Middle-Upper Cambrian dolomites in Shimen

Hunan Province

are mainly composed of anhedral micritic dolomite

euhedral and subhedral granular dolomites

grain dolomite.Different kinds of dolomites formed in different environments may have different models of dolomitization.The anhedral micritic dolomite shows a lower ordering degree (average 0.71)

a higher CaCO

3

mole content (average 50.83%)

higher δ

13

C and δ

18

O values (average+0.26‰ and-6.95‰PDB)

a higher Sr

2+

content and non luminescence.Grain dolomitehas a higher ordering degree (average 0.87)

a lower CaCO

3

mole content (average49.4%)

lower δ

13

C and δ

18

O values (average-0.87‰ and-9.5‰ PDB)

and a lower Sr

2+

content.The euhedral and subhedral granular dolomites

who's ordering degrees

δ

18

O and δ

13

C values

Sr

2+

content are samilar to grain dolomite

has a dark red to red in lumi-nescence.All evidences show that there were three origins of the dolomites in the study area.Anhedral micritic dolomite formed in high-magnesium water in tidal flat;grain dolomite formed in shoal mixing water;euhedral and subhedral granular dolomites were the products of dolomitization in deep burial mixing water.