白坪井田太原组上段底部砂岩沉积环境分析及其意义

白坪井田太原组上段主要由三层灰岩（L7、L8、L9）、泥岩和薄煤层组成,L7灰岩位于该段底部,是一7煤层顶板。根据井田西部钻孔资料,相当于L7灰岩层位,往往相变为砂岩。该砂岩以中、粗粒砂岩为主,向上渐变为细砂岩,正粒序特征明显,具板状交错层理和波状层理,底部多为粗砂岩,见冲刷面,其厚度与L7灰岩厚度相当,剖面上砂体呈连续的透镜状,与两侧的L7灰岩呈突变接触关系,砂岩体平面上呈条带状分布,与地层走向垂直,综合分析认为该砂体属潮道沉积相,是在潮坪上潮汐通道部位形成的砂质沉积属潮道沉积相。对该砂体分布的圈定,意味着一7煤在此范围的缺失,这一结论有助于解决太原组煤岩层的对比问题。

Baiping Minefield Taiyuan Formation Upper Member Basal Sandstone Depositional Environment Analysis and Its Significance

The upper member of Taiyuan Formation in Baiping minefield is composed of three limestone layers （L7, L8 and Lg）, mudstone and thin coal seams. The L7 limestone is just located at bottom of the member and the roof of I7 coal seam. According to borehole revealed in western minefield, the L7 limestone horizon is usually changed into sandstone facies. The sandstone is mainly medium-, coarse-grained sandstone, gradually changed into fine grained sandstone upward with obvious normal grading. Tabular cross-bedding and wavy bedding, mostly coarse-grained sandstone is located at the bottom with a scouring plane and its thickness equivalent to the L7 limestone＇s. The sand body shows itself continuous lenses, abrupt contact with limestone at both ends, planar banded distribution and perpendicular to strata strike. Comprehensive analysis has figured out that the sand body was formed at tidal channel in a tidal flat and belongs to tidal channel sedimentary facies. The existence of the sand body predicted hiatus of I7 coal seam in the extent, this conclusion is redounding to Taiyuan Formation coal and rock correlation.