破译结核中的沉积环境和同沉积构造活动信息——以黔湘边界地区黑色岩系为例

黑色岩系赋存油气、煤、页岩气等能源资源和铁、锰、磷、钡等多种固体资源，沉积成藏和沉积成矿条件的恢复是资源预测的基石，古沉积环境和同沉积构造的恢复因而受到额外重视。在黔湘边界地区的黑色岩系中有大量结核，而结核对原始记录有封存特性，因此，在对野外露头剖面观察和室内显微分析的基础上，通过沉积作用—构造作用的一体化分析，发现不同层位的结核在矿物成分和结构类型上差别很大：(1)上震旦统—寒武系纽芬兰统留茶坡组(Z€l)的结核是重晶石、钙质、磷质和硅质等多成分的集合体，砾屑或砂屑结构；两层结核的胶结温度不同，直接覆盖重晶石矿的结核层温度较高；(2)寒武系第二统杷榔组(€₂p)的结核以黄铁矿为主要成分，发育三期生长构造：核心层呈草莓状结构，外面两层呈肾状结构；(3)寒武系第二统乌训组(€₂w)结核的矿物成分为钙质和黄铁矿，并以钙质为主，黄铁矿呈星点状散布其中，有四期生长构造，第一和第三期黄铁矿含量较高。从不同层位的结核中分别破译出不同的古沉积环境条件和同沉积构造的活动信息：(1)留茶坡组含重晶石结核属低温热液成因，还原环境局限在断裂带附近；(2)杷榔组黄铁矿结核形成于氧化还原界面附近，环境具备高浓度活性铁的介质条件；(3)乌训组钙质—黄铁矿结核形成于低浓度铁的周期性还原环境，推测为基底的幕式陷落引发频繁的相对海平面变化，从而导致水介质氧化还原性的频繁变化。因此，结核研究有助于重建黑色岩系的介质条件，对资源预测有重要意义。

Decoding sedimentary environment and synsedimentary tectonic activity information in nodules: a case study of the black rock series in the border area of Guizhou and Hunan

The black rock series contains energy resources such as oil and gas, coal, shale gas, and various solid resources such as iron, manganese, phosphorus, and barium. The restoration of sedimentary reservoir formation and sedimentary mineralization conditions is the cornerstone of resource prediction, and the restoration of ancient sedimentary environments and synsedimentary tectonics has therefore received additional attention. There are a large number of nodules in the black rock series in the border area of Guizhou and Hunan, and the nodules have sealing properties on the original records. Therefore, based on the observation of exposed profiles in the field and laboratory microscopic analysis, and through the integrated analysis of sedimentation and tectonic processes, it is found that there are significant differences in mineral composition and textural types among nodules in different layers: (1) The nodules of Upper Sinian Series-Cambrian Terreneuvian Series Liuchapo Formation (Z€l) are an assemblage of multi-components such as barite, calcium, phosphorus, and silicon, with texture of gravel or sand fragments. The cementation temperature of the two nodule layers is different, and the one directly covering the barite ore is relatively higher; (2) The nodules of Cambrian Series 2 Palang Formation(€2p) are mainly composed of pyrite and three stages of growth structure are developed: the core layer shows a framboidal texture, and the outerside two layers show a nephritic shape; (3) The nodule components of Cambrian Series 2 Wuxun Formation (€2w) are calcium and pyrite, of which calcium is dominated, with scattered pyrite. There are four stages of growth structures, with relatively higher content of pyrite in the first and third stages. Different paleose-dimentary environmental conditions and synsedimentary tectonic activity information can be decoded from nodules at different layers: (1) The barite bearing nodules in the Liuchapo Formation belong to low-temperature hydrothermal origin, and the reduction environment is limited near the fault zone; (2) The pyrite nodules in the Palang Formation are formed near the redox interface, and the environment has medium conditions of high concentration of active iron; (3) The calcareous and pyrite nodules of the Wuxun Formation were formed in a periodic reducing environment of low concentration iron, which is speculated to be caused by frequent relative sea level fluctuation caused by episodic subsidence of the basement, leading to frequent changes in the redox properties of the water medium. Therefore, the study of nodules helps to reconstruct the medium conditions of black rock series and is of great significance for resource prediction.