Upper Triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern Utah

Abstract

The Chinle Formation and the lower part of the overlying Wingate Sandstone and Moenave Formation were deposited in fluvial, lacustrine, paludal, and eolian environments during the Norian and Rhaetian stages of the Late Triassic (~230 to 201.3 Ma), during which time the climate shifted from subtropical to increasingly arid. In southern Utah, the Shinarump Member was largely confined to pre-Chinle paleovalleys and usually overprinted by mottled strata. From southeastern to southwestern Utah, the lower members of the Chinle Formation (Cameron Member and correlative Monitor Butte Member) thicken dramatically whereas the upper members of the Chinle Formation (the Moss Back, Petrified Forest, Owl Rock, and Church Rock Members) become erosionally truncated; south of Moab, the Kane Springs beds are laterally correlative with the Owl Rock Member and uppermost Petrified Forest Member. Prior to the erosional truncation of the upper members, the Chinle Formation was probably thickest in a southeast to northwest trend between Petrified Forest National Park and the Zion National Park, and thinned to the northeast due to the lower Chinle Formation lensing out against the flanks of the Ancestral Rocky Mountains, where the thickness of the Chinle is largely controlled by syndepositional salt tectonism. The Gartra and Stanaker Members of the Ankareh Formation are poorly understood Chinle Formation correlatives north of the San Rafael Swell. Osteichthyan fish, metoposaurid temnospondyls, phytosaurids, and crocodylomorphs are known throughout the Chinle Formation, although most remains are fragmentary. In the Cameron and Monitor Butte Members, metoposaurids are abundant and non-pseudopalatine phytosaurs are known, as is excellent material of the paracrocodylomorph Poposaurus; fragmentary specimens of the aetosaurs Calyptosuchus, Desmatosuchus, and indeterminate paratypothoracisins were probably also recovered from these beds. Osteichthyans, pseudopalatine phytosaurs, and the aetosaur Typothorax are especially abundant in the Kane Springs beds and Church Rock Member of Lisbon Valley, and Typothorax is also known from the Petrified Forest Member in Capitol Reef National Park. Procolophonids, doswelliids, and dinosaurs are known but extremely rare in the Chinle Formation of Utah. Body fossils and tracks of osteichthyans, therapsids, crocodylomorphs, and theropods are well known from the lowermost Wingate Sandstone and Moenave Formation, especially from the St. George Dinosaur Discovery Site at Johnson Farm.

Paleontology of the Bears Ears National Monument: history of exploration and designation of the monument

“…In northern BENM and vicinity, the Kane Springs beds are at least partly correlative to the Petrified Forest Member and are the lowest Chinle unit in this area (Blakey andGubitosa, 1983, 1984;Martz et al, 2014Martz et al, , 2017; these strata comprise a complex mix of poorly drained floodplain and meandering stream deposits that sometimes incise as paleovalleys into the underlying Moenkopi Formation (Blakey, 1978;Blakey andGubitosa, 1983, 1984;Martz et al, 2014;Hartley and Evenstar, 2018). The Owl Rock Member overlies these two units throughout BENM, and also comprises well-drained overbank and minor channel deposits (Blakey and Gubitosa, 1983;Dubiel, 1994;Dubiel and Hasiotis, 2011); crayfish burrows extending from channel and levee facies into underlying finer-grained paleosols are common Mitchell, 1989, 1993;Hasiotis, 1995).…”

“…Laterally, they grade into and are overlain by the braided stream deposits of the Moss Back Member, which represent the larger trunk streams of the same fluvial system (Blakey andGubitosa, 1983, 1984;Dubiel, 1983aDubiel, , 1987Dubiel, , 1994. In southern BENM, the Moss Back is overlain by the well-drained paleosols and meandering stream deposits of the Petrified Forest Member, preserving the increasingly arid and seasonal conditions during the Norian (Blakey and Gubitosa, 1983;Dubiel, 1987Dubiel, , 1994Dubiel and Hasiotis, 2011;Martz et al, 2017).…”

Paleontology of the Bears Ears National Monument: history of exploration and designation of the monument

“…In the south-central and southeastern portions of BENM, near Bears Ears proper and Comb Ridge, the Monitor Butte and Moss Back members interfinger (Stewart et al, 1972a;Blakey and Gubitosa, 1983;Dubiel, 1994), making them difficult to differentiate (Lewis et al, 2011); in these areas, for stratigraphic convenience we refer to this portion of the formation as the Monitor Butte Member, following Gay and St. Aude (2015). To the north, in the Abajo Mountains and Indian Creek areas, the lower portion of the Chinle Formation is absent, and the base of the unit is equivalent to the Petrified Forest Member elsewhere (Blakey and Gubitosa, 1983;Martz et al, 2014Martz et al, , 2017. In these areas, the recognized subdivisions comprise from oldest to youngest: Kane Springs beds, Owl Rock Member, and Church Rock Member (Witkind, 1964;Blakey andGubitosa, 1983, 1984;Martz et al, 2014Martz et al, , 2017.…”

“…To the north, in the Abajo Mountains and Indian Creek areas, the lower portion of the Chinle Formation is absent, and the base of the unit is equivalent to the Petrified Forest Member elsewhere (Blakey and Gubitosa, 1983;Martz et al, 2014Martz et al, , 2017. In these areas, the recognized subdivisions comprise from oldest to youngest: Kane Springs beds, Owl Rock Member, and Church Rock Member (Witkind, 1964;Blakey andGubitosa, 1983, 1984;Martz et al, 2014Martz et al, , 2017.…”

“…In the BENM area, the Chinle Formation is overlain by the Upper Triassic-Lower Jurassic Wingate Sandstone of the Glen Canyon Group, which acts as a resistant cliff-forming "cap" (Baker, 1936;Sears, 1956;Stewart, 1957;Witkind et al, 1963;Witkind, 1964;O'Sullivan and MacLachlan, 1975;Martz et al, 2014Martz et al, , 2017. Although predominantly an eolian sandstone, the base of this unit locally preserves fluvially-deposited sands (e.g., Martz et al, 2014).…”