Tectonic and eustatic control of Mesaverde Group (Campanian−Maastrichtian) architecture, Wyoming-Utah-Colorado region, USA

We describe and analyze the depositional history and stratigraphic architecture of the Campanian and Maastrichtian succession of the southern greater Green River basin of Wyoming, USA, and surrounding areas to better understand the interplay between tectonic and eustatic drivers that built the stratigraphy. By integrating new measured sections with published outcrop, well-log, and paleogeographic data, two new stratigraphic correlation diagrams, 35 new paleogeographic reconstructions, and six new tectonic diagrams were created for this part of the Western Interior Seaway. From this work, two time-scales of organization are evident: (1) 100−300 k.y.-scale, mainly eustatically driven regressive-transgressive shoreline oscillations that generated repeated sequences of alluvial-coastal plain-shoreline deposits, passing basinward to subaqueous deltas, then capped by transgressive estuarine/barrier lagoon deposits, and (2) 3.0−4.0 m.y.-scale, tectonically driven groups of 10 to 15 of these eustatically driven units stacked in an offset arrangement to form larger clastic units, which are herein referred to as clastic wedges. Four regional clastic wedges are recognized, based on the architectures of these clastic packages. These are the: (1) Adaville, (2) Rock Springs, (3) Iles, and (4) Williams Fork clastic wedges. Pre-Mesaverde deposition in the Wyoming-Utah-Colorado (USA) region during the Middle Cretaceous was characterized by thickening of the clastic wedge close to the thrust-front, driven primarily by retroarc foreland basin (flexural) tectonics. However, a basinward shift in deposition during the Santonian into the early Campanian (Adaville clastic wedge) signaled a change in the dominant stratigraphic drivers in the region. Shoreline advance accelerated in the early to middle Campanian (Rock Springs clastic wedge), as the end of activity in the thrust belt, growing importance of flat-slab subduction, and steady eastward migration of the zone of dynamic subsidence led to loss of the foredeep and forebulge, with the attendant formation of a low-accommodation shelf environment. This “flat-shelf” environment promoted large shoreline advances and retreats during sea-level rise and fall. During the middle to late Campanian (Iles clastic wedge), deep erosion on the crest of the Moxa Arch, thinning on the crests of the Rock Springs and Rawlins uplifts, and subsequent Laramide-driven basin formation occurred as the Laramide blocks began to partition the region. The next clastic package (Williams Fork clastic wedge) pushed the shoreline over 400 km away from the thrust belt during the late Campanian. This was followed by a very large and persistent marine transgression across the region, with the formation of a Laramide-driven deepwater turbidite basin with toe-of-slope fans into the early Maastrichtian. The Mesaverde Group in the Wyoming-Utah-Colorado region is thus characterized by: (1) a succession of four tectonically driven classic wedges, each comprised of a dozen or so eustatically driven packages that preserve large basinward and landward shoreline shifts, (2) broad regional sand and silt dispersal on a low-accommodation marine shelf setting, (3) a progressive, tectonically driven, basinward shift of deposition with offset, basinward stacking of successive clastic wedges, and (4) the gradual formation of various uplifts and sub-basins, the timing and sizes of which were controlled by the movement of deep-seated Laramide blocks. The Mesaverde Group in the Wyoming-Utah-Colorado region provides an outstanding opportunity to study the dynamic interaction among the tectonic control elements of a subducting plate (crustal loading-flexure, dynamic subsidence/uplift, and regional flat-slab basin partitioning), as well as the dynamic interaction of tectonic and eustatic controls.

Risk of groundwater contamination widely underestimated because of fast flow into aquifers

Groundwater pollution threatens human and ecosystem health in many regions around the globe. Fast flow to the groundwater through focused recharge is known to transmit short-lived pollutants into carbonate aquifers, endangering the quality of groundwaters where one quarter of the world’s population lives. However, the large-scale impact of such focused recharge on groundwater quality remains poorly understood. Here, we apply a continental-scale model to quantify the risk of groundwater contamination by degradable pollutants through focused recharge in the carbonate rock regions of Europe, North Africa, and the Middle East. We show that focused recharge is the primary reason for widespread rapid transport of contaminants to the groundwater. Where it occurs, the concentration of pollutants in groundwater recharge that have not yet degraded increases from <1% to around 20 to 50% of their concentrations during infiltration. Assuming realistic application rates, our simulations show that degradable pollutants like glyphosate can exceed their permissible concentrations by 3 to 19 times when reaching the groundwater. Our results are supported by independent estimates of young water fractions at 78 carbonate rock springs over Europe and a dataset of observed glyphosate concentrations in the groundwater. They imply that in times of continuing and increasing industrial and agricultural productivity, focused recharge may result in an underestimated and widespread risk to usable groundwater volumes.

Performance of Sweetpotato Varieties Grown Using Black Plastic Mulch in Pennsylvania

Sweetpotato (Ipomoea batatas) production in Pennsylvania and the northeastern United States has been increasing steadily. The performance of eight commercially available sweetpotato varieties and two unreleased accessions grown on raised beds and covered with black plastic mulch in Pennsylvania was evaluated. All varieties and accessions were evaluated in 2 successive years (2018 and 2019) at Rock Springs, PA. There were statistically significant differences in total marketable yield (TMY), but not in all yield components in both years. ‘Orleans’, ‘Beauregard’, ‘Averre’, and ‘Covington’ consistently produced high marketable yields and suitable U.S No.1 grade storage roots. ‘Bonita’ (tan skin/white flesh) and ‘Carolina Ruby’ [red skin/orange flesh (OF)] produced consistent yields in both years (range, 330–430 bushels/acre; 50-lb bushel). NC413 [purple skin (PS)/purple flesh (PF)] produced the lowest yield in 2018 and was discarded for future trials. In 2019, NCP13-0030 (PS/PF) produced good yields and shapes comparable to OF varieties. Overall total yields (TYs) measured in this study compared satisfactorily with average nationwide yields, with several varieties producing more than 500 bushels/acre.

Experimental investigation of the effect of compliant pores on reservoir rocks under hydrostatic and triaxial compression stress states

The presence of compliant pores in rocks is important for understanding the stress–strain behaviors under different stress conditions. This paper describes findings on the effect of compliant pores on the mechanical behavior of a reservoir sandstone under hydrostatic and triaxial compression. Laboratory experiments were conducted at reservoir temperature on Weber Sandstone samples from the Rock Springs Uplift, Wyoming. Each experiment was conducted at three sequential stages: (stage 1) increase in the confining pressure while maintaining the pore pressure, (stage 2) increase in the pore pressure while maintaining the confining pressure, and (stage 3) application of the deviatoric load to failure. The nonlinear pore pressure – volumetric strain relationship governed by compliant pores under low confining pressure changes to a linear behavior governed by stiff pores under higher confining pressure. The estimated compressibilities of the matrix material in sandstone samples are close to the typical compressibility of quartz. Because of the change in pore structures during stage 1 and stage 2 loadings, the estimated bulk compressibilities of the sandstone sample under the lowest confining pressure decrease with increasing differential pressure. The increase in crack initiation stress is limited with increasing differential pressure because of similar total crack length governed by initial compliant porosity in sandstone samples.

Subsurface Reinterpretation of Ordovician and Devonian Strata in Southwest Wyoming with Implications for Upwarping Across the Transcontinental Arch

A new interpretation of the subsurface geometries of the Ordovician Bighorn Dolomite and overlying Devonian strata across southwestern Wyoming arises from revising the stratigraphy in a core from the Mountain Fuel Supply UPRR #11–19–104–4 well drilled on the crest of the Rock Springs Uplift in 1962. One of only a few wells to penetrate all or part of the Lower Paleozoic succession in the subsurface of southwestern Wyoming, the well was almost continuously cored through the Devonian–Cambrian succession. From a reinterpretation of the stratigraphy in the core, 22 ft of Bighorn Dolomite is recognized based on the characteristic Thalassinoides bioturbation fabric in skeletal dolowackestone typical of Late Ordovician subtidal carbonate facies ranging from Nevada to Greenland along the western margin of the Great American Carbonate Bank. This lithology is in complete contrast with the alternating dolomitic flat-pebble conglomerate and dolomudstone of the underlying Cambrian Gallatin Limestone and the cyclical units of brecciated anhydritic dolomudstone and quartzose sandstone of the overlying Devonian Lower Member of the Jefferson Formation. Stratigraphic re-interpretation yields insights regarding Ordovician–Devonian stratal geometries across southwestern Wyoming. More widespread than previously portrayed, the Bighorn Dolomite pinches out on the eastern flank of the Rock Springs Uplift. Similar to past interpretations, Devonian strata pinch out east of the Rock Springs Uplift at Table Rock Field. A true-geometry multi-datumed stratigraphic cross section yields insights not obtainable by mapping. Regionally, top truncation of stratigraphic units below the base-Madison Limestone unconformity normally progresses stratigraphically deeper eastward. However, in southwestern Wyoming, the Devonian Lower Member of the Jefferson Formation overlaps the older Bighorn Dolomite by marked onlap across the Rock Springs Uplift and then pinches out by top truncation/onlap near Table Rock Field, forming an “abnormal” overlap relationship along the northern margin of the Transcontinental Arch. The underlying Bighorn Dolomite shows little to no onlap onto the underlying Cambrian section, but is markedly top truncated below the Lower Member of the Jefferson Formation. Comparing proportions of onlap versus top truncation for the two formations constrains the timing of two successive upwarping episodes along the northern margin of the Transcontinental Arch across southwestern Wyoming. The first is arguably Middle Devonian, and the second spans the Devonian–Mississippian boundary. Two subtle and different angular unconformities created by these two episodes imply a persistent fold or tilt axis that sequentially was reactivated along the northern margin of the Transcontinental Arch in southwestern Wyoming.

Source to sink sandstone-mudstone proportion and facies distribution across a third-order clastic wedge, Cretaceous Western Interior Seaway

The Iles Clastic Wedge is a 500 m thick, 3 My duration, third-order sequence that built out eastward in the Cretaceous Western Interior Seaway. The wedge also contains high-frequency regressive-to-transgressive sequences that are irregularly stacked in a basinward-stepping pattern (lower limb) and in a landward-stepping pattern (upper limb). The entire wedge and the component cycles were analyzed in terms of vertically monitored sandstone-mudstone proportion, thickness, and facies distribution. The measured profiles through the Iles Clastic Wedge form a 300 km long, source-to-sink transect from southeast Rock Springs uplift, Wyoming to Kremmling, Colorado. The sandstone proportion in the entire wedge (and also in the basinward-stepping half of the wedge) attains a maximum in the proximal reaches (fluvial and tidal-fluvial/estuarine channels) of the study transect and decreases unsteadily toward the medial and distal zone. A slight secondary increase in sand proportion also appears irregularly in the medial shoreline zone. On the other hand, the sandstone proportion in the landward-stepping half of the wedge reaches a maximum in the medial (tidal-fluvial and estuarine channels and delta-front) to distal zone (basinal regressive delta) of the wedge and decreases slightly sourceward. Along individual fourth-order sequences, the sandstones and mudstones indicate a more nuanced partitioning, with three marked sandstone maxima (proximal, medial, and distal zones), separated by zones with abundant mudstone. These sandstone peaks are produced by the presence of fluvial and tidal-fluvial/estuarine channel sandstones in the most proximal zone, delta front/shoreface in the medial reaches, and basinal regressive delta front in the distal zone. The mudstone peaks represent the muddy, coal-bearing coastal plain and the prodelta area. This accentuated sandstone and mudstone partitioning at shorter time scales (few 100 Ky) becomes blurred at the longer time scale (3 My) because of the progressive basinward, then landward, offset of successive high-frequency sequences that form the larger clastic wedge.