地学前缘 ›› 2009, Vol. 16 ›› Issue (5): 107-.

• 论文 • 上一篇    下一篇

藏南地区海相白垩系富有机质沉积的影响因素浅析

王立成 王成善 李亚林 魏玉帅   

  1. 1中国地质大学 地质过程与矿产资源国家重点实验室, 北京 100083
    2中国地质大学(北京) 地球科学与资源学院, 北京 100083
    3西藏自治区 地质调查研究院, 西藏 拉萨 850000
  • 出版日期:2009-09-10 发布日期:2009-09-10
  • 作者简介:王立成(1983—),男,博士研究生,矿产普查与勘探专业,主要研究方向为青藏高原海相盆地沉积学研究。Email: waynewlc3@126.com
  • 基金资助:

    国家重点基础研究发展计划“973”项目(2006CB701400);国家自然科学基金项目(40672086);财政部国家油气专项“青藏高原油气资源战略选区调查与评价”(XQ200406)

A simple analysis of influential factors for Cretaceous marine organicrich sediments in Southern Tibet.

WANG Li-Cheng WANG Cheng-Shan LI E-Lin WEI Yu-Shuai   

  1. 1State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China 2School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 100083, China 3Tibet Institute of Geological Survey, Lhasa 850000, China
  • Online:2009-09-10 Published:2009-09-10

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摘要：

藏南地区白垩纪时期广泛沉积了一套海相富有机质沉积物,而其中与CT界线缺氧事件有关的黑色页岩引起了广泛关注。但是,其有机碳含量与西特提斯相比明显偏低。因此,有关该区对海相白垩纪富有机质沉积影响机制的认识显得尤为重要。文中选取前人研究程度较高的岗巴宗山Ⅱ剖面、定日贡扎剖面和江孜加不拉剖面、床得剖面,利用其相关数据,定量计算了这些剖面的沉积速率、堆积速率和古生产力值。结果表明,藏南地区沉积速率以CT界线时期最高,而岗巴、定日地区与江孜地区的沉积速率表现出较大的差异,这主要与沉积环境有关;并且在沉积速率<4 cm/ka时,随着沉积速率的增加,有机碳含量随之增加,而沉积速率较大时,则关系不明显。江孜地区初级生产力较低,其缺氧期黑色页岩的形成并不是高生产力的结果,可能与缺氧条件的保存作用相关;对于岗巴和定日地区而言,尽管计算的古生产力较低,但碳同位素正偏以及推测存在的沿岸上升洋流表明,该区白垩纪富有机质沉积拥有高的初级生产力和缺氧的保存条件,表明该区有良好的古海洋条件,富有机质沉积的形成是高生产力、缺氧的保存条件以及低的沉积速率(<4 cm/ka)共同作用的结果。而产生有机碳偏低,从而使得计算的古生产力值偏低的原因,则可能与成岩后期强烈的风化作用,导致有机碳的损失有关;另外定日地区CT期有机碳含量偏低则还与其沉积物粒度有关。

关键词: 关键词：沉积速率;堆积速率;古生产力;有机碳;藏南

Abstract:

 A marine Cretaceous organicrich sequence deposited extensively in Southern Tibet, and the black shale therein correlated with CenomanianTuronian Anoxic Events has been receiving extensive interest. However, the TOC content is much lower than the black shale in West Tethys. Therefore, understanding the dominated mechanism of the organicrich sediments is important to the problem. We selected 4 cross sections in  Southern Tibet,which have been studied more intensively by the predecessors, namely, the Gamba ZongshanⅡ, the Tingri Gongzha, the Gyangze Jiabula and the Chuangde, to calculate the sedimentation rate, accumulation rate and paleoproductivity by using related data. The result showed that the highest sedimentation rate occurred at CenomanianTuronian, and the Gamba, Tingri and Gyangze areas had different sedimentation rate owing to their different deposited environments. Moreover, when the sedimentation rate <4 cm/ka, the content of TOC will increase with the increasing sedimentation rate; but there is no obvious correlation at the higher sedimentation rate. The primary paleoproductivity in Gyangze is lower, and the formation of the black shale is not the result of high paleoproductivity; it may be related to anoxia.  Although calculated paleoproductivity in Gamba and Tingri is also lower, the excursion of carbon isotope and speculated coastal upwelling indicates that the Cretaceous organicrich sediments had high primary paleoproductivity. The condition of paleooceanography e.g. high paleoproductivity and anoxia, which is excellent for the deposition of organicrich sediments, existed in Gamba and Tingri area. The interplay of these two factors together with the sedimentary rate controlled the deposition of the organicrich sediments. The cause of low TOC content and  thus of low calculated paleoproductivity was the intensive weathering at the late stage of diagenesis.

Key words: Key words: sedimentation rate; accumulation rate; paleoproductivity; TOC; Southern Tibet