地学前缘 ›› 2021, Vol. 28 ›› Issue (1): 60-76.DOI: 10.13745/j.esf.sf.2020.5.8

• 构造沉积响应 • 上一篇    下一篇

陆相坳陷湖盆沉积对深时古气候的响应信号: 以准噶尔盆地西北缘安集海河组为例

王彤1,2(), 朱筱敏1,2,*(), 董艳蕾1,2, 杨道庆3, 苏彬1,2, 谈明轩4, 刘宇1,2, 伍炜5, 张亚雄6   

  1. 1. 中国石油大学(北京) 地球科学学院, 北京 102249
    2. 油气资源与探测国家重点实验室, 北京 102249
    3. 中国石化 河南油田分公司, 河南 南阳 473132
    4. 河海大学 海洋学院, 江苏 南京 210098
    5. 中国石化华东油气分公司 泰州采油厂, 江苏 泰州 225300
    6. 中国石化石油勘探开发研究院, 北京 100083
  • 收稿日期:2019-07-15 修回日期:2020-11-19 出版日期:2021-01-25 发布日期:2021-01-28
  • 通讯作者: 朱筱敏
  • 作者简介:王彤(1995—),女,硕士研究生,地质学专业。E-mail: tovawang0821@outlook.com
  • 基金资助:
    国家重大科技专项“陆相湖盆层序地层与岩性圈闭形成机制”(2017ZX05001-002-002)

Signals of depositional response to the deep time paleoclimate in continental depression lakes: Insight from the Anjihaihe Formation in the northwestern Junggar Basin

WANG Tong1,2(), ZHU Xiaomin1,2,*(), DONG Yanlei1,2, YANG Daoqing3, SU Bin1,2, TAN Mingxuan4, LIU Yu1,2, WU Wei5, ZHANG Yaxiong6   

  1. 1. College of Geosciences, China University of Petroleum(Beijing), Beijing 102249, China
    2. State Key Laboratory of Petroleum Resources and Prospecting, Beijing 102249, China
    3. SINOPEC Henan Oilfield Company,Nanyang 473132, China
    4. College of Oceanography, Hohai University, Nanjing 210098, China
    5. Taizhou Oil Production Plant, Sinopec East China Company,Taizhou 225300, China
    6. SINOPEC Petroleum Exploration and Production Research Institute, Beijing 100083, China
  • Received:2019-07-15 Revised:2020-11-19 Online:2021-01-25 Published:2021-01-28
  • Contact: ZHU Xiaomin

摘要:

“深时”古气候研究范围为前第四纪地质记录,目的在于为未来气候预测提供依据。准噶尔盆地西北缘安集海河组沉积期,研究区处于早古近纪极热气候(PETM)时期,由于其温室气体排放与当前工业废气排放水平相当,对于全球变化以及地球系统科学研究具有重要意义,一直以来都是古近纪气候研究的热点。准噶尔盆地西北缘在早古近纪沉积期发育大范围分布的典型陆相坳陷湖盆沉积,因其远小于海洋的沉积规模而具有远高于海洋系统的气候变化敏感度,能够更加精确地记录古气候演化对湖盆沉积体系的控制作用。本文以准噶尔盆地西北缘安集海河组为主要研究对象,选取28块砂岩样品和23块泥岩样品分别进行粒度分析和微量元素测试。实验结果显示:研究区安集海河组砂岩中值粒径分布在7.58~393 μm,平均值为74.44 μm,属于细砂级别;微量营养元素Ni、Cu和Zn的富集指示高生产力水平,元素Mo、Re、V、Co、Cr组合以及Re/Mo、V/Sc、V/Cr和Ni/Co指示氧化型沉积环境,Sr/Cu指示干燥炎热的气候条件。综合岩心观察和镜下鉴定等手段,针对坳陷湖盆对极热气候事件的响应进行系统分析,从岩石学和生物地球化学两个方面寻找沉积物中的信号记录。在极热气候条件下,研究区整体处于干旱炎热的气候环境,随着干旱进程的不断加剧,湖盆蒸发作用强烈,湖平面下降,沉积物粒度逐渐变粗,沉积物暴露水面遭受氧化,形成大面积展布的陆相红层沉积,同时,水体中CO2分压不断上升,导致碳酸盐矿物浓度达到过饱和状态,以基底式碳酸盐胶结物的形式析出;受干旱气候加剧的影响,湖水持续浓缩,水体盐度上升,整体表现为陆相半咸水沉积环境,水体氧化性逐渐增强,古生产力水平呈现先增后降的变化趋势。

关键词: 古近纪极热事件, 沉积响应, 氧化-还原条件, 古生产力, 陆相坳陷湖盆

Abstract:

The deep time paleoclimate study concerns with the pre-Quaternary geological records and aims at predicting climate change in the future. In the northwestern Junggar Basin, the Anjihaihe Formation period coincided with the Paleocene-Eocene Thermal Maximum (PETM), an abrupt warming event in the early Paleogene and one of the most pronounced transient climatic events in the geological record. This warming event was likely related to the greenhouse gas emission from seafloor gas-hydrate accumulations. On a millennial timescale, the rate of greenhouse gas emission is, to large extend, comparable to current industrial events, thus providing a unique insight into our uncertain climate future. Therefore, this event has always been a hotspot in Paleogene climate research. During the early Paleogene, typical basin lake deposits were widely distributed in the northwestern Junggar Basin. However, the much smaller scale lacustrine sediments were much more sensitive to climate change than the oceanic system, thus providing more accurate recordings of the paleoclimate evolution that controlled the sedimentary system of the lake basin. In this study, we selected 28 sandstone and 23 mudstone samples from the Anjihaihe Formation for the grain-size analysis and trace element testing, respectively. The results showed that the median diameter of the sandstone grains varied from 7.58 to 393 μm, averaging at 74.44 μm and belonging to fine sand. Furthermore, the enrichments of Ni, Cu and Zn indicated high paleoproductivity during the Anjihaihe Formation period; the Mo, Re, V, Co and Cr contents and Re/Mo, V/Sc, V/Cr and Ni/Co ratios demonstrated the study area was developed in an oxidizing environment; and the Sr/Cu ratio suggested dry and hot climate. We next studied comprehensively the response of continental depression lake to the PETM using core observation and microscopic identification methods, searching response signals from geological archives of both sedimentary and biogeochemical records. Under the conditions of the PETM, the entire study area was in a hot and dry climate. As drought condition intensified, intense evaporation caused lake level to fall. As a result, sediment grain size gradually coarsened, and exposed sediment near the water surface was oxidized to form expansive continental red beds. Meanwhile, due to increasing partial pressure of CO2 in lake water, supersaturated carbonate minerals precipitated in the form of basement carbonate cement. Continuing concentration of lake water also caused rising salinity, creating a continental brackish water sedimentary environment. Oxidability of water increased too, whereas paleoproductivity increased first and then decreased.

Key words: PETM, sedimentary response, redox condition, paleoproductivity, continental depression lake basin

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