Abstract: The Stratigraphic Organization of Incised-Valley Systems

Ron Boyd, Brian A. Zaitlin, Robert W. Dalrymple

An incised-valley system consists of an incised valley eroded during a relative sea level fall and a valley fill which accumulated during one or more relative sea level cycles. We define an incised valley system as a fluvially-eroded, elongate paleotopographic low, typically larger than a single channel, displaying an abrupt basin ward shift of facies at its base. The valley fill typically begins to accumulate during base-level rise, and may contain deposits of the following highstand and subsequent sea-level cycles.

The fill of incised valley systems is divisible into three segments: (1) the seaward reaches of the incised-valley (SEGMENT 1) is characterized by backstepping (transgressive) fluvial and estuarine deposits, overlain by transgressive marine sands and shelf muds; (2) the middle reaches of the incised valley (SEGMENT 2) consist of the drowned-valley estuarine complex that is developed at the time of maximum transgression, overlying a lowstand to transgressive succession of fluvial and estuarine deposits; and (3) the innermost reaches of the incised-valley (SEGMENT 3) characterized by fluvial deposits developed headward of the transgressive marine limit, and extends to the point where eustatically-driven changes in base level no longer control fluvial style.

The stratigraphic organization of incised-valley systems is characterized by a number of stratigraphically-significant surfaces including: a sequence boundary, an initial flooding surface, a tidal-ravinement surface, a wave-ravinement surface, and a maximum flooding surface. A sequence stratigraphic approach to the study of incised valley systems results in a model for the predictable organization of facies and surfaces based on the interaction of sediment supply and relative sea level.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994