冰川型海平面变化控制下的台地碳酸盐岩成岩作用:以陕西镇安西口石炭-二叠系界线剖面为例

Carbonate Diagenesis Controlled by Glacioeustatic Sea-Level Changes:A Case Study of the Carboniferous-Permian Boundary Section at Xikou,Zhen'an County,Shaanxi Province,China

以陕西镇安西口石炭-二叠系界线剖面为具体实例,探讨了冰川型海平面变化控制下的台地碳酸盐岩成岩作用规律.描述了陕西镇安西口石炭-二叠系界线剖面碳酸盐岩的各种成岩作用类型.根据成岩组构将研究区碳酸盐岩的成岩环境分为海水、大气淡水和埋藏环境.综合分析了各种成岩作用及其成岩环境的纵向分布特征.研究表明,剖面上碳酸盐岩成岩作用和成岩环境的特征与岩石在高频旋回中的相对位置存在明显的对应关系,受大振幅、高频率的冰川型海平面变化控制.早期海平面相对上升,形成旋回的下部单元,岩石首先经历海底成岩作用,随着上覆沉积物的增加,逐渐进入浅埋藏环境,成岩作用表现为以压溶、重结晶作用发育为主要特征.晚期形成旋回的上部单元,由于海平面相对下降,沉积物逐渐抬升,早期海底成岩作用尚未充分发育就脱离海水环境,进入大气淡水成岩环境,以强烈的大气淡水成岩作用为特征.

Based on the case study on the platform-facies carbonate rocks of the Carboniferous-Permian boundary section being well developed and outcropped in Xikou, Zhen＇an County, Shaanxi Province, China, this paper probes into the carbonate diagenesis controlled by glacioeustatic sea-level changes and its different patterns. In terms of mineralogical composition and microfabrics, diagenetic environments in the study area are divided into marine, near surface meteoric and burial environments. Comprehensive analysis is made on all patterns of carbonate diagenesis and the vertical distribution features of diagenetic environments. The analytical results reveal that carbonate diagenesis in the Carboniferous-Permian boundary section is related to the relative stratigraphic position of the rocks in the depositional cyclothem and is controlled by the glacioeustatic sea-level changes. There are distinctive differences in diagenetic patterns between lower transgressive sequence and upper regressive sequence in a cyclothern. The former is mainly characterized by pressure solution and recrystallization of mudstone and wackstone in burial environments, while the latter by cementation and leaching of freshwater in meteoric environments.