Knowledge Resource Center for Ecological Environment in Arid Area
| 甘肃天水-秦安地区新生代沉积物物源示踪研究 | |
| 其他题名 | Provenances of the different Cenozoic deposits in the Tianshui-Qinan regions |
| 曾方明 | |
| 出版年 | 2011 |
| 学位类型 | 博士 |
| 导师 | 郭正堂 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 六盘山以西的新近纪风尘堆积为揭示过去22 Ma以来亚洲内陆荒漠和季风气候的演化提供了极其重要的陆相记录。本文在QA-I等新近纪风尘堆积与风成第四纪黄土和晚中新世-上新世红粘土等沉积物的地球化学组成对比研究的基础上，对天水-秦安地区新生代不同类型沉积物（现代河流沉积物、古近纪洪积砾岩、新近纪河湖相沉积物和新近纪黄土）<75 μm的硅酸盐组分的Sr-Nd同位素和微量元素组成进行了测试和研究。其目的是示踪不同类型沉积物的来源，并探讨物源示踪结果对研究区地貌演化的指示意义。获得如下结论：\n古近纪洪积砾岩的Sr-Nd同位素组成（87Sr/86Sr：0.719687 ~ 0.723183；εNd(0)：–12.56 ~ –12.46）与西秦岭现代河流沉积物的组成（87Sr/86Sr：0.717597 ~ 0.722705；εNd(0)：–12.31 ~ –11.14）一致，指示了它们都来自西秦岭。尧店和喇嘛山剖面新近纪河湖相沉积物的Sr-Nd同位素组成（87Sr/86Sr：0.709401 ~ 0.719242；εNd(0)：–10.49 ~ –8.84）与西秦岭现代河流沉积物和古近纪洪积砾岩相比具有较低的87Sr/86Sr和较高的εNd(0)值，表明它们的源岩在物质组成上的差别。与上述沉积物不同，新近纪黄土样品的Sr-Nd同位素组成（87Sr/86Sr：0.717218 ~ 0.722418；εNd(0)：–10.40 ~ –8.90）与秦岭剥蚀物质有显著差别。新近纪黄土与其它亚洲粉尘记录具有一致的Sr-Nd同位素组成，而且22 ~ 6 Ma期间新近纪黄土与北太平洋深海粉尘的Nd同位素演化具有非常一致的趋势，进一步支持了新近纪黄土为亚洲内陆荒漠源区物质经风力搬运的产物，支持其它方法得出的结论。\n结合过去发表的QA-I剖面样品的微量元素组成特征，发现QA-I剖面样品与研究区的现代河流沉积物、古近纪洪积物、新近纪河湖相沉积物样品的Zr/Hf和稀土元素配分模式存在比较明显的区别。QA-I剖面样品具有最低的Zr/Hf比值和较低的LREE/HREE比值，可能与其源岩地球化学组成特征有关，与秦岭山麓的近源物质有明显区别。\n研究区沉积物的Sr-Nd同位素和微量元素组成示踪的结果一致。上述结果表明天水-秦安地区的新近纪风尘堆积与近源的秦岭风化剥蚀产物明显不同，而与其它亚洲粉尘记录高度一致，进一步证实了这套堆积的风成成因。同时也表明研究区堆积黄土的高地和发育河湖相沉积的小型盆地的地貌分异至少形成于22 Ma前，这些沉积物为典型的同期异相沉积，支持甘肃群沉积多样性的特点。 |
| 英文摘要 | The Neogene loess-soil sequences from the western Chinese Loess Plateau are important record for understanding the evolution of Asian inland desertification and monsoon climate since 22 Ma. This study presents the Sr-Nd isotopic data for the <75 μm silicate fraction of the Cenozoic sediments (modern floodplain sediments in the Qinling Mountain area, Paleogene alluvial conglomerates, Neogene fluvial-lacustrine sediments, Neogene loess deposits) from the Tianshui-Qinan regions. Trace elements of the sediments were also determined. The study aims to investigate the sources of different sediments, and to discuss the geomorphic implications by these geochemical data.\nThe Paleogene alluvial deposits have 87Sr/86Sr ratios of 0.719687 ~ 0.723183 and εNd(0) of –12.56 ~ –12.46, similar to the modern river sediments from the Qinling Mountains (87Sr/86Sr ranges between 0.717597 and 0.722705, εNd(0) between –12.31 and –11.14). These suggest that the Paleogene alluvial deposits probably source from the Qinling Mountains.\nThe fluvial-lacustrine deposits from Yaodian and Lamashan sections show a 87Sr/86Sr range from 0.709401 to 0.719242 and an εNd(0) range from –10.49 to –8.84. The lower 87Sr/86Sr ratios and higher εNd(0) values than for the modern river sediments and the Paleogene fluvial conglomerates samples, suggest different sources.\nThe isotopic ratios (87Sr/86Sr 0.717218 ~ 0.722418, εNd(0) –10.40 ~ –8.90) of the Neogene loess are clearly different from the above sediments. On the contrary, the Sr-Nd signatures of the Neogene loess are well consistent with those of the red clay and Quaternary loess deposits in the eastern Loess Plateau, as well as with the Asian dust from the central North Pacific, Greenland ice core, Dunde ice core. These strongly support its eolian origin. εNd(0) shows similar trends from 22 Ma to 6 Ma between the dust in the central North Pacific GPC3 core and the Neogene loess deposits. These indicate their common sources from the desert in the Asian interior.\nTrace element data from QA-I section showed different characteristics in Zr/Hf and in the rare earth elements chondrite-normalised patterns from the modern river sediments in Qinling, from the Paleogene alluvial deposits, and from the Neogene fluvial-lacustrine sediments.\nIn summary, Sr-Nd isotope data and trace elements consistently indicate that the sources of the Neogene loess deposits are radically different from those of the materials denudated and transported from the Qinling, but charateristic of Asian dust deposits. Additionally, the geochemical signatures support that the geomophological contrast of the studied region has been formed at least by the early Miocene. |
| 中文关键词 | 物源 ; Sr-Nd同位素 ; 微量元素 |
| 英文关键词 | Sr-Nd isotope trace elements eolian deposits |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 第四纪地质学 |
| 来源机构 | 中国科学院地质与地球物理研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/286929 |
| 推荐引用方式 GB/T 7714 | 曾方明. 甘肃天水-秦安地区新生代沉积物物源示踪研究[D]. 中国科学院大学,2011. |
| 条目包含的文件 | 条目无相关文件。 | |||||
| 个性服务 |
| 推荐该条目 |
| 保存到收藏夹 |
| 导出为Endnote文件 |
| 谷歌学术 |
| 谷歌学术中相似的文章 |
| [曾方明]的文章 |
| 百度学术 |
| 百度学术中相似的文章 |
| [曾方明]的文章 |
| 必应学术 |
| 必应学术中相似的文章 |
| [曾方明]的文章 |
| 相关权益政策 |
| 暂无数据 |
| 收藏/分享 |
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。
