Systematic field investigation and thin section observation as well as electron microprobe determination reveal that dolomitization is common in the Changing and Feixianguan formations in Panlongdong

northeastern Sichuan Basin.Various types of dolomites are developed and distributed vertically in obvious zonation.From bottom to top

they are biological clasitic dolomite

reef dolomite

crystalline dolomite

oolitic dolomite and micrite dolomite respectively.Our study showed that three genetic models could account for the formation process of the dolomites

including mixed-water dolomitization

infiltration and circumfluence dolomitization as well as penecontemporaneous dolomitization.The biological clasitic and reef dolomites were mainly formed through the mixed-water dolomitization

which occurred in relatively open diagenesis environment with meteoric water input.These dolomites had different δ

13

C values and more negative δ

18

O values and remained original sedimentary structure of rocks which restricted dolomitization.The infiltration and circumfluence dolomitization resulted in the formation of the crystalline and oolitic dolomites which have same δ

13

C values

less negative δ

18

O valuse

Fe and Mn contents.The penecontemporaneous dolomitization created the micrite dolomite with tight lithology and less negative δ

13

C and δ

18

O values.