桂西北早、中二叠世常么期和栖霞期含地层及分带

The Permian Changmean Chihsian Fusulinid bearing Strata and the Fusulinid Zones of Northwest Guangxi

桂西北早中二叠世常么期和栖霞期地层为一套浅海碳酸盐岩相连续沉积，其中类化石十分丰富，自下而上可划分为５个化石带、４个亚带：１）Ｐａｍｉｒｉｎａ－Ｓｃｈｗａｇｅｒｉｎａ带（Ｐａｍｉｒｉｎａｐｕｌｃｈｒａ亚带；Ｓｃｈｗａｇｅｒｉｎａｃｕｓｈｍａｎｉ亚带）；２）Ｓｃｈｗａｇｅｒｉｎａｇｕｅｍｂｅｌｉ带；３）Ｃｈａｌａｒｏｓｃｈｗａｇｅｒｉ－ｎａ－Ｒｏｂｕｓｔｏｓｃｈｗａｇｅｒｉｎａ带（Ｃｈａｌａｒｏｓｃｈｗａｇｅｒｉｎａｖｕｌｇａｒｉｓ亚带；Ｒｏｂｕｓｔｏｓｃｈｗａｇｅｒｉｎａｌｏｎｇｌｉｎｅｎｓｉｓ亚带）；４）Ｂｒｅｖａｘｉｎａｄｙｈｒｅｎｆｕｒｔｈｉ带；５）Ｍｉｓｅｌｉｎａｃｌａｕｄｉａｅ带。同时对命名地点常么组的定义、时代及岩相特征、生物群面貌进行了讨论。

Marine Early and Middle Permian strata (Changmean-Chishsian) are fully developed in Northwest Guangxi.They contain rich fossils,including fusulinids,foraminifers,corals,brachiopods,etc.The Changme section is composed of grey and light grey crystalline thick bedded to massive limestones.It can be divided into two formations,comprising five fusulinid zones and four subzones: 1) Pamirina Schwagerina Zone This zone (Beds 8—12, 30.2m thick) is characterized by the presence of Pamirina pulchra Schwagerina cushmani fauna.They have a smaller and tightly coiled shell,such as Pamirina,Biwaella,Minojapanella,Staffella,Darvasites,Schwagerina and Schubertella. The fusulinid fauna shows an even greater diversity of genera and species,marking a full flourishing period in the course of fusulinid evolution. 2) Schwagerina guembeli Zone The first appearance of Schwagerina guembeli marks the base of this zone (Beds 13—14, 14.4m thick).Fusulinids of this zone are dominated by Schwagerina, in association with Pseudofusulina,Rugosofulina,Paraschwagerina,Chalaroschwagerina and Laxifusulina, the latter two of which are the newly occurring forms.In this zone the schwagerinids are of more advanced types with larger shells and much stronger septal fold. 3) Chalaroschwagerina Robustoschwagerina Zone This zone (Beds 15—19, 26.9m thick) is characterized by the first appearance of Robustoschwagerina longlinensis and Chalaroschwagerina vulgaris. In this zone the Robustoschwagerina are of the more advanced types with larger shells,very well developed chomata in the juvenarium; Chalaroschwagerina are larger,whorls loosely coiled,spirotheca thicker,proloculus large,strong and complex septal folds. 4) Brevaxina dyhrenfurthi Zone This zone (Beds20—21, 10.8m thick) is characterized by the presence of Brevaxina dyhrenfurthi, which has well developed parachomata and foramina throughout most part of the shell,in association with Misellina,Minojapanella,Pseudofusulina,Schubertella and Staffella etc. 5) Misellina claudiae Zone The first appearance of Misellina claudiae marks the beginning of this zone,in which the fusulinid generic assemblage is similar to Brevaxina otakiensis (Beds 22—25, 28.7m thick). The Pamirina Schwagerina Zone,the Schwagerina guemberli Zone and the Chalaroschwagerina Robustoschwagerina Zone belong to the Early Permian Changme Stage.The Brevaxina dyhrenfurthi Zone and the Misellina claudiae Zone belong to the Middle Permian Chihsia Stage.