Dakota Sandstone Research Articles

An ichnotaxonomic assessment of the Cretaceous Dakota Group, Front Range, Colorado, USA, and its comparison to other Western interior seaway deposits

The Aptian-Cenomanian Dakota Group along the Colorado Front Range is known for its dinosaur tracks; however, it also contains extensive invertebrate marine and continental trace fossils. The Dakota Group in Colorado is subdivided into the Lytle, Plainview, Glencairn (Cañon City), Skull Creek Shale (Denver, Fort Collins), and Muddy formations. Thirty-two invertebrate ichnogenera and 34 ichnospecies were identified: Archaeonassa, Arenicolites, Asterosoma, Asthenopodichnium, Aulichnites, Chondrites, Cochlichnus, Conichnus, Cruziana, Cylindrichnus, Diplocraterion, Gyrolithes, Lockeia, Macaronichnus, Margaritichnus, Naktodemasis, Ophiomorpha, Palaeophycus, Planolites, Protovirgularia, Rhizocorallium, Rosselia, Rusophycus, Schaubcylindrichnus, Scolicia, Skolithos, Taenidium, Teichichnus, Teredolites, Thalassinoides, Treptichnus, and Zoophycos. Six tetrapod ichnogenera and three ichnospecies were identified: Caririchnium, Dromaeosauripus, Hatcherichnus, Ostendichnus, Magnoavipes, and Tetrapodosaurus. Three tetrapod ichnogenera Chelonipus, Ignotornis, and Mehliella have been reported at other sites in the Dakota Group, but none were found at our study sites. Rhizohaloes are reported in the Muddy Formation. Three vertebrate ichnogenera and two ichnospecies were previously described elsewhere by other workers. The Dakota Group trace fossils comprise eight ichnocoenoses–Caririchnium, Diplocraterion, Lockeia, Naktodemasis, Rhizohalo, Scolicia, Skolithos-Teichichnus, and Zoophycos–representing dwelling, deposit- and filter-feeding, and locomotion behaviors of plants, invertebrates, and tetrapods. Twelve previously unreported ichnogenera were identified: Archaeonassa, Asthenopodichnium, Conichnus, Cylindrichnus, Gyrolithes, Macaronichnus, Naktodemasis, Protovirgularia, Rusophycus, Taenidium, Treptichnus, and Zoophycos. This study is the first systematic ichnotaxonomic assessment of the invertebrate trace fossils of the Dakota Group along the Colorado Front Range, which has the highest reported ichnodiversity when compared to other Western Interior Seaway deposits.

Efficient prediction of hydrogen storage performance in depleted gas reservoirs using machine learning

Underground hydrogen (H2) storage (UHS) has emerged as a promising technology to facilitate the widespread adoption of fluctuating renewable energy sources. However, the current UHS experience primarily focuses on salt caverns, with no working examples of storing pure H2 in porous reservoirs. A key challenge in UHS within porous rocks is the uncertainty in evaluating storage performance due to complicated geological and operational conditions. While physics-based reservoir simulations are commonly used to quantify H2 injection and withdrawal processes during storage cycles, they are computationally demanding and unsuitable for providing rapid support to UHS operations. In this study, we develop efficient reduced-order models (ROMs) for UHS in depleted natural gas reservoirs using deep neural networks (DNNs) based on comprehensive reservoir simulation data sets. The ROMs can accurately forecast UHS performance metrics (H2 withdrawal efficiency, produced H2 purity, produced gas-water ratio) across various geological and operational conditions and are over 22000 times faster than physics-based simulations. Then, we employ the ROMs for sensitivity analysis to assess the impact of geological and operational parameters on UHS performance and conduct uncertainty quantification to characterize potential performance and associated probabilities. Lastly, we present a field case study from the Dakota formation of the Basin field in the Intermountain-West (I-WEST) region, USA. Based on the ROMs’ predictions, Dakota formation is favorable for UHS due to its high H2 withdrawal efficiency and purity, and low water production risk. By optimizing operational parameters, we can further improve the storage performance in Dakota formation and reduce the uncertainty in UHS performance prediction. This study introduces an efficient ROM-based approach to assess and optimize UHS performance, supporting the development of effective UHS projects in depleted gas reservoirs.

An unusual plane tree from the Early Cretaceous of Kansas, USA

We present a new genus and species of platanaceous inflorescences from the Hoisington III locality of Barton County, Kansas, USA. This locality lies within the Albian Dakota Formation, which was formed from deposits along the eastern margin of the mid-Cretaceous North American Western Interior Seaway. The elongate inflorescences documented here are unusual for Platanaceae, which is known for its globose, unisexual inflorescences. Distefananthus hoisingtonensis Huegele and Wang gen. et sp. nov. has elongate, cylindrical, ellipsoid, pedunculate inflorescences bearing apocarpous achenes with long styles, borne in florets of 3-4, with over 100 fruits per inflorescence, and stamens with short filaments and hairy apical connectives. The small and relatively fixed number of parts per floret ((3-)4 fruits and c. 3-4 stamens) is seen in other Cretaceous Platanaceae inflorescences and may have facilitated insect pollination. The state of perianth development is unclear, and the fruits lack basal dispersal hairs. The Hoisington material encompasses a developmental sequence; younger inflorescences bear a mix of stamens and immature carpels (thin with long styles) while mature inflorescences bear developed fruits (thicker and often with broken styles) and have lost all stamens. Like the typical globose capitula, the elongate inflorescences probably originated from the reduction of a compound inflorescence. The elongate inflorescences may represent a less compressed, ancestral or pleisiomorphic condition for Platanaceae. The only other species from this family known for elongate inflorescences is from the Paleocene and Eocene of western North America. The inflorescences from Hoisington co-occur with Sapindopsis leaves. At this locality, Sapindopsis powelliana occurs at a similar frequency to the elongate inflorescences and is a possible candidate for the leaves associated with them. The Hoisington material marks the earliest known occurrence of bisexual inflorescences in Platanaceae. The discovery of Distefananthus hoisingtonensis offers new insight into the diversity of platanaceous inflorescences in the mid-Cretaceous, a critical early period in the history of Platanaceae.

Red pigment in the Central Plains: A Pawnee case at Kitkahahki Town

James Murie, early twentieth century ethnographer and member of the Pawnee Nation, once wrote that the “things that are most acceptable to the Pawnee gods are smoke, fat, paint, and flesh” (Murie 1981:466). Here we describe red paint at Kitkahahki Town, a late eighteenth–early nineteenth-century Kitkahahki Pawnee village in north-central Kansas. Using laser ablation inductively coupled plasma mass spectroscopy and Raman spectroscopy, we compare archaeological paint and pigment samples to three pigment materials – pipestone powder, vermilion, and ochre – all documented in the Great Plains after European colonization. We ultimately find no evidence of pipestone powder or vermilion as pigment at Kitkahahki Town and conclude that ochre (some of which may be from the Lower Cretaceous Dakota formation) is the most likely pigment material at the site. Ochre may have been especially significant because of links between this earth pigment and Pawnee sacred geography.

Quantifying the Cryptic Topography of the High Plains

AbstractThe origin of the presently high topography of the High Plains of the western United States has been a topic of considerable debate. We remove the directly quantifiable effects of thrust loading and post‐Early Cretaceous sedimentation to identify topography supported by subsurface means. We term this amount of unexplained topography cryptic topography. To determine the amount of topography that can be attributed to sedimentation, thrust loading, and the flexural response of the lithosphere, we estimate the thickness and density of the sedimentary rocks that overly the Dakota Formation from well logs. We then calculate the flexure that results from the emplacement of these rocks as well as the thrust load of the Rocky Mountains. We then subtract these effects from the present day Dakota horizon. The results of removing these effects indicate that between ∼1 and 1.5 km of topography at the western edge of the High Plains is cryptic and demands some change in the deeper crust or mantle since the deposition of the Dakota Formation.

Early Cretaceous mealybug herbivory on a laurel highlights the deep-time history of angiosperm-scale insect associations.

Insect fluid-feeding on fossil vascular plants is an inconspicuous and underappreciated mode of herbivory that can provide novel data on the evolution of deep-time ecological associations and indicate the host-plant preferences of ancient insect herbivores. Previous fossil studies have documented piercing-and-sucking herbivory but often are unable to identify culprit insect taxa. One line of evidence are punctures and scale-insect impression marks made by piercing-and-sucking insects that occasionally provide clues to the systematic identities and relationships of particular insect herbivores. We report here the earliest occurrences of piercing and sucking on early angiosperms as evidenced by scale insect covers, impression marks, punctures and body fossils - notably a mealybug - from the Lower Cretaceous Rose Creek Flora of the Dakota Formation (c. 103Ma), in southeastern Nebraska, USA. The mealybug, two other scale insect taxa, and several distinctive damage types on laurel leaves and seed-plant stems at Rose Creek document a diverse guild of piercing-and-sucking insects on early angiosperms. The discovery of an Early Cretaceous female mealybug indicates an early herbivorous association with a laurel host. These data provide direct evidence for co-associations and possible coevolution of scale insects and their plant hosts during early angiosperm diversification.

Crocodylian swim tracks from the Gates Formation (Albian), British Columbia, Canada: comparisons with Cretaceous crocodylian ichnology in western USA

Numerous crocodylian swim tracks occur in the late Early Cretaceous and earliest Late Cretaceous of western North America, in coastal plain deposits marginal to the Cretaceous interior seaways. New assemblages from the lower Albian Gates Formation, within the Tumbler Ridge UNESCO Global Geopark Quintette site (TRUGG-Q) in British Columbia, Canada, resemble those from Albian-Cenomanian Dakota Sandstone sites in Colorado, Kansas and Utah, and facilitate comparative analysis of how such assemblages are registered and preserved. The Gates Formation track assemblage formed on the southwest margin of the ‘Moosebar Sea’ that filled the foredeep of the Western Canada Foreland Basin in the Early Albian. Northeast-prograding sandy deltas were backed by low-lying and heavily-vegetated coastal plains, inhabited by track-making dinosaurs, birds, and crocodylians. The base of a tidal channel-fill at the TRUGG-Q site preserves crocodylian swim traces indicating progression largely parallel to the channel axis, as also inferred for some USA sites. Swim track lengths can be categorized on a short–long spectrum which reflects swimming behavior, with short, wide toe tip traces indicating firm digging-in of toes (‘punting’ or ‘poling’ behavior), and elongate scrape marks indicating light touch-down (or substrate ‘raking’) by buoyant animals making intermittent contact with a subaqueous substrate. The body lengths size of crocodylian trackmakers can be calculated from rare complete ‘walking’ track footprints or from the widths, not lengths, in the case of ‘swim’ traces. The mean size of the Canadian tracks indicates individuals with body lengths in the range of ~1.0 m, with larger trackmakers up to ~4.0 m more common at the USA sites.

Comments: Water Pressures

Drought conditions rated as “moderate or worse” affected 31 US states as of 8 June, as reported by the US National Integrated Drought Information System. Particularly dry are the West and Upper Midwest regions, relevant to the Permian and Bakken, respectively. While not a record-level drought, attention is turning to the Missouri River in North Dakota where streamflow levels are at low levels for this time of year—about 48% below the seasonal average. About 96% of the water in North Dakota’s rivers and streams flows through it, making it one of the main sources of fresh water for oil and gas production in the Bakken. In the extreme drought, water restrictions could come into play. Throughout the industry, recycling and reuse of frac and produced water have been studied, and where the chemical makeup of the frac or produced water is suitable for optimal and economical treatment, it has been implemented. However, Bakken production is typically associated with 1.0 to 1.5 bbl of produced water per barrel of oil (a water cut of approximately 50%). It is highly saline with total dissolved solids (TDS) ranging up to 350,000 mg/L (seawater is about 35,000, or 10 times less salty than Bakken brine). Treatment options for such high TDS levels are limited and often cost-prohibitive. The Bakken’s produced water volumes increased fourfold since 2008 to about 740 million bbl per year due to increasing volumes per well and increasing water cut. Produced water disposal volumes in the same period increased fivefold to about 680 million bbl per year. More than 95% of saltwater disposal (SWD) targets the Inyan Kara Formation, the lowermost sandstone interval of the Dakota Group. The increase in SWD volumes has resulted in localized areas of high pressure in the formation in geographic regions associated with high levels of oil and gas activity. This increased pressure affects the economics and risk associated with the drilling of new wells that now require additional intermediate casing strings (“Dakota Strings”), adding a cost of $300,000 to $700,000 per well. About 200 wells to date have been identified with additional casing strings, according to the Energy & Environmental Research Center (EERC). Faced with the challenges of high salinity in recycling/reuse of produced water, constraints on SWD injection, freshwater limitations, pressure regulation, and inflated drilling costs, a 2-year project was begun in January 2020 which may hold promise for greater use of the produced water. Participants in the $1.3-million project are EERC, Nuverra Environmental Solutions, and the US Department of Energy.

Florivory of Early Cretaceous flowers by functionally diverse insects: implications for early angiosperm pollination.

Florivory (flower consumption) occurs worldwide in modern angiosperms, associated with pollen and nectar consumption. However, florivory remains unrecorded from fossil flowers since their Early Cretaceous appearance. We test hypotheses that earliest angiosperms were pollinated by a diverse insect fauna by evaluating 7858 plants from eight localities of the latest Albian Dakota Formation from midcontinental North America, in which 645 specimens (8.2%) were flowers or inflorescences. Well-preserved specimens were categorized into 32 morphotypes, nine of which displayed 207 instances of damage from 11 insect damage types (DTs) by four functional-feeding groups of hole feeding, margin feeding, surface feeding and piercing-and-sucking. We assessed the same DTs inflicted by known florivores on modern flowers that also are their pollinators, and associated insect mouthpart types causing such damage. The diverse, Dakota florivore–pollinator community showed a local pattern at Braun's Ranch of flower morphotypes 4 and 5 having piercing-and-sucking as dominant and margin feeding as minor interactions, whereas Dakotanthus cordiformis at Rose Creek I and II had an opposite pattern. We found no evidence for nectar robbing. These data support the rapid emergence of early angiosperms of florivore and associated pollinator guilds expressed at both the local and regional community levels.

High Plains groundwater isotopic composition in northeastern New Mexico (USA): relationship to recharge and hydrogeologic setting

In the High Plains (HP) region of northeastern New Mexico (NE NM), USA, underlying bedrock aquifers are utilized where the High Plains Aquifer is thin, absent, or unsaturated. These usage patterns, aquifer depletion, and increasing regional aridity imply that NE NM is a possible analogy for more easterly portions of the central HP. To examine the relationship between recharge, residence time, and hydrogeologic setting, 85 well and spring samples were analyzed for environmental tracers (δD, δ18O, δ13C, and limited tritium and carbon-14 activities). Approximately half of the wells were open to strata of the Dakota Group. δD was −105.0 to −41.7‰ (median −58.2‰) and δ18O was −13.7 to −4.4‰ (median −8.1‰). Overall, isotopic composition is correlated with elevation and influenced by hydrogeologic setting. Ten anomalously depleted waters, most near volcanic-capped mesas, may represent higher-elevation or winter-biased recharge, a different modern precipitation source, or recharge from a cooler climate. Recharge, estimated by chloride mass balance using groundwater chloride concentrations, averages 6 mm/year below 2,000-m elevation and 16 mm/year above 2,000 m. Tritium (nondetectable to 5.7 tritium units) and carbon-14 activities (modern carbon fraction 0.23–1.05) suggest that Holocene to modern waters occur, possibly as mixtures, and that alluvial channels and other surficial features promote recharge, likely at higher rates than regional averages. It is noteworthy that isotopically depleted waters in this study tended to be tritium-free. Additional residence time tracers and seasonal precipitation isotopic sampling could address recharge and the origin of depleted waters.

Low‐accommodation and backwater effects on sequence stratigraphic surfaces and depositional architecture of fluvio‐deltaic settings (Cretaceous Mesa Rica Sandstone, Dakota Group, USA)

AbstractThe adequate documentation and interpretation of regional‐scale stratigraphic surfaces is paramount to establish correlations between continental and shallow marine strata. However, this is often challenged by the amalgamated nature of low‐accommodation settings and control of backwater hydraulics on fluvio‐deltaic stratigraphy. Exhumed examples of full‐transect depositional profiles across river‐to‐delta systems are key to improve our understanding about interacting controlling factors and resultant stratigraphy. This study utilizes the ~400 km transect of the Cenomanian Mesa Rica Sandstone (Dakota Group, USA), which allows mapping of down‐dip changes in facies, thickness distribution, fluvial architecture and spatial extent of stratigraphic surfaces. The two sandstone units of the Mesa Rica Sandstone represent contemporaneous fluvio‐deltaic deposition in the Tucumcari sub‐basin (Western Interior Basin) during two regressive phases. Multivalley deposits pass down‐dip into single‐story channel sandstones and eventually into contemporaneous distributary channels and delta‐front strata. Down‐dip changes reflect accommodation decrease towards the paleoshoreline at the Tucumcari basin rim, and subsequent expansion into the basin. Additionally, multi‐storey channel deposits bound by erosional composite scours incise into underlying deltaic deposits. These represent incised‐valley fill deposits, based on their regional occurrence, estimated channel tops below the surrounding topographic surface and coeval downstepping delta‐front geometries. This opposes criteria offered to differentiate incised valleys from flood‐induced backwater scours. As the incised valleys evidence relative sea‐level fall and flood‐induced backwater scours do not, the interpretation of incised valleys impacts sequence stratigraphic interpretations. The erosional composite surface below fluvial strata in the continental realm represents a sequence boundary/regional composite scour (RCS). The RCS’ diachronous nature demonstrates that its down‐dip equivalent disperses into several surfaces in the marine part of the depositional system, which challenges the idea of a single, correlatable surface. Formation of a regional composite scour in the fluvial realm throughout a relative sea‐level cycle highlights that erosion and deposition occur virtually contemporaneously at any point along the depositional profile. This contradicts stratigraphic models that interpret low‐accommodation settings to dominantly promote bypass, especially during forced regressions. Source‐to‐sink analyses should account for this in order to adequately resolve timing and volume of sediment storage in the system throughout a complete relative sea‐level cycle.

Thermochronological and Geochronological Constraints on Late Cretaceous Unroofing and Proximal Sedimentation in the Sevier Orogenic Belt, Utah

AbstractA source‐to‐sink analysis incorporating geochronometric and thermochronometric data from the Sevier fold‐thrust belt (SFTB) and proximal synorogenic strata of the Canyon Range Conglomerate (CRC) and Indianola Group (IG) provides new insights into orogenic exhumation, erosional unroofing, and the interplay between thrusting and coarse clastic deposition in the Cretaceous Cordilleran foreland basin of western North America. Zircon (U‐Th)/He ages from the Pavant and Nebo thrust sheets record significant Cenomanian cooling indicative of synchronous exhumation and thrusting along a large segment of the SFTB in central and northern Utah. Detrital zircon (U‐Th)/He (DZHe) ages indistinguishable from depositional ages from the Cenomanian Dakota Formation and lower CRC also record rapid unroofing of the SFTB and synchronous deposition. DZHe data from wedge‐top deposits of the CRC record two significant unroofing episodes: Albo‐Cenomanian exhumation of the Pavant thrust and progressive unroofing of the Canyon Range culmination. For the IG, the presence of Paleozoic DZHe ages along with Paleozoic‐Mesozoic DZ U‐Pb ages in the Cenomanian Sanpete Formation suggests derivation from Paleozoic to Jurassic strata exhumed in the frontal Pavant and Nebo thrust sheets. After the Cenomanian episode of rapid exhumation, proximal foredeep strata recorded a widespread DZ provenance shift in the Turonian. Short DZHe lag time values from Campanian CRC and IG deposits reveal rapid exhumation of the SFTB during the Campanian. The synchroneity of major shortening and Campanian and Cenomanian changes in foreland basin architecture and provenance supports models proposing that active shortening in the fold‐thrust belt coincides with coarse clastic influx in foreland basins.

Internal mouth‐bar variability and preservation of subordinate coastal processes in low‐accommodation proximal deltaic settings (Cretaceous Dakota Group, New Mexico, USA)

AbstractMouth bars are the fundamental architectural elements of proximal deltaic successions. Understanding their internal architecture and complex interaction with coastal processes (fluvial, tide and wave‐dominated) is paramount to the interpretation of ancient deltaic successions. This is particularly challenging in low‐accommodation systems, because they are commonly characterized by thin, condensed and top‐truncated sections. This study analyses the exhumed Cenomanian Mesa Rica Sandstone (Dakota Group, Western Interior Seaway, USA), a fluvio‐deltaic system covering a ca 450 km depositional dip‐parallel profile. The study targets the proximal deltaic expression of the system, using 22 sedimentary logs (total of 390 m) spatially correlated within a ca 25 km2 study area at the rim of the Tucumcari Basin. Analysis of facies distributions, depositional architecture and spatial extent of stratigraphic surfaces reveals a 6–10 m thick, sharp‐based and sand‐prone deltaic package, comprising several laterally extensive (>1.4 km width) mouth bars. Composite erosional surfaces infilled with multi‐storey fluvial and marine‐influenced channel deposits (12–20 m thick, 100–250 m wide) scour locally into the deltaic package. Based on differences in sedimentary structures, bed thicknesses, occurrence of interflood beds and bioturbation indexes, four different sub‐environments within single mouth bars were distinguished. These range from mouth‐bar axis, off‐axis, fringe to distal‐fringe deposits, which reflect waning depositional energy with increasing distance from the distributary channel mouth. The interpreted mouth‐bar components also show internal variability in dominant process regime, with overall river dominance but local preservation of tide influence in the fringe and distal fringe components. Mouth‐bar deposits amalgamate to form an extensive sand‐rich sheet body throughout the study area, in which interflood mudstone to very‐fine grained sandstone beds are nearly absent. These features reflect successive coalescence of mouth bars in a low accommodation/supply (A/S) setting. These conditions promoted recurrent channel avulsion/bifurcation and thus the potential reworking of previously deposited mouth‐bar fringe and distal‐fringe sediments, where time and background processes are better recorded. Results of this study evidence internal process‐regime variability within mouth‐bar components. They also caution against the possible loss of preservation of subordinate coastal processes (e.g. tidal indicators), and consequent underestimation of the true mixed influence in low‐accommodation deltaic settings.

Microbial structures and dinosaur trackways from a Cretaceous coastal environment (Dakota Group, Colorado, U.S.A.)

ABSTRACT Microbially induced sedimentary structures may help preserve unique glimpses of ancient shoreline habitats, but are little known from Mesozoic epicontinental settings. To help fill this knowledge gap, we describe a diverse suite of microbial structures from the Upper Cretaceous “J” Sandstone (South Platte Formation, Dakota Group) that are spectacularly exposed at Dinosaur Ridge in Morrison, Colorado, USA. Structures include “tattered” bed surfaces and ferruginous sand chips in supratidal flat facies. A large over-flip structure is preserved in a channel locally known as Crocodile Creek. In upper-intertidal facies, multidirectional ripple marks occur. Perhaps the most well-known microbial structures are exposed on extensive bedding surfaces known as “Slimy Beach,” where lower supratidal-flat facies are dominated by decimeter-scale erosional remnants and pockets. Morphologies and superposition of the structures allows identification of three generations of erosional pockets. Generation A of these erosional pockets exhibit size similarities to ornithomimid, sauropod, and ornithopod dinosaur tracks from adjacent bedding planes, raising the question of whether initial disturbance of the mat-bound surface could have been from track making. Generation B erosional pockets are older and record continuous erosion of the initial pockets until they were eventually overgrown and sealed by microbial mats. Generation C pockets are the oldest ones, exposing wide areas of barren sediment that could not be overgrown by microbial mats anymore. In concert, the microbial structures point to seasonally variable meteorological conditions along the coastline of the Western Interior Seaway and indicate that the “Slimy Beach” bedding plane represents a multi-year record of dinosaur locomotion.

Hydrogeochemical and mineralogical factors influencing uranium in background area groundwater wells: Grants, New Mexico

Study regionLower San Mateo Creek Basin (SMCB), New Mexico Study focusGroundwater in the alluvial aquifer of the lower SMCB has a high concentration of total dissolved solids, alkalinity, and dissolved uranium at concentrations above USEPA limits; the source of the water quality was investigated through evaluation of geology, mineralogy, and geochemistry of sediments and groundwater. Surface-expressing bedrock in the larger Basin is dominated by uranium-bearing units such as the Morrison Formation and Dakota Sandstone; erosion of these units contributed sediment to Quaternary alluvium valley fill in the Basin with heterogeneous distribution of uranium. The potential for uranium-bearing alluvial fill to affect the groundwater quality was investigated upgradient of the Grants Reclamation Project (GRP), a former uranium milling facility in the lower SMCB, by hydrogeochemical and geophysical methods. New hydrological insights for the regionUranium is primarily associated with fine-grained materials (clay/silt) and is labile depending upon sediment geochemical conditions. Natural occurrence of uranium minerals in SMCB alluvial sediments here results in concentrations in groundwater greater than the USEPA water quality standards; as such, site-specific standards are established and supported by the findings of this work. Regional groundwater systems, derived from weathered mineralized bedrock, require careful evaluation of water quality to understand background conditions; uranium in groundwater results from hydrogeochemical processes at the interface of fine and coarse grained sediments within the aquifer.

Coalesced Delta-front Sheet-like Sandstone Bodies from Highly Avulsive Distributary Channels: The Low-accommodation Mesa Rica Sandstone (Dakota Group, New Mexico, U.S.A.)

AbstractLow-accommodation deltaic systems are often challenging to interpret due to their condensed, low-gradient nature, which often results in extensive, sheet-like sandstone bodies. As a result, detailed studies of such systems are scarce, and their internal depositional architecture is still poorly understood. We analyze one such system, the Cenomanian deltaic Mesa Rica Sandstone (Dakota Group), which was deposited in the Western Interior Seaway, in east-central New Mexico, USA. A > 20-km-long escarpment, subparallel to the main delta progradation direction, allows a detailed analysis of facies distribution, depositional architecture, and the spatial extent of stratigraphic surfaces. Results reveal an arrangement of laterally variable shallowing-upward facies successions with three depositional cycles preserved. The first cycle is characterized by deltaic sheet-like sandstone bodies that are consistently overlain by sand-filled amalgamated distributary-channel deposits. The two successive cycles record a progressive reduction of sediment supply into the basin. Vertical and lateral relationships between facies associations and architectural geometries allow the recognition of regional key stratal surfaces, incised-valley fills, and the presence of lagoonal deposits at a sub-regional scale.The Mesa Rica deltaic system represents a river-dominated delta with multiple distributary channels. The sheet-like delta-front sandstone bodies are interpreted as the result of the combined effect of high sandy-sediment supply and low accommodation. The latter acted as an accelerator for autogenic depositional mechanisms such as mouth-bar deposition and abandonment, and for the highly avulsive character of distributary channels. After deposition, minor wave reworking facilitated lateral sand redistribution and favored bioturbation. This study demonstrates that sheet-like delta-front sandstone geometries from low-accommodation systems can be formed without the dominance of wave redistribution processes. This cautions against interpretations of amalgamated shoreline systems based solely on apparent sandstone geometries, without taking into account the preservation potential and postdepositional modification of primary deltaic characteristics.

Revisions to the fossil sporophyte record of Marsilea

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

Detrital zircon ages from Proterozoic, Paleozoic, and Cretaceous clastic strata in southern New Mexico, U.S.A.

ABSTRACTU-Pb ages were obtained from detrital zircon grains from Proterozoic, Ordovician, Devonian, Pennsylvanian, and Cretaceous clastic sedimentary rocks in southern New Mexico and are compared to previously published data from Proterozoic, Cambrian, Permian, and other Cretaceous strata. This provides the first combined data set from most of the known pre-Cenozoic clastic formations in southern New Mexico, albeit in a reconnaissance fashion. Proterozoic quartzite, conglomerate, and lithic sandstone yield mostly 1.65-Ga zircon ages that were derived from the Mazatzal province, with minor 1.8–1.7-Ga zircon ages from the Yavapai province. The Cambrian–Ordovician Bliss Sandstone is dominated by Grenville-age grains and Cambrian grains inferred to be locally derived. Newly acquired ages from the Ordovician Cable Canyon Sandstone are dominated by 1.7–1.6-Ga Mazatzal province zircon grains, whereas new data from the Devonian Percha Shale indicate subequal contributions from 1.7–1.6-Ga and ~1.4-Ga sources, along with 1.8–1.7-Ga zircon ages. Both of these formations likely had mainly distal sources as the Precambrian basement in the region was largely buried by older Paleozoic strata. New data from a sandstone in the Pennsylvanian La Tuna Formation show mostly Yavapai grains and minor Paleozoic zircon grains, including Cambrian zircon grains sourced from the nearby Florida Mountains landmass postulated to have been exposed during Pennsylvanian time. The Permian ‘Abo tongue’/Robledo Mountains Formation of the Hueco Group has mostly Neoproterozoic and Grenville-age zircon grains and was derived from Ancestral Rocky Mountain uplifts that did not have a large ~1.4-Ga component. The Aptian Hell-to-Finish Formation of the Bisbee Group has mostly Yavapai-aged zircon grains in the pre-1000-Ma age group, but younger Albian- and Campanian-age sandstones have mostly Grenville-age zircon grains. New data from the Albian Beartooth Quartzite indicate syndepositional volcanic grains at 102 Ma and support correlations with the Mojado Formation rather than the younger Dakota Sandstone. Archean zircon ages are rare overall in all of the strata in southern New Mexico, but zircon grains with ages of ~2.74 Ga are most abundant. These grains could have been derived from basement rocks in the Wyoming or Superior provinces, or recycled from sediment originally derived from those sources.

Early Eudicot flower and fruit: Dakotanthus gen. nov. from the Cretaceous Dakota Formation of Kansas and Nebraska, USA

AbstractAn extinct plant that populated the eastern margin of the Cretaceous Midcontinental Seaway of North America about 100 million years ago has attracted interest as one of the earliest known bisexual flowers in the fossil record. Reexamination of the type specimen of Carpites cordiformis Lesq., and corresponding specimens from sandstones and clays of the Dakota Formation of Kansas and Nebraska and the correlative Woodbine Sandstone of Texas, with both light microscopy and micro CT scanning, leads to a revised concept of the morphology and affinities of the “Rose Creek flower”. The moderately large flowers (22–30 mm diameter) have two perianth whorls: five basally fused sepals and five free spatulate petals. The gynoecium is pentacarpellate with five styles. A crescent-shaped nectariferous pad occurs at the base of the gynoecium aligned with each sepal. Ten stamens are inserted at the level of the nectaries, one whorl organized opposite the sepals and another opposite the petals. In situ pollen is oblate, brevitricolporate and finely verrucate. The fruits are loculicidal capsules with persistent calyx and disk. Comparing the full suite of observed characters with those of extant angiosperms indicates particularly close similarity to the monogeneric fabalean family Quillajaceae, with shared features of perianth number and morphology, nectary position and morphology, stamen number and morphology, and gynoecium merosity, although the fossil differs from extant Quillaja in fruit type (capsule vs basally syncarpous follicles) and especially in pollen morphology (10 μm oblate, microverrucate, vs 30–40 μm prolate, striate).

Cenomanian-Turonian flooding cycles: U.S. Gulf Coast and Western Interior

Cenomanian-Turonian ages, 100.5 Ma to 89.8 Ma, represented an extraordinary Cretaceous time interval when continental seaways expanded, tropical waters interchanged with Polar waters, global climates warmed, and at the end of the Cenomanian large amounts of organic carbon were buried. This was a time of major evolutionary changes in marine pelagic and benthic ecosystems, and in terrestrial plant ecosystems. A new comprehensive chronostratigraphic Cretaceous database is built upon reference sections of each Cretaceous stage and is calibrated to the 2016 Geologic Time Scale. This database is composed of bioevents, chemostratigraphic events, radioisotope measurements, and magnetochrons integrated with nearly 3000 species by projecting the section measurements of the events to the numeric time scale.This new database calibrates numerical ages of Cenomanian-Turonian sequence boundaries in Tunisian reference sections. These deep-shelf successions of limestone/marl/shale record biostratigraphically well dated, continuous deposition and serve as a model of Cenomanian-Turonian cycles. The Cretaceous database enables stratigraphic correlation experiments to test the time equivalency of Tunisian depositional cycles with sequences in Europe, in the Eagle Ford Group in Texas and with stratigraphic sequences in the Western Interior. New accurate and precise correlation of Cenomanian-Turonian depositional sequences between the Gulf Coast and the Western Interior test new biostratigraphic and radioisotopic data of the Eagle Ford Group on the Texas Comanche shelf. The Albian-Cenomanian boundary as defined by planktic foraminifers and ammonites in Texas projects between upper Albian shale units and the Dakota Group and associated sandstone units. The Mowry Shale and its endemic ammonites correlate with upper lower Cenomanian zones.