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首页> 外文期刊>Paleoceanography >A biogenic origin for anomalous fine-grained magnetic material at the Paleocene-Eocene boundary at Wilson Lake, New Jersey
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A biogenic origin for anomalous fine-grained magnetic material at the Paleocene-Eocene boundary at Wilson Lake, New Jersey

机译：新泽西州威尔逊湖古新世-始新世边界的异常细粒磁性材料的生物成因

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摘要

The Paleocene-Eocene Thermal Maximum, which occurred similar to 55.5 Ma, was caused by a massive release of carbon, as indicated by an similar to 3% negative carbon isotope excursion recorded in the marine, atmospheric, and terrestrial reservoirs. One suggested source for the carbon, a cometary impactor, is based on the sudden appearance and high concentration of single-domain (SD) magnetite in Paleocene-Eocene (P-E) boundary cores from the North Atlantic continental margin. We evaluate the potential sources of SD magnetite at the P-E boundary by presenting new magnetic hysteresis, low-temperature magnetic remanence, and transmission electron microscopy data from the North Atlantic coastal ocean. Our results show a similar increase in SD material but demonstrate that the magnetic material has a biogenic origin. These findings indicate that the high concentrations of SD magnetite immediately above the P-E boundary are the result of unusual accumulations and/or preservation of magnetotactic bacteria. Such bacteria typically occupy the oxic-anoxic transition zone near the sediment-water interface or in the water column. The high abundances of SD magnetite in sediments from across the shelf may be an artifact of nonsteady state redox conditions and exceptional preservation of SD magnetite. It may also indicate that the oxic-anoxic redox boundary shifted into the water column. The latter explanation implies transient eutrophy of the coastal ocean in this region, most likely due to seasonally enhanced runoff, and increased stratification and nutrient loading.
机译：古新世-始新世的热最大值发生在类似于55.5 Ma的位置，是由于碳的大量释放引起的，正如海洋，大气和陆地储层中记录的类似于3％的负碳同位素偏移所表明的那样。一种建议的碳源（彗星撞击器）是基于北大西洋大陆边缘古新世-始新世（P-E）边界岩心中突然出现的高浓度单域（SD）磁铁矿。我们通过提出新的磁滞，低温剩磁和北大西洋沿岸海洋的透射电子显微镜数据，评估了P-E边界处SD磁铁矿的潜在来源。我们的结果表明SD材料的增加类似，但表明磁性材料具有生物起源。这些发现表明，在P-E边界正上方的高浓度SD磁铁矿是趋磁细菌异常聚集和/或保存的结果。这些细菌通常占据沉积物-水界面附近或水柱中的有氧-缺氧过渡区。来自整个架的沉积物中大量的SD磁铁矿可能是非稳态氧化还原条件和SD磁铁矿异常保存的产物。这也可能表明氧-缺氧的氧化还原边界已移入水柱。后一种解释暗示了该区域沿海海洋的短暂富营养化，最有可能是由于季节径流增加，分层和养分含量增加所致。

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