STRATIGRAPHICAL CLASSIFICATION AND CORRELATION OF THE UPPER PRECAMBRIAN IN DONGCHUAN, YUNNAN

Dongchuan is the key area in the study of the upper Precambrian of Sichuan and Yunnan, where the upper Precambrian are widespread. The Kunyang Supergroup of Dongchuan may be subdivided in descending order as follows: Sinian System: Dengying Fm. Grey, grey-white siliceous dolomite Unconformity Upper Precambrian Kunyang Supergroup Dongchuan Group 10. Madi Fm.: Dark grey, greyish-white thin-to medium-bedded banded 1imestone intercalated with slate and marble; stromatolite Schancharia tenu- iseptata Kor. found. Thickness 800-1480m. 9. Xiaohekou Fm.: Upper part, yellowish-green, greyish-green spilite interbedded with thin-to medium-bedded metamorphosed quartzose sandstone, thickness 200-310m: lower part, grey, greyish-white medium-to thick-bedded quartzite, Thickness 400-2300m. 8. Liubatang Fm. （Dayingpan Fm.）: Black, greyish-black, dark-grey tbin-bedded carbonaceous slate, banded slate, phyllite and phyllitic slate inter- calated with argillaceous dolomite, marls and quartzose sandstone; slate con- tains microplants Trachysphaeridium rude Sin et Liu, T. minor Sin et Liu, T. incrassatum Sin, Pseudozonosphaera asperella Sin et Liu, Asperatopso- phosphaera partialis Schep. and A. incrassa Wang. Thickness 3100--5000m. 7. Luzhijiang Fm. （Qinglongshan Fm.）: Greenish-grey medium-to thick- bedded dolomite intercalated with marls and slate; contains stromatolites Conophyton garganicus Kor., C. cf., oncoliths Qsagia cf., microplants Aspe- ratopsophosphaera umishanensis Sin et Liu and Taeniatum crassum Sin et Liu. Thickness 500--1800m. 6. Etouchang Fm. （Heishan Fm.）: Upper part, black thin-bedded car- bonaceous slate intercalated with tuffaceous sandstone; middle part, darkgrey thin-to medium-bedded marls, limestone and argillaceous dolomite; lower part, grey-black bark-grey thin-bedded slate intercalated with blue-greyish slate clay. Total thickness 1110-1635m. Yields microplants Asperatopsophosphaera incrassa Wang and Taeniatum crassum Sin et Liu. Isotopic age 1163 and 1020 Ma. 5. Luoxue Fm.:: Greenish-grey, light-red, thick-bedded dolomite; the basal part thin-bedded sandy and argillaceous dolomite. Thickness 40-500m. Contains stromatolites Paniscollenia emergens Komar, Collenia columnaris Fe- nton et Fenton, Pseudogymnosolen mopanyuensis Liang et Tsao, Paraconophy- ton tangdanensis Cao and Paracolonnella laohudingensis Liang et Tsao in Tangdan, Conophyton garganicus var. nodicus Komar. Raaben et Semikhatov in Luoxue and Gymnosolen asymmetrica Raaben in Tuobuka, and microplants Taeeniatum crassum Sin et Liu, Asperatopsophosphaera umishanensis Sin et Liu and Trachysphaeridium simplex Sin. Isotopic age 1039 Ma. 4. Yinmin Fm.: Purplish-grey, purple thick-bedded slate intercalated with dolomitic sandstone and argillaceous and sandy dolomite. Thickness 100-360 m. Contains microplants Taeniatum crassum Sin et Liu and Asperatopsophosphaera umishanensis Sin et iiu. Isotopic age 1330 Ma. Unconformity Yuxi Group 3. Meidang Fm.: Yellowish-green, greyish-black sericite slate intercalated with marls, calcareous slate, dolomite and quartzose sandstone. Calcareous slate became hollow slate after weathered, Thickness 286. 4-1450m. Yields micro- plants Taeniatum crassum Sin, Trachysphaeridium incrassatum Sin, T. rude Sin et Liu, T.rugosum Sin and Pseudozonosphaera sinica Sin. 2. Dalongkou Fm.: Grey, dark-grey micrite and dolomite intercalated with minor sericite slate. Contains stromatolites Conophyton cylindricus Maslov, C. lituus Maslov and Boxonia cf. Thickness 640m. 1. Heishantou Fm.: Grey, greyish-black quartzose sandstone, quartzite and siltstone intercalated with phyllite, slate, limestone and dolomite; rhythms and banded structure developed. Thickness 440-947 m.