The paleoenvironment of Ordovician in southwestern Ordos basin are discussed by using both inorganic and organic parameters

trying to identify potential hydrocarbon source rocks.In the strata with TOC

>

0.2%

V/(V+Ni)

>

0.50

Zr/Rb

<

2

Rb/K

>

30×10

4

Z

>

122

Zn

Mo and Ba are enriched

and the δ

18

O and δ

13

C

carb

have positive excursion.These characteristics indicate a stagnant and anoxic sedimentary environment with higher organic matter productivity and better preservation condition.These strata have δ

13

C

org

<

-28‰(iv- type kerogen)

and high hydrocarbon-generating potential

so they can be regarded as potential hydrocarbon source rocks.The strata with TOC≤0.2% whose inorganic and organic parameters show a high energy

oxic

littoral-neritic environment with δ

13

C

org

between-24% and-28‰(( type kerogen)have low hydrocarbon-generating potential.Such environment is unfavorable for preservation of organic matters

and development of hydrocarbon source rocks.The integration of inorganic parameters(trace element

stable isotope composition etc.) with general organic data can be regarded as important environmental factors for identifying development of effective marine hydrocarbon source rocks.