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首页> 外文期刊>Studia Geophysica et Geodaetica >Magnetic Stratigraphy from Deep Clastic Turbidites: An Example from the Eocene Hecho Group (Southern Pyrenees)
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Magnetic Stratigraphy from Deep Clastic Turbidites: An Example from the Eocene Hecho Group (Southern Pyrenees)

机译：深层碎屑浊积岩的磁性地层学：始新世Hecho群的一个例子（南比利牛斯山脉）

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摘要

A paleomagnetic study of a 2200-meter thick section of clastic turbidites from the Eocene Hecho group (southcentral Pyrenees, Spain) allows defining its magnetostratigraphic record. Natural remanent magnetization is carried by up to three components: a viscous low-temperature component; a second component unblocked between 300°C and 345°C, likely carried by iron-sulphides; and a third component which demagnetizes at temperatures higher than 345°C and is likely carried by magnetite. The second and third components may display opposite polarities at the same site. The “magnetite” component delineates different polarity zones and has a more consistent behavior along section if compared with the “iron-sulphide” component, which displays either a normal or a reverse direction without any stratigraphic consistency along section. The bulk of iron sulphides are interpreted to be secondary in origin and to carry diagenetic overprints acquired at different times after deposition and the “magnetite” component is taken as the characteristic primary magnetization. As supported by biostratigraphy, the section is correlated from chrons C20r to C18n.2n (Lutetian-Bartonian transition), which indicates a mean sediment accumulation rate of about 52 cm/ky for the studied section. The new chronostratigraphy allows constraining the age of the upper Hecho Group (Banastón and Jaca allogroups) to an unprecedented level and is consistent with previous magnetostratigraphic work in younger sediments from the Jaca Basin. Deep clastic sedimentary systems should not be neglected as a target for magnetostratigraphic studies despite diagenetic growth of secondary minerals may mask the primary signal.
机译：对始新世Hecho组（比利牛斯中南部，西班牙）的一块2200米厚的碎屑浊积岩进行古磁研究，可以定义其磁地层记录。自然剩磁由三部分组成：粘性低温成分；在300°C至345°C之间畅通的第二种组分，很可能由硫化铁携带；第三成分在高于345°C的温度下会消磁，并可能由磁铁矿携带。第二和第三组件可以在同一位置显示相反的极性。与“硫化铁”成分相比，“磁铁矿”成分描述了不同的极性区域，并且沿剖面具有更一致的行为，“铁硫化物”成分显示的是法向或反方向，而沿剖面没有任何地层一致性。大部分的硫化铁被认为是次生的，并携带沉积后在不同时间获得的成岩叠印，“磁铁矿”成分被视为主要的磁化强度。在生物地层学的支持下，该断层从年代C20r到C18n.2n（Lutetian-Bartonian跃迁）相关，这表明该断层的平均沉积速率约为52 cm / ky。新的年代地层学将赫霍族上部（Banastón和Jaca等位族）的年龄限制到了前所未有的水平，并且与以前在Jaca盆地较年轻沉积物中的磁性地层学工作相一致。尽管次生矿物的成岩作用可能掩盖了主要信号，但深层碎屑沉积系统不应被忽略作为磁地层学研究的目标。

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