Late Miocene erosion and evolution of topography along the western slope of the Colorado Rockies

In the Colorado Rocky Mountains, the association of high topography and low seismic velocity in the underlying mantle suggests that recent changes in lithospheric buoyancy may have been associated with surface uplift of the range. This paper examines the relationships among late Cenozoic fluvial incision, channel steepness, and mantle velocity domains along the western slope of the northern Colorado Rockies. New ⁴⁰Ar/³⁹Ar ages on basalts capping the Tertiary Browns Park Formation range from ~11-6 Ma and provide markers from which we reconstruct incision along the White, Yampa and Little Snake Rivers. The magnitude of post-10 Ma incision varies systematically from north to south, increasing from ~500 m along the Little Snake River to ~1500 m along the Colorado River. Spatial variations in the amount of late Cenozoic incision are matched by metrics of channel steepness; the upper Colorado River and its tributaries (e.g. Gunnison and Dolores Rivers) are two to three times greater than the Yampa and White Rivers, and these variations are independent of both discharge and lithologic substrate. The coincidence of steep river profiles with deep incision suggests that the fluvial systems are dynamically adjusting to an external forcing, but is not readily explained by a putative increase in erosivity associated with late Cenozoic climate change. Rather, channel steepness 34 correlates with the position of the channels relative to low velocity mantle. We suggest that the history of late Miocene – present incision and channel adjustment reflects long-wavelength tilting across the western slope of the Rocky Mountains

Thiol redox homeostasis in neurodegenerative disease

This review provides an overview of the biochemistry of thiol redox couples and the significance of thiol redox homeostasis in neurodegenerative disease. The discussion is centred on cysteine/cystine redox balance, the significance of the xc- cystine-glutamate exchanger and the association between protein thiol redox balance and neurodegeneration, with particular reference to Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and glaucoma. The role of thiol disulphide oxidoreductases in providing neuroprotection is also discussed

Dissecting the Shared Genetic Architecture of Suicide Attempt, Psychiatric Disorders, and Known Risk Factors

Background Suicide is a leading cause of death worldwide, and nonfatal suicide attempts, which occur far more frequently, are a major source of disability and social and economic burden. Both have substantial genetic etiology, which is partially shared and partially distinct from that of related psychiatric disorders. Methods We conducted a genome-wide association study (GWAS) of 29,782 suicide attempt (SA) cases and 519,961 controls in the International Suicide Genetics Consortium (ISGC). The GWAS of SA was conditioned on psychiatric disorders using GWAS summary statistics via multitrait-based conditional and joint analysis, to remove genetic effects on SA mediated by psychiatric disorders. We investigated the shared and divergent genetic architectures of SA, psychiatric disorders, and other known risk factors. Results Two loci reached genome-wide significance for SA: the major histocompatibility complex and an intergenic locus on chromosome 7, the latter of which remained associated with SA after conditioning on psychiatric disorders and replicated in an independent cohort from the Million Veteran Program. This locus has been implicated in risk-taking behavior, smoking, and insomnia. SA showed strong genetic correlation with psychiatric disorders, particularly major depression, and also with smoking, pain, risk-taking behavior, sleep disturbances, lower educational attainment, reproductive traits, lower socioeconomic status, and poorer general health. After conditioning on psychiatric disorders, the genetic correlations between SA and psychiatric disorders decreased, whereas those with nonpsychiatric traits remained largely unchanged. Conclusions Our results identify a risk locus that contributes more strongly to SA than other phenotypes and suggest a shared underlying biology between SA and known risk factors that is not mediated by psychiatric disorders.Peer reviewe

Quaternary incision rates and drainage evolution of the Uncompahgre and Gunnison Rivers, western Colorado, as calibrated by the Lava Creek B ash

ABSTRACT The Quaternary erosional history of western Colorado is documented in terraces of the Colorado, Gunnison, and Uncompahgre Rivers that contain the Lava Creek B ash (0.64 Ma). This paper reports an important new ash locality that dates ca. 100-m-high river gravels associated with the paleo-confluence of the Gunnison and Uncompahgre Rivers upstream from Grand Junction. Provenance analysis reveals paleo-Gunnison River gravels (containing granite and gneiss clasts) and paleo-Uncompahgre River gravels (containing Uncompahgre Group quartzite and San Juan volcanic field rocks). The paleo-Uncompahgre River gravels are 3 m directly beneath Lava Creek B ash, and the areal distribution of terraces indicates that this area was the paleo-confluence between the Gunnison and Uncompahgre Rivers. This confluence has shifted 11 km to the east since 0.64 Ma due to events related to stream piracy and drainage reorganization. Gunnison terrace straths near the paleo-confluence are estimated to be 106 m above the modern strath, giving an estimated incision rate of 165 m/Ma. Because of excellent age and geologic control, this is one of the best incision-rate data points in the upper Colorado River system. It is similar to previously reported regional rates, but is substantially lower than upstream incision rates in the Black Canyon of the Gunnison River. This dated Gunnison River terrace anchors the projection of Lava Creek B-bearing Grand Mesa pediment surfaces (e.g., Petrie Mesa) to regional base level and helps constrain a regional reconstruction of the 0.64-Ma profile of the paleo-Gunnison River. This reconstruction shows dramatic differences in incision rate in the Gunnison River system since 0.64 Ma, and that a transient knickpoint migrated past Sawmill Mesa prior to 0.64 Ma. This incision data point has important implications for evaluating major Quaternary changes in the configuration of this part of the Rocky Mountain drainage system. It also provides evidence for a young, disequilibrium drainage system that is responding to base-level changes downstream driven by a stream capture event, which in turn may have been driven by tectonic or climatic perturbations

Resolving Time-Space Histories of Late Cenozoic Bedrock Incision along the Upper Colorado River, USA

The upper Colorado River basin drains the western slope of the Rocky Mountains province of North America and hosts a rich record of fluvial terraces and volcanic deposits that provide an archive of bedrock river incision since the Late Miocene. Here we present new geochronology from fluvial deposits and associated volcanic units using multiple methods (luminescence, cosmogenic-burial, 40Ar/39Ar basalt and detrital sanidine, and U/Pb detrital zircon) to reconstruct a detailed record of bedrock incision in the upper Colorado River over timescales ranging from Miocene to Late Pleistocene. Late Miocene (ca. 11–8 Ma) basalt flows perched 800–1700 m above the Colorado River, and the oldest known ancestral Colorado River deposits preserved beneath basalt flows on Grand Mesa, provide the basis for average, long-term (∼107 yr) incision rates. Rates range from ∼110–160 m/Ma between Grand Junction (downstream) and Glenwood Canyon (upstream), with rates decreasing upvalley. Intermediate-scale (∼105–106 yr) incision rates are ∼200–320 m/m.y. over the past 1–3 Ma, and these rates are faster than the average over the past 8–11 Ma. Short-term (ka) bedrock incision rates are highly variable, and range from ∼250–725 m/m.y. The large variation in rates is interpreted to reflect the inherently unsteady nature of climate-driven incision when measured over time intervals (103–104 yr) that are shorter than the duration of ∼100 ky climate cycles. Finally, episodes of anomalously rapid (∼2000–3700 m/m.y.) short-term bedrock incision appear to be the consequence of stream piracy and drainage reorganization and are confined to specific reaches of the system. Collectively, these data provide a substantially refined picture of the history of incision through space and time that is consistent with headward erosion of the Colorado River into the uplifting flanks of the Rocky Mountains since at least the Late Miocene. We argue that the long-term pace of incision is not completely accounted for by isostatic rebound in response to exhumation, and that ongoing differential uplift driven by mantle buoyancy sets the background rates of fluvial incision (100–150 m/m.y.). Pulses of more rapid incision are a consequence of non-steady incision related to climatically-driven changes in erosion efficiency and/or drainage reorganization. Highlights: —The ancestral upper Colorado River existed by ca. 11 Ma. —Basalt flows support ∼800–1700 m of Neogene fluvial bedrock incision. —Incision was paced by mantle-driven uplift (∼0.5–1.0 km). —The Colorado River eroded headward into the uplifting Rockies. —Climatic episodes and stream-piracy events are superimposed on mantle-driven uplift

Abandonment of Unaweep Canyon (1.4–0.8 Ma), western Colorado: Effects of stream capture and anomalously rapid Pleistocene river incision

Cosmogenic-burial and U-series dating, identification of fluvial terraces and lacustrine deposits, and river profile reconstructions show that capture of the Gunnison River by the Colorado River and abandonment of Unaweep Canyon (Colorado, USA) occurred between 1.4 and 0.8 Ma. This event led to a rapid pulse of incision unlike any documented in the Rocky Mountains. Following abandonment of Unaweep Canyon by the ancestral Gunnison River, a wave of incision propagated upvalley rapidly through Mancos Shale at rates of ̃90-440 km/m.y. The Gunnison River removed 400-500 km3 of erodible Mancos Shale and incised as deep as 360 m in 0.17-0.76 m.y. (incision rates of ̃470-2250 m/m.y.). Prior to canyon abandonment, long-term (ca. 11-1 Ma) Gunnison River incision averaged ̃100 m/m.y. The wave of incision also caused the subsequent capture of the Bostwick-Shinn Park River by the ancestral Uncompahgre River ca. 0.87-0.64 Ma, at a location ̃70 km upvalley from Unaweep Canyon. This event led to similarly rapid (to ̃500 m/m.y.) but localized river incision. As regional river incision progressed, the juxtaposition of resistant Precambrian bedrock and erodible Mancos Shale within watersheds favored the development of significant relief between adjacent stream segments, which led to stream piracy. The response of rivers to the abandonment of Unaweep Canyon illustrates how the mode and tempo of long-term fluvial incision are punctuated by short-term geomorphic events such as stream piracy. These shortterm events can trigger significant landscape changes, but the effects are more localized relative to regional climatically or tectonically driven events