Great Divide Basin Research Articles

Folsom obsidian conveyance at the Great Divide Paleoindian sites, Wyoming

We present a study of obsidian artifacts found in Folsom contexts from the Great Divide Paleoindian sites (Great Divide Basin, Wyoming) to evaluate Paleoindian mobility patterns in the central and southern Rocky Mountains. Obsidian sourcing using pXRF demonstrates conveyance from Obsidian Cliff (400 km), Teton Pass (300 km), and the Green River/Engineer Quarry source. Other chipped stone raw materials from Folsom localities derive from sources in the upper Green River Basin, thus partially establishing a Folsom mobility pattern between the Yellowstone Plateau, upper Green River Basin, and Great Divide Basin of Wyoming. This study supports the notion that Paleoindians regularly transported lithic raw materials great distances even in relatively raw material rich regions like the interior of the Rocky Mountains and is further evidence for a sparsely documented Younger Dryas-aged use of the Yellowstone Plateau.

Geochemical exploration for buried sandstone-hosted uranium mineralization using mobile U and Pb isotopes: case study of the REB deposit, Great Divide Basin, Wyoming

Mobile radiogenic lead isotopes ( 206 Pb, 207 Pb, 208 Pb and 210 Pb) represent products of radioactive decay of their parental uranium and thorium isotopes ( 238 U, 235 U, 232 Th), and are considered potential geochemical pathfinders of buried sandstone-type uranium deposits. Soil samples collected along a geochemical traverse intersecting buried uranium roll front mineralization at the REB deposit in the Great Divide Basin, Wyoming, USA were studied. Mineralization of this deposit is hosted in weakly lithified arkosic sands, at a depth of 120–200 m, without a strong surficial expression of its presence at depth, which makes discovery of this deposit type difficult, slow and expensive. All soil samples have been analysed for ratios of the mobile long-lived Pb isotopes and their parental U and Th isotopes, determined from partial leach products obtained using a weak acid leaching technique. The samples were also analysed for trace elements, assayed both in the partial leach products and using conventional whole-soil sample assays. Ratios of the mobile radiogenic Pb isotopes to their parental U and Th isotopes ( 206 Pb/ 238 U, 207 Pb/ 235 U and 208 Pb/ 232 Th) determined in the partial leach products exhibit anomalous contents in the soil samples collected above the uranium rolls. The anomalous values are several times greater than background values, to lateral distances of 350–400 m outside of the roll fronts. Notably, conventional whole-soil assays have failed to detect the anomalies that were detected using mobile Pb isotopes. Supplementary material : Minor and trace elements assays of the geochemical samples are available at https://doi.org/10.6084/m9.figshare.c.5610980

New earliest Paleocene (Puercan) periptychid ‘condylarths’ from the Great Divide Basin, Wyoming, USA

An earliest Paleocene (Puercan) locality in the China Butte Member of the Fort Union Formation in the Great Divide Basin (GDB) of Wyoming contains a diverse mammalian faunal assemblage, including a number of ‘condylarth’ taxa. From UCM locality 2011035, we describe three new periptychid ‘condylarths’ and report first occurrences of Maiorana noctiluca, Ampliconus antoni and Conacodon harbourae from the GDB. The new genus and species Miniconus jeanninae is characterized by a ridge-like metaconid and incipient paraconid on p4, and a molar parastylid. Based on its similarity to M. jeanninae and differences from other species of Oxyacodon, O. archibaldi is placed within the new genus Miniconus. A second new genus and species Beornus honeyi is characterized by its large size with inflated premolars and molars, and small molar paraconid. A new species of Conacodon, C. hettingeri, is similar to other species of Conacodon but differs in its m3 morphology. To examine the relationships of the three new GDB taxa to each other and to other Puercan ‘condylarths’ from the Western Interior of North America, a phylogenetic analysis was performed using 28 Puercan periptychid and arctocyonid taxa as well as the eutherian outgroup taxon Procerberus formicarum and 64 dental characters. The resulting strict consensus tree of 210 steps confirms that the three new species from the GDB fall within Periptychidae. Beornus honeyi forms a polytomy with Mithrandir gillianus and Hemithlaeus kowalevskianus. Conacodon hettingeri is recovered as the basal member of a clade that includes the other species of Conacodon. Miniconus jeanninae is the sister to M. archibaldi. Additionally, the early Puercan Mimatuta spp. and Maiorana noctiluca fall within the Arctocyonidae, supporting the phylogenetic placement of these taxa by other recent analyses. The occurrence of the three new periptychids in the GDB indicates that mammalian diversity is higher than previously suggested for the early Puercan. http://zoobank.org/urn:lsid:zoobank.org.pub:4F31F461-814D-4C4A-99A9-3D7ED5D6701C

Use of Topographic Map Evidence From Drainage Divides Surrounding Wyoming’s Great Divide Basin to Compare Two Fundamentally Different Regional Geomorphology Paradigms

Divide crossings (or low points or gaps) notched into the North American east-west continental divide segments completely encircling Wyoming’s Great Divide Basin interior drainage region (as observed on detailed topographic maps) are used to compare the commonly accepted regional geomorphology paradigm with a fundamentally different and new regional geomorphology paradigm. Paradigms are sets of rules governing how a scientific discipline conducts its research and are judged on their ability to explain observed evidence. Published literature is used to contrast an accepted paradigm interpretation that east-oriented drainage previously flowed across what is now the Great Divide Basin with the new paradigm basic requirement that mountain range and continental divide uplift occurred while immense south-oriented floods flowed across them. Numerous divide crossings are notched into the continental divide segments now completely encircling the relatively flat-floored Great Divide Basin interior drainage area and divide crossings observed along each of the Great Divide Basin’s north, east, south, and west margins are described and interpreted first from the accepted paradigm perspective (using published literature interpretations to the extent possible) and second from the new paradigm perspective. The published literature does not mention most of the described divide crossings, much less provide explanations for their origins, perhaps because the accepted paradigm cannot satisfactorily explain those origins. In contrast the new paradigm successfully explains most if not all of the described (and observed, but undescribed) divide crossings, although the new paradigm requires a completely different middle and late Cenozoic regional geologic history than what most published regional geology literature describes.

A new middle Paleocene (early Tiffanian) mammalian fauna from the Overland Member of the Fort Union Formation, Great Divide Basin, Wyoming, U.S.A.

A new middle Paleocene (early Tiffanian) mammalian fauna from the Overland Member of the Fort Union Formation, Great Divide Basin, Wyoming, U.S.A.

Origin of condensates and natural gases in the Almond Formation reservoirs in southwestern Wyoming, USA

Condensates and natural gases are significant resources that frequently occur together in many petroleum systems. Unraveling their origins is crucial for effective petroleum exploration and exploitation. This is often a challenge because light crudes are volatile, deficient in biomarkers, and commonly altered. The origin of condensates and natural gases in the Upper-Cretaceous Almond Formation in southwestern Wyoming was unraveled through use of improved analytical and interpretative geochemical approaches constrained by regional geologic perspectives and basin modeling. Here, an improved GC–MS/MS method allowed simultaneous determination of saturate and aromatic biomarkers, diamondoids, and organo-sulfur compounds in the whole crudes. Furthermore, basin-specific calibration of diamondoid-based thermal maturity parameters, through correlation of measured indices for diamondoids in rock extracts versus measured reflectance of vitrinite from the same rocks, allowed reliable interpretation of maturity of the most likely source rocks. Modified interpretation schemes for C7-hydrocarbon distributions, and compositions of C1-C30 alkanes, aromatic and organosulfur compounds, and δ13C1-C5 together indicated that the condensate and natural gas from each well are likely co-generated and thermogenic products from non-marine source rocks, although methane is partially biogenic. The bulk thermogenic petroleum are too mature to have originated in the rocks adjacent to the producing reservoirs. The geochemical, geologic, and modeling interpretations collectively indicate that the condensates and associated natural gases were most likely generated, expelled, and migrated from the downdip, highly mature, near-shore/transitional humic source rocks of the Almond Formation/Mesaverde Group in the Washakie Basin and Great Divide Basin at >1.3% Ro and ∼30 Ma.

An Object-Oriented Approach to Extracting Productive Fossil Localities from Remotely Sensed Imagery

Most vertebrate fossils are rare and difficult to find and although paleontologists and paleoanthropologists use geological maps to identify potential fossil-bearing deposits, the process of locating fossiliferous localities often involves a great deal of luck. One way to reduce the role of serendipity is to develop predictive models that increase the likelihood of locating fossils by identifying combinations of geological, geospatial, and spectral features that are common to productive localities. We applied GEographic Object-Based Image Analysis (GEOBIA) of high resolution QuickBird and medium resolution images from the Landsat 8 Operational Land Imager (OLI) along with GIS data such as slope and surface geology layers to identify potentially productive Eocene vertebrate fossil localities in the Great Divide Basin, Wyoming. The spectral and spatial characteristics of the image objects that represent a highly productive locality (WMU-VP-222) were used to extract similar image objects in the area covered by the high resolution imagery and throughout the basin using the Landsat imagery. During the 2013 summer field season, twenty-six locations that would not have been spotted from the road in a traditional ground survey were visited. Fourteen of the eighteen localities that were fossiliferous were identified by the predictive model. In 2014, the GEOBIA techniques were applied to Landsat 8 imagery of the entire basin, correctly identifying six new productive localities in a previously unsurveyed part of the basin.

A new earliest Paleocene (Puercan) arctocyonid mammal from the Fort Union Formation, Great Divide Basin, Wyoming, and its phylogenetic position among early ‘condylarths’

A new arctocyonid ‘condylarth’, Sigynorum magnadivisus gen. et sp. nov., is described from a recently discovered earliest Paleocene (early Puercan) fauna from the China Butte Member of the Fort Union Formation in the Great Divide Basin, southern Wyoming. Based on a sample of 18 specimens (including 14 partial dentaries) whose combined dentitions represent the p2, p4 and m1–3, the new taxon appears most similar in size and molar morphology to the early Puercan arctocyonid Oxyprimus erikseni, but differs in its p4 morphology. To examine the relationship between S. magnadivisus and other Puercan ‘condylarths’ from the Western Interior of North America, a phylogenetic analysis was performed, utilizing 23 taxa (including 21 ‘condylarth’ species and the outgroup taxa Cimolestes and Gypsonictops) and 73 dental characters. The resulting strict consensus tree of 248 steps confirms the close relationship between S. magnadivisus and O. erikseni. Interestingly, our phylogenetic analysis also suggests that Puercan Periptychidae is paraphyletic; the early Puercan periptychids Mimatuta morgoth, Mimatuta minuial, Maiorana noctiluca and Auraria urbana appear more closely allied with arctocyonid and hyopsodontid taxa, while other Puercan periptychids Conacodon spp., Ampliconus browni, Alticonus gazini, Oxyacodon spp. and Mithrandir gillianus fall into a separate monophyletic clade. This analysis is among the first to focus on a large set of Puercan ‘condylarth’ taxa across geographically widespread localities, and, with the addition of the new species from the Great Divide Basin, suggests that diversity among early Puercan ‘condylarths’ is higher than previously recognized.http://zoobank.org/urn:lsid:zoobank.org:pub:4BF2E9D5-1803-43E9-82FF-EC4723203A87

Drastic Disturbance of Salt-Affected Soils in a Semi-Arid Cool Desert Shrubland

Disturbing soils in arid regions can mix subsurface materials with surface soils salvaged for reclamation. Pre-disturbance assessment of soils can minimize impacts of disturbance, and better understanding of drastic disturbance in arid soils will improve reclamation success. Reclaimed well pads have undergone stockpiled soil respreading, tillage, and seeding after drilling is complete. Soil texture and chemical properties were analyzed at 0–15 cm depth in saline and sodic soils from eight paired undisturbed and recently reclaimed sites in the Great Divide Basin of Wyoming. Soil organic matter and structural properties were analyzed in additional samples from two of the paired sites (one sodic, one saline-sodic). Paired difference analysis across the eight well pads indicated that disturbed/reclaimed soils had higher electrical conductivity (EC) than undisturbed soils (12.2 and 3.0 dS m−1, respectively) and higher sodium adsorption ratios (SAR) (26.1 and 1.3, respectively). Analysis of variance of soil organic C (SOC), total N, and soil structural properties indicate that disturbed soils had nearly one-third less total N and two-thirds less SOC than undisturbed soils, and over 65 times more >9.5 mm dry aggregates by weight, representing predominance of large clods in disturbed soils on both sites. Disturbed soils contained significantly smaller proportions of smaller dry aggregate fractions (<53 µm, 53–250 µm, and 250 µm–1 mm) than undisturbed soils, and saturated hydraulic conductivity (Ksat) was about 25% of that in undisturbed soils. Disturbed soils exhibited lower organic materials, higher salt contents, altered soil structure, and low potential for eventually supporting successful native plant communities.

Multi-component Paleoindian surface sites in the Great Divide Basin of Wyoming

The Wyoming Basin contains several smaller depressions one of which is the Great Divide Basin formed by the Continental Divide that splits, resulting in internal drainage area of nearly 11,000 km2. The lowest elevation of the Great Divide Basin is at the Chain Lakes Flat and is the location of numerous playas. In this 140 km2 are four surface concentrations of Paleoindian materials beginning with Folsom and ending with Late Paleoindian. Based on typology, human occupation ended with Late Paleoindian and began again in Middle Archaic an estimated 2,500–3,000 years later. This is an unusual concentration of Paleoindian artifacts and a strong contender for further research and testing for subsurface deposits.

Sandstone hosted uranium deposits of the Great Divide Basin, Wyoming, USA

The Great Divide basin is located in the southern part of the state of Wyoming in USA. Wyoming is the second largest uranium province in that country after the Colorado Plateau. The Great Divide basin represents an intermontane depression of Tertiary age surrounded by major structural uplifts composed of Precambrian rocks including uraniferous Precambrian granite. The main uranium resources of the Great Divide basin are hosted in the weakly lithified sandstone of the Eocene Battle Spring Formation which terminates the sedimentary sequence at the basin. Uranium occurs in the form of rolls and the tabular mineralisation is usually associated with carbonaceous debris in the host sediments. Because of close spatial relationships between uranium and detrital carbonaceous debris the uranium mineralisation of the Great Divide basin is referred to as detrital carbon–uranium roll-type which is a special class of Phanerozoic sandstone hosted uranium deposits. The deposits of the Great Divide basin contain from 2 to 15 kt of U3O8 each, which occurs as uranium rolls and tabular mineralisation, some of which is fault controlled. Their formation is related to multi-episodic uplifts of the Precambrian basement which is exposed along the margins of the basin.

The Early Eocene Rodent Tuscahomys (Cylindrodontidae) from the Great Divide Basin, Wyoming: Phylogeny, Biogeography, and Paleoecology

ABSTRACT A new species of the cylindrodontid rodent Tuscahomys Dawson and Beard, 2007, is very well represented by maxillary, mandibular, and dental remains from the late early Wasatchian Smiley Draw local fauna in the Great Divide Basin of Sweetwater County, Wyoming. Tuscahomys walshi , new species, is more derived than earlier Wasatchian members of the genus in showing greater lingual hypsodonty on its upper cheek teeth and a more discrete hypocone on P4, but less derived than its Bridgerian relative Mysops Leidy, 1871, in having less lingually hypsodont upper cheek teeth and a less trenchant protoloph on P4. Tuscahomys walshi thus partly fills a previously existing gap in the early fossil record of cylindrodontids. Tuscahomys shows an unusual pattern of faunal association and relative abundance. It typically occurs as a surprisingly common element of some, but by no means all, early Wasatchian faunas, and it frequently co-occurs with the “condylarths” Meniscotherium Cope, 1874, and Haplomylus Matthew, ...

An artificial neural network-based approach to identifying mammalian fossil localities in the Great Divide Basin, Wyoming

Successful identification of fossil-bearing sedimentary deposits in the field typically requires expert knowledge in geology and anatomy and some degree of luck. One way to reduce the role of serendipity is to develop an empirical model that increases the likelihood of locating productive fossil-bearing deposits by identifying combinations of geological, geospatial and spectral features that are common to productive localities. In this example, a neural network classifier successfully identified Eocene mammalian fossil localities in the Great Divide Basin, Wyoming. This approach has broad implications for many other types of anthropological field research that also involve unique geospatially distributed phenomena.

Finding fossils in new ways: An artificial neural network approach to predicting the location of productive fossil localities

Chance and serendipity have long played a role in the location of productive fossil localities by vertebrate paleontologists and paleoanthropologists. We offer an alternative approach, informed by methods borrowed from the geographic information sciences and using recent advances in computer science, to more efficiently predict where fossil localities might be found. Our model uses an artificial neural network (ANN) that is trained to recognize the spectral characteristics of known productive localities and other land cover classes, such as forest, wetlands, and scrubland, within a study area based on the analysis of remotely sensed (RS) imagery. Using these spectral signatures, the model then classifies other pixels throughout the study area. The results of the neural network classification can be examined and further manipulated within a geographic information systems (GIS) software package. While we have developed and tested this model on fossil mammal localities in deposits of Paleocene and Eocene age in the Great Divide Basin of southwestern Wyoming, a similar analytical approach can be easily applied to fossil-bearing sedimentary deposits of any age in any part of the world. We suggest that new analytical tools and methods of the geographic sciences, including remote sensing and geographic information systems, are poised to greatly enrich paleoanthropological investigations, and that these new methods should be embraced by field workers in the search for, and geospatial analysis of, fossil primates and hominins.

Climate-induced formation of a closed basin: Great Divide Basin, Wyoming

Large closed basins are often associated with regions of active tectonics. In contrast, we provide the example of the Great Divide Basin, in southern Wyoming, where climate change, through its impact on erosion and fl exure, provides the primary mechanism of basin closure. Two- and three-dimensional fl exural models that incorporate the effects of local basin abandonment due to aridity as well as minor extrabasinal extension demon- strate that basin closure with 40 m of base- ment relief (tilt) could have been achieved in the Great Divide Basin under reasonable assumptions of sediment rock density and fl exural rigidity. The primary drive for ba- sin abandonment was insuffi cient discharge that retarded river downcutting. Continued erosion in the surrounding drainage led to fl exural rebound, against which erosion by the outlet from the Great Divide Basin was unable to compete. Eventually, the basin became detached and isolated from the sur- rounding drainage, and a few tens of meters of differential tilt developed between the ba- sin fl oor and spillover point. An extra amount of tilt, up to a few meters, could have been at- tained by rift shoulder effects associated with minor nearby extension outside of the basin to the north. Hence, closure of the Great Di- vide Basin took place with no internal fault- ing, nor did it require any extrabasinal tec- tonic activity to force basin closure. Hence, basin closure and/or drainage reorganization need not record tectonic activity in all cases. Differential erosion provides an alternative hypothesis that does not refl ect local tectonic timing. Our model of the evolution of the Great Divide Basin illustrates a mechanism by which basins can become closed by cli- matic effects alone.

An anachronistic Clarkforkian mammal fauna from the Paleocene Fort Union Formation (Great Divide Basin, Wyoming, USA)

The Clarkforkian (latest Paleocene) North American Land Mammal Age (NALMA) remains a relatively poorly sampled biostratigraphic interval at the close of the Paleocene epoch that is best known from the Bighorn Basin of northwestern Wyoming. A period of global warming between the cooler early and middle Paleocene and the extreme warming of the early Eocene, the Clarkforkian witnessed significant floral and faunal turnover with important ramifications for the development of Cenozoic biotas. The combination of warming global climates with mammalian turnover (including likely intercontinental dispersals) marks the Clarkforkian and the succeeding Wasatchian (Earliest Eocene) NALMAs as periods of intense interest to paleobiologists and other earth scientists concerned with aspects of biostratigraphy and with the biotic effects of climate change in the past. In this paper we describe a new Clarkforkian mammalian fauna from the Great Divide Basin of southwestern Wyoming with some surprising faunal elements that differ from the typical suite of taxic associations found in Clarkforkian assemblages of the Bighorn Basin. Several different scenarios are explored to explain this “anachronistic” assemblage of mammals from southern Wyoming in relation to the typical patterns found in northern Wyoming, including the concepts of basin-margin faunas, latitudinal and climatic gradients, and a chronologically transitional fauna. We suggest that the observed faunal and biostratigraphic differences between southern and northern Wyoming faunas most likely result from latitudinal and associated climatic differences, with floral and faunal changes being reflected somewhat earlier in the south during this period of marked climate change.

Structural analysis of a Laramide, basement-involved, foreland fault zone, Rawlins uplift, south-central Wyoming

The western border of the Hanna Basin is defined by the Rawlins uplift, a Laramide, basement-involved, faulted arch. This north-northwest–south-southeast-trending structure separates the Hanna Basin on the east from the Great Divide Basin (part of the greater Green River depositional basin) on the west. The Rawlins uplift is a west–southwest-vergent, macroscale, fault-related fold. Detailed geologic mapping, construction of serial cross sections, and the incorporation of data from a seismic-reflection profile indicate that displacement along the fault zone flanking the uplift's western margin cannot account for the net structural relief between the Hanna and Great Divide Basins (∼37,000 vertical ft [∼11,285 vertical m] and ∼27,000 vertical ft [∼8,235 vertical m], respectively). The exposed frontal fault traces are interpreted as high-angle (∼70°) splays off a shallowly dipping (∼25°), master fault zone developed within Archean granitic rocks of the Wyoming province. A low-dipping, braided, plastic-to-brittle thrust-fault zone in the Precambrian basement is inferred to accommodate much of the fault displacement and thus account for the structural relief between the core of the uplift and the adjacent basins. Within the study area, displacement along the exposed frontal fault zone decreases from south to north. Within the map area, bedding attitudes along the southwest limb (forelimb) of the uplift range from ∼30–90° with only local areas of overturned beds. However, southwest of the map area, Upper Cretaceous strata are sub-vertical to overturned. On the homoclinal backlimb, dips are ∼10–15° east-northeast into the Hanna Basin. Eastward structural bends at the southern and northern margins of the uplift suggest a component of left-lateral, oblique-slip displacement along the southern margin and right-lateral, oblique-slip displacement along the northern margin. Pre-existing basement anisotropies or discontinuities are likely responsible for these important changes in structural grain.

Upper Cretaceous Lewis Shale, Great Divide Basin, WY: Seal Characterization and Occurrence within a Sequence Stratigraphic Framework

Upper Cretaceous Lewis Shale, Great Divide Basin, WY: Seal Characterization and Occurrence within a Sequence Stratigraphic Framework

ABSTRACT: A Petrographic Study of the Dad Sandstone, Lewis Shale, Great Divide and Washakie Basins, Wyoming

ABSTRACT: A Petrographic Study of the Dad Sandstone, Lewis Shale, Great Divide and Washakie Basins, Wyoming

Abstract: Sequence Stratigraphic-Based Correlation Strategy of the Lewis Shale and Fox Hills Sandstone, Great Divide and Washakie Basins, Wyoming&amp;nbsp;

Abstract: Sequence Stratigraphic-Based Correlation Strategy of the Lewis Shale and Fox Hills Sandstone, Great Divide and Washakie Basins, Wyoming&amp;nbsp;