1998 Vol. 4, No. 4

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ON TECTONOCLIMATIC CYCLE OF QUASI PERIOD OF 1.2Ma IN LATE CENOZOIC
WU Xihao, WANG Sumin, AN Zhisheng, JIANG Fuchu, XIAO Huaguo, SUN Donghuai, XUE Bin
1998, 4(4): 1-11.
Abstract (168) PDF (463KB)(14)
Abstract:
The tectonoclimatic cycle which states that the climate is determined by tectonic movement is different from Milankovich's glacioclimatic cycle.However,both of them are controlled by the Earth's orbit.On the basis of the late Cenozoic geological records in the Qinghai-Xizang (Tibet) Plateau and the Loess Plateau,with the magnetostratigraphy as timescale and the maximal amplitude position of ecliptic tilt (ε) as model age,the major cyclothems of tectonoclimatic cycle with a quasiperiod of 1.2Ma in the last 8Ma are divided as MTC7、MTC6、MTC5、MTC4、MTC3、MTC2、MTC1、MTC0,whose horizon lines in the red clay loess sequence and boundary ages in the ε curve are RCL4/Br 7.3Ma,RCL3/RCS4 6.1Ma,RCL2/RCS3 4.9Ma,RCL1/RCS2 3.7Ma,WL3/RCS1 2.5Ma,L15/WS1 1.3Ma and L2/S2 0.2Ma B P,respectively.And an analysis of the evolution of the eolian deposits of Loess Plateau in periods of about 1.2Ma and the tectonic uplift of Qinghai-Xizang Plateau shows that there existsa causality between them that the climate depends on the uplifting.
The uplift model of the Qinghai-Xizang Plateau constructed by the related information indicates that it has undergone different tectonic stages.First,the pre plateau stage,in which no integrated Qinghai-Xizang block had been formed,existed before 7.3Ma B P in the late Miocene.Second,the stage of isostatic adjustment of the newly- formed inner plateau block ensued during a time from 7.3 to 2.5 Ma B P,in which the uplift of the West Kunlun Mts.has began since 3.7Ma B P.Third,the stage of forming plateau surface followed from 2.5 to 1.3Ma B P,in which the Qilian-Qaidam block coalseced with the major part of the plateau,to form an initial Qinghai-Xizang Plateau similar to its present cnfiguration,and the aggradational plateau surface reached a mean altitude of 2400m.An en bloc uplifting stage has commenced since 1.3Ma B P in which the plateau surface has uplifted from a mean altitude of ca.2400m,successively to ca.2900m(0.9Ma B P),ca.3600m(0.6Ma B P),ca.4200m(0.13Ma B P),ca.4560m(0.09 Ma B P) and today's mean altitude of ca.4800m.
It is evident that the differences of climatic and environmental effects on the eastern China monsoon area,including the Loess Plateau,have been produced around the time of formation and uplift of the Qinghai-Xizang Plateau,in which the change of seasonality resulting from the stage-strengthening winter monsoon is most important.At first the winter monsoon was not conspicuous for a time span of 7.3-3.7Ma B P and strengthened somewhat after 3.7Ma B P.Afterwards,the East Asian monsoon being typical of a much stronger winter monsoon than summer monsoon have been formed.Then,in the process of winter monsoon strengthening,it abruptly changed before 2.5Ma B P,transformed before 1.3Ma B P and altered progressively before 0.2Ma B P,in which the different features of strong-weak associations of the winter and summer monsoon have been shown in every variation,enhanced seasonality step by step and resulted in the differentiation of ecological environment between south ant north,east and west.
ON MANGSHAN LOESS STRATIGRAPHY IN CHINA CENTRAL PLAINS
JIANG Fuchu, WU Xihao, SUN Donghuai, XIAO Huaguo, WANG Sumin, AN Zhisheng, TIAN Guoqiang, LIU Ke, YIN Weide, XUE Bin
1998, 4(4): 12-18.
Abstract (188) PDF (333KB)(9)
Abstract:
The Zhaoxiayu loess section in Mangshan Yuan which is located at the transitional zone between the North China Plains and the Loess Plateau is typical of the loess stratigraphy in China Central Plains.The section is exposed from the top of Mangshan Yuan to the valley bottom of the Huanghe River,the loess-paleosol sequence from S0 to S10,with a total thickness of 172.1 m.It is known from the results of optically stimulated luminescene dating and thermoluminescene dating and the magnetostratigraphy that,the B/M boundary was recorded at the top of S8.The sequence is characterized by a relatively thick paleoso S1 (15.7m) and a thick loess L1 (77.3m) of the Late Pleistocene.
Mangshan loess is a kind of near-source sandy dust deposit with the source area lying just at the head of an alluvial fan at the lower reaches of Huanghe River.There is great difference in the average rate of sedimentation of loess in different glaciations or stades and of paleosol in different interglaciations or interstades in Zhaoxiayu loess profile.The sedimentation rate of loess L1LL1,paleosol L1SS 1,and loess L1LL2 in the Last Glaciation is as high as 3.45 mm/a,0.38 mm/a,1.51mm/a,respectively,and that of paleosol S1 of the Last Interglaciation is 0.28mm/a,a rate not only higher than that of paleosol S2(0.05 mm/a),but also higher than that of loess L2 (0.18 mm/a).It has been shown that an abrupt change of the dust sedimentation rate happened in the end of penultimate glaciation,about 150 ka B P (equivalent to the top of L2).The reason for this may be that the Huanghe River might have cut through the Sanmenxia Gorge to flow eastwards transporting abundant materials to the source area since that time.
The magnetic susceptibility of loess and paleosol is related to the strength of pedogenisis,and can be served as a proxy index for variations of summer monsoon.Magnetic susceptibility values of loess in Zhaoxiayu section,30×10-5 SI or so,approximates to the background values of dust deposit that has undergone no little or no pedogenisis.And that of paleosol,70-170×10-5 SI,and that of immature paleosol,50-60×10-5 SI,can not be considered as a simple reflection of the strength of summer monsoon in interglaciation or interstades.They should also be affected by sedimentation rate.
PRELIMINARY STUDY OF OSL DATING OF THE MALAN LOESS AT MANGSHAN PLATEAU, ZHENGZHOU,HENAN PROVINCE
ZHAO Hua, JIANG Fuchu, LU Yanchou
1998, 4(4): 19-29.
Abstract (191) PDF (496KB)(10)
Abstract:
Twenty-four loess samples collected from the Malan loess of a thickness of 87m,at Zhaoxiayu section (34° 58'N and 113° 22'E) in Mangshan hill,Henan province,have been dated for the fine grains using IRSL,with a wavelength of 340-480nm,and GLSL,with a wavelength of 340±25nm,in an automated Daybreak 1100 TL/OSL system with background counting rate of 70-80 photons per second,and stimulated by an infrared beam (880±80nm,18mW) and a green beam (514±14nm,15-16mW) respectively.The regenerated luminescence method was employed for equivalent dose (De) determination of each sample.Environmental dose rate of the sample was calulated from the uranium,thorium and potassium analysis by using the compilation of Aitken (1985),taking into account the water content and cosmic ray contribution.On the basis of the OSL dating results of these samples,the following preliminary conclusions can be drawn.1.Comparison of De values and dates obtained from IRSL analysis with those from GLSL measurement for eight samples shows that they are in agreement within 1-2σ,except one sample.So it may provide a possible cross checking technique for reliability of sediment OSL dating.2.The deposition rate varies significantly from 0.4 m/ka to 5.6 m/ka with different horizons of the sediments and is approximately coincident with the variations of the magnetic susceptbility of the section.There are at least four rapidly depositing layers (deposition rate>3m/ka) with lower susceptibility and three slowly depositing layers (deposition rate <0.5 m/ka) with a higher or remarkably different susceptibility.There are a series of transition layers between.3.The Malan loess can be divided into three units at Zhaoxiayu section,the Upper unit at a depth of 2.7m to 27.5m,the Middle unit composed of paleosol and loess alternations at a depth from 27.5m to 57.9m and the Lower unit at a depth of 57.9m to 87.9m their age heing estimated as 10 8-36.2ka B P,36.2-70.3 ka B P and 70.3-80.2 ka B P respectively.A detalled time-scale of loess-paleosol sequence of the Malan loess is discussed.
VEGETATION AND ENVIRONMENT DURING THE LATE PLEISTOCENE IN LOESS PLATEAU,CHINA
SUN Jianzhong, KE Manhong, WEI Mingjian, ZHAO Jingbo, LI Bingcheng
1998, 4(4): 30-41.
Abstract (233) PDF (453KB)(8)
Abstract:
We have worked out quite a few pollens and spores from the commonly spore pollen poor loess,and first plotted some concentration pollen-spore diagrams of the loess strata.The evolution of vegetation and the corresponding climate in time and space in the region has been brought to light by an analysis of the variation of pollen-spore assemblages in many seetions.There are three interstadials,warmmer than present and two cooler stadials in the Last Interglaciation.They are correlated with the substages 5a,5b,5c,5d and 5e of the deep sea oxygen isotopic curves.The climate in the stadials was severely cold,with a mean annual temperature 14℃ lower than the present.The climate in the interstadials was relatively warmer,with a mean annual temperature 3-9℃ lower than the present.The temperature in the stadials of the Last Interglaciation was the same as that in the interstadials.The temperature in the interstadials was 1-3℃ higher than the present.It is know by comparing the pollen-spore cliagrams from ten sections in the Loess plateau,that,the change of vegetation in time is very similar,This implies that they were controlled by the same global climatic change.But the vegetation may vary from place to place due to change of local natural environment.The paleotemperature curve is reconstructed from the variation of vegetation during the Late Pleistocene.
A PRELIMINARY STUDY ON THE RELATION BETWEEN VOLUMETRIC WEIGHT OF LOESS AND PALEOSOL AND MONSOON CLIMATE CHANGE
XIAO Huaguo, WU Xihao, JIANG Fuchu, TIAN Guoqiang, LIU Ke, YIN Weide
1998, 4(4): 42-45.
Abstract (216) PDF (190KB)(8)
Abstract:
Taking Zhaoxiayu section,Mangshan,Zhengzhou as an example,this paper has studied the volumetric weight of loess-palaeosol sequences and its relation with susceptibility as well as its grain size.It is shown that volumetric weight bears an evident positive correlation to the summer monsoon variations indicated by the susceptibility,an evident inverse correlation to the winter monsoon variations indicated by the content of coarse fraction,and the natural compaction contributes very little to volumetric weight of loess-palaeosol sequences above S10.Volumetric weight can thus be regarded as an indicator to the variations of the combination of winter monsoon and summer monsoon.
CLIMATIC INSTABILITY CHARACTERISTIC IN LOESS PLATEAU DURING THE LAST INTERGLACIAL AGE
LI Zhenghua, YE Hao, CHEN Yun, WANG Yuhai, ZHANG Junpai
1998, 4(4): 46-49,75.
Abstract (99) PDF (238KB)(5)
Abstract:
Ice Core information of EEC Greenland Ice Plan(GRIP) has revealed the rapid climatic change during the last interglacial age. However, no evidence of this change was found in the United States Greenland Icecap Plan (GISP2).The study of substitutive paleo climatic index from several sections in Loess Plateau suggests the existence of large climatic fluctuations during last interglacial age, especially in its early stage, which agrees with the result of GRIP. It is shown that the loess in China which contains climatic information characteristic of the polar area and the northern Atlantic provides the ideal record for global change analysis.
PALAEOMAGNETIC RECORDS FROM SHUINAN CAVE SEDIMENTS, GUILIN AND ITS BEARING ON PALAEOCLIMATIC CHANGES
LI Bin, FRANK Hauge, REIDAR Lovlie, STEIN-Erik Lauritzen, YUAN Daoxiao, LIN Yushi, ZHANG Meiliang
1998, 4(4): 50-57.
Abstract (205) PDF (346KB)(5)
Abstract:
A detailed palaeomagnetic study of a 2.5m thick section of cave sediment has been made in order to retrieve a record of palaeoenvironmental change in Guilin area. The palaeomagnetic results and geological evidence show that the sediments might have been deposited during the Jaramillo Polarity subchron, i.e. from 0.97 Ma to 0.90 Ma. Based on the susceptibility, the magnetic minerals(S ratios, SIRM etcs.), and sediments characteristics), and a correlation with the loess records in north China, a conceptual model of the palaeoclimatic changes in Guilin area in proposed as follows:1. a warm and wet period (since 0.90 Ma) characterised by travertine deposit; 2. a dry and cold period(0.92 to 0.90 Ma) characterised by yellowish-brown clay with less calcareous content, high coercivity minerals and low susceptibility; 3. a warm and period (0.94 to 0.92Ma) characterised by the interbedded redish-brown clay, calcareous material and travertine, low coercivity minerals and high susceptibility; 4. a dry and cold period (0.96 to 0.94Ma) characterised by greyish-brown clay with less calcareous material, high coercivity minerals and low susceptibility; and 5. a warm and wet period(>0.96 Ma) characterised by the sandy gravel (underground river facies).
SPORE-POLLEN RECORDS AND TENTATIVE PALEOCLIMATE RECONSTRUCTION IN TAIBAI MOUNTAIN IN THE LAST 1000 YEARS
TONG Guobang, WU Xihao, TONG Lin, XIA Huaguo
1998, 4(4): 58-63.
Abstract (272) PDF (263KB)(6)
Abstract:
The spore pollen records and time sequence of the paleoclimate parameters at Foyechi Pond of Taibai Mountain reveal the character of Little Ice Age and Medieval Warm Period.Little Ice Age spans from 1420 AD to 1920 AD.The annual mean temperature in January and July during this period has shown considerable inconsistency of the changes of winter monsoon and summer monsoon in this area.At the beginning of Little Ice Age,there was a strengthening of the winter monsoon and consequent southwards expansion,with the summer monsoon weakened and fluctuated,and the annual total precipitation increased.At the end of Little Ice Age,there was a gradual decline of winter monsoon and a sudden strengthening of summer monsoon,with decreased annual total precipitation.The precursor of end of Little Ice Age was gradually weakening winter monsoon,abruptly enhanced summer monsoon,and relatively rare precipitation.The Medieval Warm Period (1200-1340 AD) was witnessed violent disastrous climate with warm summer and cold winter.
EVOLUTION OF PALEOCLIMATE AND PLANT COMMUNITY IN THE LAST 800 ka B P IN DATONG AREA
FAN Shuxian, TONG Guobang, ZHENG Hongrui
1998, 4(4): 64-68.
Abstract (154) PDF (244KB)(7)
Abstract:
A sporopollen analysis of the Dongshuitou section, Xiaobeizhuang section and Nansigou section of the Heishan hill, Datong, Shanxi, shows that the vegetation since 800 ka B P has gone through four stages developing from forest through sylvosteppe and steppe to desertsteppe, Corresponding to the changes of paleoclimate, i.e. three climatic cycles, including nine subcycles, each beginning with a cold and dry climate, and ending in a warm and humid one.
THE PALAEOCLIMATIC EVOLUTION OF THE YELLOW RIVER SOURCE AREA SINCE 130ka B P
ZHANG Yufang, ZHANG Junpai, XU Jianming, LIN Fang
1998, 4(4): 69-75.
Abstract (115) PDF (328KB)(7)
Abstract:
By a comprehensive analysis of the proxy indices of climate such as readily soluble salt and spore-pollen of borehole profiles in Dougeyong Basin,the palaeoclimatic evolution pattern of the Yellow River source area since 130 ka B P has been revealad:1.From 130 ka B P to 110 ka B P,it was cold and dry;2.From 110 to 82 ka B P,cold but more humid;3.From 82 to 10.4ka B P,cold and dry;4.From 10.4 ka B P to recent(i.e.,Holocene),there was an alternation of warm-humid and cold-dry climate.And the climate in Holocene can further be divided into three stages:1)10.4-7.6 ka B P it was Anathermal;2)7.5-3.5 ka B P Megathermal;3)3.5 ka B P present Katathermal.In general palaeoclimate the area has a longer and earlier cold period and a shorter and later warm period as compared to other regions of the world.The climate fluctuations since Holocene have occurred at a time scale of one thousand years.Since Late Holocene there has been a gradual decreasein temperature and humidity.
SEDIMENTARY CHARACTERISTICS AND CLIMATIC EVOLUTION OF CORE HQ IN HEQING BASIN YUNNAN PROVINCE
JIANG Xuezhong, WANG Sumin, YANG Xiangdong
1998, 4(4): 76-81.
Abstract (87) PDF (282KB)(6)
Abstract:
The environment evolution history of the Heqing Basin since 600 ka B P has been established based on the analysis of the colour,granularity,stratification and lithological assemblage of the sediments from the HQ core in combination with the study of the magnetic stratigraphy,susceptibility,content of carbonates,total organic carbon and the carbonlnitrogen ration of the sequence.There were two distinet tranformations of the enviroment connected to the tectonic movement.At a depth of 4.1m of the column,the lake basin was entrenched by rivers at about 14.2 ka B P,leading to a sudden change of the envionment.
ABRUPT FORMATION OF THE CHARHAN SALT LAKE AND THE MEGAEVOLUTION OF THE EARTH SURFACE SYSTEM-ON THE BASIS OF OSTRACODA
WANG Qiang
1998, 4(4): 82-87.
Abstract (199) PDF (303KB)(7)
Abstract:
Based on the study on Ostracoda collected from a total of six drilling holes in the Charhan lake area,Qinghai Province,four ostracods assemblages indicative respectively of Saline,brackish, fresh-water and swamp facies have been recognized.It was found that since 0.78 Ma B P the area was characterized by a dominance of shallow lake and littoral environment during the long duration of cold,dry climate.The appearance of peat sediments also indicates the Presence of littoral zone at the southeast part of the lake.It was only at the beginning of the last Great Glacial Stage(c.24 ka B P) that the salt lake was abruptly formed.At the west part of the Qaidam Basin the salt deposits have been formed since Late Pliocene.But the lake had undergone some freshening as a result of climatic changes.The extinetion of fresh-water or brackish lake was related to the sudden decrease in rainfall and runoff resulting in little or no solution of the salt deposits even in the locene times.So the formation of the Charhan salt lake is thought to be the result of the Earth surface system megaevolution.
CHRONOLOGICAL STUDIES ON ACTIVE FAULTS AND GROUND FISSURES IN GUANZHONG AREA, SHAANXI PROVINCE,CHINA
SUN Jianzhong, ZHANG Jingzhao, PENG Jianbing, ZHANG Jun, LI Bingcheng
1998, 4(4): 88-97.
Abstract (265) PDF (400KB)(7)
Abstract:
12 Thermoluminecence datings of the fault gouge and the adjoining cleaved loess of the area gives an age of 20-240 ka B P.It shows that the faults have been active during the late middle pleistocene to Late Pleistocene.Geomorphological and geological evidences are provided to show the alternation of rapid movement and show creep of the faults.The ground fissures in Xi'an City are in fact active faults,having been triggered to revive by pumping water from the confined aquifer.