AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Facies Architecture of a Compound Incised Valley System in the Ferron Notom Delta, Southern Utah
(1) Earth and Atmospheric Sciences, University of Houston, Houston, TX.
Extensive outcrop exposures of a compound incised valley system in the Turonian Ferron Notom Delta in southern Utah allow a detailed bed-scale facies architectural study within a recently developed high-resolution sequence stratigraphic framework. This allows us to link internal facies variability to relative sea level change, as well as evaluating the diachroneity of the basal composite erosional discontinuity.
The incised valley system can be correlated for 30 km in both depositional strike and dip directions. The erosional base of the valley is interpreted as a regional composite sequence boundary. Erosional relief ranges from a few up to 25 meters. Across the erosional surface, there is an abrupt basinward shift in depositional facies from lower shoreface below to pure fluvial or locally tidal estuarine deposits above. Three episodes of cutting and filling are recorded by the incised valley fill. The oldest valley fill 1, is characterized by estuarine tidal sand ridges with concave-up lens-shaped sandbodies containing bar-scale centimeter to decimeter thick mud drapes and abundant tidal bundles. The tidal sand ridges, immediately above the valley 1 floor, suggest that deposition occurred close to the shoreline, possibly during a subsequent short-lived transgression. The second overlying valley erodes these estuarine terrace deposits and cuts into the lower shoreface. Valley 2 contains purely fluvial channel deposits at the base that are overlain by tidally-influenced fluvial channel storeys. Valley 2 shows a multistory fill and represents a renewed fall followed by a transgression. The fluvial lower storeys in Valley 2 were deposited farther inland than the tidal facies in valley 1, and may indicate a less vigorous transgression. The third valley erodes into the two older valleys, and is composed of multistory fluvial channel deposits which lack tidal influence. The composite valley-fill thus shows a complex cutting and filling history. Older terraces are more marine-influenced, whereas younger valley fills record increasingly proximal fluvial facies. The successively more fluvial-dominated nature of each successive valley fill may correlate with a longer-term, prolonged relative sea level fall, punctuated by decreasingly vigorous transgressions. The main composite erosional discontinuity was not formed instantaneously but is highly diachronous and records a complex history of stepped falls punctuated by decreasingly effective transgressions.