Eolian Event Stratigraphy--A Conceptual Framework

KOCUREK, G., and K. G. HAVHOLM, University of Texas at Austin, Austin, TX

A basis for eolian event stratigraphy is to distill the impact of events into fundamental processes and products. For accumulation (net deposit through time) to occur, the sediment budget must be positive (amount of sand entering the area is greater than that exiting). If the sediment budget becomes neutral (equal amounts of sand entering and exiting), or negative (the amount of sand exiting exceeds that entering), accumulation ceases and a bypass or erosional super bounding surface, respectively, forms capping the genetic unit. Within the three types of eolian systems (dry, wet, stabilized), the mechanisms of accumulation and super-surface formation differ. In the dry system, accumulation occurs because of areal deceleration of sand-carrying winds. Because of dune-interdune flow cond tions, accumulation begins when interdune flats are closed, requiring sand supply, time, and conditions for dune growth at the expense of interdune flats. Super-surface formation requires a decrease in sediment-saturation level of the incoming flow and/or lessening of areal deceleration. In the wet system, accumulation of dune and interdune deposits occurs by trapping with a rising water table. Accumulations vary with the nature of the water table rise, proportion of dunes and interdune flats, and interdune topography. Super surfaces form where the water table becomes static or falls. In the stabilized system, accumulation occurs with rapid stabilization of elements of active eolian systems; super surfaces form when the causes of stabilization cease. Super surfaces can be further describ d by substrate condition (dry or damp, stabilized or unstabilized), reflecting the control on the level of deflation. The eolian rock record consists of preserved accumulations and super surfaces. Accumulation space is distinct from preservation space (accommodation space is their coincidence in marine systems). Preservation space is made by subsidence and water table rise. Without preservation space, an unconformity results. The dominance of subsidence versus water table rise is reflected in dry and wet accumulations respectively, such as the Jurassic Navajo and Entrada sandstones.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)