North Horn Formation Research Articles

Northern Cedar Mountains Red Beds, Tooele County

Recent mapping for the Tooele 30' x 60' quadrangle geologic map revealed more information about interesting exposures of red beds cropping out in an 11-mile (18-km) swath along the northwestern flank of the Cedar Mountains (Clark and others, 2017, 2019 in review). They are unusual because such rocks are seldom preserved in northwestern Utah, an area known for thick thrust sheets of Paleozoic marine carbonate and sandstone. These rocks were first mapped by Robert Maurer for his Ph.D. dissertation on the geology of the Cedar Mountains (Maurer, 1970). He called them North Horn (?) Formation and noted the presence of fresh-water snails (Gyraulus sp.) that a paleontologist said were probably of late Paleocene or Eocene age. The North Horn Formation is considered Late Cretaceous (Maastrichtian age) to Paleocene or Eocene (~70 to 60 Ma) in age. However, recent detrital zircon analysis from sandstone in the unit suggest a much older age, with the youngest grains (maximum depositional age) of 117 Ma, or Early Cretaceous, Aptian (UGS and O’Sullivan, 2017). Two samples of gray mudstone taken for fossil pollen in the unit did not produce any usable material. Inspection of these rocks by Don DeBlieux (Utah Geological Survey paleontologist) revealed no bone or other biological material at this location.

Remembering the Alamosaurus: Jensen Relocates Gilmore's Alamosaurus Quarry, USNM 15560, North Horn Formation, Emery County, Utah, and Discovers a Second Individual Alamosaurus

Alamosaurus sanjuanensis was originally described from a left scapula (USNM 10846) and right ischium (USNM 10847) discovered in the Late Cretaceous Ojo Alamo Formation of New Mexico in 1921 (USNM quarry 15560). In 1937 a second specimen was found in the North Horn Formation of Utah, consisting of a partial skeleton (USNM 15560), comprised of a mostly complete pelvis and caudal vertebral series, from the Late Cretaceous. A sacral complex with five vertebrae was observed in the field but was not collected. In 1966 James “Jim” Jensen of the Brigham Young University Earth Science Museum relocated the Gilmore quarry and found the sacrum, which, by then, had “rotted down into brown soil” and could not be recovered. Nearby, Jensen discovered the proximal heads of a humerus and femur and an isolated proximal caudal vertebra, none of which belonged to USNM 15560. Mike Morales and a team from the University of California at Berkeley discovered additional caudal vertebrae in the vicinity also, none of which belonged to the specimen collected by Gilmore. The specimens recovered by Jensen and Morales are significant because they indicate the presence of additional Alamosaurus specimens in the North Horn Formation. Additionally, the humerus is the most complete Alamosaurus humeral head yet discovered.

First record of Kimbetohia campi (Mammalia, Multituberculata) from the Paleocene part of the North Horn Formation, Utah

Kimbetohia is a rare genus of multituberculate that is only definitively known from New Mexico (Weil and Krause, 2008). Kimbetohia campi was described by Simpson (1936) based on a skull fragment (U...

Tyrannosaurus rex from the Upper Cretaceous (Maastrichtian) North Horn Formation of Utah: biogeographic and paleoecologic implications

Tyrannosaurus rex from the Upper Cretaceous (Maastrichtian) North Horn Formation of Utah: biogeographic and paleoecologic implications

Mechanisms of PETM global change constrained by a new record from central Utah

Catastrophic carbon release and global warming during the Paleocene-Eocene thermal maximum (PETM) profoundly affected continental climate and ecosystems. Understanding of the details and mechanisms of these effects is limited by the poor geographic coverage of existing continental PETM records. Here, we extend the record of this event in North America through identification of the PETM carbon isotope excursion within a sequence of paleosols in the North Horn Formation of central Utah, some 500 km to the south of previous records from northern Wyoming. Data from the new site suggest that patterns of climatological change were similar across a meridional transect of western North America but that PETM climate was relatively more arid in the southern Rocky Mountains, possibly reflecting diversion of precipitation from middle to high latitudes. Our results are consistent with two proposed mechanisms explaining variation in the amplitude of continental PETM carbon isotope records in terms of changes in floral composition or varying environmental wetness, and they present opportunities for future tests of proposed north-south biotic dispersal during the PETM.

First Record of Stygimys (Mammalia, Multituberculata, Eucosmodontidae) from the Paleocene (Puercan) Part of the North Horn Formation, Utah, and a Review of the Genus

A single tooth referred to Stygimys kuszmauli recovered at the Gas Tank Hill locality from Puercan strata of the North Horn Formation represents the first record of Stygimys from Utah. S. kuszmauli now occurs in both proposed north–south late Puercan biogeographic provinces, which reduces statistical support for provinciality. A new species from Texas, Stygimys vastus, is described. Of the five species previously referred to Stygimys, S. kuszmauli, Stygimys camptorhiza, Stygimys jepseni, and Stygimys teilhardi are valid, but Stygimyscupressus is synonymous with S. kuszmauli. The type of S. jepseni is restricted to a single p4 as the m1 thought to be from the same individual represents another multituberculate genus. Five sites, including Gas Tank Hill that comprise the Gas Tank Hill Local Fauna are widely dispersed in slumped strata which may differ in age, are located in a mostly floodplain depositional setting, and are small surface collected samples. Therefore, biogeographic analyses that compare the Gas Tank Hill Local Fauna to large samples collected from channel fills using screenwash techniques should be employed with caution. Stygimys has a relatively broad geographic and geochronologic distribution, but it is usually rare in Late Cretaceous and Early Paleocene mammalian assemblages. The recent recovery of Stygimys after more than 60 years of collecting in the North Horn Formation suggests that further sampling in other non-marine basins in Western North America will eventually yield additional specimens of the genus.

RANGE EXTENSION OF SOUTHERN CHASMOSAURINE CERATOPSIAN DINOSAURS INTO NORTHWESTERN COLORADO

T he Williams Fork Formation preserves a diverse dinosaur fauna containing at least nine saurischian and five ornithischian species. Among the dinosaur specimens recovered is a partial ceratopsian skull (SDMNH 43470) referable to the ceratopsid subfamily Chasmosaurinae (Diem, 1999). Chasmosaurines, or long-frilled ceratopsians, existed throughout western North America during the Campanian and Maastrichtian (Judithian, Edmontonian, and Lancian). Recent discoveries have renewed debate over the phylogenetic relationships and biogeographic history among the chasmosaurines (Forster et al., 1993; Lehman, 1996; Holmes et al., 2001). There are some latitudinal differences in occurrences of taxa. Northern chasmosaurines include Anchiceratops ornatus (Brown, 1914), Chasmosaurus belli (Lambe, 1902), C. irvinensis (Holmes et al., 2001), and C. russelli (Sternberg, 1940) from the upper Campanian Dinosaur Park Formation of Alberta, Canada (Dodson and Currie, 1990; Godfrey and Holmes, 1995; Holmes et al., 2001; Ryan and Russell, 2001). A. ornatus has also been reported from the upper Campanian to Maastrichtian Horseshoe Canyon Formation of Alberta, Canada (Eberth, 1997), as has Arrhinoceratops brachyops (Parks, 1925; Dodson and Currie, 1990). The common late Maastrichtian species Triceratops horridus (Marsh, 1889) ranges from Colorado in the south to Alberta and Saskatchewan in the north, while the less common Torosaurus latus (Marsh, 1891) has a slightly smaller, but similar range (Dodson and Currie, 1990), both occurring in the Lance and Hell Creek Formations or their equivalents. In the southern area, another Maastrichtian species of Torosaurus (Marsh, 1891), T. utahensis (Gilmore, 1946) from the North Horn Formation of Utah, Kirtland Shale in northwestern New Mexico, and the Javelina Formation of southwestern Texas, is sometimes recognized (Lehman, 1996). Some authors treat Torosaurus utahensis as a synonym of T. latus (Dodson and Currie, 1990). If this synonymy is correct, T. latus maintained a geographic range from Saskatchewan, Canada, in the …

Pedogenic carbonate proxies for amount and seasonality of precipitation in paleosols

The depth to carbonate nodular (Bk) horizon in soils ( D in cm) is correlated with mean annual precipitation ( P in mm), so that Bk horizons are deep in subhumid regions, but shallow in semiarid regions. Previous quantifications of this relationship are unchanged by this new compilation of 807 soils: P = 137.24 + 6.45 D + 0.013 D 2 , where R 2 = 0.52, and standard error (S.E.) = ±147 mm. In most North American postglacial soils, the Bk horizon is thin and well defined, whereas in monsoonal tropical soils of Pakistan and Kenya, the Bk horizon is thick and diffuse. Data from 675 modern soils define the relationship between the thickness of soil with nodules ( T in cm) and mean annual range of precipitation ( M in mm difference between monthly means of wettest and driest months): M = 0.79 T + 13.71, where R 2 = 0.58, and S.E. = ±22 mm). The relationship between carbonate nodule size ( S in cm) and soil age ( A in ka) is quantified by 9 radiocarbon-dated soils from Las Cruces, New Mexico: A = 3.92 S 0.34 , where R 2 = 0.57, and S.E. = 1.8 k.y. These transfer functions are applied to reconstructing paleoclimatic change from Paleocene–Eocene paleosols of the North Horn Formation and Flagstaff Limestone of Axhandle Canyon, Utah. The terminal Paleocene spike of warmth recorded by fossil plants in nearby Wyoming was coincident with a brief peak in both mean annual precipitation and mean annual range of precipitation in Utah.

Footprints of Utah's Last Dinosaurs: Track Beds in the Upper Cretaceous (Maastrichtian) North Horn Formation of the Wasatch Plateau, Central Utah

Abstract Dinosaur track beds occur at several localities in the uppermost Cretaceous (Maastrichtian) North Horn Formation in the Wasatch Plateau, central Utah. The track bed localities, separated by up to 80 km, also contain dinosaur body fossils. At the type locality at North Horn Mountain in Emery County, more than 100 individual exposures and/or stratigraphic levels within a 1.2-km2 study area exhibit tracks in vertical cross-sectional view. These biogenic structures are similar to others that have been interpreted elsewhere as deep dinosaur tracks. At the type section, track beds vertically span at least 183 m from the base of the formation up to a few meters below the highest dinosaur eggshells, which are interpreted to occur immediately below the Cretaceous-Tertiary (K-T) boundary interval. Track occurrence in the North Horn Formation demonstrates that large dinosaurs were present in central Utah until very shortly before the K-T boundary. The track structures feature deformation, overprinting, and ...

Faunal implications of an environmental change before the Cretaceous-Tertiary (K-T) transition in central Utah

The North Horn Formation at North Horn Mountain in central Utah records a shift in the composition of the upper Maastrichtian vertebrate fossil assemblage below the Cretaceous-Tertiary (K-T) boundary. Dinosaurs (Alamosaurus,Tyrannosaurus , Torosaurus, and hadrosaurs), turtles (Basilemys), mammals, and lizards(Polyglyphanodon ) occur in the lowest unit of the formation. The environment changed from semi-arid to wetter conditions, and several of the mostly terrestrial vertebrate taxa no longer appeared in the type area. Several taxa that dominated the vertebrate assemblage low in the formation are replaced in the succeeding unit below the K-T boundary by different dinosaur taxa that are represented by eggshells. This altered vertebrate assemblage was more tolerant of, or was adapted to, wetter conditions, but it, too, disappeared at the type locality by the end of the Cretaceous. This wetland dinosaur assemblage is not identical to that found in semi-arid dinosaur assemblages or to dinosaur assemblages in other K-T boundary sites that represent different paleolatitudes. Most of the faunas in the succeeding unit are represented by aquatic forms (crocodilians, turtles, fish, mollusks, and ostracods) which persisted after the dinosaurs disappeared. There appears to be no current tectonic or biostratigraphic reason to conclude that a significant stratigraphic gap exists immediately below the K-T boundary in the North Horn Formation in central Utah.

Marsupial mammal from the Upper Cretaceous North Horn Formation, Central Utah

Little is known of the non-dinosaurian fauna from the Cretaceous (Maastrichtian) part of the North Horn Formation, despite its biogeographic importance. Herein we describe a new marsupial mammal from the unit, founded on an exceptionally complete specimen of a juvenile individual, and present new information on the incisor region of early marsupials, based on comparison with complete specimens from the early Paleocene of Bolivia. Alphadon eatoni, new species, is the smallest Lancian species of the genus, and departs from a presumed marsupial morphotype in having the second lower incisor enlarged. The species is, however, primitive in lacking a “staggered” pattern to the incisor series and in having a labial mandibular foramen, and in these respects it differs from Paleocene and later marsupials. Poor representation of other taxa precludes meaningful comparison to most other North American Cretaceous marsupials, although Eodelphis, thought to be distantly related, also has an enlarged i2. Although Alphadon is characterized by many primitive features, the relative development of the incisors is not what would be predicted in a morphological antecedent to later Marsupialia.

Palynostratigraphy of Upper Cretaceous-Lower Tertiary strata, Price Canyon, Utah

Palynological analysis of the Price Canyon section in east-central Utah, USA, confirms a late Campanian to late Paleocene age for the interval of Castlegate Sandstone, Price River Formation, and North Horn Formation. This 1100 m thick section represents a series of transgressive-regressive cycles of intertonguing coastal plain, fluvial, coastal margin and nearshore marine sedimentary deposits. Forty-five palynologically productive samples were analyzed. Ranges of the species or generic groups of palynomorphs were compared with time equivalent palynofloras mainly from North America. Two hiatuses were recognized, the most important of which includes the K-T boundary interval. Four biostratigraphic zones, Ka, Kb, Ta and Tb, were defined, and their relative ages correlated with those of other sections in western North America.

Sequential architecture in a fluvial succession; sequence stratigraphy in the Upper Cretaceous Mesaverde Group, Prince Canyon, Utah

ABSTRACT Five unconformity-bounded sequences have been documented within a 1300 m thick succession of predominantly fluvial Upper Cretaceous and Lower Tertiary deposits in the Price Canyon area of the westernmost part of the Book Cliffs, east-central Utah, U.S.A. This area experienced major tectonically induced changes in the paleogeography during deposition. The earliest fluvial deposits in the study area were formed in a relatively simple foreland basin setting in front of the Sevier Orogenic Belt, and contain more marine influence than previously recorded. Following a gradual termination of thrusting, sedimentation became increasingly controlled by uplift of the San Rafael Swell to the southeast. Our studies suggest that the fluvial systems in the upper part of the succession alternated bet een being confined within a valley open towards the north and being more directly eastward flowing. On the basis of the observed sequences, an idealized model of alluvial sequences, whose internal architecture can be related to a fall-rise-fall cycle of the stratigraphic base level, has been established. Upward or downward changes in the position of this base level dictate the creation and destruction of accommodation on the alluvial plain and therefore exert a direct control on the sequential architecture and sandstone body geometry of fluvial successions. In our model, the basal sequence boundary is overlain by an amalgamated fluvial sandstone sheet. The sheet is succeeded by a fining-upward, more mudstone-rich level with more isolated sandstone bodies, and this level may culminate in a marine or lacustrine transgression. The upper part of the sequence may show a coarsening-upward trend heralding the next phase of base-level fall and sequence-boundary generation. Use of the suggested model has the potential to refine existing lithostratigraphic schemes and, given the higher resolution and more detailed correlation, may significantly improve paleogeographic reconstructions and aid in prediction of potentially hydrocarbon-bearing reservoirs. A revised and refined lithostratigraphy has been established on the basis of alluvial sequence analysis. The lower half of the succession forms the youngest part of a major eastward-prograding clastic tongue, the Mesaverde Group, and is Campanian. We divide this part into the Blackhawk, Castlegate, and Price River Formations. The rest of the succession is Maastrichtian to Paleocene and is referred to the North Horn Formation. This formation was deposited in an intermontane setting.

Evolution of latest Cretaceous–Eocene nonmarine deposystems in the Axhandle piggyback basin of central Utah

Research Article| March 01, 1995 Evolution of latest Cretaceous–Eocene nonmarine deposystems in the Axhandle piggyback basin of central Utah P. J. Talling; P. J. Talling 1University of Southern California, Los Angeles, California 90089-0740 Search for other works by this author on: GSW Google Scholar T. F. Lawton; T. F. Lawton 2New Mexico State University, Las Cruces, New Mexico 88003 Search for other works by this author on: GSW Google Scholar D. W. Burbank; D. W. Burbank 3University of Southern California, Los Angeles, California 90089-0740 Search for other works by this author on: GSW Google Scholar R. S. Hobbs R. S. Hobbs 4Exxon Petroleum Company, Houston, Texas 77210-4279 Search for other works by this author on: GSW Google Scholar Author and Article Information P. J. Talling 1University of Southern California, Los Angeles, California 90089-0740 T. F. Lawton 2New Mexico State University, Las Cruces, New Mexico 88003 D. W. Burbank 3University of Southern California, Los Angeles, California 90089-0740 R. S. Hobbs 4Exxon Petroleum Company, Houston, Texas 77210-4279 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1995) 107 (3): 297–315. https://doi.org/10.1130/0016-7606(1995)107<0297:EOLCEN>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation P. J. Talling, T. F. Lawton, D. W. Burbank, R. S. Hobbs; Evolution of latest Cretaceous–Eocene nonmarine deposystems in the Axhandle piggyback basin of central Utah. GSA Bulletin 1995;; 107 (3): 297–315. doi: https://doi.org/10.1130/0016-7606(1995)107<0297:EOLCEN>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Axhandle basin of central Utah is a piggyback basin produced by disruption of the proximal Sevier foreland basin by the Gunnison thrust system during Late Cretaceous time. Alluvial and lacustrine fill of the basin, represented by the North Horn Formation, ranges in age from 75 to 51 Ma. The eastern basin margin is defined by a system of west-verging thrust faults that were active episodically during North Horn deposition. Along this margin, well-exposed strata, 10 km wide and 1.2 km thick, displays striking changes in adjacent depositional facies, sediment provenance, and sediment dispersal directions. Two-dimensional mapping and precise paleomagnetic dating of these strata provide evidence for deciphering the evolution of and controls upon deposition in the basin. Sediment accumulation rates in the eastern part of the basin alternated between times of rapid aggradation and times of incision or nondeposition with a cyclicity of 5–8 m.y. This alternation was caused by the interaction of flexural lithospheric subsidence and uplift of the basin by the underlying Gunnison thrust system. Competition between the relative rates of these processes also determined the nature of depositional facies in the basin, such that active uplift of the basin margin did not correspond to a unique facies type. Uplift of the basin margin on thrust structures of the Gunnison system is associated with two different types of sedimentologic response: (1) channel-belt incision during and after the formation of well-drained, mature paleosols on interfluves; and (2) deposition of lacustrine, palustrine, and poorly drained flood-plain sediment. The former response probably resulted from rapid uplift of the basin during times of low rates of regional subsidence, whereas the latter resulted from basin uplift during times of greater regional subsidence. Lack of correspondence between basin-margin uplift and load-induced subsidence indicates that motion on the Gunnison thrust and loading by out-of-sequence thrusting within the Sevier orogenic belt were out of phase.Channel deposits that mark the position of major fluvial systems are stacked vertically within the basin. North of this stacked channel system, fluvial channels are rare, and deposits of the basin are dominated by overbank and lacustrine facies associations. Fluvial incision of the eastern basin margin apparently fixed the position at which rivers flowed across the basin-bounding uplift and into the adjacent foreland. The observed concentration of channel deposits within the basin persisted for >24 m.y. This long-term feature may have been caused by pinning of drainage paths either where rivers crossed the western basin margin or at a reentrant in the interior of the thrust belt. This study demonstrates that structural controls may fix the location where major rivers drain from a thrust belt through significant periods of thrust belt evolution. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Thermal Maturity, Porosity, and Facies Relationships Applied to Gas Generation and Production in Tertiary and Cretaceous Low-Permeability Sandstones, Uinta Basin, Utah

Uinta basin rocks include a thick sequence of low-permeability (tight) sandstones that contain a large volume of gas. Most known gas accumulations occur in the eastern part of the basin in the Upper Cretaceous Mesaverde Group; uppermost Cretaceous to early Eocene North Horn Formation; and the Paleocene and Eocene Wasatch, Colton, and Green River formations. Most successful tight-gas completions are in Tertiary strata, but rocks in the underlying, largely undrilled Mesaverde Group in the north-central part of the basin are potential targets as well. To characterize the gas-bearing sandstones, the authors have constructed a series of interrelated maps and cross sections showing thermal maturity, porosity, fluid pressures, and lithofacies relations for the Uinta basin. Vitrinite reflectance (R{sub m}) for each of these low-permeability sequence increases to the north and levels of thermal maturation are sufficient for gas generation over large areas of the basin. Projection of maturity values and fluid-pressure data into undrilled parts of the basin reveals the probability of a regional, overpressured, basin-entered gas accumulation, where gas is likely to be generating at present. Plots of porosity vs. R{sub m} allow prediction of porosity for Mesaverde sandstones in unexplored areas of the basin. The authors data indicates amore » large area of organic-rich, overpressured strata probably underlies the northern part of the Uinta basin. Wells drilled in the Mesaverde and lower part of the Tertiary, in the areas where R{sub m} at the base of the Mesaverde is greater than 1.1%, should have the best potential for gas production. Overpressured gas reservoirs are likely to have no free water and be enveloped by successive zones of mixed water and gas and of water only.« less

Reactivation of a Cretaceous Thrust Surface by Basin-and-Range Extension, Southwestern Gunnison Plateau, Central Utah

Recent work in central Utah has outlined the broader features of the area's thrust geometry. Although individual interpretations differ, most models indicate the region is similar to better understood segments of the Cordilleran thrust belt. Poor and limited seismic data and the paucity of drill-hole information has hindered the investigation of the south- west quadrant of the Gunnison Plateau. Detailed surface mapping of a centrally located quadrangle has provided strati- graphic evidence for a previously unrecognized Cretaceous-Paleocene thrust fault. The present expression of the thrust surface requires reactivation with a reverse sense of motion during Tertiary extension. Drastic facies changes in the Late Cretaceous-Early Paleocene North Horn Formation occur over a short distance - essentially across a fault. The gray, eastern lithofacies is dominated by massive conglomerate, sandstone, and oncolitic limestone. Maximum thickness is 253 m (830 ft). Clast composition indicates a local source/positive area of Cretaceous lndianola Group. The thinner 38 m (126 ft), red, western lithofacies consists of pebbly sandstone, sandstone, and mudstone. Reddish brown mudstones and intrac lasts suggest red beds, possibly the Cretaceous Cedar Mountain Formation and/or the Jurassic Twist Gulch Formation and Arapien Shale, as a primary source. After careful consideration of several hypotheses, the only valid conclusion seems to be the presence of thrusted Indianola, creating a topo- graphic barrier between the two separate and unique basins. Two major structural features can be traced to the north, an area of better seismic and drill-hole data. The southern terminus of the Wasatch fault zone, has been interpreted by numerous investigators as eithera reactivated Cretaceous thrust (with a reverse sense of motion) or a high-angle planar Tertiary normal fault. The Escarpment fault, the eastern boundary of a Basin and Range graben, has also been presented in both configurations (listric or high-angle planar). No observations were made to support a listric geometry for the Fayette fault. The Escarpment fault, however, appears to have been active during North Horn time, thrusting lndianola conglomerate into a topographic/structural high. The upper plate underwent a reversed sense of motion in the Tertiary to create the present Chriss/Mellor graben.

Fluvial Systems of Upper Cretaceous Mesaverde Group and Paleocene North Horn Formation, Central Utah: Record of Transition from Thin-Skinned Deformation in Foreland Region: ABSTRACT

Nonmarine strata of the upper part of the Mesaverde Group and North Horn Formation exposed between the Wasatch Plateau and the Green River in central Utah record a late Campanian tectonic transition from thrust-belt deformation to basement-cored uplift. Mesaverde Group sediments were deposited by synorogenic braided and meandering rivers. During most of Campanian time, sediment transport was east and northeast away from the thrust belt across a fluvial coastal plain. Subsequent development of the San Rafael swell, a basement uplift, between western and eastern localities caused erosional thinning of the section. Sandstones within the upper part of the Mesaverde Group form two distinct compositional suites, a lower quartzose petrofacies and an upper lithic petrofacies. Lithic grain populations of the upper petrofacies are dominated by sedimentary rock fragments on the west and volcanic rock fragments on the east. Sedimentary lithic grains were derived from the thrust belt, whereas volcanic lithic grains were derived from a volcanic terrane to the southwest. Tributary streams carrying quartzose detritus from the thrust belt entered a northeast-flowing trunk system and caused a basinward dilution of volcanic detritus. Disappearance of volcanic grains and local changes in paleocurrent directions in latest Campanian time reflect initial growth of the San Rafael swell and development of an intermon ane trunk-tributary fluvial system. Depositional onlap across the Mesaverde Group by the post-tectonic North Horn Formation indicates a minimum late Paleocene age for uplift of the San Rafael swell. End_of_Article - Last_Page 854------------

Tectonic Significance of Depositional Patterns in Nonmarine North Horn Formation, Central Utah: ABSTRACT

The Maestrichtian through Paleocene(?) North Horn Formation is a nonmarine sequence of interbedded and intertonguing synorogenic conglomerate, sandstone, algal limestone, and claystone. Deposition occurred within an interior drainage system restricted by the Sevier highlands to the west and the San Rafael swell to the east. It extended south to at least Salina Canyon in central Utah and north to the southern margin of the Uinta basin. The base of the formation is diachronous, unconformably overlying Campanian rocks. Earliest deposition began along the eastern Wasatch Plateau, then shifted westward until late Paleocene beds onlapped deformed Mesozoic rocks associated with Sevier thrusting. Paleocurrent measurements indicate a general west to east transport direction. Four major depositional facies are recognized: alluvial fan, proximal braid plain, distal braid plain, and lacustrine. Work has been concentrated on the alluvial fan and braid plain facies west of the Wasatch Plateau. Massive clast-supported cobble to boulder conglomerate characterizes alluvial-fan facies. Deposition on fan surfaces was primarily by sheet-flood or braided stream processes. Conglomerate shows skewed clast populations. Northeast of Mt. Nebo, 60-70% of clasts are carbonate rocks. Clasts range up to 1 m (3 ft) in diameter. Thick Paleozoic carbonate beds associated with the Nebo fold nappe furnished most of them. Upward-fining sequences of massive to crudely stratified clast-supported conglomerate, conglomeratic sandstone, and sandstone characterize proximal and distal braid plain facies. During transport down the braid plain, mixing of Eocambrian and Cambrian quartzite, Paleozoic carbonate, and Mesozoic sandstone occurred. Conglomerate was deposited in bars within braided stream channels. It displays imbrication of flattened clasts with long axes transverse (^cong40-70°) and intermediate axes subparallel to flow direction. Sandstone displays poorly developed cross-stratification, planar stratification, and massive bedding. Rapidly fluctuating episodes of sedimentation with high sediment loads on the proximal braid plain, and extensive bioturbation by infauna on the distal braid plain, ar indicated. End_of_Article - Last_Page 953------------

Late Cretaceous Fluvial Systems and Inferred Tectonic History, Central Utah: ABSTRACT

Upper Campanian nonmarine sedimentary rocks exposed between the Wasatch Plateau and the Green River in central Utah record a tectonic End_Page 1346------------------------------ transition from thin-skinned deformation in the thrust belt to basement-cored uplift in the foreland region. Thick sections of the Mesaverde Group in the Wasatch Plateau on the west and the Book Cliffs on the east are separated by the San Rafael swell, a basement uplift across which the group is erosionally thinned. Strata in the west (Castlegate Sandstone and Price River Formation) were deposited by east to northeast-flowing braided rivers. Time-equivalent eastern sections comprise a lower sequence of mixed braided fluvial deposits (Castlegate Sandstone and Bluecastle Tongue of Castlegate, coastal swamp and meander-belt deposits (Neslen Formation), and nearshore marine deposits (Buck Tongue of Mancos Shale and Sego Sandstone), and an upper sequence that coarsens upward from meander-b lt deposits (Farrer Formation) into pebbly braided river deposits (Tuscher Formation). Paleocurrent data indicate that rivers of the lower sequence flowed east, while those of the upper sequence flowed northeast. Figure Sandstones within the section consist of two distinct compositional suites, a lower quartzose petrofacies and an upper lithic petrofacies. The compositional boundary occurs at the top of the Bluecastle Tongue and can be correlated across the San Rafael swell. The quartzose suite contains mostly compositional quartzarenites and sublitharenites; the lithic suite is composed of litharenites and feldspathic litharenites. Lithic grain populations of the upper petrofacies are dominated by sedimentary fragments in sections of the Wasatch Plateau and volcanic fragments in sections near the Green River. The sedimentary lithic grains were transported generally eastward from miogeoclinal strata uplifted within the thrust belt. The volcanic lithic grains of the Farrer and Tuscher Formations were erived from more distal arc sources to the southwest, and transported through the thrust belt somewhere west of the Kaiparowits region, where time-equivalent sedimentary rocks are also rich in volcanic lithic fragments. Disappearance of volcanic lithics and appearance of pebbles at the top of the Tuscher Formation is interpreted to reflect a latest Campanian reorganization of drainage patterns that marked initial growth of the San Rafael swell and similar basement uplifts to the south of the swell. Contemporaneous fluvial systems that deposited the uppermost part of the Price River Formation in the Wasatch Plateau were apparently unaffected by the uplift and continued to flow northeast. Depositional patterns thus indicate that initial growth of the San Rafael swell was probably concurren with late deformation in the thrust belt. Depositional onlap across the Mesaverde Group by a largely post-tectonic assemblage of fluvial and lacustrine strata (North Horn Formation) indicates a minimum late Paleocene age for growth of the San Rafael swell and deformation within the thrust belt. End_of_Article - Last_Page 1347------------

A new genus of picrodontid primate from the Paleocene of Utah.

A new picrodontid primate, Draconodus apertus, is described from the North Horn Formation, Dragon Canyon, central Utah, USA. The fauna from Dragon Canyon is considered to be early middle Paleocene (early Torrejonian) in age by faunal and paleomagnetic correlation with the sequence in the San Juan Basin, New Mexico. Draconodus is the earliest known member of the family Picrodontidae, and possesses a flattened, squared-off first upper molar with separated postpara- and premetacristae (thus forming incomplete centrocrista) and other primitive characters. The morphology of the teeth suggests that the last three upper teeth of the family Picrodontidae are homologous with M1M2M3 of other primates as traditionally designated, rather than 'P5'M1M2. If Draconodus is close to the stem of the picrodontids, then Picrodus and Zanycteris probably represent separate lineages within the family.