摘要
浙江常山上奥陶统砚瓦山组竹叶状灰岩具有高度观赏性,然而长期以来其成因还存在很大争议.竹叶状灰岩中竹叶状碎屑与基质显示出很大差异性.竹叶状碎屑颜色均一,均为肉红色,主要矿物为方解石,鲕绿泥石作为微量组分存在,赤铁矿含量极低;竹叶状碎屑的总铁含量低(1.04%~1.21%),Fe2O3/FeO比值高(1.28~1.75).基质颜色由岩层上部的(紫)红色向下渐变为蓝绿色,主要矿物为黏土矿物(伊利石+鲕绿泥石),鲕绿泥石为常量组分,赤铁矿含量很低;基质总铁含量较高(4.16%~5.64%),Fe2O3/FeO比值较低(0.63~1.4).笔者认为砚瓦山组竹叶状灰岩是两个不同环境形成的物质沉积混合的结果:竹叶状碎屑是海盆斜坡相对氧化环境形成的肉红色沉积物,基质是海盆沉积物,形成于相对还原的环境;在地震作用下,海盆斜坡上的肉红色沉积物滑塌、破碎成竹叶状碎屑,并与周围海水形成重力流,滑入海盆的沉积物(基质)中,混合、再沉积形成竹叶状灰岩.其颜色主要是因细菌铁还原作用引起基质沉积物从岩层上部的(紫)红色逐步过渡到下部的蓝绿色.
The wormtalk limestone from the Upper Ordovician Yanwashan Formation exposed in the Changshan County,Zhejiang Province,is highly ornamental.Its genesis has long-term been debated.Our studies suggest that the wormtalk limestone from the Yanwashan Formation is composed of flat-pebble and matrix with distinctive differences each other.The flat-pebbles show an uniform flesh-red color and the major component is calcite with low-content chamosite and hematite.Chemically,the FeO*value(=Fe2 O3+FeO)of the flat-pebbles is low ranging from 1.04% to 1.21% whereas the Fe2O3/FeO ratio is high(1.28~1.75).The matrix color changes from the purple red in the top to the blue-green in the bottom of strata.The matrix mainly consists of clay minerals including chamosite and illite as well trace-content hematite.The chemical composition of the matrix shows a high FeO*value(4.16%~5.64%)and low Fe2O3/FeO ratio(0.63~1.4).This study proposed that the wormtalk limestone derived from diagenesis,resulting from mixing of two-kinds sediments formed in different environments.The flesh red flat-pebble was accumulated in a relatively oxidizing environment and the matrix was formed in a relatively reduced environment in the same neritic basin.Under the action of earthquake,the flesh red sediments on the slope of the neritic basin may collapse and break into numerous flat-pebbles.Soon afterwards,following the formation of gravity flow,these pebbles were transported and dropped into the depositing carbonate sediments(matrix)in the neritic basin,mixed each other and re-deposited,and finally generated wormtalk limestone.The color change of the matrix was mainly caused by bacterial iron reduction,resulting in the gradually change of color from(purple)red in the top part to bluegreen in the bottom part.
作者
陈小明
王徳滋
舒良树
Chen Xiaoming;Wang Dezi;Shu Liangshu(School of Earth Sciences and Engineering,Nanjing University,Nanjing,210023,China;State Key Laboratory for Mineral Deposits Research,Nanjing University,Nanjing,210023,China)
出处
《南京大学学报（自然科学版）》
CAS
CSCD
北大核心
2020年第6期847-861,共15页
Journal of Nanjing University（Natural Science）
基金
国家自然科学基金(42072062)。
关键词
上奥陶统
竹叶状灰岩
颜色
沉积学
浙江常山
Upper Ordovician Series
wormtalk limestone
color
sedimentology
Changshan of Zhejiang
