Abstract:
In this paper，we discussed the genesis of the nodular limestones from the Ordovician Yanwashan Formation in the Huangnitang section(the first GSSP)，Changshan，Zhejiang Province on the basis of mineral component，texture，structure，chemical composition，and particularly the stable C-O isotopic composition of both the nodule and matrix. The research results indicate that there is an apparent difference between the nodule and matrix of the nodular limestones. The nodules are mainly composed of micritic calcite(70％～98％)，while the primary component of the matrix is clay mineral(40％～78％)with only 20％～58％ calcite. The δ13CVPDB values of calcite of the nodule and matrix are 0.5‰ to 1.4‰(average 0.9‰)and -0.4‰ to 1.1‰(average 0.2‰)，respectively. The δ18OVPDB values of calcite of the nodule and matrix are -12.8‰ to -8.0‰(average -10.6‰)and -11.7‰ to -9.0‰(average -10.3‰)，respectively. The nodule always shows higher δ13C value and formation temperature than those of the matrix for the same sample. All features imply that the nodular limestones from the studied section are formed due to a combined processes of the periodical dissolution of bottom current during the sedimentary period and the differential compaction and pressure solution during the diagenesis. There are three existing types of the nodular limestones: banded nodular limestone，discontinuous nodular limestone and random nodular limestone. The occurrence mode of the nodular limestone is determined by the insoluble residue content of country rock of nodules and the pressure solution intensity.
Key words:
nodular limestone,
carbon and oxygen isotopes,
genesis,
Yanwashan Formation,
Ordovician,
Huangnitang section,
Zhejiang Province
摘要： 对浙江常山黄泥塘剖面奥陶系砚瓦山组瘤状灰岩中瘤体和基质的矿物组成、结构、构造、化学成分及碳氧同位素等做了系统研究，并从其基本特征、尤其是碳氧同位素特征出发，结合前人研究成果，对瘤状灰岩的成因进行了初步探讨。研究表明，瘤状灰岩的瘤体和基质存在明显差异：瘤体主要由方解石组成（70％～98％），基质则以黏土矿物为主（40％～78％），方解石次之（20％～58％）；瘤体和基质的δ13CVPDB值分别为0.5‰～1.4‰和-0.4‰～1.1‰，平均值分别为0.9‰和0.2‰， δ18OVPDB 值分别为-12.8‰～-8.0‰和-11.7‰～-9.0‰，平均值分别为-10.6‰和-10.3‰；每个样品中瘤体的碳同位素值和形成温度均比基质高。黄泥塘剖面砚瓦山组瘤状灰岩是沉积物沉积时期周期性底流溶解和成岩过程中差异性压实和压溶共同作用的产物，瘤体原岩中非碳酸盐组分含量及后期压溶作用强度的差异导致瘤状灰岩不同的存在形式，有条带状、断续状和杂乱状3种。
关键词:
瘤状灰岩,
碳氧同位素,
成因,
砚瓦山组,
奥陶系,
黄泥塘剖面,
浙江省
CLC Number:
Zhang Xia, Lin Chunming, Ling Hongfei, Jiang Shaoyong, Li Yanli, Gao Likun, Yao Yulai, Liu Xiao. Nodular limestone and its genesis from the Ordovician Yanwashan Formation in western Zhejiang Province[J]. JOURNAL OF PALAEOGEOGRAPHY, 2009, 11(5): 481-490.
张霞, 林春明, 凌洪飞, 蒋少涌, 李艳丽, 高丽坤, 姚玉来, 刘晓. 浙西地区奥陶系砚瓦山组瘤状灰岩及其成因探讨*[J]. 古地理学报, 2009, 11(5): 481-490.