Outcrop Regions Research Articles

Concentration and distribution patterns of rare earth elements (REEs) in stream sediments of Pakistan

Currently, the metals of Rare Earth Elements (REEs) have become very critical to various modern technologies ranging from cell phones and televisions to LED light bulbs and wind turbines. This work was carried out as the Pakistani contribution to the National-scale Geochemical Survey of South and Central Asia (NGSSCA) project. The objective of this study was to document and study the amounts and distribution of REEs in stream sediment of Pakistan, where such national-scale geochemical mapping was launched for the first time. A total of 4277 regular and 168 duplicate samples were collected, encompassing approximately 360,000 km2 of Pakistani outcrop regions. The findings from the geochemical analysis of stream sediment in Pakistan revealed a spectrum in the total Rare Earth Elements (ΣREE) concentration, spanning from 10.22 mg/kg to 1403.1 mg/kg, averaging at 132.5 mg/kg. LREEs are relatively enriched compared to HREEs with an average of LREEs/HREEs of 3.08. The distribution patterns of REEs in stream sediment are demonstrated. It's has been concluded that high concentrations of REEs are mainly distributed in the Himalayan fold and thrust belt, the Karakoram terrane and the Kohistan island arc in the northern part of Pakistan. The bedrock mineralogy and lithology significantly affect the distribution patterns of REEs in stream sediments. The national geochemical mapping of Pakistan provides a useful method for locating alkaline igneous rocks and identifying potential REE mineralization.

Spiciness anomalies in the upper North Pacific based on Argo observations

The density-compensated salinity anomalies (spiciness anomalies) in the upper North Pacific were investigated using Argo float profiles during 2004–2018. The freshening of the subtropical thermocline was found within the Central Mode Water (CMW) and the North Pacific Intermediate Water (salinity minimum). Meanwhile, the increase of salinity was found in the lighter layer within the North Pacific Tropical Water (salinity maximum). The interannual and longer spiciness anomalies were interpreted with three-dimensional evolutions and were linked to the fate of three mode waters (i.e., Subtropical Mode Water (STMW), Eastern Subtropical Mode Water (ESTMW), and CMW) for the first time. In the STMW, the salinity was dominated by a quasi-decadal variability, which was consistent with the KE variability with a 1-year lag, and did not show rapid freshening. In the CMW, the salinity decreased with a quasi-decadal variability, which was weaker and out of the phase compared with the STMW. In the ESTMW, the salinity was dominated by year-to-year variability. The spiciness anomalies originated mainly in the outcrop region of the isopycnals, where they were accompanied by the formation and the subduction of the mode waters. They also propagated and decayed downstream the geostrophic currents. However, a few of the interannual anomalies found in the northern part of the CMW were almost dampened before their spread further south. In addition, some anomalies in the ESTMW appeared and intensified without a connection to the mixed layer. These anomalies occurred far from the outcrop line, suggesting these were caused likely by salt fingering associated with the modification of the mode waters. Furthermore, the propagation of the spiciness anomalies in the western to the central subtropics was significantly faster than the geostrophic current and inclined to the inner side of streamlines. These indicated the transport by eddies in addition to the mean geostrophic currents.

Subsurface Cooling in the Tropical Pacific Under a Warming Climate

AbstractThe present study investigates the subsurface temperature trend in the tropical Pacific in historical and SSP2‐4.5 simulation by 14 models from Coupled Model Intercomparison Project Phase 6. Robust cooling trends exist between 100 and 200 m in the off‐equatorial region (2°–8°N/S) of both the North and South Pacific during 1950–2100. Both spiciness variation and thermocline heave are important in driving this off‐equatorial subsurface cooling at a fixed level. The cooling spiciness trends in the off‐equatorial region originates from the eastern subtropical Pacific along isopycnal streamlines. Besides, the contribution of the thermocline heave to the cooling is governed by the large wind stress curl trend. Furthermore, the maximum negative spiciness trends occur in the eastern subtropics of both the North and South Pacific. The consistently poleward migration of outcropping lines makes cooler subducting water at higher latitudes directly flow into the subtropical subsurface, which induces the negative spiciness trends here. The generation of the negative spiciness trends is also partly attributed to the anomalous advection process on distinct isopycnal surfaces. These two processes both contribute to the generation of spiciness variation in both the North and South Pacific. The generation region is partly covered by the outcropping region, thus, the strong vertical mixing within the mixed layer may weaken the effect of the subduction and advection. This study mainly highlights the significance of the spiciness variation in the projection of the subsurface temperature trend on a longer time scale under global warming.

Appraising the factors favouring uranium mobilization and associated health risk assessment in groundwaters of north-western India

An attempt has been made in this study to evaluate the factors favoring the uranium mobilization into the groundwater of Northwest India using uranium isotope activity ratio (234U/238U), radon (222Rn) and environmental isotopes of water (2H, 18O and 3H). The values range from 23 - 597 µg/L for total uranium and 634–3210 Bq/m3 for radon and the corresponding annual effective dose is estimated to be 18.9–490 µSv/a and 6.2–31.5 μSv/a respectively. Uranium activity ratio (UAR) varies from 0.68 - 1.17 and maximum samples indicate secular equilibrium. Environmental isotopic data indicates that the source to groundwater is vertical percolation of rainwater in the case of shallow zone while regional flows from outcrop areas recharge the deep groundwater. A wide scatter is noticed in environmental 3H content (0.23–6.62 TU) indicating both fast and sluggish water flows. The UAR phase diagram suggests that leaching process controls the uranium mobilization into the groundwater. The correlations among UAR, uranium and Uexcess further indicate oxidative nature of leaching process. Statistical treatment of the obtained data along with available geochemical and isotope evidences suggest that source of uranium is common but the driving processes are different for shallow and deep zone. Influences of root zone CO2, oxic species from irrigation return flows and water level fluctuations are also evaluated. Low uranium, low UAR, low 3H and high 222Rn activity in deep zone suggest uranium being released from the roll front as well as transported from outcrop regions. This study highlights the application of uranium isotope ratio, radon and environmental isotopes in assessing vulnerability of alluvial aquifers towards uranium contamination.

Ontogeny, evolution and palaeogeographic distribution of the world's largest ammonite Parapuzosia (P.) seppenradensis (Landois, 1895).

The world’s largest ammonite, Parapuzosia (P.) seppenradensis (Landois, 1895), fascinated the world ever since the discovery, in 1895, of a specimen of 1.74 metres (m) diameter near Seppenrade in Westfalia, Germany, but subsequent findings of the taxon are exceedingly rare and its systematic position remains enigmatic. Here we revise the historical specimens and document abundant new material from England and Mexico. Our study comprises 154 specimens of large (< 1 m diameter) to giant (> 1m diameter) Parapuzosia from the Santonian and lower Campanian, mostly with stratigraphic information. High-resolution integrated stratigraphy allows for precise cross-Atlantic correlation of the occurrences. Our specimens were analysed regarding morphometry, growth stages and stratigraphic occurrence wherever possible. Our analysis provides insight into the ontogeny of Parapuzosia (P.) seppenradensis and into the evolution of this species from its potential ancestor P. (P.) leptophylla Sharpe, 1857. The latter grew to shell diameters of about 1 m and was restricted to Europe in the early Santonian, but it reached the Gulf of Mexico during the late Santonian. P. (P.) seppenradensis first appears in the uppermost Santonian- earliest Campanian on both sides of the Atlantic. Initially, it also reached diameters of about 1 m, but gradual evolutionary increase in size is seen in the middle early Campanian to diameters of 1.5 to 1.8 m. P. (P.) seppenradensis is characterized by five ontogenetic growth stages and by size dimorphism. We therefore here include the many historic species names used in the past to describe the morphological and size variability of the taxon. The concentration of adult shells in small geographic areas and scarcity of Parapuzosia in nearby coeval outcrop regions may point to a monocyclic, possibly even semelparous reproduction strategy in this giant cephalopod. Its gigantism exceeds a general trend of size increase in late Cretaceous cephalopods. Whether the coeval increase in size of mosasaurs, the top predators in Cretaceous seas, caused ecological pressure on Parapuzosia towards larger diameters remains unclear.

Flow patterns and aquifer recharge controls under Amazon rainforest influence: The case of the Alter do Chão aquifer system

The present study clarifies the role of rainforests in the recharge processes of the Alter do Chão Aquifer System in the outcropping region based on a dataset collected in reference areas. Different methods and techniques commonly applied to hydrogeology studies were integrated to achieve this objective, including soil profile description (in field and laboratory), potentiometric analysis, hydrochemistry data, and stable isotopic evaluation. The Alter do Chão Aquifer System occurs as an unconfined and semiconfined groundwater reservoir in the Amazonian plateau regions, with the following profile sequence: topsoil (higher porosity and hydraulic conductivity), yellow clay (mean porosity of 18% with small pore throats, resulting in lower hydraulic conductivity), aluminous iron crusts, and solid bauxite (highest hydraulic conductivity values resulting from porosity values from 30 to 45%), and at the bottom, the mottled stratified argillite (acting as an aquitard layer, with leaky confining attributes). The relief pattern with high plateau areas cut by shallow and deeper valleys allows regional and local hydrogeological flow systems. The dense forest cover acts as a vital recharge control due to bioturbation by the roots, observed up to 15 m deep. This bioturbation causes preferential flow zones and is responsible for increasing the hydraulic conductivity in the pelitic layers. Oxygen and deuterium stable isotope data demonstrate that recharge is due to rainwater infiltration because the local groundwater line is plotted next to or over the regional meteoric water line. Tritium data indicate that the aquifer is supplied by relatively recent rainfall or at least by mixtures containing recent rainwater. The conceptual flow model for the semiconfined and unconfined portions of the Alter do Chão Aquifer System is represented by the following processes: infiltration of large volumes of rainwater, high loss by forestry evapotranspiration, loss by interflow at the interfaces of contrasting hydraulic conductivity layers, and local loss due to regional lateral flow to the discharge areas. Considering a 1 km2 polygon, it is possible to determine a recharge amount of at least 236,400 and 350,000 m3/year for the semiconfined and unconfined portions of the aquifer, respectively.

Subantarctic Mode Water and its long-term change in CMIP6 models

AbstractThe Subantarctic Mode Water (SAMW) is a major water mass in the South Indian and Pacific oceans and plays an important role in the ocean uptake and anthropogenic heat and carbon. The characteristics, formation, and long-term evolution of the SAMW are investigated in the “historical” and “SSP245” scenario simulations of the sixth Coupled Models Intercomparison Project (CMIP6). Defined by the low potential vorticity, the simulated SAMW is consistently thinner, shallower, lighter, and warmer than in observations, due to biases in the winter mixed layer properties and spatial distribution. The biases are especially large in the South Pacific Ocean. The winter mixed layer bias can be attributed to unrealistic heat loss and stratification in the models. Nevertheless, the SAMW is presented better in the CMIP6 than CMIP5, regarding its volume, location, and physical characteristics. In warmer climate, the simulated SAMW in the South Indian Ocean consistently becomes lighter in density, with a reduced volume and a southward shift in the subduction region. The reduced heat loss, instead of the increased Ekman pumping induced by the poleward intensified westerly wind, dominates in the SAMW change. The winter mixed layer shoals in the northern outcrop region and the SAMW subduction shifts southward where the mixed layer remains deep. The projected reduction of the SAMW volume is likely to impact the heat and freshwater redistribution in the Southern Ocean.

Isotope and hydrochemical systematics of groundwater from a multi-tiered aquifer in the central parts of Indo-Gangetic Plains, India – Implications for groundwater sustainability and security

The Indo-Gangetic multi-aquifer system provides water supplies to the most populous regions of the Indian subcontinent, however precise knowledge on the sources and dynamics of groundwater is still missing. Environmental isotopes (2H, 18O, 13C, 3H and 14C) and hydrochemical modeling tools were used in this study in the multi-tiered aquifers underlying the Middle Gangetic Plains (MGP) to investigate the source of recharge, aquifer dynamics and inter-connectivity among aquifers. Within a depth span of 300 m, three aquifers, with contrasting recharge sources and dynamics, were delineated in this Sone-Ganga-Punpun interfluve region, with limited cross-aquifer hydraulic interconnections. The chemistry evolves from Ca-HCO3 to Na-Ca-HCO3 in the shallow semiconfined Aquifer-I with a mean transit time of 20–23 years. The dominant recharge to Aquifer-I is from the river inflows and rainwater percolation through paleochannels. The semi-confined to confined Aquifer-II holds fresh quality groundwater with mixed water facies (Mg/Ca-Na-HCO3). The modeled age of Aquifer-II groundwater is found to be 205–520 years, which is supported by presence of negligible tritium and minor variations in stable isotopes. Outcrop regions of Aquifer-II sediments in the marginal alluvial areas and deep-seated paleochannels in the southwestern part are the potential zones for Aquifer-II recharge. A deep confined Aquifer-III with fresh quality of groundwater is identified below 220 m. This aquifer is characterized by old age (~3.5 to 4.7 ka BP) and enriched δ18O (−5.7‰). These results along with the existing paleoclimate records of this region infer that Aquifer-III is recharged during an arid climate. The marginal alluvial plains are the probable recharge zones for Aquifer-III. This study helped in conceptualizing the groundwater flow paths in multi-tiered aquifers of MGP. The knowledge and understanding would extend crucial inputs for the sustainable development of deep aquifers not only in the MGP but also in other regions of Indo-Gangetic Plains.

Spiciness Anomalies of Subantarctic Mode Water in the South Indian Ocean

AbstractThis study investigates spreading and generation of spiciness anomalies of the Subantarctic Mode Water (SAMW) located on 26.6 to 26.8 σθ in the south Indian Ocean, using in situ hydrographic observations, satellite measurements, reanalysis datasets, and numerical model output. The amplitude of spiciness anomalies is about 0.03 psu or 0.13°C and tends to be large along the streamline of the subtropical gyre, whose upstream end is the outcrop region south of Australia. The speed of spreading is comparable to that of the mean current, and it takes about a decade for a spiciness anomaly in the outcrop region to spread into the interior up to Madagascar. In the outcrop region, interannual variability in mixed layer temperature and salinity tends to be density compensating, which indicates that Eulerian temperature or salinity changes account for the generation of isopycnal spiciness anomalies. It is known that wintertime temperature and salinity in the surface mixed layer determine the temperature and salinity relationship of a subducted water mass. Considering this, the mixed layer heat budget in the outcrop region is estimated based on the concept of effective mixed layer depth, the result of which shows the primary contribution from horizontal advection. The contributions from Ekman and geostrophic currents are comparable. Ekman flow advection is caused by zonal wind stress anomalies and the resulting meridional Ekman current anomalies, as is pointed out by a previous study. Geostrophic velocity is decomposed into large-scale and mesoscale variability, both of which significantly contribute to horizontal advection.

Observed Triple Mode of Salinity Variability in the Thermocline of Tropical Pacific Ocean

AbstractA well‐defined Triple MOde of Salinity (TMOS) variability in the tropical Pacific thermocline layer (24–25.5 σθ isopycnal surfaces) is revealed from the Argo observations during 2004–2018. Thermocline salinity in the tropical northern and southwestern Pacific Ocean varies out of phase on interannual to near‐decadal time scales with that in the tropical southeastern Pacific Ocean. The TMOS is attributed to anomalous advection of mean salinity as well as advection of anomalous salinity by the mean oceanic current on isopycnal surfaces. While the TMOS pattern is quite different from the thermal patterns associated with the El Niño‐Southern Oscillation (ENSO) or the Pacific Decadal Oscillation (PDO), it is significantly associated with the ENSO and PDO indices with a time lag of 10 months. Isopycnal propagation of salinity anomalies and anomalous freshwater input in the outcropping region, also both associated with ENSO and PDO, are important in the formation of TMOS. The propagation speed of isopycnal salinity anomalies is close to documented phase speeds of baroclinic Rossby waves and velocities of zonal currents. The TMOS acts to shape the basin‐scale Pacific water masses and potentially plays an important role in climate.

Responses of plant water uptake to groundwater depth in limestone outcrops

The study of plant water uptake from groundwater is important to garner an improved understanding of ecohydrological processes and groundwater management. However, little is known about how fluctuations in groundwater depth influence plant water absorption in carbonate outcrop regions. This study quantified the plant water uptake patterns and plant responses to different groundwater depths at four distinct sites. The aquifers of the boreholes CF10 (4 to 10 m groundwater level) and CF12 (2 to 9 m groundwater level) basically consisted of porous and fissure media. The aquifer of borehole CF13 (historically sustained 0 to 1 m groundwater level) was dominated by fissure and conduit media, while that of borehole CF18 (2 to 3 m groundwater level) was comprised on rocks with considerable small-sized dissolution pores and seams. Borehole water, referred to as rock water in this study, is defined as a potential water source that plants can absorb. The IsoSource model, based on the dual stable isotopes of δ D and δ18O was employed to estimate soil and rock water contributions to the plant xylem water. The results revealed that the groundwater depth of the CF10, CF12, and CF13 boreholes had significant negative correlations with the total precipitation of the previous ten days. At the CF10 site, Toona sinensis and Caesalpinia decapetala absorbed soil water during the rainy season, and rock water during the dry season. At the CF12 site, Toona sinensis primarily absorbed rock water during rainy season and soil resident moisture during the dry season, while the water utilization proportion of Caesalpinia decapetala fluctuated significantly in different seasons. At the CF13 site, rock water was the dominant water source for both plant species during the rainy and dry seasons, while soil water was the main water source for both plants in the CF18 site. The proportion of rock water absorption by plants did not directly statistically correlate with groundwater depth; however, it did with the total precipitation of the previous two and fifteen days, respectively. Nevertheless, groundwater depth is a comprehensive embodiment of precipitation and the structure of karst water-bearing media. Therefore, the plant absorption of rock water is not only contingent on groundwater depth but also on the karst water-bearing media. For the first time, the isotopic values of borehole water were employed to estimate the contributions of plant water sources to improve calculations. The above results indicated that field surveys of hydrogeological structures and high precision monitoring were equally indispensable toward facilitating the restoration of vegetation and groundwater management in fragile rocky desertified ecosystems.

Long‐Term Thermohaline Variations in the North Pacific Subtropical Gyre From a Repeat Hydrographic Section Along 165°E

AbstractLong‐term thermohaline variability in the North Pacific subtropical gyre for 1996–2018 was investigated by repeat hydrography along 165°E conducted by the Japan Meteorological Agency. Potential temperature (θ) and salinity (S) in North Pacific Tropical Water (NPTW), characterized by the salinity maximum, exhibit an interannual or longer‐timescale variation with significant warming and salinification. The θ–S of NPTW originates from mixed layer temperature (MLT) and salinity (MLS) in the isopycnal outcrop region. In the NPTW formation region, the MLS determines surface density and controls the meridional position of the outcrop region. High (low) MLS and the associated southward (northward) migration of the outcrop region increase (decrease) θ–S anomalies in NPTW. The θ–S in the main thermocline/halocline associated with subtropical mode water (STMW) shows a decadal‐scale variation, with a significant cooling and freshening. These properties also derive from MLT and MLS in the isopycnal outcrop region. In the central North Pacific, including the eastern part of the STMW formation region, the MLT controls meridional migration of the outcrop region; during high (low) MLT, the outcrop region migrates northward (southward), and cold and fresh (warm and salty) STMW is formed. The signals are passed into the main thermocline/halocline through subduction of STMW. Consideration of the mechanism that generates θ–S anomalies via migration of the outcrop regions leads us to suggest surface warming and salinification in the subtropical gyre associated with global warming cause a cooling and freshening in the main thermocline/halocline and warming and salinification in NPTW, respectively.

Climate impact on fluvial-lake system evolution, Eocene Green River Formation, Uinta Basin, Utah, USA

AbstractIn light of a modern understanding of early Eocene greenhouse climate fluctuations and new highly seasonal fluvial system faces models, the role of climate in the evolution of one classically-cited continental, terminal lake system is re-examined. Detailed stratigraphic description and elemental abundance data from fifteen cores and seven outcrop regions of the Green River Formation were used to construct a ∼150 km cross section across the Uinta Basin, Utah, USA. Lake Uinta in the Uinta Basin is divided into five lake phases: (1) post-Paleocene Eocene Thermal Maximum, (2) peak Eocene hyperthermal, (3) waning hyperthermal, Early Eocene Climatic Optimum (EECO), (4) post-hyperthermal, and (5) post-EECO regimes, based primarily on climatically driven changes in fluvial style in combination with sedimentary indicators of lacustrine carbonate deposition, organic matter preservation, salinity, and lake depth. Basinwide siliciclastic dominated intervals were deposited by highly seasonal fluvial systems and record negative organic carbon isotope excursions associated with early Eocene abrupt, transient global warming (hyperthermal) events. Carbonate dominated or organic rich intervals record stable, less seasonal climate periods between hyperthermals, with lower siliciclastic sediment supply allowing the development of carbonate and organic matter preservation. The stratigraphic progression from alternating organic rich and lean zones to the overlying organic rich Mahogany and R8 zones represents the global transition out of the pulsed early Eocene hyperthermal climate regime to a time of sediment starvation and lake stratification, sequestering sedimentary organic carbon. This study provides a novel approach to terrestrial paleoclimate reconstruction that relies largely on unique sedimentary indicators and secondarily on isotopic proxy records within the context of a large basin-wide sedimentologic and stratigraphic data set, thus setting the stage for future detailed geochemical terrestrial paleoclimate proxy development.

A North‐South Contrast of Subsurface Salinity Anomalies in the Northwestern Pacific From 2002 to 2013

AbstractThis paper finds a north‐south contrast of subsurface salinity trend during 2002–2013 in the northwestern Pacific. Both Argo float data and long‐term repeat hydrographic measurements along the 137°E section show that salinity anomalies along the isopycnals of 24.5–25.4 kg/m3 exhibit a pronounced decreasing trend north of 15°N and an increasing trend south of 15°N. We perform a quantitative analysis based on satellite‐derived data and a qualitative analysis that used a lower‐order isopyncal salinity model that represents key balance terms (i.e., evaporation E, precipitation P, and wind forcing advection). Both of the analyses consistently show that the subsurface salinity anomalies in the north and south of 15°N are induced by different physical processes. Fresher surface waters in the northwestern subtropical outcrop region due to an excess freshwater supply (E − P &lt; 0) contribute to the freshening of subsurface waters north of 15°N. In contrast, saltier surface waters in the northeastern subtropical subduction region induced by a deficit of freshwater (E − P &gt; 0) and anomalous ocean circulation associated with the recent accelerated trade winds of the tropical Pacific cause the saltiness of subsurface waters south of 15°N. The results imply that the salinity north‐south contrast may play an important role in changing ocean thermocline structure and upper ocean stratification in the northwestern Pacific.

Spiciness Anomalies in the Upper South Indian Ocean

AbstractThis study investigates an isopycnal temperature/salinity T/S, or spiciness, anomaly in the upper south Indian Ocean for the period from 2004 to 2015 using observations and reanalyses. Spiciness anomalies at about 15°S on 24–26σθ are focused on, whose standard deviation is about 0.1 psu in salinity and 0.25°C in temperature, and they have a contribution to isobaric temperature variability comparable to thermocline heave. A plausible generation region of these anomalies is the southeastern Indian Ocean, where the 25σθ surface outcrops in southern winter, and the anticyclonic subtropical gyre advects subducted water equatorward. Unlike the Pacific and Atlantic, spiciness anomalies in the upper south Indian Ocean are not T/S changes in mode water, and meridional variations in SST and sea surface salinity in their generation region are not density compensating. It is possible that this peculiarity is owing to freshwater originating from the Indonesian Seas. The production of spiciness anomalies is estimated from surface heat and freshwater fluxes and the surface T/S relationship in the outcrop region, based on several assumptions including the dominance of surface fluxes in the surface T/S budget and effective mixed layer depth proposed by Deser et al. The result agrees well with isopycnal salinity anomalies at the outcrop line, which indicates that spiciness anomalies are generated by local surface fluxes. It is suggested that the Ningaloo Niño and El Niño–Southern Oscillation lead to interannual variability in surface heat flux in the southeastern Indian Ocean and contribute to the generation of spiciness anomalies.

Unconfined hypogene evaporite karst: West Texas and southeastern New Mexico, USA

Diverse karst phenomena occur throughout the Gypsum Plain where the Castile Formation crops out over ~1800 km2 in West Texas and southeastern New Mexico. Hypergene karst is extensive and widespread, while traditional hypogene karst manifestations (both caves and intrastratal dissolution) occur in high frequency in the western outcrop region where surface denudation has been the greatest so as to induce surficial breaching. Unconfined hypogene karst occurrences have been recently identified, including two general variations: 1) artesian-like discharge features; and 2) venting structures. Artesian-like discharge features arise at surficially-breached hypogene caves and through high permeability regions on the margins of breccia pipes; these occur when aquifer pressures within the underlying Bell Canyon siliciclastics are sufficiently elevated subsequent to anomalously high precipitation events. Venting structures associated with condensation corrosion-like processes coupled with ascending moisture-rich vapor occur as fracture vents and hydration buckles; fracture vents develop along near-vertical joint sets and hydration buckles form at intermittent zones of high permeability within the core regions of breccia pipes. All venting structures form highly porous, low density, secondary sulfate mineralization at the land surface, creating local topographic highs decimeters to a meter in scale that preclude interception of meteoric waters into these unconfined hypogene karst features. The Gypsum Plain hosts complex karst phenomena that present unique engineering challenges as variable geohazard occurrences ranging from shallow, hypergene caves to deep, complex, hypogene features both formed in semi-confined and unconfined speleogenetic conditions.

Quarrying Companies Royal Engineers in World War I: a geologically constrained innovation to support British armies on the Western Front

Abstract Quarrying Companies were a new type of unit first raised within the Royal Engineers in World War I. Thirteen served in northern France, on the Western Front: two from late 1916 (198 and 199 Quarrying Companies) and 11 more from 1917 (320–329 and 348 Quarrying Companies). Recruited from Great Britain, Ireland and the Channel Island of Guernsey, each consisted of four officers and 264 soldiers; over 3000 men in total, assisted by c. 4000 less skilled labourers. They were used to support the British Expeditionary Force by providing ‘stone’, mostly from existing quarries near Marquise, NE of the port of Boulogne. There they excavated Devonian and Carboniferous ‘limestones’ in the Ferques Inlier, relatively strong rocks within a region of wide Mesozoic and Cenozoic outcrop. As the British Expeditionary Force expanded to a peak of five armies and c. 1.5 million troops, ‘stone’ was required for the enhancement or repair of the roads, railways and associated facilities that formed a crucial element of its infrastructure, essential for the efficient movement of soldiers and their copious supplies of food, stores and ammunition. The requirement ceased soon after the end of hostilities and all Quarrying Companies Royal Engineers were disbanded in 1919.

Propagation of the subsurface freshening water and its major source in the northwestern Pacific

AbstractPrevious studies of the exchanges of the subtropical‐tropical salinity in the North Pacific are still not conclusive. Some studies suggest that surface salinity anomalies formed in the northeastern subtropics can subduct and penetrate to the subsurface of the northwestern Pacific, whereas others demonstrate that subsurface salinity anomalies in the northwestern Pacific cannot be traced back to those of the eastern subtropics. This study examined the variability of subsurface salinity in the northwestern Pacific, with focus on its propagation characteristic and forcing mechanism in its outcrop region. It is found that salinity anomalies on 24.5–25.4 kg m−3 isopycnals exhibited a pronounced freshening trend in the northwestern Pacific during 2003–2012. This freshening can be traced back to the surface salinity anomalies in the outcrop zone of the northwestern subtropical gyre, rather than that of northeastern subtropics. The representative transit time from its outcrop region to the eastern Luzon Strait is about 1–3 years. The surface salinity anomalies in the outcrop zone are mainly controlled by air‐sea freshwater flux change, although the contribution of horizontal advection is also important, in particular for year‐to‐year variation. Compared to the air‐sea freshwater flux and horizontal advection, the contribution of mixed‐layer depth to the surface salinity anomalies is smaller and can be neglected in the outcrop zone of the northwestern Pacific.

Cryptic sub-ice geology revealed by a U-Pb zircon study of glacial till in Dronning Maud Land, East Antarctica

We have targeted the southern side of the Dronning Maud Land (DML) mountains in search of moraine material that might reveal the geology in the ice-covered region of the East Antarctic polar plateau. Nine samples of unconsolidated moraine material, carried by the northward flowing East Antarctic ice sheet to the southern side of the DML escarpment, were collected and processed for U-Pb zircon analyses. The analyses resulted in ca. 1100 new U-Pb zircon spot ages between ca. 2000 and 500Ma. The oldest, Palaeoproterozoic rocks come from the easternmost localities with a probable source region between the Sør Rondane Mountains and Dome Fuji. The samples have major Stenian and early Tonian age peaks. Early Tonian rocks are well known from the SW Terrane in the Sør Rondane Mountains and characterise the major Tonian Oceanic Arc Super Terrane (TOAST). Stenian ages are far less common in the outcropping region. Although Stenian ages are common in both the Maud Province of western-central DML as well as in the Rayner Complex, our samples differ with respect to composition and/or isotope geochemistry; they are juvenile, subduction-related and resemble an early phase of oceanic arcs that was so far unknown in this region. In the westernmost sample, the oldest age peak is ca. 800–720Ma with possible counterparts in the Schirmacher Oasis. All samples show a protracted Late Neoproterozoic/Early Palaeozoic metamorphic overprint, accompanied by igneous addition, most likely related to the East African-Antarctic Orogen. This overprint appears most intense in clasts collected from the westernmost locality, lasted for ca. 150Ma and an eastward younging of metamorphic ages is observed. The new moraine samples together with previous outcrop studies reveal that this region has undergone two major phases of oceanic arc/terrane accretion; the first one from ca. 1100 to 900Ma is probably related to accretion tectonics outboard of Rodinia, the second one from ca. 850 to 580Ma occurred as a result of ocean closure and finally Gondwana amalgamation. No significant old components are found, but the high proportion of Late Neoproterozoic/Early Palaeozoic ages confirms that the East African-Antarctic Orogen transects DML and East Antarctica.

Recharge contribution to the Guarani Aquifer System estimated from the water balance method in a representative watershed.

The contribution of recharge to regional groundwater flow systems is essential information required to establish sustainable water resources management. The objective of this work was to determine the groundwater outflow in the Ribeirão da Onça Basin using a water balance model of the saturated soil zone. The basin is located in the outcrop region of the Guarani Aquifer System (GAS). The water balance method involved the determination of direct recharge values, groundwater storage variation and base flow. The direct recharge was determined by the water table fluctuation method (WTF). The base flow was calculated by the hydrograph separation method, which was generated by a rain-flow model supported by biweekly streamflow measurements in the control section. Undisturbed soil samples were collected at depths corresponding to the variation zone of the groundwater level to determine the specific yield of the soil (drainable porosity). Water balances were performed in the saturated zone for the hydrological years from February 2004 to January 2007. The direct recharge ranged from 14.0% to 38.0%, and groundwater outflow from 0.4% to 2.4% of the respective rainfall during the same period.