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• RESEARCH ARTICLE
Minfang YANG, Zhaobiao YANG, Bin SUN, Zhengguang ZHANG, Honglin LIU, Junlong ZHAO
Frontiers of Earth Science, 2020, 14(4): 673-683. https://doi.org/10.1007/s11707-020-0837-x

Flowability of gas and water through low-permeability coal plays crucial roles in coalbed methane (CBM) recovery from coal reservoirs. To better understand this phenomenon, experiments examining the displacement of water by gas under different displacement pressures were systematically carried out based on nuclear magnetic resonance (NMR) technology using low-permeability coal samples of medium-high coal rank from Yunnan and Guizhou, China. The results reveal that both the residual water content (Wr) and residual water saturation (Sr) of coal gradually decrease as the displacement pressure (P) decreases. When P is 0–2 MPa, the decline rates of Wr and Sr are fastest, beyond which they slow down gradually. Coal samples with higher permeability exhibit higher water flowability and larger decreases in Wr and Sr. Compared with medium-rank coal, high-rank coal shows weaker fluidity and a higher proportion of irreducible water. The relationship between P and the cumulative displaced water content (Wc) can be described by a Langmuir-like equation, Wc = WLP/(PL + P), showing an increase in Wc in coal with an increase in P. In the low-pressure stage from 0 to 2 MPa, Wc increases most rapidly, while in the high-pressure stage (P>2 MPa), Wc tends to be stable. The minimum pore diameter (d') at which water can be displaced under different displacement pressures was also calibrated. The d' value decreases as P increases in a power relationship; i.e., d' the coal gradually decreases with the gradual increase in P. Furthermore, the d' values of most of the coal samples are close to 20 nm under a P of 10 MPa.

• RESEARCH ARTICLE
Frontiers of Earth Science, 2020, 14(4): 828-841. https://doi.org/10.1007/s11707-020-0827-z

Bangladesh is a riparian country that is crisscrossed by the many tributaries and distributaries of the mighty Ganges, Brahmaputra, and Meghna river systems. Gorai-Madhumati, a distributary of the Ganges River is an example where morphological development of the river is associated with frequent channel shifting within the catchment area. The main objective of this research is to quantify the extent of channel migration, erosion-accretion, river width, sinuosity, and charland morpho-dynamics from 1972 to 2018 using geospatial techniques combined with satellite images and hydrological data. The study also addressed the impacts of Farakka Barrage construction in India on the shifting, flow behavior, and siltation of Gorai-Madhumati River. The study shows that bar surface areas have abnormally increased in both segments after 1975 due to the construction of Farakka Barrage. Water flow in the Gorai-Madhumati has dropped remarkably in the downstream and instigated huge sedimentation in this region. Analysis of the time series satellite images revealed that the morphology of the river channel experienced huge changes simultaneously with the changes in the seasonal flow and sedimentation all over the study period. Migration trend has frequently shifted and taken place in the NW and NE direction in the observed sections of the river. Throughout the study period, total amount of accretion was greater than the net percentage of erosion on both banks of the river. River discharge, bar accretion, and erosion history show that the Gorai-Madhumati River will no longer exist with the present flowing condition without attention and proper river management.

• RESEARCH ARTICLE
Yongjuan LIU, Jianjun CAO, Liping WANG, Xuan FANG, Wolfgang WAGNER
Frontiers of Earth Science, 2020, 14(4): 695-710. https://doi.org/10.1007/s11707-020-0819-z

Landforms with similar surface matter compositions, endogenic and exogenic forces, and development histories tend to exhibit significant degrees of self-similarity in morphology and spatial variation. In loess hill–gully areas, ridges and hills have similar topographic relief characteristics and present nearly periodic variations of similar repeating structures at certain spatial scales, which is termed the topographic relief period (TRP). This is a relatively new concept, which is different from the degree of relief, and describes the fluctuations of the terrain from both horizontal and vertical (cross-section) perspectives, which can be used for in-depth analysis of 2-D topographic relief features. This technique provides a new perspective for understanding the macro characteristics and differentiation patterns of loess landforms. We investigate TRP variation features of different landforms on the Loess Plateau, China, by extracting catchment boundary profiles (CBPs) from 5 m resolution digital elevation model (DEM) data. These profiles were subjected to temporal-frequency analysis using the ensemble empirical mode decomposition (EEMD) method. The results showed that loess landforms are characterized by significant regional topographic relief; the CBP of 14 sample areas exhibited an overall pattern of decreasing TRPs and increasing topographic relief spatial frequencies from south to north. According to the TRPs and topographic relief characteristics, the topographic relief of the Loess Plateau was divided into four types that have obvious regional differences. The findings of this study enrich the theories and methods for digital terrain data analysis of the Loess Plateau. Future study should undertake a more in-depth investigation regarding the complexity of the region and to address the limitations of the EEMD method.

• RESEARCH ARTICLE
Olga E. KIKVADZE, Vasilii Yu. LAVRUSHIN, Boris G. POLYAK
Frontiers of Earth Science, 2020, 14(4): 738-757. https://doi.org/10.1007/s11707-019-0810-8

The generation temperatures of gas-water fluids released from mud volcanoes in different provinces of the Caucasian region have been constrained using Mg/Li (ТMg/Li) chemical geothermometry. Mud volcanic fluids in the Taman Peninsula (Kerch-Taman mud volcanic province) were generated at temperatures (ТMg/Li) from 41 to 137°С. The depths of the respective mud reservoirs estimated from ТMg/Li values and local geothermal gradient are in a range of 1.0 to 3.4 km which spans the Maykop Formation of marine shale. For the South Caspian province, the ТMg/Li values of waters vary from 18 to 137°C and the respective root depths НMg/Li of mud volcanoes range from ~ 0.85 to 6.5 km. The obtained TMg/Li values for the analyzed mud volcanic waters from Caucasian provinces are in positive correlation with НСО3 contents and water oxygen isotope compositions ($δ 18OH2O$ and Δ$δ 18OH2O$) and in high negative correlation with Cl. The increase of ТMg/Li toward the Greater Caucasus Range, as well as the lateral TMg/Li patterns in the Taman and South Caspian mud volcanic provinces, support the idea that mud volcanic fluids generate at temperatures increasing progressively toward the Alpine orogenic belt.

• RESEARCH ARTICLE
Ying LIU, Xudong WU, Xudong SUN, Chenghe GUAN, Bo ZHANG, Xiaofang WU
Frontiers of Earth Science, 2020, 14(4): 803-815. https://doi.org/10.1007/s11707-020-0822-4

As the major primary energy importer in the world, China has engaged in considerable efforts to ensure energy security. However, little attention has been paid to China’s embodied primary energy exports. Separating the international export from regional final demand, this paper focuses on quantifying provincial primary energy requirement arising from China’s exports, and tracing its concrete interprovincial supply chains using multi-regional input-output analysis and structural path analysis. Results show that China’s embodied primary energy uses in exports (EEE) reached 633.01 Mtce in 2012, compared to 565.15 Mtce in 2007. Four fifths of the EEE were supplied through interprovincial trade. Eastern coastal provinces accounted for nearly 70% of the national total EEE, while their primary energy supply mainly sourced from the central and western provinces. Most interprovincial supply chain paths of embodied primary energy exports were traced to the coal mining sectors of Shanxi, Inner Mongolia and Shaanxi. Critical receiving sectors in the final export provinces were Chemical industry, Metallurgy, Electronic equipment, Textile and other manufacturing sectors. Important transmission sectors were Electricity and hot water production and supply and Petroleum refining, coking, etc. In view of the specific role of exports in primary energy requirements, provincial energy uses are largely dependent on its domestic trade position and degrees of industrial participation in the global economy. Managing critical industrial sectors and supply chain paths associated with the international exports provide new insights to ensure China’s energy security and to formulate targeted energy policies.

• RESEARCH ARTICLE
Chang Dok WON, HanLie HONG, Kum Ryong PAK
Frontiers of Earth Science, 2020, 14(4): 684-694. https://doi.org/10.1007/s11707-020-0826-0

Crystallinity, polytype, and morphology of clay minerals in the Luochuan loess-palaeosols in Shaanxi Province, northwest China were studied in order to have an insight into their origin using X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) methods. The SEM observations showed that the morphology of some illites seems to be lath-shaped crystals. An analysis of illite crystallinity (IC) on the Luochuan section indicated that the origin of illite was related to the rocks of an anchizone. Most illite in the Luochuan loess-palaeosol section were of 2M1 polytype, but some were of 1M polytype formed by weathering of feldspar in the process of pedogenesis. Illite in the Luochuan section has undergone both physical and chemical weathering. These results revealed that most illite were of detrital origin related to the source area of an anchizone, but parts of the illite were of an authigenic origin formed during pedogenesis after sedimentation. Chlorites in the samples of the Luochuan section were mainly composed of irregular flaky grains and their crystallinity was good. These showed that chlorite had the detrital origin formed by physical weathering. Kaolinite crystallinity was relatively good. The value of CIA on the Luochuan section ranges from 61.9 to 69, and therefore kaolinite could not be formed during weathering and pedogenesis. These results indicated that the kaolinite had a detrital origin. Morphology of smectite seems to be capillaceous. The XRD patterns of all samples contained diffraction peaks at 1.5218 Å (nontronite) and 1.5052 Å (montmorillonite), thus indicating an intermediate composition between trioctahedral and dioctahedral smectite. The smectite crystallinity was very poor. These results revealed that smectite in the study area was authigenic rather than detrital origin.

• RESEARCH ARTICLE
Wei JU, Jian SHEN, Chao LI, Kun YU, Hui YANG
Frontiers of Earth Science, 2020, 14(4): 770-782. https://doi.org/10.1007/s11707-020-0831-3

Unconventional reservoirs are generally characterized by low matrix porosity and permeability, in which natural fractures are important factors for gas production. In this study, we analyzed characteristics of natural fractures, and their influencing factors based on observations from outcrops, cores and image logs. The orientations of natural fractures were mainly in the ~N-S, WNW-ESE and NE-SW directions with relatively high fracture dip angles. Fracture densities were calculated based on fracture measurements within cores, indicating that natural fractures were not well-developed in the Benxi-Upper Shihezi Formations of Linxing Block. The majority of natural fractures were open fractures and unfilled. According to the characteristics of fracture sets and tectonic evolution of the study area, natural fractures in the Linxing Block were mainly formed in the Yanshanian and Himalayan periods. The lithology and layer thickness influenced the development of natural fractures, and more natural fractures were generated in carbonate rocks and thin layers in the study area. In addition, in the Linxing Block, natural fractures with ~N-S-trending strikes contributed little to the overall subsurface fluid flow under the present-day stress state. These study results provide a geological basis for gas exploration and development in the Linxing unconventional reservoirs of Ordos Basin.

• RESEARCH ARTICLE
Fangyan ZHU, Heng WANG, Mingshi LI, Jiaojiao DIAO, Wenjuan SHEN, Yali ZHANG, Hongji WU
Frontiers of Earth Science, 2020, 14(4): 816-827. https://doi.org/10.1007/s11707-020-0820-6

Climate change, a recognized critical environmental issue, plays an important role in regulating the structure and function of forest ecosystems by altering forest disturbance and recovery regimes. This research focused on exploring the statistical relationships between meteorological and topographic variables and the recovery characteristics following disturbance of plantation forests in southern China. We used long-term Landsat images and the vegetation change tracker algorithm to map forest disturbance and recovery events in the study area from 1988 to 2016. Stepwise multiple linear regression (MLR), random forest (RF) regression, and support vector machine (SVM) regression were used in conjunction with climate variables and topographic factors to model short-term forest recovery using the normalized difference vegetation index (NDVI). The results demonstrated that the regene-rating forests were sensitive to the variation in temperature. The fitted results suggested that the relationship between the NDVI values of the forest areas and the post-disturbance climatic and topographic factors differed in regression algorithms. The RF regression yielded the best performance with an R2 value of 0.7348 for the validation accuracy. This indicated that slope and temperature, especially high temperatures, had substantial effects on post-disturbance vegetation recovery in southern China. For other mid-subtropical monsoon regions with intense light and heat and abundant rainfall, the information will also contribute to appropriate decisions for forest managers on forest recovery measures. Additionally, it is essential to explore the relationships between forest recovery and climate change of different vegetation types or species for more accurate and targeted forest recovery strategies.

• RESEARCH ARTICLE
Sergei RASSKAZOV, Aigul ILYASOVA, Sergei BORNYAKOV, Irina CHUVASHOVA, Eugene CHEBYKIN
Frontiers of Earth Science, 2020, 14(4): 711-737. https://doi.org/10.1007/s11707-020-0821-5

In the western part of the South Baikal Basin, spatial-temporal distribution of earthquake epicenters shows quasi-periodic seismic reactivation. The largest earthquakes that occurred in 1999 (MW = 6.0) and 2008 (MW = 6.3) fall within seismic intervals of 1994–2003 and 2003–2012, respectively. In the seismic interval that began in 2013, the 234U/238U activity ratio (AR) in groundwater was monitored assuming its dependence on crack opening/closing that facilitated/prevented water circulation in an active boundary fault of the basin. Transitions from disordered, high-amplitude fluctuations of AR values to consistent, low-amplitude fluctuations in different monitoring sites were found to be sensitive indicators of both small seismic events occurring directly on the observation area, and of a large remote earthquake. The hydroisotopic responses to seismic events were consistent with monitoring data on deformation and temperature variations of rocks. The hydroisotopic effects can be applied for detecting a seismically dangerous state of an active fault and prediction of a large future earthquake.

• RESEARCH ARTICLE
Kaixiu ZHANG, Wen QIN, Fang TIAN, Xianyong CAO, Yuecong LI, Jule XIAO, Wei DING, Ulrike HERZSCHUH, Qinghai XU
Frontiers of Earth Science, 2020, 14(4): 789-802. https://doi.org/10.1007/s11707-020-0834-0

Pollen productivity is a critical parameter in the interpretation of pollen-vegetation relationships, and in the quantitative reconstructions of past vegetation from fossil pollen records. One-year monitoring records were collected for 143 pollen traps in various parts of northern China, together with modern vegetation data. Absolute Pollen Productivity Estimates (APPE) were calculated for 11 taxa using the ratio of pollen influx to plant coverage at each applicable sampling site, in which the plants of the target taxon were present. Relative Pollen Productivity Estimates (RPPE) were calculated for the 11 taxa (taking Poaceae as the reference taxon) at those sites in which each taxon occurred together with Poaceae. Artemisia and Chenopodiaceae were found to have the highest RPPEs and the largest RPPEs ranges, while Pinus and Quercus also had higher RPPEs than Poaceae; Abies, Betula, Larix, Picea and Cyperaceae had relatively low RPPEs. Variations in RPPE between different areas may be explained by variations in climatic conditions, plant coverage and land use practices which might influence plant growing situation. Marked effect that variations in pollen productivity can have on vegetation reconstructions was demonstrated by applying these distinct RPPEs to reconstructions of Holocene vegetation in the Lake Daihai area (northern China), such as a large range of RPPE produces a large range of plant coverage. Variations in RPPEs within a single taxon, related to vegetation coverage and climatic conditions, therefore need to be considered in future vegetation reconstructions.

• RESEARCH ARTICLE
Junhua ZHU, Jianwei QIAO, Feiyong WANG, Quanzhong LU, Yuyun XIA, Ransheng CHEN, Haiyuan ZHAO, Jingliang DONG
Frontiers of Earth Science, 2020, 14(4): 758-769. https://doi.org/10.1007/s11707-020-0840-2

Liangjia Village earth fissure, one of the 79 earth fissures along the Kouzhen–Guanshan fault located in the northern Weihe Basin, causes severe damage to buildings and farmlands. Since the late 1950s, 40 earth fissures have occurred in a similar east–west (EW) direction parallel to the Kouzhen–Guanshan fault, and a further 39 earth fissures have occurred with north-west, east-north, or north-east orientations intersecting the fault. In this study, a case study of Liangjia Village earth fissure was conducted to investigate the mechanisms of fissure generation in detail. Geotechnical and geophysical methods including measurements, trenching, drilling, and seismic exploration were used to reveal the basic characteristics, geological background, and origin model of the Liangjia Village earth fissure. This earth fissure, with a total length of 800 m in 2014, runs EW parallel to the Kouzhen–Guanshan fault, and it has damaged buildings and farmlands by forming sinkholes, gullies, subsidence, and a scarp. The trenching results indicated that this fissure underwent multi-phase activity. Analysis of geological drilling and shallow seismic profiling results showed that the fissure also possessed characteristics of a syn-sedimentary fault. Regarding its genesis, the fissure was formed through the combined actions of three factors: an earthquake created the fissure, the Kouzhen–Guanshan fault controlled its development, and loess erosion and groundwater runoff subsequently enlarged the fissure. Regional extension first generated many buried faults along the hanging wall of the Kouzhen–Guanshan fault before seismic activity caused the buried faults to propagate to the surface, where loess erosion and groundwater runoff promoted the formation of the current earth fissure.

• RESEARCH ARTICLE
Xin YANG, Xianyu HUANG
Frontiers of Earth Science, 2020, 14(4): 783-788. https://doi.org/10.1007/s11707-020-0829-x

This study investigates the molecular, carbon, and hydrogen isotope compositions of n-alkanes in eight pairs of a holoparasitic plant (Cuscuta chinensis) and its hosts. It is unexpected that C. chinensis has a higher concentration of n-alkanes than its hosts in seven of the eight pairs, and it is preferentially dominated by n-C29 alkane (representing>75% of the total n-alkanes). In addition, the d13C values of C29 alkane in C. chinensis are less negative (avg. 1.8‰) than those in the hosts, while the d2H values of C29 alkane are more negative in C. chinensis (the difference averages 48‰). We propose that the 2H-depletion of n-alkanes in the stem parasite C. chinensis may result from the utilization of stem water with less influence from evapotranspiration or the use of newly synthesized carbohydrates which is 2H-depleted relative to stored sugars. These results highlight the importance of plant nutrient status on the molecular and isotopic compositions of leaf waxes, which shed light on the (paleo)ecological potential of leaf wax d2H values.