华南渣拉沟剖面纽芬兰世沉积水体氧化还原状态演化

摘要

为研究纽芬兰世斜坡—盆地环境背景下的水下隆起的沉积水体氧化还原性质的垂向演化，本文选取黔东南渣拉沟剖面，进行总有机碳含量（TOC）、铁组分、黄铁矿硫同位素（δ34 Spy ）、干酪根的碳和硫同位素（δ13 Ckero、δ34 Skero ）等方面的分析。本文依据硅质岩、磷块岩、多金属硫化物层和干酪根碳同位素等对比标志，对渣拉沟剖面进行地层对比，认为：渣拉沟剖面本文分析层段大体与滇东纽芬兰世石岩头组的中下部相对应。铁组分和TOC／Spy显示渣拉沟剖面老堡组硅质岩段处于缺氧非硫化环境，其上覆的渣拉沟组分析层段以硫化环境为主，其间间断性的发育缺氧非硫化环境，并最终回复到缺氧非硫化环境。δ34 Spy与δ34 Skero在老堡组的缺氧非硫化环境都较渣拉沟组中的硫化环境重，可能与前者的细菌硫酸盐还原反应主要发育在相对封闭的孔隙系统，后者的细菌硫酸盐还原反应主要发育在相对开放的沉积水体有关。%To explore the evolution of oceanic redox state during the Terreneuvian Epoch,South China,total organic carbon (TOC ),iron speciation,sulfur isotopic composition of pyrite and kerogen and carbon isotopic compositions of kerogen were analyzed on the Zhalagou section,Guizhou Province.The studied section was deposited in an isolated palaeotopographic high under the slope-basinal background.On the basis of combined tools for stratigraphic correlation,including redox sensitive metal elements (such as Mo, U,V and Ni)-,sulfide-,and organic matter-rich horizon,the chert units,phosphate-bearing layer,and organic carbon isotope in kerogen,the analyzed intervals in the Zhalagou section were time-equivalent with the lower to middle parts of Shiyantou Formation.The high FeHR/FeT ratio (reactive iron to total iron:>0.38 ),and low Fepy/FeHR ratio (pyrite iron to high reactive iron:<0.6 )indicate that the Laobao Formation were deposited under anoxic,non-sulfidic environment.Conversely,the high FeHR/FeT ratio (> 0.38),and high Fepy/FeHR ratio (mostly >0.7)indicate that the major parts of overlying Zhalagou Formation were deposited under anoxic and sulfidic environment and that the rests were deposited under transient anoxic,non-sulfidic environment.The more enriched values ofδ 34 Spy andδ 34 Skero in the Laobao Formation demonstrate that the bottom water was under anoxic and non-sulfidic conditions,and that bacterial sulfate reduction mainly occurred in the relatively closed pore waters.The more depleted values ofδ 34 Spy andδ 34 Skero in the sulfidic intervals of Zhalagou Formation,demonstrate that H2 S accumulated into the bottom seawater,and that bacterial sulfate reduction proceeded under an open system with a larger fractionation.