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The Moenkopi Formation is a geological formation that is spread across the U.S. states of New Mexico, northern Arizona, Nevada, southeastern California, eastern Utah and western Colorado. This unit is considered to be a group in Arizona.
This chart is for general use, because changes in grain size and flow depth can change the bedform present and skip bedforms in certain scenarios. Bidirectional environments (e.g. tidal flats) produce similar bedforms, but the reworking the sediments and opposite directions of flow complicates the structures.
Ripple marks in Moenkopi Formation rock. Local climatic conditions were wetter and more tropical in the Early Triassic than they were previously. In the Capitol Reef area the resulting Moenkopi Formation is divided into four members (from oldest to youngest): [6] Black Dragon Member; Sinbad Limestone Member, Torrey Member, and; Moody Canyon Member.
Ancient wave ripple marks in sandstone, Moenkopi Formation, Capitol Reef National Park, Utah. In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water (current or waves) or directly by wind.
Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition.. Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment, with different particle sizes are deposited on top of each other. [1]
The formation rests on the "lower red member" of the Moenkopi Group and underlies the Shnabkaib Member of the Moenkopi Group. [4] More recently, the Virgin Formation is interpreted as a formation of the Thaynes Group. [6] The formation is interpreted as having been deposited in a near-shore shallow marine environment.
Typically, the Chinle rests unconformably on the Moenkopi Formation. The Chinle Formation was probably mostly deposited in the Norian stage, according to a plethora of chronological techniques. It is a thick and fossiliferous formation with numerous named members (subunits) throughout its area of deposition.
Lucas and Hunt subsequently reduced the unit to member rank within the Moenkopi Formation, [2] [3] but its inclusion in the Moenkopi has not been universally accepted. [6] Some red beds previously mapped as Bernal Formation , particularly in its more northern and western exposures, are now thought to belong to the Anton Chico.