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

asin; Moore and Straub (2001) assigned 313 feet (95 m) of strata in CedarCanyon as likely equivalent to the Smoky Hollow Member.Upper, John Henry-equivalent strata are slope-forming, variegated, gray,brown, and reddish-brown mudstone and thin- to thick-bedded, grayish-orange toyellowish-brown, fine-grained subarkosic sandstone; stacked or amalgamatedsandstone beds make up most of the upper part of the unit; upper contactcorresponds to the base of the lower conglomerate of the Grand Castle Formation(which may be the Drip Tank Member of the Straight Cliffs Formation asdescribed above); deposited in fluvial and floodplain environments of a coastalplain (Eaton and others, 2001); biotite from an ash bed about 800 feet (245 m)above the base of the upper unit in Cedar Canyon yielded an 40 Ar/ 39 Ar age of86.72 ± 0.58 Ma (early Coniacian) (Eaton, 1999; Eaton and others, 1999b);probably about 900 to 1000 feet (275-300 m) thick in Cedar Canyon (Moore andStraub, 2001).We tentatively assign strata previously mapped as the Iron SpringsFormation in Parowan Canyon and in the Summit quadrangle to the StraightCliffs Formation; these strata consist of ledge-forming, calcareous, cross-bedded,fine- to medium-grained sandstone and less-resistant, slope-forming mudstone;the formation here is variously colored grayish orange, pale yellowish orange,dark yellowish orange, white, pale reddish brown, and greenish gray and is locallystained by iron-manganese oxides; Liesegang banding is locally common in thesandstone beds; thin coal seams and oyster coquinas are present in the lower partof the section in both areas, suggesting correlation to the brackish deposits of theSmoky Hollow Member; incomplete section is about 1100 feet (335 m) thick inParowan Canyon (Maldonado and Moore, 1995).The striking difference in facies and outcrop habit of correlative stratabetween Cedar and Parowan Canyons has long been noted (see, for example,Eaton and others, 2001). However, only about the upper 1000 feet (300 m) ofstrata previously assigned to the Iron Springs Formation is exposed in ParowanCanyon, where it is characterized by repetitive ledge-forming tabular sandstonebeds and interbedded, slope-forming mudstone. Equivalent strata to the south inCedar Canyon, widely correlated to the John Henry Member of the Straight CliffsFormation, are characterized by generally poorly exposed, typically slopeforming,stacked or amalgamated sandstone and relatively little mudstone;mudstone, however, dominates the lower part of the John Henry in Cedar Canyon.KstTibbet Canyon Member (Upper Cretaceous, Turonian) − Grayish-orange toyellowish-brown, generally medium- to thick-bedded, planar-bedded, fine- tomedium-grained quartzose sandstone and minor interbedded, grayish-orange togray mudstone and siltstone; locally contains pelecypods, gastropods, and thin tothick beds of oyster coquina; forms bold cliffs in Cedar Canyon and in the Westand East Forks of Braffits Creek south of Summit; upper contact corresponds to apronounced break in slope and is placed at the top of a coquinoid oyster bed andbase of overlying thin coal and carbonaceous shale interval that caps the member;forms the riser of the Gray Cliffs part of the Grand Staircase; represents initialprogradational (overall regressive) strata of the Greenhorn Cycle deposited in57