North-central Wyoming Research Articles

New interpretations of the Piney Creek thrust and associated Granite Ridge tear fault, northeastern Bighorn Mountains, Wyoming

The northwest-striking, northeast-directed Piney Creek thrust on the northeastern flank of the Bighorn Mountains in north-central Wyoming is traditionally interpreted as abruptly terminated on the northwest by the transverse Granite Ridge fault zone (new name). The structure of the mountain front north of this fault generally has been described as an unfaulted monocline. However, seismic-reflection, gravity, and borehole data, and the requirement of reasonable shortening balance along the mountain front indicate subsurface continuity of the (buried) Piney Creek thrust northward from the Granite Ridge fault zone—perhaps to the Tongue River lineament near the Montana border. Based on these subsurface data, the Granite Ridge fault is described here as a true tear fault confined to the hanging wall of an uninterrupted, ∼30°-dipping Piney Creek thrust, segmenting hanging-wall thrust displacement between the Piney Creek block on the south and Walker Mountain block on the north. Slip on the Granite Ridge tear fault is expressed at the surface along the eastern margin of the Bighorn Mountains, west of Story, Wyoming, as a resequent fault-line scarp with ∼2000 ft (600 m) of relief, and with ∼3.3 mi (∼5.3 km) of left separation of steeply dipping, Paleozoic rocks. Based on measurement between piercing points produced by the lines of intersection of the steeply, east-dipping Cambrian-Precambrian unconformity with the Piney Creek thrust surface along either side of the Granite Ridge tear fault, a (reverse) left-oblique slip of ∼15,000 ft (∼4500 m) is measured on this tear fault zone. Thus, 30,000 ft (9100 m) of net slip on the Piney Creek thrust in the Piney Creek block decreases to 15,000 ft (4500 m) of net slip in the Walker Mountain block, and slip on the thrust further declines northward. The described Granite Ridge tear fault–Piney Creek thrust geometry may provide a useful model in the investigation of similar fault-offset mountain fronts within the Laramide foreland province of the Middle Rocky Mountains.

Sego Lilies and Prehistoric Foragers: Return Rates, Pit Ovens, and Carbohydrates

Three experiments or simulations were undertaken to obtain a clearer understanding of the role of pit ovens and roots from dry, sagebrush-covered habitats in prehistoric forager subsistence. The archaeological record of north-central Wyoming containing cylindrical pits near dense stands of sego lily served as a model for these studies. They revealed that: (1) the post-encounter return rates for collecting and processing sego lily is relatively low at 207kcal/h; (2) the design of pit ovens of this sort was for long-term moderate heat; and (3) long-term moderate heat transformed the large complex polysaccharides (probably starch) of sego lily into more easily digestible disaccharides and monosaccharides. Given the results of the experiments and archaeological and ethnographic evidence, small groups of foragers probably baked sego lily bulbs or a similar resource near the collection patches for immediate consumption. The use of this predictable, stationary resource would have served to buffer risk and would have provided required carbohydrates in the spring at the end of the nutritionally stressful time of the year.

Waterfowl management on grass-sage stock ponds

We studied waterfowl use of grass-sage stock ponds in north-central Wyoming during the 1988 and 1989 breeding seasons. Dabbling ducks, particularly mallards, were the most common breeders. Indicated breeding pair density averaged 2.7 pairs/ha of wetland surface, while brood density averaged 1.0 brood/ha of wetland surface. Waterfowl use and productivity were greatest on large (> 3 ha), clear, deep ponds with grass shorelines and abundant submergent macrophytes. Pair use was positively correlated with water clarity, pond area, and macroinvertebrate diversity. Brood use was related to macroinvertebrate diversity, pond depth, and Shoreline Development Index. We recommend management priority be given to ponds that are deeper than 1 m to provide more water that is clear so macrophytes can be established. Macroivertebrates should be artificially introduced into ponds. Fencing should be used to improve ponds for waterfowl use and brood rearing.

Watershed analysis of forest fragmentation by clearcuts and roads in a Wyoming forest

Remotely sensed data and a Geographic Information System were used to compare the effects of clearcutting and road-building on the landscape pattern of the Bighorn National Forest, in north-central Wyoming. Landscape patterns were quantified for each of 12 watersheds on a series of four maps that differed only in the degree of clearcutting and road density. We analyzed several landscape pattern metrics for the landscape as a whole and for the lodgepole pine and spruce/fir cover classes across these maps, and determined the relative effects of clearcutting and road building on the pattern of each watershed. At both the landscape- and cover class-scales, clearcutting and road building resulted in increased fragmentation as represented by a distinct suite of landscape structural changes. Patch core area and mean patch size decreased, and edge density and patch density increased as a result of clearcuts and roads. Clearcuts and roads simplified patch shapes at the landscape scale, but increased the complexity of lodgepole pine patches. Roads appeared to be a more significant agent of change than clearcuts, and roads which were more evenly distributed across a watershed had a greater effect on landscape pattern than did those which were densely clustered. Examining individual watersheds allows for the comparison of fragmentation among watersheds, as well as across the landscape as a whole. Similar studies of landscape structure in other National Forests and on other public lands may help to identify and prevent further fragmentation of these areas.

Abstract: Facies Architecture of The Tensleep Sandstone Bighorn Basin, North-Central Wyoming

Abstract: Facies Architecture of The Tensleep Sandstone Bighorn Basin, North-Central Wyoming

Provenance, Source Terrain Evolution, and Depositional Constraints on Foreland Basin Sequences: Upper Cretaceous Frontier Formation, North-Central Wyoming: ABSTRACT

Provenance, Source Terrain Evolution, and Depositional Constraints on Foreland Basin Sequences: Upper Cretaceous Frontier Formation, North-Central Wyoming: ABSTRACT

A Comparison of Characteristics, Regional Expenditures, and Economic Impact of Visitors to Historical Sites with Other Recreational Visitors

This article compares the trip and demographic characteristics of visitors stopping at historical sites with those of other summer visitors to a four-county study area in northcentral Wyoming. The regional economic impact of the two types of visitors is also estimated on a per-party basis.

Carved Steatite and Sandstone Tubes: Pipes for Smoking or Shaman’S Paraphernalia

Six broken and refitted carved stone pipes or tubes were recovered at the Coal Draw site (48H0469) in the southern Bighorn Basin in north-central Wyoming. In addition there were an unbroken tube and pieces offive others. Several different types of carvable stone are represented, many of which are not found locally. These items may or may not be associated with a large Dinwoody style petroglyph panel nearby. They may also have been burial offerings, since a human skull fragment and a probable human molar were found in the immediate area. Ritual breakage of most of the items is suggested. It is also suggested that this occurred while the items were in containers such as pipe bags, and that they were not removed afterward.

Dynamics of Vegetation along and Adjacent to an Ephemeral Channel

Ephemeral channels may be greater contributors to nonpoint sediment loads than perennial channels because of their abundance and lower vegetative cover. This study examines above- and belowground standing crop responses of selected vegetation classes and density of shrubs to grazing use and yearly weather variation along an ephemeral stream in northcentral Wyoming. Aboveground biomass standing crop was determined yearly in channel, floodplain, and upland habitats in ungrazed and grazed pastures during the 4-year study. Belowground biomass and shrub densities were determined yearly in the channel habitat only. Perennial grass standing crop in channels did not respond to grazing but decreased up to 73% with decreases in frequency and amount of precipitation. In floodplains, perennial grasses were not responsive to grazing; annual grasses were twice as abundant in grazed pastures. Vegetation standing crop in uplands was not influenced by grazing. Over the study period in all pastures, standing crop of blue grama (Bouteloua gracilis (H.B.K.) Lag. ex Griffiths) declined 4 fold while cool-season grasses increased 5 fold. Shrub density did not increase as much in grazed as in ungrazed pastures. Root biomass of the channel decreased 23% in years with less precipitation but was greater by 24% on concave than convex bank types. Location on channels influenced root biomass but grazing did not. Lack of general negative grazing influences on vegetation suggest short periods (10 days) of grazing as used in this study represent a sustainable management alternative for grazing in the cold desert.

Habitat Selection by Cattle along an Ephemeral Channel

Because of widespread concern about cattle grazing effects on riparian zones of public lands, seasonal habitat selection by cattle was studied along a cold desert area ephemeral waterway of northcentral Wyoming. Little is known of grazing effects on ephemeral streams compared to perennial streams. Cattle activity was monitored in small pastures and a surrounding large allotment in spring, summer, and fall. Observations included activity and habitat where it occurred. Concomitantly, utilization levels, protein content, and dry matter content of forages were determined in the small pastures. A higher percent of cattle selected channel and floodplain habitats than percent area of habitats while a lower percent of cattle selected upland habitat than percent of this habitat in the area. Utilization levels of forages except greasewood (Sarcobatus vermiculatus (Hook.) Torrey) in the floodplain were not greatly different among habitats. Protein and dry matter content of forages did not vary greatly among habitats, except greasewood had higher protein and lower dry matter than other species and received much higher use. Forage quality declined in summer and fall. Animal preference for channel habitat was attributed to more available forage in the channels. In contrast, selection of floodplains was due to succulence and high protein content of greasewood. Comparison of cattle selectivity between small pastures and the large allotment indicates that greater avoidance of upland areas by cattle is likely due to greater distances to drinking water in the large allotment.

Effect of ectoparasitism by larvae of the blow fly Protocalliphora parorum (Diptera: Calliphoridae) on nestling House Wrens, Troglodytes aedon

We investigated the effect of ectoparasitism by hematophagous larvae of the blow fly Protocalliphora parorum on nestling House Wrens (Troglodytes aedon) over 2 years in north-central Wyoming, U.S.A. Approximately 85% of wren nests contained P. parorum larvae. Mean parasite load was approximately 10 larvae per nestling. Nestling tarsus length, primary feather length, and hematocrit measured just before fledging did not differ significantly with parasite load. However, parasitized birds weighed approximately 8% more than unparasitized birds just prior to fledging. Parasites possibly delay the recession in weight that normally occurs as tissues mature late in the nestling stage. Delayed development may result in increased nestling or fledgling mortality.

Enigmatic Uppermost Permian-Lowermost Triassic Stratigraphic Relations in the Northern Bighorn Basin of Wyoming and Montana

Abstract Nineteen measured sections in the northern Bighorn Basin of Wyoming and Montana provide the basis for an analysis of Permian-Triassic stratigraphic relations. The Permian-Triassic unconformity is well-defined in north-central Wyoming where gray, yellowish-weathering, calcareous siltstones of the Lower Triassic Dinwoody Formation disconformably overlie carbonates of the Upper Permian Ervay Member of the Park City Formation with little physical evidence of a significant hiatus. The Dinwoody is gradationally overlain by red beds of the Lower Triassic Red Peak Formation of the Chugwater Group. The Dinwoody depositionally thins to zero near the Wyoming-Montana state line. Northward, the erathem boundary is enigmatic because fossils are absent, Permian rocks change facies to resemble the Dinwoody, and there is no record of a Permian-Triassic unconformity. Discontinuous exposures and the restrictive access policies of the Crow Indian Reservation also contribute to the problem. Some previous workers assigned these rocks to the Permian, while others considered them Triassic in age. Up to 12 m (37 feet) of Dinwoody-like Permian rocks unconformably overlie the Pennsylvanian Tensleep Sandstone and grade into the Lower Triassic Red Peak Formation in the westernmost surface exposures along the eastern flank of the Bighorn Basin in Montana. South and east of this area, but north of the Dinwoody termination, Ervay carbonate is overlain by up to 24 m (74 feet) of red siltstone capped by.25 (0.8 feet) to 0.5 m (1.6 feet) of laminated dolomitic limestone. This interval is assigned to the basal Red Peak. Thin Lower Triassic dolomitic mudstones within the Dinwoody and basal Red Peak are commonly laminated, with associated peloidal micrite and coarse quartz silt. These carbonates are also poorly fenestral, and may contain small quantities (1% or less) of small peloidal rip-ups and very fine-grained quartz sand. Carbonates within the Dinwoody-like Permian are similar, but contain variable quantities of sand-size quartz and little to no coarse quartz silt.

Genetic Sequences and Unconformities in Shallow Marine to Fluvial Depositional Systems, Mesaverde Group, North-Central Wyoming

Continuous exposures of the Mesaverde Group (Campanian) in the Bighorn basin area, Wyoming, were utilized to establish regional facies architecture and to test sequence stratigraphic concepts along and perpendicular to the general trend of the shoreline of the Western Interior Cretaceous Seaway. Sections along the west flank of the basin begin with stacked seaward stepping, wave dominated beach sandstones that are fed by widely spaced river systems. These sandstones grade eastward into storm influenced intercalated shale/sandstone beds of the lower shoreface-shelf transitional zone. Bioturbated lower and upper shoreface deposits are often truncated by a laterally continuous erosion surface and overlain by coastal swamp and channel deposits, suggesting a regional regressive unconformity. The overlying fluvial units exhibit a distinct transition in architecture from single and multistoried, lens-shaped, avulsion-controlled, low sinuosity channel bodies to single-storied sheets of high sinuosity channels that consist exclusively of gently dipping, heterolithic lateral accretion units. The uppermost depositional sequence of the Mesaverde is the Teapot Sandstone, a conspicuous multistoried sheet sandstone that consists of laterally amalgamated, vertically stacked low to high sinuosity channels. Floodplain sediments are only represented by shale rip-up clasts in channel lags. Laterally persistent ferricrete horizons, containing plant impressions, are time significant surfaces withinmore » the Teapot and indicate a rhythmic pattern of sedimentation, nondeposition, and pedogenesis. The base of the Teapot unconformably overlies weathered lower shoreface sandstone along the east flank of the Bighorn basin and thus represents a regional sequence boundary.« less

Geochemistry of the Cretaceous Shales and Its Implication on Regional Tectonics and Correlation: Wyoming and Montana

The Cretaceous strata of north-central Wyoming and south-central Montana consist of shale, mudstone, and sandstone with minor conglomerate, coal, and bentonite. The primary objective in this paper is to utilize the mineralogical and geochemical data of the critical and dominant lithofacies group comprised of shale and mudstone to reevaluate regional tectonics, provenance aspects, and correlation of the Cretaceous foreland basin sediments. Relative abundances of nickel, zinc, lanthanum, and cerium in the marine samples can be attributed largely to the organic-rich nature and presence of mineral phase apatite in the marine group. The abundance of these trace elements is presumably related to the proximity of local bedrock source region and distinctive clay mineral suite in the marine sediments. Low concentrations of zirconium, titanium, and chromium in nonmarine Cloverly mudrock indicate an alkaline to peralkaline original sediment (ash) composition as opposed to trachytic to dacitic component for the marine group. Furthermore, the marine sequences in the Cretaceous foreland basin are related to thrust load-induced flexure. Overall geochemical behavior of the analyzed samples seems to be related more to confidently to tectonism rather than different provenance. This geochemical classification can be utilized for stratigraphic correlation of the several lenticular sandstone members encased withinmore » the various Cretaceous units and offers an excellent opportunity for future oil and gas exploration in this region.« less

Influence of climate and eolian dust on the major-element chemistry and clay mineralogy of soils in the northern Bighorn basin, U.S.A.

Soil chronosequences in the northern Bighorn basin permit the study of chronologic changes in the major-element chemistry and clay mineralogy of soils formed in different climates. Two chronosequences along Rock Creek in south-central Montana formed on granitic alluvium in humid and semiarid climates over the past two million years. A chronosequence at the Kane fans in north-central Wyoming formed on calcareous alluvium in an arid climate over the past 600,000 years. Detailed analyses of elemental chemistry indicate that the soils in all three areas gradually incorporated eolian dust that contained less zirconium, considered to be chemically immobile during weathering, than did the alluvium. B and C horizons of soils in the wettest of the chronosequences developed mainly at logarithmic rates, suggesting that leaching, initially rapid but decelerating, dominated the dust additions. In contrast, soils in the most arid of the chronosequences developed at linear rates that reflect progressive dust additions that were little affected by leaching. Both weathering and erosion may cause changes with time to appear logarithmic in A horizons of soils under the moist and semiarid climatic regimes. Clay minerals form with time in the basal B and C horizons and reflect climatic differences in the three areas. Vermiculite, mixed-layer illite-smectite, and smectite form in the soils of the moist-climate chronosequence; smectite forms in the semiarid-climate chronosequence; and smectite and palygorskite form in the arid-climate chronosequence.

Eolian dune types preserved in the Tensleep Sandstone (Pennsylvanian-Permian), north-central Wyoming

The Tensleep Sandstone is one component of an erg system that prograded southward out of north-central Wyoming from Middle Pennsylvanian to Early Permian time. Each erg advance was temporarily interrupted by regional marine transgression. Interpretation of dune types deposited in these ergs is developed from an analysis of the relative proportions of eolian stratification types comprising foreset strata, geometry and relationships of bounding surfaces, and paleodispersal patterns. Two basic morphologic dune types are inferred: simple dunes and compound crescentic dunes. The simple dunes are dominant and are subdivided into 1–2 km wavelength and 1.0 km saddle-spacing slightly crescentic, and 0.1–0.2 km wavelength straight-crested subtypes based on their first-order bounding surface geometries. Foresets are composed of grainfall and wind-ripple strata; avalanche strata are rare. The compound crescentic dunes had wavelengths of 0.5–1 km and saddle spacings of 0.8 km. Foresets are dominated by avalanche and wind-ripple strata. A morphodynamic classification of the dune types is inferred from considerations deduced from paleodispersal patterns and comparison with paleocirculation models. The simple dunes were demonstrably oblique to some elements of the wind field and less oblique to others. The compound crescentic dunes had a predominantly transverse configuration.

A Late Paleoindian Animal Trapping Net from Northern Wyoming

A net made of juniper (Juniperus sp.) bark cordage and designed for capturing animals the size of deer or mountain sheep has been radiocarbon dated to late Paleoindian times. It was recovered in the Absaroka Mountains of north-central Wyoming and provides insight into prehistoric animal procurement strategies that did not require the use of stone artifacts.

Mesotidal Barrier Complex, Sundance Formation, North-Central Wyoming: ABSTRACT

Mesotidal Barrier Complex, Sundance Formation, North-Central Wyoming: ABSTRACT

Geochemical and Mineralogical Analysis of Tatman Formation, Big Horn Basin, Wyoming: ABSTRACT

The Tatman Formation of north-central Wyoming is a lower to middle Eocene fluvial and lacustrine deposit. It occurs as isolated erosional remnants in the Big Horn basin and consists of sandstones, mudstones, reworked volcanic ash, coal, and kerogen-rich shale. The remnants are part of a once much larger Tatman deposit. Extensive carbonaceous shales and claystones in the lower Tatman represent a decrease in gradient relative to the underlying fluvial sandstone and mudstone deposits of the Willwood Formation. Tatman sandstones are dominantly very fine to fine-grained quartz-arenites with lithic wackes occurring in places. Beach-derived sandstones are common in the upper Tatman at Squaw Buttes, whereas sandstones at Tatman Mountain are fluvial. Commonly, biotite books occur within the sandstone and are undergoing alteration. Other heavy minerals are of extremely low concentration. Calcite is the dominant cementing agent, whereas, iron oxide plays a lesser role. X-ray diffraction studies of the fine-grained sediments revealed that greenish, smectite-rich claystones were present in the lower Tatman represented reworked volcanic ash. An organic geochemical analysis of six coal horizons involved removing extractable organics and identifying compounds using gas chromatography-mass spectroscopy. This analysis isolated and identified biomarkers, principally steranes, from the extractable organics. The relative abundance of C-27,more » C-28, and C-29 steranes was then established, and the steranes were correlated to their sterol precursors and plotted onto a ternary diagram for use in paleoenvironment determination.« less

The rock magnetism of the Mississippian Madison Limestone north-central Wyoming

Summary. A history of remanence acquisition in the Madison Limestone in north-central Wyoming suggests that many processes affected the primary magnetization, including (1) dolomitization, (2) solution of evaporites during uplift in the Late Mississippian and (3) partial remagnetization in the Late Cretaceous or Cenozoic. The stability and intensity of the magnetization was greatest in the dolomitic limestones, while the dolomites and the less intense fossiliferous limestones contained magnetization of intermediate directional stability. The coarse- and fine-grained limestones gave erratic directions. The preservation of the Mississippian magnetization in the dolomitic limestone from the lower portion of the Madison testifies to the delicate mechanism of the dolomitization process, and suggests that the dolomitization may even have aided in the preservation of the magnetization. The presence of solution features corresponds closely to the presence of unstable directional behaviour. It appears that the formation of these features by solution of the evaporite beds led to the destruction of the primary remanence in the upper portion of the Madison. Thermomagnetic curves indicate the presence in the lower portion of the Madison of almost pure magnetite. Although thermomagnetic curves from the upper portion are irreversible, alternating field and thermal demagnetization experiments show intensity changes similar to those from the lower portion, suggesting a similar magnetic mineral. Isothermal remanent magnetization acquisition curves also suggest the presence of a large amount of hematite or goethite in over half the samples which apparently did not contribute significantly to the natural remanent magnetization.