ENHANCED UNDERSTANDING OF NAVAJO DUNE MORPHOLOGY THROUGH ICHNOLOGY

The Navajo Sandstone at Moccasin Mountain near Kanab, Utah provides a unique combination of sedimentary structures with abundant fossil trackways and trampled surfaces. Local drainages provides 3D exposure over an area greater than 2400 s.m. The area is important because trackways have marked several surfaces that are unequivocal time horizons. Correlating conditions associated with dune aggradation and migration with that of vertebrate ethology provides a unique combination that enhances visualization of instantaneous dune morphology and processes.

The main objective is to present a spatial distribution of the dune architectural units in the study area and the positions of trackways relative to dune surfaces and depositional units. The classification for bounding surfaces, superposition surface orientation, and foreset geometry followed Baristow, 2013; Hunter, 1977; Kokureck, 1991, 2007.

We found 16 superposition surfaces with average dips 2 of degrees. Several superposition surfaces truncate one or more older surfaces with their associated sediments. Some surfaces show diagenetic alteration. Sixteen depositional units with cross strata dips of up to 24 degrees and with a vertical extent of over 50 meters were mapped. Some tracked and trampled beds have tangential terminations. Individual bedsets range from 0.5 to 20 m thick. Foreset geometry of preserved cross strata varied from oblique to tangential with vertebrate trace fossils limited to depositional unit 9. Trampled surfaces appear to occur in a cyclical pattern.

We present a map of the architectural features and distribution of tracks, trackways, and trampled surfaces. Dune architecture varies in complexity over time and local paleowind direction also shows variability. Conditions that favored the production and/or preservation of abundant tracks were only present when depositional unit 9 was deposited. The cyclical pattern of trampled surfaces indicates variable depositional conditions. Our tentative model for track preservation is controlled by episodic pluvial conditions.