Paper No. 11
Presentation Time: 4:20 PM
THE MIDDLE JURASSIC TEMPLE CAP FORMATION, SOUTHERN UTAH—RADIOMETRIC AGE, PALYNOLOGY, AND CORRELATION WITH THE GYPSUM SPRING MEMBER OF THE TWIN CREEK LIMESTONE AND HARRIS WASH MEMBER OF THE PAGE SANDSTONE
The Temple Cap Formation overlies the Navajo Sandstone (separated by the J-1 unconformity) and underlies the Carmel Formation (thought to be separated by the J-2 unconformity). Classic Temple Cap in Zion National Park consists of the lower fine-grained sandstone to mudstone (marginal marine) Sinawava Member and the upper large-scale cross-bedded sandstone (eolian) White Throne Member. West of Zion, the Temple Cap consists of mudstone to fine-grained sandstone and gypsum (marginal marine and marine) of the Sinawava; the White Throne Member is missing. Air-fall ash beds containing sanidine, biotite, and zircon indicate the Temple Cap is 177.8-171.4 ± ~1.5 Ma (2σ). Palynology near the top of the Temple Cap indicates marine deposition of Bajocian age. Well data from central Utah show the Gypsum Spring Member of the Twin Creek Limestone is fine-grained sandstone to mudstone, gypsum, and limestone; it overlies the Navajo Sandstone and underlies the Sliderock Member of the Twin Creek Limestone. Core from the Wolverine Federal 17-3 well (Covenant field) shows the Navajo is overlain by reddish fine-grained sandstone to siltstone with glauconite topped by large-scale cross-bedded sandstone with thin interbedded limestone. Palynomorphs from the limestone include Middle Jurassic marine dinoflagellate cysts. This interval between the Navajo and Sliderock is lithologically and temporally similar to the Sinawava and White Throne Members of the Temple Cap, and we believe it intertongues westward with beds of the Gypsum Spring. The Page Sandstone in south-central Utah overlies the Navajo Sandstone and is thought to be separated by the J-2 unconformity. The Page includes the lower Harris Wash and upper Thousand Pockets Members where the intertonguing Judd Hollow Member of the Carmel Formation is present. Published ages of 171.09 ± 0.49 Ma (40Ar/39Ar, biotite 2σ) and 171.5 ± 1.9 Ma (U-Pb, zircon, 2σ) from air-fall ash beds within the Harris Wash Member indicate it is equivalent to the Temple Cap. The Judd Hollow is Bajocian and its palynology is consistent with the basal member of the Carmel Formation to the west. The Temple Cap, Gypsum Spring, and Page overlie the Navajo Sandstone on the J-1 unconformity. The White Throne Member intertongues with marine strata westward and irregularly thins eastward to the Harris Wash Member of the Page.