Bearpaw Formation Research Articles

Evaluation of the photosensory characteristics of the lateral and pineal eyes of Plioplatecarpus (Squamata, Mosasauridae) based on an exceptionally preserved specimen from the Bearpaw Shale (Campanian, Upper Cretaceous) of southern Alberta

ABSTRACT The skull of Plioplatecarpus possesses large orbits and a large parietal foramen. Although the large orbits suggest that Plioplatecarpus possessed large eyes with enhanced visual performance, none of the previously described skulls include a sclerotic ring, and so it has been impossible in the past to reconstruct their size or optical properties. A recently collected skull with a sclerotic ring preserved in situ provides for the first time the data to do so. The dimensions of the sclerotic ring demonstrate that, although the f-number of the eyeball was not low enough to support the hypothesis that Plioplatecarpus was adapted to low light conditions, the eyeball was nevertheless large and possessed increased visual acuity and sensitivity that enabled the mosasaur to operate efficiently in both light-rich and light-poor conditions and possibly other conditions of reduced visibility. Proportions of this skull also suggest that Plioplatecarpus possessed a relatively wide binocular field of vision, providing stereoscopic vision, and further increasing both acuity and sensitivity, enhancing its ability to effectively detect and track quickly moving objects under a wide range of light conditions. A greatly enlarged parietal foramen implies the presence of a large parietal eye, the significance of which is uncertain, but it may have enhanced the ability to regulate migratory behavior.

A large, new dercetid fish (Teleostei: Aulopiformes) from the Campanian Bearpaw Formation of Alberta, Canada

Two new fossil fish specimens were recovered from deposits of the Bearpaw Formation of southern Alberta, Canada. These deposits represent the Western Interior Seaway in the Campanian. The remains can be confidently assigned to the aulopiform genus Dercetis in the extinct family Dercetidae. The two specimens are here described as Dercetis magnificus sp. nov. Based on a phylogenetic analysis, this new species is placed as the sister-group to the only other valid species of the genus, D. elongatus and D. triqueter. The genus Dercetis was previously documented from the western area of the Tethys and the Western Interior Seaway by only a small individual from Mexico and an incomplete braincase from Alberta, Canada, neither of which was assigned to a particular species. The new species is represented by specimens that are larger than the any other previously reported Dercetis, documenting the potential to attain a very large body size in the genus Dercetis and Dercetidae.

A giant barnacle (Crustacea, Cirripedia, Thoracica) from the Upper Cretaceous (Maastrichtian) of Canada revisited

The cirripede Calantica? saskatchewanensis Russell, 1967, from the Maastrichtian Bearpaw Formation of Saskatchewan (Canada), is redescribed on the basis of new material and transferred to the genus Pachyscalpellum Buckeridge, 1991. This considerably extends the known range of the genus from the eastern Tethys (Australasia, Tunisia) to the northern part of the Western Interior Seaway of North America. Species of the genus achieved an exceptionally large size for stalked barnacles, with a projected possible height (capitulum and peduncle) of 150–200 mm.

Filling the Bearpaw gap: Evidence for palaeoenvironment-driven taxon distribution in a diverse, non-marine ecosystem from the late Campanian of west-Central Alberta, Canada

Patterns of Late Cretaceous terrestrial vertebrate diversity across North America have been interpreted primarily in terms of biogeographic provincialism driven by latitude or coastal-inland habitat gradients. A major difficulty in determining the influence of these two gradients is the existence of some large gaps in the terrestrial fossil record, notably the ‘Bearpaw gap’ caused by a transgression of the inland Bearpaw Seaway during the latter part of the Campanian. In this context, the terrestrial fauna preserved in the Campanian deposits of the Wapiti Formation (west-central Alberta, Canada) is crucial for addressing the information deficit. Deposited at the edge of the palaeo-circumpolar region, Unit 3 of the strictly terrestrial Wapiti Formation (WU3) is coeval with the ‘Bearpaw gap’, a period when the terrestrial record from better-sampled areas elsewhere in Canada and the U.S.A. gives way to marine sediments. Here we show, based largely on evidence from the recently discovered DC (Dinosaur-Chelonian) Bonebed locality, that the diverse WU3 vertebrate fauna shares similarities with lowland to marginal marine ecosystems in the Oldman and Dinosaur Park formations which were deposited in southern Alberta prior to the Bearpaw gap. In addition, a major change in faunal composition demarcates the upper boundary of WU3, related to the disappearance of the Bearpaw Sea in Canada. Data presented here help, first and foremost, to bridge an ~1.2-million-year gap in the North American record of Campanian terrestrial vertebrates. Resemblances between the WU3 vertebrate fauna and slightly older assemblages from southern Alberta underscore the importance of determining the spatiotemporal changes in environmental factors (e.g., coastal proximity). The occurrence of one seemingly endemic lizard, together with differences in relative taxon abundance, suggest additional latitude-correlated factors, implicating both latitudinal and coastal-inland habitat gradients in driving the taxonomic composition of Late Cretaceous terrestrial faunas. • We introduce a new microvertebrate site from the late Campanian of western Canada. • A diverse non-marine fauna coeval with the Bearpaw Formation is discussed. • Vertebrate community is compared with others from the Campanian of Alberta. • Data help filling the information deficit related to the ‘Bearpaw Gap’.

The oldest occurrence of brachylophosaurin hadrosaurids in Canada

Hadrosaurids are a diverse and widely distributed group of ornithischian dinosaurs that are particularly well represented in the upper Campanian Dinosaur Park Formation of the Belly River Group of Alberta. However, the origin of this hadrosaurid diversity in Alberta is poorly understood, as the lower Campanian terrestrial deposits of the underlying Oldman and Foremost formations of the group have produced comparatively few body fossils. Here we provide the first description of a partially articulated hadrosaurid and hadrosaurid material from a bonebed from the Foremost Formation and refer it to the brachylophosaurin Probrachylophosaurus sp. indet. The material represents the oldest occurrence of Brachylophosaurini in Alberta and the oldest known hadrosaurid diagnostic to the genus level from Canada. In Alberta, Hadrosaurinae display a distinct pattern of replacement with the tribes Brachylophosaurini and Kritosaurini being confined to the lower to middle Campanian strata (below the marine Bearpaw Formation) and replaced above the Bearpaw Formation by members of Saurolophini (Prosaurolophus, Saurolophus) and Edmontosaurini (Edmontosaurus), with the latter clade persisting to the end of the Maastrichtian. Although the worldwide stratigraphic distribution of the Hadrosaurinae is complex, this pattern generally holds true for northern Laramidian hadrosaurine tribes, suggesting that their pattern of evolution and replacement may be driven by some common underlying factor such as an environmental response to fluctuations in the margins of the Western Interior Seaway due to sea level change.

Taphonomy and taxonomy of a juvenile lambeosaurine (Ornithischia: Hadrosauridae) bonebed from the late Campanian Wapiti Formation of northwestern Alberta, Canada.

Hadrosaurid (duck-billed) dinosaur bonebeds are exceedingly prevalent in upper Cretaceous (Campanian–Maastrichtian) strata from the Midwest of North America (especially Alberta, Canada, and Montana, U.S.A) but are less frequently documented from more northern regions. The Wapiti Formation (Campanian–Maastrichtian) of northwestern Alberta is a largely untapped resource of terrestrial palaeontological information missing from southern Alberta due to the deposition of the marine Bearpaw Formation. In 2018, the Boreal Alberta Dinosaur Project rediscovered the Spring Creek Bonebed, which had been lost since 2002, along the northern bank of the Wapiti River, southwest of Grande Prairie. Earlier excavations and observations of the Spring Creek Bonebed suggested that the site yielded young hadrosaurines. Continued work in 2018 and 2019 recovered ~300 specimens that included a minimum of eight individuals, based on the number of right humeri. The morphology of several recovered cranial elements unequivocally supports lambeosaurine affinities, making the Spring Creek sample the first documented occurrence of lambeosaurines in the Wapiti Formation. The overall size range and histology of the bones found at the site indicate that these animals were uniformly late juveniles, suggesting that age segregation was a life history strategy among hadrosaurids. Given the considerable size attained by the Spring Creek lambeosaurines, they were probably segregated from the breeding population during nesting or caring for young, rather than due to different diet and locomotory requirements. Dynamic aspects of life history, such as age segregation, may well have contributed to the highly diverse and cosmopolitan nature of Late Cretaceous hadrosaurids.

Evolution of the Western Interior Seaway in west-central Alberta (late Campanian, Canada): Implications for hydrocarbon exploration

This study presents the first integrated, high-resolution stratigraphic analysis of a large area of the Cretaceous Western Interior Basin in Alberta (western Canada), providing new tools to discriminate sedimentary processes and stratigraphic patterns of transgressive-regressive (T-R) cycles in correlative marine and non-marine domains. We integrate gamma ray well-log analysis, measured sections, and paleontological data to determine sediment accumulation and distribution during the second-order T-R cycle of the late Campanian Western Interior Seaway over a previously unstudied area encompassing approximately 97,000 km2 of the Alberta foreland basin. The Bearpaw Formation, historically regarded as the product of a single transgression, is shown to include two T-R cycles, whose timing is constrained by new chronostratigraphic data that provides an unprecedented resolution (~200 kyr) for the Cretaceous of western North America. Seven reference stratigraphic markers were mapped across the study area from the marine deposits into the fluvial domains. 3D-modelled stratigraphic surfaces and stratigraphic intervals resulted in isopach maps for consecutive systems tracts, allowing detailed interpretations of their architecture and patterns of sediment accumulation. Our analysis provides paleogeographic maps for the Western Interior Seaway, focusing primarily on the evidence of the paleo-coastlines during the documented cycles. The distribution of fine-grained, primarily marine, sediments resulted in an effective seal for hydrocarbon accumulation in the Belly River Group. Further oil migration upsection, within the Edmonton group, was prevented by the occurrence of these sealing units. Data support the interpretation that eustasy provided the main control on the evolution of the Western Interior Seaway during the late Campanian.

Large Scaphitid Ammonites (Hoploscaphites) from the Upper Cretaceous (Upper Campanian–Lower Maastrichtian) of North America: Endless Variation on a Single Theme

We describe three species of large scaphitid ammonites (Ammonoidea: Ancyloceratina) from the Upper Cretaceous (upper Campanian–lower Maastrichtian) of the Western Interior of North America. Each species occurs as two dimorphs, referred to as macroconch and microconch. All three species share a similar pattern of ornamentation consisting of long, thin, nonbifurcating ribs on the adoral part of the phragmocone, suggesting that they constitute a single monophyletic clade. Macroconchs of Hoploscaphites crassus (Coryell and Salmon, 1934) are characterized by a globose whorl section, with closely spaced ventrolateral tubercles on the body chamber, usually persisting to the aperture. Macroconchs of Hoploscaphites plenus (Meek and Hayden, 1860) differ from those of H. crassus in having a more subquadrate whorl section with flatter flanks, and fewer, larger, and more widely spaced ventrolateral tubercles. Macroconchs of Hoploscaphites peterseni, n. sp., closely resemble those of H. crassus, but differ in being nearly circular in side view with a more compressed whorl section. All three species lived at approximately the same time in the same general area and depositional environment. They are abundant in the Baculites baculus Zone but also occasionally occur in the B. eliasi Zone and possibly lower part of the B. grandis Zone. They are present in the Pierre Shale of east-central Montana and east-central Wyoming, the Lewis Shale of south-central Wyoming, and the Bearpaw Shale of northeast Montana. It is possible that these three species represent subspecies within a single species or a “flock” of very closely related species, similar to the “species flocks” observed in modern cichlid fishes.

Volcaniclastic member of the richly fossiliferous Kaiparowits Formation reveals new insights for regional correlation and tectonics in southern Utah during the latest Campanian

Lithostratigraphic investigation of the richly fossiliferous Kaiparowits Formation in southern Utah reveals the presence of a previously unidentified stratigraphic unit herein named the Upper Valley Member. The 255-m-thick Upper Valley Member is latest Campanian to earliest Maastrichtian in age and records a significant sedimentological change in the Kaiparowits Formation. This change is illustrated in the member by a significant increase in near syn-sedimentary aged zircons, coincident with the introduction of white, volcaniclastic sandstones, as well as a paucity of Jurassic grains, which dominate the provenance of the rest of the formation. The source of the late Campanian volcaniclastic material, including near syn-sedimentary zircons, is most likely from nearby volcanic centers within the Laramide porphyry copper province to the south of the Kaiparowits Plateau in the Mogollon region. Measured sections reported here stratigraphically expand the Kaiparowits Formation to a total of 1005 m and find that the upper boundary of the formation is largely gradational with the overlying Canaan Peak Formation. Lithological changes documented in this study are interpreted to signify a sedimentological response to proximal magmatism and emerging uplifts within the Cordilleran foreland basin during early Laramide orogenesis, which resulted in paleo-drainage rearrangement in southern Laramidia in the latest Campanian. The fossil-bearing Upper Valley Member can be correlated regionally to the Kirtland, Tuscher and Bearpaw formations and other latest Campanian – and possibly early Maastrichtian – units across western North America and represents the capping member one of the most continuous terrestrial records of the Campanian biosphere found anywhere in the world.

High-precision U–Pb CA–ID–TIMS dating and chronostratigraphy of the dinosaur-rich Horseshoe Canyon Formation (Upper Cretaceous, Campanian–Maastrichtian), Red Deer River valley, Alberta, Canada

The non-marine Horseshoe Canyon Formation (HCFm, southern Alberta) yields taxonomically diverse, late Campanian to middle Maastrichtian dinosaur assemblages that play a central role in documenting dinosaur evolution, paleoecology, and paleobiogeography leading up to the end-Cretaceous extinction. Here, we present high-precision U–Pb CA–ID–TIMS ages and the first calibrated chronostratigraphy for the HCFm using zircon grains from (1) four HCFm bentonites distributed through 129 m of section, (2) one bentonite from the underlying Bearpaw Formation, and (3) a bentonite from the overlying Battle Formation that we dated previously. In its type area, the HCFm ranges in age from 73.1–68.0 Ma. Significant paleoenvironmental and climatic changes are recorded in the formation, including (1) a transition from a warm-and-wet deltaic setting to a cooler, seasonally wet-dry coastal plain at 71.5 Ma, (2) maximum transgression of the Drumheller Marine Tongue at 70.896 ± 0.048 Ma, and (3) transition to a warm-wet alluvial plain at 69.6 Ma. The HCFm’s three mega-herbivore dinosaur assemblage zones track these changes and are calibrated as follows: Edmontosaurus regalis – Pachyrhinosaurus canadensis zone, 73.1–71.5 Ma; Hypacrosaurus altispinus – Saurolophus osborni zone, 71.5–69.6 Ma; and Eotriceratops xerinsularis zone, 69.6–68.2 Ma. The Albertosaurus Bonebed — a monodominant assemblage of tyrannosaurids in the Tolman Member — is assessed an age of 70.1 Ma. The unusual triceratopsin, Eotriceratops xerinsularis, from the Carbon Member, is assessed an age of 68.8 Ma. This chronostratigraphy is useful for refining correlations with dinosaur-bearing upper Campanian–middle Maastrichtian units in Alberta and elsewhere in North America.

The Formation of a Marine Bonebed at the Upper Cretaceous Dinosaur Park - Bearpaw Transition of West - Central Saskatchewan, Canada

A marine bonebed from the Campanian (Upper Cretaceous) Bearpaw – Dinosaur Park Formation transition, containing both micro- and macrovertebrate fossils and trace fossils, was discovered in west-central Saskatchewan, Canada. The bonebed formed during transgression of the Western Interior Seaway, with the stratigraphy of the area displaying extensive interfingering of these terrestrial and marine facies. The macrovertebrate fossils occur in a layer of fine-grained, unconsolidated sand. Directly overlying this stratum is a layer of sulfur-rich, medium-grained sandstone, containing the microvertebrate fossils. Most of the material in both layers is highly encrusted in gypsum. The bonebed formed in a barrier island system over three stages: original deposition of marine reptile bones in a silled basin over a period of sediment starvation, redeposition and burial of the bone material due to higher energy flow through the basin, and deposition of bony and cartilaginous fish material during a period of water stratification and subsequent euxinic conditions. Because sediment deposition rates were low when the marine reptile bones accumulated, these elements spent extended periods at the sediment-water interface, allowing them to become bioeroded. The bioerosion at this site takes two main forms: parallel-sided boreholes about one cm wide, and extensive hollowing out of the cancellous bone. Although the invertebrate tracemakers were not preserved the boreholes resemble clavate borings made by bivalves, and the hollowing could have been caused by polychaete worms or grazing gastropods. The presence of sulfur-rich deposits and chemosymbiotic Chondrites isp. traces in the layer above the bonebed suggest the development of a stratified water column in the basin, with euxinic (anoxic and sulfuric) conditions near the seafloor. Disruption of the water column culminated in a mass die-off of non-air breathing vertebrates in the surface waters and constitutes the microvertebrate layer of the bonebed. Marine reptile bonebeds are rare in the fossil record, and this site represents the first time a vertebrate assemblage has been described from a barrier island system in Saskatchewan. This study will help further our understanding of the transition between the Dinosaur Park and Bearpaw formations, two of the best-known Campanian fossil-bearing deposits in Canada.

Description of Two Species of Hoploscaphites (Ammonoidea: Ancyloceratina) from the Upper Cretaceous (Lower Maastrichtian) of the U.S. Western Interior

Two species of scaphitid ammonites (Ammonoidea: Ancyloceratina) from the Upper Cretaceous (lower Maastrichtian) of the Western Interior of North America are described. Hoploscaphites macer, n. sp., is medium size, with coarse ribs on the phragmocone, which become finer on the body chamber, and closely spaced ventrolateral tubercles. It occurs in the upper part of the Baculites baculus Zone and lower part of the overlying B. grandis Zone in the Pierre Shale in Montana, Wyoming, and Colorado, and in the Bearpaw Shale in Montana. Hoploscaphites criptonodosus (Riccardi, 1983) is larger and more coarsely ornamented, including one or two rows of lateral tubercles on the flanks of the phragmocone. It occurs in the upper part of the Baculites baculus Zone and overlying B. grandis Zone in the Pierre Shale in Montana, Wyoming, Colorado, and possibly South Dakota, and in the Bearpaw Shale in Montana and Saskatchewan, Canada. Both species form part of an evolving lineage of Hoploscaphites that first appears in the Western Interior of North America in the middle Campanian.

Ichnology and depositional environments of the Upper Cretaceous Dinosaur Park – Bearpaw formation transition in the Cypress Hills region of Southwestern Saskatchewan, Canada

The upper Campanian Dinosaur Park Formation (DPF) is a south- and eastward-thinning fluvial to marginal-marine clastic wedge in the Western Canadian Sedimentary Basin. The DPF is overlain by the Bearpaw Formation (BF), a fully marine clastic succession representing the final major transgression of this epicontinental sea across western North America. In southwestern Saskatchewan, the DPF is comprised of marginal-marine coal, carbonaceous shale, and heterolithic siltstone and sandstone grading vertically into marine sandstone and shale of the BF. Historically these deposits have been interpreted as the record of fluvial delta systems along a paleocoastline. This study revisits this interpretation using integration of ichnologic, sedimentologic, and sequence stratigraphic concepts.Detailed facies analysis indicates the upper DPF does not record sedimentation in a delta system, but rather was deposited in a low-relief coastal plain with a wave-dominated, tidally influenced, fluvially modified shoreline. Marginal-marine facies, interpreted as lagoons, tidal flats and estuaries, are bioturbated, showing a typical brackish-water trace-fossil assemblage, including Asterosoma isp., Chondrites isp., Cylindrichnus concentricus, Teichichnus rectus, and Skolithos isp. Fine-grained sandstone was deposited in an estuarine mouth-bar and barrier-island complex that protected the coast from wave reworking. As the seaway transgressed across the coast, fully marine wave-dominated parasequences replaced those of the coastal plain. Typical trace fossils include Asterosoma isp., Chondrites isp., Diplocraterion isp., Nereites missouriensis, Phycosiphon incertum, Planolites isp., Rhizocorallium isp., and Zoophycos isp., reflecting open, fully marine conditions. This study provides new insights into the evolution of depositional environments in the Late Cretaceous of southwestern Saskatchewan, and provides a framework for further geological and paleontological studies ongoing in the region.

Description of juvenile specimens of Prosaurolophus maximus (Hadrosauridae: Saurolophinae) from the Upper Cretaceous Bearpaw Formation of southern Alberta, Canada, reveals ontogenetic changes in crest morphology

ABSTRACTThree juvenile specimens of Prosaurolophus maximus, represented by articulated to disarticulated skeletons, are the smallest known individuals for the taxon. Cranial anatomy of the juvenile specimens indicates that diagnostic characters of P. maximus are ontogenetically variable. In the smallest individual, the crest and deeply excavated fossa at the caudal margin of the circumnarial depression are poorly developed or absent. The crest approaches adult-like morphology in large juveniles, whereas crest robusticity and the deep excavation of the circumnarial depression occur only in subadult and adult individuals. The shape of the caudal margin of the circumnarial depression is consistent between juvenile and adult individuals, potentially making this feature a reliable character for taxonomic identification at younger ontogenetic stages. The crest of P. maximus grows isometrically during ontogeny, unlike the positive allometric growth of lambeosaurine hadrosaur crests, suggesting that this taxon may have had soft tissue structures associated with the narial-crest region, rather than the bony crest itself, selected for sexual display. Recovered from sediments of the Bearpaw Formation deposited during the Baculites compressus ammonite zone and magnetochrons 33n.3n to 33n.2n, the juvenile specimens are stratigraphically younger than P. maximus specimens from the Dinosaur Park Formation (Alberta) and contemporaneous with most specimens from the Two Medicine Formation (Montana), extending the temporal range of the taxon to 75.7–74 Ma. The occurrence of P. maximus in well-drained terrestrial deposits of the Dinosaur Park and Two Medicine formations and marine sediments of the Bearpaw Formation indicates that this taxon inhabited various paleoenvironments in western North America.

A new species of tylosaurine mosasaur from the upper Campanian Bearpaw Formation of Saskatchewan, Canada

Mosasaurs assigned to the genus Tylosaurus have been reported from the North Atlantic Circle Basin, including the Western Interior Seaway in North America and Europe, from the Turonian of Chihuahua, Mexico, to the early Maastrichtian of Belgium. The youngest record of Tylosaurus in North America is from the middle Campanian of the Pierre Shale, South Dakota. Data obtained by examination of an almost complete skull and associated postcranial elements of a large tylosaurine mosasaur from the upper Campanian of Saskatchewan supports the recognition of this specimen as a new species, Tylosaurus saskatchewanensis sp. nov. The specimen, collected from the Bearpaw Formation, southern Saskatchewan, Canada, presents unique features and combinations of features. It is recognized as a tylosaurine based on: edentulous rostrum; relatively long suprastapedial process of quadrate not reaching infrastapedial process; predental anterior extension of dentaries; and 12–13 maxillary and dentary teeth. Some of the characters that support recognition of the new species include: exclusion of prefrontal from dorsal rim of orbit by anterior process of postorbitofrontal; frontal extends anteriorly well into narial openings; well developed dorsal midline eminence of frontal; straight margins of parietal table; small infrastapedial process of quadrate located high on quadrate shaft almost touching suprastapedial process; thick tympanic ala of quadrate; 55 vertebrae anterior to chevron-bearing caudals; and rounded astragalus with big semicircular crural emargination. The new species represents the most northern occurrence of the genus and the subfamily and extends the stratigraphical distribution of the genus Tylosaurus in North America, occupying the northern Western Interior Seaway during the late Campanian.http://zoobank.org/urn:lsid:zoobank.org:pub:55338D44-B3C7-4F9C-8B51-C29DB9B99364

The role of mechanical stratigraphy in the lateral variations of thrust development along the central Alberta Foothills, Canada

Fold-thrust belts generally exhibit significant variations in structural styles such as differences in thrust geometries and frequencies in imbrication. A natural laboratory of this pattern is preserved in the central Alberta Foothills of the Canadian Rockies, where differences in thrust geometries are represented by the existence vs. non-existence of triangle zones. To seek the factors that make this difference in these regions in terms of structural geometry, stratigraphic thickness variations and mechanical stratigraphy of the sedimentary layers, structural interpretation is conducted based on admissible cross-sections and well log interpretations. In northern region, a backthrust is detached from an incompetent layer (viz. Nomad Unit of the Wapiabi Formation), which gets thinner from the Foothills to the Plains, indicating that it is developed where the shale layers are pinched out where triangle zone is developed. Backthrust is also developed in the southern region, where mechanical strengths of strata (viz. Bearpaw Formation) increase toward the foreland. In the central region, however, only forethrusts are developed along the weak continuous decollement layers (viz. Turner Valley and Brazeau formations), forming an imbricate fan without development of the triangle zone. Incompetent layers such as the top Wapiabi (Nomad), Brazeau (Bearpaw), Coalspur and Paskapoo formations are also pinched out laterally, forming fault glide horizons in different stratigraphic levels in each region. These results indicate that, along the transport direction, triangle zone is developed in relation to the stratigraphic pinch out of the Nomad Unit in the northern region, and is formed associated with the variations in strengths of the layers constituting the Bearpaw Formation in the southern region. It is notable that all the glide horizons are developed along incompetent layers. However, triangle zones are not developed in the areas of continuous stratigraphy of the Nomad Unit, which does not serve as a glide horizon in the central region. This suggests that factors such as stratigraphic thickness changes of incompetent layers and mechanical stratigraphy of the sedimentary layers play an important role in the development of lateral variations in thrust system evolution in terms of triangle zone vs. imbricate fan in the central Alberta Foothills.

40Ar/39Ar date of a bentonite associated with a methane seep deposit in the upper Campanian Baculites compressus Zone, Pierre Shale, South Dakota

40Ar/39Ar dating of a bentonite associated with a cold methane seep deposit in the upper Campanian Baculites compressus Zone of the Pierre Shale in South Dakota yields an age of 73.79 ± 0.36 Ma. This is in close agreement with the previously published age of 74.05 ± 0.39 Ma for this zone (Obradovich, 1993) and nearly identical to an unpublished age of 73.70 ± 0.13 Ma for the same zone, both samples of which are from a more proximal locality near the base of the Bearpaw Shale in Montana, as recalculated relative to a Fish Canyon standard age of 28.201 Ma. We also report dates for two bentonites from the upper Campanian Exiteloceras jenneyi and Didymoceras stevensoni zones.

Analysis of Tyrrell Sea Deposits from the Vicinity of the Victor Diamond Mine: Comparison of Three North American Clay Deposits

he De Beers Victor Mine is an open pit diamond mine, and is located in the James Bay lowlands. The lowlands are characterized by extensive peatlands overlying Tyrell Sea sediments. One of the potential impacts of open pit mining, and the focus of the current work, is the potential for differential subsistence in the Tyrell Sea sediments owing to continuous groundwater withdrawal from the underlying limestone aquifers. To fully understand the potential effects of subsistence, a better understanding of the nature and properties of the Tyrell Sea sediments is needed. This will be achieved by analyzing various properties of samples collected from the Victor Diamond Mine, and comparing those properties with values from Lake Agassiz sediments and Bearpaw Shale. Properties such as hydraulic conductivity, grain size, plastic and liquid limit, and mineralogy will be compared. It is expected that the samples from the Victor Mine are a rock flour dominated by clay fraction, composed mostly of finely ground carbonates. The sediments are expected to have high plasticity, low hydraulic conductivity, and moisture content too low for that of true clay.

A late Campanian euselachian assemblage from the Bearpaw Formation of Alberta, Canada: some notable range extensions

Herein, we report an euselachian assemblage from the late Campanian Bearpaw Formation recovered from southern Alberta, Canada. This small yet uniquely diverse fauna includes the northernmost occurrences of Paraorthacodus andersoni, Squalus worlandensis, Odontaspis aculeatus, and Archaeotriakis ornatus within the Western Interior Seaway. It also constitutes the first record of P. andersoni, S. worlandensis, and A. ornatus from Canadian deposits. Moreover, we report the stratigraphically youngest record of Cretoxyrhina mantelli. This assemblage is unique in that all the identifiable euselachian species are either pelagic or benthopelagic but not benthic. This is in stark contrast to the batoid-rich euselachian assemblage of the Lethbridge Coal Zone that immediately underlies the Bearpaw Formation in southern Alberta. We attribute this difference to dysoxic bottom waters during the deposition of the formation, rather than to sampling bias.

On the Theory of Solitons of Fluid Pressure and Solute Density in Geologic Porous Media, with Applications to Shale, Clay and Sandstone

We here analyze a new model of transients of pore pressure p and solute density ρ in geologic porous media. This model is rooted in the nonlinear wave theory, its focus is on advection and effect of large pressure jumps on strain. It takes into account nonlinear and also time-dependent versions of the Hooke law about stress, rate and strain. The model solutions strictly relate p and ρ evolving under the effect of a strong external stress. As a result, the presence of quick and sharp transients in low permeability rocks is unveiled, i.e., the nonlinear “Burgers solitons”. We, therefore, show that the actual transport process in porous rocks for large signals is not only the linear diffusion, but also a solitons presence could control the process. A test of a presence of solitons is applied to Pierre shale, Bearpaw shale, Boom clay and Oznam-Mugu silt and clay. An application about the presence of solitons for nuclear waste disposal and salt water intrusions is also discussed. Finally, in a kind of “theoretical experiment” we show that solitons could also be present in higher permeability rocks (Jordan and St. Peter sandstones), thus supporting the idea of a possible occurrence of osmosis also in sandstones.