Ordovician System in Keping area of Northern Tarim Basin is dominated by carbonate sediments and can be divided into platform and platform-basin factes zones and subdivided into five different factes types: restricted platform

open platform

platformmarginal shoal

neritic shelf and basin.Geochemical analyses indicates that geochemical characters are closely related tosedi-mentary environment in the study area:1.Different factes types have different geo-chemical characters

the contents of elements K

Na

Fe

Al and trace elements Sr

Ba

Mn

V

Niand B are low in the platform factes zone

but increase largely in the platformbasin factes zone

e. g.

the everage content of K is less than 0.01% in the platform factes zone

and it is 0. 95% in the platform-basin factes zone.2.The everage Sr contentand Sr/Ca×1000 ratio tend to increase gradually from restricted platform→open platform→platform marginal shoal→neritic shelf→basin

the ratio increases from 2.9→3.8→5.3→6.0→6.4. The author agrees with J. Veizer at al that this is related to differentprimary carbonate minerals in different sedimentary environments.