Rock magnetic identification and geochemical process models of greigite formation in Quaternary marine sediments from the Gulf of Mexico (IODP Hole U1319A)
Rock magnetic identification and geochemical process models of greigite formation in Quaternary marine sediments from the Gulf of Mexico (IODP Hole U1319A)
复制标题
DOI：
10.1016/j.epsl.2008.07.034
复制
发表时间：
2008-11
影响因子：
5.3
通讯作者：
Yanzhe Fu;T. Dobeneck;C. Franke;D. Heslop;S. Kasten
中科院分区：
文献类型：
--
作者：
Yanzhe Fu;T. Dobeneck;C. Franke;D. Heslop;S. Kasten
利用古磁学和岩石磁学方法，研究了德克萨斯州Brazos-Trinity斜坡内盆地体系中160 m的晚更新世浊积层序（IODP Expedition 308, Hole U1319A）。通过诊断磁性能检测到大量的氧化铁耗尽层和富含铁磁性硫化铁矿物（Fe3S4）的层。根据这些层的分布、地层背景和地球化学分带，提出了两种非稳定沉积环境下灰长岩形成的概念反应模型。“硫化模型”预测了单硫化铁与多硫化物在硫酸盐甲烷转变（SMT）周围不完全转变形成的单或双灰长岩层。“氧化模型”解释了在向下移动的氧化锋期间，铁氧化还原边界附近的单硫化铁部分氧化形成灰长岩。地层记录提供的证据表明，这两种灰长岩的形成过程在这里的典型深度约为12-14平方英尺和3-4平方英尺。许多“化石”灰长岩层很可能是由氧化还原带的快速向上移动保存下来的，表明过去的SMT和以停滞的半深海沉积条件为特征的海底位置。综合各种磁滞和剩余物学参数，划分了从原始磁铁矿为主到完全灰长岩为主的6个成岩阶段。
A 160 m mostly turbiditic late Pleistocene sediment sequence (IODP Expedition 308, Hole U1319A) from the Brazos-Trinity intraslope basin system off Texas was investigated with paleo- and rock magnetic methods. Numerous layers depleted in iron oxides and enriched by the ferrimagnetic iron-sulfide mineral greigite (Fe3S4) were detected by diagnostic magnetic properties. From the distribution of these layers, their stratigraphic context and the present geochemical zonation, we develop two conceptual reaction models of greigite formation in non-steady depositional environments. The “sulfidization model” predicts single or twin greigite layers by incomplete transformation of iron monosulfides with polysulfides around the sulfate methane transition (SMT). The “oxidation model” explains greigite formation by partial oxidation of iron monosulfides near the iron redox boundary during periods of downward shifting oxidation fronts. The stratigraphic record provides evidence that both these greigite formation processes act here at typical depths of about 12–14 mbsf and 3–4 mbsf. Numerous “fossil” greigite layers most likely preserved by rapid upward shifts of the redox zonation denote past SMT and sea floor positions characterized by stagnant hemipelagic sedimentation conditions. Six diagenetic stages from a pristine magnetite-dominated to a fully greigite-dominated magnetic mineralogy were differentiated by combination of various hysteresis and remanence parameters.