South Basin Research Articles

マルチプレックスPCR 法を用いた琵琶湖水系産タモロコ属2種のミトコンドリアDNAの簡易識別法：手法開発と南湖の産着卵への適用

マルチプレックスPCR 法を用いた琵琶湖水系産タモロコ属2種のミトコンドリアDNAの簡易識別法：手法開発と南湖の産着卵への適用

Analyzing the frequency of non-stationary hydrological series based on a modified reservoir index

Human activities and climatic changes have caused severe changes in hydrological values in recent decade. On the other hand, extreme values such as those of flood have non-stationary properties and using its data for hydrological studies requires stationary properties, while most meteorological variables have stationary properties. Some dams established in the Lake Urmia Basin (LUB) have provided an opportunity to control all hydrological variable of catchment area. In this study, extreme values were simulated and confirmed in an annual scale for hydrometric stations constructed after constructing the reservoir using modified reservoir index (MRI) in Zarinehrood basin in south of Lake Urmia. Results obtained from evaluating trend of studied values expressed that the Nezamabad (NA) hydrometric station is influenced by Shahid Kazemi and Norouzlo reservoirs among stations in the Zarinehrood basin. MRI was used to rebuild studied data. Statistical tests were used to evaluate accuracy of the method. Results of correlation coefficient between maximum flow discharge data of NA hydrometric station and upstream station showed a 53% correlation. Also, results obtained for trend of rebuild series indicated that there is no significant trend in time series. Results also showed that the two sets of time series distribute the same statistics by evaluating statistical distribution fit on rebuild maximum flow discharge and maximum flow discharge of upstream station. Results obtained from measuring MRI demonstrated high efficiency of this method in producing maximum flow discharge for stations constructed after construction of the dam.

Ретроспективный анализ динамики уловов и промысловых запасов красноперки в Волго-Каспийском и Северо-Каспийском рыбохозяйственных подрайонах

Rudd is one of the most abundant species in the large group of minnow in the Volga-Caspian and Northern-Caspian fishery subareas of the Volga–Caspian fishery basin south. The article contains the data on its catches and usable stocks during ХХ – ХХI centuries. A long term analysis of the rudd catches and the runoff volume during the spring high water showed no substantial connection between these processes due to the rudd’s ecological peculiarities. The dynamics of the rudd catches and the level of the Caspian Sea are connected in inverse ratio. Inverse correlations with high determination coefficients between the rudd catches, the usable stocks, and the sea level were obtained.

Sand injection and polygonal faulting in the Great South Basin, New Zealand

Abstract Subsurface sediment remobilization phenomena, including sand injection complexes and mud volcano systems, have been recognized to play a significant role in basinal fluid flow and in some cases are an important part of petroleum systems. Seismic-scale wing-like anomalies, interpreted as sand injections based on their similarities with North Sea examples, have been identified within the upper Paleocene sediments of the Great South Basin, New Zealand. The structures were observed on three-dimensional seismic data at about 2.5–2.7 s two-way time beneath the seabed. The sand injections occur below a well-developed polygonal fault system within the uppermost Paleocene sediments. The wing-shaped sand injections are often located near the downward extent of polygonal fault tips, possibly implying that the injections affected polygonal fault formation. This is the first time that a seismic-scale sand injection complex has been described in the southeastern hemisphere. The study adds to an emerging realization that sand injection complexes occur in many deep-water basins and has direct implications for basin evolution and hydrocarbon exploration in the Great South Basin.

Perceptions of the Challenges and Opportunities of Utilising Organic Waste through Urban Agriculture in the Durban South Basin.

Waste management has become pertinent in urban regions, along with rapid population growth. The current ways of managing waste, such as refuse collection and recycling, are failing to minimise waste in cities. With urban populations growing worldwide, there is the challenge of increased pressure to import food from rural areas. Urban agriculture not only presents an opportunity to explore other means of sustainable food production, but for managing organic waste in cities. However, this opportunity is not taken advantage of. Besides, there is a challenge of mixed reactions from urban planners and policymakers concerning the challenges and benefits presented by using organic waste in urban agriculture. The current paper explores the perceived challenges and opportunities for organic waste utilisation and management through urban agriculture in the Durban South Basin in eThekwini Municipality in KwaZulu-Natal (KZN) Province of South Africa. It is anticipated that this information will be of use to the eThekwini Municipality, policymakers, researchers, urban agriculture initiatives, households and relevant stakeholders in the study areas and similar contexts globally. Two hundred (200) households involved in any urban farming activity and ten (10) key informants (six (6) staff from the Cleaning and Solid Waste Unit of the eThekwini Municipality and four (4) from the urban agricultural initiative) were selected using convenient sampling. Descriptive statistics and inductive thematic analysis were used to analyse data. The significant perceived challenges and risks associated with the utilisation of organic waste through urban agriculture included lack of a supporting policy, climatic variation, lack of land tenure rights, soil contamination and food safety concerns. Qualitative data further showed that the difficulty in segregating waste, water scarcity, difficulty in accessing inputs, limited transportation of organic waste, inadequate handling and treatment of organic waste, and being a health hazard were some important challenges. On the other hand, the significant perceived benefits associated with the utilisation of organic waste through urban agriculture were enhanced food and nutrition security, and opportunities for business incubation. Other important benefits established through qualitative data were an improved market expansion for farmers and improved productivity. Overall, despite the perceived challenges and risks, there is an opportunity to manage organic waste through urban agriculture. It is imperative for an integrated policy encompassing the food, climate and waste management to be developed to support this strategy. All stakeholders—the government, municipal authorities and urban agricultural initiatives should also, guided by the policy, support urban farmers, for example, through pieces of training on how to properly manage and recycle organic waste, land distribution, inputs availability and water usage rights among other things.

ANALISIS AMPLITUDE VERSUS OFFSET (AVO) MENGGUNAKAN PARAMETER PETROFISIKA LAMBDA MU RHO (LMR) DAN EXTENDED ELASTIC IMPEDANCE (EEI) UNTUK KARAKTERISASI RESERVOAR KARBONAT

The research that refers to the characterization of carbonate reservoir to identify lithology and fluid had been done to the Baturaja Formation in South Sumatera Basin. The method used is analyzed of Amplitude Versus Offset (AVO) by utilizing the petrophysics parameter of Lambda Mu Rho (LMR) and Extended Elastic Impedance (EEI). The goal of the research is to find out the comparison of the application of petrophysics parameter LMR and EEI to characterization carbonate reservoir, besides finding a prospect location or proposed well. The result of data analysis of Al-Fatah well shows that the carbonate reservoir position with liquefied gas is located deeper around 350 meters with a thickness of around 7.62 meters. Interpretation of seismic from inversion result by using the petrophysics parameter of LMR and EEI shows the presence of a prospect location to the CDP 4253 up to 4301, which is carbonate reservoir with fluid accumulation (gas).

Occurrence and risk assessment of organic micropollutants in freshwater systems within the Lake Victoria South Basin, Kenya

The unintended release of chemicals to the environment has led to global concern on water quality prompting widespread research on the occurrence of these compounds in water. While increasing information on organic micropollutants (OMPs) in European water resources is available, there is still limited information on the occurrence of OMPs in African water systems. In this study, a multi-residue analysis covering 428 chemicals using liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS) was performed on water samples collected from 48 surface water sites within the Lake Victoria South Basin, Kenya. A total of 75 compounds including pharmaceuticals, personal care products (PPCPs), pesticides, and industrial chemicals were detected and an additional three compounds (nevirapine, lamivudine and adenosine) were identified through suspect screening. Four compounds including diphenhydramine, simazine, triethylphosphate and acetyl-sulfamethoxazole (A-SMX) were detected in >80% of the sites showing their ubiquitous nature in the study area. Individual compound concentrations were detected up to 24 μg L−1. Concentrations above 1 μg L−1 were also reported for triethylcitrate, N-ethyl-o-toluenesulfonamide, hexazinone, nevirapine, adenosine and carbendazim. While crustaceans were potentially the taxon at risk for acute toxicity (toxic unit (TU) up to 2) with diazinon driving this risk, lower but substantial acute risk (TU 0.5) was observed for algae. Chronic risks were observed in 11 sites for algae (TU > 0.02) and in 5 sites for fish (TU > 0.01). A total of 16 compounds were prioritized based on frequency and extent of the exceedance of thresholds for acute and chronic risks to algae, crustaceans and fish and another 7 compounds prioritized by applying lowest Predicted No-Effect Concentrations (PNEC). Based on these indicators, this study provides candidate priority compounds for monitoring, assessment and abatement in western Kenya.

Evaluation of high-resolution satellite products for streamflow and water quality assessment in a Southeastern US watershed

Study regionSeneca River Basin South Carolina, USA. Study focusThis study focuses on evaluating different precipitation products on streamflow and water quality modeling. We used 13 years (2001–2014) of daily data from multiple precipitation products. The precipitation products are classified into three categories: (1) products based on observed precipitation data (rain gauges located within the study area and PRISM data), (2) five satellite-based precipitation products (3B42, 3B42RT, PERSIANN-CDR, PERSIANN, and GPCP-1DD); and (3) one Reanalysis product (CFSR). The Soil and Water Assessment Tool (SWAT) was calibrated and validated using these precipitation products against monthly observed streamflow, total nitrogen (TN) loads, and total phosphorus (TP) loads within the Seneca River Basin situated in northwest of South Carolina, USA. For each precipitation product, the best performing model parameters was determined using the Sequential Uncertainty Fitting Procedure (SUFP2). New hydrological insights for the regionResults showed that the spatio-temporal pattern of precipitation products varies and further influenced the streamflow and water quality simulations. Most of the precipitation products achieved at least satisfactory performance (R2 > 0.50, NS > 0.50, and PBIAS ≥ ±15) for streamflow and water quality. PRISM product showed the best overall performance, followed by 3B42 and PERSIANN-CDR, whereas CFSR and PERSIANN products comparatively performed poorly for streamflow and water quality simulations. The uncertainty in the precipitation products was reflected in the streamflow that further affected the water quality simulations (TN and TP loads). In addition, this study showed that the parameter uncertainty significantly varies among precipitation products, leading to a considerable uncertainty in simulation results, especially for TN and TP. Our results suggest that using multiple precipitation products can increase the level of confidence in hydrologic model simulation, particularly in water quality modeling.

Estimation of long-term external nutrient loading from watersheds to Lake Biwa by a combined rainfall-runoff model and loading-discharge curve approach

External nutrient loadings to Lake Biwa were estimated using a combined tank model and loading-discharge curve approach. The model was applied to collective drainage basins of the lake’s Imazu (northwest), Hikone (northeast), and Otsu (south) areas. The hourly model was conducted using particular discharges from Kita (Ado) river, Takatoki (Ane) river, and Yasu River to obtain loading curves for phosphate (PO4) and silica (SiO2) by assimilating measured concentrations (2002–2003). The tank model was updated by adding an evapotranspiration routine and direct paths of groundwater discharges to the lake floor. The daily model was calibrated through analysis of water budget among the basin, inflow, lake and outflow, and then validated. The model was established and combined into a loading-discharge curve to determine the long-term external nutrient loadings entering the lake (1980–2017). Seasonal variation in nutrient loadings increased during spring and summer and decreased during winter. Annual phosphate-phosphorus (PO4-P) loading ranged from 217 to 296 tons yr–1 in the North Basin and 45 to 76 tons yr–1 in the South Basin, while SiO2 loading fluctuated from 16,027 to 32,655 tons yr–1 and 2,518 to 5,490 tons yr–1 in the North and South Basins, respectively.

The Study of Condition of the South Bug River Basin with Using Geoecological Methods

Purpose. Assess the current state of the Southern Bug River basin and the degree of anthropogenic impact on it (transformation) Methods. The methodology of complex field geographic research (according to S. Kurlov) was chosen for the research. On its basis, water samples were taken at the appropriate points of the river basin, which directly covered the Southern Bug River itself, as well as its tributaries, and the composition of coastal soils was analyzed. Laboratory experiments were performed on the basis of a licensed laboratory of the Uman National University of Horticulture Results. Based on the analysis of the data set of the main hydrochemical indicators of the surface water quality of the Southern Bug river basin and the analysis of the soil, it was found at some experimental points that the MPC content of the studied indicators was exceeded. The content is exceeded at all sampling points, due to the high content of complexes with humic acid salts, secondary waterlogging of reclaimed lands. The nitrite content is exceeded in the following places: r. Southern Bug (Vinnitsa and Ladyzhin), r. Ustya (Nemyriv), r. Udych litskiy district) and r. Dohna (Bershad district). The main reason for the intake of nitrates into the water is the washout of fertilizers from fields and vegetable gardens. All surface water bodies have increased water hardness, its acidity is within normal limits. The soils adjacent to the streams under consideration bear clear signs of hydrogenic accumulation of substances (carbonates, gypsum, salts) and deltaic conditions of formation (horizontal stratification, horizons buried, remnants of freshwater fauna). Conclusions. The concentration of pollutants increases with the approach of the tributaries of the Southern Bug River and the relief formed by them to their base of erosion. Excess concentrations of alkaline hydrolyzed nitrogen, as well as phosphorus and potassium compounds at the sampling points indicate a high level of intensity of the farming system, in which the use of agrochemicals is given priority. However, long-term ingress of these compounds into the water body will accelerate the process of eutrophication in the near future. The loss of humus in the soils of agricultural lands adjacent to the rivers Sob, Dokhna, Ustya was revealed. In general, the geosystem of the Southern Bug River suffers from a complex anthropogenic impact, the main source of which is agricultural production.

Annual changes in abundance of bluegill Lepomis macrochirus in the south basin of Lake Biwa

Annual changes in abundance of bluegill <I>Lepomis macrochirus</I> in the south basin of Lake Biwa

Multi-proxy records of Holocene fluvio-lacustrine sediments in the southern Liaodong Peninsula, China

The Liaodong Peninsula is located in the present Asian summer monsoon (ASM) area and has frequent land-sea interactions that make it sensitive to climate change. Terrestrial sediments can continuously record climate change with high resolution. The range and time of the East Asian summer monsoon (EASM), the main Holocene climate change driver, can be better explained by the change in the sedimentary environment in the region. This paper presents the chronology, sedimentology and geochemistry of the Holocene fluvio-lacustrine sediments in the Paozi basin south of Liaodong Peninsula, China. The multi-agent records show that the temperature and humidity are slightly higher from before 5.2ka.cal.BP to warm / wet stage, and the relative transition time from the warmest / wet stage to cold / dry stage is from 5.2ka.cal.BP to 3.5ka.cal.BP. Then, the regional climate shifted to relatively drier and colder conditions after 3.5 ka.cal.BP. Compared with other records near our site, the climate and variations in the water level change of this palaeolake were controlled by the change in the Holocene EASM precipitation, and the insolation-driven temperature co-determined the dynamics. Furthermore, the formation and disappearance of the palaeolake was due to the strengthening and decline in the EASM, respectively.

Seasonal variation in trophic structure and restoration effects in a deep perialpine lake (Lake Lugano, Switzerland and Italy)

Using monitoring data from the South Basin of Lake Lugano (Switzerland and Italy), we examined seasonal responses of phytoplankton and herbivorous zooplankton biomass to nearly three decades (1989–2017) of phosphorus (P) management to ask: [1] what is the trophic structure of the lake, [2] whether trophic structure and the effects of nutrient management varied seasonally, and [3] what are the implications of the existent trophic structure for the restoration of the lake. Trophic structure varied seasonally, including a structure consistent with strong consumer control (exploitation food chain) in spring and fall, and an unexpected structure in summer, characterized by a negative correlation between phytoplankton biomass and phosphorus. This structure was explained by accumulation of inedible phytoplankton (mainly cyanobacteria) at low P concentrations. Owing to a lack of apparent resource (P) control, P-management had no detectable effects on phytoplankton biomass. The trophic structures identified in the lake provides explanations for this lack of response to P-management and for the differences between the responses of the South Basin of Lake Lugano and other perialpine lakes. Based on the results, lake restoration practice would benefit from a greater understanding and an increased ability to predict trophic structure within and across lakes.

Determination of stress in the geological medium on the basis of well data using acoustoelastic correlations

A method has been developed to determine normal components of the stress tensor in deformed geological media on the basis of geophysical well logging. The theoretical basis of the method is the acoustic correlations of the non-classical linearized approach of nonlinear elastodynamics. Analytical formulae are obtained to calculate the stress in the geological medium in cases of small and large deformations. Geophysical well logging data located in the South Caspian basin have been used. Thin-layered one-dimensional models of the medium have been compiled on velocities of pressure and shear waves, density and lithology of rocks. The thickness of each layer of the model is several centimeters, which is equal to the observations in the well. The data of each model related to the same rock lithology is divided into clusters using artificial neural networks to consider the influence of changes of thermobaric conditions of the geological medium on acoustic properties of rocks. Values of elasticity moduli of the second and third orders and components of normal stress tensor have been calculated according to models for each lithology of rocks and a cluster of data. It has been revealed that elasticity moduli of the third order are much more sensitive to the variability of elastic properties of the medium than moduli of the second order. The obtained numerical results on all clusters of each lithology of rocks are averaged. At the same time, the number of medium layers on each data cluster has been used as weights. The number of medium layers in each rock has been used as weights while averaging the results for all the rocks. The correlations between numerical values of normal components of stress tensor caused by geostatic pressure and similar values caused by geodynamic changes of stress tensor have been studied. It has been revealed that values of stress bulk caused by geostatic pressure are significantly lower than stress caused by geodynamic changes. The obtained acoustic formulae allow determining values of stress in the geological medium of any region considering the influence of modern geodynamic processes.

Mercury loading within the Selenga River basin and Lake Baikal, Siberia

Mercury (Hg) loading in Lake Baikal, a UNESCO world heritage site, is growing and poses a serious health concern to the lake’s ecosystem due to the ability of Hg to transform into a toxic form, known as methylmercury (MeHg). Monitoring of Hg into Lake Baikal is spatially and temporally sparse, highlighting the need for insights into historic Hg loading. This study reports measurements of Hg concentrations from water collected in August 2013 and 2014 from across Lake Baikal and its main inflow, the Selenga River basin (Russia, Mongolia). We also report historic Hg contamination using sediment cores taken from the south and north basins of Lake Baikal, and a shallow lake in the Selenga Delta. Field measurements from August 2013 and 2014 show high Hg concentrations in the Selenga Delta and river waters, in comparison to pelagic lake waters. Sediment cores from Lake Baikal show that Hg enrichment commenced first in the south basin in the late-19th century, and then in the north basin in the mid-20th century. Hg flux was also 20-fold greater in the south basin compared to the north basin sediments. Hg enrichment was greatest in the Selenga Delta shallow lake (Enrichment Ratio (ER) = 2.3 in 1994 CE), with enrichment occurring in the mid-to late-20th century. Local sources of Hg are predominantly from gold mining along the Selenga River, which have been expanding over the last few decades. More recently, another source is atmospheric deposition from industrial activity in Asia, due to rapid economic growth across the region since the 1980s. As Hg can bioaccumulate and biomagnify through trophic levels to Baikal’s top consumer, the world’s only truly freshwater seal (Pusa sibirica), it is vital that Hg input at Lake Baikal and within its catchment is monitored and controlled.

Seasonal Use of a Nonnatal Marine Basin by Juvenile Hatchery Chinook Salmon

AbstractInformation on the movement patterns of fishes is essential for managers that are making critical resource decisions. We examined the frequency of a keystone species, Chinook Salmon Oncorhynchus tshawytscha that migrated from different marine basins to the Nisqually River estuary, which lies within the southernmost marine basin (hereafter, “South basin”) in Puget Sound (Washington, USA). Hatchery‐reared juvenile fish were sampled by using beach seine, lampara seine, and fyke nets to determine seasonal trends in frequency, habitat use, and the influence of different capture methods. The captured fish originated from three marine basins, nine Puget Sound rivers, and fourteen hatcheries. The data revealed a consistent pattern showing that most of the tagged fish (72%) were from the nearby Nisqually River (in the South basin), but fish from more northerly marine basins (hereafter, “Outbasin”) were also common. Although the majority of the tagged fish (99%) that were captured during April and May were originally released into rivers adjacent to the South basin, 90% of the fish that were captured in August and September had originated from rivers adjacent to Outbasin locations (up to 130 km distant). A comparison of sampling methods showed that the beach seine produced 27% Outbasin fish compared with 53% that were obtained with the lampara seine. The analysis of habitat use suggested that during June and July, more Outbasin fish (&gt;40%) were captured in delta flats and nearshore habitats than in estuarine emergent marsh habitat (26%). Release location (river basin), but not distance, appeared to be an important factor that influenced the percentage of Outbasin fish that were captured in the South basin. However, it appeared that the fish that were released at light weights and early dates were more likely to be captured. Information on the movement of juvenile salmon to a nonnatal marine basin may help to increase our understanding of features of life history and survival, and it has application elsewhere, as many marine species are artificially propagated, released in large numbers, and have the potential to use nonnatal habitats.

A Preliminary inventory of alien and cryptogenic species in Monastir Bay, Tunisia: spatial distribution, introduction trends and pathways

The Mediterranean Sea is a marine biodiversity hotspot under threat. One of the major impacts on its biological resources and services comes from the invasiveness of non-indigenous species (NIS). Nevertheless, NIS monitoring programs in the south basin of the Mediterranean Sea are in an early implementation stage. This study aims to describe NIS and cryptogenic species distribution in Monastir Bay (Tunisia) and to identify risk areas for the introduction and spread of invasive species, providing a baseline for future monitoring programs. To this end, a series of Rapid Assessment Surveys were carried out to identify NIS and cryptogenic species in one marina, five fishing ports, two aquaculture farms and the Special Conservation Area of the Kuriat islands. 24 species were found, of which 11 constitute new records for Monastir Bay, which represent a 33.3% of the total NIS reported in this Bay. Assemblages differed between substrata types, being NIS more abundant in artificial than in natural substrata. Regarding locations, Cap Monastir Marina was the most invaded site, the most transited by vessels and the only one visited by international sailing. Hence, this marina constitutes the main risk area to be monitored, although the fishing ports and fishing farms in the semi-enclosed coastal lagoon of Monastir Bay can also be considered as risk areas. Nevertheless, more research effort is needed in Monastir Bay in order to update the records of NIS and cryptogenic species and increase insight on the ecological evolution of these species and their related impacts on natural communities and marine resources.

Investigating polygonal fault topological variability: Structural causes vs image resolution

The topology of three polygonal fault sets is investigated to determine potential causes of variations in connectivity (as measured by nodes and branches) between, and vertically within the fault sets. Two faults sets (from the Great South Basin (GSB), New Zealand, and Southeast Asia (SEA)) are imaged by 3D seismic reflection data, a third data set (Al Farafra Oasis, Egypt) is imaged from satellite data. The values measuring connectivity for the GSB and SEA polygonal fault sets plot in ternary diagrams in similar areas to other complex normal fault sets from rifts. These data sets are dominated by faults with either isolated fault tips (I nodes) or with abutting or splaying geometries (Y nodes). The similarities in node and branch topology of polygonal faults, and complex fault patterns in rifts (associated with multi-phase rifting, complex local stress rotations, or inherited fabrics), which are imaged on 3D seismic, indicates that topology describes the complexity of fault connectivity, but in general, by itself, cannot discriminate the causes of normal fault pattern variations. The Al Farafra Oasis faults sets (areas 2 and 3) provide an end member example of fault patterns with a very high degree of connectivity associated with cross-cutting fault sets (X-nodes) that are more rarely present in other fault sets. Some faults forming X-nodes may be hybrid tensile-shear failure fractures, or even calcite vein-filled tensile fractures. Much of the difference between the seismic and satellite image data sets may be related resolution, indicating that comparisons of topology characteristics are best made between data sets of similar resolution.

Terrane Boundary Reactivation, Barriers to Lateral Fault Propagation and Reactivated Fabrics: Rifting Across the Median Batholith Zone, Great South Basin, New Zealand

AbstractProminent preexisting structural heterogeneities within the lithosphere may localize or partition deformation during tectonic events. The NE‐trending Great South Basin, offshore New Zealand, formed perpendicular to a series of underlying crustal terranes, including the dominantly granitic Median Batholith Zone, which along with the boundaries between individual terranes exert a strong control on rift physiography and kinematics. We find that the crustal‐to‐lithospheric scale southern terrane boundary of the Median Batholith Zone is associated with a crustal‐scale shear zone that was reactivated during Late Cretaceous extension between Zealandia and Australia. This reactivated terrane boundary is oriented at a high angle to the faults defining the Great South Basin. We identify a large granitic laccolith along the southern margin of the Median Batholith, expressed as subhorizontal packages of reflectivity and acoustically transparent areas on seismic reflection data. The presence of this strong granitic body inhibits the lateral southwestward propagation of NE‐trending faults, which segment into a series of splays that rotate to align along the margin as they approach. Further, we also identify two E‐W‐ and NE‐SW‐oriented basement fabrics, likely corresponding to prominent foliations, which are exploited by small‐scale faults across the basin. We show that different mechanisms of structural inheritance are able to operate simultaneously, and somewhat independently, within rift systems at different scales of observation. The presence of structural heterogeneities across all scales needs to be incorporated into our understanding of the structural evolution of complex rift systems.

Middle Pleistocene formation of the Rio Grande Gorge, San Luis Valley, south-central Colorado and north-central New Mexico, USA: Process, timing, and downstream implications

The Rio Grande is the fourth longest river in North America extending over 3,000 km from the Rocky Mountains to the Gulf of Mexico. The Pleistocene evolution of this river from individual subbasins into a coalesced fluvial system has been long debated. Herein, we constrain the middle Pleistocene evolution of the northernmost and largest Rio Grande basin, the San Luis basin, and the timing of incision of the Rio Grande Gorge, based on new geologic mapping, 3He surface exposure dating, and U-series dating on pedogenic carbonates. 3He dating of shoreline deposits of closed basin Lake Alamosa and fluvially scoured bedrock along the Rio Grande gorge rim indicate the San Luis basin was connected with southerly Rio Grande basins and progressively incised since ∼400 ka. Waning tectonic activity, coupled with the hydrologic response to intensified middle Pleistocene glaciation, drove southward spillover of Lake Alamosa ∼400 ka, expanding the river's drainage basin by nearly 24,000 km2, and adding recharge areas in the high-altitude, glaciated San Juan, Tusas, and Sangre de Cristo Mountains. Geologic barriers to streamflow on the Taos Plateau were breached and basin tributary drainages were integrated and inset into their present canyons ∼250-200 ka, with approximately 120 m of incision during ∼400-200 ka. Previous work demonstrates that southerly streamflow through basins south of the SLB terminated into a large, rift-related bolson complex until the middle Pleistocene, and most axial Rio Grande river incision has occurred since 630 ka. We propose that middle Pleistocene integration of the SLB was the major geomorphic event that eroded Plio-Pleistocene tectonic and volcanic barriers and re-established flow of the Rio Grande from the Rocky Mountains to the Gulf of Mexico.