云南广南早二叠世生物礁的基本特征及其造架生物——串管海绵化石

在我国西南南盘江地区广泛分布着二叠系生物礁。可分为两种类型:1)堤礁;2)孤立礁。前者一般沿碳酸盐台地的边缘分布,后者发育于盆地内孤立碳酸盐台地的边缘。广南生物礁的礁后灰岩由浅灰色块状骨架岩组成。造架生物以串管海绵、纤维海绵、tabulozoans等为主,往往有蓝绿藻包覆。骨架生物之间有极为发育的纤状方解石胶结物。本文共描述了串管海绵8属12种,它们是Waagenella salinaria irregalaris Zhang,Waagenella sp., Rhabdactinita of columnaria Yabe and Sugiyama, Rhabdactinia sp., Intrasporeocoelia hubeiensis Fan and Zhang,Intrasporeocoelia sp., Uvanella guangnanensis sp. nov., Girtycoelia sp., Colospongia of dubia Laube, Colospongta sp., Verticillites sp.,Lichuanospongta typica Zhang.

ON THE MAIN FEATURE OF LOWER PERMIAN REEFS IN GUANGNAN COUNTY, SE YUNNAN PROVINCE AND THEIR FRAME-BUILDING ORGANISMS——SPHINCTOZOANS

Permian reefs are widely distributed in the so-called Nanpan Jiang(Nanpan River)re gion in the neighboring parts of eastern Yunnan, southwestern Guizhou and northwestern Guangxi, Two types of reef occurrences are recognized by their stratigraphic and geographical distributions, 1)a barrier reef belt along a carbonate platform margin and 2)reefs that rim isolated carbonate platforms that occur irregularly within basin facies deposits. The Guangnan recfs. of lower Permian age occur within the barrier reef belt and are typical of reefs within the Nanpan Jiang area. These reefs are well-exposed at Dongnameng, a small village about 5 km southeast of Guangnan City and crop out on the west flank on the Guangnan anticline which has been truncated by a major fault. Basin facies deposits occur east of the fault and equivalent carbonate platform depsosits occur west of the fault.A succession of reefs occurs in the late early Permian Maokou Formation and early late Permian Wujiaping Formation. The top of the upper Permian sequence is cut out by faults on the Guangnan anticline and elsewhere is directly overlain by middle Triassic rocks. The preserved upper Permian part may be equivalent to the Wujiaping Formation. The major time of reef development, however, was during early Permian.The reefs have foundations of light gray, thick-bedded, intraclastic-bioclastic grainstones that contain abundant fossils of shallow-water benthic organisms. These limestones represent subtidal bank deposits at the platform margin and functioned as foundations for most of the Permian reefs in the Nanpan Jiang area. Reef limestones consist of light gray, massive, fra-mestones with distinctive textures and abundant fossils. Frame-building organisms are sphinc-tozoans, inozoans, tabulozoans, bryozoans and hydrozoans. Frame-building organisms total 40-50% of the volume of the reef masses. Binding organisms are dominantly blue green algae, with subordinate fistuloporid bryozoans and Tubiphytes. Accessory organisms include echinoderms, fusulinids, gastropods, brachiopods, calcareous algae and foraminifers as skeletal debris. The frame-building organisms are generally encrusted by lamellar blue-green algae, which commonly are incorporated fine-grained skeletal fragments. Well developed fibrous cal-cite cement fills between frame-building organisms to form a typical framestone texture.Gray, thick-bedded, bioclastic packstones and wackestones overlie the reefs. This stratigra-phic relationship suggests that reefs were drowned and that reef development ceased because of the increasing depth.Twelve species of 8 genera of sphinctozoans are described in the present paper. These include: Waagenella salinaria irregularis Zhang, Waagenella sp., Rhabdactinia cf. columnaria Yabe and Sugiyama, Rhabdactinia sp., Intrasporeocoelia hubeiensis Fan and Zhang, Intrasporeocoelia sp., Uvanella guangnanensis sp. nov., Ginycoelia sp., Colospongia cf. dubia Laube, Colospongia sp., Verticillites sp., Lichuanospongia typica Zhang, and of these Uvanella guan-gnanensis is a new species.Two sizes of sphinctozoans can be differentiated in the collections. The smaller genera include Waagenella, Colospongia, Ginycoelia, and Uvanella. They also make up a smaller volumes of the reefs, as compared to the larger forms such as Intrasporeocoelia and Rhabdactinia. The large sphinctozoans are abundant and baffled lime muds during growth of the reefs. All of the sphinctozoans mentioned above also occur in upper Permian reefs of the Lichuan district of west Hubei Province but the diversity in the Nanpan Jiang reefs is much less than in reefs in the Lichuan district. The sphinctozoan faunas from Guangnan may be compared with those of lower Permian reefs in the Bled district of Yugoslavia.