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Serripes groenlandicus shells were collected alivefrom the eastern regions of the Bering and Chukchi seas whereAlaskan Coastal Water occupies dominantly. High-resolution sta-ble isotope profiles of the shell carbonates exhibit distinct, appar-ently annual, cycles caused by seasonal variations of temperature,seawater isotopic composition and other factors. The shell d18Oprofiles show a moderately high-amplitude seasonal temperaturecycle with considerable interannual variability. Superimposed onthe temperature-controlled cycles are periodic excursions whichare associated with reduced salinity, and more negative seawaterd18O, related presumably to an increased freshwater flux to theAlaskan Coastal Current during the summer. Comparison betweentwo oxygen isotope profiles supports the occurrence of seasonaland interannual variability of Alaskan Coastal Water in the east-ern part of the Bering and Chukchi Shelf. The cycles in the d13Cprofiles are interpreted as being controlled primarily by phy-toplankton productivity and seasonal temperature. In addition, atrend of more negative d13C values towards the later stage ofgrowth may reflect physiological changes associated with sexualmaturity, gametogenesis, and slower growth rate. The oxygen andcarbon isotope profiles as a biorecorder of bivalve shells are sub-stantiated in the subarctic environments, probing the seasonal andinterannual variation of Alaskan Coastal Water.
In order to evaluate the human risks of multiplechemicals through multiple exposure routes, it was assumed thathumans are exposed to all the pollutants listed in the Korean SoilEnvironment Preservation Act (KSEPA) through multiple expo-sure routes. The combined carcinogenic risk and hazard indexwere 8.07E-05 and 4.04, respectively, so there might be concern forpotential adverse health effects if no remediation were to occursince both of these values exceeded the target values. Comparinghealth risks by the exposure routes and chemicals, the main por-tion was contributed from dermal contact with soil and polychlo-rinated biphenyls (PCBs), respectively. The carcinogenic risks ofarsenic and PCBs were so high that it is necessary to reconsiderthe regulatory concentration levels in KSEPA. It appeared that thehazard index of hydrophilic phenol and volatile benzene was rel-atively high in the groundwater and air, respectively. In the case ofBTEX compounds, it might be not reasonable to use the concen-tration of BTEX mixture as the current warning level because oftheir different toxicities and properties.
We undertook U-Pb-Hf isotope testing of detrital zircons from Late Paleozoic sedimentary rocks in the Jilin Province, NE China, with the aim of constraining the tectonic evolution of eastern Central Asian Orogenic Belt. The age populations of the detrital zircons from the sandstone of the Jiefangcun Formation in the Songliao Block are ~2234, ~1782, ~1030–921, ~817, ~540, and ~381–254 Ma, whereas those of the zircons from the greywacke of the Permian Kedao Formation in the Songliao Block yield are ~2436, ~1905, ~1692, 1146–1170, ~554–498, and ~342–255 Ma. Combined Hf isotope characteristics, these ages reveal that: (1) rocks from the Jiefangcun and Kedao formations were deposited after 254 and 255 Ma, respectively; (2) these formations were sourced mainly from the Songliao Block and the Jiamus Terrane in the eastern CAOB and to a lesser amount, from the northern margin of the NCC; and (3) it appears that several remnants of ancient Precambrian basement occur adjacent to these Late Paleozoic strata that occur within the microcontinental blocks. Detrital zircons from the silty sandstone of the Miaoling Formation in the western margin of the Khanka Terrane yield peak age populations of 508–476, 463–396, and 348–258 Ma, having similar εHf(t) values to those obtained from zircons within the Jiamusi Terrane. These data indicate that (1) deposition of the Miaoling Formation in the western margin of the Khanka Terrane had started by 258 Ma, and (2) these sediments were sourced mainly from the Jiamusi Terrane and local magmatic rocks. The widespread occurrence of detrital zircons with ages of 480–550 Ma and positive εHf(t) values within the Late Paleozoic strata in the Songliao Block and the Jiamusi–Khanka Terrane, indicates that the amalgamation of these blocks took place during the middle stage of the Paleozoic, probably after the Silurian, prior to the Late Permian.
A tensile test using a half ring (HR) shaped specimen is attempted for the determination of the tensile strength of rock materials. The HR test is a 3-point bend test similar to the semicircular bend (SCB) test. However, the HR specimen is a curved prismatic bar. The theoretical tensile strength of this special bar can be obtained by an analytical formula derived from a basic theory of strength of materials. Owing to the eccentricity of the HR specimen, the possibility for a single tensile fracture to begin at the intended location can increase. This may give results that are more accurate than the conventional bending tests. In this paper, after the concept and formula of the HR test are introduced, its applicability to brittle rocks is investigated by FEM simulations and laboratory tests. In the processes, the theories of the Brazilian test and a special SCB test, which is an alternative to the Brazilian test, are used to examine the accuracy of the HR test.
A rockburst is a kind of dynamic geological hazard faced by engineers and researchers. Identification of a potential rockburst risk area (PRBRA) allows effective, targeted measures to be taken mitigate these hazards. To provide a reference for determining PRBRA in longwall panels with similar conditions, an in situ investigation that lasted for over three years was conducted on LW3401 in the Junde coal mine which experienced a total of 22 rockbursts. The investigation involves rockburst consequences (including the location, length, degree, and modes of the ensuing damage), seismic features of rockburst (including the source and seismic energy), and the relationship between rockbursts and microseismicity. Results show that damaged areas are mostly within the 18 m behind the excavation face, or up to 30 m ahead of the coalface. Lengths of damaged sections of roadways are within 95 m (and 115 m) during roadway excavation (and coalface advancing operations). The seismic energy of rockbursts ranges from 1.60 × 104 to 8.21 × 106 J. Sources of rockbursts lie mostly within 145 m of damage locations. Before a rockburst, sources of microseismic (MS) events begin to cluster around the roadway or coalface. Daily total energy and MS event counts rose, then fell, before a rockburst occurred. PRBRAs in a roadway lie within a certain distance behind the excavation face, or ahead of the coalface. When high-energy MS events are found in close proximity to a PRBRA, the rockburst risk in a given panel increases.
This study presents an evolutionary history of thesouthwestern Ulleung Basin margin on the basis of sequencestratigraphic and structural analyses of multi-channel seismicreflection profiles. Ten sequences and geologic structures identifiedin the late Tertiary strata sugest three distinct stages of basindevelopment in the early Miocene to Pliocene. In the early Miocene,the basin, bordered on the west by a step basement fault with nor-mal sense of offset, experienced a rapid subsidence giving rise to adeep-marine depositional setting. The movement of the basin-bor-dering fault ceased at the end of the early Miocene, then the basinsubsidence progressively slowed, which, coupled with increased ter-rigenous sediment input, resulted in the development of progradingshelf margin. In the late midle to late Miocene time (12.5-5.5Ma), the basin was characterized by compressional readjustmentby thrusting and folding. The sequential effects of this tectonicevent include local and regional angular unconformities, progra-dation-dominant shelf-margin depositional system and frequenttriggering of large-scale mass-failures in front of the thrust belt.Since the early Pliocene, the basin has progressively subsidedagain, forming aggradation-dominant shelf-slope system.
Seismic attributes are often used to identify lithology and evaluate reservoir properties. However, interpretation based only on structural attributes and without knowledge of the Vp/Vs ratio can limit the ability to evaluate changes in heavy oil reservoirs. These limitations are often due to less obvious impedance differences. In order to investigate pieces of evidence of a heavy-oil shaly-sand reservoir from seismic data, besides geochemistry, we studied seismic attributes and characterized the reservoir using seismic stack data and well logging data. The study area was the Muglad rift basin in South Sudan. We conducted a seismic complex analysis to evaluate the target reservoir. To delineate the frequency responses of the different lithological units, we applied the spectral decomposition method to the target reservoir. The most unexpected result was continuous bands of strong seismic reflectors in the target reservoir, which extended across the borehole. Spectral decomposition analysis showed that the low-frequency zone of 25 Hz dominant frequency was consistent with instantaneous attributes. This approach can identify lithology, reveal frequency anomalies, and filter the stacked section into low- and high-frequency bands. The heavy-oil reservoir zones exhibited velocity attenuation and the amplitude was strongly frequency dependent.
We examined the dynamic processes of hyporheic exchange and temperature distribution in a riparian zone in response to low-temperature water fluctuations downstream of the Xin'an River Dam, China, using analytical and mainly hydrodynamic methods. For this purpose, we installed six HM21 piezometers (R, P1–P5) between the river water and the groundwater at an interval of approximately 2 m perpendicular to the flow path. We also installed 20 PT100 thermistors (T1–T20) along the transect at depths of 1.19 m to 3.58 m and monitored the temperatures of river and air. Water levels and temperatures were automatically logged every 5 min by the real-time system from November to December 2014 and sent to the remote platform through the remote terminal unit. Results revealed that the intensity and direction of the hyporheic exchange (Q) between the river water and the groundwater varied periodically (t = 1 d) with the water level of the river. In each cycle, the Q was in a counterclockwise loop curve with the water level of the river and with the non-uniform distribution along the transect perpendicular to the river, which showed that the farther the lateral exchange was away from the river, the lower its intensity and the more hysteretic the alteration of its direction. The daily exchange width and residence time had no necessary connection with the average river stage, but mainly depended on the amplitude of the fluctuating river stage and the duration of river infiltration and established a strong linear relationship with their product. The temperature distribution of the riparian aquifer was mainly affected by the surface radiation and river water infiltration. It was characterized as “cool on the surface and warm at the bottom” in the vertical direction and could be divided into low-, medium-, and high-temperature zones along the horizontal direction. The horizontal infiltration distance (L) increased by power functions with the increase in infiltration rate (v) and decrease in river temperature (T).
Multiple generations of sub-vertical and sub-horizontal foliations preserved as inclusion trails in garnet in mylonitic rocks from the hanging wall of the Main Central Thrust in the Himalayas indicate that these porphyroblasts did not rotate during thrusting. This result is predicated by (i) a consistent succession of 5 changes in FIA trend (foliation inflection/intersection axes in porphyroblasts) for samples where the orientation changes from porphyroblast cores to rims; (ii) sub-vertical and sub-horizontal foliations occur as inclusion trails around each of the 5 FIAs in the succession, which would not be the case if the garnet porphyroblasts rotated during subsequent phases of deformation as tectonism continued; (iii) a change in inclusion trail asymmetry immediately prior to the commencement of mylonitzation indicates top to the south thrusting only if the porphyroblasts had not rotated as they grew; (iv) the latter asymmetry matches truncated crenulation relics preserved within the mylonitic matrix foliation that indicate top to the south thrusting as the latter foliation formed. Partitioning of deformation into shortening and shearing components stops rotation of porphyroblasts during their growth and during following periods of ductile tectonism. This can be replicated via computer modelling by duplicating the crenulation-hinge-like coaxial environment in which porphyroblasts nucleate and grow before the strain intensifies. This was done using Drucker-Prager constitutive models with temperature-dependent strain softening behaviour and resulted in no porphyroblast rotation when followed by non-coaxial deformation no matter how intense. Furthermore, strain localization in the model containing competent objects of variable size, shape and orientation, produced no rotation during deformation involving components of shortening and shearing. These approaches to modelling mechanically resolve the sub-vertical/sub-horizontal foliations defined by inclusion trails and consistent FIA trend successions obtained from the Main Central Thrust rocks as well as in orogens elsewhere.
The Mohe Formation is one of the important source rocks for oil-gas and gas hydrates in the Mohe Basin. In this paper, mudstone from cores of the M-1 and M-3 wells and argillite from cores of the MK-2 well of the Mohe Basin were studied. The depositional environment, organic matter source, thermal maturity, kerogen type, and hydrocarbon generation potential of the core samples were determined using organic and inorganic geochemistry. The dual sources of organic matter were terrestrial plants and aquatic organisms. The organic matter was deposited in a reducing lacustrine environment. The lake water salinity was higher when argillite was deposited. The late stage of the sedimentary filling of the lacustrine basin was characterized by high sulfate contents. The source rocks primarily contained Type II2–III kerogen. The present-day thermal maturity parameters reveal that the organic matter of the Mohe Formation is mature to overmature, indicating that this unit is capable of generating gas condensate and dry gas. In addition, we compared the organic geochemistry characteristics of mudstone and argillite. The results indicate that TOC, S1 + S2, and HI are lower in argillite than in mudstone. Although the biomarker maturity parameters cannot reflect the thermal evolution of the source rocks, they reflect the source of the organic matter and the depositional environment. The results provide important constraints for the evaluation of the hydrocarbon potential of lacustrine source rocks of the Mohe Formation from the Upper Jurassic and for the location of petroleum resources in the Mohe Basin.