鄂尔多斯盆地徐庄组碳酸盐岩风暴沉积发育特征及其地质意义

摘要/Abstract

摘要：

鄂尔多斯盆地寒武系徐庄组发育碳酸盐岩风暴沉积现象。风暴沉积主要包括侵蚀底面、风暴砾屑层、丘状和洼状层理等沉积构造。沉积构造在不同的条件下会形成不同的沉积序列,理想的沉积序列包括5个沉积单元,从下到上依次为:A侵蚀底面及砾屑段,代表风暴高峰期和衰减期的沉积作用,底面有突变的底界及特殊的沉积构造;B粒序段,为风暴减弱时沉积物从下向上变细的层段;C平行纹层段;D丘状纹层段,为风暴衰减期流体性质逐渐由密度流变为牵引流时形成的产物;E水平层理泥岩和泥晶灰岩段,为风暴停息期晴天条件下的产物。经野外考察发现研究区共可识别出5种不同类型的沉积序列组合,每种序列组合有不同的沉积特点,代表的沉积环境也不同。研究区寒武系徐庄组碳酸盐岩风暴沉积的发现和研究,对于古板块演化与古纬度恢复、鄂尔多斯盆地古地理研究具有重要的意义。

关键词: 鄂尔多斯盆地, 徐庄组, 风暴岩, 风暴沉积, 风暴序列

Abstract:

The tempestites which developed in the Cambrian Xuzhuang Formation in Ordos Basin mainly includes many sedimentary structures,such as erosional base, storm flow-generated gravelstones,hummocky and swaley cross-stratification. Sedimentary structure in different conditions can form different storm sedimentary sequences. The ideal storm sedimentary sequence includes five units, from bottom to top, which are composed of A-erosional base and conglomerates representing the deposition of storm peaks and decay period,B-graded bedding with grain-size decreasing upward when storm weakened, C-parallel lamination,D-hummocky cross-stratification representing fluid property changes from density flow to tractive current in storm attenuation period, E-mudstone with horizontal bedding and micrite limestone forming in storm rest period.Based on outcrop observation in the field, there are five types of depositional sequence. Different types of depositional sequence have different sedimentary characteristics and different sedimentary environments. The carbonate tempestites in Cambrian Xuzhuang Formation have important significances in evolution of palaeoblocks and restoration of ancient latitudes, and in research of Ordos Basin palaeogeography.

Key words: Ordos Basin, Xuzhuang Formation, storm deposit, tempestite, storm sedimentary sequence

中图分类号:

TE121.3

白一鸣, 张元福, 胡晨林, 王振. 鄂尔多斯盆地徐庄组碳酸盐岩风暴沉积发育特征及其地质意义[J]. 现代地质, 2017, 31(06): 1233-1232.

BAI Yiming, ZHANG Yuanfu, HU Chenlin, WANG Zhen. Characteristics and Geological Significances of Xuzhuang Formation Carbonate Tempestites in Ordos Basin[J]. Geoscience, 2017, 31(06): 1233-1232.

图/表 5

图1 鄂尔多斯盆地研究区主要露头位置与寒武系地层划分图

Fig.1 Main outcrops in the study area of Ordos Basin and stratigraphic division of Cambrian

图2 鄂尔多斯盆地西缘及东缘寒武系徐庄组风暴沉积构造 a.黄色虚线为平缓波状起伏冲刷面,幅度为0.3~1 cm,可见微型冲刷沟槽;b.黄色虚线为不规则波状起伏冲刷面,幅度为0.8~1.5 cm,起伏较明显但不规则;c.黄色虚线为冲刷面,红色箭头为渠模,渠模宽为10 cm,深为3 cm;d.黄色虚线为冲刷面,红色箭头为渠模,渠模宽为10 cm,深为2 cm;e.风暴砾屑,呈放射状排列,可见菊花状构造,砾屑呈倒“小”字形排列;f.风暴砾屑,可见风暴撕扯构造,砾屑根部仍与原岩层相连;g.黄色实线为简单丘状层理,长20 cm,高1~2 cm,纹层较为平缓,纹层厚度薄,为2 mm;h.黄色实线为复合式丘状层理,长30~40 cm,高5~8 cm, 纹层厚度为5 mm,可见多个丘状交错层理的相互重叠,层系之间存在截切现象;i.平行层理,单层厚度为0.5~3 cm

Fig.2 Storm sedimentary structures of Xuzhuang Formation western and eastern margin of Ordos Basin

图3 理想风暴沉积序列示意图

Fig.3 Ideal storm sedimentary sequences

图4 鄂尔多斯盆地西缘及东缘寒武系徐庄组风暴序列类型

Fig.4 Types of storm sedimentary sequences in Xuzhuang Formation, western and eastern margins of Ordos Basin

图5 鄂尔多斯盆地西缘及东缘寒武系徐庄组不同风暴沉积序列野外和镜下特征 a.序列组合Ⅰ,冲刷面起伏较大,可见渠模,充填物为泥质灰岩,向上为风暴砾屑层厚度为40 cm,再向上过渡为丘—洼状交错层理段,厚度为15 cm,二者之间界面平直;b. 序列组合Ⅰ风暴砾屑层镜下特征,为泥晶灰岩,可见竹叶状砾屑,砾屑内部部分被选择性发生白云石化;c.序列组合Ⅱ,不同期次的冲刷面;d.序列组合Ⅱ生屑灰岩镜下特征,可见三叶虫碎片;e.序列组合Ⅴ,侵蚀底面及砾屑段厚度为8 cm,砾屑总体以顺层排列为主,少数为高角度排列,底部有微波状冲刷面,平行纹层段厚度为3 cm; f.序列组合Ⅴ镜下特征,为竹叶状灰岩,视域为单个竹叶状砾屑的局部

Fig.5 Outcrops and microscopic characteristics of different storm sedimentary sequences of Xuzhuang Formation in western and eastern margin of Ordos Basin

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