Dakota Sandstone Research Articles

A new species of Donlesia (Ceratophyllaceae) from the Early Cretaceous of Kansas, USA

A new species of Donlesia (Ceratophyllaceae) from the Early Cretaceous Cheyenne Sandstone of Kansas, USA is reported. The fruits of Donlesia cheyennensis sp. nov. are achenes with four lateral spines, a stylar spine, and a long pedicel. The four lateral spines are arranged on two perpendicular planes. The leaves associated with D. cheyennensis fruits dichotomize three to four times. The fruit morphology of D. cheyennensis differs from Donlesia dakotensis, from the younger Dakota Formation, other fossil and extant members of Ceratophyllaceae in its tetra-radial symmetry, the presence of four lateral spines, and its long pedicel. The presence of Donlesia in the Cheyenne Sandstone extends the fossil record of Ceratophyllaceae to the earliest late Albian and this indicates that the Ceratophyllaceae clade probably diverged from its sister clade at least 105 million years ago in the Early Cretaceous.

Early Cretaceous angiosperm leaves from the Dakota Formation, Hoisington III locality, Kansas, USA

Early Cretaceous angiosperm leaves from the Dakota Formation, Hoisington III locality, Kansas, USA

New theropod display arena sites in the Cretaceous of North America: Clues to distributions in space and time

Previously-unknown large scale scrapes attributed to Cretaceous theropod dinosaurs from the Naturita Formation (formerly the Dakota Sandstone) of western Colorado were recently named as Ostendichnus bilobatus and interpreted as evidence of “nest scrape display,” a type of courtship behavior previously known only in extant avians. However, comparatively little is known of the morphology, distribution and preservation potential of either modern or ancient nest scrapes. Further study of the initially described samples combined with new discoveries brings the total number of known in Colorado sites to five, one with two scrape-bearing levels. Combined, these sites preserve a total of more than 100 recognizable scrapes from all these sites. We also identify the first O. bilobatus-like scrape from the Cretaceous of Canada. Although variable, a majority of the large sample of Colorado scrapes have the diagnostic characteristics of O. bilobatus, with two lateral troughs separated by a median ridge, and are sufficiently distinct to allow measurement of salient features such as scrape size, depth, and median ridge and average trough width. These provide data which indicate that theropod nest scrapes range from ∼50 to ∼200 cm in length and up to ∼25 cm in depth, presumably indicate dinosaurs of different sizes, and variable time and energy spent in creation of individual scrapes. Scrape orientations are highly variable. Three of the sites occur at about the same stratigraphic level, although they are ∼3.0–∼6.0 km apart, suggesting that display arena sites may have been large, involving many dinosaurs and repeat activity in sequential breeding seasons. High-precision U–Pb zircon analyses by the CA-ID-TIMS method from a volcanic ash bed above the scrape bearing levels at Roubideau Creek (Colorado) yielded a weighted mean 206Pb/238U date of 97.689 ± 0.037 Ma (2σ internal error) and indicate a Cenomanian age for O. bilobatus scrapes in western Colorado.

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.

The late Cenomanian oyster Lopha staufferi () – the oldest ribbed oyster in the Upper Cretaceous of the Western Interior of the United States

Abstract Lopha staufferi (Bergquist, 1944) is a medium-sized, ribbed, Late Cretaceous oyster with a slightly curved axis and a zigzag commissure; it appears suddenly and conspicuously in upper Cenomanian rocks in the Western Interior Basin of the United States. At maturity, the ribs on both valves thicken into steep flanks that allow the oyster to increase interior volume without increasing its exterior footprint on the seafloor. Lopha staufferi is the first (earliest) ribbed oyster in the Late Cretaceous of the Western Interior, but has no ancestor in the basin. It disappears from the rock record as suddenly as it appeared, leaving no direct descendent in the basin. In the southern part of the basin where it is well constrained, L. staufferi is restricted stratigraphically to the upper Cenomanian Metoicoceras mosbyense Zone (= Dunveganoceras conditum Zone in the north). Lopha staufferi has an unusual paleogeographic distribution, occurring in only two, widely scattered areas in the basin. It has been found at several localities near the western shoreline of the Late Cretaceous Seaway in west-central New Mexico and adjacent Arizona, and in localities 1,900 km (1,200 mi) to the northeast near the eastern shoreline in northeastern Minnesota, but nowhere in between. In west-central New Mexico and adjacent Arizona, L. staufferi is a guide fossil to the Twowells Tongue of the Dakota Sandstone.

Field guide to Laramide basin evolution and drilling activity in North Park and Middle Park, Colorado

This two-day field trip provides an overview of the geologic history of the North Park–Middle Park area and its past and recent drilling activity. Stops highlight basin formation and the consequences of geologic configuration on oil and gas plays and development. The trip focuses on work from ongoing U.S. Geological Survey research in this area (currently part of the Cenozoic Landscape Evolution of the Southern Rocky Mountains Project funded by the National Cooperative Geologic Mapping Program). Surface mapping is integrated with perspective from petroleum exploration within the basin. The starting point is the west flank of the Denver Basin to compare and contrast the latest Cretaceous through Eocene basin fill on both flanks of the Front Range. The next stop continues on the south end of the North Park–Middle Park area, about 60 miles [95km] west from the first stop. A general clockwise loop is described by following U.S. Highway 40 from Frasier via Granby and Kremmling to Muddy Pass after which CO Highway 14 is followed to Walden for an overnight stay. On the second day after a loop north of Walden, the Continental Divide is crossed at Willow Creek Pass for a return to Granby via Highway 125. The single structural basin that underlies both physiographic depressions of North Park and Middle Park originated during the latest Cretaceous to Eocene Laramide orogeny (Tweto, 1957, 1975; Dickinson et al., 1988). It largely filled with Paleocene to Eocene sediments and is bordered on the east by the Front Range, on the west by the Park Range and Gore Range, on the north by Independence Mountain and to the south by the Williams Fork and Vasquez Mountains (Figure 1). This larger Paleocene-Eocene structural basin is continuous underneath the Continental Divide, which dissects the basin in two approximately equal physiographic depressions, the ‘Parks.’ Therefore Cole et al. (2010) proposed the name ‘Colorado Headwaters Basin’ or ‘CHB,’ rather than North Park–Middle Park basin (Tweto 1957), to eliminate any confusion between the underlying larger Paleocene-Eocene basin and the two younger depressions that developed after the middle Oligocene. The name was derived from the headwaters of the Colorado, North Platte, Laramie, Cache La Poudre, and Big Thompson Rivers which are all within or near the study area. In this field guide, we will use the name Colorado Headwaters Basin (CHB) over North Park–Middle Park basin. Several workers have described the geology in the basin starting with reports from Marvine who was part of the Hayden Survey and wrote about Middle Park in 1874, Hague and Emmons reported on North Park as part of the King Survey in 1877, Cross on Middle Park (1892), and Beekly surveyed the coal resources of North Park in 1915. Further reconnaissance geologic mapping was performed by Hail (1965 and 1968) and Kinney (1970) in the North Park area and by Izett (1968, 1975), and Izett and Barclay (1973) in Middle Park. Most research has focused on coal resources (Madden, 1977; Stands, 1992; Roberts and Rossi, 1999), and oil and gas potential (1957, all papers in the RMAG guidebook to North Park; subsurface structural geologic analysis of both Middle Park and North Park (the CHB) by oil and gas geologist Wellborn (1977a)). A more comprehensive overview of all previous geologic research in the basin can be found in Cole et al. (2010). Oil and gas exploration started in 1925 when Continental Oil's Sherman A-1 was drilled in the McCallum field in the northeast part of the CHB. It produced mostly CO2 from the Dakota Sandstone and was dubbed the ‘Snow cone’ well. Later wells were more successful finding oil and/or gas, and exploration and production in the area is ongoing, most notably in the unconventional Niobrara play in the Coalmont-Hebron area.

Managing the Increasing Water Footprint of Hydraulic Fracturing in the Bakken Play, United States.

The water footprint of oil production, including water used for hydraulic fracturing (HF) and flowback-produced (FP) water, is increasingly important in terms of HF water sourcing and FP water management. Here, we evaluate trends in HF water use relative to supplies and FP water relative to disposal using well by well analysis in the Bakken Play. HF water use per well increased by ∼6 times from 2005-2014, totaling 24.5 × 10(9) gal (93 × 10(9) L) for ∼10 140 wells. Water supplies expanded to meet increased demand, including access of up to ∼33 × 10(9) gal/year (125 × 10(9) L/year) from Lake Sakakawea, expanding pipeline infrastructure by hundreds of miles and allowing water transfers from irrigation. The projected inventory of ∼60 000 future wells should require an additional ∼11 times more HF water. Cumulative FP water has been managed by disposal into an increasing number (277 to 479) of salt water disposal wells. FP water is projected to increase by ∼10 times during the play lifetime (∼40 years). Disposal of FP water into deeper geologic units should be considered because of reported overpressuring of parts of the Dakota Group. The long time series shows how policies have increased water supplies for HF and highlights potential issues related to FP water management.

Characterization of Failure Parameters and Preliminary Slope Stability Analysis of the Cedar Canyon Landslide, Iron County, Utah

The 2011 Cedar Canyon landslide, eight miles (12.8 km) east of Cedar City, Utah, severely damaged State Route 14. Bedrock stratigraphy at the site consists of the cliff-forming Straight Cliffs Formation and the underlying slope-forming Tropic Shale and Dakota Formation. The lower part of the Straight Cliffs Formation and all of Tropic Shale and Dakota Formation are covered with a thick deposit of colluvial soil that has accumulated at the base of the steep cliff formed by the Straight Cliffs Formation. The landslide initiated in the colluvium and propagated as a translational slide along the contact between the colluvial soil and underlying bedrock units. The Utah Department of Transportation (UDOT) drilled and installed slope inclinometers in three borings and conducted a geophysical survey from the crest to the toe of the landslide. We collected orientation data for 186 discontinuities from the Straight Cliffs and Dakota Formations to determine the principal joint sets for use in kinematic analysis; tested samples of colluvial soil and bedrock to determine natural water content, density, and shear strength parameters of soil, bedrock, and the soil-bedrock contact; used SLIDE software to perform a preliminary stability analysis; and performed a sensitivity analysis with respect to varying positions of the water table. Results show that a combination of relatively steep colluvial slope (~30°), extra weight from previous rockfalls, and buildup of pore pressure due to a rainstorm prior to failure, contributed to the landslide.

The Geologic Context of Wonderstone: A Complex, Outcrop-Scaled Pattern of Iron-Oxide Cement

Abstract Although siderite is a widespread early diagenetic mineral in fluvial systems, it is unstable in oxidizing environments and destroyed in permeable rocks that experience uplift and exhumation. The products of siderite oxidation, however, (mm- to cm-scale rhombs, concretions, and complex bands of iron-oxide cement) are widespread in the rock record of fluvial systems. The fluvial channels of the Shinarump Member of the Chinle Formation in southern Utah and northern Arizona, U.S.A., provide an excellent suite of examples of diagenetic features produced by Triassic and Neogene oxidation of early diagenetic siderite. These diagenetic features also provide direct evidence of the level of the water table during deposition of the Shinarump member. Large, in situ, discoidal concretions containing preserved siderite are present in Shinarump floodplain siltstones. Rip-up clasts derived from the siltstones developed iron-oxide rinds during late-stage, near-surface oxidation. These two structures show that floodplain silts contained abundant organic matter and methanic pore water. Groundwater recharging through these silts carried reducing water through underlying sand bodies and discharged into active channels. Degassing of CO2 and methanogenesis caused rhombic crystals of siderite to precipitate in channel sands during these wet intervals. Some of this siderite may have been oxidized during dry intervals when groundwater circulation reversed, but most siderite in the channel sands was preserved until the Shinarump was exhumed during the Neogene. As oxygenated near-surface water entered joints in the lithified Shinarump, colonies of iron-oxidizing microbes living in the phreatic zone occupied redox boundaries and used the rhombic crystals of siderite in the sandstone and the spherulitic siderite in transported siltstone intraclasts as their sources of energy and carbon. The ferrous iron released from dissolving siderite within the intraclasts was oxidized at the siltstone–sandstone contact, generating rinded concretions similar to those in the Cretaceous Dakota Formation. Complex banding known as wonderstone was produced in the channel sandstones from oxidation of the rhombic siderite; the pattern is a combination of Liesegang bands and microbially mediated cements. The preserved rhombs are pseudomorphs after siderite crystals that were either oxidized during Triassic dry intervals, or escaped Neogene microbial oxidation in the phreatic zone, only to be oxidized abiotically in the vadose zone. Microbes are likely oxidizing Shinarump siderite a few kilometers down dip of outcrops with exposed wonderstone. At such locations, the Shinarump is in contact with overlying water-saturated Quaternary alluvium.

Didactyl raptor tracks from the Cretaceous, Plainview Sandstone at Dinosaur Ridge

Two natural casts of two-toed (didactyl) tracks from the Cretaceous (Albian) Plainview Sandstone (Plainview Member) of the South Platte Formation (Dakota Group) at Dinosaur Ridge, Colorado are attributed to deinonychosaurian theropod dinosaurs and placed in the ichnogenus Dromaeosauripus. This is both the first report of tracks from this unit in the Dinosaur Ridge area and the first report of deinonychosaurian tracks from Colorado. It is also only the third report of this track type from North America. The rarity of tracks from the Albian-aged, Plainview Sandstone (Dakota Group Sequence 2) contrasts with their abundance in the upper (Cenomanian) part of the overlying South Platte Formation (Dakota Group Sequence 3), which has yielded more than 120 sites mostly in Colorado, giving rise to the “Dinosaur Freeway” concept. As no deinonychosaurid tracks are known from the sequence 3 part of the South Platte Formation, despite the large vertebrate and invertebrate ichnological database available, it is evident that the sparse vertebrate ichnofauna from the Plainview Member (Sequence 2) is inherently different. This striking difference in both track abundance and track type reflects differences in both age and depositional environment. Based on the Albian age, and track type, the Plainview tracks invite comparison with the ichnofaunas of the Cedar Mountain Formation and not with those well-known from the upper part of the South Platte Formation known as the Dinosaur Freeway.

Underpressure in Mesozoic and Paleozoic rock units in the Midcontinent of the United States

Potentiometric surfaces for Paleozoic strata, based on water well levels and selected drill-stem tests, reveal the control on hydraulic head exerted by outcrops in eastern Kansas and Oklahoma. From outcrop in the east, the westward climb of hydraulic head is much less than that of the land surface, with heads falling so far below land surface that the pressure:depth ratio in eastern Colorado is less than 5.7 kPa/m (0.25 psi/ft). Permian evaporites separate the Paleozoic hydrogeologic units from a Lower Cretaceous (Dakota Group) aquifer, and a highly saline brine plume pervading Paleozoic units in central Kansas and Oklahoma is attributed to dissolution of Permian halite. Underpressure also exists in the Lower Cretaceous hydrogeologic unit in the Denver Basin, which is hydrologically separate from the Paleozoic units. The data used to construct the seven potentiometric surfaces were also used to construct seven maps of pressure:depth ratio. These latter maps are a function of the differences among hydraulic head, land-surface elevation, and formation elevation. As a consequence, maps of pressure:depth ratio reflect the interplay of three topologies that evolved independently with time. As underpressure developed, gas migrated in response to the changing pressure regime, most notably filling the Hugoton gas field in southwestern Kansas. The timing of underpressure development was determined by the timing of outcrop exposure and tilting of the Great Plains. Explorationists in western Kansas and eastern Colorado should not be surprised if a reservoir is underpressured; rather, they should be surprised if it is not.

Elias Putnam West (1820–1892) - Lawyer, Attorney General, Militia Commander, Judge, Postmaster, Archaeologist, and Paleontologist

Following his forty year career in law, and his archeological studies regarding the early Indian cultures that built the mounds along the Missouri River, Judge E.P. West became interested in geology and paleontology. Well into his sixties, he moved to Lawrence, Kansas where he became associated with Professor F.H. Snow at the University of Kansas. Under the guidance of Professor Snow, he began collecting fossil leaves in central Kansas and vertebrate remains from the Late Cretaceous Smoky Hill Chalk in the late 1880s. West's name is associated with several significant discoveries in Kansas, including a rich deposit of fossil leaf impressions from the Dakota Formation in Ellsworth County and the type specimen of the elasmosaurid plesiosaur, Styxosaurus snowii from the Smoky Hill Chalk of Logan County. The specimens he discovered greatly enriched the early paleontology collections at the University of Kansas and illustrations of many of them were included in scientific publications by the University of Kans...

A revised checklist of Nepticulidae fossils (Lepidoptera) indicates an Early Cretaceous origin.

With phylogenetic knowledge of Lepidoptera rapidly increasing, catalysed by increasingly powerful molecular techniques, the demand for fossil calibration points to estimate an evolutionary timeframe for the order is becoming an increasingly pressing issue. The family Nepticulidae is a species rich, basal branch within the phylogeny of the Lepidoptera, characterized by larval leaf-mining habits, and thereby represents a potentially important lineage whose evolutionary history can be established more thoroughly with the potential use of fossil calibration points. Using our experience with extant global Nepticulidae, we discuss a list of characters that may be used to assign fossil leaf mines to Nepticulidae, and suggest useful methods for classifying relevant fossil material. We present a checklist of 79 records of Nepticulidae representing adult and leaf-mine fossils mentioned in literature, often with multiple exemplars constituting a single record. We provide our interpretation of these fossils. Two species now are included in the collective generic name Stigmellites: Stigmellites resupinata (Krassilov, 2008) comb. nov. (from Ophiheliconoma) and Stigmellites almeidae (Martins-Neto, 1989) comb. nov. (from Nepticula). Eleven records are for the first time attributed to Nepticulidae. After discarding several dubious records, including one possibly placing the family at a latest Jurassic position, we conclude that the oldest fossils likely attributable to Nepticulidae are several exemplars representing a variety of species from the Dakota Formation (USA). The relevant strata containing these earliest fossils are now dated at 102 Ma (million years ago) in age, corresponding to the latest Albian Stage of the Early Cretaceous. Integration of all records in the checklist shows that a continuous presence of nepticulid-like leaf mines preserved as compression-impression fossils and by amber entombment of adults have a fossil record extending to the latest Early Cretaceous.

Impact of the Dakota Aquifer on major-ion chemistry of Rock Creek discharge, eastern Nebraska, Midwest region

Examination of historical water-quality data (major cations and anions and total dissolved solids [TDS]) for Rock Creek, located in eastern Nebraska’s saline wetlands north of the Platte River, revealed that concentrations of sodium (Na), chloride (Cl), and TDS increased significantly in the downstream reach below the town of Ceresco, exceeding the U.S. Environmental Protection Agency (USEPA) secondary drinking water standards of 250 mg/L for Cl and 500 mg/L for TDS. Research into the probable source(s) of these inorganic constituents revealed that the Dakota Formation of Late Cretaceous age subcrops in the study area and typically yields water with elevated concentrations of Na, Cl, and TDS in southeastern Nebraska. This brackish to saline water upwells to the surficial aquifer and Rock Creek streambed. Additionally, the significant levels of Na and Cl correlate well with the occurrence of unique saline wetlands along Rock Creek downstream from Ceresco. Public-domain geochemical speciation software codes (Visual MINTEQ and NETPATH) were used to characterize and investigate aqueous geochemistry of Rock Creek discharge and to calculate mixing proportions of Dakota Formation water and stream discharge. The NETPATH output suggests that 3.3%–18% of discharge in Rock Creek approximately 10 km (6.2 mi) southeast of Ceresco, Nebraska, originates from the Dakota Formation and probably the underlying Pennsylvanian bedrock. Hopefully, this paper will be the impetus for an up-to-date, comprehensive, and geochemical-rich data investigation of the Dakota Aquifer’s impact on the inorganic water quality of Rock Creek.

High precision U–Pb zircon geochronology for Cenomanian Dakota Formation floras in Utah

The Cretaceous Dakota Formation on and near the Colorado Plateau represents the time-transgressive shoreline deposits of the Western Interior Seaway and is a rich repository of fossil plants and animals. However, given the basin architecture and depositional setting, correlations between localities are difficult without geochronology. Here we present new high precision ID-TIMS U–Pb zircon dates from five air-fall ash deposits from Westwater (n = 3) and Henrieville (n = 2) that obey stratigraphic superposition and precisely constrain the ages of these two floras. Three air-fall ashes from the Westwater locality record weighted mean Th-corrected 206Pb/238U dates of 97.949 ± 0.037/0.12 Ma, 97.943 ± 0.023/0.12 Ma, and 97.601 ± 0.049/0.13 Ma, providing the first U–Pb dates from this locality. Two ash beds from the Henrieville locality record weighted mean Th-corrected 206Pb/238U dates of 95.070 ± 0.036/0.12 Ma and 94.879 ± 0.032/0.11 Ma. The new dates indicate that the two floras are separated by ca 2.5 Ma and are both within the Cenomanian. The assemblage of fossil plants collected from the mudstone and ash-bed localities at Westwater show no compositional overlap, despite the presence of 28 distinct morphotypes. This lack of compositional overlap is repeated between the mudstone facies from the Westwater and Henrieville localities, where two different morphotypes of “Liriodendron” are the taxa in common. The species incongruence at Westwater is likely due to rapid colonization of early successional plants post deposition of the volcanic ash. For the mudstone floras at Westwater and Henrieville, the different floral composition may be due to rapid species evolution during the rise of angiosperms, the influence of climate in the mid-Cretaceous, the expression of high regional diversity of localities separated by 300 km, or a highly partitioned floodplain vegetation. Estimated sediment accumulation rates from the new radioisotopic dates, combined with existing proxy records for pCO2, suggest that the rise in pCO2 preceding Ocean Anoxic Event 2 (OAE2) began 513 ka (range from 384 to 641 ka) prior to the positive δ13C excursion that defines the event. This estimate from terrestrial rocks is within error of estimates for the timing of changes in δ34Ssulfate (570 ka; range from 420 to 814 ka) in marine sections at the GSSP for the Cenomanian–Turonian boundary. The overlap indicates synchronous perturbation of marine and terrestrial environments related to an increase in pCO2 prior to the onset of OAE2, providing further support for the volcanic initiation hypothesis.

Detrital zircons from Cretaceous midcontinent strata reveal an Appalachian Mountains–Cordilleran foreland basin connection

U-Pb ages ( n = 403) of detrital zircons from the Dakota Formation in western Iowa and eastern Nebraska provide evidence for westward-flowing fluvial systems that stretched from the Appalachian highlands to the western U.S. Cordilleran foreland basin during Albian–Cenomanian time. Approximately 78% of detrital zircon grains match the ages of Grenvillian (1.3–1.0 Ga), Pan-African (750–500 Ma), and Paleozoic (500–310 Ma) bedrock sources located within the present-day Appalachian Mountains. The presence of minor detrital zircon grains of Paleoproterozoic (2.5–1.5 Ga) or Archean age (>2.5 Ga) indicates that northern source regions in Minnesota, Wisconsin, and Canada did not contribute a significant volume of sediment, as had been previously interpreted. Based on similarities between detrital zircon signatures in the midcontinent strata and time-equivalent Cordilleran foreland basin strata, Appalachian sources may have contributed a previously unrecognized volume of sediment to the Albian–Cenomanian foreland basin system. Sediment flux from the Appalachian region to the Cordilleran foreland basin during middle Cretaceous time may have been related to increased uplift and exhumation due to passage over a mantle plume track.

The Archaeology and Paleoecology of the Aubrey Clovis Site (41DN479) Denton County, Texas

This report contains the results of interdisciplinary investigations of the Aubrey Clovis Site (41DN479}, located at Lake Ray Roberts, Denton County, Texas, and conducted by the Center for Environmental Archaeology, University of North Texas for the U.S. Army Corps of Engineers, Fort Worth District. Exposed by construction of the artificial outlet channel for the reservoir, the site is a multi-cluster complex of archaeological features and artifact-fauna! concentrations buried 7-9 meters below the flood plain of the Elm Fork Trinity River. The Clovis-age materials are geologically situated on a paleo surface within a 14 m thick sequence of late Quaternary deposits, associated with spring, lacustrine, alluvial and colluvial sedimentary environments. A stratigraphically consistent set of 23 radiocarbon ages establishes a sound chronometric frame for these deposits between 1.6 Ka and 14.2 Ka. The Clovis occupations are directly dated by two radiocarbon ages of ca. 11,550 Ka determined on charcoal from a hearth. These ages are securely bracketed by stratigraphically and numerically consistent ages above and below, within the period of ca. 12,300 to 10,940 Ka. Paleoenvironmental reconstructions for the periods before, during and after Clovis occupations have been afforded by pollen, insects, mollusks, vertebrate faunas as well as sedimentary and geochemical data. In the early post-glacial period, the site environs was a cool grassland with moderate effective precipitation, that evolved towards significantly warmer and drier conditions prior to Clovis occupations. The environment ameliorated at about the time of occupations, but exhibited a maximum of Late Quaternary mammalian biodiversity. Clovis artifacts and faunas occur in multiple clusters, including ·camps 8 and F" that contain ca. 9,800 lithic artifacts, over 4,000 fauna! remains and features including hearths, lithic concentrations and a pit considered to be a well. These concentrations were adjacent to a Clovis-age pond and river. Bison bones and associated artifacts indicate a butchering (and "kill"?) locus on the pond shore opposite Camp 8 . Subsistence data from the camps indicate exploitation of a broad set of animals, ranging from mega-mammals (Bison and possibly Mammoth) down to small game, fish and birds. Lithic artifacts show procurement from a minimum of almost 200 km from the site, with materials dominated by Tecovas quartzite, white Novachert and Edwards chert, and including chalcedony, Alibates chert, and Morrison or Dakota sandstone. The assemblage is dominated by repair and maintenance debris associated with bifacial and unifacial tools. Latest stage manufacture is indicated for a biface(s), while all other activities were apparently performed with only resharpening/ repair of other stone tools. Detailed spatial patterning indicates quite well differentiated activities within and between these occupation clusters. Overall, the uniquely detailed record of Clovis occupations at Aubrey registers an adaptive strategy characterized by high mobility, broad exploitation of dispersed, variable resources, long-distance raw material procurement coupled with efficient blank and tool depletion, and a probable combination of functional flexibility and strong within group task differentiation and integration.

Profitable prairie restoration: The EcoSun Prairie Farm experiment

O ngoing conversion of grassland to cropland in the northern Great Plains, declining wildlife populations, and worsening soil and water quality prompted a South Dakota group to search for agricultural practices that would balance environmental concerns with farm economics. Thus was born the EcoSun Prairie Farm ( ), an experimental working farm based on the land ethic and philosophy of Aldo Leopold. EcoSun's primary objective was to see if converting cropland to native tallgrass prairie could simultaneously improve the environment—especially soil and water quality; prairie wetlands; and biodiversity, including wildlife—and provide sufficient income to support a farm family through the sale of grassland products. Six years later, EcoSun continues to sell native plant seed, hay, and beef, and to share lessons learned. As the restoration has progressed, many amphibians, game birds, and neotropical migrant birds have already returned to the farm, but an important measure of the project's long term success will be the number of producers that adopt the farming approach advocated and demonstrated by EcoSun. EcoSun was founded as a nonprofit organization by three faculty members at South Dakota State University and one research scientist from the USDA Agricultural Research Service in Mandan, North Dakota. These four serve on the…

A Method To Perform Multiple Diagnostic Fracture Injection Tests Simultaneously in a Single Wellbore

Summary This paper presents a unique process for deriving reservoir properties (i.e., minimum horizontal stress, kh/u, and reservoir pressure) in isolated reservoir layers intersected by the same vertical wellbore. It is based on simultaneously performing multiple diagnostic fracture-injection tests (DFIT) with extended multiday shut-in periods using downhole shut-in tools and bottomhole memory gauges. A case study of 58 vertical wells completed in the Mesaverde and Dakota sandstones of the San Juan basin is used to describe and assess the above application. These intervals are gas productive, slightly to significantly subpressured, and possess a very low permeability pore network enhanced by natural fracture networks. As many as seven individual intervals per well were tested using the simultaneous process in an area spanning the entire San Juan basin. Large-scale, multistage hydraulic fracturing is necessary to establish commercial production from these intervals. The diagnostic tests were done before the large-scale fracture treatments, yet did not impede the subsequent implementation of the treatments. In the Dakota interval, the diagnostic testing results agreed well with the kh derived from post-fracture production analysis and led to a process of treatment design optimization. In the Mesaverde interval, less agreement was found between diagnostic-test and production-analysis results. Despite the lack of validation, fluid leakoff rates measured during the diagnostic testing provided insight into fracture half-length differences documented in a previous study of microseismic mapping. As part of the case study, procedural guidelines and best practices developed in the process of performing over 200 tests will be discussed.

Cenomanian-Turonian (Upper Cretaceous) foraminifera from the westernmost Colorado Plateau, southwest Utah, U.S.A

Foraminifera from the Cenomanian-Turonian Dakota Formation, Straight Cliffs Formation, Iron Springs Formation, and Tropic Shale of southwest Utah are described and illustrated in detail. The assemblage comprises 37 taxa including 27 agglutinated species and only nine calcareous taxa. The associations of the foraminifera can be summarized on the basis of their distributions relative to geologic age and formation. The lowermost units of theDakota Formation in southwestUtah and Coal Mine Mesa Arizona are characterized by a Trochammina rutherfordi mellariolium-Verneuilinoides perplexus association. The uppermost strata of the Dakota Formation and lower Tropic Shale (upper Cenomanian) are characterized by a Trochamminoides apricarius-Haplophragmium arenatum association. Strata assigned to the lower-to middle Turonian Iron Springs and Straight Cliffs Formation are highly variable with respect to foraminiferal distributions. Lower Turonian deposits fromthe Tropic Shale, however, contain an association of Reophax inordinata and Ammomargulina lorangerae. The temporal and spatial variability of the foraminifera are attributed to transgressive-regressive facies shifts during deposition of the Greenhorn Marine Cycle. We recognize four paleoecological associations of agglutinated foraminifiera that include: (1) a marsh assemblage dominated by Trochammina and Miliammina; (2) a central estuary assemblage dominated by Ammobaculites and Trochammina; (3) a distal estuary assemblage dominated by Verneuilinoides, Textularia, and Trochamminoides; and (4) a shelf assemblage dominated by Haplophragmium and Reophax.