米仓山宝塔期碳酸盐岩海底峡谷的发现及其意义THE DISCOVERY OF AN ORDOVICIAN CARBONATE SUBMARINE CANYON SYSTEM IN THE MICANGSHAN AREA AND ITS IMPLICATION
王永和,焦养泉,周志强,雷桂侠,李建星
摘要(Abstract)：
在米仓山元坝子一带,野外调查和室内显微岩石学研究发现宝塔组下部存在一套与正常宝塔组多角形网纹状泥晶灰岩完全不同的紫红色生物碎屑灰岩。紫红色生物碎屑灰岩具有特征的外部形态和内部结构。横向上,它以透镜状形式与多角形网纹状泥晶灰岩呈明显的相变关系,宽为2—2.5km,厚29.3m;纵向上,暴露地表的部分长度达600m。该沉积体以发育多级别的、典型正粒序沉积韵律为特征,构成生物碎屑灰岩的主要为异地搬运来的生物碎屑,它们具有明显的重力流色彩,是一种浊积水道沉积,将其解释为碳酸盐岩海底峡谷。区域调查与沉积学、古生物学研究表明,研究区的海底峡谷发育于晚奥陶世卡拉道克中期,实测古水流方向指向为北西向,这与研究区总体处于浅外陆棚向深边缘海盆地过渡的古地理背景相吻合。宝塔组碳酸盐岩海底峡谷的发现,不仅为扬子地台西北缘奥陶纪古环境恢复提供了沉积学依据,同时也可以预测在研究区向西北方向可能存在海底峡谷—浊积扇沉积体系。
关键词(KeyWords)： 岩石地层;古地理;海底峡谷;宝塔组;奥陶系;米仓山;陕西
基金项目(Foundation): 中国地质调查局西北矿产资源潜力评价项目(No.1212010881632)
作者(Author): 王永和,焦养泉,周志强,雷桂侠,李建星
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