High-resolution seismicity imaging and early aftershock migration of the 2023 Kahramanmara?(SE Türkiye)M_W7.9&7.8 earthquake doublet

We build a high-resolution early aftershock catalog for the 2023 SE Türkiye seismic sequence with PALM,a seamless workflow that sequentially performs phase picking,association,location,and matched filter for continuous data.The catalog contains 29,519 well-located events in the two mainshocks rupture region during 2023-02-01–2023-02-28,which significantly improves the detection completeness and relocation precision compared to the public routine catalog.Employing the new PALM catalog,we analyze the structure of the seismogenic fault system.We find that the Eastern Anatolian Fault(EAF)that generated the first M_(W)7.9 mainshock is overall near-vertical,whereas complexities are revealed in a small-scale,such as subparallel subfaults,unmapped branches,and stepovers.The seismicity on EAF is shallow(<15 km)and concentrated in depth distribution,indicating a clear lock-creep transition.In contrast,the SürgüFault(SF)that is responsible for the second M_(W)7.8 mainshock is shovel-shaped for the nucleation segment and has overall low dip angles(~40°–80°).Aftershocks on the SF distribute in a broad range of depth,extending down to~35 km.We also analyze the temporal behavior of seismicity,discovering no immediate foreshocks within~5 days preceding the first mainshock,and no seismic activity on the SF before the second mainshock.

The naked planet Earth:Most essential pre-requisite for the origin and evolution of life

我们的蓝行星地球长被考虑了带充满为自从行星的出生，招待生活的营养素。这里，我们推测导致了在地球上的早年生活和它的余殃的出生的过程，最后导致 metazoans 的进化。我们评估：(1 ) 营养素的来源，(2 ) 初发的海洋的化学，(3 ) 海洋的起始的团，并且(4 ) 行星的尺寸。在生活大楼营养素之中，磷和钾起一个关键作用。仅仅岩石的三种类型能担任营养素的足够的来源：(a) 形成大陆的 TTG (花岗石) ，启用原始生活的进化到 metazoans；(b) 有 KREEP (钾，稀土元素元素，和磷) 的初发的大陆带一种粒状火成岩暗岩，它是的关键忍受生活；(c) carbonatite 岩浆，在象 U 和 Th 那样的放射产生的元素充实，它能引起变化加快进化并且在大陆人裂缝背景支持新种类的出生。第二个重要因素是海洋化学。初发的海洋是极其酸的(pH = 12 ) 并且在卤素(Cl， F 和其它) 充实， S， N 和金属性的元素(Cd， Cu， Zn，和其它) ，禁止生活的出生。在防碍 RNA 的这些元素上面清洗的板 tectonics。蓝海洋最后与 pH = 出现在 Phanerozoic 7 通过和由捱过，侵蚀和交通进海洋的表面大陆人外壳的广泛的相互作用。起始的海洋团也是重要的。生活的出生和进化的余殃深在有 35 km 的适于居住的地区是可能的能供应足够的营养素的海洋。没有一个巨大的大陆，营养素不能仅仅由山脉热水的循环被供应进海洋在地府。最后，行星的尺寸起一个关键作用。巨大的行星冷却不比更小的有效，以便进披风的海水的回来流动不发生直到中央恒星完成他们的主要顺序。由于土的合适的尺寸， Phanerozoic 的黎明见证海水的回来流动的开始进披风，导致巨大的大陆在上面的出现海平面，并且全球规模上的营养素的分发。氧泵也起了一个关键作用从那以后把 high-PO2 放在空气，导致入侵陆地的臭氧层和创新动物和植物的出现。满足紧密的条件使地球适于居住，初发的土的形成机制是一个重要因素。起初，一个干燥地球必须通过巨大的影响被做，由岩浆海洋列在后面漂浮充实营养素的初发的大陆(一种粒状火成岩 + KREEP ) 。从星状的带的迟了的轰炸供应了水使 35 km 成为厚海洋，并且在凉爽的木星以外不从从 Kuiper 的冰冷的陨星系上带子。满足与发展生活形式作为一个适于居住的行星启用了地球的上述条件是必要的。我们为在地球上的生活的出生和进化评估的紧密的限制将为寻找在 exo 太阳的行星的生活的行星的科学家提供重要指南。

High-velocity frictional behavior of Longmenshan fault gouge from Hongkou outcrop and its implications for dynamic weakening of fault during the 2008 Wenchuan earthquake

High-velocity friction experiments were conducted on clayey fault gouge collected from Hongkou outcrop of Beichuan fault,located at the southwestern part of Longmenshan fault system that caused the disastrous 2008 Wenchuan earthquake.The ultimate purpose of this study is to reproduce this earthquake by modeling based on measured frictional properties.Dry gouge of about 1 mm in thickness was deformed dry at slip rates of 0.01 to 1.3 m/s and at normal stresses of 0.61 to 3.04 MPa,using a rotary-shear high-velocity frictional testing machine.The gouge displays slip weakening behavior as initial peak friction decays towards steady-state values after a given displacement.Both peak friction and steady-state friction remain high at slow slip rates are examined and gouge only exhibits dramatic weakening at high slip rates,with steady-state friction coefficient values of about 0.1 to 0.2.Specific fracture energy ranges from 1 to 4 MN/m in our results and this is of the same order as seismically determined values.Low friction coefficients measured on experimental faults are in broad agreement with lack of thermal anomaly observed from temperature measurements in WFSD-1 drill hole(Wenchuan Earthquake Fault Scientific Drilling Project),which can be explained by even smaller friction coefficient for the Wenchuan earthquake fault.High-velocity friction experiments with pore water needs to be done to see if even smaller friction is attained or not.Shiny slickenside surfaces form at high slip rates,but not at slow slip rates. Slip zone with slickenside surface changes its color to dark brown and forms duplex-like microstructures,which are similar to those microstructures found in the fault gouges from the Hongkou outcrop.Detailed comparisons between experimentally deformed gouge samples and WFSD drill cores in the future will reveal how much we could reproduce the dynamic weakening processes in operation in fault zones during Wenchuan earthquake at present.

Geospatial characteristics of fire occurrences in southern hemispheric Africa and Madagascar during 2001-2020

For this study of long-term spatial patterns and trends of active fires in southern hemispheric Africa and on Madagascar from 2001 to 2020,active fire data from the MODIS FIRMS global fire data products were analyzed.The annual center of fire concentration tended to migrate toward the preserved rainforests and nature conservation areas in the Congo Basin and the mountain forests on the northeastern coast of Madagascar.Fire frequency varied seasonally at both study areas.We used geo statistical analysis techniques,such as measures of dispersion and emerging hot spot analysis,to reveal long-term trends in spatial patterns of fire events.In southern hemispheric Africa,the observed active fires tended to drift northward toward the Zambia-DRC border in the Congo basin.This northward migration progressed toward humid rainforests,which were better suited to sustaining repeated fire events.On Madagascar,the observed active fires tended to migrate toward the east coast in protected mountain forests.The spatial patterns of long-term trends showed a concentration of fires in the tropical regions of southern hemispheric Africa.Moreover,smaller clusters of new hot spots were located over eastern South Africa,overlapping with undifferentiated woodlands.On Madagascar,both hot and cold spots were identified and were separated by the highland region in the center of the island.Most of the eastern island was characterized by cold spots that received less precipitation than did the rest of the island.The presence of increasing hots spots in the densely vegetated areas highlights the urgent need for fire prevention and management in this region.

Chemical and physical studies of metallic alloy-based old Indian coins with LIBS coupled with multivariate analysis

The present work aims to demonstrate the capabilities of Laser-induced Breakdown Spectroscopy(LIBS)coupled with a multivariate technique for rapid quantification and classification of old Indian coins made of various alloys.Thirteen old Indian coins in different years of circulation,(1922–1986)were selected for the study.The concentrations were determined by Calibration free LIBS(CF-LIBS)method.The concentration of cuprum(Cu)is negligible,and aluminum(Al)is maximum in the first five coins,and vice-versa in the remaining eight coins.Two different multivariate methods,Principal Component Analysis(PCA)and Soft Independent Modelling of Class Analogy(SIMCA)have been used to classify and identify the coins.PCA classified all thirteen samples into four main alloy categories.The discernment of unknown samples to their probable class membership of alloy was performed using SIMCA.The surface hardness(Brinell hardness number)is linearly correlated with the plasma temperature and LIBS intensity ratios.The sample surface of the first and fifth coin belongs to Al-alloy,having the least surface hardness,and it became harder for Cu–Ni alloy,Ni-brass alloy,and bronze alloy.The hardness of the surface is more for bronze sample twelve.It is also observed that the plasma temperature increases monotonically with the Brinell hardness number.This analysis provides valuable information on fabrication methodology and explains large diversification in the elementary composition of old coins.

A combination of tides and nontidal variations in ocean bottom pressure may generate interannual slip fluctuations in the transition zone along a subduction plate interface

The tidal triggering of earthquakes has been studied for many years.The discovery of slow earthquakes in the early 2000s,including slow slip,has urged scientists to investigate the tidal responses of these earthquakes due to their sensitivity to weak stress perturbations.Previous studies have shown that slow earthquakes correlate with diurnal and semidiurnal tides and seasonal variations in surface loads more clearly than ordinary earthquakes.However,little is known about long-term responses to external stresses.In this paper,based on a widely accepted frictional law for faults,a mechanism is proposed by which nontidal variations in ocean bottom pressure,when combined with tides,pro mote the occurrence of slow earthquakes.Because slow earthquakes accompany a slip on the plate interface,this mechanism allows one to estimate slip modulations.A one-degree-of-freedom slip model is constructed and applied to Ise Bay in the Tonankai region of southwestern Japan,where large-scale ocean mass redistributions have occurred.The model calculated with parameters determined from the observation of tectonic tremors is quantitatively consistent with the slip during 1997-2013 inferred from GNSS data,suggesting that the decrease in the sea-level change in approximately 2006 could cause the accele ration of a slip observed after that.This result implies that the decreases in sea level in approximately 1996 and 2014 could also cause subsequent slip accelerations.These three slip acceleration periods temporally coincide with the increases in background seismicity in a shallower portion of the plate interface.These changes in seismicity are common to shallow earthquakes in the Tokai area,and a similar model can reproduce them.Further studies are expected to reveal causality between shallow earthquakes and long-term slip fluctuations based on modeling that considers changes in the frictional property along the plate interface.

U and Th Contents and Th/U Ratios of Zircon in Felsic and Mafic Magmatic Rocks:Improved Zircon-Melt Distribution Coefficients

U 和 Th 内容和锆石的 Th/U 比率上的高精确的数据获得了使用第二等的离子团 spectrometry 分析从文学被收集了。在花岗石的岩石中的锆石有 350 ppm U， 140 ppm Th，和 Th/U=0.52 的中部的价值；推荐锆石融化分区系数为杜是 81 并且 8.2 为 DTh。在从 mafic 和中间的岩石的锆石，中部的价值是 270 ppm U ， 170 ppm Th ，和 Th/U=0.81 ，并且推荐 zirconmelt 分区系数为杜是 169 并且 59 当锆石与melt 在平衡结晶时，为 DTh ， magmatic 锆石的 U 和 Th 内容和 Th/U 比率是低的。增加的岩浆温度应该相对 U 内容支持更高的 Th 内容，导致为在到比在花岗石的岩石中的中间的岩石的 mafic 的锆石的更高的 Th/U 比率。然而，当锆石与 melt 在不平衡结晶时， U 和 Th 更容易能进入锆石格子，并且他们的内容和 Th/U 比率主要取决于不平衡的度。在 magmatic 锆石的 U 和 Th 的行为能被用作 geochemical 指示物决定起源和 magmatic 锆石的结晶化环境。

Internal structure of Longmenshan fault zone at Hongkou outcrop,Sichuan,China,that caused the 2008 Wenchuan earthquake

This paper reports the internal structures of the Beichuan fault zone of Longmenshan fault system that caused the 2008 Wenchuan earthquake,at an outcrop in Hongkou,Sichuan province,China.Present work is a part of comprehensive project of Institute of Geology,China Earthquake Administration,trying to understand deformation processes in Longmenshan fault zones and eventually to reproduce Wenchuan earthquake by modeling based on measured mechanical and transport properties.Outcrop studies could be integrated with those performed on samples recovered from fault zone drilling,during the Wenchuan Earthquake Fault Scientific Drilling(WFSD) Project,to understand along-fault and depth variation of fault zone properties.The hanging wall side of the fault zone consists of weakly-foliated,clayey fault gouge of about 1 m in width and of several fault breccia zones of 30-40 m in total width.We could not find any pseudotachylite at this outcrop.Displacement during the Wenchuan earthquake is highly localized within the fault gouge layer along narrower slipping-zones of about 10 to 20 mm in width.This is an important constraint for analyzing thermal pressurization,an important dynamic weakening mechanism of faults.Overlapping patterns of striations on slickenside surface suggest that seismic slip at a given time occurred in even narrower zone of a few to several millimeters,so that localization of deformation must have occurred within a slipping zone during coseismic fault motion.Fault breccia zones are bounded by thin black gouge layers containing amorphous carbon.Fault gouge contains illite and chlorite minerals,but not smectite.Clayey fault gouge next to coseismic slipping zone also contains amorphous carbon and small amounts of graphite.The structural observations and mineralogical data obtained from outcrop exposures of the fault zone of the Wenchuan earthquake can be compared with those obtained from the WFSD-1 and WFSD-2 boreholes, which have been drilled very close to the Hongkou outcrop.The presence of carbon and graphite,observed next to the slipping-zone,may affect the mechanical properties of the fault and also provide useful information about coseismic chemical changes.

Geomorphic indices and relative tectonic uplift in the Guerrero sector of the Mexican forearc

Tectonically active areas,such as forearc regions,commonly show contrasting relief,differential tectonic uplift,variations in erosion rates,in river incision,and in channel gradient produced by ongoing tectonic deformation.Thus,information on the tectonic activity of a defined area could be derived via landscape analysis.This study uses topography and geomorphic indices to extract signals of ongoing tectonic deformation along the Mexican subduction forearc within the Guerrero sector.For this purpose,we use field data,topographical data,knickpoints,the ratio of volume to area(Rva).the stream-length gradient index(St),and the normalized channel steepness index(k_(sn)).The results of the applied landscape analysis reveal considerable variations in relief,topography and geomorphic indices values along the Guerrero sector of the Mexican subduction zone.We argue that the reported differences are indicative of tectonic deformation and of variations in relative tectonic uplift along the studied forearc.A significant drop from central and eastern parts of the study area towards the west in values of R_(VA)(from ~500 to^300),St(from ~500 to ca.400),maximum St(from ~1500-2500 to ~ 1000) and k_(sn)(from ~150 to ~100) denotes a decrease in relative tectonic uplift in the same direction.We suggest that applied geomorphic indices values and forearc topography are independent of climate and lithology.Actual mechanisms responsible for the observed variations and inferred changes in relative forearc tectonic uplift call for further studies that explain the physical processes that control the forearc along strike uplift variations and that determine the rates of uplift.The proposed methodology and results obtained through this study could prove useful to scientists who study the geomorphology of forearc regions and active subduction zones.

Petrology and SHRIMP zircon geochronology of granulites from Vesleknausen, Lützow-Holm Complex, East Antarctica: Neoarchean magmatism and Neoproterozoic high-grade metamorphism

We report new petrological data and geochronological measurements of granulites from Vesleknausen in the highest-grade section of the Lützow-Holm Complex, part of the Gondwana-assembling collisional orogen in East Antarctica. The locality is dominated by felsic to intermediate orthogneiss(charnockite and minor biotite gneiss), mafic orthogneiss, and hornblende-pyroxene granulite, with deformed and undeformed dykes of metagranite and felsic pegmatite. Pseudosection analysis of charnockite in the system NCKFMASHTO, supported by geothermometry of mafic orthogneiss, was used to infer peak metamorphic temperatures of 750-850 ℃, approximately 150 ℃ lower than those estimated for metasedimentary gneisses from Rundvagshetta, 6 km to the northeast. SHRIMP U-Pb analysis of zircons from feldspar-pyroxene gneiss, which corresponds to a partially molten patch around mafic orthogneiss,yielded a Concordia upper intercept ages of 2507.9 7.4 Ma, corresponding to the time of formation of the magmatic protolith to the orthogneiss. Partial melting during peak metamorphism probably took place between 591 and 548 Ma, as recorded in rims overgrew around magmatic zircon. Our results suggest that Rundvagshetta-Vesleknausen-Strandnibba region in southwestern Lützow-Holm Bay, where orthogneisses are dominant, consists of a single crustal block, possibly formed by ca. 2.5 Ga arc magmatism. The Neoarchean magmatic terrane was tectonically mingled with other fragments(such as metasedimentary units in northern Lützow-Holm Bay) by subduction/collision events during the assembly of Gondwana supercontinent, and subsequently underwent w850 C granulite-facies metamorphosed during Neoproterozoic to Cambrian final collisional event.

Genesis of the Gold Deposit in the Indus-Yarlung Tsangpo Suture Zone,Southern Tibet:Evidence from Geological and Geochemical Data

The Nianzha gold deposit,located in the central section of the Indus-Yarlung Tsangpo suture(IYS) zone in southern Tibet,is a large gold deposit(Au reserves of 25 tons with average grade of 3.08 g/t) controlled by a E-W striking fault that developed during the main stage of Indo-Asian collision(~65-41 Ma).The main orebody is 1760 m long and 5.15 m thick,and occurs in a fracture zone bordered by Cretaceous diorite in the hanging wall to the north and the Renbu tectonic melange in the footwall to the south.High-grade mineralization occurs in a fracture zone between diorite and ultramafic rock in the Renbu tectonic melange.The wall-rock alteration is characterized by silicification in the fracture zone,serpentinization and the formation of talc and magnesite in the ultramafic unit,and chloritization and the formation of epidote and calcite in diorite.Quartz veins associated with Au mineralization can be divided into three stages.Fluid inclusion data indicate that the deposit formed from H_2O-NaCl-organic gas fluids that homogenize at temperatures of 203℃-347℃ and have salinities of 0.35wt%-17.17wt%NaCl equivalent.The quartz veins yield δ^(18)O_(fluid) values of 0.15‰-10.45‰,low δD_(V-SMOW)values(-173‰ to-96‰),and the δ^(13)C values of-17.6‰ to-4.7‰,indicating the ore-forming fluids were a mix of metamorphic and sedimentary orogenic fluids with the addition of some meteoric and mantle-derived fluids.The pyrite within the diorite has δ^(34)S_(V-CDT) values of-2.9‰-1.9‰(average-1.1‰),^(206)Pb/^(204)Pb values of 18.47-18.64,^(207)Pb/^(204)Pb values of 15.64-15.74,and ^(208)Pb/^(204)Pb values of 38.71-39.27,all of which are indicative of the derivation of S and other ore-forming elements from deep in the mantle.The presence of the Nianzha,Bangbu,and Mayum gold deposits within the IYS zone indicates that this area is highly prospective for large orogenic gold deposits.We identified three types of mineralization within the IYS,namely Bangbu-type accretionary,Mayum-type microcontinent,and Nianzha-type ophiolite-associated orogenic Au deposits.The three types formed at different depths in an accretionary orogenic tectonic setting.The Bangbu type was formed at the deepest level and the Nianzha type at the shallowest.

Petrography and Geochemistry of Peridotite Xenoliths from Hannuoba and Significance for Lithospheric Mantle Evolution

The compositions of the whole rocks and trace elements of minerals in peridotites can reflect the characteristics of the lithospheric mantle. The nature and evolution of the Cenozoic lithospheric mantle beneath Hannuoba , located on the north edge of the intra-North China orogenic belt, are discussed based on the in-situ LAM-ICPMS detected trace element compositions of clinopyroxenes in the Hannuoba peridotitic xenoliths combined with detailed petrography and geochemistry studies. The Hannuoba lithospheric mantle was formed by different partial meltings of the primitive mantle. Most of the samples reflect the partial melting degree of lower than 5% with a few samples of 15%-20%. Major element compositions of the whole rocks and geochemical compositions of clinopyroxenes reveal the coexistence of both fertile and depleted mantle underneath the Hannuoba region during the Cenozoic. This was probably caused by the asthenospheric mantle replacing the aged craton mantle through erosion, intermingling and modification. Our conclusion is further supported by the existence of both carbonatitic magmatic material and silicate melt/fluid metasomatism as magnified by the trace elements of the clinopyroxenes from the Hannuoba lithospheric mantle.

Surface wave tomography on a large-scale seismic array combining ambient noise and teleseismic earthquake data

We discuss two array-based tomography methods,ambient noise tomography (ANT) and two-planewave earthquake tomography (TPWT),which are capable of taking advantage of emerging large-scale broadband seismic arrays to generate high resolution phase velocity maps,but in complementary period band:ANT at 8-40 s and TPWT at 25-100 s period.Combining these two methods generates surface wave dispersion maps from 8 to 100 s periods,which can be used to construct a 3D v S model from the surface to ～200 km depth.As an illustration,we apply the two methods to the USArray/Transportable Array.We process seismic noise data from over 1 500 stations obtained from 2005 through 2009 to produce Rayleigh wave phase velocity maps from 8 to 40 s period,and also perform TPWT using ～450 teleseismic earthquakes to obtain phase velocity maps between 25 and 100 s period.Combining dispersion maps from ANT and TPWT,we construct a 3D vS model from the surface to a depth of 160 km in the western and central USA.These surface wave tomography methods can also be applied to other rapidly growing seismic networks such as those in China.

Effects of slab geometry and obliquity on the interplate thermal regime associated with the subduction of three-dimensionally curved oceanic plates

We investigated the relationships among slab geometry,obliquity,and the thermal regime associated with the subduction of oceanic plates using a three-dimensional(3D) parallelepiped thermal convection model.Various models with convex and concave slab shapes were constructed in the numerical simulation,and the temperature and mantle flow distributions were calculated.The results revealed that when the slab dip angle increases,or the obliquity of subduction becomes steeper,the interplate temperature decreases remarkably.Cooler(warmer) zones on the plate interface were identified from the modeling where there was a larger(smaller) subduction angle.Consequently,the interplate temperature distribution is partly controlled by the true subduction angle(TSA),which is a function of the slab dip angle and the obliquity of subduction.The rate of change of the interface temperature for the TSA was10-50 ℃(10°<TSA < 20°) at depths ranging from(TSA- 10) × 5 km to 60 +(TSA- 10) × 5 km for a flat slab after a subduction history of 7 Myrs.The along-arc slab curvature affects the variation in TSA.The slab radius also appeared to influence the radius of induced mantle flow.

Reactions between olivine and CO2-rich seawater at 300℃:Implications for H2 generation and CO2 sequestration on the early Earth

To understand the influence of fluid CO_2 on ultramafic rock-hosted seafloor hydrothermal systems on the early Earth,we monitored the reaction between San Carlos olivine and a CO_2-rich NaCl fluid at 300 C and 500 bars.During the experiments,the total carbonic acid concentration(∑XO_2) in the fluid decreased from approximately 65 to 9 mmol/kg.Carbonate minerals,magnesite,and subordinate amount of dolomite were formed via the water-rock interaction.The H_2 concentration in the fluid reached approximately 39 mmol/kg within 2736 h,which is relatively lower than the concentration generated by the reaction between olivine and a CO2-free NaCl solution at the same temperature.As seen in previous hydrothermal experiments using komatiite,ferrous iron incorporation into Mg-bearing carbonate minerals likely limited iron oxidation in the fluids and the resulting H_2 generation during the olivine alteration.Considering carbonate mineralogy over the temperature range of natural hydrothermal fields,H_2 generation is likely suppressed at temperatures below approximately 300℃ due to the formation of the Mg-bearing carbonates.Nevertheless,H_2 concentration in fluid at 300℃ could be still high due to the temperature dependency of magnetite stability in ultramafic systems.Moreover,the Mg-bearing carbonates may play a key role in the ocean-atmosphere system on the early Earth.Recent studies suggest that the subduction of carbonated ultramafic rocks may transport surface CO_2 species into the deep mantle.This process may have reduced the huge initial amount of CO_2 on the surface of the early Earth.Our approximate calculations demonstrate that the subduction of the Mg-bearing carbonates formed in komatiite likely played a crucial role as one of the CO_2 carriers from the surface to the deep mantle,even in hot subduction zones.

Redox history of the Three Gorges region during the Ediacaran and Early Cambrian as indicated by the Fe isotope

The Ediacaran-Cambrian transition is characterized by numerous events such as the emergence of large multi-cellular metazoans and surface environmental disturbances.Based on geological evidence,it has been proposed that this transition coincided with the increase in the atmospheric oxygen level that was key to the evolution of life.Even though ancient redox conditions can be inferred from the composition of sedimentary iron mineral species,this method is not necessarily applicable to all rocks.In the Earth system,the cycling of iron is of considerable interest owing to its sensitivity to redox conditions.Information regarding the paleo-oceanic iron cycle is revealed in the iron isotopic composition of ironbearing minerals.Unfortunately,only limited iron isotopic data exists for Ediacaran-to Cambrianperiod oceans.To circumvent this deficiency,we drilled a fossiliferous Ediacaran to Early Cambrian sedimentary succession in the Three Gorges region,South China.We analyzed the iron isotope ratios(δ^(56/54)Fe)of pyrite grains in the drill cores using laser ablation multi collector inductively coupled plasma mass spectrometry.The results demonstrate large variations inδ^(56/54)Fe,from-1.6 to 1.6‰,and positive iron isotope ratios are observed in many successions.The presence of positiveδ^(56/54)Fe in pyrite indicates that the ferrous iron in the seawater was partially oxidized,suggesting that seawater at Three Gorges was ferruginous during the Ediacaran and Early Cambrian periods.However,aggregated pyrite grains in organic carbon-rich black shales at Member 4 of the Doushantuo Formation and the base of the Shuijingtuo Formation yield near-zeroδ^(56/54)Fe values;this suggests that the ocean was transiently dominated by sulfidic conditions during these periods.Notably negativeδ^(56/54)Fe values,lower than-1‰,can be interpreted as a signature of DIR.The DIR also might contribute in part to the re-mineralization of organic matter during the largest negative carbon isotope anomaly in the Ediacaran.

Roles of thermospheric neutral wind and equatorial electrojet in pre-reversal enhancement,deduced from observations in Southeast Asia

Previous studies have proposed that both the thermospheric neutral wind and the equatorial electrojet(EEJ)near sunset play important roles in the pre-reversal enhancement(PRE)mechanism.In this study,we have used observations made in the equatorial region of Southeast Asia during March–April and September–October in 2010–2013 to investigate influences of the eastward neutral wind and the EEJ on the PRE’s strength.Our analysis employs data collected by the Gravity Field and Steady-State Ocean Circulation Explorer(GOCE)satellite to determine the zonal(east-west direction)neutral wind at an altitude of~250 km(bottomside F region)at longitudes of 90°–130°E in the dusk sector.Three ionosondes,at Chumphon(dip lat.:3.0°N)in Thailand,at Bac Lieu(dip lat.:1.7°N)in Vietnam,and at Cebu(dip lat.:3.0°N)in Philippines,provided the data we have used to derive the PRE strength.Data from two magnetometers—at Phuket(dip lat.:0.1°S)in Thailand and at Kototabang(dip lat.:10.3°S)in Indonesia—were used to estimate the EEJ strength.Our study is focused particularly on days with magnetically quiet conditions.We have found that the eastward neutral wind and the EEJ are both closely correlated with the PRE;their cross-correlation coefficients with it are,respectively,0.42 and 0.47.Their relationship with each other is weaker:the cross-correlation coefficient between the eastward neutral wind and the EEJ is just 0.26.Our findings suggest that both the eastward neutral wind and the EEJ near sunset are involved in the PRE mechanism.Based on the weak relationship between these two parameters,however,they appear to be significantly independent of each other.Thus,the wind and the EEJ are likely to be influencing the PRE magnitude independently,their effects balancing each other.

Sedimentological/Palaeogeographic Data as Fundamental Building Blocks of the DDE Project:Critical Underpinning of Reconstructing Deep-time Earth Systems

1 Introduction Sedimentary rocks archive important information for understanding how the earth system operates and how life and environments have evolved through earth history.Properly identifying characteristics of sedimentary rocks,along with the subsequent interpretation of depositional processes and sedimentary environments in a basin or locality.