(1) Institute for Energy Research, University of Wyoming, Laramie, WY
ABSTRACT: Architecture and Sequence Stratigraphy of Inner Estuary Tide-dominated Valley Fills - the Muddy Sandstone in NE Wyoming
Ancient tide-dominated estuarine successions are less well known than wave-dominated estuarine deposits. However, tide-dominated estuaries form important hydrocarbon reservoirs because they are efficient traps of sandy sediments and have high preservation potential. Outcrop studies are therefore important in increasing our understanding of these successions and the presented data provides a sedimentological and sequence stratigraphic study of the inner part of a Lower Cretaceous tide-dominated estuary. Data consists of detailed measured sections, photo-mosaics covering most outcrops and geophysical profiles.
The strongly tide-dominated succession was deposited in a narrow incised valley in the lowstand and transgressive systems tracts. The facies are dominated by sandy tidal to tidally-influenced fluvial channel deposits consisting of up to 10 m thick lateral accretion sets. Foresets are sandy and separated by thin single and double mud drapes. Foreset thicknesses are bundled and contain a marine to brackish trace fossils assemblage. The lateral accretion channel deposits display a very complex and amalgamated architecture in which four orders of bounding surfaces are recognised. The surfaces mark changes in inner estuary dynamics caused by downstream relative sea level variations, upstream changes in sediment supply and autocyclic channel migration/avulsion. Subordinate facies are upper flow regime tidal sand flat, tidal sand bar, tidal mud flat, central estuary mudstones and coaly marsh deposits.
The study provides new insight into the facies architecture and dynamics of the inner tidal-to-fluvial zone of tide-dominated estuaries. The presented depositional model can be used as reservoir analogue for the often complicated and compartmentalised estuarine incised valley fill reservoirs.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado