Wave-to-Tide Facies Change in a Campanian Shoreline Complex, Chimney Rock Tongue, Wyoming-Utah, U.S.A.
Piret Plink- Björklund, 2008. "Wave-to-Tide Facies Change in a Campanian Shoreline Complex, Chimney Rock Tongue, Wyoming-Utah, U.S.A.", Recent Advances in Models of Siliciclastic Shallow-Marine Stratigraphy, Gray J. Hampson, Ronald J. Steel, Peter M. Burgess, Robert W. Dalrymple
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The Upper Cretaceous, Campanian Chimney Rock Tongue is exposed in a dip-oriented outcrop belt ca. 15 km long in the Flaming Gorge area, Utah-Wyoming, U.S.A. The Chimney Rock Tongue has three distinct stratigraphic intervals: (1) wave-dominated-delta deposits, (2) mixed-energy-estuary deposits as an incised-valley fill, and (3) tide-dominated-estuary deposits.
The wave-dominated delta succession, ca. 95 m thick, consists of eastward-prograding clinoforms. The clinoforms are dominated by wave deposits, but in places sediment-gravity-flow and mass-transport deposits, as well as fluvially dominated mouth-bar deposits, occur. Tops of the individual clinoforms are locally cut by distributary channels. The distributary channels are filled with fluvial and tide- influenced fluvial deposits. Tops of the youngest deltaic clinoforms are severely eroded by a subaerial unconformity that can be walked out across the whole outcrop belt for 15.5 km. The subaerial unconformity cuts down at least 30 m across the outcrop belt. The unconformity is locally marked by roots (locally calcite filled), calcite concretions, limonite precipitation, and mottling.
An estuarine succession onlaps the unconformity in the landward and lateral directions, indicating that the estuary was confined in an incised valley. The estuarine succession, ca. 30 m thick, consists of tide-influenced fluvial channels, bay-head deltas, inner-estuarine tidal bars, central-basin mudstones, flood-tidal deltas, estuary-mouth-barrier deposits, and tidal-inlet deposits. The inner-estuary tidal bars consist of fluvially derived but tidally reworked sands with ubiquitous single and double mudstone drapes. The wave-generated estuary-mouth barrier indicates wave dominance in the estuary mouth. This distribution of tide and wave deposits indicates thatthe estuarine succession is of mixed-energy type. The mixed-energy estuary succession is retrogressive, except for the very top of the succession, which is regressive within the inner-estuary setting. This latter suggests in situ infilling of the incised valley.
The third and uppermost stratigraphic unit, ca. 60 m thick, consists of three transgressive-regressive units in an overall aggradational setting. The transgressive-regressive units consist of tide-influenced fluvial deposits, tidal-flat and marsh deposits in inner-estuary reaches, and upper-flow-regime tidal-flat and tidal-sand-bar deposits in outer-estuary reaches. The transgressive-regressive units, 16-26 m thick, are based by tidal ravinement surfaces, and indicate flooding and consequent in situ infilling of the river mouths.
The transition from a wave-dominated delta to a mixed-energy estuary and then to a tide-dominated estuary suggests an apparent change in process regime from wave dominance to tide dominance triggered by a relative sea-level rise. The tidal influence was, however, also present during the deposition of the wave-dominated deltaic succession, as seen by the tide-influenced fluvial infill of the distributary channels. Thus, the tidal influence did not switch on when the depositional system changed from deltaic to estuarine. Nor did the wave influence switch off, as the estuary mouth was wave-dominated in the mixed-energy estuary. Instead, the effect of tides was locally increased. Due to valley incision and later drowning, the inner areas of the valley were protected from waves. The tidal range, however, increased, as the mixed-energy estuary was replaced by a tide-dominated estuarine system, commonly assigned to macrotidal settings. This change in process regime occurred after the incised valley was filled, and the tide-dominated estuaries occupied river mouths in a high-subsidence regime.