This paper presents a 457-year reconstruction of precipitation in the southeastern Qinghai-Tibet Plateau using tree-ring records.Tree-ring samples were collected from the Hengduan Mountains in the southeastern part of the Qinghai-Tibet Plateau,China.A nearly 500-year chronology was developed using tree-ring width records.Correlation analysis shows moisture is the main factor limiting tree growth in this region.Ring-widths were significantly positively correlated with the Palmer Drought Severity Index(PDSI) and precipitation in many months.The highest correlation coefficient was found between the annual growth of trees and precipitation from the previous September to the current June(0.738).Based on this relationship,we reconstructed the precipitation history from 1509 to 2006.The reconstruction explains 54.4%(Radj2=53.5%,N=49,F=56.12) of the actual precipitation variation during the calibration period(1958-2006).During the reliable period of the reconstruction(1549-2006),some low-frequency climate signals are included,indicating this region has been getting wetter in the last 20 years.The reconstruction documents six apparently dry and five pluvial periods and the 17th century dry period lasted longer than any other.When compared with other recent studies,this study and these earlier reconstructions show a similar trend in the variation of drought and pluvial.Further spatial correlation analysis confirms that the reconstructed precipitation adequately represents the rainfall history of the entire Hengduan Mountain area.The Multi-taper method,a type of spectral analysis,reveals that precipitation in this area had significant(P<0.01) spectral peaks at 3-5 a,60 a and 79-85 a.
To investigate characteristics of H isotope variation in long-chain n-alkanes (δDn-alkanes) from higher plants in surface soils under a single ecosystem, 12 samples from a basalt regolith were randomly collected from Damaping in Wanquan County of Zhangjiakou in North China. Molecular distribution and C (δ13Cn-alkanes) and H isotopes of long-chain n-alkanes, as well as C isotopes of TOC (δ13CTOC), were analyzed. Both δ13CTOC and δ13Cn-alkanes values from four representative dominant long-chain n-alkanes (n-C27, n-C29, n-C31, n-C33) derived from terrestrial higher plants show minor variations among the 12 samples, indicating the major contributor is from local grasses with a uniform C3 photosynthetic pathway. In contrast, variations in δDn-alkanes values of the four long-chain n-alkanes are relatively large, with the more abundant homologs generally showing more negative δDn-alkanes values and less variation. However, variation of <30‰ among weighted averaged δDn-alkanes values of the four long-chain n-alkanes is not only less than that among δDn-alkanes values for different modern terrestrial C3 grasses from the specific locations, but also less than the literature values of δDn-alkanes of long-chain n-alkanes for single species over different seasons. Thus, because the sources of long-chain n-alkanes in surface soils and sediments are similarly from multiple individual plants, our results are significant in confirming that paleoclimatic, paleoenvironmental and paleohydrological information can be interpreted more accurately from δDn-alkanes values of long-chain n-alkanes from sediments, particularly terrestrial sediments with organic matter derived from in-situ plants.
The western Qinling (秦岭) orogenic belt is one of the outermost ranges in the northeas-tern Tibetan Plateau. Its tectonic uplift history is therefore essential to insight on the evolution history of the plateau. However, the timing of deformation and uplift history is still poorly known. Fortunately, its Cenozoic orogenic history is recorded in an excellent synorogenic sedimentary sequence exposed in the Tianshui (天水) Basin, the northeastern foot of western Qinling. According to sedimentary-tectonic analysis of the Yaodian (尧店) and Lamashan (喇嘛山) sections based on the previous magnetostratigraphy studies, we speculated that two stages (occurred at 9.2-7.4 and ～3.6 Ma) of variation in depositional facies were attributed to the uplift and deformation of the western Qinling, and the modern structure geomorphic frame of the northeastern Tibet formed after 2.6 Ma. Furthermore, four stages of active processes along the western Qinling occurred at 49-41, 34-27, 25-19 and ～13 Ma, are deciphered from an integrated detrital apatite fission-track data of the Ganquan (甘泉), Yaodian main sections and seven small ones. The former two are represents the exhumation episodes triggered by tectonism and the others attributed to the volcanic signals.
This paper reports a loess-paleosol sequence located in the Danube River basin,Serbia,which formed at least since the latest part of the early Pleistocene,and before the paleomagnetic B/M boundary.Various magnetic parameters of the Serbian V-L1-V-S4 loess-paleosol sequence have been measured and analyzed in the Titel Loess Plateau.These parameters show a very similar magnetic behavior compared with that of the Chinese loess.There is a general positive relationship between magnetic susceptibility() and pedogenesis.The main contributors to are the magnetic grains of SP(superparamagnetic) and SD(single domain) magnetic domains,while MD(multi domain) contributes only a small percentage.The difference in between loess and paleosol mainly is caused by pedogenesis.The very fine magnetic minerals increase gradually with increasing soil development(from loess to soil),and they lead to higher.The thermomagnetic curves show thatmagnetic minerals in the loess layers are magnetite and maghemite,both providing a major contribution to.In contrast the paleosol layers mainly are composed of magnetite,with almost no or a very small amount of maghemite,as implied by a reversible thermomagnetic behavior.This indicates that pedogenic conditions during V-S3 and V-S4 strong soil development have resulted in maghemite that is no longer stable,and has been resolved or converted to other stable phase minerals.This likely indicates that soil moisture during V-S3 and V-S4 development exceeded a critical condition of maghemite stability.
LIU XiuMingLIU ZhiLü BinMARKOVI S BCHEN JiaShengGUO HuiMA MingMingZHAO GuoYongFENG Hua
