Wasatch Formation Research Articles

Evidence for enhanced fluvial channel mobility and fine sediment export due to precipitation seasonality during the Paleocene-Eocene thermal maximum

Abstract The Paleocene-Eocene thermal maximum (PETM) was the most extreme example of an abrupt global warming event in the Cenozoic, and it is widely discussed as a past analog for contemporary climate change. Anomalous accumulation of terrigenous mud in marginal shelf environments and concentration of sand in terrestrial deposits during the PETM have both been inferred to represent an increase in fluvial sediment flux. A corresponding increase in water discharge or river slope would have been required to transport this additional sediment. However, in many locations, evidence for changes in fluvial slope is weak, and geochemical proxies and climate models indicate that while runoff variability may have increased, mean annual precipitation was unaffected or potentially decreased. Here, we explored whether changes in river morphodynamics under variable-discharge conditions could have contributed to increased fluvial sand concentration during the PETM. Using field observations, we reconstructed channel paleohydraulics, mobility, and avulsion behavior for the Wasatch Formation (Piceance Basin, Colorado, USA). Our data provide no evidence for changes in fluvial slope during the PETM, and thus no evidence for enhanced sediment discharge. However, our data do show evidence of increased fluvial bar reworking and advection of sediment to floodplains during channel avulsion, consistent with experimental studies of alluvial systems subjected to variable discharge. High discharge variability increases channel mobility and floodplain reworking, which retains coarse sediment while remobilizing and exporting fine sediment through the alluvial system. This mechanism can explain anomalous fine sediment accumulation on continental shelves without invoking sustained increases in fluvial sediment and water discharge.

Spring origin of Eocene carbonate mounds in the Green River Formation, Northern Bridger Basin, Wyoming, USA

AbstractModern and ancient lacustrine carbonate build‐ups provide uniquely sensitive sedimentary and geochemical records for understanding the interaction between tectonics, past climates, and local and regional scale basin hydrology. Large (metre to decametre), well‐developed carbonate mounds in the Green River Formation have long been recognized along the margins of an Eocene lake, known as Lake Gosiute. However, their mode of origin and significance with respect to palaeohydrology remain controversial. Here, new sedimentological, Sr isotope data and structural evidence show that significant spring discharge led to the formation of a decametre size complex of shoreline carbonate mounds in the upper Wilkins Peak Member of the Green River Formation at Little Mesa and adjacent areas in the Bridger Basin, Wyoming, USA. Sedimentological evidence indicates that spring discharge was predominantly subaqueous but was, at times, also subaerial, which produced tufa cascades and micro‐rimstone dam structures. The 87Sr/86Sr ratios measured from these subaerial spring deposits are less radiogenic (87Sr/86Sr = 0.71040 to 0.71101) than contemporaneous palaeolake carbonates (87Sr/86Sr = 0.71195 to 0.71561) because their parent groundwaters likely interacted with less‐radiogenic Palaeozoic carbonate. Calcite‐cemented sandstone cones and spires (87Sr/86Sr = 0.71037 to 0.71057) in the Wasatch Formation directly below the spring deposits suggest that groundwaters derived from Palaeozoic carbonates preferentially flowed along thrust faults. These results imply that high spring discharge coincided with lake high stands of the upper Wilkins Peak Member, suggesting that recharge at the north‐west margin of the Bridger Basin contributed to Lake Gosiute’s water budget and lowered the salinity of an underfilled, evaporative lake basin. The findings of this study provide criteria for the recognition of groundwater discharge in palaeolake systems which may lead to the discovery of palaeospring systems in other ancient lake deposits.

Preliminary detrital zircon U-Pb Geochronology of the Wasatch Formation, Powder River Basin, Wyoming

The lower Eocene Wasatch Formation is more than 1500 m thick in the Powder River Basin of Wyoming. The Wasatch is a Laramide synorgenic deposit that consists of paludal and lacustrine mudstone, fluvial sandstone, and coal. U-Pb geochronologic data on detrital zircons were gathered for a sandstone unit in the middle part of the succession. The Wasatch was collected along Interstate 90 just west of the Powder River, which is about 50 km east of the Bighorn Mountain front. The sandstone is lenticular in geometry and consists of arkosic arenite and wacke. The detrital zircon age spectrum ranged (n=99) from 1433-2957 Ma in age, and consisted of more than 95% Archean age grains, with an age peak of about 2900 Ma. Three populations of Archean ages are evident: 2886.6±10 Ma (24%), 2906.6±8.4 Ma (56%) and 2934.1±6.6 Ma (20%; all results 2 sigma). These ages are consistent with the age of Archean rocks exposed in the northern part of the range. The sparse Proterozoic grains were likely derived from the recycling of Cambrian and Carboniferous strata. These sands were transported to the Powder River Basin through the alluvial fans adjacent to the Piney Creek thrust. Drainage continued to the north through the basin and eventually into the Ancestral Missouri River and Gulf of Mexico. The provenance of the Wasatch is distinct from coeval Tatman and Willwood strata in the Bighorn and Absaroka basins, which were derived from distal source (>500 km) areas in the Sevier Highlands of Idaho and the Laramide Beartooth and Tobacco Root uplifts. Why the Bighorn Mountains shed abundant Eocene strata only to the east and not to the west remains enigmatic, and merits further study.

Revisions to the fossil sporophyte record of Marsilea

Abstract The fossil record of Marsilea is challenging to assess, due in part to unreliable reports and conflicting opinions regarding the proper application of the names Marsilea and Marsileaceaephyllum to fossil leaves and leaflets similar to those of modern Marsilea. Specimens examined for this study include material assigned to Marsileaceaephyllum johnhallii, purportedly the oldest fossil record of a Marsilea-like sporophyte from the Lower Cretaceous of the Dakota Formation, Kansas, U.S.A.; leaves and leaf whorls of the extinct aquatic angiosperm Fortuna from several Late Cretaceous and Paleocene localities in western North America; and leaves and leaflets resembling Marsilea from the Eocene Green River Formation, Colorado and Utah, U.S.A. Literature on the fossil record of Marsilea was also reviewed. As a result, several taxonomic changes are proposed. Marsileaceaephyllum johnhallii is reinterpreted as an aquatic angiosperm that shares some architectural features with the genus Fortuna, although Marsileaceaephyllum is here maintained as a distinct genus with an emended diagnosis; under this reinterpretation, the name Marsileaceaephyllum can no longer be applied to sporophyte organs with affinities to Marsileaceae. Three valid fossil Marsilea species are recognized on the basis of sporophyte material that includes characteristic quadrifoliolate leaves and reticulate-veined leaflets: Marsilea campanica (J. Kvaček & Herman) Hermsen, comb. nov., from the Upper Cretaceous Grünbach Formation, Austria; Marsilea mascogos Estrada-Ruiz et al., from the Upper Cretaceous Olmos Formation, Mexico; and Marsilea sprungerorum Hermsen, sp. nov., from the Eocene Green River Formation, U.S.A. The species are distinguished from one another based on leaflet dimensions. Leaves from the Eocene Wasatch Formation, U.S.A., are transferred from Marsileaceaephyllum back to Marsilea, although not assigned to a fossil species. Finally, an occurrence of Marsilea from the Oligocene of Ethiopia is reassigned to Salvinia. A critical evaluation of the fossil record of Marsilea thus indicates that (1) the oldest fossil marsileaceous sporophytes bearing Marsilea-like leaves are from the Campanian; (2) only four credible records of sporophyte material attributable to Marsilea are known; and (3) the oldest dispersed Marsilea spores are known from the Oligocene.

Depositional environment, sediment provenance and oxygen isotope paleoaltimetry of the early Paleogene greater Green River Basin, southwestern Wyoming, U.S.A.

Depositional process, sediment provenance, and paleotopography are critical to paleogeographic reconstruction during the coeval Laramide and Sevier orogenies in the Cordillera orogenic system. Here we conduct lithofacies analysis, sediment provenance, and paleoelevation studies in the fluvial lower Paleogene Fort Union and the main body of the Wasatch formations in the center of the greater Green River Basin in order to reconstruct paleogeography. The depositional environment changed from low-energy floodplains and associated meandering river during the Paleocene to braided rivers during the earliest Eocene. The lowermost Eocene strata have more Precambrian basement-derived feldspar grains compared to the Paleocene strata. This change in sediment provenance was associated with the change to dominant northwestward paleoflow direction, suggesting major uplift of the Laramide Uinta Mountains during the earliest Eocene. The δ18O values of authigenic carbonates were stable during the early Paleocene, but decreased gradually from −10 permil during the late Paleocene to −18 permil during the earliest Eocene, suggesting the lack of highland precipitation in the basin catchment during the early Paleocene, and significant surface uplift and arrival of highland precipitation from the Uinta Mountains during the earliest Eocene. The reconstructed paleoelevation of the Uinta Mountains was at least 3 km, possibly greater than 3.5 km, and the paleoelevation of the greater Green River Basin floor was at most 1 km, and the paleorelief between the greater Green River Basin and Uinta Mountains was ∼ 2 km during the earliest Eocene. Our record of the earliest Eocene establishment of high topography of the Uinta Mountains through renewed uplift is 4 to 6 Myr older than previously thought. If the carbonate cements in the Fort Union Formation record the isotope compositions of surface water from the Sevier orogen, their high δ18O values likely suggest that the Sevier orogen had rugged topography during the Paleocene.

Interflag sandstone laminae, a novel sedimentary structure, with implications for Ediacaran paleoenvironments

Interflag sandstone laminae are thin, silty to sandy, layers between thicker sandstone beds, and a new name for sedimentary structures recently called “shims”, and “microbial mat sandwiches”, from Ediacaran fossil localities of Nilpena, South Australia. They have been regarded as structures unique to Precambrian marine environments, but both the age and environmental associations are reinterpreted in this study. Interflag sandstone laminae from Eocene (Wasatch Formation, Colorado, U.S.A.) and Pennsylvanian (Mansfield Formation, Indiana, U.S.A.) fluvial levees and scroll bars were studied in the field, and by means of petrographic thin sections and granulometry. Climbing translatent ripples and distinct grain size distributions are evidence that interflag sandstone laminae were eolian, whereas intervening flagstones were deposited by fluvial traction currents. Other evidences of exposure to wind include microbial earth textures, shallow cracking structures, zibars, setulfs, root traces, and insect trackways. Other evidences of flagstone deposition in traction currents include intraformational claystone breccias, oscillation and current ripples, and microbial mat textures. Similarly distinct beds can be seen in modern sandy river levees, such as the Murchison River of Western Australia and Green River of Utah (U.S.A.). These observations reveal that interflag laminae are created by exposure and wind-drift, but flagstones are produced by floods. Quartzose flagstones of demonstrable marine origin, with fossil brachiopods and trilobites, have also been examined, but lack interflag sandstone laminae. Interflag sandstone laminae are evidence of alternating flood and wind, only known from fluvial environments, and are further support for the idea that Ediacaran vendobionts from South and central Australia, and Namibia lived on land.

The influence of lateral topographic confinement on fluvial channel‐belt clustering, compensation and connectivity – lower Wasatch Formation and Dakota Sandstone, Utah, USA

AbstractFluvial channel‐belt clustering has recently been documented using quantitative metrics for systems dominated by autogenic controls. It has long been recognized that allogenic forcing (tectonic and eustatic controls) can lead to confinement of fluvial systems, resulting in clustering of channel belts. To date, no study has quantitatively documented the differences in channel‐belt clustering, compensational stacking of channel belts and interchannel‐belt connectivity in unconfined and confined systems. This study quantitatively compares world‐class outcrops of an unconfined fluvial system (Palaeocene lower Wasatch Formation) with outcrops of a confined fluvial system (Cretaceous Dakota Sandstone). Two new methods have been developed to quantitatively document channel‐belt clustering and intrachannel‐belt connectivity. These new methods, and other previously developed methods, are used to document an increase in channel‐belt clustering and intrachannel‐belt connectivity downdip in both systems. Additionally, it was found that channel belts within the unconfined system stack more compensationally than those in the confined system. These new methods and empirical relationships can be used for predicting intrachannel‐belt connectivity, and accurately modelling unconfined and confined fluvial systems in the subsurface.

Provenance Signals In the Piceance Creek Basin: Unroofing of the Sawatch Range and Extent of the Early Paleogene California River System (Colorado, U.S.A.)

Abstract: New and compiled U-Pb detrital zircon ages (n = 495) and sandstone petrographic compositions (n = 45) indicate a largely similar provenance throughout deposition of the Paleocene and lowermost Eocene Wasatch Formation in the Piceance Creek basin of northwest Colorado, U.S.A. Age spectra are dominated by Cretaceous- and Precambrian-age zircons from fluvial sand bodies composed of compositional litharenites and feldspathic litharenites. Our comparison with age spectra from other geologic formations exposed in surrounding Laramide uplifts indicates the Wasatch Formation is most similar to Upper Cretaceous fluvio-deltaic and marine strata of the Mesaverde Group, Mancos Shale, and their equivalents. Age spectra and paleodrainage directions from the lower Paleogene Wasatch and underlying Ohio Creek formations suggests recycling of these strata off the Sawatch and Uncompahgre uplifts from south and southeast of the basin. The data are inconsistent with previous hypotheses that Yavapai–Mazatzal crystalline basement in the Sawatch Range and Mesozoic eolianites in the Uncompahgre uplift contributed significant sediment to the basin. Based on these provenance insights and estimates of maximum depositional ages from detrital-zircon ages and biostratigraphy it appears that exposure and erosion of sedimentary strata of the Sawatch Range began between 65 and 60 Ma. This timing is significantly younger than the previously hypothesized ∼ 72 Ma unroofing of the crystalline basement in the uplift. Furthermore, we find no provenance evidence that sediment was transported across the Douglas Creek arch into the Piceance Creek basin from the Uinta basin. Thus, we infer this subdued Laramide structure was sufficient to block sediment dispersal from the paleo–California River system, which contemporaneously deposited ∼ 3000 km 3 of sediment, transported from the magmatic arc, in the Uinta basin.

Stratigraphy, mammalian paleontology, paleoecology, and age correlation of the Wasatch Formation, Fossil Butte National Monument, Wyoming

AbstractFieldwork conducted in the Wasatch Formation in and around Fossil Butte has yielded a diverse assemblage of early Eocene vertebrates. Fossil vertebrates are distributed through three discrete stratigraphic intervals within the uppermost 180 m of the main body of the Wasatch Formation underlying the Green River Formation. These assemblages were derived primarily from fluvial overbank mudstone units overprinted with variably well-developed paleosols. The lowest (20 m) and highest (60 m) sections are characterized by less mature and more hydromorphic paleosols, whereas the middle section (100 m) is typified by more mature paleosols and more abundant channel sandstones.The combined assemblages contain at least 46 species of mammals. Faunal characteristics include high abundances of equid perissodactyls and a relatively high abundance and diversity of notharctines primates, an apparent absence of omomyid primates, relatively high rodent diversity, and relatively diverse and abundant artiodactyls. One new genus (Eoictopsnew genus) and three new species (Eoictops novacekinew species,Palaeosinopa lacusnew species, and ?Notoparamys blochinew species) are included in the Fossil Butte assemblage. Also recorded are late occurrences of two hyopsodontid condylarths and an early occurrence of a rare phenacodontid condylarth. The relatively high abundances of equids and notharctines suggest that vertebrate samples were derived from relatively open paleohabitats that included forested areas along water courses.All three assemblages contain characteristic Lysitean (Wasatchian biochron Wa-6) elements, but the occurrence of the palaeotheriid perissodactylLambdotheriumin the uppermost horizon indicates a Lostcabinian (Wa-7) age for at least the top of the Wasatch Formation. The overlying predominantly fish-bearing Fossil Butte Member of the Green River Formation also containsLambdotheriumand is therefore Wa-7 in age as well.

An early Eocene fish fauna from the Bitter Creek area of the Wasatch Formation of southwestern Wyoming, U.S.A.

ABSTRACTEarly Eocene fluvial ichthyofaunas of Wyoming are relatively poorly known compared with the better-preserved lake deposits of the Green River Formation. We describe the teleost fishes from a single floodplain locality in the main body of the Wasatch Formation that immediately predates the formation of Lake Gosiute, in the Washakie Basin of Wyoming. This assemblage was deposited during the Graybullian substage of the Wasatchian Stage, corresponding to the onset of the rapid climatic warming leading to the Early Eocene Climatic Optimum. In addition to a lepisosteiform and an amiid, the locality has a teleost ichthyofauna comprising Diplomystus (Ellimmichthyiformes), a gonorynchiform probably representing Notogoneus, amblyopsid-like percopsiforms that may represent up to three taxa, and perciforms among which are probably an indeterminate centrarchid and ‘Priscacara.’ The fauna demonstrates that many of the Green River Formation fish taxa were already present in fluvial environments prior to the formation of the Green River lakes, indicating that the subsequent climate warming had little effect on these fishes. Some of the elements recognized here as probably representing Notogoneus were previously recovered from Late Cretaceous deposits from Utah to Alberta, suggesting that this gonorynchid was wide-ranging in North American fluvial environments since Mesozoic times, as were several other taxa identified here. Furthermore, the ichthyofauna indicates that the depositional environment was well vegetated and well oxygenated. These waters were shallow, with gentle flow strengths, which, together with the high oxygen content, suggests that the sediments of the locality were deposited in small ponds connected to an active river system.Citation for this article: Divay, J. D., and A. M. Murray. 2016. An early Eocene fish fauna from the Bitter Creek area of the Wasatch Formation of southwestern Wyoming, U.S.A. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1196211.

Early Eocene (Wasatchian) rodent assemblages from the Washakie Basin, Wyoming

Rodent assemblages are described from two early Eocene (Wasatchian North American Land Mammal Age; Graybullian subage) localities from the Main Body of the Wasatch Formation in the Washakie Basin, Wyoming. One locality (UCMP V71237) represents a catastrophic death assemblage and the other (UCMP V71238) is a channel lag which immediately overlies it. Quarrying and screen-washing at these localities has resulted in the recovery of 81 specimens from V71237 and 224 specimens from V71238 and comprising a uniquely rich, stratigraphically controlled sample. The rodent fauna from these localities include Paramys copei, P. taurus, Lophiparamys murinus, Microparamys hunterae, Tuscahomys ctenodactylops, and Knightomys cf. K. minor. These specimens provide substantial new morphological data for the previously poorly-known M. hunterae, T. ctenodactylops, and L. murinus. Comparison of relative abundances demonstrates that T. ctenodactylops is the most common in both localities, but that the smaller bodied species M. hunterae and Knightomys cf. K. minor are much rarer in the lag deposit.

Stratigraphic Architecture of a Fluvial-lacustrine Basin-fill Succession at Desolation Canyon, Uinta Basin, Utah: Reference to Walthers’ Law and Implications for the Petroleum Industry

A continuous window into the fluvial-lacustrine basin-fill succession of the Uinta Basin is exposed along a 48-mile (77-kilometer) transect up the modern Green River from Three Fords to Sand Wash in Desolation Canyon, Utah. In ascending order the stratigraphic units are: 1) Flagstaff Limestone, 2) lower Wasatch member of the Wasatch Formation, 3) middle Wasatch member of the Wasatch Formation, 4) upper Wasatch member of the Wasatch Formation, 5) Uteland Butte member of the lower Green River Formation, 6) lower Green River Formation, 7) Renegade Tongue of the lower Green River Formation, 8) middle Green River Formation, and 9) the Mahogany oil shale zone marking the boundary between the middle and upper Green River Formations. This article uses regional field mapping, geologic maps, photographs, and descriptions of the stratigraphic unit including: 1) bounding surfaces, 2) key upward stratigraphic characteristics within the unit, and 3) longitudinal changes along the river transect. This information is used to create a north-south cross section through the basin-fill succession and a detailed geologic map of Desolation Canyon. The cross section documents stratigraphic relationships previously unreported and contrasts with earlier interpretations in two ways: 1) abrupt upward shifts in the stratigraphy documented herein, contrast with the gradual interfingering relationships proposed by Ryder et al., (1976) and Fouch et al., (1994), 2) we document fluvial deposits of the lower and middle Wasatch to be distinct and more widespread than previously recognized. In addition, we document that the Uteland Butte member of the lower Green River Formation was deposited in a lacustrine environment in Desolation Canyon. Two large-scale (member-scale) upward patterns are noted: Waltherian, and non-Waltherian. The upward successions in Waltherian progressions record progradation or retrogradation of a linked fluvial-lacustrine system across the area; whereas the upward successions in non-Waltherian progressions record large-scale changes in the depositional system that are not related to progradation or retrogradation of the ancient lacustrine shoreline. Four Waltherian progressions are noted: 1) the Flagstaff Limestone to lower Wasatch Formation member records the upward transition from lacustrine to fluvial—or shallowing-upward succession; 2) the upper Wasatch to Uteland Butte records the upward transition from fluvial to lacustrine—or a deepening upward succession; 3) the Uteland Butte to Renegade Tongue records the upward transition from lacustrine to fluvial—a shallowing-upward succession; and 4) the Renegade Tongue to Mahogany oil shale interval records the upward transition from fluvial to lacustrine—a deepening upward succession. The two non-Waltherian progressions in the study area are: 1) the lower to middle Wasatch, which records the abrupt shift from low to high net-sand content fluvial system, and 2) the middle to upper Wasatch, which records the abrupt shift from high to intermediate net-sand content fluvial system.

Borings in early Eocene turtle shell from the Wasatch Formation, South Pass, Wyoming

AbstractBorings in fossil turtle shells collected from the lowermost beds of the early Eocene Cathedral Bluffs Tongue of the Wasatch Formation in the northwestern part of the Green River Basin near South Pass, Wyoming, are herein described. Individual turtle shells in the study area are characterized by as few as one or two and as many as >100 borings. The borings include both non-penetrative forms (those which do not pass fully though the shell) as well as penetrative forms (those which pass fully from the exterior to the interior surface of the shell). All non-penetrative forms occur on external surfaces of the carapace and plastron (i.e. those that would have been accessible while the host taxon was alive). Two new ichnogenera and four new ichnospecies are established to describe these borings.Karethraichnus(new ichnogenus) includes three ichnospecies:K.lakkos(new ichnospecies),K.kulindros(new ichnospecies), andK.fiale(new ichnospecies).Karethraichnus lakkosare shallow (non-penetrating), hemispherical pits with rounded, to flattened bases.Karethraichnus kulindrosare deep, non-penetrative traces with a cylindrical profile, an axis approximately perpendicular to the substrate surface and with rounded to flattened, hemispherical termini.Karethraichnus fialeare penetrative traces with a cylindrical to bi-convex or flask-shaped profile, and an axis approximately perpendicular to the substrate surface.Thatchtelithichnus(new ichnogenus)Thatchtelithichnus holmani(new ichnospecies) consist of non-penetrative borings into a bone substrate. They consist of a ring-shaped trace, with a central pedestal or platform. The position of the borings on the shells, and evidence of syn-emplacement healing of the borings in several of the turtles, indicates that these borings were emplacement by ectoparasites/mesoparasites while the animals were living. Similar traces in modern emydid turtles are attributed to ticks, leeches, or spirorchid liver flukes.

A new species ofLimnofregata(Pelecaniformes:Fregatidae) from the Early Eocene Wasatch Formation of Wyoming: implications for palaeoecology and palaeobiology

AbstractA humerus and a coracoid from the Early Eocene Wasatch Formation in the Washakie Basin of south‐western Wyoming are the oldest materials (by ~2 million years) of the pelecaniformLimnofregata(Aves) and represent a new large species,Limnofregata hutchisonisp. nov. This fossil is the oldest known member of the frigatebird lineage. Other than its large size relative toLimnofregata azygosternonandL. hasegawai, the new material is very similar morphologically to other knownLimnofregataspecimens. The size of this new species is comparable to the largest living species (e.g.Fregata minorandFregata magnifiscens) and much larger than the two described species ofLimnofregata. This fossil indicates that the hard minimum date previously advocated for molecular calibration of the split between Fregatidae and Suloidea is an underestimate by approximately two million years. The presence of early pelecaniform bird lineages (represented byLimnofregataandMasillastega) in limnic ecosystems prior to their known occurrences in marine deposits/habitats appears to indicate that some clades of pelecaniform birds may have undergone an evolutionary transition from freshwater to marine habitats in a pattern reminiscent of what has been suggested during the evolution of pinnipeds or that their palaeoecology included broader niches ranging across a variety of aquatic habitats. That transition in habitat occupation and the origin of many of the characteristic biological aspects present in the crown frigatebird clade likely occurred during a significant temporal gap (> 45 million years) in the fossil record of the frigatebird lineage after these earliest occurrences in the Early Eocene and before the oldest records of the extantFregataspecies in the Pleistocene.

Aceroryctes dulcis, a new palaeoryctid (Mammalia, Eutheria) from the early Eocene of the Wasatch Formation of southwestern Wyoming, USA

The Palaeoryctidae are a group of small-bodied, likely insectivorous mammals known principally from the Paleocene and early Eocene (from approximately 65 to 53 Ma) of North America. Here we report on a new palaeoryctid from the early Eocene (early Wasatchian (Wa3) North American Land Mammal Age) Main Body of the Wasatch Formation, Washakie Basin, near Bitter Creek station in southwestern Wyoming, USA. Acerorcytes dulcis gen. et sp. nov. is unique among palaeoryctids in having a double-rooted P2 with a small anterior cusp, P3 with pronounced para- and metastylar cusps and a reduced but conspicuous metacone, P4 with a weakly developed metacone and an anteroposteriorly compressed protocone, and M1-2 with deep ectoflexus and a sharp metastylar blade. A phylogenetic analysis based on 32 dental characters of the nine known North American palaeoryctid species, including Aceroryctes dulcis, recovered eight equally parsimonious cladograms. Similar to prior studies, the analysis suggests that the genus Palaeoryctes is non-monophyletic, with Palaeoryctes cruoris and Aaptoryctes ivyi closely related. Aceroryctes dulcis is grouped with Ottoryctes winkleri and positioned in a more inclusive clade with Eoryctes melanus; the remaining palaeoryctid taxa, including Lainoryctes youzwyshyni, are part of an unresolved polytomy. These new findings indicate that early Eocene palaeoryctids were more diverse than previously thought, with genus richness during the early Eocene at least as great as that during the middle Paleocene.

A hierarchical approach for evaluating fluvial systems: Architectural analysis and sequential evolution of the high net-sand content, middle Wasatch Formation, Uinta Basin, Utah

Well-exposed three-dimensional fluvial outcrops of the high net-sand content middle Wasatch Formation in Three Canyon, Uinta Basin, Utah, were used to create and develop a new methodology for describing the architecture of fluvial systems. The methodology builds on the works of Campbell, Jackson, Allen, and Miall, and addresses sedimentary processes, scale, and temporal context for reservoir and non-reservoir bodies. The methodology developed herein is a three-level hierarchical framework that classifies meso- and macroscale architecture of fluvial systems. The three-level hierarchy contains, from smallest to largest: stories, elements, and archetypes. Eight story types provide the foundational building blocks of this framework and account for sedimentation in both channel-belt and floodplain-belt elements, including (1) downstream accreting; (2) laterally accreting; (3) erosionally-based fine-grained fill; (4) fine-grained fill associated with laterally accreting; (5) levee; (6) splay; (7) crevasse or overbank channels; and (8) floodplain fines. Two types of elements are recognized: (1) channel belt and (2) floodplain belt. An archetype consists of a channel-belt element and its genetically related floodplain-belt elements. Two distinct upward-stacking patterns differentiate braided and meandering archetypes. In deconstructing the evolution of archetypes, three distinct associations between channel-belt elements and their adjacent splays are documented: (1) unassociated splays; (2) associated coeval splays; and (3) associated non-coeval splays.Width and thickness for stories, channel-belt elements, and archetypes are documented providing dimensional constraints for analog high-net-sand-content fluvial systems. Additionally, this methodology provides object-based models with shape-defined reservoir and nonreservoir geobodies that realistically compare to fluvial systems.

Correction to “Early Eocene Lizards of the Wasatch Formation near Bitter Creek, Wyoming: Diversity and Paleoenvironment during an Interval of Global Warming”

Correction to “Early Eocene Lizards of the Wasatch Formation near Bitter Creek, Wyoming: Diversity and Paleoenvironment during an Interval of Global Warming”

Additions to the latest Paleocene Buckman Hollow local fauna, Chappo Member of the Wasatch Formation, Lincoln County, southwestern Wyoming

Additions to the latest Paleocene Buckman Hollow local fauna, Chappo Member of the Wasatch Formation, Lincoln County, southwestern Wyoming

Early Eocene Lizards of the Wasatch Formation near Bitter Creek, Wyoming: Diversity and Paleoenvironment during an Interval of Global Warming

Lizards (nonophidian squamates) from a vertical series of localities in the early Eocene Wasatch Formation (Washakie Basin, Wyoming, USA) deposited during an interval of global warming are described on the basis of isolated cranial and some postcranial bones. At least 24 species are present. New material supports a close relationship of the iguanid Paranolis to Anolis (to the exclusion of Anolbanolis). Records of Tinosaurus and Scincoideus are the earliest in North America; a potential affinity of the latter, a new species, with Lacertidae is explored. A new species of Palaeoxan tusia and two species related to Neotropical Night Lizards, Lepidophyma, are named. A rhineurid amphisbaenian is present. New material of Apodosauriscus minutus further bolsters the case for its relationship to living Anniella. Glyptosaurine anguids are also present, including new species referred to Xestops, Arpadosaurus, and Glyptosaurus, the last with distinctive crushing posterior teeth. A distinctive new anguimorph lineage, Entomophontes, may be related to Xenosaurus. Considerable cranial material is referred to a new species of Provaranosaurus; we argue that this lineage is closely related to extant Shinisaurus. Restes-like remains are smaller and rare. Helodermatidae is represented by a single osteoderm. The varanid Saniwa is present. The four localities examined here record an interval of warming in the Rocky Mountain interior, when temperatures rose toward their Cenozoic acme in the Eocene Climatic Optimum. Faunal composition shows only two major deviations at a higher taxonomic level, suggesting a prevailing stability. Maximal within-locality species diversity (richness), based on cranial material (18 species), is seen at the top of the section. The diversity difference between the upper and lower part of the section is statistically significant. There is an underlying component of noise to the diversity data with regard to rarer taxa. Diversity changes primarily as a result of dispersal on a local level.

New Uintasoricine (?Primates, Plesiadapiformes) From the Earliest Bridgerian, Latest Early Eocene of Wyoming

Uintasoricines are diminutive plesiadapiforms that are found in the latest Paleocene through middle Eocene, predominantly in North America. They are not a diverse group but individual species may be locally abundant and they are a persistent element of the plesiadapiform radiation in North America surviving over a span of approximately 16 million years. Recent field work in southern Wyoming at South Pass has led to the discovery of a new genus and species of uintasoricine. The new form is smaller in tooth dimensions compared to other known uintasoricines, being slightly smaller thanUintasorex montezumicusfrom California. Both the newly described taxon andU. montezumicusare among the smallest plesiadapiforms yet known with body weights estimated to be 20 to 25 g. The sediments of the Cathedral Bluffs Tongue of the Wasatch Formation at South Pass contain a unique upland fauna—the presence of a distinctive uintasoricine in this assemblage adds further evidence to support the notion that this upland environment was a biodiversity hotspot during the latest early Eocene.