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| 泥河湾盆地虎头梁叠层石的时代研究 | |
| 引用本文： | 韩志勇,杨淳,王永,闵隆瑞.泥河湾盆地虎头梁叠层石的时代研究[J].第四纪研究,2005,25(1):86-92. |
| 作者姓名： | 韩志勇 杨淳 王永 闵隆瑞 |
| 作者单位： | 南京大学城市与资源学系,南京,210093;中国科学院地球环境研究所黄土与第四纪地质国家重点实验室,西安,710075;中国地质科学院地质研究所,北京,100037 |
| 摘 要： | 阳原县虎头梁的泥河湾层夹有两层第四纪的叠层石,即上、下叠层石。文章分析了从3个地点采集的叠 层石样品,分别用热电离质谱铀系法和α能谱铀系法测量了它们的年龄。同一样品致密部分和非致密部分的年龄 及铀含量明显不一致,同时致密部分的铀系年龄出现倒序,此结果表明虎头梁的叠层石不适合用铀系法测年。根 据沉积物光谱光度测量,文章发现亮度值随剖面深度的变化曲线与北太平洋的风尘通量曲线形态相似,通过对比, 可以尝试将后者的时间标尺转移到前者上来,从而可建立虎头梁的泥河湾层的亮度时间标尺。它指示阳原县虎头 梁杏沟剖面上、下叠层石的年龄分别为73kaB.P.和274kaB.P.,分别是间冰期晚期和冰期的产物,前人所报道的孢 粉组合所代表的古气候环境支持这个年龄。 |
| 关 键 词： | 泥河湾层 铀系法 叠层石 亮度时间标尺 |
| 文章编号： | 1001-7410(2005)01-86-07 |
| 收稿时间： | 2004-07-05 |
| 修稿时间： | 2004年7月5日 |
AGE OF STROMATOLITES AT HUTOULIANG IN NIHEWAN BASIN |
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| Han Zhiyong,Yang Chun,Wang Yong,Min Longrui.AGE OF STROMATOLITES AT HUTOULIANG IN NIHEWAN BASIN[J].Quaternary Sciences,2005,25(1):86-92. | |
| Authors: | Han Zhiyong Yang Chun Wang Yong Min Longrui |
| Institution: | 1. The Department of Urban and Resources Sciences, Nanjing University, Nanjing 210093; 2. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi′an 710075; 3. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037 |
| Abstract: | Two stromatolite layers, namely the Upper Stromatolite and the Lower Stromatolite, are intercalated in the fluvial-lacustrine Nihewan Beds at Hutouliang, Yangyuan. It is assumed that the stromatolites are formed by microbial activities of blue algae. These quasi-fossil materials have attracted attention of geologists since the paleoenvironment can be reconstructed by analyzing them. Accurately determining the age of stromatolites at Hutouliang is a key problem to address paleoenvironmental issues. Numerical dating of stromatolites has been attempted. However, evidence of stratigraphical subdivision and correlation does not support the reported data, moreover, these data also contradict a Lightness Time Scale that was established at Hutouliang recently. Using the U-series method we may reliably date Middle and Late Pleistocene carbonates. But the content of 232Th of terrestrial samples is often high as a result of remarkable detritus incorporation, which invalidates the direct measurement. Direct dating is only feasible if the “dirty” carbonate samples are rich in uranium. This is the case for stromatolites at Hutouliang. Stromatolite samples collected for the first time were measured by using the TIMS U-series dating method. Results show that ages of two stromatolite layers are likely in reverse order. In order to confirm this, samples collected for the second time were analyzed by using alpha spectrometry U-series dating method in another laboratory. The age of the Lower Stromatolite of Yujiagou is equal to that of the Upper Stromatolite of Guoshenggou. But we find that dates are also in reverse order if we take the Lower Stromatolite of Xinggou into account. Results derived from two laboratories are consistent, all pointing to a fact that U-series data of two stromatolite layers are indeed in reverse order. We also analyzed different parts of an identical stromatolite, both dates and uranium content of compact parts are inconsistent with that of incompact parts. We conclude that the U-series dating is inapplicable to stromatolites at Hutouliang. Its aragonite component and cryptocrystalline structure are supposed to be two possible causes for this failing dating. A chronostratigraphical method to determine the age of stratum at Hutouliang was tried. The lightness (L ), one spectrophotometric parameter, was measured on sediments of Xinggou section. This record can be compared with the aeolian flux record in North Pacific. By correlating and interpolating between selected time control ties from the lightness curve to aeolian flux curve, we can utilize the detailed chronology of the SPECMAP curve and establish a preliminary Lightness Time Scale of sediments at Hutouliang. More data are required to confirm the lightness is a proxy indicator of the aeolian flux. But the suggested correlation is reasonable considering two facts. One is these two records are nearly of same age span; Second fact is our lightness value time series for the Xinggou section was developed using only a few correlation tie points to V21-146, nevertheless, it also shows spectral peaks close to the primary Milankovitch periodicities. After slight adjustment of the Lightness Time Scale and further field examination, now the age of the Upper Stromatolite and the Lower Stromatolite of Xinggou were assigned to be 73kaB.P. and 274kaB.P., corresponding to Marine Oxygen Stage 5 and 8 respectively. This reveals that these stromatolites likely deposited during either the glacial period or the late stage of interglacial period. The environment indicated by the assemblage of sporopollen supports this age estimation. |
| Keywords: | Nihewan Beds U-series stromatolite Lightness Time Scale |
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