An open-accessed inventory of landslides triggered by the M_(S)6.8 Luding earthquake,China on September 5,2022

This study constructs a preliminary inventory of landslides triggered by the M_(S) 6.8 Luding earthquake based on field investigation and human-computer interaction visual interpretation on optical satellite images.The results show that this earthquake triggered at least 5007 landslides,with a total landslide area of 17.36 km^(2),of which the smallest landslide area is 65 m^(2)and the largest landslide area reaches 120747 m^(2),with an average landslide area of about 3500 m^(2).The obtained landslides are concentrated in the IX intensity zone and the northeast side of the seismogenic fault,and the area density and point density of landslides are 13.8%,and 35.73 km^(-2) peaks with 2 km as the search radius.It should be noted that the number of landslides obtained in this paper will be lower than the actual situation because some areas are covered by clouds and there are no available post-earthquake remote sensing images.Based on the available post-earthquake remote sensing images,the number of landslides triggered by this earthquake is roughly estimated to be up to 10000.This study can be used to support further research on the distribution pattern and risk evaluation of the coseismic landslides in the region,and the prevention and control of landslide hazards in the seismic area.

Stratigraphic framework and sedimentary evolution during the Cryogenian-Ediacaran transition in northeastern Sichuan Basin,South China

The northeastern Sichuan area in the northern Yangtze margin has unique Ediacaran geological records,especially the Doushantuo Formation(DST),and become a hot research area in recent years.However,the Cryogenian-Ediacaran(C-E)boundary has not been precisely identified,which restricts the in-depth study of geological information during this crucial transitional period and is unfavorable for a systematic and complete understanding of the Yangtze Block and even the global paleogeographic pattern.This study conducted stratigraphy,sedimentology,and chronostratigraphy to establish the stratigraphic framework and sedimentary evolution of the C-E transition strata in northeastern Sichuan.The results showed that the Ediacaran sediments,without the cap dolomite,unconformably overlaid the Cryogenian sediments in the studied area.The Member II of the DST,characterized by 50-160 m of red-green sandstone(approximately equivalent to the original Chengkou“Guanyinya Formation”),directly overlaid the Cryogenian sediments and displayed a 623±2.3 Ma maximum depositional age from the detrital zircon U-Pb dating.Regional stratigraphic correlations indicate that the C-E transition strata in northeastern Sichuan had a consistent lithological association and sedimentary sequence characteristics but differed from the Three Gorges.Typically,the upper Nantuo massive glacial diamictites transition to the icebergs rafted lonestone-bearing mudstones at the top,then change upward to DST barrier coast sandstones.The proposed DST of the northeastern Sichuan Basin was divided into three lithostratigraphic members without the regional Member I cap dolomite:(i)Member II purple-red,gray-green sandstone strata,(ii)MemberⅢblack mudstone strata,and(iii)Member IV P-Mn bearing strata.During the C-E transition,the study area experienced(i)the global deglaciation stage in the terminal Marinoan glaciation and(ii)the filling-leveling up stage with clastic rocks in the early Ediacaran.Overall,the early Ediacaran of northeastern Sichuan succeeded the paleogeographic features of the late Cryogenian.

Physico-Chemical Properties and Enzyme Activities of the Arable Soils in Lhasa,Tibet,China

An understanding of the physical,chemical,and biological properties of a soil provides a basis for soil use and management.This paper reports the major physico-chemical properties and enzyme activities of the soils of Lhasa's main arable lands and the factors that influence these soil properties.Composite and core samples were taken from the three main arable soil types(alluvial soil,subalpine arable steppe soil,and subalpine arable meadow soil) and were analysed using standard methods.The bulk density and the ventilation porosity ratio of the soils were close to the recommended values for arable lands,and the dominant soil texture was sandy.The soil moisture release rates were arable steppe soil > alluvial soil > arable meadow soil.Soil organic matter content,Cation-Exchange Capacity(CEC),total and available nitrogen content,and catalase activity of the arable meadow soil were higher than those of the alluvial and the arable steppe soils,while soil pH in the arable meadow was lower.Most of the measured properties did not show a significant variance among these three soils.However,the measured indices(apart from the total potassium) indicate that there are notable differences among the three types of soil.The results implied that the utilisation patterns of the arable soil or human activities,such as tillage practices and fertiliser applications,have a substantialeffect on the soil properties in this region.Our results suggest that the cultivation practices in the region have apparently positive impact on the soil organic matter,nutrient contents and bulk density probably due to the sound fertiliser management such as the applications of farmyard manure and chemical fertilisers.However,intense cultivation practices lowered the activity of most soil enzymes.The results demonstrate that the choice of soil management strategy had a significant impact on the soil physicochemical and biological properties in the region studied.

Geological characteristics and tectonic signifcance of unconformities in Mesoproterozoic successions in the northern margin of the North China Block

Several stratigraphic breaks and unconformities exist in the Mesoproterozoic successions in the northern margin of the North China Block. Geologic characters and spatial distributions of five of these un- conformities, which have resulted from different geological processes, have been studied. The uncon- formity beneath the Dahongyu Formation is interpreted as a breakup unconformity, representing the time of transition from continental rift to passive continental margin. The unconformities beneath the Gaoyuzhuang and the Yangzhuang formations are considered to be the consequence of regional eustatic fluctuations, leading to the exposure of highlands in passive margins during low sea-level stands and transgressive deposition on coastal regions during high sea-level stands. The unconformity atop the Tieling Formation might be caused by uplift due to contractional deformation in a back-arc setting, whereas the uplift after the deposition of the Xiamaling Formation might be attributed to a continental collision event. It is assumed that the occurrences of these unconformities in the Mesoproterozoic successions in the northern margin of the North China Block had a close bearing on the assemblage and breakup of the Columbia and Rodinia supercontinents.

Spatial distribution characteristics and main controlling factors of germanium in soil of northern Dabie Mountains, China

With the increasing application of germanium(Ge)elements in modern industry,military and medical health industries,especially with the growing demand for Ge-rich agricultural products,the study of Ge-rich soil has become particularly important,but the enrichment pattern and control factors of Ge-rich soil are still not well understood due to the high dispersion and high migration of Ge-rich soil.In this paper,495 surface soil(0-20 cm)and 149 deep soil(150-200 cm)samples were collected from the northern foothills of Dabie Mountain using a double-layer grid layout,and the spatial distribution and enrichment characteristics of Ge were studied by high-resolution method,and the controlling factors affecting the distribution of Ge-rich soil was analyzed by geo-statistics and spatial analogy.The results show an average Ge content of 1.34 mg/kg for the surface and 1.36 mg/kg for the deep soil.In the assessment grade classification of surface and deep soil for Ge,the abundant and sub-abundant grades account for 37.97%and 31.70%,respectively,covering 752 km2 and 634 km2.Surface Ge-rich regions are distributed in concentrated strips in the north-central part of the studied region,and there is no clear pattern in the spatial distribution of deep soils.In the areas under study,such as Fenlukou,Dingji,and Jiangjiadian,the surface soil is very rich in Ge and has a high enrichment factor,which is valuable for agricultural development.In surface soils,river deposits and shallow metamorphic rock parent materials have the highest content of Ge,while in deep soils,the highest content has been found in the parent material of moderately acidic rock.Both surface and deep soils have the highest Ge content in purple paddy soils and plain areas.The source of Ge in the soils of the study area is most influenced by the lithology of the soil-forming parent material,while the distribution of Ge in the surface soils is jointly influenced by pH,SiO_(2),TFe_(2)O_(3),and Al_(2)O_(3) in the soil.This study has implications for understanding the enrichment pattern of Ge in soil and its controlling factors as well as for the development of Ge-rich agricultural products.

Carbon Oxygen Isotope Analysis and Its Significance of Carbonate in the Zhaogezhuang Section of Early Ordovician in Tangshan,North China

In the Early Ordovician Zhaogezhuang Section of Tangshan , North China, the Yeli Formation is composed of an entire third-order sequence, with facies ranging from the inner ramp restricted platform and open marine to the middle and even outer ramps. The Liangjiashan Formation is dominated by highstand system tracts （HST） with predominantly inner ramp grain-shoal and lagoon facies. Analyzing the carbon and oxygen isotope during the whole-rock carbonate reveals the 613C values in the Yeli Formation range from -7.11%o-0.76%o （PDB）, with the mean value at -2.98%0, while the 6180 values range of-9.09%o- -4.65%o with the mean value at -6.12%o. The 613C values in the Liangjiashan Formation range of -1.15%o-0.3%o, and the mean value of -0.57%0; the 61SO values are -8.76%0- -7.48%0, and the mean value is -8.06%o. The 613C values in the Yeli Formation decrease, but at the bottom of the Liangjiashan Formation the values increase steadily. In the middle-upper formation, there is an extended fluctuation between 0- -1.00%o. The 613C trend in the studied section is similar to that of the contemporary sections, except that it has much lower 613C values and a more negative excursion. The correlation between the 613C changes and the eustatic events, as well as the sedimentary facies, indicates that in the Tangshan area, the carbon isotope evolution can be attributabled to the processes of the eutrophic sea/oligotrophic sea, the seafloor organism- mediated oxidation in shallow water and the organic reduction after maximum flooding. The changes in the carbon isotope contents were primarily affected by the regional relative sea level changes. Compared to the other coeval data, the Early Ordovician of the Tang shan area is also severely depleted in 180, with all of the 6180sample values being Delow 5%o, except for one sample with a value ot -4.02%0. Witlt the ancient sea- water having a 6180 value of-5.5%0 （SMOW）, it is reasonable to delineate a temperature of less than 37 C.

Manganese carbonate stromatolites of the Ediacaran Doushantuo Formation in Chengkou,northern Yangtze Craton,China

The origin process of manganese ores remains unsolved worldwide.Exploring the origins of stromatolites that contain manganese may be a key to deciphering the sedimentary environments and metallogenic processes of these deposits.However,only a few manganese stromatolites have been discovered and described until now.Microbialites are well developed in the manganese deposits,located near the top of the Ediacaran Doushantuo Formation in Chengkou area of Chongqing,northern Yangtze Craton,but has not been explicitly studied;and whether they are true stromatolites or Epiphyton microbialites remains controversial.Based on field and core observations and thin section microscopy,the characteristics of five types of manganese stromatolites and their growth modes are described in detail in this study.The results show that these stromatolites grew in a biostrome in shoal and lagoon environments and were syngenetic with oncolites and oolites on a carbonate ramp behind the shoal.Manganese stromatolites can be categorized into three forms:(1)stratiform;(2)columnar,which includes branched and columnar types;and(3)stratiform-columnar,which is a transitional type.Based on a criterion that the diameter is less than or greater than 1 mm,columnar stromatolites are further divided into micro-columnar(<1 mm)and columnar(>1 mm)columns,which display synchronous growth and are similar to Pseudogymnosolenaceae.Their shapes are mainly controlled by water depths and hydrodynamic strengths.The greater the water depth,the more columnar the columns tend to be.Excessively strong hydrodynamic conditions decrease the growth rate of stromatolites,and they even stopped growth due to wave damage.Furthermore,pillared laminar textures(not Epiphyton),which consist of dendritic,micro-branched and microcolumnar stromatolites,are a common feature of the larger stratiform,stratiform-columnar and columnar stromatolites.The alternations of laminae with different internal textures record subtle fluctuations in water depths and hydrodynamic strengths,which indicate that stromatolite growth is controlled by tidal cycles at the lamina level.Therefore,it is possible that the vertical evolution of the stromatolites could reveal the changing characteristics of both local and regional sedimentary environments,i.e.,stromatolite shape changes from columnar to stratiform can represent the onset of shallower environments with weak hydrodynamic conditions.In addition,as important reef builders in shallow carbonate ramps,microstromatolites accelerate the development from ramp to platform.Indicators of microbial control on stromatolite shapes and manganese sedimentation processes include the fabric of stromatolite laminae,organic rhodochrosite with a micritic texture that is usually clotted,spherical,tubular,fibrous or dendritic,which suggests that the laminae resulted from microbially induced in situ precipitation.