--> Abstract: Sedimentary and Hillslope Response to Active Fold Growth, by N. Brozovic, D. W. Burbank, A. J. Meigs, and J. J. Roering; #90937 (1998).

Datapages, Inc.Print this page

Abstract: Sedimentary and Hillslope Response to Active Fold Growth

BROZOVIC, NICHOLAS, Dept. of Geology and Geophysics, University of California, Berkeley, CA 94720; DOUGLAS W. BURBANK, Dept. of Geosciences, Pennsylvania State University, University Park, PA 16802; ANDREW J. MEIGS, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125; JOSHUA J. ROERING, Dept. of Geology and Geophysics, University of California, Berkeley, CA 94720 

The topographic expression of an actively growing fold is determined by the interplay of its displacement field with erosion and sedimentation. For folds with surface relief, ongoing deformation will tend to push the emergent limbs across progressive geomorphic thresholds of channel initiation and landsliding, controlling rates and styles of erosion and associated deposition. We present a simple model which relates dominant surface processes and their depositional products to the deformation above a blind thrust. Surface displacement fields are predicted with an elastic half-space model, and simple slope-area relationships delineate regions of channelization and shallow landsliding. Channel downcutting controls local base level, leading to further hillslope oversteepening and failure. As the fold propagates, points on the surface experience a sequence of geomorphic processes with time. This sequence is used to infer depositional style and stratigraphy for the anticline and adjacent areas. We compare the predictions of this model to digital topographic, geomorphologic, structural and sedimentologic data from Wheeler Ridge, a growing, asymmetric anticline and producing oil field on the southern margin of the San Joaquin Valley, California. We compare measurements of surface slopes and eroded volumes to the spatial distribution of modern-day surface processes, subsurface geology and local stratigraphy and use the ergodic hypothesis (substitution of space for time) to suggest progressive changes in surface processes along the forelimb and backlimb of the anticline through time. Our analysis suggests that on anticlines such as Wheeler Ridge, where the limb slopes reach a constant value soon after the structure breaches the surface, slope length is an important variable in determining the dominant surface process. Both field data and modeling highlight the considerable geomorphic and stratigraphic complexity produced from the growth of simple structures.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah