渭南黄土剖面的年龄测定及十五万年来高分辨时间序列的建立

作者对渭南黄土剖面连续采取的样品进行了系统的_１４Ｃ和ＴＬ年龄测定，测得的_１４Ｃ年龄做了δ_１３Ｃ校正和日历年龄校正，并与ＳＰＥＣＭＡＰ比较，取得了很好的结果。根据测得的年龄，Ｓ０底部１４３ｃｍ处的_１４Ｃ年龄为１０３００ａＢ．Ｐ，即全新世起始于１０３００ａＢ．Ｐ．；Ｌ１可划分五层，其中Ｌ(１－２)和Ｌ(１－４)为古土壤层，Ｌ(１－２)顶部_１４Ｃ年龄为２２０００ａＢ．Ｐ．，深度为３６１ｃｍ，Ｌ(１－４)．底部有一层明显的碳酸盐结核，其ＴＬ年龄为５１９１０ａＢ．Ｐ．，深度为６４０Ｃｍ；Ｌ１底部的ＴＬ年龄为７３０００ａＢ．Ｐ．，深度为８５５ｃｍ，这便是马兰黄土的起始年龄；Ｓ１底部为１３４５００ａＢ．Ｐ．，深度为１２１６ｃｍ。与深海沉积物氧同位素阶段对比，马兰黄土相当于１—４阶段，Ｓ１相当于５阶段。

DATINGS AND RECONSTRUCTION OF THE HIGH RESOLUTION TIME SERIES IN THE WEINAN LOESS SECTION OF THE LAST 150 000 YEARS

Abstract:The high resolution time series possesses great potentiality in reconstruction ofpaleoclimates. Some specialists established time scale for Quaternary depositional sequences by the measurement of magnetic events and susceptibility, or by tuning tothe Earth's orbital parameters as well as by in comparision with the deep-sea oxygenisotope stages, all of which are reluctant to yielding numerical dates of Quaternarysediment for its difficulties of accurate determination. Whereas the establishment ofstratigraphic time series is still reliable .to the ways fit to determine the numericaldates.The authors located a loess profile at Yangguo Town, Weinan, with stratigraphicstability and. well developed paleosols, on which the systematic sampling was applied,and (14)C dating by AMS on organic materials (humins and humicacid) and TL datingwere carried out, resulting in desirable dates in a agreement with SPECMAP aftercalibration.A high resolution time series of the past 150 000 years is constructed along theprofile on the basis of dating measures: The hasal age of S0 is 10 270±380 a B.P.(abbrev. 10 300 a B.P.), located 143 cm below the top soil. There developed twopaleosols in L, which is 310 cm thick including two paleo-sols, having the top ageof 21 990±320 a B.P. (abbrev. 22 000a B.P.) at the level 361 cm and the hasal ageof 51 910±2 100 a B. P. (abbrev. 52 000 a B. P.) at the level 640 cm where underlying a thinner layer of calcites. The age of the boundary between L1 and S1 wasdated 73 000 a B. P. at the level of 855 cm, where the Malan Loess originates andwas thereby designated (73 b00a B.P.). All the above suggest that L1 correspond withphase 2,3,4 of the deep-sea oxygen isotopes.S1 is 361 cm in thickness with highly intensified pedogenesis, brown or darkbrown, comprising clay, clayey silt or silty clay, featured with massy, irregularcolumns or grands. It falls into three subdivisions: the first, 95cm, with hasal age98 760± 12 350a B.P., in contrast with the hasal age of S1--134 500 a B.P.. It is assumed that S1 is consistent with phase 5 of the deep-sea oxygen isotopes.