鄂尔多斯盆地三道坎组混合沉积的生物扰动构造与古地理
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中国石油天然气总公司勘探研究项目与石油大学(北京)科研基金项目联合资助。


Bioturbation structures and paleogeography of mixed deposits of the Lower Ordovician Sandaokan Formation, Ordos basin
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    摘要:

    提要:首次在鄂尔多斯盆地西北缘桌子山地区下奥陶统三道坎组发现遗迹化石,其中绝大部分为无法鉴定遗迹属种的生物扰动构造。该组属碳酸盐岩与陆源碎屑岩互层的混合沉积,按岩性及韵律性将其分为5段,分析概括了生物扰动构造的分布、特征及形成的沉积环境。本组沉积期出现的古地理环境主要包括前滨沙滩及沙坝、云坪及含沙云坪、局限台地潮下低能、台地粒屑滩(介壳滩)和开阔台地潮下带。采用沉积学与实体化石及生物扰动构造半定量分析相结合的研究方法,阐述了各古地理单元的特征与各段沉积期的古地理环境,认为:本组沉积早期先后以含沙云坪环境、局限台地潮下低能环境为主,中、晚期则开阔台地潮下带环境频繁出现并时而占优势,反映了海平面上升的总体趋势;同时在海进的背景下,前滨沙滩、沙坝与云坪、含沙云坪或开阔台地潮下带等环境的交互出现,则反映了阿雷尼格中期本区是接近古陆的,随着相邻古陆的周期性抬升或海平面的周期性上升,出现了海陆争夺、频繁的海水进退的古地理变化,从而混合沉积发育。直形壳鹦鹉螺类化石产出状态的研究等表明三道坎组古流向是自北而南的。据岩性和古生物化石分析,本组沉积期气候干热,桌子山地区应归属早奥陶世华北亚热带干旱气候区。

    Abstract:

    Abstract:For the first time trace fossils have been discovered in the Lower Ordovician Sandaokan Formation in the Zhuozishan area at the northwestern margin of the Ordos basin. Most of them are bioturbation structures whose ichnogenera and ichnospecies cannot be identified. The Sandaokan Formation comprises mixed deposits composed of alternating beds of carbonate rocks and terrigenous clastic rocks. It is divided into five members according to the lithology and rhythmicity. The distributions and characteristics of the bioturbation structures and the sedimentary environments where they were formed are analyzed and summarized in this paper. The paleoenvironments during deposition of the formation are mainly foreshore sand beaches, sandbars, dolomite flats, sandy dolomite flats, low-energy subtidal restricted platforms, coquina banks and subtidal open platforms. The characteristics of each paleogeographic unit and paleoenvironments in the depositional period of each member are expounded by the sedimentological and body fossil study, combined with the semi-quantitative analysis of bioturbation structures. It is suggested that the paleoenvironment in the early depositional period of the Sandaokan Formation was successively mainly marked by sandy dolomite flats and low-energy subtidal restricted platforms, while the subtidal open platform environment appeared repeatedly and predominated sometimes in the middle and late depositional periods of the formation, which reflects the general trend of sea-level rise. Meanwhile in the background of transgression, foreshore sand beaches, sandbars and dolomite flats, sandy dolomite flats or subtidal open platforms appeared alternately, which reflects that the Zhuozishan area was near an old land during the Middle Arenigian age. With the periodical rise of the old land or the sea level, transgression and regression and land and sea change occurred frequently; as a result, mixed deposits were developed. Study of the attitudes of the fossil orthocone nautiloids indicate that the paleo-currents were from north to south during the deposition of the Sandaokan Formation. According to analyses of the lithology and fossils, the climate was dry and hot during the deposition of the formation. The Zhuozishan area should be classed as an Early Ordovician North China subtropical dry climatic province.

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费安玮 刘成林 甘 军 张忠涛. 鄂尔多斯盆地三道坎组混合沉积的生物扰动构造与古地理[J]. 中国地质, 2004, 31(4): 347-355.
FEI An-wei, LIU Cheng-lin, GAN Jun, ZHANG Zhong-tao. Bioturbation structures and paleogeography of mixed deposits of the Lower Ordovician Sandaokan Formation, Ordos basin[J]. Geology in China, 2004, 31(4): 347-355(in Chinese with English abstract).

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