Late Triassic compositional changes of aeolian dusts in the pelagic Panthalassa: Response to the continental climatic change
Late Triassic compositional changes of aeolian dusts in the pelagic Panthalassa: Response to the continental climatic change
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DOI：
10.1016/j.palaeo.2013.10.014
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
R. Nakada;K. Ogawa;N. Suzuki;S. Takahashi;Y. Takahashi
中科院分区：
文献类型：
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作者：
R. Nakada;K. Ogawa;N. Suzuki;S. Takahashi;Y. Takahashi
卡尼期洪积事件（CPE）被认为是西特提斯地区卡尼期（晚三叠世）发生的剧烈环境变化。虽然一些研究表明，CPE是一个全球性事件，但没有研究提到与CPE有关的远洋环境。为了揭示卡尼期的远洋环境，利用X射线吸收精细结构（XAFS）分析了日本丹波-美浓-芦尾带Ladinian-Carnian地层中硅质岩样品中的铁物种。X射线吸收近边结构（XANES）分析表明，所有的红色硅质岩都含有赤铁矿与粘土矿物，如伊利石，蒙脱石和蒙脱石的组合。这些矿物的存在是使用扩展XAFS（EXAFS）来识别的。绿色和白色硅质岩的XANES分析没有显示出任何赤铁矿特征，而EXAFS分析则显示出赤铁矿数量的增加。本研究中观察到的含铁成分的地层变化可分为三个阶段：（i）矿物成分相对稳定的阶段在卡尼早期（朱利安）沉积的硅质岩中观察到（伊利石+伊利石+赤铁矿），（二）矿物成分的突然变化在研究剖面的中部区域观察到（缺乏钙钛矿，出现蒙皂石），对应卡尼期的中部（iii）卡尼期晚期（图瓦卢期）矿物组成恢复到以前的稳定状态。这些变化的矿物组成的远洋硅质岩可以解释为意味着大陆的气候条件发生了变化，在卡尼，不同的粘土组分被交付到远洋地区。这些数据，结合以前的研究结果进行了周围的大陆领域，可以解释如下：（一）有一个相对稳定的干旱气候之前的CPE，（二）有越来越多的降水量由于CPE，和（三）气候恢复到干燥的条件下类似于那些之前的CPE。
The Carnian pluvial event (CPE) is considered as the drastic environmental change that occurred in the western Tethys during the Carnian (Late Triassic). Although some studies have suggested that the CPE was a global event, no studies have referred to pelagic environment related to the CPE. To reveal the pelagic environment during the Carnian, X-ray absorption fine structure (XAFS) analysis was used to determine the iron (Fe) species in chert samples collected from the Ladinian–Carnian strata in the Tamba–Mino–Ashio Belt, Japan. The X-ray absorption near-edge structure (XANES) analysis shows that all the red cherts contain hematite with a combination of clay minerals, such as illite, chlorite, and smectite. The existence of these minerals is identified using extended XAFS (EXAFS). The XANES analysis of the green and the white cherts does not show any hematite signatures, while the EXAFS analysis indicated increasing amounts of chlorite.The stratigraphic change in the Fe-bearing compositions observed in this study can be divided into three stages: (i) a stage where a relatively stable mineral composition (chlorite + illite + hematite) is observed in cherts deposited during the early Carnian (Julian), (ii) the abrupt change in mineral composition (lack of chlorite and appearance of smectite) observed in the middle area in the studied section and corresponding to the middle part of Carnian (late Julian–early Tuvalian), and (iii) the recovery of the previous stable mineral composition during the late Carnian (Tuvalian). These variations in the mineralogical composition of pelagic cherts can be interpreted to mean that the continental climate conditions changed during the Carnian, and different clay fractions were delivered to the pelagic region. These data, combined with the results of previous studies performed around the continental realm, can be interpreted as follows: (i) there was a relatively stable dry climate before the CPE, (ii) there were increasing amounts of precipitation owing to the CPE, and (iii) the climate returned to dry conditions similar to those prior to the CPE.