The upper part of the Upper Triassic Chinle Formation and related rocks, southeastern Utah and adjacent areas

Abstract

In northeastern Arizona the Owl Rock Member of the Chinle Formation is overlain by a unit of reddish-orange very fine grained sandstone and siltstone. Previously, this reddish-orange unit has been referred to informally as division A of the Chinle Formation. Division A is rerognized throughout northeastern Arizona; stratigraphic studies show that the unit extends not more than 8 miles into southeastern Utah. In different parts of northeastern Arizona, division A is named the Rock Point Member of the Wingate Sandstone or the Church Rock Member of the Chinle Formation. In southeastern Utah and parts of northeastern Arizona a fluviatile sandstone-the Hite Bed-is at the top of the Chinle Formation, and stratigraphic studies show it to be equivalent to division A. In much of southeastern Utah a unit of reddish-orange very fine grained sandstone and siltstone is present below the Hite Bed and is also called Church Rock Member of the Chinle Formation. However, the stratigraphic relations, grain-size analyses, clay minerals, and fossil content show that it is a separate unit equivalent to the Owl Rock Member of the Chinle Formation. It is the author's opinion that rocks formerly assigned to division A of the Chinle Formation be everywhere called the Rock Point Member of the Wingate Sandstone and that the so-called Church Rock of southeastern Utah be renamed. A widespread unconformity that separates the Chinle Formation, as here defined, from overlying rocks extends from southern Nevada across southwestern Utah and northeastern Arizona to northwestern New Mexico. The unconformity overlies the Owl Rock Member in most of northeastern Arizona and overlies older parts of the Chinle Formation to the west in Nevada and to the east in northwestern New Mexico. In southeastern Utah the unconformity probably lies at the base of rocks equivalent to the Hite Bed, where present, or .at the base of the Wingate Sandstone.

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

“…However, based on recent investigations, it seems likely that the beds below the unconformity are pre-Chinle strata, and probably part of the Moenkopi Formation; this conclusion follows the interpretations of Dane (1935) andO'Sullivan andMacLachlan (1975, p. 135) in Richardson Amphitheater. The overall sequence of strata is far more consistent with Chinle Formation sections throughout the salt anticline region if strata below the angular unconformity are excluded.…”

“…Parker, unpublished data), and it is moreover possible that these strata are not all precisely correlative. O'Sullivan (1970) claimed that the type section of the Church Rock Member in northern Arizona (Witkind and Thaden, 1963) was only correlative with the Hite Bed at the very top of the strata assigned to the Church Rock Member in southern Utah. He referred to the younger southern Utah strata as the "reddish-orange siltstone member. "…”

“…The bulk of work on the lithostratigraphy and depositional systems of the Chinle Formation has been done in southern Utah and northern Arizona. The lithostra-tigraphy of the Chinle Formation in southern Utah was described in detail by several studies published between the late 1950s and early 1970s (Stewart, 1956(Stewart, , 1957Harshbarger and others, 1957;Stewart and others, 1959;Poole and Stewart, 1964;Wilson and Stewart, 1967;Repenning and others, 1969;O'Sullivan, 1970;Stewart and others, 1972a;O'Sullivan and MacLachlan, 1975;O'Sullivan and Green, 1977). These studies established much of the stratigraphic nomenclature that is still in use for the members within the Chinle Formation, and correlated these members across the region.…”

High-precision U-Pb zircon geochronology of the Late Triassic Chinle Formation, Petrified Forest National Park (Arizona, USA): Temporal constraints on the early evolution of dinosaurs

“…By contrast, many workers have noted evidence of large-scale incision and infi lling in the Chinle stratigraphy (Repenning et al, 1969;O'Sullivan, 1970;Stewart et al, 1972;Blakey and Gubitosa, 1983;Kraus and Middleton, 1987). The dissected paleotopography, in concert with the well-documented lenticular, repetitive nature of fl uvial facies (Miall, 1983;e.g., Fastovsky, 1987), has been used to challenge the lateral continuity of the members and formations recognized in the region (Dubiel et al, 1999;Therrien et al, 1999).…”