长江三角洲晚更新世暗绿色硬粘土的早期成岩作用

EARLY DIAGENESIS OF LATE PLEISTOCENE DARK-GREEN STIFF CLAY IN THE YANGZI RIVER DELTA

李萍 陈刚

Li Ping Chen Gang

长江三角洲晚更新世暗绿色硬粘土层是一个埋藏的古土壤层。它具有土壤的基本性质:(1)具植物根孔、植物碎屑及网状黑色腐殖质;(2)具粘土化作用;(3)存在淋溶、淀积作用;(4)缺乏层理。但与一般土壤却又有明显的区别;(1)上部致密、坚硬,超固结比2.1～2.2,下部则固结程度较差,与一般土壤剖面正好相反;(2)呈绿色和黄绿色;(3)普遍合形态各异的结核,其成分由上至下为黄铁矿→菱铁矿、菱锰矿→褐铁矿、软锰矿,反映由还原-氧化环境的过渡。原因在于早期成岩作用的改造使其特征发生了变化。富氧的海水在细菌的作用下,使古土壤中的有机质被分解,从而使其具备了早期成岩作用的条件。伴随着游离氧的消耗以及氧化离子的还原作用,形成硫化氢、低价铁、低价锰等,使古土壤的颜色、硬度、结核和粘土矿物发生了明显的变化,从而改变了古土壤的整体面貌。

Dark-green stiff clay of Late Pleistocene in the Yangzi River Delta is a buried Paleosol Bed.It possesses the basic property of soil:1.contains root holes,fragments and dark network humus of plants;2.underwent clayization;3.eluviaton and illuviation could be found;4.lacking of lamination.The distinct defferences between the paleosol and ordinary soil are:1.The upper part of the paleosol is light,stiff,and the ratio of hyperconsolidation is 2.1～2.2,but the lower part is less consolidated.This is contrary to ordinary soil; 2.The paleosol is green and yellow-green;3.The paleosol contains various types of nodules.They are mainly pyrite→siderite→dialogite→limonite and pyrolusite from top to bottom,reflecting a transition process of reducing-oxidizing environment.Oxygen-rich sea-water resolved the organic matter in the paleosol through the action of bacteria.With the consumption ot free oxygen and the reduction of oxidized ions,HS,Fe,Mn thus formed.This resultes in distinct changes of the colour,the hardness,the nodules and the clay minerals of the paleosol,thus changing the whole of the soil's property.

10.11743/ogg19950403