Based on a methodic sedimentological analysis, the Late Jurassic (Oxfordian) Curtis Formation unravels the intricate facies variability which occurs in a tide-dominated, fluvially starved, low-gradient, semi-enclosed epicontinental basin. This unit crops out in east-central Utah, between the eolian deposits of the underlying Middle Jurassic (Callovian) Entrada Sandstone, from which it is separated by the J-3 unconformity, and the conformable overlying supratidal Summerville Formation of Oxfordian age. A high-resolution sedimentary analysis of the succession led to the recognition of eight facies associations (FA) with six sub-facies associa­tions. Based on the specific three-dimensional arrangement of these eight facies associations, it is proposed to separate the Curtis Formation into three sub-units: the lower, middle and upper Curtis. The J-3 unconformity defines the base of the lower Curtis, which consists of upper shoreface to beach deposits (FA 2), mud-domi­nated (FA 3a) and sand-dominated heterolithic subtidal flat (FA 3b), sand-rich sub- to supratidal flat (FA 4a) and correlative tidal channel infill (FA 4c). It is capped by the middle Curtis, which coincides with the sub- to intertidal channel-dune-flat complex of FA 5, and its lower boundary corresponds to a transgressive surface of regional extent, identified as the Major Transgressive Surface (MTS). This surface suggests a potential correla­tion between the middle and the upper Curtis and the neighboring Todilto Member of the Wanakah Forma­tion or Todilto Formation. The upper Curtis consists of the heterolithic upper sub- to intertidal flat (FA 6) and coastal dry eolian dunes belonging to the Moab Member of the Curtis Formation (FA 7), and it conformably overlies the middle Curtis.

Based on a methodic sedimentological analysis, the Late Jurassic (Oxfordian) Curtis Formation unravels the intricate facies variability which occurs in a tide-dominated, fluvially starved, low-gradient, semi-enclosed epicontinental basin. This unit crops out in east-central Utah, between the eolian deposits of the underlying Middle Jurassic (Callovian) Entrada Sandstone, from which it is separated by the J-3 unconformity, and the conformable overlying supratidal Summerville Formation of Oxfordian age. A high-resolution sedimentary analysis of the succession led to the recognition of eight facies associations (FA) with six sub-facies associations. Based on the specific three-dimensional arrangement of these eight facies associations, it is proposed to separate the Curtis Formation into three sub-units: the lower, middle and upper Curtis. The J-3 unconformity defines the base of the lower Curtis, which consists of upper shoreface to beach deposits (FA 2), mud-domi­nated (FA 3a) and sand-dominated heterolithic subtidal flat (FA 3b), sand-rich sub- to supratidal flat (FA 4a) and correlative tidal channel infill (FA 4c). It is capped by the middle Curtis, which coincides with the sub- to intertidal channel-dune-flat complex of FA 5, and its lower boundary corresponds to a transgressive surface of regional extent, identified as the Major Transgressive Surface (MTS). This surface suggests a potential correlation between the middle and the upper Curtis and the neighboring Todilto Member of the Wanakah Forma­tion or Todilto Formation. The upper Curtis consists of the heterolithic upper sub- to intertidal flat (FA 6) and coastal dry eolian dunes belonging to the Moab Member of the Curtis Formation (FA 7), and it conformably overlies the middle Curtis. The spatial distribution of these sub-units supports the distinction of three different sectors across the study area: sector 1 in the north, sector 2 in the south-southwest, and sector 3 in the east. In sector 1, the Curtis Formation is represented by its three sub-units, whereas sector 2 is dominated by the middle and upper Curtis, and sector 3 encompasses the extent of the Moab Member of the Curtis Formation. This study also highlights the composite nature of the J-3 unconformity, which was impacted by various processes occurring before the Curtis Formation was deposited, as well as during the development of the lower and middle Curtis. Local collapse features within the lower and middle Curtis are linked to sand fluid over­pressure within a remobilized sandy substratum, potentially triggered by seismic activity. Furthermore, the occurrence of a sub-regional angular relationship between the middle Curtis and substratum implies that the area of study was impacted by a regional deformational event during the Late Jurassic, before the deposition of the middle Curtis. The spatial distribution of these sub-units supports the distinction of three different sectors across the study area: sector 1 in the north, sector 2 in the south-southwest, and sector 3 in the east. In sector 1, the Curtis For­mation is represented by its three sub-units, whereas sector 2 is dominated by the middle and upper Curtis, and sector 3 encompasses the extent of the Moab Member of the Curtis Formation. This study also highlights the composite nature of the J-3 unconformity, which was impacted by various processes occurring before the Curtis Formation was deposited, as well as during the development of the lower and middle Curtis. Local collapse features within the lower and middle Curtis are linked to sand fluid over­pressure within a remobilized sandy substratum, potentially triggered by seismic activity. Furthermore, the occurrence of a sub-regional angular relationship between the middle Curtis and substratum implies that the area of study was impacted by a regional deformational event during the Late Jurassic, before the deposition of the middle Curtis.

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Our studies of the Neoproterozoic Uinta Mountain Group focus on the Red Pine Shale in the western Uinta Mountains and the undivided clastic strata in the eastern Uinta Mountains, which record deltaic-marine and braided-fluvial to shoreline deposition, respectively. We conclude that the Red Pine Shale postdates the < 770 Ma eastern clastic strata, and the Uinta Mountain Group represents deposition in a rift basin predating the rift episode recorded at ~ 700 Ma in western Laurentia.Measured sections and stratigraphic mapping of the Red Pine Shale show that it is ~ 550-1200 m thick in the western part of the range, thins to < 300 m in the east-central range, and is missing in the eastern range. Measured sections show organic-rich shale interbedded with medium-to coarse-grained sandstone. Sedimentary structures include graded bedding, hummocky cross stratification, parallel to ripple lamination, tabular crossbeds, ripple marks, and slump folds. Fossils include Bavlinella faveolata, filaments, leiosphaerid acritarchs, and, more rarely, vase-shaped microfossils and ornamented acritarchs. Preliminary whole-rock ! 13 C org analysis of organic-rich shales reveal 13.9‰ (PDB) variability (values range from -16.9 to -30.8‰ PDB) and TOC values range from 0.07 to 5.9%. Combined data suggest deposition below and near fair-weather wave base in a marine deltaic system, and correlation with the ~ 770 to > 742 Ma Chuar Group, Grand Canyon.The undivided clastic strata of the Uinta Mountain Group, eastern Uinta Mountains, are dominated by trough-and tabular-cross-bedded and massive sandstones showing south-southwesterly paleocurrent flow. At least three laterally continuous (kilometer-scale) ~ 50-m-thick intervals of gray-green, organic-bearing shale have been mapped amongst these sandstone intervals and contain ripple marks, mud-crack casts, ripple cross laminae, and gypsum casts and molds. The lowermost shale interval allows subdivision of the clastic strata into three informal units. Fossils from shale in the middle-upper (?) interval of the clastic strata include acritarchs and possible vase-shaped microfossils. Simple sphaeromorphs and carbonaceous filaments have also been found in black to green shale near the base of the section. The clastic strata represent a sandy braid system with possible marine drowning events from the west. In addition to an alluvial-fan setting, the Jesse Ewing Canyon Formation, the basal unit of the UMG below the clastic strata, represents high-energy shoreline and fan-delta deposition.

A new local flora of silicified logs and wood has been discovered in the Upper Jurassic Morrison Formation in the Rainbow Draw area near Dinosaur National Monument, northeastern Utah, USA. Fossil logs and wood were found in the Salt Wash Member at nine sites at Rainbow Draw and at one site near Miners Draw, south of Blue Mountain. The fossil logs are large and relatively intact, the longest measuring 11 m. The wood is well preserved, coniferous, and can be identified to the species level. Diagnostic anatomical features include resin plugs in the ray cells and axial tracheids, araucarioid tracheary pitting and crossfield pitting, and the lack of resin canals and true, regularly occurring growth rings. This taxon of fossil wood, originally described as Araucarioxylon hoodii Tidwell et Medlyn, is recognized here as a new combination, Agathoxylon hoodii (Tidwell et Medlyn) Gee, Sprinkel, Bennis et Gray, which pertains to the conifer family Araucariaceae. Based on the preserved girth of the logs, the minimum height of the trees could be reconstructed. The largest fossil logs measured at least 127 cm in diameter and hence reached a minimum height of 28 m. Judging from the growth habit of all naturally occurring araucariaceous trees today, the fossil plants likely formed forests of moderately tall trees and were well over 100 years old. The lack of true growth rings shows that there was no seasonality in the local paleoclimate, neither variations in summer–winter temperatures, nor wet–dry cycles. Thus, during the Late Jurassic, tall conifer forests with Agathoxylon hoodii grew in at least two areas in what is now Utah: east of the city of Vernal and near Mt. Ellen in the Henry Mountains. Coupled with the fossil evidence of conifer seed cones and pollen found in the Morrison Formation throughout eastern Utah, the newly discovered fossil logs and wood argue for the reconstruction of Upper Jurassic habitats in this region as mesic and wooded, and the climate as equable, not seasonal, nor semi-arid or arid.