摘要
广西的一些重要泥盆系剖面如横县六景、环江北山、永福凤凰和军屯、象州大乐、罗城龙岸,融安古当等都有明显的白云岩化。1984年作者之一得到部、局批准在广西石油队、区调队、科研所野外工作的基础上选取了256块标本带到英国作进一步研究(图1)。 在显微镜鉴定的基础上,对其中沉积成岩环境特别有意义的82块标本,在伯明翰大学进行了计点的统计分析、阴极发光分析、X光衍射分析。电子探针分析、电子显微镜扫描、背散分析、以及原子吸收光谱分析和酸不溶残余物分析;
There are mainly three types of dolomitization in Devonian carbonates in Guangxi. Their different δ(18)O, δ13C values and contents of trace elements , Na+, Sr++, Mn++, Fe(++), indicate clearly the differentiation of sedimentary environments and diagenetic process.
TYPE Ⅰ In this type of dolomite , δ18O values are from-3.961‰ to-5.498&, averagely-3.816‰. However, that of the contemporaneous dolomite is -3.861‰, diagenetic dolomite, -3.961‰, higher than the former. The δ13C values are all negative , varying from -0.806‰ to -3.583‰. This type of dolostones and their parent rocks were reefs or organic banks originally at the margin of the carbonate platforms , affected by the meteoric -sea water mixing zone.
TYPE Ⅰ δ18O values are less than those of Type Ⅰ , from -5.110 to-8.210‰, averagely -7.516‰, those of the parent micrite, -3 . 840‰to -8.21 ‰, δ13C values vary from -4.304 to +4.348‰. The sedimentary environments was semiclosed or closed back reef basins, the dolomicrite or micritic dolostone containing evaporate minerals were formed there during dry period of time, nevertheless, during the wet seasons , under the affection of the mixing zone of meteoric and sea water.
Type Ⅰδ18O values are from -7.681 to -10.762‰, averagely -8.519‰; those of parent limestome are -4.781‰ to - 7.414‰ averagely -6.098‰ . δ13C values vary near zero, from -1.100 to +0.433‰. The sedimentary environment was intertidal flat or the upper part of shelf, where the biomi-crite and biopelintrasparite were dolomitized under the affection of the mixing zone of meteoric - sea water.
