Lake Formation Research Articles

LO STATO ATTUALE DEI GHIACCIAI ITALIANI E LA LORO RECENTE EVOLUZIONE

Mountain glaciers represent an important hydrological and touristic resource, and their recent evolution provides a dramatic evidence of climate change for the general public. Glacier inventories, quantifying glacier characteristics and evolution, are an important tool to describe and manage high mountain glacier environments and Italy has developed a long tradition in this sector. Our country was the first to provide itself with a glacier inventory, compiled by Comitato Glaciologico Italiano and CNR, showing a glacier surface of 530 km2. A recent project, coordinated by Università Statale di Milano with the support of private bodies and the cooperation of Comitato EvK2CNR and Comitato Glaciologico Italiano, led to the development of the new Italian Glacier Inventory, a national atlas produced from the analysis of color orthophotos at high resolution acquired between 2005 and 2011. The New Italian Glacier Inventory lists 903 glaciers, covering an area of 370 km2. The largest part of glacier area is located in Val d’Aosta (36.15% of the total), followed by Lombardia and South Tyrol. 84% of glaciers (considering the number of glaciers) have an area lower than 0.5 km2 and jointly account for 21% of the total glacier surface. Glaciers larger than 1 Km2 make up 9.4% of the total number, but cover 67.8% of the total glacier area. The comparison between data from the New Italian Glacier Inventory and the CGI-CNR inventory (1959-1962) shows a 30% reduction in glacier area in Italy; considering instead the World Glacier Inventory or WGI, published at the end of the ‘80s, which reported 1381 glaciers and an area of 609 km2, glacier loss sums up to 478 glaciers and an area of 239 km2 (-39%). This shrinkage has led to rapid and significant changes to high mountain landscapes, notably glacier fragmentation, an increase in deglaciated areas, the formation of proglacial lakes and the development of pioneer vegetation.

Tectono-stratigraphic basin evolution in the Tehuacán-Mixteca highlands, south western México.

The morphological evolution of the basins in the Sierra Madre del Sur (SMS), southern México is poorly understood. This work explains for the first time the geomorphological development of the tectonic, fluvially-interconnected SMS basins named San Juan Raya (SJRb) and Zapotitlán (ZAPb). The evolution of the SJRb and ZAPb are analysed within the context of the transformations of the well-studied Tehuacán basin (TEHb). A new interpretation of a series of tectonic features of the TEHb valley area is also presented. Published geological data and extensive field work provided the basis for our geomorphological and evolutionary interpretation of basin evolution of this part of Mesoamerica during the late Cenozoic. Stratigraphic and sedimentary records suggest that after the late Cretaceous-early Cenozoic orogeny the TEHb and ZAPb were closed basins, and that the TEHb graben system was activated during the Paleogene as a response to the dominant regional NW-SE trending faults. We propose that the ZAPb and SJRb formed sequentially during the Neogene as a result of new E-W, N-S and NE-SW faults. The continuation of the TEHb extension during the Oligocene widened its lowland area and allowed the formation of an extensive lake. No alluvial or fluvial records of this interval are found in the ZAPb and SJRb. No sedimentation rather than formation and subsequent erosion of such sediments is supported by the basin morphology and by the absence of re-worked alluvial deposits at the outlet area where both connect to the TEHb. By middle to late Miocene the TEHb lost its endorheic configuration, ending the lake-type deposition while new faults initiated the opening of the ZAPb. Intensive tectonics, alluvial deposition and the confinement of the Tehuacán lake to the north sector of this basin characterised the Pliocene. During the late Pliocene to the early Pleistocene the formation of the SJRb was initiated. Quaternary faulting related to basin extension along the north watershed of the SJRb and ZAPb is supported by independent data on the biogeography of the cactus Mammillaria pectinifera. We introduce the idea that the departure from the regional NW-SE fault alignment that formed the major Miocene basins to a more local E-W trend that formed Neogene-Quaternary basins was probably a response to the latest post-orogenic relaxation of the crust in the Mixteca terrane.

Red Chert Quarries in the Munsungun Lake Formation: Moving beyond Norway Bluff

ABSTRACTRed chert attributed to the Munsungun Lake geologic formation located in northern Maine is common in terminal-Pleistocene, fluted-point-period lithic assemblages throughout New England. A visually identical material also appears in some later-period sites in coastal Maine. Until recently no bedrock source for this red chert showing convincing evidence of precontact use was known. Here we present the NKP site complex, a series of quarry-related stone-tool-manufacturing workshop sites associated with outcrops of high-quality red/green chert. These outcrops represent the only known source of this material with evidence of precontact human use within the Munsungun Lake formation. Although unequivocal fluted-point-period artifacts, such as fluted bifaces, are not yet documented at the NKP complex, the recurrent appearance of red Munsungun chert in fluted-point-period lithic assemblages in New England suggests the manufacture of fluted points took place in the vicinity of these outcrops.

Glacial Lake Changes and Identification of Potentially Dangerous Glacial Lakes in the Yi’ong Zangbo River Basin

The southeastern Tibetan Plateau, where monsoonal temperate glaciers are most developed, has a huge number of glacial lakes. Based on Landsat Operational Land Imager (OLI) images, 192 glacial lakes with a total area of 45.73 ± 6.18 km2 in 2016 were delineated in the Yi’ong Zangbo River Basin. Glacial lakes with areas of less than 0.1 km2 accounted for 81.77% of the total number, and glacial lakes located above 4500 m elevation comprised 83.33%. Dramatic glacier melting caused by climate warming has occurred, resulting in the formation and expansion of glacial lakes and the increase of potential glacial lake outburst floods (GLOFs) risk. From 1970 to 2016, the total area of glaciers in the basin has decreased by 35.39%, whereas the number and total area of glacial lakes have, respectively, increased by 86 and 1.59 km2. In that time, 110 new glacial lakes emerged, whereas 24 of the original lakes disappeared. The newly formed lakes have a smaller mean area but higher mean elevation than the lakes that disappeared. Based on five indicators, a first-order method was used to identify glacial lakes that pose potential threats. We identified 10 lakes with very high, 7 with high, 31 with medium, and 19 with low GLOF susceptibility, out of 67 moraine-dammed glacial lakes with areas larger than 0.02 km2. Understanding the behavior of glaciers and glacial lakes is a vital aspect of GLOFs disaster management, and the monitoring of glacial lakes should be strengthened.

Potential future lakes from continued glacier shrinkage in the Aosta Valley Region (Western Alps, Italy)

Aosta Valley (Western Alps, Italy) is the region with the largest glacierized area of Italy. Like other high mountain regions, it has shown a significant glacier retreat starting from the end of the ‘Little Ice Age’ that is expected to continue in the future. As a direct consequence of glacier shrinkage, glacier-bed overdeepenings become exposed, offering suitable geomorphological conditions for glacier lakes formation. In such a densely populated and developed region, opportunities and risks connected to lakes may arise: 1) economic exploitation for hydropower production, tourism and water supply; 2) environmental relevance for high mountain biodiversity and geodiversity; 3) potential risks due to outbursts and consequent floods.In this study, the locations of potential future glacier lakes over large glacierized areas (183 glaciers covering 163,1 km2) of Aosta Valley were assessed by using the GlabTop2 model.46 overdeepenings larger than 10,800 m2 were identified, covering an area of 3.1 ± 0.9 km2 and having a volume of 0.06 ± 0.02 km3. The majority of the overdeepenings are located in the Monte Rosa-Cervino massif and a mean depth <10 m characterizes them. Moreover, an estimation of the most recent total ice volume for the Aosta Valley was provided (5.2 ± 1.6 km3 referred to 2008).Thanks to the validation by the proposed “backward approach” and GPR (Ground Penetrating Radar) data, we can confirm that the location of the overdeepenings is robust while their actual dimensions are subject to considerable uncertainties. Almost all of large lakes (area > 10,000 m2), potentially the most dangerous, are modelled. Finally, we suggest choosing medium pixel size (about 60 m) of the DEM in order to obtain, at least, the location of the largest lakes and to avoid overestimations of ice thickness and thus a great number of false positive overdeepenings.The results presented here can be useful for understanding how the alpine environment will look in the future and can help the management of water resources and risks related to glacier lakes.

Monitoring Supraglacial lakes Formation and Risk of Outburst Flooding in the Himalayan Cryosphere of Pakistan

The dramatic rise in warm temperatures in the Himalayan region has caused the formation and expansion of numerous supraglacial lakes, some of which pose a serious flood hazard for the downstream communities. In this study, we have investigated the risk of flood hazards associated with supraglacial lakes in the Hindu Kush, Karakoram and Himalayan ranges of Pakistan using Landsat 8 OLI (Operational Land Imager) data of 2013 and field observations. Among the total of 438 supraglacial lakes, the majority were identified in the Karakoram (378) followed by the Hindu Kush range (39). The concentration of lakes was high within 3500-4000 m elevation (168) followed by 4000-4500 m elevation range (116). The lakes had shown more than a two-fold increase during the 2001-2013 period in the three mountain ranges. The increase in lake number was pronounced over valley glaciers likely due to increasing hydro-glacial activity under changing climate. Two types of supraglacial lakes were identified based on geographic characteristics, for example those rolling over glaciers surface away from the margins (called rolling supraglacial lakes ‘RSLs’) and the lakes found near the margins of glaciers mostly stationary in nature (called static supraglacial lakes ‘SSLs’). Most of the glacial lakes outburst flood (GLOF) events have been observed from SSLs in this region. However, the hydrodynamic process exaggerating the risk of GLOF from supraglacial and englacial lakes needs in-depth research for effective disaster risk reduction in this region in future.

Interpreting basal sediments and plant fossils in kettle lakes: insights from Silver Lake, Michigan, USA

We report on pollen, plant macrofossils, and associated lithostratigraphy of a sediment core extracted from the base of Silver Lake, a kettle lake in northern Lower Michigan, USA, which reveal a complex deglacial scenario for ice block melting and lake formation, and subsequent plant colonization. Complementary multivariate statistical and squared chord distance analyses of the pollen data support these interpretations. The basal radiocarbon age from the core (17 540 cal years BP) is rejected as being anomalously old, based on biostratigraphic anomalies in the core and the date’s incongruity with respect to the accepted regional deglaciation chronology. We reason that this erroneous age estimate resulted from the redeposition of middle-Wisconsin-age fossils by the ice sheet, mixed with the remains of plants that existed as the kettle lake formed at ca. 10 940 cal years BP by ice block ablation. Thereafter, the kettle lake became a reliable repository of Holocene-age fossils, documenting a mature boreal forest that existed until 10 640 cal years BP, followed by a pine-dominated mixed forest, an early variant of the mixed conifer–hardwood forest that persists to the present day. Our study demonstrates that researchers investigating kettle lakes, a common depositional archive for plant fossils in deglaciated landscapes, should exercise caution in interpreting the basal (Late Pleistocene/early Holocene-age) part of lake sediment cores.

Tracking of areas of thermokarst occurrences from satellite images (on the example of the main water pipeline route in Central Yakutia)

&amp;nbsp; In the areas of distribution of permafrost rocks and development of the ice complex, lake thermokarst is the main relief-forming process, which forms a characteristic alas relief. In addition to the formation of lakes, as a result of thermokarst subsidence, accompanied by water runoff, forms the thermo-sculptured relief including Baydzharakh and hummock-hollow forms. This leads to formation of thermokarst occurrences. The object of this research is thermokarst occurrences, namely, polygonal microrelief and frost splitting, explored in the section of the main water pipeline &amp;ldquo;Lena &amp;ndash; Tuora-Kyuel &amp;ndash; Tatta&amp;rdquo;, near the settlement of Maya Megino-Kangalassky Ulus of the Sakha Republic (Yakutia). These thermokarst occurrences were identified from the satellite images that are publicly available on the Internet. The author also applied processing technique of engineering and geological data, literary and library materials were also used in the work. Field research and simple photography were also used for determining the shape and size polygons. The main conclusion consists in suggesting simple method that allows to conduct area zoning of the territory for activation of the polygonal microrelief as thermokarst occurrences. The research results of area zoning related to distribution of cryogenic processes can be used in technical-economic substantiation of the choice of routes of linear and other constructs. &amp;nbsp;

Lake Evolution, Hydrodynamic Outburst Flood Modeling and Sensitivity Analysis in the Central Himalaya: A Case Study

Climate change has led to the formation of numerous high-altitude lakes of glacial origin in the Himalaya. Safed Lake is one of the largest glacial lakes, located at an elevation 4882 m a.s.l. in the state of Uttarakhand, central Himalaya, India. A temporal analysis of the lake surface using satellite imagery shows that the lake has grown more than double its size from 0.10 km2 to 0.23 km2 over the past 50 years. In this study, we performed a hazard assessment of the lake using 1D and 2D hydrodynamic modeling. We identified the potential glacial lake outburst flood (GLOF) triggering factors and evaluated the impact of a moraine breach event of the lake on the nearest village located 16.2 km downstream of the lake. A series of dynamic simulations were performed for different scenario-models based on varied breach depths, breach widths and time of moraine failure. In a worst-case GLOF scenario where breach depth reached up to 60 m, hydrodynamic routing of the breach hydrograph along the given channel revealed inundation depth up to 5 m and flow velocities up to 3.2 m s−1 at Milam village. Considering the flat geometry of the frontal moraine, hazard assessment of the lake was performed by for different breach incision depths (30 and 15 m). In addition, the study incorporated a series of hydrodynamic routing to understand the sensitivity of GLOF to different model input parameters and terrain conditions. The sensitivity of the initial GLOF hydrograph to breach formation time (Tf) was evaluated by considering different hypothetical breach scenarios with a varied time of failure. Increases of 11.5% and 22% in the peak flooding were recorded when the moraine failure time was decreased by 15 and 30 min respectively. The two-dimensional sensitivity revealed flow velocity (m s−1) to be more sensitive to change in Manning’s N when compared to the inundation depth (m). Changes of 10.7% and 0.5% in the mean flow velocity (in m s−1) and flow depth (in m) were recorded when dN was 0.01. The flow velocity was more sensitive to the slope and the top-width of the channel when compared to the inundation depths. A regression of flow velocity versus slope gives a correlation coefficient of 0.76. GLOF flow hydraulics are sensitive to changes in terrain elevation, where flow depth and velocity vary in a similar manner.

Characterization of Kyagar Glacier and Lake Outburst Floods in 2018 Based on Time-Series Sentinel-1A Data

Early recognition of glacial lake outburst floods (GLOFs) is required for timely and cost-effective remedial efforts to be implemented. Although the formation of ice-dammed lakes is known to begin as a pond or river that was blocked by ice from the glacier terminus, the relationship between glacier dynamics and lake development is not well understood. Using a time-series of Sentinel-1A synthetic aperture radar (SAR) data acquired just before and after the lake outburst event in 2018, information is presented on the dynamic characteristics of Kyagar Glacier and its ice-dammed lake. Glacier velocity data derived from interferometry show that the glacier tongue experienced an accelerated advance (maximum velocity of 20 cm/day) just one month before the lake outburst, and a decreased velocity (maximum of 13 cm/day) afterward. Interferometric and backscattering properties of this region provide valuable insight into the diverse glaciated environment. Furthermore, daily temperature and total precipitation data derived from the ECMWF re-analysis (ERA)Interim highlight the importance of the sustained high-temperature driving force, supporting empirical observations from previous studies. The spatial and temporal resolution offered by the Sentinel-1A data allows variations in the glacier surface motion and lake evolution to be detected, meaning that the interaction mechanism between the glacial lake and the associated glacier can be explored. Although the glacier surge provided the boundary conditions favorable for lake formation, the short-term high temperatures and precipitation caused the melting of ice dams and also a rapid increase in the amount of water stored, which accelerated the potential for a lake outburst.

Mass Loss From Calving in Himalayan Proglacial Lakes

The formation and expansion of Himalayan glacial lakes has implications for glacier dynamics, mass balance and glacial lake outburst floods (GLOFs). Subaerial and subaqueous calving is an important component of glacier mass loss but they have been difficult to track due to spatiotemporal resolution limitations in remote sensing data and few field observations. In this study, we used near-daily 3 m resolution PlanetScope imagery in conjunction with an uncrewed aerial vehicle (UAV) survey to quantify calving events and derive an empirical area–volume relationship to estimate calved glacier volume from planimetric iceberg areas. A calving event at Thulagi Glacier in 2017 was observed by satellite from before and during the event to nearly complete melting of the icebergs, and was observed in situ midway through the melting period, thus giving insights into the melting processes. In situ measurements of Thulagi Lake’s surface and water column indicate that daytime sunlight absorption heats mainly just the top metre of water, but this heat is efficiently mixed downwards through the top tens of metres due to forced convection by wind-blown icebergs; this heat then is retained by the lake and is available to melt the icebergs. Using satellite data, we assess seasonal glacier velocities, lake thermal regime and glacier surface elevation change for Thulagi, Lower Barun and Lhotse Shar glaciers and their associated lakes. The data reveal widely varying trends, likely signifying divergent future evolution. Glacier velocities derived from 1960/70s declassified Corona satellite imagery revealed evidence of glacier deceleration for Thulagi and Lhotse Shar glaciers, but acceleration at Lower Barun Glacier following lake development. We used published modelled ice thickness data to show that upon reaching their maximum extents, Imja, Lower Barun and Thulagi lakes will contain, respectively, about 90 × 106 , 62 × 106 and 5 × 106 m3 of additional water compared to their 2018 volumes. Understanding lake–glacier interactions is essential to predict future glacier mass loss, lake formation and associated hazards.

Application of multiple Roux-en-Y hepaticojejunostomy reconstruction by formation of bile hilar duct lake in the operation of hilar cholangiocarcinoma.

Hilar cholangiocarcinoma is the most common malignant tumor of the extrahepatic bile duct. Until now, radical resection has been the most effective method for the long-term survival of patients with the disease. However, many problems have emerged in the field of hepatobiliary surgery for a long time, including complex surgical procedures, low resection rate, and postoperative complications. We have adopted the "multiple Roux-en-Y hepaticojejunostomy reconstruction by formation of a bile duct lake" technique in the treatment of hilar cholangiocarcinoma since 2008, and obtained satisfactory short- and long-term results. To examine the feasibility of the application of multiple Roux-en-Y hepaticojejunostomy reconstruction by formation of a bile duct lake in the operation of hilar cholangiocarcinoma. A retrospective analysis was performed for the clinical data, surgical methods, and results of 76 patients with hilar cholangiocarcinoma who were treated with hilar bile duct lake-forming multiple Roux-en-Y hepaticojejunostomy reconstruction at Gansu Provincial Hospital. In all 76 cases, the operation was successful and no operative death occurred. The mean (range) operation time was 215.4 ± 53.5 min (124-678 min), and the amount of bleeding during the operation was 428.2 ± 63.8 mL (240-2200 mL). The overall 1-year survival rate was 78.9%, and the 3-year survival rate was 32.8%. The multiple Roux-en-Y hepaticojejunostomy reconstruction technique with formation of a bile duct lake is safe and effective for the surgical treatment of hilar cholangiocarcinoma.

Zooplankton trajectory before, during and after a hydropower dam construction

Abstract: Aim Understanding the impact of anthropogenic activities is central for supporting management and conservation efforts. In aquatic ecosystems, the construction of dams for hydroelectric power plants is a major environmental change that turns the riverine ecosystem into a reservoir lake. Such environmental deep alteration causes profound impacts in biota. The goal of this study is to make a comprehensive description of zooplankton trajectory following the construction of a reservoir in the transition from the hotspot Cerrado to Amazon, Central Brazil. Methods We used data sampled before, during and after the formation of the reservoir lake in 10 sampling units each period. We evaluated compositional changes, shifts in spatial organization, and a variation in beta-diversity from before to after the dam constructions using a set of multivariate analyses. We evaluated effects for Rotifers, Copepods and Cladocerans separately. Results Compositional changes were evident for all zooplankton groups: Rotifers, Copepods and Cladocerans. Besides, spatial community organization was also affected but depending on the beta-diversity facet and data resolution – mainly turnover using abundance data, except for Copepods. Finally, an increase in nestedness occurred for all groups during the formation of the reservoir lake. Conclusions In summary, our study showed the deep impacts for zooplankton that the formation of a reservoir lake causes. We innovate by making a complete assessment, which indicate clearly the complexity of evidencing impacts in aquatic communities. We also suggest that long-term monitoring should continue in reservoirs for scientific purposes. The changes in biota also make clear that the construction of dams should be accompanied by preservation of other pristine riverine ecosystems.

Sulfate Mineral Lakes of Western Transbaikalia: Formation Conditions and Chemical Composition of Waters and Bottom Sediments

Abstract —The paper presents the formation of the chemical composition of water in the sulfate mineral lakes of western Transbaikalia. It is shown that sodium sulfate water in the regional lakes forms in two zones of continental salinization, the Barguzin and Gusinoe Ozero–Orongoi depressions. The average mineralization of the lakes reaches 30.8 g/L, pH = 7.90–8.84, the fractional content of sulfate ion is 55.2–81.8% eq, and the fractional content of sodium ion is 59.1–82.1% eq. The paper presents the major-ion and trace-element composition of lake waters and the chemical and mineral composition of bottom sediments. It is shown that groundwater enriched in sodium sulfate plays a major role in the lake formation.

Дистанционное и георадарное исследование ледника Радде хребта Мунку-Сардык (Восточный Саян)

The Munku-Sardyk (Eastern Sayan) glacier has been described and studied for more than 100 years. The first largest glacier of Peretolchina was studied in the most detailed detail. Radde's second-largest glacier is much weaker. Monitoring of surface characteristics of the Radde glacier by ground methods and using data of remote sensing of the Earth (RSE) has been carried out since 2006. In 2018, georadar profiling of this glacier was performed for the first time. As a result, it was possible not only to clarify its surface characteristics, but also to assess the power of the ice and the internal structure (a layer of firn, ice, bed). According to the RSE, its geometric changes have been revealed. Over 120 years, the open part of the Radde Glacier has shrunk from 0.4 to 0.09 km2, and the length from 1 to 0.4 km. It also revealed the division of the glacier into two parts and the intensive reservation of the bottom of the main part of the tongue by surface moraines and the formation of a glacial lake on the glacier itself in the lower part of the second half. Radar research using the Oko-2 georadar, allowed to determine the volume of ice of this glacier 0.003 km3 and the greatest thickness of the main ice body 42 m. The main glacier flows down from the Eskadriliy top, 3168 m, to the north, flows on the cross-bar and from it turns to the northeast, and at the bottom of the kar will continue to flow north again.

МАКСИМАЛЬНАЯ ГРАНИЦА СКАНДИНАВСКОГО ЛЕДНИКОВОГО ПОКРОВА В ВАЛДАЙСКУЮ (ВИСЛИНСКУЮ) ЭПОХУ И ОСОБЕННОСТИ РЕЛЬЕФА ЕГО ПЕРИФЕРИЧЕСКОЙ ЗОНЫ

After the end of the Mikulino interglacial, in connection with the rising cooling trend, the Scandinavian ice sheet began to form on the territory of Fennoscandia. Its development to the maximum boundaries was accompanied by the ice sheet advances and retreats that reflected the succession of colder and warmer climate phases over a long period, called the Valdaian (Weichselian, Vistulian) ice age. The Scandinavian ice sheet did not reach its maximum simultaneously at different lobes. The age of the maximum boundary on becomes younger from west to east, which is associated with the paleoclimatic situation in the North of Eurasia due to the formation of an extra-continental climate. Climate continentality increased eastward along the periphery of the ice sheet. These climate features and the ice sheet response determined the nature of glacial morphogenesis in the proglacial zone. The conditions for the formation of a peripheral ice sheet and an increase in the number of mudflows and the formation of glacial lakes were more favorable during the ice sheet degradation than its expansion. Therefore, the forms of active and dead ice, especially the terminal moraines and kames of different types, the valleys of marginal channels and outwash plains serve as the hallmarks of the stages of warming and degradation of ice sheets.

Geochemical constraints on the depositional environment of the 1.84 Ga Embury Lake Formation, Flin Flon Belt, Canada

AbstractThe Flin Flon Belt of Canada contains Paleoproterozoic volcanic–sedimentary sequences that are related to the Trans‐Hudson Orogeny. The sequences include island arc volcanic and volcaniclastic rocks (Amisk Group) that are unconformably overlain by subaerial sedimentary rocks (Missi Group), and younger deep facies sediments. In the Flin Flon area, several north–south trending faults divide the sequences into blocks and obscure the depositional environment of the deep facies sediments. Locally, within the Flin Flon area, the Embury Lake Formation is in fault contact with island arc volcanic–sedimentary sequences of the Amisk and Missi Groups. To identify the depositional environment of the Embury Lake Formation, we used lithologic and geochemical approaches. Here, we report carbon isotopic values in organic matter (δ13Corg) and sulfur isotopes (δ34S), as well as total organic carbon and total sulfur measurements for the black shale in the formation. Samples were taken from a drill core that contains alternating bands of sandstone and black shale. Pyrite in the black shale is divided into four textural types: euhedral, vein‐type, elliptical, and microcrystalline. Microcrystalline pyrite is typically generated by microbially mediated sulfate reduction. An extremely low S/C ratio (avg. = 0.04) is consistent with lacustrine deposition. The ranges of δ13Corg (−36 ‰ to −27 ‰) and δ34S (+3.0 ‰ to +7.7 ‰) values can be explained by bacterial photosynthesis that involved Calvin cycle and acetyl CoA pathways, and sulfate reduction in a low‐sulfate environment. Considering the depositional age reported in a previous study of &lt; 1.84 Ga, the Embury Lake Formation was likely emplaced in a lacustrine setting during the Trans‐Hudson Orogeny.

Analysis of bottom sediments of small lakes in Central Karelia

Data on the particle size distribution of bottom sediments in small lakes of Central Karelia are presented. Sediment fraction sizes in the study area Lake Torosjarvi varied from very fine sand to silty clay. The prevalent fraction was coarse silt. The paleo-hydrodynamic environment for sedimentation of the rocks was analyzed using the genetic diagram by R. Passega. Three intervals were characterized as turbidite deposits, the rest of the intervals fell in the zone of deposits left by low-velocity streams. The study of changes in sedimentation in Lake Torosjarvi suggests there occurred five shifts in the dynamic water regimes in the course of the lake formation.

Stitch in the ditch: Nutzotin Mountains (Alaska) fluvial strata and a dike record ca. 117–114 Ma accretion of Wrangellia with western North America and initiation of the Totschunda fault

AbstractThe Nutzotin basin of eastern Alaska consists of Upper Jurassic through Lower Cretaceous siliciclastic sedimentary and volcanic rocks that depositionally overlie the inboard margin of Wrangellia, an accreted oceanic plateau. We present igneous geochronologic data from volcanic rocks and detrital geochronologic and paleontological data from nonmarine sedimentary strata that provide constraints on the timing of deposition and sediment provenance. We also report geochronologic data from a dike injected into the Totschunda fault zone, which provides constraints on the timing of intra–suture zone basinal deformation. The Beaver Lake formation is an important sedimentary succession in the northwestern Cordillera because it provides an exceptionally rare stratigraphic record of the transition from marine to nonmarine depositional conditions along the inboard margin of the Insular terranes during mid-Cretaceous time. Conglomerate, volcanic-lithic sandstone, and carbonaceous mudstone/shale accumulated in fluvial channel-bar complexes and vegetated overbank areas, as evidenced by lithofacies data, the terrestrial nature of recovered kerogen and palynomorph assemblages, and terrestrial macrofossil remains of ferns and conifers. Sediment was eroded mainly from proximal sources of upper Jurassic to lower Cretaceous igneous rocks, given the dominance of detrital zircon and amphibole grains of that age, plus conglomerate with chiefly volcanic and plutonic clasts. Deposition was occurring by ca. 117 Ma and ceased by ca. 98 Ma, judging from palynomorphs, the youngest detrital ages, and ages of crosscutting intrusions and underlying lavas of the Chisana Formation. Following deposition, the basin fill was deformed, partly eroded, and displaced laterally by dextral displacement along the Totschunda fault, which bisects the Nutzotin basin. The Totschunda fault initiated by ca. 114 Ma, as constrained by the injection of an alkali feldspar syenite dike into the Totschunda fault zone.These results support previous interpretations that upper Jurassic to lower Cretaceous strata in the Nutzotin basin accumulated along the inboard margin of Wrangellia in a marine basin that was deformed during mid-Cretaceous time. The shift to terrestrial sedimentation overlapped with crustal-scale intrabasinal deformation of Wrangellia, based on previous studies along the Lost Creek fault and our new data from the Totschunda fault. Together, the geologic evidence for shortening and terrestrial deposition is interpreted to reflect accretion/suturing of the Insular terranes against inboard terranes. Our results also constrain the age of previously reported dinosaur footprints to ca. 117 Ma to ca. 98 Ma, which represent the only dinosaur fossils reported from eastern Alaska.

Barrier lake formation due to landslide impacting a river: A numerical study using a double layer-averaged two-phase flow model

A granular landslide impacting a river may lead to the formation of a landslide dam blocking the streamflow, and subsequently create a barrier lake. Should a barrier lake outburst, the flood may be destructive and spell disastrous consequences downstream. The last decade or so has witnessed a number of experimental and numerical investigations on barrier lake outburst flooding, whilst studies on barrier lake formation remain rare – a physically enhanced and practically viable mathematical model is still missing. Generally, barrier lake formation is characterized by multi-physical, interactive processes between water flow, multi-sized sediment transport and morphological evolution. Here, a new double layer-averaged two-phase flow model is proposed, which is an advance on existing continuum models that involve a single-phase flow assumption and presume a single sediment size, and discrete models that preclude fine grains and assume narrow grain size distributions. The proposed model is first validated against data from previous laboratory experiments of waves due to landslides impacting reservoirs and landslide dam formation over dry valleys. Then it is applied to explore the complicated mechanism and threshold for barrier lake formation. The water and grain velocities are shown to be disparate, characterizing the primary role of grains in driving water movement during subaqueous landslide motion and also demonstrating the need for a two-phase flow approach. The grain size effects are revealed, i.e., coarse grains and grain-size uniformity favour barrier lake formation. A new threshold condition is proposed for barrier lake formation, integrating the landslide-to-river momentum ratio and grain size effects. The present work facilitates a promising modelling framework for solving barrier lake formation, thereby underpinning the assessment of flood hazards due to barrier lakes.