珠江口盆地珠江组碳酸盐岩阴极发光特征及成岩阶段划分

Cathodoluminescence features and diagenetic stage division of carbonates in the Zhujiang Formation,Pearl River Mouth Basin

通过精细岩石学特征研究和阴极发光技术,研究珠江口盆地珠江组碳酸盐岩阴极发光特征并进行成岩阶段划分。结果表明:①珠江组碳酸盐岩总体具有较弱的阴极发光,海相流体在成岩过程中发挥了主导作用,少数样品具有强—极强的阴极发光,表明其局部受到非海相流体的强烈改造;②在相同的阴极发光条件下,不同的岩石类型显示出不同的阴极发光特征:生物礁灰岩具有极弱—不发光和强—极强阴极发光2个极端端元式的分布特征,白云岩化礁灰岩总体表现为极弱的阴极发光,生物碎屑灰岩以极弱—不发光特征为主,少数陆源碎屑矿物含量高的显示出极强的橘黄色阴极发光,白云岩化生物碎屑灰岩大多表现为白云岩化部分具有极弱—无阴极发光,而未白云岩化部分具有中等—强阴极发光;③方解石胶结物生长期次为纤维状/叶片状方解石—马牙状方解石—粒状(或块状)方解石—充填裂缝或沿缝合线分布方解石,其中纤维状、叶片状环边方解石普遍无阴极发光;④根据不同成岩环境胶结物组构类型及其相应的阴极发光特征分析,将珠江组碳酸盐岩成岩阶段划分为准同生—同生阶段、早成岩阶段和中—晚成岩阶段。

Based on detailed petrographic and cathodoluminescence analysis,the cathodoluminescence characteristics and diagenetic stage division of carbonates in the Zhujiang Formation of the Pearl River Mouth Basin were studied. The results show that:①Carbonate minerals of the Zhujiang Formation generally emit weak CL indicating the leading role of seawater during diagenesis of Zhujiang Formation carbonates;while some samples show strong-very strong CL,which was locally influenced by non-marine fluids. ②Different rock types exhibit different CL features under the same conditions of cathode.Reef limestone are with two end-member CL of very weak-no visible or strong-very strong CL,whereas dolomitized reef limestone emits extremely weak CL. Bioclastic limestone are characterized by very weak or no CL in general,but a few samples with terrigenous minerals show strong orange CL,while bioclastic dolomitized limestone shows the features of very weak or no CL with dolomite and weak-strong CL with non-dolomitized parts. ③Three or four phases of calcite cements development are recognized in turn:fringing fibrous calcite(or bladed spar calcite)-scalenohedral calcite-equant or blockycalcite-calcite filling in micro-fractures or distributing along the stylolites. Fibrous or annular leaf calcite commonly has no CL. ④ Diagenesis of Zhujiang carbonates experienced four stages:penecontemporaneous sedimentary,contemporaneous sedimentary,early diagenetic and middle-late diagenetic according to the fabric of cements under different dagenetic stages and environments and their cathodoluminescence characteristics.