Well-developed late Precambrian sequenc s with abundant stromatolit s occur in the Beishan Region

which is situated in the border areas b twe n Gansu and Xinjiang. Based on stromatolits

a preliminary of th Beishan Region is make with regions in North China and other parts of Sinkiang. An amendment is proposal for th stratigraphic subdiviaion and of the borders between formamations. The stratigr:phic seluences of this region are as follows: In addition to the stratigraphic sec ious given in detail

the stro. matolites and oncolites ar described sysematically for the first time in the Bishan Region. They total 12 groups and 20 forms with 2 new groups. 8 new forms and 2 unn msd forms. One group and two of oneolite are also described. Three stromatolite assemblages are recognisod. Th one in the Jixian System consists of Lower and upper two subassemblages. The lower subas- semblage yields:Cryptozoon for. Pseudoeryptozoon subeiense (gr

et for nov.) etc: the upper subassemblage is very abundant and is represented by Conophyton. codomenia

including Conophyton distortum(for. nov.) Con. subeiense (for

nov

) Con. cylindricum

Fusunis bintoushanensis (gr. et for. nov.) Baicalia rara

B. minuta

Collenia undosa etc. The stromatolite assemblage of Dahuoluoshan Group in th chingbaikou System also consists of Lower and upper two subassemblages. The lower subassemblage

represented by Linella.Boxonia

contains Linella beishanensis

L. strumosa (for. nov. ). Inzeria? tjomusi

kotuikania cf. torulosa

Baicalic baicaliea etc.: The upper subassemblage isrepresented by Scopulimorpha- Gymnosolen

including

Scopulimorpha regularis

S

unka

Conophyton acthum (for. nov.) C. for.

Tungussia for.

Paracolonnella shuangyinaha. nensis (for. nov.)

Gymnosolen of. loves

G. ramsayi etc. Oncolites pre present in this subassemblage

namdy. Osagia simplex (for

onv.)

Osagia eylindrica (for. nov.) etc. The above-mentioned stromatolite assemblages are similar to a certain extend to those from Yenshan and E. Liaoning of North China and areas in Anhui and Jiangsu. They also show similarities with some forms found in Pal- gan in eastern Quruq-tagh

Sinkiang. The assemblage of Pingtoushan Group in Jixian Syatem is compared roughly to the atromatolite assemblage No. IV from the Yenshan areas. In the Beishan region

however

there exist some new forms so far unknown in E. china. On the other hand

small collumnar stromato- lites such as Paeudogymnosolen etc. common in E. China are unkne n in the Pingtoushan Group

and non of th common forms such as Jurusania

Katavia etc. of the Chingpaikou System including Lianan Sys em have been found in the Beishan Region. Some of the stromatolites in Beishan occur in horizons which do not correspond stratigraphically to those of E. China

e

g

the Group Scopulimorpha occurring in Tieling Formation of top Jixian System

whereas in Beishan region it occurs in the upper part of the Chingbaikou Syst m in asso- eiation with Gymnosolen. All this shows that owing to the insufficeney in the stromatolite study in China

thcugoh rough correlations by stromatolites can be made stratigraphically and geochrenologically between different tectonic units

significant differences do exis in the composition of ass mblages and in their evolution

which still awaits further study. as yet

detoiled stratigraphic corre laticns have ptoved effective only within restricted regions