浙江长兴煤山二叠-三叠系混生层1中微球粒的发现及其意义

<正> 浙江长兴煤山是中国南部上二叠统长兴阶和二叠、三叠系界线层型剖面(共A,B,C,D,E,Z六条剖面)的所在地。孙亦因等(1984)在D剖面的界线粘土及其上覆的灰黑色泥岩中发现铱异常,提出了二叠、三叠纪交替时可能发生了一次地外来的陨击事件。然而,人们更关心的似乎是作为铱异常物质来源最可靠证据的宇宙尘或微玻陨石是否也存

Discovery of microspherules from the Permo-Triassic mixed fauna bed No. 1 of Meishan in Changxing, Zhejiang and its significance

The samples described herein were collected from the lowermost part of the lower Triassic Lower Chinglung Formation in sections A and D of Meishan, Changxing, Zhejiang, which can be subdivided into Mixed-fauna Beds of Nos. 1, 2 and 3 ascendingly. More than 198 microspherules are seen only in Mixed-fauna Bed No. 1 (i. e. Bed 23). Judging from the shape, surface texture and chemical composition, they may be grouped into the following five Types: Type 1, cauliflowerklike—acicular spherules; Type 2, pellet-like spherules; Type, 3, flake-like spherules; Type 4, microlite-like spherules; Type 5, smoothlsurfaced spherules. Among them, Types 1, 2 and 3 are of terrestrial origin, while the rest may belong to the impacting bodies of extraterrestrial rare impact event. Finding of microspherules in the Permian-Triassic Mixed-fauna Bed No. 1 at Meishan is the first discovery in the world. Hence, the present discovery not only supports strongly the current hypothesis that the extraterrestrial rare impact event probably happened curing the period from Paleozoic to Mesozoic, but also provides new valuable data for the study of the cause of changes in cnvironment, climate, biomass and the nature of boundary event at that time.