Carbon-isotope stratigraphy from terrestrial organic matter through the Monterey event, Miocene, New Jersey margin (IODP Expedition 313)
Carbon-isotope stratigraphy from terrestrial organic matter through the Monterey event, Miocene, New Jersey margin (IODP Expedition 313)
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DOI：
10.1130/ges00851.1
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发表时间：
2013-10
期刊：
影响因子：
2.5
通讯作者：
Linhao Fang;C. Bjerrum;S. Hesselbo;U. Kotthoff;F. McCarthy;Baoqi Huang;P. Ditchfield
中科院分区：
文献类型：
--
作者：
Linhao Fang;C. Bjerrum;S. Hesselbo;U. Kotthoff;F. McCarthy;Baoqi Huang;P. Ditchfield
对美国新泽西州边缘浅海陆架的中新世硅质碎屑沉积物中陆地有机质碳同位素值的地层学效用进行了探索（综合海洋钻探计划 [IODP] 第 313 次探险）。这些富含陆地有机质的浅海地层提供了相当于蒙特雷事件的沉积记录，这是一个较长的时间间隔，其特征是从许多海洋环境中的有孔虫碳酸盐记录的相对正的碳同位素值。在孢粉学制剂残留物、浓缩的木本植物碎屑和从新泽西沉积物中单独采摘的木本植物碎屑中，一致地观察到一致的地层趋势和短期同位素偏移。大量有机质曲线显示出有些不同的地层趋势，但当根据测量的碳氮比对海洋-陆地成分的混合进行校正时，观察到与木本植物碎屑记录高度一致。然而，假设基于锶同位素值和生物地层学的相关性是正确的，新泽西边缘的碳同位素记录与之前从海洋环境记录的碳同位素记录形成对比（即，陆地有机质中的碳同位素值在朗吉阶阶段缺乏正偏移）。可能使当地陆地碳同位素记录产生偏差的因素包括旧沉积物的改造、退化和成岩作用，以及影响沉积物源区植被的环境因素。这些可能的因素是根据热解数据、扫描电子显微镜观察以及与环境变化的孢粉学指数的比较来评估的。发现了一些旧木本植物碎屑局部降解和/或改造的证据，但在发生此类过程的地方，它们并不能轻易解释观察到的碳同位素值。结论是，可交换碳库的整体碳同位素特征被扭曲，以至于蒙特雷事件偏移不易识别。最可能的解释是，植物碎屑的改造确实发生在斜形坡趾相中，但在布尔迪加阶中产生相对重的碳同位素值的原因仍然不清楚。
The stratigraphic utility of carbon-isotope values from terrestrial organic matter is explored for Miocene siliciclastic sediments of the shallow shelf, New Jersey margin, USA (Integrated Ocean Drilling Program [IODP] Expedition 313). These shallow marine strata, rich in terrestrial organic matter, provide a record of deposition equivalent to the Monterey event, a prolonged interval of time characterized by relatively positive carbon-isotope values recorded from foraminiferal carbonate in numerous oceanic settings. Coherent stratigraphic trends and short-term isotopic excursions are observed consistently in palynological preparation residues, concentrated woody phytoclasts, and individually picked woody phytoclasts obtained from the New Jersey sediments. A bulk organic matter curve shows somewhat different stratigraphic trends but, when corrected for mixing of marine-terrestrial components on the basis of measured C/N ratios, a high degree of conformity with the woody phytoclast record is observed. However, assuming that the correlations based on strontium-isotope values and biostratigraphy are correct, the carbon-isotope record from the New Jersey margin contrasts with that previously documented from oceanic settings (i.e., lack of positive excursion of carbon-isotope values in terrestrial organic matter through the Langhian Stage). Factors that may potentially bias local terrestrial carbon-isotope records include reworking from older deposits, degradation and diagenesis, as well as environmental factors affecting vegetation in the sediment source areas. These possible factors are assessed on the basis of pyrolysis data, scanning electron microscope observations, and comparison to palynological indices of environmental change. Some evidence is found for localized degradation and/or reworking of older woody phytoclasts, but where such processes have occurred they do not readily explain the observed carbon-isotope values. It is concluded that the overall carbon-isotope signature for the exchangeable carbon reservoir is distorted, to the extent that the Monterey event excursion is not easily identifiable. The most likely explanation is that phytoclast reworking has indeed occurred in clinoform toe-of-slope facies, but the reason for the resulting relatively heavy carbon-isotope values in the Burdigalian remains obscure.