四川龙门山马角坝组铁质鲕粒成因及沉积环境

Genesis and sedimentary environments of the ferruginous ooids from the Majiaoba Formation in northern Longmen Mountains,Sichuan

本文应用显微镜和扫描电镜对下石炭统马角坝组顶部的铁质鲕粒的研究发现:铁质鲕粒由核心和同心圈层组成,核心成分主要是赤铁矿碎屑和石英颗粒,圈层厚度较小,整体呈胶状形态,由赤铁矿围绕核心呈致密板状平行排列,整体上结构一致;铁质鲕粒是在适合的pH、Eh条件下,大量铁质围绕石英碎屑或矿物碎屑转动时胶体沉积形成的,沉积环境为潮间-潮下的浅水动荡环境,是大规模海退暴露后海平面初始上升期的产物。

The ferruginous ooids from the Majiaoba Formation in northern Longmen Mountains, Sichuan consist of nuclei and concentric circles on the basis of the microstructures indicated by microscope and SEM examination. The nuclei are composed of hematite and quartz in colloids, whereas the concentric circles comprise hematite with the thickness of 3 - 5 um in densed tabular parallel arrangements. The ferruginous ooids cited above are interpreted as the products formed in the favourable pH and Eh conditions in the intertidal to the subtidal shallow-water environments during the initial rising of sea level after large-scale regressions.