OXYGEN AND CARBON ISOTOPIC COMPOSITION AND DIAGENESIS OF CARBONATE ROCKS
(Wang Yinhua Liu Benli Chen Chengye Zhau Xiulian)(Department of Geology, Beijing University)
While taking into consideration the oxygen and carbon isotopic composition controlling and affecting the diagenesis of carbonate rocks, the authors measured δ~(18)O and δ~(13)C values of some samples of modern carbonate sediments from the South China Sea, beach rocks, cave pearls in caves of Holocene carbonate rocks, oolitic limestones and micrites with different degrees of diagenesis, fine-and medium-grained limestones with relict textures, and grey fine-grained and yellow coarsegrained siderite. A comparison of measured data shows that when fresh atmospheric water takes part in the diagenesis, the samples all have higher negative δ~(13)C values and that δ~(18)O shows a trend of changes from lower negative values to higher ones (PDB) with an increase in degree of diagenesis. A study of the trends of changes in δ~(18)O and δ~(13)C of different ore facies of stratified siderite can likewise prove that the above-mentioned trend of changes in δ~(18)O is also present in the ore districts with different degrees of diagenesis and modification, while the δ~(18)O and δ~(13)C values of the ores and various country rocks in the same ore district show marked consistency. Therefore, this preliminary result indicates that the regularity of the changes in δ~(18)O and δ~(13)C can be used not only to determine the degree and nature of diagenesis but also to study the origin of stratabound deposits.