川南马边县老河坝剖面麦地坪组小壳生物地层特征及意义  

SMALL SHELLY FOSSIL BIOSTRATIGRAPHY OF THE MAIDIPING FORMATION IN MABIAN, SOUTHERN SICHUAN PROVINCE

作　　者：胡强 庞艳春[1] 冀文虎 梁思雨 何阳剑 张梦韶 HU Qiang;PANG Yan Chun;JI Wen Hu;LIANG Si Yu;HE Yang Jian;ZHANG Meng Shao(Institute of SedimentaryGeology,Chengdu University of Technology,Chengdu610059)

机构地区：[1]成都理工大学沉积地质研究院,四川成都610059

出　　处：《地层学杂志》2022年第3期245-254,共10页Journal of Stratigraphy

基　　金：国家自然科学基金(41872007);四川省科技计划项目(2018JY0491)共同资助。

摘　　要：川南马边地区位于扬子地台西南缘,寒武系麦地坪组出露连续,为一套含磷、硅的碳酸盐岩。麦地坪组可明显分为两段:一段主要为浅灰—灰黑色砂砾屑磷块岩、磷质白云岩和条带状含磷白云岩;二段主要为灰—灰黑色砂砾屑灰岩、泥晶灰岩和瘤状灰岩。该组小壳化石丰富,自下而上可识别出3个小壳化石带:第一个小壳化石组合带(Anabarites trisulcatus-Protohertzina anabarica组合带)、第二个小壳化石组合带(Paragloborilus subglobosus-Bemella simplex组合带)和第三个小壳化石带(Watsonella crosbyi带)。其中,第一个小壳化石组合带位于麦地坪组一段,第二个和第三个小壳化石组合带位于麦地坪组二段。马边地区小壳化石组合带的特征及与国际寒武系纽芬兰统的对比结果表明,麦地坪组一段和二段下部属于寒武系纽芬兰统幸运阶,麦地坪组二段中上部属于纽芬兰统第二阶。本区发现的Watsonella crosbyi化石仅出现在麦地坪组二段的中上部,具有保存完整、特征明显、时限短、分布广泛等优势。本区小壳化石带的更替及演化序列中,Watsonella crosbyi的首现层位及其所在化石带的生物面貌明显不同于第二个小壳化石组合带,进一步证明了用Watsonella crosbyi的首现作为定义寒武系纽芬兰统第二阶底界的参考标准具有广泛的实用性和可对比性。另外,老河坝剖面的幸运阶与第二阶出露连续且完好,可作为研究幸运阶与第二阶界线的重要剖面之一。The Maidiping Formation at Laoheba section, Mabian County, southern Sichuan Province is composed of phosphorus and silicious carbonates, and is further subdivided ascendingly into Member 1 and Member 2. The Member1 is mainly composed of light gray to grayish black phosphorite, phosphorous dolostone and banded dolostone,and the Member 2 is mainly composed of gray to grayish black clastic limestone, micritic limestone and nodular limestone. Three small shelly fossil(SSF) biozones are recognized for the Maidiping Formation at the Laoheba section,Mabian, which are in ascending order: the Anabarites trisulcatus-Protohertzina anabarica Assemblage Zone, the Paragloborilus subglobosus-Bemella simplex Assemblage Zone, and the Watsonella crosbyi Zone. The A. trisulcatus–P.anabarica Assemblage Zone is recognized in the Member 1, while the P. subglobosus-B. simplex Assemblage Zone and the W. crosbyi Zone in the Member 2. The characteristics of these small shell fossil assemblages in the Mabian area and their correlation show that the Member 1 and the lower part of the Member 2 of the Maidiping Formation correspond to the Fortunian Stage, while the middle upper part of the Member 2 corresponds to the Stage 2 of the Terreneuvian Series.The biostratigraphically diagnostic W. crosbyi is recorded restrictedly in the middle to upper part of the Member 2 of the Maidiping Formation, characterized by complete preservations, distinct morphology, short range and wide geographic distribution. The W. crosbyi Zone shows obvious differences from that of the preceding P. subglobosus-B.simplex Assemblage Zone, confirming that the first appearance datum(FAD) of W. crosbyi can be adopted to define the base of the Stage 2 of Cambrian. In addition, the continuous and autochthonous successions of the Fortunian and the Stage 2 at the Laoheba section may serve as a reference section for the base boundary of the Stage 2 of the Cambrian System.

关 键 词：扬子地台 寒武系 纽芬兰统 麦地坪组 生物地层 Watsonella crosbyi 

分 类 号：P534.41[天文地球—古生物学与地层学]