Interim Geologic Map of the West Part of - Utah Geological Survey

leached white under the Cretaceous unconformity; poorly cemented and soweathers to vegetated slopes, or, locally, badland topography; upper contact is atthe base of a pebble conglomerate, which marks the Cretaceous unconformity;deposited on a broad, sandy mudflat (Imlay, 1980; Blakey and others, 1983); 250feet (75 m) thick in Cedar Canyon.JcpJcxJccParia River Member (Middle Jurassic, Bathonian) – Consists of three parts notmapped separately: (1) upper part is about 50 feet (15 m) of cliff-forming, olivegray,micritic and argillaceous limestone and calcareous mudstone; laminated invery thick beds; locally contains small pelecypod fossils; (2) middle part is about20 feet (6 m) of reddish-brown and greenish-gray shale that forms slope; and (3)lower part is gypsum and minor interbedded shale as much as 80 feet (25 m) thickin nodular, highly fractured and contorted beds and as thin, laminated beds.Upper contact is sharp and planar; deposited in shallow-marine and coastalsabkhaenvironments (Imlay, 1980; Blakey and others, 1983); 173 feet (53 m)thick in Cedar Canyon.Crystal Creek Member (Middle Jurassic, Bathonian) – Thin- to mediumbedded,reddish-brown siltstone, mudstone, and fine to medium-grainedsandstone; commonly gypsiferous and contains local contorted pods of gypsum;forms vegetated, poorly exposed slopes; upper contact is sharp and broadly wavyand corresponds to the base of the thick Paria River gypsum bed; Kowallis andothers (2001) reported two 40 Ar/ 39 Ar ages of 167 to 166 million years old foraltered volcanic ash beds within the member near Gunlock that were likelyderived from a magmatic arc in what is now southern California and westernNevada; deposited in coastal-sabkha and tidal-flat environments (Imlay, 1980;Blakey and others, 1983); 294 feet (90 m) thick in Cedar Canyon.Co-op Creek Limestone Member (Middle Jurassic, Bajocian) − Thin- tomedium-bedded, light-gray micritic limestone and calcareous shale; locallycontains Isocrinus sp. columnals, pelecypods, and gastropods; forms sparselyvegetated, ledgy slopes and cliffs; Kowallis and others (2001) reported several40 Ar/ 39 Ar ages of 168 to 167 million years old for altered volcanic ash beds withinthe lower part of the member in southwest Utah that were likely derived from amagmatic arc in what is now southern California and western Nevada; depositedin a shallow-marine environment (Imlay, 1980; Blakey and others, 1983);probably about 400 feet (120 m) thick, but may be about 300 feet (90 m) thick ifthe lower gypsiferous part is the Temple Cap Formation; the member is as muchas about 350 feet (105 m) thick on the Kolob Terrace north of Zion National Park(Biek and Hylland, 2007).unconformity (J-2?) (Pipiringos and O’Sullivan, 1978); formed about 169 to 168 millionyears ago in southwest Utah (Kowallis and others, 2001). New research suggests that theTemple Cap Formation, lower part of the Page Sandstone (Harris Wash Tongue of southcentralUtah), and Gypsum Springs Member of the Twin Creek Limestone (of central andnorthern Utah) are time equivalent (Dickinson and Gehrels, 2009a, b; Dickinson and64