Abstract

The Dox Formation is part of the Unkar Group, which forms the lowermost 2,000 m of upper Precambrian strata in the Grand Canyon. At the original type section near Dox Castle, the Dox is incomplete, but it is fully exposed in the easternmost Grand Canyon where it is 950 m thick and is divided into four members. The lowermost Escalante Creek Member is tan to brown, lithic and arkosic sandstone interbedded with green to brown mudstone, and is 390 m thick. The Solomon Temple Member consists of red mudstone and sandstone 280 m thick. The Comanche Point Member occupies more than half the Dox outcrop area in eastern Grand Canyon and is a slope-forming succession of orange-red mudstone 188 m thick. It contains five distinct white bleached marker zones, one of which overlies a stromatolite bed. The uppermost Ochoa Point Member is 91 m of slope-forming, reddish-brown mudstone that only rarely exhibits bedding. Lithology and sedimentary structures in the Dox indicate deposition in shallow-marine or transitional environments ranging from lagoonal to possible deltaic-plain, tidal-flat, and fluvial.

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