皖南赣北地区早、中奥陶世含笔石黑色岩系地层地球化学的研究

<正> 地层地球化学是研究地球物质元素组成在地层中元素富存形式及其演化,即地层中物质元素组成的时空规律(侯德封,1959)。元素在地层中的分布和演变反映了自然条件和沉积环境的变化历史,元素的共生组合揭示岩石的成因和形成条件,所以地层地球化学是地层研究中的一个重要内容。同时,地层地球化学研究对于进一步揭示生物群兴衰、演替绝灭的历史,及其与环境介质变化之间的关系也有着十分重要的意义。 皖南赣北地区早、中奥陶世宁国组和胡乐组含笔石黑色岩系发育较好,地层出露完整,笔石化石丰富,笔石带序列齐全,生物地层研究较为详细(许杰,1934;陈旭等,1964;钱

Geochemical study of the Early and Middle Ordovician black graptolit bearing rock series in the southern Anhui-northern jiangxi area

The Early and Middle Ordovician graptolitic black shales of the Ningkuo Formation and Hule Formation, from southern Anhui and northern Jiangxi Province, consist of a va-rirty of sedimentary rocks including shales, mudstones and cherts mostly black or dark grey in colour. In this paper, a total of 65 geochemical samples were collected from three main inliners of Hule, Yushan and Wuning areas, and zoned by their graptolitic assemblages. The authors made studies on the stratigeochemical characteristics of major elements (Si, AI, K, Na, Ca, Mg, Fe, etc.), 23 trace elements (As, Ba, Be, Co, Cr, Cu, Ga, Li, Mn, P, Pb, Sr, V, Zn, etc.) and rare earth elements. These studies reveal that major elements and most of trace elements o?the graptolitic black shales have a systematic change up the succession based on decreasing or increasing contribution of clay mineral to these sediments. The study of the R-Factor analysis of trace elements expounds although the concentration of most of elements especially lithopbile elements may be related to clay minerals by their correlation coefficients with Al2O3 and K2O, there exsits differention in trace element assemblages of three areas, and it reflects that the sedimentary environments of three areas were different. According to the composition of rare earth elements, it was suggested that the graptolitic black shales should be deposited in a shallow and restricted continental shelf environment based on the slightly Ce negative anomaly(δCe - 0.81--0.98), and on the other hand, the sources of these sediments of three areas should become more complex as the increasing of clay minerals and terrigenous debris in sedimentary environments.