摘要： 鄂尔多斯盆地中东部奥陶系马家沟组马五₆亚段硬石膏产状类型多样,基于系统的宏观与微观岩石学分析,识别并区分出星散状(A1型)、纹层状(A2型)、致密块状(A3型)、结核状或团块状(A4型)、鸡雏状或角砾状(A5型)等硬石膏产状类型。单井高频旋回和微相分析表明,马五₆亚段发育与潮坪、潟湖、鲕粒滩、砂屑滩、微生物丘等有关的5种高频向上变浅序列,硬石膏的产状类型、产出位置和分布形式等与向上变浅序列有很好的耦合关系。A1型和A2型硬石膏发育于高频向上变浅序列的下部和中部,主要与膏云质或云膏质潟湖相关,属于潟湖相原生化学沉积成因。A3型硬石膏分布于高频向上变浅序列的上部,受膏质潟湖控制,也属于原生化学沉积成因。经典的结核状硬石膏(A4-1)呈随机分布形式产于潮坪沉积序列,为成岩期交代作用或者膏化作用成因,与传统萨布哈交代成因的膏质结核相似。A4-2型硬石膏主要出现在颗粒岩和微生物岩中,主要由富含CaSO₄的下渗卤水在溶蚀孔洞中沉淀形成;A5型硬石膏发育于向上变浅序列的上部和顶部,与高频暴露有关,为准同生期以溶蚀—充填为主的岩溶改造成因。发育完整的单个高频旋回,大致经历了高频快速海侵早期、高频快速海侵晚期至缓慢海退早期、高频缓慢海退晚期和高频海退末期暴露4个演化阶段,形成了与之耦合的海相碳酸盐岩与硬石膏共生序列。这些认识将对马家沟组沉积古环境的再认识具有重要的参考意义。

关键词: 硬石膏, 产状类型, 向上变浅序列, 马五₆亚段, 鄂尔多斯盆地

Abstract: There are diverse anhydrite in Ma5₆ submember of Ordovician Majiagou Formation in central and eastern Ordos Basin. Based on systematic macroscopic and microscopic petrography analysis,different types of anhydrite were identified and distinguished,such as scattered(A1),laminar(A2),dense massive(A3),nodular or clumpy(A4),squiggly or brecciated(A5).The analysis of high frequency cycles and microfacies of a single well showed that five kinds of high-frequency,shallowing-upward sequences were developed in the Ma5₆ submember,which are respectively related to tidal flat,lagoon,oolitic shoal,Fragmental shoal and microbial mound. It was found that the occurrence type,production position and distribution form of the anhydrite had a good coupling relationship with the shallower sequences.Type A1 and A2 anhydrite occur in the lower and middle part of the high-frequency,shallowing-upward sequence,which is mainly related to the dolomite lagoon or gypsum lagoon,and belongs to the primary chemical sedimentary origin of the lagoon facies. The A3 type anhydrite is distributed in the upper part of the high-frequency,shallowing-upward sequence,which is controlled by the gypsum lagoon,and also belongs to primary chemical sedimentary origin. The classic nodular anhydrite(A4-1)occurs in tidal flat sedimentary sequence in a random distribution form,and is caused by diagenetic metasomatism or gypsification,which is similar to the traditional sabha metasomatism gypsum nodules.A4-2 anhydrite mainly occurs in grainstone and microbialite,and is mainly formed by precipitation of CaSO₄-rich subsurface brine in dissolution pore and small caves.A5 type anhydrite occurs at the upper and top of the shallowing-upward sequence,which is related to high frequency exposure and is caused by karst transformation of dissolution and filling in the syngenetic period.A fully developed single high-frequency cycle has roughly experienced four evolutionary stages: early high-frequency rapid transgression,late high-frequency rapid transgression to early slow regression,late high-frequency slow regression,and exposure at the end of high-frequency regression,which formed a coupled marine carbonate and anhydrite co-occurrence sequence. These understandings will have important referential significance for the re-understanding of the sedimentary paleoenvironment during the deposition of the Majiagou Formation.

Key words: anhydrite, occurrence types, shallowing-upward sequence, Ma5₆ submember, Ordos Basin

中图分类号: 

• P588.2