Basal Sediments Research Articles

Radar‐Detected Englacial Debris in the West Antarctic Ice Sheet

AbstractStructural glaci‐geological processes can entrain basal sediment into ice, leading to its transportation and deposition downstream. Sediments potentially rich in essential nutrients, like silica and iron, can thus be transferred from continental sources to the ocean, where deposition could enhance marine primary productivity. However, a lack of data has limited our knowledge of sediment entrainment, transfer, and distribution in Antarctica, until now. We use ice‐penetrating radar to examine englacial sediments in the Weddell Sea sector of the West Antarctic Ice Sheet. Radargrams reveal englacial reflectors on the leeside of nunataks and subglacial highlands, where Mie scattering analysis of the reflectors suggests particle sizes consistent with surface moraine sediments. We hypothesize that these sediments are entrained at the thermal boundary between cold and warm‐based ice. Conservative estimates of >130 × 109 kg of englacial sediment in Horseshoe Valley alone suggest that the ice sheet has significant entrainment potential unappreciated previously.

New evidences on groundwater dynamics from the Souss-Massa system (Morocco): Insights gained from dissolved noble gases

The Souss-Massa plain, an important agriculture area of the Middle Western of Morocco, is a depression zone filled with Plio-Quaternary sediments which are overlying a complex multi-layered sedimentary basement. Over the last decades, population growth, agriculture development and recurrent droughts have been increasing the pressure on the aquifers of the region. The shallow aquifer is intensively exploited. About 94% of the water resources in the basin are used for agriculture. Groundwater levels show a general, continuous depletion. Chemical tracers indicate a progressive deterioration of groundwater quality in many areas with multiple sources of salinity. Another consequence of overexploitation and water use for agriculture is the increase of nitrate concentrations in groundwater.This multiple isotope investigation (18O, 2H, 14C, 3H, noble gases) confirms that the aquifer is mainly recharged by waters derived from the High Atlas Mountains, where the precipitation rate is higher than in the study area. The spatial variations of stable and radioactive isotope concentrations indicate that active mixing of recently recharged and old groundwater within the aquifer system. The recent recharge is observed mainly along the Souss River and in the irrigated areas.The evolution of the fluids can be observed on a locale scale in the 3He/4He ratios, which are largely controlled by the amount of 4He, indicating the addition of terrigenic He to groundwater and/or mixing processes. The finding of mantle helium signature in shallow aquifer generally supports the assumption of the deep, permeable faults in the area of the Souss depression (El Klea and Biougra faults).This study indicates the extent of groundwater renewability and allows establishing a scientifically-based water management model for sustainable exploitation of water resources in the Souss-Massa basin.

Stress characterization and temporal evolution of borehole failure at the Rittershoffen geothermal project

Abstract. In the Upper Rhine Graben, several innovative projects based on enhanced geothermal system (EGS) technology exploit local deep-fractured geothermal reservoirs. The principle underlying this technology consists of increasing the hydraulic performances of the natural fractures using different stimulation methods in order to circulate the natural brine at commercial flow rates. For this purpose, knowledge of the in situ stress state is of central importance to predict the response of the rock mass to different stimulation programs. Here, we propose a characterization of the in situ stress state from the analysis of ultrasonic borehole imager (UBI) data acquired at different key moments of the reservoir development using a specific image correlation technique. This unique dataset has been obtained from the open-hole sections of the two deep wells (GRT-1 and GRT-2, ∼2500 m) at the geothermal site of Rittershoffen, France. We based our analysis on the geometry of breakouts and drilling-induced tension fractures (DITFs). A transitional stress regime between strike-slip and normal faulting consistent with the neighboring site of Soultz-sous-Forêts is evident. The time-lapse dataset enables us to analyze both in time and space the evolution of the structures over 2 years after drilling. The image correlation approach developed for time-lapse UBI images shows that breakouts extend along the borehole with time and widen (i.e., angular opening between the edges of the breakouts) but do not deepen (i.e., increase in the maximal radius of the breakouts). The breakout widening is explained by wellbore thermal equilibration. A significant stress rotation at depth is evident. It is shown to be controlled by a major fault zone and not by the sediment–basement interface. Our analysis does not reveal any significant change in the stress magnitude in the reservoir.

Sedimentary records of paleoseismic events in the Late Pleistocene sediments of the Southern Yangtze River deltaic plain, East China, and their implications for differential subsidence of the Taihu block

Drilling cores from the Hangjiahu Coastal plain in the southwestern corner of the Southern Yangtze River deltaic plain, East China, contain a variety of soft-sediment deformation structures in the Late Pleistocene lacustrine and tidal sediments. They include load-flame structures, ball-and-pillow structures, diapir structures, liquefied sand veins, liquefied breccias, syn-sedimentary fault, seismo-cracks and brittle breccias. Sedimentary facies assessment of host deposits and development features rule out an exogenic origin of the soft-sediment deformation structures, such as gravity-flow, storm activity, wave action or flood. These soft-sediment deformation structures in the study area are interpreted as seismites, their spatial distribution suggest that the earthquakes were sourced from the intersection of the Majin-Wuzhen Fault and the Huzhou-Jiashan Fault. Seismites recognized in cores indicate three episodes of short and sudden seismicity (magnitude > 5), which are interpreted as a response to syn-depositional tectonic activity and differential subsidence of the Taihu block during the Late Pleistocene period. Systematic study of spatial and temporal distribution of these seismites improves the understanding of the tectonic context and evolutionary history of sedimentary basement.

Central and Eastern Europe Paleoscience: From Local to Continental Perspective

Dagmar Cave, Czech Republic, is the first locality in the Moravian Karst where sediments of Cromerian age have been discovered and it is the first locality with such a large number of species of molluscs of this age. It was originally a swallow hole initiated in the Neogene, which has since accumulated sediments. Basal sediments are palaeontologically-sterile stream boulders, originating from weathered Lower Carboniferous rock. After this, fossiliferous, loamy sediments were carried in from the entrance by streams and/or gravity. Molluscan and vertebrate assemblages, along with palynological remains, are indicative of interglacial conditions. Faunal analysis determined that this could only consist of one interglacial, either Cromerian III or IV. This is the first record of Middle Pleistocene molluscan fauna in the Moravian Karst. Palynology demonstrated a humid and thermophilic vegetation typical of a Cromerian interglacial, with forest, and probably water, and an open grassy/bushy area close to the cave. The age is constrained by a MIS 7 U-Th date (182 ka) on the calcite flowstone that overlies the interglacial material and underlies the palaeontologically more sterile upper sediments.

The brittle-ductile transition in active volcanoes

Contrasting deformation mechanisms precede volcanic eruptions and control precursory signals. Density increase and high uplifts consistent with magma intrusion and pressurization are in contrast with dilatant responses and reduced surface uplifts observed before eruptions. We investigate the impact that the rheology of rocks constituting the volcanic edifice has on the deformation mechanisms preceding eruptions. We propose a model for the pressure and temperature dependent brittle-ductile transition through which we build a strength profile of the shallow crust in two idealized volcanic settings (igneous and sedimentary basement). We have performed finite element analyses in coupled thermo-hydro-mechanical conditions to investigate the influence of static diking on the local brittle-ductile transition. Our results show that in active volcanoes: (i) dilatancy is an appropriate indicator for the brittle-ductile transition; (ii) the predicted depth of the brittle-ductile transition agrees with the observed attenuated seismicity; (iii) seismicity associated with diking is likely to be affected by ductile deformation mode caused by the local temperature increase; (iv) if failure occurs within the edifice, it is likely to be brittle-dilatant with strength and stiffness reduction that blocks stress transfers within the volcanic edifice, ultimately damping surface uplifts.

Lithology and U–Pb Geochronology of Basement of Cenozoic Yitong Basin in Northeastern China: Implication for Basin Architecture and New Horizon of Deep Natural Gas Exploration

The lithology and formation age of basement rocks are significant for the understanding of the nature of basin architecture, evolution and the potential of hydrocarbons of a basin. In this study, the basement lithology of the Cenozoic Yitong Basin is investigated through the petrological analysis of cores, cuttings, and thin sections. The results suggest that the basement rocks of the Yitong Basin are mostly composed of unique igneous rocks that are different from nearby basins’ sedimentary and metamorphic basement. The igneous rocks are dominated by intrusive monzonite granite and alkali feldspar granite. Additionally, U–Pb zircon geochronology of basement samples by LA-ICP-MS and the geological interpretation of apparent resistivity data indicate that the igneous basement in major part of the basin was mainly formed by a lateral intrusion of granite into the Permian sedimentary stratum in the Yanshanian period from 177 to 170 Ma. The results also reveal the two-layer basin architecture with coal-bearing Carboniferous–Permian strata below the igneous basement covered with Tertiary sediments, thus providing a new geologic horizon for deep natural gas exploration in the older coal-bearing sedimentary rocks beneath the current igneous basement.

Seawater recirculation through subducting sediments sustains a deeply buried population of sulfate-reducing bacteria.

Subseafloor sulfate concentrations typically decrease with depth as this electron acceptor is consumed by respiring microorganisms. However, studies show that seawater can flow through hydraulically conductive basalt to deliver sulfate upwards into deeply buried overlying sediments. Our previous work on IODP Site C0012A (Nankai Trough, Japan) revealed that recirculation of sulfate through the subducting Philippine Sea Plate stimulated microbial activity near the sediment-basement interface (SBI). Here, we describe the microbial ecology, phylogeny, and energetic requirements of population of aero-tolerant sulfate-reducing bacteria in the deep subseafloor. We identified dissimilatory sulfite reductase gene (dsr) sequences 93% related to oxygen-tolerant Desulfovibrionales species across all reaction zones while no SRB were detected in drilling fluid control samples. Pore fluid chemistry revealed low concentrations of methane (<0.25mM), while hydrogen levels were consistent with active bacterial sulfate reduction (0.51-1.52nM). Solid phase total organic carbon (TOC) was also considerably low in these subseafloor sediments. Our results reveal the phylogenetic diversity, potential function, and physiological tolerance of a community of sulfate-reducing bacteria living at ~480m below subducting seafloor.

Quaternary structural and paleo-environmental evolution of the Alpine Fault near Haast, New Zealand, from 2D seismic reflection and gravity data

ABSTRACTThe geometry of the upper-crustal portion of the Alpine Fault plate boundary on New Zealand’s South Island, is poorly constrained where it cuts through the sedimentary units of the Westland coastal plain. Two seismic reflection and gravity lines are presented here to better image the upper km of the fault beneath the most recent fault rupture scarps south of the Haast River. Analysis of the seismic lines suggests that multiple fault strands have cut across post-glacial sedimentary strata that overlie the glacially eroded basement. Total combined fault offsets of 39 m at the Haast River and 33 m at the Turnbull River over <17 ka is consistent with previously determined uplift rates. Dip on the fault strands is interpreted to be between ∼53 and ∼76° SE. 2D gravity profiles constrain the interpretation of the interface between sedimentary units and basement, which has considerable 3D variability resulting from glacial erosion processes.

Authigenic and Detrital Minerals in Peat Environment of Vasyugan Swamp, Western Siberia

Studies of mineral-forming processes in modern peat bogs can shed light on metal concentrations and their cycling in similar environments, especially in geological paleoanalogs. In terms of the mineralogical and geochemical evolution of peat bog environments, the Vasyugan Swamp in Western Siberia is a unique scientific object. Twelve peat samples were collected from the Vasyugan Swamp up to the depth of 275 cm at 25 cm intervals. The studied peat deposit section is represented by oligotrophic (0–100 cm), mesotrophic (100–175 cm), and eutrophic (175–275 cm) peat, and this is underlain by basal sediments (from 275 cm). About 30 minerals were detected using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The observed minerals are divided into detrital, clay, and authigenic phases. The detrital minerals found included quartz, feldspar, ilmenite, rutile, magnetite, zircon, and monazite. When passing from basal to oligotrophic bog sediments, the clay minerals changed from illite-smectite to kaolinite. Authigenic minerals are represented by carbonates (calcite and dolomite), iron (hydro-)oxides, galena, sphalerite, pyrite, chalcopyrite, Zn-Pb-S mineral, barite, baritocelestine, celestine, tetrahedrite, cassiterite, REE phosphate, etc. The regular distribution of mineral inclusions in peat is associated with the (bio)geochemical evolution of the environment. The formation of authigenic Zn, Pb and Sb sulfides is mainly confined to anaerobic conditions that exist in the eutrophic peat and basal sediments. The maximum amount of pyrite is associated with the interval of 225–250 cm, which is the zone of transition from basal sediments to eutrophic peat. The formation of carbonate minerals and the decreasing concentration of clay in the association with local sulfide formation (galena, sphalerite, chalcopyrite, stibnite) begins above this interval. The peak of specific carbonation appears in the 125–150 cm interval of the mesotrophic peat, which is characterized by pH 4.9–4.5 of pore water. Kaolinite is the dominant clay mineral in the oligotrophic peat. Gypsum, galena, chalcopyrite, sphalerite, and relicts of carbonate are noted in association with kaolinite. Changes in oxygen concentrations are reflected in newly formed mineral associations in corresponding intervals of the peat. This can be explained by the activity of microbiological processes such as the anaerobic oxidation of methane (AOM) and bacterial sulfate reduction (BSR), expressed in specific carbonatization (100–225 cm) and sulfidization (175–250 cm), respectively.

Study of Distribution Metal From Shellfish at Coastal Beach in District of Central Tapanuli, Indonesia

The research of heavy metals spread in shellfish in the coastal area a zone of the high seas and zones of settlements waters in Central Tapanuli has done with the aim of knowing the content of heavy metals of Cu, Cr, Pb with parameters of the river water, sea water, shellfish and clamshell, basic sediments. Testing of river water, sea water, and shell meat was conducted using Atomic Absorption Spectrometer (AAS) by adsorption principle of light by atoms. Testing basic sediment and clamshell has done with XRD and TEM. The test results of river water showed are Cu ˂0,025 mg/l, Cr ˂0.006 mg/l - ˂0.025 mg/l, Pb ˂0.005 to 0.03 mg/l, in the conditions of under the river water quality standard. The test results on the sea water obtained are metal content of Cu. ˂0.006 mg/l, Cr ˂0,025 mg/l, Pb 0.13 to 0.24 mg/l. The test results show the shell meat are Pb. ˂0.005 to 2.34 mg/kg, Cu 0.85 to 14.4 mg/kg. The test results of clamshell with XRD showed peaks of CaCO3 aragonite. With TEM showed that crystalline, by electron diffraction pattern formed by irregular dot, which means the elements contained in the various clamshells. Differences levels of heavy metals at every point stations predicted has their natural factors such as the direction of ocean currents, rainfall and sediment material and anthropogenic factors such as demographics residential waste pollution, industrial and port activity.

Combining chemical and X-Ray microtomography investigations on crustal xenoliths at Mount Etna: evidence of volcanic gas fluxing

Crustal xenoliths embedded in lavas offer chances to provide information on the lithology of the volcano basement and the process occurring during magma ascent. In this work we studied seven xenoliths found among the scoriae ejected during several paroxysms occurred between 2011 and 2016 at the South East Crater (SEC) of Mount Etna volcano. These samples are characterized by massive presence of glass and vesicles resulting in a foam-like appearance of their texture. A detailed study of their textural and chemical features was carried out combining XRF, SEM-EDS, two-dimensional observation and Synchrotron X-ray microtomography (3D imaging). This multidisciplinary approach allowed us to identify and quantify the components of the samples, individuate the likely provenance rock, ascribable to the Numidian Flysch outcropping west of the Etnean edifice. 2D and 3D imaging were successfully applied to estimate the amount of the phases constituting the samples (grains + glass + vesicles) and the degree of partial melting that occurred during the interaction with the basaltic melt and gaseous phase. The sedimentary rocks underwent profound changes led by partial melting, gas fluxing, vesiculation and selective alkali enrichment. These processes could not be driven exclusively by the prolonged contact with the molten phase but must be considered as result of a significant contribution from the volatiles rising through the plumbing system and the sedimentary basement.

PRESSURE DROP MODELS FOR PARAFFINIC OIL FLOW

Wax deposition is a common phenomenon that occurs when crude oil flows in a pipeline. It is one of the main problems related to flow maintenance, because it leads to flux limitation and pressure drop increase. In addition, it can produce major damage to equipment, creating high-risk in operation or even a complete shutdown of production, impacting profitability negatively. Thus, this research aims to show pressure drop models based on Darcy-Weisbach and Power Fluid model for single-phase flow of paraffinic oils in horizontal lines. It will investigate aspects such as different flows, outdoor temperatures, and the BSW (Basic Sediments and Water) values observing their influence on flow pressure. Experimental data from paraffinic oil wells were used to validate the models. The results showed good fit of the models to the data of the eight experiments, with high values of adequacy coefficient (R2) above 0.97. Experiments with higher BSW content and lower ambient temperature had a greater impact on the pressure drop, being well represented by the two models.

Mercury in the Sedimentary Cover and Basalts of the Basement in the Recent Hydrothermal Activity Area, Middle Valley, Juan de Fuca Ridge

The content and distribution of mercury in Holocene–Upper Pleistocene turbidites, hemipelagic sediments intercalating therein, as well as basement basalts are studied. Samples of sediments were taken from the core of Holes 858A, 858B, 858C, 858D, and 858F. Basalt samples were taken from Holes 858F and 858G drilled during Leg 139 ODP in the Middle Valley (Juan de Fuca Ridge) in the Dead Dog hydrothermal field with a high heat flow (4–20 W/m2) and numerous vents with temperature ranging from 234 to 276°C. Samples of sediments and basalts with the background Hg content were taken from the core of Holes 855A, 855C, and 855D are located beyond the hydrothermal system in the base of the fault scarp on the eastern Middle Valley. In rocks, the content of Hg and its occurrence form were determined by the atomic absorption spectrometry with thermal atomization method; the chemical composition, by the XFA and ICP-MS methods. Sections of the sedimentary cover and basalt basement are marked by an alternation of “layer cake” type units with low and high contents of Hg. Mercury occurs in rocks in the physically adsorbed and mineral forms. The Hg concentration in some parts of the sedimentary section is anomalously high: up to 9696 ppb in Hole 858B and 7260 ppb in Hole 858C. In metalliferous sediments, the Hg content is 3130 ppb. Its maximum content (up to 23200 ppb) is recorded in basalts.

Caracterización Caracterización y Análisis Comparativo de Biodiésel a Base de Higuerilla B10, Respecto de Diésel Comercial de Alta Calidad

En este artículo se presenta la caracterización fisicoquímica de diésel comercial (Premium), y de biodiésel a base de aceite de higuerilla, en proporción B10. Se ha realizado un análisis comparativo en cuanto a las características obtenidas para ambos tipos de combustible y se muestran los resultados alcanzados. Las propiedades fisicoquímicas tratadas son: Punto de inflamación, viscosidad cinemática, sedimentos básicos y agua (BSW), corrosión a la lámina de cobre, azufre e índice de cetano calculados. Las propiedades del biodiésel están influenciadas por las características físicas de la composición de ácidos grasos, tales como el grado de insaturación, el porcentaje de ácidos grasos saturados, ácidos grasos mono-insaturados, y el ácido graso poliinsaturado. Las propiedades de los combustibles son los factores clave para determinar la idoneidad de cualquier combustible alternativo. Los resultados muestran que las características del biodiésel B10 están dentro de los rangos estipulados por normativa internacional, además de reducir significativamente emisiones contaminantes. La caracterización de los combustibles ha sido realizada en base a la norma INEN 1489 y normas ASTM.

Shallow structure of the Tangshan fault zone unveiled by dense seismic array and horizontal-to-vertical spectral ratio method

The Tangshan fault zone has been considered to be a potential seismogenic fault from the devastating 1976 Ms 7.8 Tangshan earthquake. Based on the dense seismic array with interstation distance of ∼1 km and length of ∼40 km, HVSR (horizontal-to-vertical spectral ratio) curves at 37 stations are obtained with the micro-tremor seismic waveforms, and the two-dimensional Quaternary sedimentary structures cross the Tangshan fault zone are imaged by frequency-to-depth conversion. Results suggest that two significant seismic impedance interfaces at ∼100 m and 300–800 m depth are clearly revealed, respectively. The interface at ∼100 m depth can be attributed to the strong contrasts between the unconsolidated sand-clay and semi-consolidated silt, which suggests very small variations and is well consistent with the seismic reflection interface from shallow seismic reflection exploration. While the deeper interface at 300–800 m depth can be attributed to the Quaternary sedimentary basement, which increases from 300 to 800 m from the west to the east, and is also consistent with the results in previous studies. Rapid variations (∼200 m) of the Quaternary sedimentary basement depth just beneath the fault zone well agrees with spatial characteristics of the fault revealed by deep seismic reflection profiling. Our work suggests that the Tangshan fault zone has been significantly ruptured and modified by strong earthquake activities since Quaternary. This study also suggests that the HVSR method with dense seismic array is an efficient, effective, non-invasive and low-cost method for investigating active faults in shallow sediments. It is useful for probing the active faults buried by thick sediments in the densely populated urban settings where seismic investigation with explosive sources are too hazardous to carry out.

Dagmar Cave (Czech Republic, Moravian Karst), a unique palaeontological site of the Cromerian Interglacial

Dagmar Cave, Czech Republic, is the first locality in the Moravian Karst where sediments of Cromerian age have been discovered and it is the first locality with such a large number of species of molluscs of this age. It was originally a swallow hole initiated in the Neogene, which has since accumulated sediments. Basal sediments are palaeontologically-sterile stream boulders, originating from weathered Lower Carboniferous rock. After this, fossiliferous, loamy sediments were carried in from the entrance by streams and/or gravity. Molluscan and vertebrate assemblages, along with palynological remains, are indicative of interglacial conditions. Faunal analysis determined that this could only consist of one interglacial, either Cromerian III or IV. This is the first record of Middle Pleistocene molluscan fauna in the Moravian Karst. Palynology demonstrated a humid and thermophilic vegetation typical of a Cromerian interglacial, with forest, and probably water, and an open grassy/bushy area close to the cave. The age is constrained by a MIS 7 U-Th date (182 ka) on the calcite flowstone that overlies the interglacial material and underlies the palaeontologically more sterile upper sediments.

Warm-based basal sediment entrainment and far-field Pleistocene origin evidenced in central Transantarctic blue ice through stable isotopes and internal structures

ABSTRACTStable isotopes of water (δ18O and δ2H) were measured in the debris-laden ice underlying an Antarctic blue ice moraine, and in adjoining Law Glacier in the central Transantarctic Mountains. Air bubble content and morphology were assessed in shallow ice core samples. Stable isotope measurements plot either on the meteoric waterline or are enriched from it. The data cluster in two groups: the ice underlying the moraine has a δ2H:δ18O slope of 5.35 ± 0.92; ice from adjoining portions of Law Glacier has a slope of 6.69 ± 1.39. This enrichment pattern suggests the moraine's underlying blue ice entrained sediment through refreezing processes acting in an open system. Glaciological conditions favorable to warm-based sediment entrainment occur 30–50 km upstream. Basal melting and refreezing are further evidenced by abundant vapor figures formed from internal melting of the ice crystals. Both the moraine ice and Law Glacier are sufficiently depleted of heavy isotopes that their ice cannot be sourced locally, but instead must be derived from far-field interior regions of the higher polar plateau. Modeled ice flow speeds suggest the ice must be at least 80 ka old, with Law Glacier's ice possibly dating to OIS 5 and moraine ice older still.

Soil degassing at the Los Humeros geothermal field (Mexico)

The Los Humeros geothermal field is the third most important producer of geothermal electricity (70MW) in Mexico. Geothermal fluids are hosted in fractured andesitic lavas and mostly consist of high enthalpy steam with limited water content (vapor fraction>0.9). Despite the high reservoir temperature (~300–400°C), thermal manifestations at the surface are scarce and locally appear as steaming grounds, weak steam vents and advanced argillic alteration. Geothermal fluid upflow from the reservoir towards the surface is limited by welded ignimbrite deposits that act as a low-permeability barrier. In this study, we present the first measurements of CO2, CH4 and H2S degassing rates from the soil performed at Los Humeros. Flux measurements were complemented with δ13C composition of degassing CO2 and soil temperatures to discuss gas origin and thermal anomalies. We measured high soil degassing rates (up to 7530gm−2d−1 CO2, 33gm−2d−1 CH4 and 22gm−2d−1 H2S) in three localized areas (Humeros North – HN, Humeros South – HS and Xalapazco – XA) as well as high soil temperatures reaching the boiling temperature at the local altitude (90.6°C). The particular location of these three areas suggests that the steam-dominated reservoir degases to the surface through permeable faults crossing the ignimbritic deposits. The remaining surveyed areas are characterized by weak CO2 fluxes (≤44gm−2d−1), non-detectable CH4 and H2S fluxes, and lower soil temperatures (5–21°C). The compositions in δ13CCO2 from HN-HS-XA areas (δ13CCO2=−7.94 to −2.73‰) reflect a magmatic source with some possible contribution from the sedimentary basement, as well as fractionation induced by boiling and CO2 dissolution in shallow water bodies. We also discuss the processes causing the spread in CO2/CH4 flux ratios. Finally, we estimate the heat output from the three high degassing areas to a value of 16.4MWt.

Structure of the Northwestern Boundary of the Middle Amur Sedimentary Basin (Russian Far East) from Audiomagnetotelluric Sounding Data

This paper reports the data on the structure of the northwestern boundary of the Middle Amur sedimentary basin which were obtained after resumption of audiomagnetotelluric soundings. The geoelectric sections for two profiles across the basin strike are constructed, the sedimentary cover and basement structures are studied, and their electrical properties are determined. The compared data of the earlier and present studies show low-resistivity zones of 50–150 Ohm m beneath high-resistivity rocks of 500–1000 Ohm m in the northwestern part of the Ul’dura–Churki uplift at a 2–4 km depth, which are absent in the southwestern part of the uplift. This fact is related to strike-slip–overthrust processes due to graben formation in the area of junction with the Jiamusi–Bureya Massif in the Kur fault zone (YYilan–Yitong branch of the Tan-Lu fault zone) and also to global left-lateral strike-slip displacements and volcanic activity.