TY - CHAP
T1 - The alluvial to eolian transition of the Chinle and Nugget Formations in the Southern Uinta Mountains, northeastern Utah
AU - Irmis, Randall B.
AU - Chure, Daniel J.
AU - Engelmann, George F.
AU - Wiersma, Jelle P.
AU - Lindström, Sofie
PY - 2015
Y1 - 2015
N2 - The Uinta Mountains of northeastern Utah preserve the northernmost outcrops of classic early Mesozoic stratigraphic
units on the Colorado Plateau, and document the transition to equivalent strata further north in Wyoming. In this
region, the predominantly fluvial Upper Triassic Chinle Formation is overlain by the predominantly eolian Upper
Triassic-Lower Jurassic Nugget Sandstone, which may be partially or wholly equivalent to the Glen Canyon Group further south. Previous work on these units has reached little consensus on where the boundary between the Chinle and
Nugget should be placed, whether this boundary is conformable, and what lithostratigraphic nomenclature should
be used. Our stratigraphic and sedimentologic investigation of outcrops in and around the western portion of Dinosaur National Monument and north of Vernal, Utah, indicate that the orange sandstone interval and overlying purple
interval are assignable to the upper member of the Chinle Formation. This purple interval is interpreted as ephemeral
sheet-flow deposits dominated by mud flats. The Chinle-Nugget contact appears conformable in many areas, with no
evidence of the J-0 unconformity. The lowermost 10-20 meters of the Nugget Sandstone show extensive evidence
of subaqueous deposition and/or modification, with only occasional thin cross-bedded eolian units, and these transitional layers commonly contain vertebrate tracks, some of which suggest a Triassic age. Taken together, these data
indicate the gradual drying of the Chinle river and floodplain system at the same time as the encroachment of the
Nugget/Wingate erg. Trace and body fossils indicate this erg margin was populated by a wide variety of invertebrate
and vertebrate organisms, including early dinosaurs
AB - The Uinta Mountains of northeastern Utah preserve the northernmost outcrops of classic early Mesozoic stratigraphic
units on the Colorado Plateau, and document the transition to equivalent strata further north in Wyoming. In this
region, the predominantly fluvial Upper Triassic Chinle Formation is overlain by the predominantly eolian Upper
Triassic-Lower Jurassic Nugget Sandstone, which may be partially or wholly equivalent to the Glen Canyon Group further south. Previous work on these units has reached little consensus on where the boundary between the Chinle and
Nugget should be placed, whether this boundary is conformable, and what lithostratigraphic nomenclature should
be used. Our stratigraphic and sedimentologic investigation of outcrops in and around the western portion of Dinosaur National Monument and north of Vernal, Utah, indicate that the orange sandstone interval and overlying purple
interval are assignable to the upper member of the Chinle Formation. This purple interval is interpreted as ephemeral
sheet-flow deposits dominated by mud flats. The Chinle-Nugget contact appears conformable in many areas, with no
evidence of the J-0 unconformity. The lowermost 10-20 meters of the Nugget Sandstone show extensive evidence
of subaqueous deposition and/or modification, with only occasional thin cross-bedded eolian units, and these transitional layers commonly contain vertebrate tracks, some of which suggest a Triassic age. Taken together, these data
indicate the gradual drying of the Chinle river and floodplain system at the same time as the encroachment of the
Nugget/Wingate erg. Trace and body fossils indicate this erg margin was populated by a wide variety of invertebrate
and vertebrate organisms, including early dinosaurs
M3 - Chapter in book
SN - 9780980048988
SN - 0980048982
VL - 44
T3 - Utah Geological Association Publication
SP - 13
EP - 48
BT - Geology of Utah’s Uinta Basin and Uinta Mountains
A2 - Vanden Berg, Michael D.
A2 - Ressetar, Robert
A2 - Birgenheier, Lauren P.
PB - Utah Geological Association
ER -