Table of Content

20 June 2015, Volume 21 Issue 2

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StudyontheBitumenandCu-bearingMineralSpherulitefrom BasalticDruseinSouthSichuan

ZHANG Liangju，HU Huiyi，ZENG Weilai，LI Dongsheng，ZENG Nanshi， RUAN Qingfeng，SONG

2015, 21(2):  177. 

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Quartz,bitumem,prehniteandCu-bearingmineralswidelyoccurinamygdaloidbasalticdrusefromPugecounty,south Sichuan. According to their occurrences and relationships, three types of basaltic druse are divided: quartz-bitumen druse, rock crystal-bitumendruse,rockcrystal-prehnitedruse.Themineralassemblagesfromrockcrystal-prehnitedrusedisplaythefeatureof nodules, which outward include prismatical rock crystals, prehnite spherulites and Cu-bearing minerals spherulites. Moreover, Cu-bearingmineralsspheruliteshavethefeatureofcirclelayeredstructure,includingnativecopper(core),tenorite(mantle)and chalcostaktite-malachite(crust).Observationsinfieldandundermicroscopeshowthattheshapesandoccurrencesofnativecopper controlthepatternoftheCu-bearingmineralsaggregations.Cu-bearingmineralsspherulitesaremainlydistributedintheconvergences amongtheprehnitespherulites,andthecoreisgranularnativecopper.Cu-bearingmineralsveinsincludestretchnativecopper, tenorite,chalcostaktite,occurinthefracturesofdruses.Thecarbonisotopeandinfraredspectrumsuggestthatasphaltisofbiogenesis andoriginatedfromthecarbonaterocksinPermianstrata(P13).Themineralsinbasalticdrusescrystallizedfromtheorganicfluids,the
commonly recognized sequence is chalcedony → quartz + bitumen+ native copper → native copper + prehnite → tenorite → chalcostaktite→malachite→calcite.Thespiralgrowthpatternsofbitumen,homogenizationtemperatureofinclusionsinquartzand therelationshipsbetweenbitumenandnativecopperinrockcrystalindicatethatbitumenformedunderthethermalcrackingoforganic (crudeoil),thetemperatureis290-230℃.Nativecoppercrystallizedunder230-160℃.

SedimentaryEnvironmentandMineralizationMechanismofthe StromatoliticPhosphoriteintheEdiacaranDengyingFormation, Weng′anCountyofGuizhouProvince,China

ZHANG Wei, YANG Ruidong*, MAO Tie, REN Haili, GAO Junbo, CHEN Jiyan

2015, 21(2):  186.  DOI: 10.16108/j.issn1006-7493.2

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 Stromatolitic phosphorite in the Ediacaran Dengying Formation was initially discovered in Weng′an-Fuquan area of SouthwesternGuizhouProvince,Chinawherephosphateoresarewidelydistributed.Asanewphosphorousstratumofphosphorite,itis characterizeddominantlybytypicalstromatoliticstructures.ThephosphoriteofstromatoliteislocatedatthetopoftheEdiacaran DengyingFormationthatiscomposedoflenticularorganicreef(algalreefofstromatolite).Themajormineralcomponentsofthe stromatoliticphosphoritearephosphatesandcarbonates.Thewhitelaminatedbedsareenrichedinphosphatemineralswhilethedark laminatedbedshavelowercontentsofphosphatemineralsandcontainmainlycarbonateminerals.Analysisofthemineralogicaland geochemicalcharacteristicsindicatesthatstromatoliticphosphoriteintheEdiacaranDengyingFormationisalgalreefofstromatolite thatwasformedinasemi-restrictedsubtidalenvironment.Accordingly,itcouldbeinferredthatthephosphoriccolumnarstromatolitic reefswereformedbyenrichmentinandprecipitationofphosphorusfromtheseawaterwithrichphosphorusduetocomplexbiological orbio-chemicalactionsofalgae.Inaddition,theresultsshowthatthemineralizationofphosphaticmineralsoccurredmainlyatthe sediment-waterinterfaceinweaklyalkalineandsuboxicenvironmentwherealgaehadplayedasignificantrole.

TheForaminiferalFaunaoftheTaiyuanFormationandthe Carboniferous-PermianBoundaryinZibo,ShandongProvince

LI Shoujun, YUAN Liyuan, YIN Tiantao, ZHAO Xiuli, CUI Xiaohui

2015, 21(2):  196.  DOI: 10.16108/j.issn1006-7493.2

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 ThroughthesystematicstudyoftheforaminiferalfaunaoftheTaiyuanFormationinZibo,ShandongProvince,wehave identified11genera,22species,andsomeundeterminedspeciesofsmallforaminiferalfossils.Basedonthespatialdistributionand stratigraphicvariationintheforaminiferalfauna,twosmallforaminiferalassemblagesareestablishedfromthebottomtothetop,i.e., Bradyina-Plectogyra assemblage and Tetrataxis-Nodosaria-Palaeotextularia assemblage. By comparing our fossil data with the foraminiferalfaunainthenearbyregionsandotherareasinCentralChinaandNorthChina,andcombiningthepreviousresultsof fusulinid fossils, we have estimated the geological ages of the two fossil zones. The geological age of the Bradyina-Plectogyra assemblageshouldbeLateCarboniferous,andthegeologicalageoftheTetrataxis-Nodosaria-Palaeotextulariaassemblageshouldbe EarlyPermian.SotheCarboniferous-PermianboundaryinShandongProvinceliesatthebottomofPseudoschwagerinazone.

Study on the Origin of Molar-tooth Structure-bearing Carbonates in the Lower Neoproterozoic in Xuzhou Area

FENG Le, LI Zhuangfu, LU Lu, DOU Luxin, SHI Qingmin, ZHOU Yanzhao

2015, 21(2):  203.  DOI: 10.16108/j.issn1006-7493.

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Molar-tooth structures (MTS) and storm deposits were widely developed in the carbonate sedimentary system of shelf-ramp-platform margin from the Jiayuan Formation to the Zhaowei Formation of Neoproterozoic in Xuzhou area. Based on field observations of outcrops and indoor comprehensive analysis, MTS were divided into autochthonous MTS containing banded M1 (straight banded M1-a; branched banded M1-b), worm-like M2 (short wormlike M2-a; long wormlike M2-b), filiform M3, suspension needle-like M4, and allochthonous MTS containing clastic M5. The five types mainly occur in the area from the lower area of gentle ramp to the tidal flat. Based on the background of seven typical storm sequences of different water depths and hydrodynamic conditions, correlation analysis was performed between morphology, distribution of the MTS, and the instantaneous high-energy event deposits. The analysis shows that close correlation was found between MTS and the storm events, indicating that M3 is mainly present in the massive layers in fine weather. The M1 and M2 were mainly formed in turbulent environment during fluctuating period with frequent earthquakes and storms. While the M4 and M5 are the principal types in the layers formed during the storm upsurge period, the strength of the storm andthe water depth control the scale of the storm sequence, and further control the morphology and distribution of the MTS. Therefore, during the different stages of the storm cycle, the form of MTS includes two interrelated processes: crack formation and microspar filling under the special marine and atmospheric paleoenvironment during the Middle-late Proterozoic. During the early period and the climax period of a storm, the storm wave has influenced mainly on the crack opening stage of the MTS formation; while the storm waves mainly influence the filling stage during the later period. Finally, Molar-tooth structure-bearing carbonate, a special type of an event carbonate in the geological history, was formed and widely distributed.

Cenozoic Fault System and Tectonic Evolution of the Eastern Liaodong Bay Depression

XU Changgui, REN Jian*, WU Zhiping, LI Wei, ZHANG Jing, ZHANG Xiaoqing

2015, 21(2):  215.  DOI: 10.16108/j.issn1006-7493.

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Development characteristics of a fault system are an important manifestation of the structural evolution of the eastern Liaodong Bay Depression in the Cenozoic period. Based on plenty of three dimensional seismic data, this paper describes the horizontal decreased and sectional characteristics of fault systems in detail in the study area and analyzes the formation mechanism of the fault systems. The result shows that the fault systems in the Paleocene and the Eocene mainly consist of NNE trending extensional faults. And the fault systems in the Oligocene have the strike-slip characteristics. The vicinity of main faults has significantly stress-increased area and stress-decreased area due to the strike-slip effect. The flower-liking structures and“Y”-type structures can be observed in the seismic profiles. The secondary faults mostly consist of NEE trending en-echelon faults. The main faults and the secondary faults can form strike-slip duplex. In Neogene, the secondary faults are still manifested as NEE trending en-echelon faults and the fault system shows characteristics of weak strik-slip. And conjugate shear fractures and antiform-negative flower structures began to appear in this period. The study of the fault system illustrates the superimposition and transformation between extension tectonic systems and strike-slip tectonic systems in the eastern Liaodong Bay Depression in the Cenozoic. Combined with dynamic evolutionary mechanism of the Bohai Bay Basin, the evolutionary stages of the eastern Liaodong Bay Depression can be divided into the weak strike-slip-strong extension period (Paleocene-Eocene） , the weak extension-strong strike-slip period (Oligocene), and the weak compression-weak strike-slip period (Neogene).

Effect of Diabase Crevices on AMS Fabrics

SHI Linquan, SHEN Zhongyue*, PAN Xiaoqing, LI Mingyue, ZHANG Zhiliang

2015, 21(2):  223.  DOI: 10.16108/j.issn1006-7493.

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As a rapid and sensitive petrofabric tool, the anisotropy of magnetic susceptibility (AMS) has been extensively used in studying rock fabrics. Sometimes it is difficult to drill an intact oriented core sample without any crevice, in which various filling minerals can be found. To analyze the crevices’ effect on diabase magnetic fabrics, 160 diabase samples with crevices are selected to study the AMS data then remove the filling minerals in the crevices in order to compare magnetic fabric characteristics of the diabase before and after the treatment. The data analysis shows that the average difference in the AMS intensity of all the specimens is less than 1% and the difference in the average direction also falls in <1°. From the results, we conclude that crevices of diabase dykes hardly have much influence on the AMS features. Mineralogy and rock magnetic studies indicate that the main mineral constituents in the diabase crevices are quartz, feldspar, hematite, pyrite, and chlorite. The AMS intensity of these filling minerals is about one thirtieth of diabase that is dominanted by ferromagnetic mineral of magnetite, which makes crevices to have no much effect on the AMS results.

A Study of Groundwater Flow and Water Quality Characteristics in the Riparian Zone of Jialu River near Zhongmu

ZHENG Yuhu, ZHANG Youkuan*, LIANG Xiuyu

2015, 21(2):  234.  DOI: 10.16108/j.issn1006-7493.

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In this study, field geological investigations, hydrogeological tests, water level monitoring, and water quality analyses were conducted to investigate the recharge and discharge between the seriously polluted Jialu River and the nearby groundwater in Henan province. The results indicate that the river stage was higher than the groundwater level because of nearby groundwater pumping, causing the river to recharge groundwater with an average water flux per unit width of 2.04 m2·d-1. The NH3 and COD pollution in the river was serious and the concentrations of NH3-N, NO2-N, and NO3-N in groundwater were all higher than the standards. The NO2 and NH3 pollution was especially serious; the NH3-N concentration in the river was much higher than that in groundwater and the NH3 pollution in groundwater near the river was more serious as a result of the river recharge, but was gradually reduced away from the river due to nitrification and adsorption. The NO3-N concentration in the river was lower than that in the groundwater and the NO3-N concentration in the groundwater gradually increases away from the river due to nitrification and infiltration of the nitrogen fertilizer applied at the land-surface.

Characterization of Land Subsidence During Recovery of Groundwater Levels in Shanghai

LUO Yue, YE Shujun*, WU Jichun, JIAO Xun, WANG Hanmei

2015, 21(2):  243.  DOI: 10.16108/j.issn1006-7493.

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Previous research was focused mainly on land subsidence during decline of groundwater levels. However, there have been few studies for land subsidence during the recovery of groundwater levels. This paper analyzes the deformation of each individual aquifer or aquitard after 1998, when groundwater levels in aquifers continued to rise due to reduced pumpage and increased artificial recharge. From 1998 to 2012, the average groundwater level in the second, third, fourth and fifth confined aquifers rose on average by 2.1 m, 3.6 m, 12.4 m and 12.7 m, respectively. Because of the recovery of groundwater levels in Shanghai, the land subsidence rate gradually decreased from 12.2 mm/a in 1998 to 1.83 mm/a in 2011. And the strata below the second confined aquifer even became uplifted after 2009. Land subsidence was primarily contributed by compaction of the first soft layer with a compaction rate of 2-4 mm/a in recent years. During the recovery of groundwater level, two kinds of deformation characteristics were recognized. One is thatdeformation basically instantaneously responds to groundwater level change in the confined aquifer, and residual deformation is small. This type of deformation occurs in the first, second, third and fifth confined aquifer and the fifth and sixth aquitard. The second type is that deformation is delayed and residual deformation is obvious, but the deformation rate decreases gradually. This type of deformation occurs in the second, third and fourth aquitard. Deformation of the fourth confined aquifer is complex and includes both kinds of deformation characteristics. The large residual deformation resulted from the fact that non-recoverable skeletal specific storage is greater than the less-recoverable skeletal specific storage. The delayed deformation resulted from the delayed response of water level within aquitard to the change in the adjacent aquifers.

Relationship Between the Xiejiabao Anticline and Landslides in the Three Gorges Reservoir Area

WANG Kongwei, ZHAO Xiaoming, ZHANG Fan

2015, 21(2):  255.  DOI: 10.16108/j.issn1006-7493.

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Geological disasters occur frequently in the Three Gorges reservoir area, but there is little research on causal relationships between landslides and structural characteristics. In particular, a number of landslides occurred in the same local structure, but their relationship has rarely been studied. Based on the related theory and the engineering geologic research, this study is focused on the Xiejiabao anticline and examining the relationship between local structures and landslide types. Hanging wall morphology controls the distribution of landslides in Chang Jiang river area and Qing Ganhe area. This makes landslide group size to decrease gradually from the west to the east. Landslide group size in the Chang Jiang river area is larger than that in the Qing Ganhe area. This is closely related to the changing dip angles of limbs of a fault-propagation fold, i.e., the dip angle in the south of Qing Ganhe is greater than that in the north of Chang Jiang River. This study shows that the large-scale landslides are related to local structure types and local river cutting structures, which control not only the evolution of landslides on the whole bonk slope, but also the evolutien of an individual landslide.

Grain-size Analysis of the Loess in China Using the Grain-size Distribution Equation

YANG Qing

2015, 21(2):  268.  DOI: 10.16108/j.issn1006-7493.

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Grain-size distribution curve is one of the most common soil properties. It can help to reduce a large amount of engineering cost if the soil grain-size distribution could be predicted using mathematical equations. Fredlund grain-size distribution equation based on Fredlund and Xing soil-water characteristic curve has proved to be effective for a large number of soil types, while few literatures have been found to verify its effectiveness for loess soils in China. This paper targets on the grain-size distribution of loess soils in 7 regions in the Chinese Loess Plateau, which were fitted with the Fredlund grain-size distribution equation. The results show that Fredlund grain-size distribution equation fits well the grain-size distribution of loess soils in China, with the stable and regularly changing parameters, which presents well the regional characteristics of loess soils in China. The parameters obtained in this paper can be used to predict grain-size distribution of loess soils in these 7 different regions, the results could also provide guidance for grain-size analysis and classification of loess soils.

Variations of Gas Content in Deep Coalbeds of Different Coal Ranks

CHEN Gang, QIN Yong, HU Zongquan, LI Wuzhong, SHEN Jian

2015, 21(2):  274.  DOI: 10.16108/j.issn1006-7493.

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Based on Langmuir isothermal adsorption equation, we carried out isothermal adsorption simulation experiments under high temperatures and high pressures for different coal ranks. The results show that when vitrinite reflectance Ro less than 3.0%, the curves of Langmuir isothermal equation appear in a zone with the rising coal rank, temperature, and pressure. The adsorption capacity is enhanced with the rising coal ranks. The Langmuir volume of different coal ranks was less affected when the temperature was lower than 55℃, while more for temperatures above 55℃. The Langmuir volume increased obviously with the rising pressures when the low rank coal under 12 MPa and mid-high rank coal below 15 MPa. We established a mathematical model for determining gas content of deep coalbed based on the measured gas content extrapolation method and the high temperature and high pressure isothermal adsorption experiments. The modeled gas content shows variable outcomes, i.e., fast increase, slow increase, no increase, and slow decrease with the buried depth. The critical depth of low rank coal is located between 1400 m to 1700 m while the mid-high rank coal is located between 1500 m and 1800 m. The mathematical model of gas content provides a basis for forecasting gas content and evaluating deep coalbed methane resources.

Distribution and Modes of Occurrence of Mercury in Coal Seams Altered by Magmatic Hydrothermal from Wolonghu Coal Mine

HUANG Xiaoyu, ZHENG Liugen*, ZHANG Qiangwei, CHU Hao,

2015, 21(2):  280.  DOI: 10.16108/j.issn1006-7493.

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Coal and rock samples from magmatic intrusion area of Wolonghu Coal Mine, Huaibei Coalfield, were systematically collected to determine contents of mercury, ash, volatile matter, and moisture and spectated sulfur, as well as to investigate the distribution and modes of occurrence of mercury in intruded coal seams. The results show that (1) the magma intrusion into coal seams resulted in the increase in ash content and the decrease in volatile matter. The main form of sulfur was pyrite sulfur (42.08% ) and inorganic sulfur (52.51%) in coal; (2) mercury in the intruded coal seams was as high as 0.23×10-6, which was 1.4, 1.2 and 1.3 times of that in the Carboniferous-Permian coals from North China, China and the USA; (3) the contents of mercury decreased with the increase in the distances between coal seams and intrusion body, and the distribution of mercury was different for the upper and lower coal seams in contact with the intrusion body; (4) mercury in the coal was mainly in inorganic form, primarily pyrite. Meanwhile, mercury bound with organic sulfur also exists. Magmatic hydrothermalism is identified as the causes accounting for the enrichment and change of forms of mercury, and the variations of coal quality.

Sedimentary Characteristics of Braided Alluvial Fan in North Tianshan Mountain and Its Significance for Oil-gas Exploration of Ancient Alluvial Fans in Northwest Junggar Basin

YU Kuanhong，JIN Zhenkui，LI Guizai，HE Miao，GUO Xiujuan，YANG Ting

2015, 21(2):  288.  DOI: 10.16108/j.issn1006-7493.

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This study was based on field study on Baiyanghe and Manas alluvial fans in North Tianshan Mountain. Braided belt is the main sedimentary area on the surface of arid braided alluvial fan. Sediments were unloaded in low potential area and sedimentary area laterally migrated along with the low potential area migrated. Braided channels show as string on the surface of alluvial fan and distributed in a wider area in the margin of fan. Gravel sediments in the braided belt have good porosity and permeability. Sedimentary characteristics and scale of alluvial fans are controlled by tectonic activities, climatic conditions, provenance supplies and river system. Braided alluvial fans are main ancient alluvial fans types in the northwest Junggar Basin and they occurred in the basin margin, showing more sedimentary characteristics of braided river.

The Genesis of Gypsum Zone in the Upper Part of the Fourth Member of Shahejie Formation in Bonan Sag.

MENG Yuzhang, LIU Peng*, WANG Ling, SUN Tingbin

2015, 21(2):  300.  DOI: 10.16108/j.issn1006-7493.

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In order to understand the genesis of gypsum zone in the upper Upper part of the fourth member of Shahejie Formation in Bonan sag, comprehensive analyses of drilling data, testing data, the developmental features, and genetic types of gypsium zone were performed. The results show that the gypsum zone is mainly composed of gypsum mudstones and gypsum rocks, and the gypsum rocks mainly occur in the depth range between 2800 m and 3600 m, and as two EW-trending wide belts. The climate was humid and lake was deep during the depositional period of gypsum zone. The distribution of igneous rocks and the gypsum zone appears to be coupled and we speculate that salts substances came from deep thermal brine. The gypsium zone belongs to the type that salt was deposited in a deep water environment. The results may help understand genesis of gypsium zones in other regions.

Advances in the Study of Fractured Reservoir Characterization and Modeling

DENG Xili, LI Jiahong, LIU Li, REN Kangxu

2015, 21(2):  306.  DOI: 10.16108/j.issn1006-7493.

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This paper introduces several main methods of fractured reservoir characterization and modeling, and summarizes their essential advantages and disadvantages. The main methods for fracture characterization include field study, core and well logging, seismic prediction, dynamic response analysis, mechanical analysis, and rock mechanical analysis. And fracture modeling is conducted mainly with by DFN (discrete fracture network) and equivalent continuum modeling. This paper reviews the application of fractal theory to outcrop fracture analysis of volcanic rocks, the application of digital core technique to micro fracture characterization, several most recent geophysical and mechanical fracture characterization and prediction methods, the impact of dynamic fracture on reservoir development, fracture stratigraphy theory proposed abroad lately, fracture characterization in unconventional reservoir, and finally the above two fractured reservoir modeling methods. On the basis of all above, challenges for fracture characterization and modeling and future research in this field are pointed out.

The Ultr-water Lake of Middle Sha-3 Formation during Paleogene in Dongying Sag, NE China

ZHONGJianhua, LI Yong, SHAO Zhufu, CHENBin, NI Liangtian, XIAO Shuming

2015, 21(2):  320.  DOI: 10.16108/j.issn1006-7493.

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Based on seismic profile and well-tie profile, the paper discusses the paleo-water depth of the lake through the study of the delta sedimentation during the Paleogene middle Es3 period in Dongying Depression, NE China, by means of combining core and well logging data and restoring the height of delta foresets. Results show that constructive deltas develop well, and the delta foresets develop extremely well especially in Niuzhuang sag. The statistical results of five seismic profiles reveal the average height of delta foresets is 485 m and the inversion overlying water depth after correction is 681 m. Therefore, the lake ′ s paleo water depth in Dongying delta can reach up to 485-681 m at the middle Es3 period. The delta foreset is mainly a set of fine-grain sediments, grey siltstone and dark mudstone as the major. The siltstone often contains floating boulder clay. These features reveal that it is a kind of sandy debris flow and turbidity deposition along the delta front slope, further reflecting a deep-water sedimentary environment

Gravel Fabric Characteristics of the Lower Cretaceous Nanxin Formationin the Nanjian Region, Yunnan Province and the Provenance Significance

ZHANGJie，XIAO Yuanfu*，TIAN Xiaomin，JI Xiangtian，PENGBo，LI Hongxiao，WANGLiaguo

2015, 21(2):  328.  DOI: 10.16108/j.issn1006-7493.

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Based on the detailed study of gravel fabric characteristics of conglomerate layers from the Lower Cretaceous Nanxin Formation in the Nanjian region, combined with the characteristics of the basin bedrock stratigraphy and lithologic characteristics of the surrounding tectonic belt, the gravel has complex composition, poor sorting, medium-good roundness and poor degree of weathering. This paper further discussed the property of the conglomerate layer, the material sources and the hydrodynamic conditions, climate, topography and tectonic setting. Our data shows that of Nanxin Formation were the coarse clastic products of alluvial fan and braided river facies in a semiarid to braided climate condition with rapid accumulation; The gravel pebbles suffered a strong physical and chemical weathering before deposition; The sediment source of the gravel was inferred to come mainly from the basal strata within the basin and the Ailaoshan tectonic belt to its eastern direction.

Seismic Sedimentology of the Palaeogene Dainan Formation in the Deep Sag Zone of Gaoyou Depression, Jiangsu Province

ZHAO Dongna, ZHU Xiaomin, LIANG Bing, MA Yingjun, BO Yongde, WU Dong

2015, 21(2):  336.  DOI: 10.16108/j.issn1006-7493.

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Seismic sedimentology is a newly emerged interdisciplinary subject, which uses seismic data to gain insights into the rocks and their forming processes. It is regarded as an effective tool for mapping high-frequency sequence and depositional systems, and plays an important role in the exploration and production of thin sandstone reservoirs. Because of the scarcity of well data in the deep sag zone, the distribution and the scale of the sandstone reservoir in the deep sag zone are very difficult to determine by using the conventional exploration method. Guided by the third-order sequence-stratigraphic correlations from seismic and wire-line log data, in this study, stratum slices were prepared from a three-dimensional seismic volume to reveal sand-body distribution in the deep sag zone and to map the associated depositional systems distributions in slopes of the depression. With the assistance of the comprehensive analysis of core, lithology and well-logging data, the slump turbidite sandstone reservoirs of different sequences in the deep sag zone were effectively predicted.

Comparison and Subdivision of Loess Strata in the Chinese Loess Plateau

WANG Yang，SUN Hongyan，TIAN Mingzhong

2015, 21(2):  346.  DOI: 10.16108/j.issn1006-7493.

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Based on the comprehensive analyses of the previous research on the loess stratigraphic classification in the Chinese Loess Plateau, and results from the three type loess/paleosol profiles, i.e., Luochuan, Baoji, and Xifeng, this article conducted detailed comparison and further subdivision of the loess strata in the Chinese Loess Plateau by using soil stratigraghy, sedimentology, magnetostratigraghy, paletontology, chronology, and geochemistry. This article adjusted the boundary of the Early Pleistocene and the Middle Pleistocene to the top of L9, which corresponds to the start time of the B/M polarity boundary, divided the Lishi Loess into three parts according to the difference in lithology and climate cycle periods, and added S8/L9 as a new boundary. As a result, S1-L5 are in the upper Lishi Loess, S5-S8 are in the middle Lishi Loess, and L9-L15 are in the lower Lishi Loess. A new problem arises that the ages of some key horizons such as the S0, L1, S1, S5, L9, L15 and L33 are different among these profiles.

Experimental Study on the Effect of Environmental Factors on the Carbon Stable Isotope Composition of the Snail Achatina fulica Shell carbonate

ZHU Lili, BAO Rui, SHENG Xuefen*

2015, 21(2):  357.  DOI: 10.16108/j.issn1006-7493.

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The stable isotope composition of land snail shell fossil is correlated with the paleo-environmental information, and therefore could be used to reconstruct the palaeo-environment. However, the debate continues on the mechanism how paleo-environment factors affect the stable isotope composition of snail shell carbonate. Recent studies focus more on the δ13C value of the modern land snail shell carbonate which could be applied to indicate the environmental and climatic information. The laboratory cultured experiment can isolate the contribution of each particular environmental factor to the δ13C value of the snail shell carbonate. In this study, the cultured experiments on the snail Achatina fulica were carried out to investigate the carbon isotope fractionation between snail shell carbonate and their diets，The results show that under constant temperature and humidity there are stable fractionation offsets among the shell carbonates when the snails were fed by the same diet. The different types of diets caused the correspondingly different carbon isotope fractionation: the average fractionation offsets between the shell carbonate and the diets of the lettuce, the corn and the forage are 16.70‰±0.2‰, 10.57‰±0.2‰, 10.65‰±0.2‰, respectively. The experiment also confirms that the incubators temperature ranging from 20 to 30oC does not affect thefractionation offset of 13C between the snail shell and its diet. An empirical equation between the δ13C values from the shell carbonate ofAchatina fulica and the diets can be described as δ13Cs=0.6665δ13Cv+6.2302 (n=26). The inorganic carbonate has negligible effect on the δ13C value of snail shell. According to the result of the end-member analysis, we concluded that the diet contributes dominantly to the carbon stable isotope composition of the shell carbonate of snail Achatina fulica with the contribution being about 80％±5％, and the another one, i.e, from the atmospheric CO2 , being 20％±5％.