深水碳酸盐岩成岩作用的稳定同位素特征

STABLE ISOTOPIC CHARACTERISTICS OF DIAGENESISIN DEEP WATER CARBONATE ROCKS

稳定同位素方法可以有效地应用于深水碳酸盐岩的成岩作用研究。根据早古生代中扬子台地东南缘斜坡带上碳酸盐岩的氧、碳稳定同位素特征，对几种成岩作用的环境因素和成岩机制进行了研究和探讨：（１）下奥陶统瘤状灰岩瘤体的δ１８Ｏ值均重于基质，证实了瘤状灰岩的早期雏形是灰泥沉积物经海底溶解胶结的反复交替作用而形成的；（２）下寒武统厚层状白云岩具有δ１８Ｏ和δ１３Ｃ值相对集中，且δ１８Ｏ略偏负的特点，而下奥陶统层状白云岩的δ１８Ｏ具有很高的负值，反映了二者分别是高盐度卤水流交代白云岩化和埋藏白云岩化的产物；（３）下奥陶统碳酸盐岩的不同岩石类型或不同结构组分均呈现１８Ｏ明显亏损，而１３Ｃ无明显变化的特征，说明受到了较强的埋藏重结晶作用的影响。

Stable isotopic method can be used effectively in the diagenetic research of deep water carbonate rocks.According to the oxygen and carbon isotopic compositions of the Early Palaeozoic deep water carbonate rocks developed along the southeastern marginal slop of the Middle Yangtze carbonate platform,some diagenetic environments and diagenetic mechanisms are as fallowe:1)the δ 18 O values of nodules of Lower Ordovician nodular limestone are always more positive than those of matrix,suggesting that the prototype of the modular limestone was the product of solution and cementation occurred repeatedly on the sea floor;2)the Lower Cambrian massive dolomite with relatively concentric values of δ 18 O and δ 13 C was the product of high density brine replaced dolomitizatin,whereas the lower Ordovician massive dolomite with high negative δ 18 O value was formed by the deep burial dolomitization;3)Burial recrystallization altered strongly the Lower Ordovician carbonate rocks,and made them to have the same high negative δ 18 O values.