An Appalachian Amazon? Magnetofossil evidence for the development of a tropical river-like system in the mid-Atlantic United States during the Paleocene-Eocene thermal maximum
An Appalachian Amazon? Magnetofossil evidence for the development of a tropical river-like system in the mid-Atlantic United States during the Paleocene-Eocene thermal maximum
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DOI：
10.1029/2009pa001783
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发表时间：
2009-12-05
期刊：
影响因子：
--
通讯作者：
Vali, Hojatollah
中科院分区：
文献类型：
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作者：
Kopp, Robert E.;Schumann, Dirk;Vali, Hojatollah
在美国中大西洋沿岸平原，古新世-始新世极热期（PETM），富含高岭石的万宝路粘土取代了古新世砂和粉砂。粘土保存了大量的磁铁矿，这些磁铁矿是由趋磁细菌和新型的、假定是真核的、铁生物矿化微生物产生的。利用铁磁共振波谱和电子显微镜技术，结合地层和碳同位素资料，绘制了磁化石分布图，并确定了粘土中的三种磁相：一种是碎屑颗粒和磁化石混合的磁相，第二种是高磁化石与碎屑比的磁相，第三种是只有瞬态磁化石的磁相。这些相的分布表明，促进磁化石生成和保存的缺氧条件发生在索尔兹伯里湾中部浅海沉积中，但只短暂地扩展到浅海沉积外部和浅海两侧。这种分布与类似于现代热带河流主导的陆架的系统的发展相一致。
On the mid-Atlantic Coastal Plain of the United States, Paleocene sands and silts are replaced during the Paleocene-Eocene Thermal Maximum (PETM) by the kaolinite-rich Marlboro Clay. The clay preserves abundant magnetite produced by magnetotactic bacteria and novel, presumptively eukaryotic, iron-biomineralizing microorganisms. Using ferromagnetic resonance spectroscopy and electron microscopy, we map the magnetofossil distribution in the context of stratigraphy and carbon isotope data and identify three magnetic facies in the clay: one characterized by a mix of detrital particles and magnetofossils, a second with a higher magnetofossil-to-detrital ratio, and a third with only transient magnetofossils. The distribution of these facies suggests that suboxic conditions promoting magnetofossil production and preservation occurred throughout inner middle neritic sediments of the Salisbury Embayment but extended only transiently to outer neritic sediments and the flanks of the embayment. Such a distribution is consistent with the development of a system resembling a modern tropical river-dominated shelf.