ORDOVICIAN STRATA IN THE NORTHERN PARTS OF THE GREATER AND LESSER KHINGAN MOUNTAINS, NORTHEAST CHINA

In 1979--1982, the author investigated the Ordovician strata in the northern parts of the Greater and Lesser Khingan Mountains. Based on fos- sils and rock characters the strata may be divided into eight formations in ascending order as follows, 1. Kunashenhe Formation It is composed mainly of sandstone intercalated with pyroclastic rocks, no fossils being found, with a thickness of about 560 m. 2. Huangbanjishan Formation It is composed mainly of siltstone and slate, bearing fossils such as bra- chiopods, trilobites and gastropods. Brachiopods are characterized by abundant Finkelnburgia battsi and F. bellatula. Trilobites include Ceratopyge and Apato- kephalus. Thus a late Tremadocian age should be assigned to this formation. Its thickness is about 300m. 3. Dazhi Formation It is composed mainly of acid tuff and calcareous tuffaceous sandstone bearing a lot of fossils, including brachiopods, graptolite and trilobites, among which the brachiopods include Fistolongonites, Orthambonites, Productorthis, Platystrophia, Diparelasma, Virgoria, Ingria, and Sinorthis. Therefore, the Dazhi Formation should be of Arenigian age, about 35m thick. 4. Xiqiuhe Formation It consists mainly of slate, tuff and sandstone, containing a lot of fossils, including brachiopods, graptolites, trilobites and bryozoans. The brachiopod assemblage of the Xiqiuhe Formation is similar to that of the Dazhi Forma- tion. But in the former formation, Axonolipa Phyllograptus, Dictyonema and Ptilograptus are mixed with Axonophora Climacograptus and Glyptograptus. the age is Arenigian to Llanvirian. About 380m thick. 5. Tongshan Formation It is composed mainly of tuff, fine-grained sandstone and siltstone inter- calated with lavas, containing a lot of fossils inducting brachiopods, graptolites and trilobites The Llandeilian age of the Tongshan Formation is determined by the brachiopod Formatiorthis the graptolites Glyptograptus, Dicellograptus and Climacograptus and the trilobites Trinodus, Encrinurus Endolaties the thickness is about 400 m. 6. Duobaoshan Formation It consists mainly of volcanic breccia,intermediate agglomerate and inter- mediate-acid lavas and tuffs. containing brachipods such as Leptellina, Titamb- onites and Glyptomena. trilobites such as Remopleurides and Geronostus,anthoz- oans and criboid stems, indicating an early Caradocian age, about 750 m thick. 7. Luohe Formation and Zhinishan Formation These two formation are synchronous and synonymous, and occur in different areas. The Luohe Formation is found in the northwestern part of the Lesser Khingan Mountains,The Zhthishan Formation occurs in the eastern part of the Greater Khingan Mountains. They are composed mainly of siltstone and fine-grained sandstone intercalated with slate, rich in fossils of brachiopods, trilobite, graptolites, gastropods bryzoans, anthozoans, crinoid stems and conodonts Among them, the brachiopods include Gunnarella, Lepta- ena, Viruella, Austinella, Paucicura, Glyptorthis, Hesperorthis and Taphorthis, and the conodonts includes Panderdus similaris. These formation should be assigned to late Caradocian age. Their thickness may range from 300--700m. 8. Aihui Formation It is represented mainly by slate, siltstone and fine-grained sandstone, containing trilobites, corals, graptolites such as Pleurograptus, Orthograptus and Pseudoclima cograptus, and to Caradocian-Ashgillian age. brachiopods such as Dedzetina, Dalmanella, Leptaena, Fardenia, Luhaia, Ravozetina and Philgedera. It is of late Caradocian to Ashgillian age. Its thickness is about 160--200m. Their contacts are conformable except for the Huanbanjishan and Dazhi Formations which show no direct contact relationships.