CAJ | 학술논문

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.
재미창산원패자일대,야외조사화실내현미암석학연구발현보탑조하부존재일투여정상보탑조다각형망문상니정회암완전불동적자홍색생물쇄설회암.자홍색생물쇄설회암구유특정적외부형태화내부결구.횡향상,타이투경상형식여다각형망문상니정회암정명현적상변관계,관위2-2.5km,후29.3m;종향상,폭로지표적부분장도체600m.해침적체이발육다급별적、전형정립서침적운률위특정,구성생물쇄설회암적주요위이지반운래적생물쇄설.타문구유명현적중력류색채,시일충탁적수도침적,장기해석위탄산염암해저협곡.구역조사여침적학、고생물학연구표명,연구구적해저협곡발육우만오도세잡랍도극중기,실측고수류방향지향위북서향,저여연구구총체처우천외륙붕향심변연해분지과도적고지리배경상문합.보탑조탄산염암해저협곡적발현,불부위양자지태서북연오도기고배경회복제공료침적학의거,동시야가이예측재연구구향서북방향가능존재해저협곡--탁적선침적체계.
Field survey and micropetrographic analysis of the Ordovician strata in the Yuanziba district of the Micangshan area show that a set of mauve bioclastic limestone, which is completely different from the polygonal reticulate micrite of typical the Baota Formation, occur in the lower part of the Baota Formation. The mauve bioclastic limestone has obvious external morphology and internal structure. It shows an obvious facies transition with the polygonal reticulate micrite of the typical Baota Formation. It forms a lense 2-2. 5km in width and 29. 3m in thickness, with an exposed length of 600m. It is characterized by multi-order and typically mormally graded beds, and the clastic composition of the bioclastic limestone is mainly allochthonous. The graded beds have features indicative of gravity flow and turbidite channel deposition, and they are interpreted as representing carbonate submarine canyon system. Regional investigation and sedimentological and paleontological study of the canyon system show that it was formed in the Middle Ca-radoc of the Late Ordovician area and the measured paleocurrent direction pointed for the north-west, which is consistent with the palaeogeographic background of the study area that is located in intermediate belt from shallow outer continental shelf to deep marginal-sea basin. The discovery of a carbonate submarine canyon in the Baota Formation not only provides sedimentary evidence for Ordovician paleoenviron-ment restoration in north-west margin of the Yangtze Block, but also predicts that there may be carbonate submarine canyon-turbidite fan deposits to the northwest of the study area.