Local Basin Research Articles

Asymptotic Behavior and Stability of a Stationary Boundary-Layer Solution to a Partially Dissipative System of Equations

A boundary value problem for a singularly perturbed partially dissipative system of two ordinary differential equations of the second and first order, respectively, is considered. An asymptotic expansion of its boundary-layer solution in a small parameter is constructed and justified. This solution is a stationary solution of the corresponding evolution system of equations with partial derivatives. The asymptotic stability of a stationary boundary-layer solution is proved, and its local basin of attraction is found.

A Diverse Array of Fluvial Depositional Systems in Arabia Terra: Evidence for mid-Noachian to Early Hesperian Rivers on Mars.

Branching to sinuous ridges systems, hundreds of kilometers in length and comprising layered strata, are present across much of Arabia Terra, Mars. These ridges are interpreted as depositional fluvial channels, now preserved as inverted topography. Here we use high‐resolution image and topographic data sets to investigate the morphology of these depositional systems and show key examples of their relationships to associated fluvial landforms. The inverted channel systems likely comprise indurated conglomerate, sandstone, and mudstone bodies, which form a multistory channel stratigraphy. The channel systems intersect local basins and indurated sedimentary mounds, which we interpret as paleolake deposits. Some inverted channels are located within erosional valley networks, which have regional and local catchments. Inverted channels are typically found in downslope sections of valley networks, sometimes at the margins of basins, and numerous different transition morphologies are observed. These relationships indicate a complex history of erosion and deposition, possibly controlled by changes in water or sediment flux, or base‐level variation. Other inverted channel systems have no clear preserved catchment, likely lost due to regional resurfacing of upland areas. Sediment may have been transported through Arabia Terra toward the dichotomy and stored in local and regional‐scale basins. Regional stratigraphic relations suggest these systems were active between the mid‐Noachian and early Hesperian. The morphology of these systems is supportive of an early Mars climate, which was characterized by prolonged precipitation and runoff.

Detrital zircons and sediment dispersal from the Coahuila terrane of northern Mexico into the Marathon foreland of the southern Midcontinent

AbstractNew analyses of U-Pb ages along with previously published analyses of detrital zircons from sandstones in the foreland of the Marathon orogen in west Texas have significant implications regarding provenance. The most prominent concentrations of U-Pb ages are at 1200–1000, 700–500, and 500–290 Ma. The accreted Coahuila terrane in the Marathon hinterland and nearby terranes with Gondwanan (Amazonia) affinity include Paleozoic volcanic and plutonic rocks, as well as Precambrian basement rocks. Late Paleozoic Las Delicias arc rocks have ages of 331–270 Ma. Detrital zircons from Upper Jurassic and Lower Cretaceous sandstones, which were deposited in local basins around the Coahuila terrane, provide a record of detritus available from proximal sources within Coahuila, including important peaks at 1040, 562, 422, 414, 373, and 282 Ma. Components of the detrital-zircon populations in the Marathon foreland have unique matches with primary and/or detrital sources in the Coahuila terrane. Although some components of the Marathon populations also have age matches in Laurentia (Appalachians), others do not; however, all components of the Marathon populations have potential sources in Coahuila. Analyses of εHft show generally more negative values in Amazonia than in Laurentia, and εHft values for Marathon sandstones have distributions similar to those in Amazonia. Therefore, the Coahuila terrane provides a provenance for all of the detrital-zircon ages in the Marathon foreland, requiring no mixing from other sources.

Assessment of heavy metals in the surface sediments and sediment-water interface of Lake Cajititlán, Mexico.

Lake Cajititlán is an endorheic tropical lake located in the state of Jalisco, Mexico, which has suffered the consequences of high levels of eutrophication. This study assessed the presence of heavy metals and metalloids in Lake Cajititlán to ascertain possible risks to its aquatic biota and the environment. Eleven monitoring sites were selected throughout the lake; from each site, one sample was taken from the sediments and another from the sediment-water interface by using an Ekman dredger and a Van Dorn bottle, respectively. The measured metals in each sample were As, Cd, Cr, Hg, Pb, Zn, Cu, Ni, Fe, Mn, and Al. The results showed the following sequence of heavy metal concentrations Al > Fe > Mn > Zn > Cu > Cr, wherein Al had the highest average concentration and Cr had the lowest. As, Cd, Hg, and Pb were practically undetectable. Because the predominant rock in the lake basin is volcanic tuff and the soil is vertisol, the high quantities of Al and Fe suggest the weathering of the basin's minerals. The analyses of the sediment-water samples contained small amounts of dissolved Al, Fe, and Mn. According to the Håkanson equations with Hg, Cd, As, Cu, Pb, Cr, and Zn, the calculations of the contamination degree and ecological risk revealed that the presence of metals and metalloids does not present a potential risk to the aquatic biota; nonetheless, the water is not suitable for local human consumption due to an unrelated factor associated with nutrient and bacteriological contamination. The results show that heavy metals in the sediments were dispersed throughout the lake mostly because of the weathering of minerals from the local basin and not because of the punctual discharges of the pollutants from the municipal wastewater treatment plants (WWTPs). However, to ensure that the small amounts of dissolved metals (Al, Fe, and Mn) do not affect the aquatic biota, the fish species and phytoplankton need to be internally analyzed.

Stratigraphy and microfossils (radiolarians and planktonic foraminifers) of the Upper Cretaceous (upper Santonian–lower Campanian) Struganik limestone (Western Serbia)

Radiolarians and planktonic foraminifers were studied from several sections of the Upper Cretaceous lithographic limestones near Struganik Village (Western Serbia). These deposits were formed in a local basin, in a low-energy sedimentary environment surrounded by a shallow-water carbonate platform. The Struganik limestone is represented by alternating micritic limestone with calcarenite, rudite and tuffaceous rocks. The sections of the Struganik limestone have a narrow stratigraphic interval that covers the upper Santonian and probably includes the lower Campanian, with a total thickness reaching 120–150 m. The radiolarian zones Crucella robusta and Afens perapediensis were traced within the unit. The foraminiferal zone Dicarinella asymetrica was tentatively identified.

Salt tectonics in the Bend Zone segment of the Carpathian fold and thrust belt, Romania

The Carpathian Bend Zone is part of the Eastern Romanian Carpathians. The stratigraphic profile contains two levels of salt: Lower Miocene (Lower Burdigalian) and Middle Miocene (Badenian). The studied segment of the fold belt was deformed during the Middle Miocene (Badenian-to-Middle Sarmatian phase) and during the Late Miocene to present (Wallachian phase). During this latter phase, the Lower Burdigalian salt was remobilized and reached the surface on several locations piercing through 2–3 km-thick post-tectonic deposits. The salt outcrops and contractional structures now form a 30 km long, NE–SW lineament at the surface. This contribution proposes kinematic models for the Lower Burdigalian salt movement during both tectonic phases. The lineament was a detachment fold in the Middle Miocene phase. Thickened Burdigalian salt and Oligocene s.l. duplex filled the core of the detachment fold. The detachment fold was subsequently peneplained with the Burdigalian salt exposed on the paleo-surface that locally redeposited during the Badenian. The Wallachian evolution is less clear and we propose two viable kinematic models. It is possible that the salt rise kept up with sedimentation and halokinetic sequences formed at the salt–sediment interface. Alternatively, the area was reactivated in a thin-skinned, right-lateral strike–slip manner with local pull-apart basins (1–2 km across) providing space for salt plugs. Currently available data do not allow us to pick a preferred model for the kinematics during the Wallachian phase. Both kinematic models are novel and are in contrast with earlier ideas.

Extensional magmatism in a continental collision zone,Tafresh area, western central Iran: structural, geochemical and mineralogical considerations

The Tafresh area, located on the middle part of Urumieh-Dokhtar magmatic arc, is a suitable area for considering the effects of tectonic structures on development of the volcanic facies in the magmatic provinces. The main structure in the area is a dextral fault (so called Rahjerd Fault) that has produced the local extensional basins and also the parallel dyke swarms (or feeder dykes) on its both sides. So, the pyroclastic deposits, basaltic-andesitic lava flows, parallel dyke swarms were appeared by explosive subaqueous and then effusive subaerial eruptions and eventually a dioritic stock intruded in the volcanic pile. Petrologically, the magmatic rocks are belonged to the calcalkaline suite that had been changed and evolved in the magma chambers of local extensional basins in a collisional tectonic setting. The mineral chemistry and geochemical modeling as well as the coexistence of different mineral paragenesis of plagioclases (An47-72 and An17-37), pyroxenes (diopside and pigeonite) and amphiboles (magnesiohastingsite and magnesiohornblende) reveal that the AFC process is a dominant process in the magma chamber. Also, according to geothermobarometric calculations, the investigated volcanic rocks of the area could be grouped into two types: one type with higher P-T (>6Kbar and about 900 °C) including Eocene pigeonite-magnesiohastingsite bearing andesites (PHA) and Miocene andesites and other with lower P-T (1-4 Kbar and 600- 800 °C) including the Eocene diopside-magnesiohornblende bearing andesites (DHA) and the dioritic stock.

Dynamical Effects of Neuron Activation Gradient on Hopfield Neural Network: Numerical Analyses and Hardware Experiments

Hyperbolic tangent function, a bounded monotone differentiable function, is usually taken as a neuron activation function, whose activation gradient, i.e. gain scaling parameter, can reflect the response speed in the neuronal electrical activities. However, the previously published literatures have not yet paid attention to the dynamical effects of the neuron activation gradient on Hopfield neural network (HNN). Taking the neuron activation gradient as an adjustable control parameter, dynamical behaviors with the variation of the control parameter are investigated through stability analyses of the equilibrium states, numerical analyses of the mathematical model, and experimental measurements on a hardware level. The results demonstrate that complex dynamical behaviors associated with the neuron activation gradient emerge in the HNN model, including coexisting limit cycle oscillations, coexisting chaotic spiral attractors, chaotic double scrolls, forward and reverse period-doubling cascades, and crisis scenarios, which are effectively confirmed by neuron activation gradient-dependent local attraction basins and parameter-space plots as well. Additionally, the experimentally measured results have nice consistency to numerical simulations.

Groundwater monitoring for evaluating the pasture carrying capacity and its vulnerability in arid and semi-arid regions: A case study of urban and mining areas in Mongolia

Arid and semi-arid regions cover 41% of the global land area and 2 billion people, 90% of which belong to developing countries, live there. Variation in precipitation due to climate change brings big large influences on ground and underground water resources, and especially it is predicted that arid and semi-arid regions are getting drier. Therefore, it is imperative to clarify impacts to environmental vulnerability caused by the variation of water cycle (VWC) due to climate change and consider options for its adaption. Mongolia is a typical country where environmental vulnerability is getting worse by VWC. Our previous studies revealed that the increase of evapotranspiration and permafrost degradation by global warming deteriorate the pasture carrying capacity (PCC) in semi-arid regions in Mongolia. In this manner, VWC is a key component of PCC, but VWC depends on not only climate change but also human activities. Recent mine development and urbanization, as well as growth of livestock, increase groundwater use, but their influences have not been clarified. To explore the influence of urbanization and mining, we have started groundwater monitoring of urban areas in semi-arid regions (Northern Mongolia) and mining areas in arid regions (Southern Mongolia) since May 2018. After investigating hundreds of wells in those areas, and finally selected 11 wells in urban areas and 7 wells in mining areas for groundwater monitoring. 22 Onset HOBO U20 Water Level Loggers (Forestry Suppliers, Inc.), including 5 Loggers for atmospheric correction, and a Water Flow Rate Sensor (Keyence Inc.) are working for measuring groundwater usage. Meanwhile, with data analyses of groundwater level at 875 wells from 2015 to 2017 measured by the local basin authority, it was found that the groundwater level of mining area had a tendency of decreasing widely comparing with that of non-mining area.

Terrigenous sedimentation on the submarine Shirshov Ridge (Bering Sea) during the last deglaciation

The submarine Shirshov Ridge is an independent system of terrigenous sedimentation, which is geomorphologically isolated from bottom terrigenous influx into the deep-water basin of the Bering Sea. Using the ridge as example, we studied background hemipelagic sedimentation of the finely dispersed terrigenous suspended material from water column and deposition of the coarser grained ice-rafted material in the western part of the deep-water basin. The grain-size and mineral composition of postglacial sediments of the Shirshov Ridge was studied in cores SO201-2-85KL and SO201-2-77KL taken from local basins in the central and southern parts of the ridge, respectively. Statistic treatment of uninterrupted grain-size distributions (GD) of terrigenous component of the postglacial sediments by end-member (EM) modelling revealed that the grain-size distributions of terrigenous sediments from two cores are determined by the mixing of three EMs. EM-1 and EM-2 reflect the hemipelagic sedimentation with and without bottom currents influence respectively, while EM-3 with mode at fine-grained sand characterizes GD of the ice-rafted material. Reconstructed mechanisms of terrigenous influx on the Shirshov Ridge involve advection of the suspended matter with surface and intermediate water masses and ice-rafting. The relative role of both mechanisms of the terrigenous sedimentation under the influence of varying bottom current velocities for intervals of Last Glacial Maximum, early deglaciation, Heinrich event 1, Bølling–Allerød, Younger Dryas, and Early Holocene is estimated. It is ascertained that the grain-size distribution of terrigenous component is defined by climate variations, sea ice coverage, sea ice drift pathways, conditions of fast ice melting, and mobility of bottom waters. High concentrations of drifting ice or seasonal sea ice cover likely existed above the southern part of the ridge during the second half of the Heinrich 1 event. The low mobility of bottom waters facilitated only the subice hemipelagic sedimentation of fine fractions from the background reserve of suspended material. A sharp reduction of ice-rafted flux was reconstructed for the Bølling–Allerød warming interval. Bottom currents affected sedimentation in the central part of the ridge during the entire deglaciation (in addition to the second half of the Heinrich 1 event), and in the southern part during the Bølling–Allerød, Younger Dryas, and Early Holocene.

Memristor initial boosting behaviors in a two-memristor-based hyperchaotic system

Abstract By substituting two resistive couplings with two memristive couplings, a two-memristor-based hyperchaotic system is proposed. This hyperchaotic system has a plane equilibrium with two zero eigenvalues and three nonzero ones, and the equilibrium plane is divided into three regions with different stabilities, including unstable saddle, stable node, and stable node-focus. Through using the local attraction basin, bifurcation diagrams and Lyapunov exponent spectra, dynamical behaviors are analyzed in the unstable saddle region, from which the bi-stability phenomenon is observed in such a hyperchaotic system. More particularly, the memristor initial boosting behaviors are found, which indicates that the attractor offset boosting is controlled by the memristor initial values. The memristor initial boosting is multi-dimension, nonlinearity and non-monotonic, completely different from the variable offset boosting. Subsequently, PSIM circuit simulations are performed to verify the numerical results.

Terrigenous Sedimentation on the Submarine Shirshov Ridge (Bering Sea) during the Last Deglaciation

The submarine Shirshov Ridge is an independent system of terrigenous sedimentation, which is geomorphologically isolated from bottom terrigenous influx into the deep-water basin of the Bering Sea. Using the ridge as example, we studied background hemipelagic sedimentation of the finely dispersed terrigenous suspended material from water column and deposition of the coarser grained ice-rafted material in the western part of the deep-water basin. The grain-size and mineral composition of postglacial sediments of the Shirshov Ridge was studied in cores SO201-2-85KL and SO201-2-77KL taken from local basins in the central and southern parts of the ridge, respectively. Statistic treatment of uninterrupted grain-size distributions (GD) of terrigenous component of the postglacial sediments by end-member (EM) modelling revealed that the grain-size distributions of terrigenous sediments from two cores are determined by the mixing of three EMs. EM-1 and EM-2 reflect the hemipelagic sedimentation with and without bottom currents influence respectively, while EM-3 with mode at fine-grained sand characterizes GD of the ice-rafted material. Reconstructed mechanisms of terrigenous influx on the Shirshov Ridge involve advection of the suspended matter with surface and intermediate water masses and ice-rafting. The relative role of both mechanisms of the terrigenous sedimentation under the influence of varying bottom current velocities for intervals of Last Glacial Maximum, early deglaciation, Heinrich event 1, Bolling–Allerod, Younger Dryas, and Early Holocene is estimated. It is ascertained that the grain-size distribution of terrigenous component is defined by climate variations, sea ice coverage, sea ice drift pathways, conditions of fast ice melting, and mobility of bottom waters. High concentrations of drifting ice or seasonal sea ice cover likely existed above the southern part of the ridge during the second half of the Heinrich 1 event. The low mobility of bottom waters facilitated only the subice hemipelagic sedimentation of fine fractions from the background reserve of suspended material. A sharp reduction of ice-rafted flux was reconstructed for the Bolling–Allerod warming interval. Bottom currents affected sedimentation in the central part of the ridge during the entire deglaciation (in addition to the second half of the Heinrich 1 event), and in the southern part during the Bolling–Allerod, Younger Dryas, and Early Holocene.

A comparison of different GRACE solutions in terrestrial water storage trend estimation over Tibetan Plateau

The Gravity Recovery and Climate Experiment (GRACE) terrestrial water storage anomalies (TWSA) estimations provide valuable information for the monitoring of land water resources changes. Multiple parameters and strategies for inversion of the water storage changes have been explored. The explorations on differences between GRACE solutions in local regions and basins are fundamental and important. This study focuses on comparisons of TWSA trends between different GRACE solutions over Tibetan Plateau (TP), both storage and flux among solutions were compared. Results show that great discrepancies exist in TWSA between GRACE solutions derived from the standard spherical harmonic approach (SSH) and the mascon approach. Three SSH-based GRACE solutions (JPL, CSR, and GFZ) detect no significant TWSA changes for the whole area of Tibetan Plateau, whereas JPL mascon solution (JPL-M) and CSR mascon solution (CSR-M) gave decreasing trends of 3.10 km3/yr and 3.77 km3/yr, respectively. This difference also exists in the Yangtze River-Yellow River basin (YYR basin) in the TP. Although five solutions derived consistent TWSA trends in northwest river basin (NWR basin) and southwest river basin (SWR basin) in the TP, the variations between different solutions are 2.88 km3/yr and 4.75 km3/yr for NWR and SWR basin respectively, which could not be neglected. The JPL-M solution, as a result, would overestimate both TWSA decreasing and increasing trends comparing with other GRACE solutions. The results of this study are expected to provide references for the studies of water resource dynamics over Tibetan Plateau and the surrounding areas based on GRACE TWSA products.

Impacts of climate change on water resources availability in Zambia: implications for irrigation development

The Zambian economy is predominantly based on exploitation of its natural resources. The water resources in particular are important for the socioeconomic development of the country. Managing water resources sustainably requires a good understanding of the current and future availability of these resources at local level: how much water is available, where is it available and when? This study assesses the spatial and temporal distribution of water resources and the impacts of projected climate change on water resource availability in Zambia. The study employs statistical downscaling of future climate scenarios and a water balance model in a hydrological modeling framework to assess the impacts of climate change on water availability. Unlike past studies done at national, regional or global levels, analysis in this study was done at the local river basin level. The main results indicate that temperature is projected to increase by 1.9 °C and 2.3 °C by 2050 and 2100, respectively, in Zambia. Rainfall is projected to decrease by about 3% by mid-century and only marginally by about 0.6% toward the end of the century across the country. These changes in rainfall and temperature will decrease water availability by 13% by the end of the century in 2100 at national level. At the river basin level, the northern basins are projected to stay the same or experience slight gains in water resources compared to those in the southern and western parts of Zambia where reductions up to 9% are projected. In particular, Zambezi, Kafue and Luangwa River basins are projected to have less water resources available due to reduced rainfall and higher temperatures. Two main implications for irrigation development follow in Zambia. More water-efficient irrigation technologies are needed and water resources will need to be better managed and regulated to cope with the projected water stresses due to climate change.

Coexisting multi-stable patterns in memristor synapse-coupled Hopfield neural network with two neurons

When possessing a potential difference between two neurons, an electromagnetic induction current appears in the Hopfield neural network (HNN), which can be emulated by a flux-controlled memristor synapse. Thus, a three-order two-neuron-based autonomous memristive HNN is presented in this paper, which is the lowest order and has not been reported in the previous studies. With the mathematical model, the detailed stability analyses for the line equilibrium are executed, so that the fold and Hopf bifurcation sets and stability region distributions in the parameter plane are obtained. Furthermore, numerical results of coexisting bifurcation patterns are investigated, which are confirmed effectively by local basins of attraction and phase plane plots. The numerical results demonstrate coexisting multi-stable patterns of the spiral chaotic patterns with different dynamic amplitudes, periodic patterns with different periodicities, and stable resting patterns with different positions in the memristive HNN. Besides, the circuit synthesis and breadboard experiments are performed to well validate the numerical simulations.

Thermodynamics and the potential energy landscape: case study of small water clusters.

We investigated the structure and the thermodynamic properties of small water clusters with the nested sampling computational technique, using two different water models, the coarse-grained mW (up to 25 molecules) and the flexible version of the TIP3P (up to 16 molecules). By mapping the entire potential energy landscape of the clusters, we calculated the heat capacity curves, located the structural transitions and identified those local minimum basins which contribute the most to the total partition function. We found that in the case of the mW model, trends in first-order-like and continuous-like transitions can be very well matched to the characteristics of the landscape: cluster sizes with fewer and narrower local minimum basins show a sharper 'melting' peak on the heat capacity curve. Trends in the case of the TIP3P model were not easily assigned to the changing occupation of basins, and the contribution of local minima was negligible, except for n = 7, 15 and 16.

СЕЙСМИЧЕСКАЯ СТРУКТУРА ЗЕМНОЙ КОРЫ В КОЛЛИЗИОННОЙ ЗОНЕ СИБИРСКОГО КРАТОНА И ВЕРХОЯНО-КОЛЫМСКОЙ СКЛАДЧАТОЙ СИСТЕМЫ (ПРОФИЛЬ 3-ДВ)

The signs of the collisional structure are expressed in the upper crust by the advanced Priverhoyansk forland and local hinterland basins is separated by a high-speed array, most likely of magmatic origin. The boundary of the craton at an angle of about 15 ° is submerged under the crust of the folded system, where the characteristic layer of the craton lower crust at velocity of 6,7–6,9 km /s is absent and the velocity in a whole crust is reduced, as well as along the Moho from 8,3 to 7,9-8,0 km / s.

Dimensionality Reduction Reconstitution for Extreme Multistability in Memristor‐Based Colpitts System

In this paper, a four‐dimensional (4‐D) memristor‐based Colpitts system is reaped by employing an ideal memristor to substitute the exponential nonlinear term of original three‐dimensional (3‐D) Colpitts oscillator model, from which the initials‐dependent extreme multistability is exhibited by phase portraits and local basins of attraction. To explore dynamical mechanism, an equivalent 3‐D dimensionality reduction model is built using the state variable mapping (SVM) method, which allows the implicit initials of the 4‐D memristor‐based Colpitts system to be changed into the corresponding explicitly initials‐related system parameters of the 3‐D dimensionality reduction model. The initials‐related equilibria of the 3‐D dimensionality reduction model are derived and their initials‐related stabilities are discussed, upon which the dynamical mechanism is quantitatively explored. Furthermore, the initials‐dependent extreme multistability is depicted by two‐parameter plots and the coexistence of infinitely many attractors is demonstrated by phase portraits, which is confirmed by PSIM circuit simulations based on a physical circuit.

The Paleozoic Mount Carlton Deposit, Bowen Basin, Northeast Australia: Shallow High-Sulfidation Epithermal Au-Ag-Cu Mineralization Formed During Rifting

Mount Carlton is a Paleozoic high-sulfidation epithermal deposit located in the northern segment of the Bowen Basin, northeast Queensland, Australia. The deposit is hosted in Early Permian volcanic and sedimentary rocks, and an open-pit mining operation includes the Au-rich V2 pit in the northeast and the Ag-rich A39 pit in the southwest. Mineralization at Mt. Carlton occurred during active rifting, partly contemporaneously with the deposition of volcanic sediments in localized half-graben and graben basins. Steep normal faults and fracture networks related to the rifting acted as fluid conduits and localized cores of silicic alteration. The silicic cores transition outward to zones of quartz-alunite alteration, which are, in turn, enveloped by a zone of quartz-dickite-kaolinite alteration. Epithermal mineralization at Mt. Carlton developed in three stages: Cu-Au-Ag mineralization dominated by enargite was overprinted by Zn-Pb-Au-Ag mineralization dominated by sphalerite, which, in turn, was overprinted by Cu-Au-Ag mineralization dominated by tennantite. Proximal Au-Cu mineralization in the V2 pit occurs in networks of steep faults associated with veins and hydrothermal breccias within a massive rhyodacite porphyry. Three distinct ore zones (Eastern, Western, and Link) are aligned, en echelon, along a broadly E trending corridor. The Western ore zone continues along ~600-m strike length to the southwest into the A39 pit, and it shows a metal zonation, from proximal to distal, of Au-Cu → Cu-Zn-Pb-Ag → Ag-Pb-(Cu) → Ag. Distal Ag mineralization in the A39 pit is concentrated in a volcanolacustrine sedimentary sequence that overlies the rhyodacite porphyry. It occurs in a stratabound position oriented parallel to primary sedimentary layering and locally exhibits synsedimentary ore textures. Such textures are interpreted to have formed as mineralizing fluids discharged into what most likely were lakes developed within localized rift basins, at the same time that the volcanolacustrine sediments were deposited. At depth, equivalent ore textures were produced within open spaces in the structural roots of the rift basins. 40Ar/39Ar dating of hydrothermal alunite yielded an age range of 284 ± 7 to 277 ± 7 Ma, which links the formation of the Mt. Carlton deposit to the Early Permian back-arc rifting stage in the Bowen Basin. Prolonged extension provided rapid burial of the deposit beneath a postmineralization, volcanosedimentary cover, which was essential for the exceptional preservation of Mt. Carlton. The same extension caused displacement of the rock pile along a series of shallowly dipping detachment faults and segmentation and rotation of the ore zones across steeply dipping normal faults. This deformation would have displaced any underlying porphyry mineralization relative to the current location of Mt. Carlton.

Mapping spatial-temporal sediment dynamics of river-floodplains in the Amazon

Water composition in floodplains plays a key role in ecological processes and is affected by both local water sources and flooding from the main river. Despite local studies, still lacks a complete understanding on the relationship between hydrological processes and sediment distribution in the river-floodplain system of the Amazon basin. This paper presents the first mapping of the dynamics of suspended sediments in rivers and lakes (>0.25 km2) of central Amazon, considering different water types. Previous studies have considered only white-water rivers with high sediment concentration. This study also describes some river-lake systems in terms of their spatial-temporal pattern of sediments and water flows. Time series between 2003 and 2017 of red and infrared reflectance of Moderate Resolution Imaging Spectroradiometer (MODIS) images were temporally filtered to retrieve incomplete and low-quality data. These images were assessed as a proxy of the surface suspended sediments concentration; and maps of the spatial-temporal variation of sediments were created, such as the class frequency map. This map represents a 15-year frequency at which each pixel remains in one of the surface suspended sediments concentration classes: high, moderate, and low, with an overall accuracy of 71%. Our findings allowed to observe the variation of sediment concentration along the Solimões-Amazonas River, such as, for instance, its increase from the confluence with the Tapajós River to the mouth. Some hydrological processes were also observed in lakes of the middle reach, such as overbank flow and resuspension of sediments in depression lakes. In some ria lakes, the main water source comes from local basin with the backwater promoting sediment input in these lakes during the low-water period. The maps produced by this study are available and useful for supporting biogeochemical studies.