Climate and soil moisture environment during development of the fifth palaeosol in Guanzhong Plain

Based on weathering characteristics of the fifth palaeosol layer (S5) of four sections in Guanzhong Plain, the thickness of the weathered profile of the paleosol is determined to be greater than the ordi- nary soil, a weathered and leached loess layer thicker than 2 m. The distribution depth of the red argil- lans, the weathered and leached loess layer, Fe2O3, CaCO3 and Sr content under the S5 all indicate that the precipitation in Guanzhong Plain was over 900 mm at that time. The distribution depth of gravity water zone reached 4.2 m at least, and the soil moisture content was generally more than 20% within the range of 4.2 m. At that time there was sufficient soil moisture and no dried earth layer developed in Guanzhong Plain, suitable for the forest to develop. When this soil developed, the mean annual pre- cipitation was more than the annual soil moisture evaporation. The value of soil moisture balance was positive and the atmospheric precipitation could supply the underground water normally. Soil water was weak acidic in the middle and late stages when S5 developed in Guanzhong Plain. It was a kind of subtropical climate and even more humid and warmer than the northern edge of the subtropical climate zone in Guanzhong Plain when the S5 developed. At that time the subtropical climate was prevailing over the northern side and southern side of Qingling Mountains, showing the Mountains no longer to be the boundary between the subtropical zone and the temperate zone in China. The summer monsoon acted intensely and could go over Qingling Mountains frequently bring abundant precipitation.     

Mineral weathering and element cycling in soil-microorganism-plant system

Soil is an essential part of the critical zone,and soil-microbe-plant system serves as a key link among lithosphere,biosphere,atmosphere and hydrosphere.As one of the habitats with the richest biodiversity,soil plays a critical role in element biogeochemistry on the earth surface(weathered crust).Here we review the soil biological processes that are relevant to mineral weathering,element cycling,and transformation,with an emphasis on rock weathering mediated by soil microbes,plant root and the rhizosphere.     

Overpressure development and oil charging in the central Junggar Basin,Northwest China: Implication for petroleum exploration

The Junggar Basin is one of the largest and most petroliferous superimposed petroleum basins in China. The central depression area has become the frontier field for petroleum exploration. The characteristics of potential source rocks and reservoir sandstones, and the pressure regime in the central Junggar Basin were studied. Permian shales are dominated by hydrogen-rich, oil-prone algal organic matter, and Jurassic mudstones are dominated by hydrogen-poor, higher-plant derived organic matter. These source rocks are widespread and have been mature for hydrocarbon generation, suggesting good to excellent exploration potential, both for crude oils and for natural gases. The deeply buried Jurassic sandstones usually have low porosity and permeability. However, sandstones beneath the Jurassic/Cretaceous unconformity display relatively high porosity and permeability, suggesting that meteoric water leaching had improved the quality of the sandstones. Overpressure developed over much of the central Junggar Basin. The overpressured rocks are characterized by slightly increased interval transit time, low sandstone permeability, increased organic matter maturity, and high relative hydrocarbon-gas contents. Mudstones in the overpressured system have quite the same clay mineral compositions as mudstones in the lower part of the normally pressured system. Overpressure generation in the central Junggar Basin is best to be explained as the result of hydrocarbon generation and fluid retention in low-permeability rocks. Petroleum generated from Permian and Jurassic source rocks could migrate laterally through preferential petroleum migration pathways and accumulated in structural traps or lithological traps in the overpressured system, or migrate vertically through faults/hydraulic fractures into the overlying, normally pressured system and accumulate in structural or lithological traps. Therefore, commercial petroleum reservoirs could be potentially found in both the overpressured system, and in the normally pressured system.     

3-D velocity images of the crust and upper mantle of the Tianshan area

（胥颐，朱介寿，刘志坚，张华卿，朱燕）３－ＤｖｅｌｏｃｉｔｙｉｍａｇｅｓｏｆｔｈｅｃｒｕｓｔａｎｄｕｐｐｅｒｍａｎｔｌｅｏｆｔｈｅＴｉａｎｓｈａｎａｒｅａ￥ＹｉＸＵ；Ｊｉｅ－ＳｈｏｕＺＨＵ；Ｚｈｉ－ＪｉａｎＬＩＵ；Ｈｕａ－ＱｉｎｇＺＨＡＮＧａｎｄＹａ...     

Crust-mantle transitional zone of Tianshan orogenic belt and Junggar Basin and its geodynamic implication

The traveling time of the reflection waves of each shot point from the crust-mantle transitional zone has been obtained by data processing using wavelet transform to the waves reflected from the crust-mantle transitional zone. The crust-mantle transitional zone of the Xayar-Burjing geoscience transect can be divided into three sections: the northern margin of the Tarim Basin, the Tianshan orogenic belt and Junggar Basin. The crust-mantle transitional zone is composed mainly of first-order discontinuity in the Tarim Basin and the Junggar Basin, but in the Tianshan orogenic belt, it is composed of 7–8 thin layers which are 2-3 km in thickness and high and low alternatively in velocity, with a total thickness of about 20km. The discovery of the crust-mantle transitional zone of the Tianshan orogenic belt and Junggar Basin and their differences in tectonic features provide evidence for the creation of the geodynamic model “lithospheric subduction with intrusion layers in crust” for the Tianshan orogenic belt.     

新疆天山地区壳幔S波速度结构特征及变形分析

天山地区地质构造复杂,地震活动频繁,其壳幔变形和深部结构一直受到学者们的高度关注.然而,由于天山地区地震台站资料较少,致使壳幔变形研究结果与解释存在诸多争议.本研究利用在天山地区（40°N-46°N,78°E-92°E）新布设的11个流动宽频带地震台站和该地区39个固定台站的观测资料,采用接收函数与面波联合反演方法,获得了研究区地壳厚度及壳幔S波速度结构.反演结果显示天山地区（41.5°N-44°N,78°E-88°E）平均地壳厚度为56 km,塔里木盆地（40°N-41.5°N,79°E-90°E）、准噶尔盆地（44°N-46°N,82°E-90°E）和吐鲁番盆地（42°N-43°N,88°E-90°E）具有较厚的沉积层,地壳平均厚度为43 km、53 km和46 km,整体表现为天山厚、盆地相对较薄的特征;在研究区南天山的最高峰（42°N,80.5°E）及北天山的最高峰（43.5°N,86°E）附近,中下地壳存在较厚的低速层,我们认为在强烈挤压作用下低速、低强度的中下地壳强烈变形可能是导致该区域快速隆升的主要原因.在研究区中部,位于塔里木盆地与准噶尔盆地之间的天山地区,中下地壳及上地幔均存在低速层,且盆地莫霍面向天山倾斜明显.结合前人的研究成果推测,在南北向构造挤压应力作用下,塔里木盆地与准噶尔盆地发生了向天山造山带方向的双向壳幔层间插入俯冲.在研究区东部,塔里木盆地东北缘与天山东部接触带的地壳内没有明显的低速层,推测应处在早期挤压变形状态,该区域的壳幔边界为缓变的速度梯度带,可能与上地幔热物质侵入或渗透有关.     

Postcollisional mantle-derived magmatism, underplating and implications for basement of the Junggar Basin

The late Paleozoic postcollisional granitoids, mafic-ultramafic complexes, and volcanic rocks are extensively distributed around the Junggar Basin; they are generally characterized by positive ε_Nd(t) values, implying that the magmas were mantle-derived and contaminated with crustal materials to some extents. The emplacement of mantle-derived magmas and their differentiates in the upper crust is the expression of deep geological processes at shallow level, while much more mantle-derived magmas were underplated in the lower crust and the region near the crust-mantle boundary, being component part of basement of the Junggar Basin. The postcollisional mafic-ultramafic complexes would not be generated by re-melting of residual oceanic crust, which was considered as the basement of the Junggar Basin, unless very high degrees of partial melting occurred. Even if old continental crust had been present before collision, it would have been strongly modified by the mantle-derived magma underplating. This interpretation is compatible with the existing geophysical data. Project supported by the National Natural Science Foundation of China (Grants Nos. 4900031 and 49272103)     

Differences of granitic weathering at the northern and southern feet of Dabie Mountains,Central China: Implication for tectonic and climatic environments

Previous studies of weathering generally started with geochemistry[1—8] and mineralogy[9—12], and have been focused on chemical weathering rates[1—3], removability-enrichment of elements[3—6] during chemical weathering, and the age of weathering profi…     

Q value structure of geoscience transect from Korla to Jimsar and its geodynamic implication

TheTOBisoneoftheyoungestandhighestintracontinentalorogenicbeltsinMiddleAsia.ItplaysaveryimportantroleinaccommodatingtheconvergencebetweenIndianContinentandtheSiberianContinent,andtherefore,itiswidelynoticedbygeoscientistsworldwide.Uptonow,severalgeoscienc…     

East Asian paleoclimate change in the Weihe Basin(central China)since the middle Eocene revealed by clay mineral analysis

Obtaining a continuous sedimentary record of Cenozoic East Asian paleoclimate change is key to understand the origin, evolution and driving mechanism of the East Asian monsoon and climate change. Based on the continuous Cenozoic fluvial and lacustrine sedimentary sequence in the Weihe Basin, central China, we carried out research on the content and crystal parameters of clay minerals. The paleoclimate change since the middle Eocene was reconstructed accordingly. The results show that smectite and illite are the dominant clay minerals in fluvial-lacustrine sediments of Weihe Basin. The crystallinity of illite,the chemical index of illite, the ratio of smectite to illite and chlorite decrease gradually, which indicates that chemical weathering in the Weihe River watershed stepwise weakened since the middle Eocene, under the background of a semi-arid and semi-humid climate. The formation of palygorskite may be affected by a weak diagenesis. In this case, the content of smectite and the illite crystallinity caused by the weathering in the corresponding period may be actually higher than that of the current,which indicates that the climate in the Weihe Basin region was relatively warm and humid from the middle Eocene to Pliocene.With the decrease of Cenozoic global temperature and the continuous accumulation of sediments, the intensity of chemical weathering in the Weihe Basin gradually weakened, and the East Asian monsoon climate gradually evolved until becoming dry in the Quaternary. Evidence from clay minerals also indicates that the aridification in the Weihe Basin from the late Eocene to the Oligocene may be a response to the global cooling event at the Eocene-Oligocene transition.     

Conceptualization of the hydrogeological system of some sedimentary aquifers in Savelugu–Nanton and surrounding areas,Northern Ghana

Groundwater resources play a pivotal role in the rural water delivery system in Ghana. The hydrogeological system of Middle Voltaian terrain was simulated using available data on hydraulic heads and boundary conditions. The objective was to characterize the general groundwater flow pattern and provide local estimates of the distribution of hydraulic conductivity and recharge fields. The results suggest a predominant NE–SW flow direction, which ties in with the general regional structural trend and indicates that the hydrogeological conditions of the rocks are controlled by structural entities created in the wake of fracturing and/or weathering of the rocks whose primary permeabilities are considerably reduced because of high compaction and low‐grade metamorphism. Calibrated hydraulic conductivities range between 1.90 and 10.81 m/d. The spatial distribution appears to reflect the intensity of fracturing and/or weathering of the rock and the proportion of the clay fraction of the weathered zone. Vertical groundwater recharge has been estimated to range between 0.3% and 4.1% of the annual rainfall. This recharge rate is quite low and reflects the imperviousness of the thick overburden because of high clay content in some places and high compaction in others. Despite this apparently low recharge rate, groundwater resources potential in the area appear to be high, and increased abstraction from existing abstraction wells by up to 50% does not appear to register significant effects on groundwater budgets at the simulated recharge rates. This suggests that the well yields are much lower than the potential of the aquifer system. The apparently low yields might be associated with poor well development and the choice of inappropriate well completion materials. This study recommends a monitoring system to be developed for a much more regional groundwater flow simulation under transient conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of Quaternary paleoclimate change on the permeability of the loess–paleosol sequence in the Loess Plateau,northern China

Permeability differences in multi-cycle loess–paleosol aeolian sediments, which are still poorly understood, have the potential to significantly improve our understanding of climatic change during the glacial–interglacial periods of the Quaternary. In this study, the permeability of a well-preserved and continuous loess–paleosol sequence in the South Jingyang Plateau was investigated. Weathering intensity was inferred using a series of climate proxies including grain-size distribution, magnetic susceptibility and mineralogy. The results of laboratory tests showed that the average saturated hydraulic conductivity of loess layers is higher than that of paleosol layers. Also, clear differences between loess and paleosol were found in terms of depth variations of the vertical and horizontal saturated hydraulic conductivities. Differences in loess–paleosol were also found for other proxies for pedogenic weathering [i.e. clay content, sand content, Kd value (ratio of coarse silt to clay), magnetic susceptibility, dolomite content and the ratios of hornblende/illite and hornblende/chlorite]. Our results showed a high permeability of loess layers associated with weak pedogenic weathering during cold/dry paleoclimatic conditions in glacial stages. On the contrary, paleosol layers developed in a warm/humid climate during the interglacial stages experienced strong pedogenic weathering that resulted in lower permeability. Based on these results, we construct a connection between Quaternary climate change theory and the modern hydrological system. This provides a scientific basis for investigating the distribution and pollution of groundwater resources in the local region. © 2020 John Wiley & Sons, Ltd.     

A study of the depth of weathering and its relationship to the mechanical properties of near-surface rocks in the Mojave Desert

Weathered granite extends 70 m deep at Hi Vista in the arid central Mojave Desert of southern California. The low strength of this granite is due to the alteration of biotite and chlorite montmorillonite. Deep weathering probably occurs in most granites, although we cannot rule out some anomalous mechanisms at Hi Vista. Geophysical instruments set in these slightly altered rocks are limited by the unstable behavior of the rocks. Thus, tectonic signals from instruments placed in shallow boreholes give vague results. Geophysical measurements of these weathered rocks resemble measurements of granitic rocks near major faults. The rheology of the rocks in which instruments are placed limits the useful sensitivity of the instruments.     

闽西晚白垩世红层的古环境探究

中国东南地区白垩纪红层通常被认为是陆相红色碎屑沉积物,是河流湖泊相沉积,但其古环境存在争论.本文以闽西晚白垩世红层为研究对象,利用环境磁学、粒度、地球化学、古土壤分析等方法,选取连城(LC)和冠豸山(GZS)两个剖面,分析探讨红层的古环境.结果显示:(1)闽西红层主要以细的粉砂颗粒为主,黏土和砂含量较少,表现为粉砂和砂互层,夹有薄层细粒砂砾层;样品磁化率偏低,主要载磁矿物为硬磁性矿物赤铁矿.(2)闽西红层有较高的风化程度,是暖湿气候下的中等风化程度;轻重稀土元素分异明显,Ce元素富集,Eu元素相对亏损,与上地壳(UCC)的分配模式相似,表明沉积物经历了充分混合,物质为混合沉积产物.(3)闽西红层虽然发育了一定的古土壤,但是成壤程度不强,没有明显的古土壤粘化层(Bt)和钙积层(Bk).由此推断,闽西红层沉积物在沉积前已在源区经过相当程度的风化过程,之后经过混合动力搬运沉积在盆地,沉积后风化成壤弱.可见,红层本身并不能直接反映沉积区环境,需结合古土壤发育特征判断沉积环境特征和变化.(4)闽西晚白垩世红层表现为相对干旱半干旱的古环境,红层中主要的着色矿物赤铁矿主要形成于源区,反映了地表透水性良好的干燥氧化条件,而不是"水成"环境.本文可为白垩纪红层古环境研究提供新的思路.     

Element geochemistry of weathering profile of dolomitite and its implications for the average chemical composition of the upper-continental crust--Case studies from the Xinpu profile,northern Guizhou Province,China

Geochemical behavior of chemical elements is studied in a dolomitite weathering profile in upland of karst terrain in northern Guizhou.Two stages can be recognized during the process of in situ weathering of dolomitite:the stage of sedentary accumulation of leaching residue of dolomitite and the stage of chemical weathering evolution of sedentary soil.Ni,Cr,Mo,W and Ti are the least mobile elements with reference to Al.The geochemical behavior of REE is similar to that observed in weathering of other types of rocks.Fractionation of REE is noticed during weathering,and the two layers of REE enrichments are thought to result from downward movement of the weathering front in response to changes in the environment.It is considered that the chemistry of the upper part of the profile,which was more intensively weathered,is representative of the mobile components of the upper curst at the time the dolomitite was formed,while the less weathered lower profile is chemically representative of the immobile constitution.Like glacial till and loess,the "insoluble" materials in carbonate rocks originating from chemical sedimentation may also provide valuable information about the average chemical composition of the upper continental crust.     

准噶尔盆地陆东-五彩湾地区石炭系火山岩电性与地震响应特征

勘探实践证实,准噶尔盆地石炭系已成为一套现实勘探层系;陆东-五彩湾地区石炭系火山岩体规模大、分布广,是重要的天然气储集体;火山岩储层有效性主要受不整合、岩性、岩相控制,识别火山结构、火山岩岩性、岩相成为判别储层有效性的关键.由于主要目的层巴塔玛依内山组特殊的三段式火山岩组合层序结构,为通过测井、地震物探手段识别火山岩岩...     

JOINT INVERSION OF SURFACE WAVE DISPERSION AND RECEIVER FUNCTIONS FOR CRUSTAL AND UPPERMOST MANTLE STRUCTURE BENEATH CHINESE TIENSHAN AND ITS ADJACENT AREAS

The Tienshan orogenic belt is one of the most active intracontinental orogenic belts in the world. Studying the deep crust-mantle structure in this area is of great significance for understanding the deep dynamics of the Tienshan orogen. The distribution of fixed seismic stations in the Tianshan orogenic belt is sparse. The low resolution of the existing tomographic results in the Tienshan orogenic belt has affected the in-depth understanding of the deep dynamics of the Tienshan orogenic belt. In this paper, the observation data of 52 mobile seismic stations in the Xinjiang Seismic Network and the 11 new seismic stations in the Tienshan area for one-year observations are used. The seismic ambient noise tomography method is used to obtain the Rayleigh surface wave velocity distribution image in the range of 10~50s beneath the Chinese Tienshan and its adjacent areas (41°~48° N, 79°~91° E). The joint inversion of surface wave and receiver function reveals the S-wave velocity structure of the crust and uppermost mantle and the crustal thickness below the station beneath the Chinese Tienshan area(41°~46° N, 79°~91° E). The use of observation data from mobile stations and new fixed seismic stations has improved the resolution of surface wave phase velocity imaging and S-wave velocity structure models in the study area.
The results show that there are many obvious low-velocity layers in the crust near the basin-bearing zone in the northern Tienshan Mountains and the southern Tienshan Mountains. There are significant differences in the structural characteristics and distribution range of the low-velocity zone in the northern margin and the southern margin. Combining previous research results on artificial seismic profiles, receiver function profiles, teleseismic tomography, and continental subduction simulation experiments, it is speculated that the subduction of the Tarim Basin and the Junggar Basin to the Tienshan orogenic belt mainly occurs in the middle of the Chinese Tienshan orogenic belt, and the subduction of the southern margin of the Tienshan Mountains is larger than that of the northern margin, and the subduction of the eastern crust is not obvious or in the early subduction stage. There are many low-velocity layers in the inner crust of the Tienshan orogenic belt, and most of them correspond to the strong uplifting areas that are currently occurring. The thickness of the crust below the Tienshan orogenic belt is between 55km and 63km. The thickness of the crust(about 63km)is the largest near the BLT seismic station in the Bazhou region of Xinjiang. The average crustal thickness of the Tarim Basin is about 45km, and that of the Junggar Basin is 47km. The S-wave velocity structure obtained in this study can provide a new deep basis for the study of the segmentation of the Tienshan orogenic belt and the difference of the basin-mountain coupling type.     

<Emphasis Type="Italic">Q</Emphasis> value structure of geoscience transect from Korla to Jimsar and its geodynamic implication

In this paper, the methods for Q value inversion in 2-D lateral inhomogeneous medium have been introduced. The 2-D Q value inversion has been conducted using seismic wide-angle reflection/refraction data of the profile from Korla to Jimsar. The result shows that the 2-D Q value structure of the transect from Korla to Jimsar is characterized by vertical stratifying and lateral zoning. Vertically, the crust can be divided into upper crust, middle crust and lower crust with the Q value increasing downwards. Horizontally, the total transect can be classified as three regions— the northern margin of the Tarim Basin, the Tianshan orogenic belt (TOB) and the southern margin of the Junggar Basin. At the northern margin of the Tarim Basin the Q value increases northwards, indicating a northward subduction of the Tarim Basin into the The Q value within the TOB jumps near Kumux, making a stage-like difference in Q value. The Q value distribution at the southern margin of the JB suggests a southward subduction of the Junggar Basin (JB) into the The double subduction pattern of the and JB into the TOB revealed by the transect from Korla to Jimsar has a big difference from the model “lithospheric subduction with intrusion of the layers into the crust” developed according to the results of the geoscience transect from Xayar to Burjing. The differences between the two provide some dynamic evidence at lithospheric scale for the segmentation of the Zhang Xiankang, Zhang Chengke, Jia Shixu et al., A summary report on exploration and research on GGT (in Chinese), 1999 Xu Xinzhong, A summary report on the results of seismic exploration on the comprehensive geophysical profile from Kktuohai to Aksai (in Chinese), 1990     

Migration and enrichment of trace elements of Lower Palaeozoic carbonate rock strata in Beijing

Analyses of trace elements of the Lower Palaeozoic carbonate rock strata in Beijing show that the contents of As, Hg, F increase from primary carbonate rocks to weathered carbonate rocks and from primary carbonate rocks to the soil coexisting with carbonate rocks, but the distribution regularity of S is not obvious. In the whole weathered stages, the sorption of As is mainly affected by Fe2O3. In soil Fe2O3 is also the main affecting factor of Hg enrichment. The main existing forms of Hg in primary carbonate rocks should simply be physical adsorption, coprecipitation and false isomorphous form between surface of carbonate rock and Hg. In soil the enrichment of F has little relationship with sul-fides and Fe2O3. In primary carbonate rocks, F is mainly absorbed by sulfides and clay minerals, etc. Weathered samples have closer genetic relationships with primary carbonate rocks. This also implies that weathered carbonate rocks have the close existing forms to that of primary carbonate rocks. In primary carbonate rocks FeS2 and FeS are the main forms of S, and sulfides have fixation effect on some heavy metals, whereas in weathered carbonate rocks and soil the fixation effect is weakened.     

Element geochemistry of weathering profile of dolomitite and its implications for the average chemical composition of the upper-continental crust

Geochemical behavior of chemical elements is studied in a dolomitite weathering profile in upland of karst terrain in northern Guizhou. Two stages can be recognized during the process ofin situ weathering of dolomitite: the stage of sedentary accumulation of leaching residue of dolomitite and the stage of chemical weathering evolution of sedentary soil. Ni, Cr, Mo, W and Ti are the least mobile elements with reference to Al. The geochemical behavior of REE is similar to that observed in weathering of other types of rocks. Fractionation of REE is noticed during weathering, and the two layers of REE enrichments are thought to result from downward movement of the weathering front in response to changes in the environment. It is considered that the chemistry of the upper part of the profile, which was more intensively weathered, is representative of the mobile components of the upper curst at the time the dolomitite was formed, while the less weathered lower profile is chemically representative of the immobile constitution. Like glacial till and loess, the “insoluble” materials in carbonate rocks originating from chemical sedimentation may also provide valuable information about the average chemical composition of the upper continental crust.