Canyon Formation Research Articles

Coahuilasaurus lipani, a New Kritosaurin Hadrosaurid from the Upper Campanian Cerro Del Pueblo Formation, Northern Mexico

The Late Cretaceous of Western North America (Laramidia) supported a diverse dinosaur fauna, with duckbilled dinosaurs (Hadrosauridae) being among the most speciose and abundant members of this assemblage. Historically, collecting and preservational biases have meant that dinosaurs from Mexico and the American Southwest are poorly known compared to those of the northern Great Plains. However, evidence increasingly suggests that distinct species and clades inhabited southern Laramidia. Here, a new kritosaurin hadrosaurid, represented by the anterior part of a skull, is reported from the late Campanian of the Cerro del Pueblo Formation, ~72.5 Ma, in Coahuila, Mexico. The Cerro del Pueblo Formation kritosaur was originally considered to represent the same species as a saurolophine from the Olmos Formation of Sabinas, but the Sabinas hadrosaur is now considered a distinct taxon. More recently, the Cerro del Pueblo Formation kritosaur has been referred to Kritosaurus navajovius. We show it represents a new species related to Gryposaurus. The new species is distinguished by its large size, the shape of the premaxillary nasal process, the strongly downturned dentary, and massive denticles on the premaxilla’s palatal surface, supporting recognition of a new taxon, Coahuilasaurus lipani. The dinosaur assemblage of the Cerro del Pueblo Formation shows higher diversity than the contemporaneous fauna of the Horseshoe Canyon Formation in Alberta. Furthermore, Kritosaurini, Lambeosaurini, and Parasaurolophini all persist into the latest Campanian in southern Laramidia after disappearing from northern Laramidia. These patterns suggest declining herbivore diversity seen at high latitudes may be a local, rather than global phenomenon, perhaps driven by cooling at high latitudes in the Late Campanian and Maastrichtian.

The Ediacara Biota of the Wood Canyon formation: Latest Precambrian macrofossils and sedimentary structures from the southern Great Basin

Fossils of the Ediacara Biota preserve the oldest indisputable evidence of macroscopic animal life. Although new finds continue to expand the near global distribution of such organisms, relatively abundant and diverse populations of these primarily soft-bodied taxa are known from just a handful of localities. More commonly, reports of late Precambrian fossils consist of comparably lower diversity assemblages (less than ∼10 genera), with a limited number of total specimens (less than ∼1000 reported macrofossils over a broad geographic area). Determining the factors responsible for such differences can help to fully appreciate preserved patterns of Ediacaran biodiversity.The lower member of the Wood Canyon Formation in the Death Valley region of the southern Great Basin, USA contains fossils of the Ediacara Biota. Here we redescribe previously recovered specimens based on new data from 3D surface scans and report several new finds from this unit. Although this allows the addition of two Ediacara taxa (Pteridinium and Charnia?) to the known diversity in the region, most potential macrofauna consist of amorphous, irregular forms with minimal preserved structures wherein an abiotic origin cannot be ruled out. A combination of factors – including variable taphonomic conditions, difficulty of identification and an original depauperate community – contribute to the observed diversity of this assemblage. Many biases that impact this record are either common (e.g., age, preservation requirements, difficulty of recognition) or comparable (e.g., paleoenvironmental and taphonomic controls) to known occurrences of Ediacara macrofauana. Thus, we argue this fossil record at least partially reflects the original community composition, suggesting that fossils of the lower Wood Canyon record a signal of relatively low diversity of the Ediacara Biota in the lead up to the Ediacaran-Cambrian boundary.

Rates of bedrock canyon incision by megafloods, Channeled Scabland, eastern Washington, USA

Pleistocene outburst floods from the drainage of glacial Lake Missoula carved bedrock canyons into the Columbia Plateau in eastern Washington, USA, forming the Channeled Scabland. However, rates of bedrock incision by outburst floods are largely unconstrained, which hinders the ability to link flood hydrology with landscape evolution in the Channeled Scabland and other flood-carved landscapes. We used long profiles of hanging tributaries to reconstruct the pre-flood topography of the two largest Channeled Scabland canyons, upper Grand Coulee and Moses Coulee, and a smaller flood-eroded channel, Wilson Creek. The topographic reconstruction indicates floods eroded 67.8 km3, 14.5 km3, and 1.6 km3 of rock from upper Grand Coulee, Moses Coulee, and Wilson Creek, respectively, which corresponds to an average incision depth of 169 m, 56 m, and 10 m in each flood route. We simulated flood discharge over the reconstructed, pre-flood topography and found that high-water evidence was emplaced in each of these channels by flow discharges of 3.1 × 106 m3 s−1, 0.65−0.9 × 106 m3 s−1, and 0.65−0.9 × 106 m3 s−1, respectively. These discharges are a fraction of those predicted under the assumption that post-flood topography was filled to high-water marks for Grand and Moses Coulees. However, both methods yield similar results for Wilson Creek, where there was less erosion. Sediment transport rates based on these discharges imply that the largest canyons could have formed in only about six or fewer floods, based on the time required to transport the eroded rock from each canyon, with associated rates of knickpoint propagation on the order of several km per day. Overall, our results indicate that a small number of outburst floods, with discharges much lower than commonly assumed, can cause extensive erosion and canyon formation in fractured bedrock.

An unusual microsite from the Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada

ABSTRACT The Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada, is among the best-studied paleoecosystems in North America. However, its microvertebrate paleocommunity structure is relatively poorly known, partly because it lacks the abundant microsites of other Upper Cretaceous deposits of Alberta. An unusual microsite (FTS-2) from the Horsethief Member of the Horseshoe Canyon Formation is described that produces abundant anuran and troodontid material, alongside perinatal material from ornithischians and tyrannosaurs. Anuran specimens representing a minimum of two separate taxa and a metatherian molar suggest that these components of the fauna were more diverse than currently recognized. The assemblage is similar to three other North American sites that produce abundant troodontid teeth alongside perinatal dinosaurs. However, environmental and taphonomic conditions of these sites vary, supporting the notion of mixed biotic and abiotic factors driving the association of troodontids alongside perinates. In part, this may stem from similar nesting preferences between troodontids and other dinosaurs, as material collected from all three sites suggests proximity to troodontid nesting sites. Sites such as FTS-2 are important for revealing the rare and small components of paleoecosystems, and hold promise for revealing interactions between these parts of the fauna.

Thrust v. stylolite

Mesostructures in subhorizontal thinly bedded calcareous mudstones of the Permian Bell Canyon Formation in the western Delaware Basin (Guadalupe Mountains foothills, west Texas) include vertical tectonic stylolites kinematically linked with low-angle thrust faults. Schmidt rebound is high (38–70) for all but a few beds, indicating competent rock. Competent beds exhibit contrasting behavior ranging from (i) no visible tectonic stylolites and numerous small-displacement (<1 cm) thrust faults, to (ii) tectonic stylolites with rare thrust faults. Thrust fault intensity correlates positively with total carbonate, and negatively with clay, clay + quartz, quartz + feldspar, and total organic carbon (TOC). Tectonic stylolites are abundant in beds with 3.5–6.5% clay. Stylolite intensity correlates positively with TOC. Lowest-rebound beds exhibit ductile flowage or internal folding rather than stylolite formation, and tend to terminate small-displacement thrust faults in adjacent beds. Tectonic stylolites and thrust faults are consistent with formation in a thrust faulting stress regime during NE-directed Laramide shortening. Fluid inclusion analyses of vein calcite from thrust faults indicate maximum burial depths of 3.3–4.2 km at the time of deformation. Deformation behaviors are highly sensitive to composition, with coeval thrust faulting in clay-poor beds versus stylolite formation in slightly more clay-rich beds.

Garzapelta muelleri gen. et sp. nov., a new aetosaur (Archosauria: Pseudosuchia) from the Late Triassic (middle Norian) middle Cooper Canyon Formation, Dockum Group, Texas, USA, and its implications on our understanding of the morphological disparity of the aetosaurian dorsal carapace.

The Late Triassic Dockum Group in northwestern Texas preserves a rich diversity of pseudosuchian taxa, particularly of aetosaurs. In this contribution, we present Garzapelta muelleri gen. et sp. nov., a new aetosaur from the Late Triassic middle Cooper Canyon Formation (latest Adamanian-earliest Revueltian teilzones) in Garza County, Texas, based on an associated specimen that preserves a significant portion of its dorsal carapace. The carapace of G. muelleri exhibits a striking degree of similarity between that of the paratypothoracin Rioarribasuchus chamaensis and desmatosuchins. We quantitatively assessed the relationships of G. muelleri using several iterations of the matrix. Scoring the paramedian and lateral osteoderms of G. muelleri independently results in conflicting topologies. Thus, it is evident that our current matrix is limited in its ability to discern the convergence within this new taxon and that our current character lists are not fully accounting for the morphological disparity of the aetosaurian carapace. Qualitative comparisons suggest that G. muelleri is a Rioarribasuchus-like paratypothoracin with lateral osteoderms that are convergent with those of desmatosuchins. Although the shape of the dorsal eminence, and the presence of a dorsal flange that is rectangular and proportionately longer than the lateral flange are desmatosuchin-like features of G. muelleri, the taxon does not exhibit the articulation style between the paramedian and lateral osteoderms which diagnose the Desmatosuchini (i.e., a rigid interlocking contact, and an anteromedial edge of the lateral osteoderm that overlaps the adjacent paramedian osteoderm).

Potential triggers and development processes of submarine landslides in the Xisha Trough Basin, South China Sea

Both submarine landslides and submarine canyons can transfer large amounts of terrigenous quantities from the continental shelf to the deep sea. In some cases, they can have a close relationship to their spatial distribution, formation and evolution. Submarine landslides on the shelf–slope can provide early depressions for submarine canyons, representing the early stage of submarine canyons. The continuous downcutting process during the evolution of submarine canyons can steepen the gradient of the canyon sidewalls, which can lead to the occurrence of submarine landslides. However, the role of submarine canyons in the initiation of slope failure has been overlooked. In this study, high-resolution multibeam bathymetry data, submarine image data and 2-D seismic data were used to investigate two adjacent submarine landslides developed on the northern slope of the Xisha Trough and the spatiotemporal relationship of these landslides to the Central Canyon. We identified a steep downslope between the submarine landslides and the Central Canyon. The Central Canyon formation age was much earlier than those of the submarine landslides. The Central Canyon is filled with modern submarine landslide deposits. The characteristics of the multiple failure scarps indicate retrogressive failure of the submarine landslides. We suggest that the submarine landslides developed on the northern slope of the Xisha Trough Basin have finally been captured by the Central Canyon. We determined that the emptying of sediments at the end of the northern slope of the Xisha Trough Basin caused by the development of the Central Canyon caused the end of the northern slope of the Xisha Trough Basin to lose support, which may have affected the slope stability and could have even played a role in the initiation of submarine landslides. Consequently, the slope area along the Central Canyon may be susceptible to slope instability and slope failure processes.

Cranial anatomy of Libognathus sheddi Small, 1997 (Parareptilia, Procolophonidae) from the Upper Triassic Dockum Group of West Texas, USA.

Libognathus sheddi, a leptopleuronine procolophonid from the Upper Triassic Cooper Canyon Formation, Dockum Group, West Texas, was based on an isolated left dentary and partial coronoid. New material referable to Libognathus sheddi, from the Cooper Canyon Formation, provides new information on the cranial anatomy. This new cranial material includes the antorbital portion of a skull, a left maxilla and premaxilla, quadratojugals, and dentaries, including intact tooth rows in the upper and lower jaws. Libognathus shows autapomorphies including; dentary deep with ventral margin oblique to tooth row immediately from the symphysis at ≥23°; anterior projecting coronoid contacting the lingual surface of the dentary underlying the last two dentary teeth; reduced contact between the lacrimal and the nasal; suborbital foramen formed by the maxilla and ectopterygoid, excluding the palatine; a posterior supralabial foramen shared by the maxilla and jugal; a Y-shaped antorbital pillar formed by the palatine, and massive orbitonasale and facial foramina (shared with unnamed southwest USA leptopleuronines). Phylogenetic analysis indicates that Libognathus is a highly derived leptopleuronine procolophonid, closely related to Hypsognathus fenneri and other southwest USA Revueltian leptopleuronines, which fall out as sister taxa to Hypsognathus, a relationship supported by a maxillary dentition restricted anterior to the orbital margin, a possibly synapomorphic orbitonasale septum in the form of an "antorbital pillar" created by the palatine, an anteroventral process of the jugal, and the presence of a small diastema between the first dentary tooth and the more posterior dentition. Libognathus exhibits a possible ankylosed protothecodont tooth implantation with frequent replacement, differing from some other proposed procolophonid implantation and replacement models. Chinle Formation and Dockum Group leptopleuronines are restricted to the Revueltian teilzone/holochronozone, making them possible Revueltian index taxa.

Types and sedimentary genesis of barriers and interlayers in the composite turbidite sand bodies of a deep-water canyon: A case study of the Central Canyon in the Qiongdongnan Basin

Deep-water oil and gas is currently the hot spot and difficulty of global oil and gas exploration, and the complex flow process inside the turbidite channels of deep-water canyons makes it difficult to characterize reservoir structures, identify barriers and interlayers and clarify the spatial distribution laws of reservoirs, which restricts the development of deep-water oil and gas. Taking the Central Canyon of the Qiongdongnan Basin as an example, this paper identifies and characterizes the barriers and interlayers of composite channel scale by means of seismic sedimentology, based on three-dimensional seismic and core data. Then, based on the turbidite filling process, barriers and interlayers are classified, and their genesis and control factors are analyzed. Finally, a development model of deep-water barriers and interlayers is established based on the quantitative analysis of sediment transportation system parameters. And the following research results are obtained. First, based on sedimentary genesis, barriers and interlayers are classified into four types, namely mudstone interlayers of lateral (aggradational) turbidite channel genesis (type A), mudstone interlayers of fine-grained turbidite channel genesis (type B), barriers of hemipelagic deep-water sediment genesis (type C), and calcareous petrophysical interlayers (type D). Second, based on the filling stage, barriers and interlayers are divided into four combination sequences, i.e., the initial canyon formation stage with strong sediment supply conditions (type A + type C and type B+ type C), the initial canyon formation stage with weak sediment supply conditions (type B + type C), the stable canyon development/late reworking stage with strong sediment supply conditions (types A + type D), and the stable canyon development/late reworking stage with weak sediment supply conditions (type D). Third, the development types and combination sequences of barriers and interlayers are controlled by the change of sediment transportation volume and terrain slope in the canyon. In the initial canyon formation stage, there is sufficient space for the development of turbidite, and the development of thin barriers and interlayers is controlled by sediment dischage volume, while the development of thick barriers and interlayers is controlled by terrain slope change. In the stable canyon development/late reworking stage, turbidite undergoes superimposed development and overbank. The sediment supply is the primary control factor of barrier and interlayer thickness, and the terrain slope change is the secondary factor. In conclusion, the development model of barriers and interlayers can be used to describe and predict the reservoir structure models under the same sedimentary background and provides a technical support for the exploration and development of deep-water oil and gas.

Craniomandibular anatomy of a juvenile specimen of Edmontosaurus regalis Lambe, 1917 clarifies issues in ontogeny and biogeography

ABSTRACT Edmontosaurus regalis is a hadrosaurid represented by abundant fossil material from the late Campanian–early Maastrichtian of what is now Alberta, Canada. Despite its prevalence, juvenile craniomandibular elements of E. regalis are poorly known. A newly collected partial skeleton from the Horseshoe Canyon Formation, UALVP 60425, represents a small saurolophine with a partial skull (skull length ∼500 mm). It can be referred to Edmontosaurini based on the presence of a postorbital fossa and anteroposteriorly long frontals that lack a dorsally oriented nasal contact and contribute significantly to the orbital margin. Despite its small size and presumed immaturity, UALVP 60425 is assigned to E. regalis based on a horizontal shelf on the postorbital process of the jugal. The deep postorbital fossa that, in part, diagnoses E. regalis is acquired during growth. UALVP 60425 shares many features with the Alaskan Prince Creek saurolophine (Ugrunaaluk kuukpikensis); both show consistent anatomical differences in the lacrimal, jugal, and postorbitals from E. annectens throughout their growth series. New data from UALVP 6025 supports referring the Alaskan saurolophine material to Edmontosaurus cf. regalis in the absence of large-sized cranial material from the Prince Creek Formation.

Cambrian explosion condensed: High-precision geochronology of the lower Wood Canyon Formation, Nevada

The geologically rapid appearance of fossils of modern animal phyla within Cambrian strata is a defining characteristic of the history of life on Earth. However, temporal calibration of the base of the Cambrian Period remains uncertain within millions of years, which has resulted in mounting challenges to the concept of a discrete Cambrian explosion. We present precise zircon U-Pb dates for the lower Wood Canyon Formation, Nevada. These data demonstrate the base of the Cambrian Period, as defined by both ichnofossil biostratigraphy and carbon isotope chemostratigraphy, was younger than 533 Mya, at least 6 My later than currently recognized. This new geochronology condenses previous age models for the Nemakit-Daldynian (early Cambrian) and, integrated with global records, demonstrates an explosive tempo to the early radiation of modern animal phyla.

Calibrating geologic strata, dinosaurs, and other fossils at Dinosaur Provincial Park (Alberta, Canada) using a new CA-ID-TIMS U–Pb geochronology

The 100 m thick stratigraphic section exposed at Dinosaur Provincial Park (DPP; southern Alberta) contains bentonites that have been used for more than 30 years to date DPP’s rocks and fossils using the K–Ar decay scheme. Limited reproducibility among different vintages of K–Ar and 40Ar/39Ar ages inhibited the development of a high-resolution chronostratigraphy. Here, we employ and further test a recently completed U–Pb geochronology and associated age-stratigraphy model to update temporal constraints on the Park’s bentonites, formational contacts, and other markers. In turn, we document rock accumulation rates and calibrate ages and durations of informal megaherbivore dinosaur assemblage zones and other biozones. Weighted mean 206 Pb/238 U ages from five bentonites range from 76.718 ± 0.020 to 74.289 ± 0.014 Ma (2σ internal uncertainties) through an interval of 88.75 m, indicating a duration of ∼2.43 Myr and an overall rock accumulation rate of 3.65 ± 0.04 cm/ka. An increase in rate above the Oldman–Dinosaur Park formational contact conforms to a regionally expressed pattern of increased accommodation at ∼76.3 Ma across Alberta and Montana. Palynological biozone data suggest a condensed section/hiatus in the uppermost portion of the Oldman Formation. Dinosaur assemblage zones exhibit durations of ∼700–600 kyr and are significantly shorter than those in the overlying Horseshoe Canyon Formation. A decreased rate in dinosaur assemblage turnovers in the last eight million years of the Mesozoic in western Canada may be explained by withdrawal of the Western Interior Seaway and the expansion of ecologically homogenous lowlands in its wake.

The first hadrosaurid trackway from the horseshoe canyon formation (campanian/maastrichtian) of Alberta, Canada

The Horseshoe Canyon Formation has provided a wealth of vertebrate skeletal fossils over the past 100 years of collection. Vertebrate trace fossils such as footprints and trackways, however, have been markedly underrepresented. Trackways can provide a wealth of information regarding behaviour and soft tissues reflective of autopodial anatomy. Discovery of several giant, high-fidelity ichnites in series from the Morrin Member represents the first definitive dinosaur trackway reported from the Horseshoe Canyon Formation. The trackway is composed of three footprint casts in series, alongside 22 associated ichnites. The ichnites were formed in soft sediment molds along a non-uniform walking surface. The deep substrates allowed for the preservation of both the plantar surface and dorsal components of the trackmakers’ feet. Some ichnites show soft tissue morphologies like interdigital webbing, toe pads, and skin impressions. Presence of these features and small kidney-shaped forelimb prints allow referral to Hadrosauropodus langstoni. The preservation of the trackway demonstrates asymmetries useful for comparison of the relief and impression surfaces of prints using both discrete and morphometric characteristics, improving confidence in identifying partial or isolated Hadrosauropodus prints of various modes of formation.

Acanthodian fauna from the Early Devonian (Emsian) of Death Valley, California

A limited assemblage of disarticulated remains from stem chondrichthyan (acanthodian) gnathostomes was found associated with more abundant pteraspidiform and cyathaspidiform (agnathan) plates and plate fragments as well as actinolepid placoderm remains in the Lippincott Member of the Lost Burro Formation, southeastern California. The acanthodian material comprises ischnacanthiform, Bryantonchus, and Machaeracanthus fin spines, ischnacanthiform dentigerous jaw bones, and an endoskeletal scapulocoracoid. The assemblage mostly matches that from the Emsian Sevy Dolomite and the lower Grassy Flat Member of the Water Canyon Formation of Utah and Nevada. Machaeracanthus has not been recorded from the latter strata, but has been described from the Coils Creek Member (?Emsian), McColley Canyon Formation, Nevada.

Improved reservoir characterization by means of supervised machine learning and model-based seismic impedance inversion in the Penobscot field, Scotian Basin

The present research work attempted to delineate and characterize the reservoir facies from the Dawson Canyon Formation in the Penobscot field, Scotian Basin. An integrated study of instantaneous frequency, P-impedance, volume of clay and neutron-porosity attributes, and structural framework was done to unravel the Late Cretaceous depositional system and reservoir facies distribution patterns within the study area. Fault strikes were found in the EW and NEE-SWW directions indicating the dominant course of tectonic activities during the Late Cretaceous period in the region. P-impedance was estimated using model-based seismic inversion. Petrophysical properties such as the neutron porosity (NPHI) and volume of clay (VCL) were estimated using the multilayer perceptron neural network with high accuracy. Comparatively, a combination of low instantaneous frequency (15–30 Hz), moderate to high impedance (7000–9500 gm/cc∗m/s), low neutron porosity (27%–40%) and low volume of clay (40%–60%), suggests fair-to-good sandstone development in the Dawson Canyon Formation. After calibration with the well-log data, it is found that further lowering in these attribute responses signifies the clean sandstone facies possibly containing hydrocarbons. The present study suggests that the shale lithofacies dominates the Late Cretaceous deposition (Dawson Canyon Formation) in the Penobscot field, Scotian Basin. Major faults and overlying shale facies provide structural and stratigraphic seals and act as a suitable hydrocarbon entrapment mechanism in the Dawson Canyon Formation's reservoirs. The present research advocates the integrated analysis of multi-attributes estimated using different methods to minimize the risk involved in hydrocarbon exploration.

Oldest record of the fossil syncarid (Crustacea) Palaeocaris from the Carboniferous Manning Canyon Formation, Utah, USA

New records documented here demonstrate that Palaeocaris Meek and Worthen, 1865 was the most cosmopolitan and longest ranging (earliest Bashkirian to Gzhelian) fossil syncarid genus. It contains three species that are primarily known from occurrences in Euramerican Carboniferous Lagerstätten. Two of these species, P. typus Meek and Worthen, 1865 and P. secretanae Schram, 1984, have previously been reported from North America. We add a third species to the North American fossil record, Palaeocaris retractata Calman, 1932, from the Manning Canyon Formation (Bashkirian) of north-central Utah, USA. This is the oldest geological record of Palaeocaris and extends the temporal range of P. retractata back from its appearance in the transitional Bashkirian to Moscovian Bickershaw Lagerstätte of England by at least 4 million years. The Manning Canyon Formation occurrence expands the paleogeographic distribution of P. retractata from western Europe (England) to the northeastern edge of the Great Basin, USA.

Estimation of Aquifer Storativity Using 3D Geological Modeling and the Spatial Random Bagging Simulation Method: The Saskatchewan River Basin Case Study (Central Canada)

Hydrosystems in the Saskatchewan River Basin of the Canadian Prairies are subject to natural and socioeconomic pressures. Increasingly, these strong pressures are exacerbating problems of water resource accessibility and depletion. Unfortunately, the geometric heterogeneity of the aquifers and the presence of lithologically varied layers complicate groundwater flow studies, hydrodynamic characterization, and aquifer storativity calculations. Moreover, in recent hydrogeological studies, hydraulic conductivity has been the subject of much more research than storativity. It is in this context that the present research was conducted, to establish a 3D hydrostratigraphic model that highlights the geological (lithology, thickness, and depth) and hydrodynamic characteristics of the aquifer formations and proposes a new uncertainty framework for groundwater storage estimation. The general methodology is based on collecting and processing a very fragmentary and diverse multi-source database to develop the conceptual model. Data were harmonized and entered into a common database management system. A large quantity of geological information has been implemented in a 3D hydrostratigraphic model to establish the finest geometry of the SRB aquifers. Then, the different sources of uncertainty were controlled and considered in the modeling process by developing a randomized modeling system based on spatial random bagging simulation (SRBS). The results of the research show the following: Firstly, the distribution of aquifer levels is controlled by tectonic activity and erosion, which further suggests that most buried valleys on the Prairies have filled over time, likely during multiple glaciations in several depositional environments. Secondly, the geostatistical study allowed us to choose optimal interpolation variographic parameters. Finally, the final storativity maps of the different aquifer formations showed a huge potential of groundwater in SRB. The SRBS method allowed us to calculate the optimal storativity values for each mesh and to obtain a final storativity map for each formation. For example, for the Paskapoo Formation, the distribution grid of groundwater storage shows that the east part of the aquifer can store up to 5920 × 103 m3/voxel, whereas most areas of the west aquifer part can only store less than 750 × 103 m3/voxel. The maximum storativity was attributed to the Horseshoe Canyon Formation, which contains maximal geological reserves ranging from 107 to 111 × 109 m3. The main contribution of this research is the proposed 3D geological model with hydrogeological insights into the study area, as well as the use of a new statistical method to propagate the uncertainty over the modeling domain. The next step will focus on the hydrodynamic modeling of groundwater flow to better manage water resources in the Saskatchewan River Basin.

A new sturgeon from the Upper Cretaceous Horseshoe Canyon Formation in central Alberta, Canada

The posterior portion of a sturgeon skull preserved in a nodule was recovered from the latest Campanian sediments of the Horseshoe Canyon Formation in the city of Edmonton, Alberta, Canada. It is described here as a new genus and species of Acipenseriformes. The skull represents an individual of at least 2 meters in total length. This species is of particular interest because different bones of the skull show a surface ornamentation with different patterns; the clavicle has large pits, the dermal skull bones have smaller pits and radiating ridges, and the subopercle shows fine radiating ridges. The new taxon, here named †Boreiosturion labyrinthicus, can be confidently included in the extant family Acipenseridae but a phylogenetic analysis does not further resolve relationships. This fossil is the first documentation of sturgeon in the latest Campanian of North America, and bridges the gap between the mid-Campanian assemblage of Dinosaur Park and the late Maastrichtian material from the Hell Creek Formation.

THE ROLE OF SURFICIAL BIOTURBATION IN THE LATEST EDIACARAN: A QUANTITATIVE ANALYSIS OF TRACE FOSSIL INTENSITY IN THE TERMINAL EDIACARAN–LOWER CAMBRIAN OF CALIFORNIA

ABSTRACT Bioturbating activities have played a vital role in shaping the marine ecosystem throughout metazoan history, influencing the abundance and preservation potential of body fossil-producing taxa and driving major environmental and geochemical changes. The earliest trace making behaviors arose during the late Ediacaran Period (∼ 560–541 Ma), disrupting the substrate previously occupied by dominantly sessile organisms. Simple dwelling and grazing behaviors exploited the organic-rich matgrounds, expanding into the underutilized microbial mat ecosystem. In the western United States, trace assemblages from Ediacaran–Cambrian boundary-spanning deposits document a thriving trace-maker ecosystem. One boundary-spanning deposit in this region, the lower member of the Wood Canyon Formation, crops out along the California-Nevada boundary and contains both trace and body fossil assemblages. The Chicago Pass section of the lower Wood Canyon Formation contains a suite of dominantly simple Ediacaran traces, which become commonplace in the upper part of the stratigraphic section, documenting the onset of prevalent trace-making behaviors in this region. While traces have been previously described from this locality, the addition of the complex trace Lamonte trevallis and quantification of trace fossil density of simple Ediacaran traces provides a more comprehensive ichnological view of the Chicago Pass section. Although Chicago Pass does not yield abundant tubicolous body fossils, as are found elsewhere in the region, the low diversity ichnoassemblages document both burgeoning surficial trace making groups and mat-targeted mining in the latest Ediacaran. The behaviors present at Chicago Pass are similar to those of the Dengying Formation in South China, and highlight the need for petrographic-based trace fossil studies. Additionally, studies of Nama Group trace fossils of the same age from Namibia report higher diversity and complexity in trace-making activities than what has been observed at Chicago Pass, but with similar, low Ediacara biota body fossil diversity. If Ediacara biota diversity is anticorrelated with trace-making behaviors, Chicago Pass represents a low-complexity end-member of the same phenomenon observed in Namibia. The effect of surface sediment disruption on the sessile Ediacaran communities may have been decoupled from complexity of the traces, more so influenced by the presence of general trace-making behaviors in aggregate, including simple traces.

Stratigraphy of the Eocene–Oligocene Titus Canyon Formation, Death Valley, California (USA), and Eocene extensional tectonism in the Basin and Range

Abstract Geologic mapping, measured sections, and geochronologic data elucidate the tectonostratigraphic development of the Titus Canyon extensional basin in Death Valley, California (USA), and provide new constraints on the age of the Titus Canyon Formation, one of the earliest synextensional deposits in the central Basin and Range. Detrital zircon maximum depositional ages (MDAs) and compiled 40Ar/39Ar ages indicate that the Titus Canyon Formation spans 40(?)–30 Ma, consistent with an inferred Duchesnean age for a unique assemblage of mammalian fossils in the lower part of the formation. The Titus Canyon Forma tion preserves a shift in depositional environment from fluvial to lacustrine at ca. 35 Ma, which along with a change in detrital zircon provenance may reflect both the onset of local extensional tectonism and climatic changes at the Eocene–Oligocene boundary. Our data establish the Titus Canyon basin as the southernmost basin in a system of late Eocene extensional basins that formed along the axis of the Sevier orogenic belt. The distribution of lacustrine deposits in these Eocene basins defines the extent of a low-relief orogenic plateau (Nevadaplano) that occupied eastern Nevada at least through Eocene time. As such, the age and character of Titus Canyon Formation implies that the Nevadaplano may have extended into the central Basin and Range, ~200 km farther south than previously recognized. Development of the Titus Canyon extensional basin precedes local Farallon slab removal by ~20 m.y., implying that other mechanisms, such as plate boundary stress changes due to decreased convergence rates in Eocene time, are a more likely trigger for early extension in the central Basin and Range.