Abstract 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 δ 13 Corg analysis of organic-rich shales reveal 13.9%o (PDB) variability (values range from -16.9 to -30.8%o 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 sandstone showing south-southwestern 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.

Abstract The Neoproterozoic Uinta Mountain Group is undergoing a new phase of stratigraphic and paleontologic research toward understanding the paleoenvironments, paleoecology, correlation across the range and the region, paleogeography, basin type, and tectonic setting. Mapping, measured sections, sedimentology, paleontology, U-Pb geochronology, and C-isotope geochemistry have resulted in the further characterization and genetic understanding of the western and eastern Uinta Mountain Group . The Red Pine Shale in the western Uinta Mountain Group and the undivided clastic strata in the eastern Uinta Mountain Group have been a focus of this research, as they are relatively unstudied. Reevaluation of the other units is also underway. The Red Pine Shale is a thick, organic-rich, fossiliferous unit that represents a restricted environment in a marine deltaic setting. The units below the Red Pine Shale are dominantly sandstone and orthoquartzite, and represent a fluviomarine setting. In the eastern Uinta Mountain Group, the undivided clastic strata are subdivided into three informal units due to a mappable 50–70-m-thick shale interval. These strata represent a braided fluvial system with flow to the southwest interrupted by a transgressing shoreline. Correlation between the eastern and western Uinta Mountain Group strata is not complete, yet distinctive shale units in the west and east may be correlative, and one of the latter has been dated (≤770 Ma). Regional correlation with the 770–742 Ma Chuar Group suggests the Red Pine Shale may also be ca. 740 Ma, and correlation with the undated Big Cottonwood Formation and the Pahrump Group are also likely based upon C-isotope, fossil, and provenance similarities. This field trip will examine these strata and consider the hypothesis of a ca. 770–740 Ma regional seaway, fed by large braided rivers, flooding intracratonic rift basins and recording the first of three phases of rifting prior to the development of the Cordilleran miogeocline .

Abstract Neoproterozoic and perhaps older metamorphic and igneous rocks in the Novaya Zemlya Archipelago are exposed in four main localities. On the South Island of Novaya Zemlya (the Southern Domain) largely metasedimentary, low greenschist facies, pelitic and flyschoidal formations, dated by acritarchs as late Riphean-Vendian occur; they are intruded by metagabbro-dolerites and lamprophyres. These rocks are overlain by Ordovician strata with sharp, angular unconformity and are therefore considered to be products of Timanian (Baikalian) tectonogenesis. On the southern part of the North Island (the Central Domain), metamorphic rocks of high greenschist to amphibolite facies are preserved which are partly migmatized and comprise metasedimentary and igneous rocks; their contact with Palaeozoic strata here is tectonic. Isotopic age determinations on metasediments and igneous rocks vary from 1550 to 598 Ma and are not yet conclusive. These relatively highly metamorphosed formations may be older than Neoproterozoic. A Neoproterozoic (late Riphean) age was determined for the Mitushev Kamen‘Granite Massif, which is located within the Main Novozemel'sky thrust zone. On the northern part of North Island, (the Northern Domain) Neoproterozoic strata (mainly turbidites) of low greenschist facies pass conformably up into Cambrian and younger strata. A major NW-trending fault (the Baidaratsky fault zone) is believed to separate the Southern Domain from Central and Northern Domains. It is concluded that the southern area is a peripheral part of the Neoproterozoic Timanian (Baikalian) fold belt. Further to the NE across the Baidaratsky fault zone, lies a broad area of possibly older basement, including the Central and Northern Domains of Novaya Zemlya and possibly the Franz Josef Land Archipelago.

Abstract Northeastern Svalbard hosts exceptionally well-preserved Neoproterozoic sediments. The glaciogenic Petrovbreen Member and Wilsonbreen Formation (Fm.) of the Polarisbreen Group crop out in a narrow, Caledonian-aged fold-and-thrust belt spanning from Olav V Land on Spitsbergen in the south to western Nordaustlandet in the north. The older Petrovbreen Member is thin (0–52 m) and patchily preserved, comprising mainly poorly stratified, dolomite-matrix diamictite likely deposited in a marine setting. The basal contact of the Petrovbreen Member erosionally truncates the upper Russøya Member, which preserves a large (12‰) negative C-isotope anomaly. The Petrovbreen Member is overlain by 200 m of dark, monotonous shales of the MacDonaldryggen Member, followed by cherty dolomite grainstone and microbiolamintes of the Slangen Member. The upper Slangen Member is an exposure surface in the southern part of the belt, but in northern Spitsbergen and on Nordaustlandet is transitional into sands of the northward-thickening Bråvika Member. The Wilsonbreen Fm. is typically 100–150 m thick and consists mostly of massively to poorly stratified diamictite, with subordinate sand beds, conglomerate lenses, and carbonates deposited in a terrestrial environment. It is overlain by the colourful Dracoisen Fm., which records, at its base, a typical post-glacial negative δ 13 C anomaly. There are no direct radiometric age constraints or reliable palaeomagnetic data from the Polarisbreen Group, but it is widely accepted that northeastern Svalbard was contiguous with East Greenland during the Neoproterozoic.