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The Cretaceous Western Interior Basin reflects the interplay between the North American craton and allochthonous terranes to the west. We divide the basinal stratigraphy into three successions, Aptian-Albian, Cenomanian-Turonian, and Santonian-Maastrichtian, each related to periods of deformation in the adjacent fold-thrust belt. Here we focus on the Cenomanian-Turonian succession, where progressive west to east uplift and fluvial incision of older Aptian-Albian sedimentary rocks (Cedar Mtn-San Pitch-Thermopolis-Skull Creek-Mannville) are interpreted as a migrating forebulge. Uplift was underway at 103 Ma in the west (Paddy-Blackleaf-Muddy sandstones) and propagated eastward throughout the trough by 99.5 Ma (Viking-Bow Island-Newcastle sandstones). The incised fluvial valleys were subsequently filled by swampy and shallow marine facies, then overlain by dark, marine Neogastroplites-bearing shale and associated bentonites of the 100-97.5 Ma Shell Creek-Mowry-Slater River-Goodrich-Shaftesbury-Westgate shales. The shales are characterized by a distinctive condensed horizon with abundant fish scales, teeth, and bones. They are interpreted as outer-trench slope deposits, with the overlying anoxic horizon representing a starved isochronous unit formed atop the slope deposits. The starved horizon is overlain by prodeltaic muddy clinoforms of easterly migrating clastic wedges (Trevor-Dunvegan-Frontier-Cintura-Mexcala) that can be traced 800 km atop the fish-scale hash and contain hinterland-derived 99-90 Ma detrital zircons. Although the Western Interior Basin has long been considered a retro-arc trough, the overall succession instead suggests that the Cretaceous-Turonian part represents a collisional foredeep created during the ~100 Ma collision between the arc-bearing Peninsular Ranges composite terrane and North America. The accretion brought tyrannosaurids, pachycephalosaurs, snakes, and marsupials to North America. Key words: foredeep basin, dinosaur invasion, Cordillera, Peninsular Ranges orogeny, stratigraphy, Western Interior Basin, Introduction Much of the western half of Cretaceous North America comprised a northerly trending couplet of distinct, yet intimately interrelated, tectonic entities: the Cordillera and the Western Interior Basin (Fig. [...]

The Liard Basin, in northwestern Canada, contains one of Canada's largest natural gas reserves. There are concerns about degradation of Dunvegan Formation groundwater quality, which is the basin's main shallow freshwater aquifer, as a consequence of oil and gas development. Previous lithostratigraphic studies interpreted the Dunvegan as conglomeratic alluvial fans. In this study, newly collected cores and surface resistivity surveys are integrated with legacy hydrocarbon well data and measured sections for improved sedimentary bedrock characterization. Rather than alluvial fans, we interpret the upper Dun-vegan as a coarse-sand to gravel bed fluvial system that was likely tributive to incised valleys associated with linked Alberta Basin base-level falls. Correlation of well logs and measured sections suggest the lower Dunvegan comprises a prograding delta complex with off-lapping clinoforms fed by smaller sand-bed rivers that grade into the upper Dunvegan conglomeratic system, which built southeast towards the Cretaceous Western Interior Seaway. This sequence stratigraphic and facies architectural approach is employed to inform the aquifer-aquitard flow system and aid in understanding the 3D groundwater flow system, once hydrogeologic characterisation confirms position and thickness of important hydrogeologic units. Resistivity surveys suggest upper Dunvegan channel-belt facies may be well-connected and laterally extensive, potentially acting as interconnected aquifer units; whereas lower Dunvegan channel belts may be discontinuous, indicating smaller-scale flow units separated by floodplain and marine shale. This revised geologic understanding provides opportunities for determining impacts or resilience from shallow and deep sources of contamination associated with human activities, including oil and gas development, land-use, and (or) climate change. Key words: Dunvegan Formation, Liard Basin, sequence stratigraphic framework, hydrogeologic conceptual model Le bassin de la Liard, dans le nord-ouest du Canada, renferme l'une des plus grandes réserves de gaz naturel de ce pays. La dégradation de la qualité de l'eau souterraine dans la Formation de Dunvegan, le principal aquifère d'eau douce peu profond du bassin, conséquence de la mise en valeur des ressources gazières et pétrolières, suscite des inquiétudes. Des études lithostratigraphiques passées ont interprété la Formation de Dunvegan comme étant formée de cônes alluviaux conglomératiques. Dans la présente étude, des carottes nouvellement prélevées et des levés de résistivité en surface sont intégrés à des données de puits d'hydrocarbure et des coupes mesurées existantes pour obtenir une meilleure caractérisation du substrat sédimentaire. Plutôt que constituée de cônes alluviaux, nous interprétons la Formation de Dunvegan comme étant un réseau fluvial de lits allant de sable grossier à du gravier qui était probablement tributaire de vallées encaissées associées à des chutes au niveau de base du bassin de l'Alberta reliées. La corrélation de profils de sondage et de coupes mesurées indiquerait que la Formation de Dunvegan inférieure comprend un complexe de delta progradant avec des clinoformes régressifs alimentés par de plus petites rivières au lit sablonneux qui passent dans le système conglomératique de la Formation de Dunvegan supérieure, qui elle s'est développée vers le sud-est et la mer intérieure de l'Ouest crétacée. Cette approche de stratigraphie séquentielle et d'architecture de faciès est utilisée pour mieux comprendre le système d'écoulement d'aquifères et d'aquitards et le réseau d'écoulement tridimensionnel de l'eau souterraine, une fois que l'emplacement et l'épaisseur d'unités hydrogéologiques importantes sont confirmés par la caractérisation hydrogéologique. Les levés de résistivité donnent à penser que le faciès de ceintures de chenaux de la Formation de Dunvegan supérieure pourrait être bien connecté et de grande étendue latérale, agissant possiblement comme des unités aquifères interconnectées, alors que les ceintures de chenaux de la Formation de Dunvegan inférieure pourraient être discontinues, indiquant des unités d'écoulement de plus petite échelle séparées par du schiste marin et de plaine inondable. Cette compréhension géologique révisée offre la possibilité de déterminer les impacts de sources de contamination profondes et peu profondes associées à des activités humaines, dont la mise en valeur de ressources gazières et pétrolières, l'occupation du sol et les changements climatiques, ainsi que la résilience à celles-ci. [Traduit par la Rédaction] Mots-clés : Formation de Dunvegan, bassin de la Liard, cadre de stratigraphie séquentielle, modèle conceptuel hydrogéologique, Introduction The Liard Basin, located in the northwest corner of the Western Canada Sedimentary Basin, spans the borders of British Columbia (BC), Yukon (YT), and Northwest Territories (NWT). The region [...]

The relative importance of tectonism in the stratigraphic record should be more clearly expressed during greenhouse times of Earth history due to the lack of overmasking effects of high-frequency and high-amplitude sea-level changes typical for icehouse periods. Establishment of the importance of tectonism, especially at temporal scales comparable to durations of typical transgressive-regressive cycles, has been plagued by poor temporal resolution. Our outcrop and subsurface-based study of a Cenomanian shallow-marine siliciclastic interval, constrained by bentonite-based geochronology and detailed biostratigraphy, examines this problem. In a 2.2 m.y. interval, we identified four tectonically driven erosional surfaces that dominate preserved stratigraphy. Biostratigraphic correlation to a sea-level curve for the Cenomanian--where coeval high-frequency low-amplitude eustatic cyclicity has been demonstrated--allows the first direct comparison of the effects of eustasy and tectonics at temporal scales of hundreds of thousands of years during a global greenhouse time. We suggest that minor tectonic pulses locally overshadow the effects of eustasy and exert the dominant control over preserved stratigraphy. While subtle tectonic control on sedimentation has been documented throughout the Cretaceous Western Interior, the results of this study suggest that much of that deformation occurred at sub-million-year frequencies and at time scales comparable to eustatic transgressive-regressive cycles. Keywords: tectonic controls, Milankovitch theory, sequence stratigraphy, biostratigraphy, erosion surfaces, foreland basins.

Storms are increasingly identified as a key depositional process. Their deposits show unique sedimentary characteristics, distinct from deposits of fair‐weather wave processes, but are not currently separated in classic ternary deltaic classification schemes. The term 'storm‐flood‐dominated delta' is proposed for a new type of delta that more fully represents deltas dominated by storm‐flood processes. This study describes several outcrop cliffs of the Gallup Formation, deposited during the Late Turonian to Early Coniacian in north‐west New Mexico, that exemplify storm‐generated facies and provide examples that can be used to generate a facies model for storm‐flood‐dominated deltas. Key identification criteria include extensive sharp‐based planar to hummocky cross‐stratified sandstone beds, commonly presenting as large‐sized gutter casts. They are interbedded with mudstones that show low bioturbation intensity and normally and inversely graded beds, suggesting direct deposition from river plumes. Major types of gutter casts are classified based on geometry and dimension. The gutter casts are interpreted as storm channels of storm‐flood‐dominated deltas and formed by erosion and infill of submerged channels resulting from offshore‐oriented downwelling currents that may include localized rip currents. These amalgamated channels are likely linked to multiple feeding rivers and distributary channels that ensured high sediment supply rates and highly efficient offshore‐directed sediment transport through hyperpycnal flows. A four‐component pyramidal classification scheme of deltaic deposition is employed to emphasize storms as a distinct process in contrast to the traditional classification that lumps storm and fair‐weather processes in a single 'wave' end‐member. The four‐component depositional model can be readily applied to interpret storm‐dominated environments and provide new insights into depositional processes of the marine realm. Recognition of storm processes in deciphering depositional evolution will also help to better understand control mechanisms of sequence stratigraphy, such as relative sea‐level changes, and to analyze sedimentary processes governing sediment transport in 'source to sink' systems. [ABSTRACT FROM AUTHOR]

Controls on high-frequency sequences formed during super-greenhouse conditions in the Late Cretaceous Western Interior Seaway remain equivocal because of the active foreland basin tectonic setting and the lack of direct evidence of polar glaciations to support a glacio-eustatic origin. This paper quantifies eustatic sea-level changes based on high-resolution sequence stratigraphic analysis and improved chronometry of shallow marine deposits of the Late Cretaceous Gallup Sandstone in New Mexico, USA. Backstripping techniques remove tectonic and compactional subsidence and enable quantification of the magnitude of eustatic sea-level change, that allow evaluation of the dominant controls on the high-frequency sequences to resolve the role of orbitally controlled, climate-driven eustasy versus tectonics. Sixty-five parasequences, constituting 29 parasequence sets and 12 sequences are identified in the ~1.2 m.y. duration of the Late Cretaceous Gallup system. New 40Ar/39Ar dating of bentonites constrains the durations of the individual parasequences, parasequence sets, and sequences, and that these match Milankovitch periodicity, indicating an orbital climate control. The magnitudes of sea-level changes between parasequences range between -28 m and +22 m, which are compatible with hypotheses of both aquifer and glacio-eustasy. Aquifer-eustasy predicts a reciprocal relationship between floodplain cycles and shallow marine sequences, such that aquifer drawdown and falling water tables should correlate to rising sea levels (highstands), whereas increased aquifer storage and rising water tables should correlate to falling sea levels (lowstands). Our preliminary observations show synchronous, versus reciprocal, relationships that may be more compatible with a glacio-eustatic origin. The results of this study support the hypothesis that the Cretaceous greenhouse was marked by high-frequency, low-amplitude glaciations driven by orbital climate cycles, but further work is required to evaluate the contribution of aquifer-eustasy. [ABSTRACT FROM AUTHOR]

Depositional facies have been hypothesized to be linked to sequence stratigraphic positions. Also, shoreline systems are built by mixed processes, including rivers, storms, fair‐weather waves and tides. Resolving the complexity of shoreline deposition requires detailed quantitative facies analysis with particular attention to heterolithic successions. In this study, 71 sections in a 130 km long outcrop belt of the Cretaceous Gallup Formation in the north‐west of the San Juan Basin were measured. Five major facies associations were identified using sedimentological and iconological interpretations, including offshore shelf, non‐deltaic shoreline sandstones, deltas, coastal bayline and fluvial. Each facies association also comprises subordinate facies. Depositional facies interpretations are placed in a high‐resolution sequence stratigraphic framework that allows for reconstructions of the palaeogeography of individual parasequence sets that demonstrate temporal and spatial evolution of facies associations and depositional processes. The results show that the Gallup is a mixed‐process‐controlled depositional system with fair‐weather and storm‐wave dominance, river influence and tide‐effect, contrasting with previous interpretations of a solely fair‐weather wave‐dominated environment. Depositional processes and the resultant facies change with sequence stratigraphic positions in response to relative sea‐level changes – particular facies are only deposited in certain systems tracts. Distinction and transition between non‐deltaic shorefaces and wave‐dominated deltas have also been documented in this study. Non‐deltaic shorefaces are characterized by homogeneous sandstones with a wide‐range bioturbation index and the absence of mudstones. Wave‐dominated deltas are subject to river influence and contain prodelta facies. This study shows the importance of detailed facies analysis with high‐resolution sequence stratigraphic control using outcrops for documenting sedimentary processes of shallow marine shoreline systems. [ABSTRACT FROM AUTHOR]