Unconformity between the Upper and Lower Paleozoic is absent from Leping of Jiangxi all the way upward, on the southeastern margin of the Yangtze platform. According to a number of Caledonian unconformities discovered recently, combined with an analysis of two phases of strong fold deformation in the Lower Paleozoic, this paper demonstrates that Caledonian folds occur in the northern segment (Zhejiang-Anhui-Jiangxi border region) of the southeastern margin of the Yangtze platform.
On the basis of the Mesoproterozoic Mengshan section in the Pujiang area of Zhejiang Province,the authors have estabilished two lithostratigraplic units and their stratotypes:Mengshan Formation and Chentangwu Formation.These two formations belong to the Pingshui Group.The lithostratigraphic unit of the Pingshui Group is reviwed and revised.The lower part of the Pingshui Group is represented by the Mengshan Formation(spilite-keratophyre)and the upper part by the Chentangwu Formation(marina facies sand-mudstone).The Pingshui Group is conformably overlain by the Shuangxiwu Group,but it lower boundary is not exposed.The Pingshui Group is the oldest basement rocks in northwestern Zhejiang.Microfloras and isotope ages in the stratotype section suggest that the Pingshui Group is Mesoproterozoic in age.Based on study and analysis of sequence stratigraphy and lithochemisty of the stratotype section the spilite-keratophyre of the Pingshui Group was formed in an island arc environment.
The paper reports Early Paleozoic palynomorphs from the Early Cambrian Hetang Formation,the Late Cambrian Huayansi Formation,the Early Ordovician Ningguo Formation,the Late Ordovician Changwu Formation and Wenchang Formation,the Early Silurian Xiaxiang Formation,Helixi Formation and Kangshan Formatiom,and the Middle Silurian Tangjiawu Formation in northwestern Zhejiang Province.These fossils include acritarchs and cryptospores assigned to 66 genera,112 species and 31 undetermined species.The geologic age and depositional environments of these palynomorph assemblages are discussed.
The Zhejiang-Anhui-Jiangxi border region was affected by the South China Caledonian tectonic event in the Caledonian period. As a result, the pre-Sinian basement and earliest Paleozoic cover were strongly uplifted and folded and the Early-Mid Carboniferous strata in the Zhejiang-Anhui-Jiangxi border region directly overlies the Mesoproterozoic low-grade metamorphic series and the Middle Carboniferous in the Qingliangfeng area at the eastern end of the region overlies the Upper Cambrian, but no evidence of Caledonian magmatism is found. In addition, the Sinian-Early Silurian covers on the southern and eastern sides of the craton are detached toward the two sides and overturned together with the basement near the contact zone to form overturned folds. The covers on the northern side are detached toward the north to form slip-superposed folds and the Linxi and Lantian relict synclinal basins. The Indosinian and Yanshanian events significantly modified the Caledonian tectonic features and finally formed the tectonic framework that in the main continues to the present.
This paper introduced sixteen fossil zones (eleven new established fossil zones) of the Upper Carboniferous to Middle Permian in Zhejiang province.The study results showed the fossil zones were distributed in the Laohudong formation, the Huanglong formation,the Chuanshan formation, the Liangshan formation,the Qixia formation, the Gufeng formation and the lower part of Longtan formation,which can be compared with nine stages of the Huashiban Stage,the Dala Stage,the Xiaoyao Stage,the Zisong Stage,the Longlin Stage,the Qixia Stage, the Xiangbo Stage,the Maokuo Stage and the Lengwu Stage.The boundaries of the Upper Carboniferous, the Lower Permian and the Middle Permian were discussed.The authors proposed that the basal boundary of Upper Carboniferous was inexistence and the sediment was lacking in Luosu Age.The basal boundary of Lower Permian was lying at the bottom of the Sphaeroschwagerina subrotunda fusulinid zone based on the standard of the first appearance of the Sphaeroschwagerina genus. Carboniferous-Permian boundary was located between Triticites subcrassulus fusulinid zone and Sphaeroschwagerina subrotunda fusulinid zone.The basal boundary of Middle Permian was lying at the bottom of the Orthotichia chekiangensis brachiopod assemblage zone based on the boundary standard of the first appearance of the Orthotichia chekiangensis.Further research indicated that the Chuanshan formation is a boundary, lithostratigraphic unit which spanned the Carboniferous-Permian.The lower part of it belonged to the Upper Carboniferous Xiaoyao Stage,the middle part belonged to the Lower Permian Zisong Stage and the upper part belonged to the Lower Permian Longlin Stage .
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