ABSTRACT: Evolution of an Incised Valley Fill--The Pine Ridge Sandstone of Southeastern Wyoming: Systematic Sedimentary Response to Relative Sea Level Change

MARTINSEN, OLE J., University of Bergen, Bergen, Norway

The Pine Ridge Sandstone of the Campanian (Upper Cretaceous) Mesaverde Group of southeastern Wyoming records the fill of an incised valley formed as a response to uplift of an early Laramide-style range and consequent relative sea level fall in the Rocky Mountain foreland.

The fill of the Pine Ridge incised valley can be divided into three distinct facies successions, reflecting a systematic change of the major controls on deposition: (1) a lowstand succession, dominated by fluvial mass flow deposits laid down during fall of relative sea level when the valley profile increased in depth because of incision and the valley sides were oversteepened; (2) an early transgressive succession, dominated by tidally influenced meandering channel sandstones, deposited during the early stages of relative sea level rise when the incised valley still retained an elongate estuarine morphology; and (3) a late transgressive succession, dominated by backstepping distributary channels and wave-dominated frontal splays of bayhead deltas as the width of the valley and estuary increased because of "overflooding" caused by an increasing rate of relative sea level rise. This morphological expansion caused an increase in the wave-climate at the expense of a decrease in the tidal regime.

The systematic change of major controls on the fill of the Pine Ridge system from fluvial mass flow deposits, through tidally influenced estuarine deposits, to wave-dominated bayhead delta deposits may suggest a general succession of events and facies expected to occur during the incision and filling of valley systems related to falls and rises of relative sea level.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)