphic Correlation across Major Growth Faults

Hongbin Xiao

It has been commonly assumed that hanging-wall deformation above a normal fault involves simple shear in a uniform direction, either vertical or antithetic to the fault. This assumption permits estimation of the fault shape from the observed hanging-wall rollover shape. However, recent work (Xiao and Suppe, 1992) shows that a concave-upward bend produces antithetic shear and a convex-upward bend produces synthetic shear. Both shear types are observed in high-quality seismic images. Rollover shapes in nongrowth strata are determined by the fault shape, the shear angle, and the fault slip. However, rollover shapes in growth strata (e.g., Gulf of Mexico) are dominated by growth axial surfaces, which have abrupt changes in sedimentation rate across them and whose orientation strongly depe ds on the ratio of sedimentation to subsidence rate, as well as the total slip after a bed is deposited.

The small number of these convex-upward bends on an overall listric fault plane produce an equal number of distinctive normal drags on hanging-wall strata. This allows rapid stratigraphic correlation for some key horizons across major growth normal faults and provides powerful constraint on the maximum slip on them. These convex-upward bends are formed either at a pregrowth-growth stratigraphic boundary, or by increase of fault dip in sandstone from overlying shale within growth stratigraphic intervals.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994