Midcontinental United States Research Articles

Tracing the Origin of Metal Ions in Mississippi Valley-Type Ore Deposits: Constraints from Lead Isotope Studies of Black Shales from the Midcontinent United States

Tracing the Origin of Metal Ions in Mississippi Valley-Type Ore Deposits: Constraints from Lead Isotope Studies of Black Shales from the Midcontinent United States

Holocene insolation and sea surface temperature influences on the polar front jet stream and precipitation in the midcontinental United States

Variability in the source and seasonality of precipitation in the midcontinental United States during the Holocene was investigated using isotopic and sedimentological data from Martin Lake, northeastern Indiana, USA. Between 7100 and 4000 years before present (yr BP; present = 1950 CE), high δ18Ocal and δ13Ccal values with low variability indicate that moisture was predominantly derived from subtropical, southerly sources and delivered primarily during the warm season. Mean state shifts toward lower δ18Ocal and δ13Ccal occurred at ca. 4000 and 2550 yr BP, respectively, indicating an increase in northerly-sourced cold-season precipitation during the Late Holocene (i.e., the past 4200 years) and a subsequent reduction in warm season duration after 2550 yr BP. Record low %lithics from ca. 5000 to 4000 yr BP indicates major reductions in warm-season rain storms, consistent with regional evidence of drought at this time. An increase in the amplitude of centennial-scale variability in δ18Ocal, δ13Ccal, and %lithics after 1900 yr BP indicates greater precipitation source variability during the Common Era. During this interval, precipitation fluctuated between southerly-sourced, convective rainstorms when the Northern Hemisphere (NH) was warm (e.g., during the Medieval Climate Anomaly; 700–1000 yr BP) and northerly-sourced rain and snow when the NH was cool (e.g., during the Little Ice Age; 150–550 yr BP). These trends, especially the change at ca. 4000 yr BP, are consistent with other North American paleoclimate records that collectively suggest a continental-scale shift in precipitation seasonality during the Middle to Late Holocene transition as the tropical Pacific Ocean transitioned from La Niña-like conditions to a more El Niño-like mean state. Concurrent NH cooling and persistent El Niño-like conditions during the Late Holocene would have favored a southerly polar front jet stream with enhanced ridge and trough atmospheric circulation over North America – conditions resembling the positive mode of the Pacific-North American teleconnection (PNA). This would have increased interactions between high-latitude and subtropical airmasses over the midcontinent, increasing the proportion of northerly precipitation with low δ18O delivered during the cold season (i.e., snowfall) and during extended periods with +PNA-like atmospheric circulation (e.g., the Little Ice Age).

Caught out in the cold: Anas platyrhynchos (Mallard) survival decreased during an extreme climatic event

Abstract Extreme climatic events (ECEs) can have profound impacts on individual fitness, affecting survival directly or indirectly. Late winter ECEs may be especially detrimental to fitness due to limited food resources and increased energetic requirements during this time. A polar vortex disruption ECE descended upon the mid-continental United States during February 7–20, 2021 with temperatures as low as −29°C in areas concurrent with ongoing research on Anas platyrhynchos (Mallard) movement ecology and survival in Arkansas, Louisiana, and Tennessee, United States spanning winters 2019–2022. Therefore, we opportunistically evaluated the effects of individual characteristics and latitude on daily survival during the ECE. We extended the survival analysis to March to test for lasting effects of the ECE on survival. We tracked 181 Global Positioning System (GPS)-marked A. platyrhynchos during February 2020, 256 in February 2021, and 324 in February 2022. We documented 22 mortalities during the February 2021 ECE (i.e., 9%), but only 6 mortalities during February 2020 (i.e., 2%) and 2022 (i.e., 1%) when conditions were average. February survival (e.g., 28-day survival) during the ECE was 0.908 (85% CI: 0.879–0.937) but was 0.982 (85% CI: 0.973–0.991) during the 2 non-ECE Februaries. The ECE effect on survival was isolated to February and did not affect March survival. Anas platyrhynchos was 5.4 times more likely to die during the ECE in 2021 compared to non-ECE Februaries. Although large-bodied waterfowl appear cold-tolerant and less sensitive to polar vortex disruptions compared to smaller-bodied passerines, direct mortalities can occur if conditions are severe enough and persist, highlighting the need to consider the influence of ECEs on common, seemingly robust species in future global climate change scenarios.

Paleoenvironmental constraints on Paleozoic shale deposition in the midcontinent United States

Paleoenvironmental constraints on Paleozoic shale deposition in the midcontinent United States

Long-chain plant wax n-alkane hydrogen isotopic evidence for increased Little Ice Age aridity in the midcontinental United States

Long-chain plant wax n-alkane hydrogen isotopic evidence for increased Little Ice Age aridity in the midcontinental United States

Constraining the provenance of black shales using rare earth elements and neodymium isotopes, Midcontinent United States

We conducted research to determine neodymium model dates (TDM), εNd values, and the relative proportions of rare earth elements (REEs) of Paleozoic black shales from the Midcontinent United States to constrain their sediment sources. Twenty-one Cambrian to Pennsylvanian shale formations of the Illinois, Cherokee, Forest City, and Arkoma basins, the Ozark Dome, and the Ouachita Mountains were examined. Findings reveal that these midcontinental shales consist primarily of felsic detrital minerals that originated from the craton. The Cambrian Mt. Simon, Eau Claire, and Tunnel City shales of the northern Illinois Basin exhibit REE patterns and Nd isotopic signatures similar to those of the Ordovician Mazarn and Womble shales of the Ouachita Mountains, which indicates derivation from a similar sediment source. Sediment was likely derived from the Superior and/or Trans-Hudson cratonic provinces. The dominant sediment source shifted during deposition of the Middle Ordovician Womble Shale due to the uplift of the Appalachian Mountains during the Taconic orogeny, as suggested by the younger TDM dates, less negative εNd values, and similar REE patterns compared to those of the older Cambrian and Early Ordovician shales. The Grenville province and Appalachian Basin remained the primary sediment source into the Pennsylvanian.

Slips, films, and material choice: Long-distance hydrothermal pigments on Middle Mississippian red ware

Using laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) and Raman spectroscopy, we investigate red pigment applied to ceramic vessels as a slip or film (pigment + liquid + binder mixture) in the midcontinental United States. We find that during the CE 1000–1200 period, potters at Cahokia and nearby sites in the American Bottom region of the Middle Mississippi Valley used pigments originating from hydrothermal deposits. The closest hydrothermal deposits are located over 50 km away in the Ozark Highlands and the pigments may have been collected from areas already exploited for other resources. Approaching slips or films as pigment + liquid + binder mixtures integrates ceramic raw materials research with pigment research and encourages us to consider a variety of pigment options, some of which require binders for use on ceramics.

Common, showy, and perennial species dominate a restoration species pool

Native seed vendors are a primary source of germplasm for restoration projects; however, most plant species are not commercially available. Preferences in the types of species that vendors grow and sell may limit the similarity between reference communities and reconstructed ones established from seed mixes. We tested whether a restoration species pool shows preference for certain groups of species, focusing on the Ozark Highland Ecoregion (midcontinent United States). We identified the pool of 1,082 candidate herbaceous plant species appropriate for restoration projects on upland habitats in this region, and then surveyed nine regional seed vendors to assess their commercial availability. Commercially available species were more likely to be forbs over graminoids, perennials over annuals, and common species with larger ranges and moderate conservatism scores. Within forbs, taller species and those with longer bloom durations were favored. Species with affinity to open habitats (e.g. grassland) were more likely to be available from multiple vendors than those from woodlands and forests. Encouragingly, 454 (42%) of the species in this regional pool were available. However, this means that most species in the region are not likely to be included in seed mixes, unless they are hand‐collected from remnant populations. This restoration pool favors common and showy species, which is consistent with previous studies showing these kinds of species tend to dominate seed mixes and restored plant communities. We identified 39 species that were not available from any of the vendors surveyed, which we recommend as candidates for expansion of the Ozark restoration species pool.

Conodont biostratigraphy of a Carboniferous–Permian boundary section in siliceous successions of pelagic Panthalassa revealed by X-ray computed microtomography

Pelagic deep-sea siliceous successions in accretionary complexes preserve precious records of a vast deep seafloor that is now lost due to plate subduction. Microfossils are the key means of age assignment of these successions, but poor preservation due to tectonic deformation and metamorphism at the subduction zone hamper biostratigraphic records. X-ray computed microtomography, while not widely used in biostratigraphic studies until now, allows us to visualize fossils that are impossible or difficult to extract from host rocks due to poor preservation. In this study, we applied this method on conodonts from a pelagic chert–claystone succession in Okoshizawa, Iwaizumi Town, Northeast Japan, using a laboratory-based X-ray microscope. This work is a first close look at conodont biostratigraphy across the Carboniferous–Permian boundary in pelagic deep Panthalassa. We identified conodonts including ten species that are used as zonal markers in intensely studied areas such as around the East European Platform and Midcontinent United States. Based on the occurrence of conodonts, the studied section in Okoshizawa was correlated to the lower Moscovian to middle Artinskian. Confirmation of Moscovian to Artinskian age diagnostic conodonts from pelagic Panthalassa strengthens their role as global biostratigraphic indicators. By identifying more numerous specimens compared to the conventional hydrofluoric acid dissolution method, we were able to obtain information about conodont faunal characteristics around the Carboniferous–Permian boundary in pelagic deep areas of Panthalassa. The dominant taxa changed from Streptognathodus to Mesogondolella in the middle Asselian, probably reflecting an ecological takeover by the latter in the deep waters.

Accelerating declines of North America’s shorebirds signal the need for urgent conservation action

Abstract Shorebirds are declining to a greater extent than many other avian taxa around the world. In North America, shorebirds, along with aerial insectivores and grassland birds, have some of the highest proportions of declining species of any group. Here, we apply a new hierarchical Bayesian model to analyze shorebird migration monitoring data from across North America, from 1980 to 2019, and present the most recent available estimates of trends for 28 species. Point estimates for survey-wide trends in abundance were negative for 26 of 28 species (93%). Despite challenges with low precision associated with migration count data, trends for 19 species had 95% credible intervals that were entirely negative. More than half of the species were estimated to have lost >50% of their abundance. Furthermore, estimated rates of decline have accelerated during the last three generations for most species. Point estimates of trend were more negative for 18 species (64%) during the most recent three-generation period in comparison to the previous three-generation period. Many species now exceed international criteria for threatened species listing. The analytic approach used here allows us to model regional variation in trends, although survey coverage and strength of inference were greatest in the eastern portions of North America (east of 100°W). We found the greatest declines at staging sites along the Atlantic Coast from North Carolina to Nova Scotia, and lesser declines along the Gulf Coast and in the midcontinental United States. The declines in shorebird populations reported here are worrisome and signal the urgent need for conservation action. In addition, it would be beneficial to validate these results through the collection and analysis of complementary data, and to initiate demographic studies throughout the annual cycle to determine where and when declines are most likely to originate. This improved information will allow for the development of more targeted efforts to reverse declines through conservation action.

Fluvial responses to late Holocene hydroclimate variability in the midcontinental United States

Long-term relationships between mean-state climatic conditions and flood frequencies in the midcontinental United States (US) are not well established because instrumental records of fluvial processes are limited to the current warm period (CWP; the last ca. 150 years) and continuous paleo-flood records are exceedingly rare. Here, we investigate climate-flood relationships in the midcontinental US by reconstructing flood frequencies at Half Moon Pond, a 1600-year-old oxbow lake on the lower White River, Indiana (watershed = ca, 29,000 km2). We used sediment accumulation rates and clastic fluxes constrained by high-resolution radiocarbon (14C) dating. Frequent flooding, as indicated by high sedimentation rates and clastic fluxes to Half Moon Pond, occurred leading up to and during the Medieval Climate Anomaly (MCA; 950–1250 CE) when paleoclimate records suggest the predominance of ocean-atmosphere mean states resembling the negative phases of the Pacific Decadal Oscillation (-PDO-like) and Pacific North American Mode (-PNA-like). Reductions in sedimentation rates and clastic fluxes, indicating reduced flooding, subsequently occurred during the transition out of the MCA and into the Little Ice Age (LIA; 1250–1830 CE) as ocean-atmosphere conditions shifted to + PDO-like and +PNA-like mean states. Sedimentation rates and clastic fluxes increased again after ca. 1800 CE, indicating increased flooding during the CWP as ocean-atmosphere conditions returned to -PDO-like and -PNA-like mean states. The White River trends were notably antiphased with sedimentation-rate-based flood frequencies for the lower Ohio River (500,000 km2 watershed) prior to 1830 CE. This antiphased relationship is consistent with flooding in moderate to small watersheds in the Midwest being sensitive to the occurrence of rainstorm events, which were more frequent leading up to and during the MCA, and flooding in large watersheds being more sensitive to large spring melts associated with extensive snowpacks, which characterized the LIA. That both the White and Ohio rivers experienced their most frequent flooding during the CWP suggests deforestation and changing land use practices increased flooding on Midwestern watersheds across scales despite a current climatic mean state that in the past only resulted in increased flooding on moderate to small watersheds. Continued increased in midcontinental rainfall are therefore likely to enhance the occurrence of floods in Midwestern watersheds across different geographic scales.

Nonlinear multidecadal trends in organic matter dynamics in Midwest reservoirs are a function of variable hydroclimate

AbstractDissolved organic matter (DOM) and particulate organic matter (POM) can influence biogeochemical processes in aquatic systems. An understanding, however, of the source, composition, and processes driving inland reservoir organic matter (OM) cycling at a regional scale over the long term is currently unexplored. Here, we quantify decadal patterns (> 20 yr) of DOM quantity and composition and POM in 40 reservoirs in the midcontinent United States. We built 184 Random Forest models to identify how the relative influence of watershed characteristics and limnological parameters on OM dynamics may vary over time and in synchrony with hydroclimatic anomalies. The reservoir OM quantity and composition varied nonmonotonically through time and in contrast to lake browning observed in the northern hemisphere. Reservoir DOM composition switched from humic and aromatic during wet summers to aliphatic, potentially autochthonous DOM during particularly prolonged dry summers in the mid‐2000s. The shift in reservoir DOM quantity and composition could be attributed to the change in time‐varying control of watershed and limnological factors mediated by the hydroclimatic conditions. Watershed control (e.g., percent crops) was predominant during wet summers, while the effect of reservoir morphology (e.g., maximum depth) and water quality parameters (e.g., Secchi depth, chlorophyll a) were evident during dry summers. Thus, future predictions of drier conditions may promote “greening” with negative implications for reservoir water quality and treated drinking water. Considering the nonlinear nature of reservoir OM dynamics and its controls will help to better mitigate water quality issues in these constructed systems increasingly impacted by global changes.

CO2 Pipeline risk assessment and comparison for the midcontinent United States

A comprehensive quantitative risk assessment for the construction and operation of CO2 transportation networks considered for the Midcontinent United States was conducted. The results showed risks associated with CO2 pipelines were significantly less than those of other pipeline types. The assessment used four conceptual pipelines of different lengths to discuss risks operators may see. The assessment evaluated the risk associated with construction and operation using data from the US Occupational Safety Health Administration to determine the risk of injury or death for pipeline workers and data from the US Pipeline and Hazardous Materials Safety Administration for CO2, natural gas distribution, natural gas transmission/gathering, and non-CO2 hazardous liquid pipelines to develop quantitative likelihood and severity values leading to risk values. The data for the assessment covered incidents from 2010 to 2017 for CO2 pipelines. The average risk for construction and 30 years of operation for four CO2 pipeline configurations ranging between 79 and 1,546 miles in length was found. The construction and operational risk averaged between $1,400,521 (approximately $0.02/tonne of CO2) for the shorter pipeline (79 miles) and $27,481,939 (approximately $0.10/tonne of CO2) for a longer pipeline (1,546 miles). The largest risks of fatality for CO2 pipelines comes from vehicle transport. The largest operational risk to the pipeline was due to leakage. Public pipeline opposition is also a significant risk; it was not quantified but is addressed.

A Trophic Cascade Following the Introduction of an Omnivorous Fish, Dorosoma cepedianum, in a Mid-continental Reservoir (Mozingo Studies IV)

Mozingo Lake, a reservoir in the mid-continental United States, was sampled 63 times between January 1999 and October 2015. Prior to 2005, phytoplankton biovolume was largely composed of Cryptomonas and cyanobacteria (mostly Aphanizomenon); these taxa correlated with the abundance of Daphnia and juvenile copepods, and were also influenced by competition between cyanobacteria and bacillariophytes. These relationships suggest the zooplankton community was primarily controlled by bottom-up processes during this time. In 2005, gizzard shad (Dorosoma cepedianum) first appeared in the lake, coinciding with the first spined and helmeted forms of Daphnia as well as their decline from 39% to 3% of zooplankton; the relative abundance of juvenile copepods increased concurrently. By 2007 phytoplankton biovolume had decreased by 88%. Although all phytoplankton phyla declined in absolute abundance, some were more heavily impacted. The relative abundance of Aphanizomenon declined from 50% to 6% of the phytoplankton biovolume; Cryptomonas remained common, but bacillariophytes became codominant. Despite the steep decline in phytoplankton biovolume, several important trophic interactions did not change: phytoplankton biovolume continued to control juvenile copepods, and competition continued between cyanobacteria and bacillariophytes. Although juvenile copepods continued to compete with Daphnia, the scarcity of the latter allowed a relative expansion of juvenile copepods and bacillariophytes. Because very few of the standard parameters correlated with phytoplankton, it seems likely that most of the changes were caused by the introduction of gizzard shad, which is an intense consumer of cyanobacteria and Daphnia. Gizzard shad likely initiated a trophic cascade both directly (through consumption) and indirectly (by shifting competition). Although other factors may have played a role, it seems clear that the introduction of gizzard shad can cause dramatic changes in both the zooplankton and phytoplankton communities by altering species relationships in top-down, bottom-up, as well as lateral control processes.

Severe Little Ice Age drought in the midcontinental United States during the Mississippian abandonment of Cahokia

Drought has long been suspected as playing an important role in the abandonment of pre-Columbian Native American settlements across the midcontinental United States between 1350 and 1450 CE. However, high-resolution paleoclimatic reconstructions reflecting local effective moisture (the ratio of precipitation to evaporation) that are located in proximity to Mississippi period (1050–1450 CE) population centers are lacking. Here, we present a 1600-year-long decadally resolved oxygen isotope (δ18O) record from Horseshoe Lake (Collinsville, IL), an evaporatively influenced oxbow lake that is centrally located within the largest and mostly densely populated series of Mississippian settlements known as Greater Cahokia. A shift to higher δ18O in the Horseshoe Lake sediment record from 1200 to 1400 CE indicates that strongly evaporative conditions (i.e., low effective moisture) were persistent during the leadup to Cahokia’s abandonment. These results support the hypothesis that climate, and drought specifically, strongly impacted agriculturally based pre-Columbian Native American cultures in the midcontinental US and highlights the susceptibility of this region, presently a global food production center, to hydroclimate extremes.

Late Paleozoic (Late Mississippian–Middle Permian) sediment provenance and dispersal in western equatorial Pangea

Late Mississippian to middle Permian sediment-dispersal networks of regional to continental scale in western equatorial Pangea, depicted here in a series of paleogeographic maps, developed in response to temporally and spatially changing influences of climate, eustasy, and a continent-wide late Paleozoic orogenic system. The orogenic system included linked Alleghanian, Ouachita-Marathon-Sonora collisional belts and associated foreland basin systems on Laurentia and magmatic arcs on Gondwana, intracratonic basement uplifts and basins of the Ancestral Rocky Mountains, flexural arches and intracratonic basins of the US midcontinent region, and basins and uplifts of the southwestern Laurentian transcurrent continental margin. Consideration of new and published U-Pb detrital-zircon datasets permits delineation of Laurentian sediment-dispersal networks of the developing supercontinent. The Transcontinental Arch deflected Late Mississippian transcontinental rivers with Alleghanian headwaters toward the southern midcontinent and nascent, deep-marine foreland basins along the Ouachita collision orogen. Pennsylvanian rivers likewise headed in the Alleghanian Orogen, transporting sediment southwest across the midcontinent and along the Alleghanian foreland basin to empty into the Arkoma Basin and Fort Worth Basin, which also received voluminous sediment from Gondwana and the Ouachita Orogen. Concomitantly, major growth of Ancestral Rocky Mountains uplifts yielded basement-derived sediment, much of which was retained in local flexural basins. Increased aridity drove ascendant eolian transport in early Permian (Artinskian) time, just as lowstand desiccation of a midcontinent seaway exposed unconsolidated silt and sand derived from eastern, western, and southern sources in an extensive interior desert sink. Eolian transport within the interior desert further mixed and deflated the already-cosmopolitan sediment, pushing it southwest toward the Permian Basin and westward beyond the Ancestral Rocky Mountains. Intercepted by newly developed monsoonal circulation, the deflated sediment came to reside in erg systems along the western marine margin of Pangea. Subtropical Pennsylvanian transcontinental fluvial networks were similar to those of modern big river systems of the eastern and midcontinent United States that drain toward the Gulf of Mexico. In contrast, Permian drainage networks yielding sediment to a continental desert more resembled Pleistocene sediment routes of the Arabian Plate; there, intermittent wadis draining western rift highlands and big rivers of the Mesopotamian foreland contribute sediment to Arabian eolian sands via zonal and monsoonal surface winds to create widespread sand seas of mixed Eurasian and Arabian provenance.

CO2 Pipeline Risk Assessment for a Regional-Scale Pipeline in the Midcontinental United States

A comprehensive quantitative risk assessment for the construction and operation of a CO2 transportation network was considered for the Midcontinent of the United States. The assessment evaluated the risk associated with construction and operation using data from the U.S. Occupational Safety and Health Administration to determine the risk of injury or death for pipeline workers and data from the U.S. Pipeline and Hazardous Materials Safety Administration for CO2, natural gas distribution, natural gas transmission/gathering, and non-CO2 hazardous liquid pipelines to develop quantitative likelihood and severity values leading to risk values. The data for the assessment covered incidents from 2010 to 2017 for CO2 pipelines. The average risk for construction and 30 years of operation for a 344-mile-long pipeline was found. The average construction and operational risk for the CO2 pipeline was $6,116,948. The average risks for natural gas distribution, natural gas transmission/gathering, and non-CO2 hazardous liquid pipelines with the same configuration were $6,264,868, $11,971,828, and $28,212,756, respectively. The results showed that the overall and operational risks for CO2 pipelines was less than that of other types of pipelines.

Identifying animate stones and sacred landscapes: Twenty-five years of native pipestone-quarries research in the American midcontinent

This paper assesses our current understanding of the native use of the major midcontinental United States pipestone quarries based on over two decades of research. Our studies indicate that combining chemical and mineralogical techniques such as shortwave infrared spectroscopy (SWIS), thin-section petrography, and X-ray diffraction (XRD) have identified pipestones with similar chemical compositions containing distinctive mineralogical suites (often including berthierine, kaolinite, diaspore, muscovite, and pyrophyllite). This research has identified unique mineral compositions at known quarries such as catlinite, Ohio Feurt Hill, Baraboo, and Barron pipestones, as well as identifying previously unknown quarries of Sterling Illinois pipestone, Cahokia Missouri flint clay, and Portsmouth Ohio Claystone. These discoveries have led to a major shift in interpretations of Cahokian and Hopewell pipe exchange. Further examination of native ethnographic quarry use identified the primary attraction of pipestone quarries lay in the perceived ritual and spiritual power of the stone rather than in its economic utility.

Diminishing Depth to Water in Cambrian-Ordovician Arbuckle Group Disposal Wells in Kansas

Industrial and municipal wastewater and oilfield brines have been disposed of into the Cambrian-Ordovician Arbuckle Group for decades in Kansas and nearby states in the midcontinent United States. The industrial and municipal wastewater disposal wells (designated Class I disposal wells) are regulated by the Kansas Department of Health and Environment. The oilfield brines are disposed of in Class II disposal wells, which are regulated by the Kansas Corporation Commission. Annual testing of formation pressure and static fluid levels in Class I wells compose a body of data that is useful in monitoring movement of water and fill-up of Arbuckle disposal zones. In western Kansas, the depth to water in wells penetrating the Arbuckle can be several hundred to more than a thousand feet (305 m) below ground surface, but in parts of southern and southeastern Kansas, the depth to water locally can be less than 100 ft (31 m). Furthermore, most Class I wells indicate Arbuckle fluid levels in central and south-central Kansas are rising ~10 ft (~3 m) annually, suggesting that at current disposal rates, the Arbuckle may lose its capacity to accept wastewater under gravity flow in parts of the state in the next few decades, principally south-central and southeastern Kansas along the Oklahoma state line. At present in parts of six Kansas counties along the Oklahoma state line, low-density (~1.0 g/cc or slightly greater density) wastewater in a wellbore does not have a sufficient hydrostatic head by gravity alone to force its way into the more dense resident Arbuckle formation water.
 In general, Arbuckle formation water flows west to east in Kansas. Arbuckle disposal wells in Kansas collectively dispose of ~800,000,000 barrels (~127,000,000 m3) of wastewater per year, although some of this is recycled from Arbuckle oil production. Declines in oil price since mid-2014 have resulted in less oilfield disposal in the Arbuckle since 2015. The number of Class I wells recording annual fluid rises have also declined since 2015, as has the median of their annual change in static fluid level, but overall, more Class I wells are still recording fluid rises. There is a poor correlation between changes in fluid levels in Class I wells and the volume of fluid disposed in them annually, thereby indicating that more regional characteristics may control water movement in the Arbuckle. More monitoring wells are needed to better understand the movement of water in the deep subsurface and to anticipate any potential problems that may occur with reduced disposal capacity and possible migration of fluids through unplugged or improperly plugged older wells.

Late glacial and Holocene paleoenvironments in the midcontinent United States, inferred from Geneva Lake leaf wax, ostracode valve, and bulk sediment chemistry

Geneva Lake in Wisconsin, USA, is > 20,000 years old and contains a 30-m thick lacustrine sediment record of mid-continent North American climate and environmental change. Here we describe a sediment record from Geneva Lake spanning the past 14,500 years. From scanning X-ray fluorescence, organic C and N concentrations and isotopes, X-ray diffraction, magnetic susceptibility, and grain size of bulk sediments, we infer changes in sediment sources over time including: abrupt decline in inputs of remobilized loess ∼13,400 cal yr BP followed by a gradual transition to organic-rich marl deposition by ∼10,400 cal yr BP as the landscape stabilized following a period of permafrost thaw and vegetation development; deposition of a minerogenic unit at ∼8,200 cal yr BP that may record enhanced eolian activity during the widespread “8.2 ka event; ” and elevated zinc, lead, and arsenic from human activities following regional industrialization. Within the Holocene marl, we also use isotopic (δ18O and δ13C) and trace metal ratio (Sr/Ca and Mg/Ca) analyses of ostracode valves paired with concentrations and hydrogen isotopic composition (δ2H) of leaf wax n-alkanes to infer climate and hydrological change. Groundwater had a large but declining influence on lake water chemistry from 11,800 to 9,700 cal yr BP, precluding inferences of regional climate from our lacustrine proxies during this period. δ2H values of terrestrial n-C29 alkanes show little variability from 9,700 to present, indicating the average isotopic composition of local precipitation was relatively stable, reflecting stable condensation temperatures and source. In contrast, a gradual trend towards more δ18O- and δ2H-depleted lake water and lower lake water Sr/Ca from 9700 cal yr BP to present suggest decreasing evaporation of lake water and increasing precipitation amounts throughout the Holocene and resulting shorter lake water residence times. Lake water Mg/Ca variations over the past 9,700 years broadly parallel regional pollen-based reconstructions of summer temperatures. Neither Mg/Ca nor terrestrial leaf wax δ2H suggest long-term directional shifts in temperature at this site through the middle to late Holocene, as climate became wetter. It appears that precipitation isotopes did not track local temperatures on millennial timescales in this part of mid-continent North America through the Holocene, and instead may have covaried with changes in Northern Hemisphere latitudinal temperature gradients driven by large Arctic temperature changes.