ALBERT

Description: The J sandstone comprises less than 46 m (151 ft) of sandstone-dominated strata within the mudrock-dominated lower Upper Cretaceous succession of northwestern Nebraska. The unit is a prolific hydrocarbon producer in this region (Denver-Julesburg Basin), but its lithostratigraphic and sequence-stratigraphic framework, critical for reservoir characterization and mapping, is poorly known. We have achieved an improved understanding of depositional history and sequence stratigraphy by describing and correlating cores and wireline logs from wells within Sioux, Dawes, and Box Butte counties, Nebraska, and Niobrara and Goshen counties, Wyoming. Coals, paleosols, fluvial or inner estuarine sandstones, estuarine mudstones, fluvial conglomerate, shoreface sandstone, and reworked volcanic fallout (bentonite) lithofacies were identified. Trace fossil assemblages representing stressed expressions of the Skolithos and Cruziana ichnofacies are common. These lithofacies are arranged vertically into three erosionally based cycles, each less than 28 m (92 ft) thick, and each grade upward from fluvial or inner estuarine sandstones into estuarine mudstones and in turn into shoreface sandstones. The lateral and vertical stacking patterns of the lithofacies are complex, however, and the upper cycles appear to fill space eroded into the underlying ones. Northeast-southwest-elongate isochore trends appear in all three cycles. Lithofacies transition downdip from inner estuarine sandstones in the northeast to estuarine basin mudstones and shoreface sandstones toward the southwest. Detrital mineralogy indicates an easterly (cratonic) provenance for the entire unit. Our data suggest that the J sandstone in northwestern Nebraska accumulated in wave-dominated estuarine settings, as part of a long-lived transgressive systems tract. The unit as a whole occupies a complexly incised landscape cut during a third-order lowstand ca. 98 Ma. Coeval cycles of similar magnitude throughout the Western Interior suggest that the three cycles represent eustatic fluctuations. The highest quality reservoirs occur at the base of the unit in inner estuarine lithofacies in the central and southwestern parts of the study area.

Description: Cretaceous low-accommodation deposits have been extensively studied in the subsurface of the Western Interior of North America because of their prolific hydrocarbon production and remaining potential. Understanding the stratigraphic complexities of these deposits in the subsurface relies strongly on detailed outcrop analogs. In this study, the Dakota Sandstone was examined along 100 km (62 mi) of semicontinuous outcrop between the towns of Hanksville and Ticaboo in the Henry Mountains of southeastern Utah. This region represented a low-accommodation setting located over the forebulge of the Cretaceous Western Interior Basin during accumulation of the unit. The Dakota Sandstone is 0 to 38 m (125 ft) thick, of Cenomanian age, and records multiple cycles of sediment accumulation. The Dakota Sandstone is subdivided into two condensed top-truncated stratigraphic sequences, the upper of which contains two parasequences. The basal parts of both sequences are composed of braided fluvial conglomerates and sandstone overlain by tidally influenced fluvial sandstone, inclined heterolithically stratified estuarine mudstone, carbonaceous shale, and coal. The overlying parasequences consist of coarsening-upward lower to upper shoreface mudstone, sandstone, tidal inlet deposits, and oyster shell concentrations. These facies define tripartite subdivisions of depositional environments typical of wave-dominated estuaries. The fluvial deposits may represent lowstand deposits, but overall sediments accumulated during transgressive systems tracts (TST). The parasequences recorded in the Henry Mountains are similar to the Dakota Sandstone of northwestern New Mexico and to high-frequency sequences identified in the Kaiparowits Plateau, approximately 80 km ([~]50 mi) to the southwest, which suggests eustatic driving mechanisms. The best potential for hydrocarbon reservoirs occurs in fluvial sandstones and conglomerates.

Description: The internal architecture and genetic-stratigraphic analysis of coastal-plain fluvial successions has applications to both academic understanding of continental-margin stratigraphy and to the economic evaluation of subsurface hydrocarbon and water reservoirs. Despite the abundance of exposed ancient examples of such coastal-plain to shallow marine transitions, however, the lateral facies changes and stratigraphic stacking patterns of such transitions remain largely unresolved in detail. This study presents a sedimentological and stratigraphic analysis of the Campanian Masuk Formation in the Henry Mountains syncline of Utah, western USA, and proposes a sequence-stratigraphic model to explain the geometries of fluvial-channel lithosomes found in the unit. At its type section, the Masuk Formation is an ~ 220-m-thick succession of interbedded sandstone, mudstone, and coal with minor intraformational breccias. Six facies are defined: Facies 1, coal and carbonaceous shale, records accumulation of organic sediments in coastal-plain mires; Facies 2, mudrock, records coastal-plain floodbasin settings; Facies 3, thinly interbedded sandstone and siltstone, represents estuarine-basin deposits with one interval of marine flooding; Facies 4, admixed siltstone-sandstone with intraformational breccia, represents chaotically filled coastal plain channels; Facies 5, interbedded sandstone-siltstone with inclined heterolithic stratification (IHS), records deposits of coastal-plain channels with variable sediment supply; and Facies 6, trough-cross-bedded sandstone, records sand-dominated coastal-plain channel deposits. Facies 4, 5, and 6 all show evidence of coastal and tidal influence on sediment accumulation (IHS, low-diversity trace-fossil assemblages, bimodal to bipolar paleocurrent distributions, mud drapes on small-scale sedimentary structures) to varying degrees. Facies analysis and tracing of key surfaces such as regionally extensive erosion surfaces (sequence boundaries) and flooding surfaces suggest that the entire Masuk Formation (and the uppermost part of the underlying Muley Canyon Sandstone) is a single depositional sequence. The typically multilateral channel bodies are traceable in a depositional strike direction over distances much greater than empirically calculated estimates of channel-belt width. This pattern suggests an allogenic control on stacking patterns. Multistory and multilateral channel bodies typically have a Facies 4 unit at the base, overlain by one or more stories of Facies 5, and in turn capped by Facies 6. This stacking pattern could reflect cycles of incision, initial lowstand channel filling, and subsequent backfilling of estuarine channels during transgressions. This pattern further hints at the possibility of preservation of high-frequency sequences nested within the longer-term sequence. This study provides new insights into the stacking patterns of coastal-plain fluvial successions and their interpretation.

Description: The Maritimes Basin of Atlantic Canada preserves a 12-km-thick stratigraphic succession deposited within a low-latitude, predominantly continental setting during the late Paleozoic. This paper examines the utility of using such successions for paleoclimate analysis, with specific reference to changes in fluvial style. Modern rivers in the subhumid and semiarid tropics preserve a suite of features that are distinct from those in humid and arid environments. These features include an abundance of sedimentary structures formed under Froude transcritical to supercritical flow conditions and the presence of in situ vegetation growing within the channel environment. This fluvial style is indicative of prolonged low-flow conditions punctuated by intense precipitation events in a strongly seasonal climatic setting. Fluvial channel bodies within the Maritimes Basin preserve a remarkably similar style compared with these modern systems, suggesting that a subhumid, strongly seasonal paleoclimate was the dominant imprint on parts of the preserved successions. Strongly seasonal deposits are concentrated within four discrete stratigraphic intervals (E1-E4), ranging in duration from 2 to 6 m.y. These intervals are correlated across the entire basin and between basins characterized by markedly different tectonic regimes, which suggests that a coherent regional climate signal is recorded. Intervals are separated by deposits characteristic of humid and arid river systems, and the alternation between these different fluvial styles implies that several pronounced, long-term changes in precipitation and runoff regimes occurred during the Carboniferous within the region. Furthermore, these intervals broadly coincide with major periods of Southern Hemisphere glaciation, which suggests that glaciation had a profound and controlling effect on paleotropical climate.

Description: Tectonic forcing of stratigraphic architecture is likely in foreland basins. Tectonic driving forces are increasingly being invoked to explain stratigraphic patterns in the Cretaceous Western Interior Seaway Basin of North America, yet the evidence is largely circumstantial, and the details of driving forces remain elusive. In this paper I show direct stratigraphic evidence for syndepositional growth of a structural arch with at least 50 m of relief during accumulation of the upper Turonian Ferron Sandstone in south-central Utah, United States. Progressive growth of the arch was superimposed on several high-frequency stratal cycles that were driven by a more regionally extensive process (geodynamic or eustatic) and that produced laterally amalgamated sandstone bodies in a depositional strike-parallel orientation (north-south). All of this stratigraphy was then truncated by a more or less planar erosion surface (sequence boundary) that can be traced physically over at least 67 km north-south. This surface was later tilted northward, such that the upper member of the Ferron Sandstone thins progressively southward from 50 to 10 m over 67 km. The facies juxtapositions revealed by the Ferron Sandstone could, if seen in exposure of limited lateral extent, be wrongly interpreted as recording regionally extensive relative sea-level drops and potentially used in error as evidence for substantial eustatic sea-level falls during the Turonian. The folding and tilting documented in this study can be clearly attributed to geodynamic and/or tectonic driving forces, likely related to migration of a forebulge.

Description: The J sandstone comprises less than 46 m (151 ft) of sandstone-dominated strata within the mudrock-dominated lower Upper Cretaceous succession of northwestern Nebraska. The unit is a prolific hydrocarbon producer in this region (Denver-Julesburg Basin), but its lithostratigraphic and sequence-stratigraphic framework, critical for reservoir characterization and mapping, is poorly known. We have achieved an improved understanding of depositional history and sequence stratigraphy by describing and correlating cores and wireline logs from wells within Sioux, Dawes, and Box Butte counties, Nebraska, and Niobrara and Goshen counties, Wyoming. Coals, paleosols, fluvial or inner estuarine sandstones, estuarine mudstones, fluvial conglomerate, shoreface sandstone, and reworked volcanic fallout (bentonite) lithofacies were identified. Trace fossil assemblages representing stressed expressions of the Skolithos and Cruziana ichnofacies are common. These lithofacies are arranged vertically into three erosionally based cycles, each less than 28 m (92 ft) thick, and each grade upward from fluvial or inner estuarine sandstones into estuarine mudstones and in turn into shoreface sandstones. The lateral and vertical stacking patterns of the lithofacies are complex, however, and the upper cycles appear to fill space eroded into the underlying ones. Northeast-southwest–elongate isochore trends appear in all three cycles. Lithofacies transition downdip from inner estuarine sandstones in the northeast to estuarine basin mudstones and shoreface sandstones toward the southwest. Detrital mineralogy indicates an easterly (cratonic) provenance for the entire unit. Our data suggest that the J sandstone in northwestern Nebraska accumulated in wave-dominated estuarine settings, as part of a long-lived transgressive systems tract. The unit as a whole occupies a complexly incised landscape cut during a third-order lowstand ca. 98 Ma. Coeval cycles of similar magnitude throughout the Western Interior suggest that the three cycles represent eustatic fluctuations. The highest quality reservoirs occur at the base of the unit in inner estuarine lithofacies in the central and southwestern parts of the study area. Jonathan Antia received his Ph.D. in geology from the University of Nebraska-Lincoln in 2009. He currently works as staff geologist at Core Laboratories in Houston, Texas. His academic research focused on coastal to shallow-marine siliciclastic depositional systems. Chris Fielding holds the Mr. & Mrs. J. B. Coffman Chair in Sedimentary Geology at the University of Nebraska-Lincoln. He received his Ph.D. from the University of Durham (United Kingdom) in 1982 and previously worked for BP Exploration and the University of Queensland in Brisbane, Australia. He is currently president-elect of SEPM. His research interests lie in the stratigraphy of continental, coastal, and shallow-marine successions. R. Matthew Joeckel is a professor in the School of Natural Resources and Department of Earth and Atmospheric Sciences at the University of Nebraska-Lincoln. He received his Ph.D. from the University of Iowa in 1993. His research interests include Pennsylvanian and Cretaceous stratigraphy, continental depositional environments and sedimentary successions, weathering processes, and paleosols.

Description: Cretaceous low-accommodation deposits have been extensively studied in the subsurface of the Western Interior of North America because of their prolific hydrocarbon production and remaining potential. Understanding the stratigraphic complexities of these deposits in the subsurface relies strongly on detailed outcrop analogs. In this study, the Dakota Sandstone was examined along 100 km (62 mi) of semicontinuous outcrop between the towns of Hanksville and Ticaboo in the Henry Mountains of southeastern Utah. This region represented a low-accommodation setting located over the forebulge of the Cretaceous Western Interior Basin during accumulation of the unit. The Dakota Sandstone is 0 to 38 m (125 ft) thick, of Cenomanian age, and records multiple cycles of sediment accumulation. The Dakota Sandstone is subdivided into two condensed top-truncated stratigraphic sequences, the upper of which contains two parasequences. The basal parts of both sequences are composed of braided fluvial conglomerates and sandstone overlain by tidally influenced fluvial sandstone, inclined heterolithically stratified estuarine mudstone, carbonaceous shale, and coal. The overlying parasequences consist of coarsening-upward lower to upper shoreface mudstone, sandstone, tidal inlet deposits, and oyster shell concentrations. These facies define tripartite subdivisions of depositional environments typical of wave-dominated estuaries. The fluvial deposits may represent lowstand deposits, but overall sediments accumulated during transgressive systems tracts (TST). The parasequences recorded in the Henry Mountains are similar to the Dakota Sandstone of northwestern New Mexico and to high-frequency sequences identified in the Kaiparowits Plateau, approximately 80 km (∼50 mi) to the southwest, which suggests eustatic driving mechanisms. The best potential for hydrocarbon reservoirs occurs in fluvial sandstones and conglomerates. Jonathan Antia received his Ph.D. in geology from the University of Nebraska-Lincoln in 2009. He currently works as a staff geologist at Core Laboratories in Houston, Texas. His academic research focused on coastal to shallow marine siliciclastic depositional systems. Chris Fielding holds the Mr. & Mrs. J.B. Coffman Chair in sedimentary geology at the University of Nebraska-Lincoln. He received his Ph.D. from the University of Durham (United Kingdom) in 1982 and previously worked for BP Exploration and the University of Queensland in Brisbane, Australia. His research interests lie in the stratigraphy of continental, coastal, and shallow marine successions.