Variations in Fluvial Style as Revealed by Architectural Elements, Kayenta Formation, Mesa Creek, Coloralk), USA: Evidence For Both Ephemeral and Perennial Fluvial Processes
Michael H. Bromley, 1991. "Variations in Fluvial Style as Revealed by Architectural Elements, Kayenta Formation, Mesa Creek, Coloralk), USA: Evidence For Both Ephemeral and Perennial Fluvial Processes", The Three-Dimensional Facies Architecture of Terrigenous Clastic Sediments and its Implications for Hydrocarbon Discovery and Recovery, Andrew D. Miall, Noel Tyler
Download citation file:
Architectural studies in the Kayenta Formation (Lower Jurassic) of the Colorado Plateau reveal the characteristics of two types of sandstone body, that reflect both ephemeral and perennial fluvial processes. The first type is composed of high-regime horizontally-laminated sandstone, forming multiple-event Storys up to 8 m thick, deposited by flash floods. The second type is composed of planar cross-beds, deformed parabolic cross-beds and massive sandstone formed under low-regime flow from a perennial river during high stage.
The style of deposition is dependent upon the degree of confinement within the boundaries of the channel system in question. Where confinement was dominant, sedimentary fill often reflects the geometry of the containing channel. Paleocurrent distribution reflects the depositing flow conditions in confined bodies. Horizontally-laminated units show strongly unimodal currents, whereas the heterolithic confined units show a wider scatter.
Where flow was unconfined (during high stage, when thalwegs were inundated), the resulting deposits are broad sheets interfingering with underlying confined sandbodies. A zone of interdigitation displays sharp changes in paleoflow direction within the same stratigraphic horizon, resulting from the simultaneous action of confined and unconfined depositional processes. The interdigitation records the incremental abandonment of channels, as large unconfined barforms encroached on them during high stage.
Discharge variability is inferred from lithofacies composition; variable but perennial discharge shows a wide range of lithofacies, including clay drapes resulting from minimum, sluggish flow. Flashy discharge shows only two lithofacies types, those representing low-regime waxing and waning flow and those representing high-regime peak flow. Clay drapes are absent