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

Abstract

<jats:p>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.</jats:p>

Osteology of the Late Triassic Bipedal Archosaur Poposaurus gracilis (Archosauria: Pseudosuchia) from Western North America

“…( A ) Map of Utah showing location of Grand Staircase‐Escalante National Monument (GSENM) with a star indicating the discovery site of YPM 57100. ( B ) Chinle Formation lithostratigraphy in the Circle Cliffs area (GSENM) (following Stewart et al, ; Martz et al, ), with a detailed stratigraphic section showing the fossiliferous level.…”

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

“…Following the seminal work on Chinle stratigraphy by Stewart et al (1972a) (Parrish and Good, 1987;Parrish, 1999), including metoposaurid temnospondyls, phytosaurs, and aetosaurs (Parrish and Good, 1987). The discovery of the phytosaur " Rutiodon tenuis " (= Machaeroprosopus pristinus -see Long and Murry, 1995) and a partial osteoderm of the aetosaur Typothorax caused Parrish and Good (1987) to correlate the Petrified Forest Member in the White Canyon region of BENM with the Petrified Forest Member in Arizona and New Mexico, consistent with lithostratigraphic correlations (e.g., Stewart et al, 1972a;Blakey and Gubitosa, 1983;Martz et al, 2017). Parrish and colleagues also discovered numerous invertebrate fossils, including bivalves, gastropods, ostracods, and conchostracans, reporting the occurrence of the molluscs Triasamnicola assiminoides , Diplodon gregori , Antediplodon sp.…”

“…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;Gubitosa, 1983, 1984;Martz et al, 2014Martz et al, , 2017.…”

Fire-scarred fossil tree from the Late Triassic shows a pre-fire drought signal

“…The Chinle Formation was deposited by meandering rivers and streams in an environment of lakes, ponds, and marshes between about 225 and 203 Ma (ref. 41 ). The Black Forest Bed has been dated to about 210 Ma 42 , 43 .…”