Luminescence chronology for identifying depositional sequences in an uplifted coast since the Middle Pleistocene, eastern Japan
Luminescence chronology for identifying depositional sequences in an uplifted coast since the Middle Pleistocene, eastern Japan
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DOI：
10.3389/feart.2022.967572
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发表时间：
2022-08
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通讯作者：
T. Tamura;H. Okazaki;T. Naya;R. Nakashima;H. Nakazato;K. Seike;J. Okuno
中科院分区：
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作者：
T. Tamura;H. Okazaki;T. Naya;R. Nakashima;H. Nakazato;K. Seike;J. Okuno
长石红外后红外受激发光（pIRIR）测年是一种关于晚第四纪沉积记录的有利的俘获电荷测年方法，因为它直接适用于碎屑沉积物和广泛的时间覆盖。它将其应用于各种沿海环境的沉积序列可能会提高我们对序列记录的长期海平面变化和区域构造的理解。日本东部关东沿海平原位于板块边界三重交界处附近的独特构造环境中，其特点是末次间冰期隆起海洋阶地的广泛发育，与长期沉降趋势形成鲜明对比。在本文中，我们记录了长石 pIRIR 测年法对从关东平原东北部海洋阶地收集的 35 米长沉积岩芯的应用，并研究了其年代学对于识别与中更新世以来相对海平面波动相关的沉积序列的有效性。沉积岩心显示出一系列从A到G的七个相单元，按升序排列，分别代表浅海到陆架（单元A到C）、河流到咸水盐沼（单元D）、滩到岸面（单元E）、河流到风积（单元F）和黄土（单元G）沉积。根据预先测试，在 50°C 下进行红外受激发光 (pIRIR225) 后，选择 225°C 下的 pIRIR 作为测年的最佳信号。 pIRIR225 的特点是适度的异常衰落，平均 g2days 值为 1.8%/十年。褪色校正的 pIRIR225 年龄与地层学一致。单位 A 和 B 的年代为海洋氧同位素阶段 (MIS) 7，单位 C 至 F 的年代为 MIS 5。然而，个体年龄估计的不确定性不允许进一步按时间顺序关联。相反，使用从特征相转变推断的海平面变化作为附加约束，单元 C 到 F 可以与 MIS 5 中的子阶段相关联。单元 E 代表 MIS 5c 海平面高位期间的海岸进积，它将核心地点周围海洋阶地的日期细化为 MIS 5c，并相应地修正了构造抬升速率。我们的结果证明了长石 pIRIR 测年法在识别与 100 kyr 冰川旋回相关的沉积序列方面的成功应用，其中，利用沉积相的附加信息，可以定义更高频率的序列。
Feldspar post-infrared infrared stimulated luminescence (pIRIR) dating is an advantageous trapped-charge dating method concerning late Quaternary sedimentary records for its direct applicability to clastic sediments and wide time coverage. Its application to depositional sequences in various coastal settings potentially improve our understanding of long-term sea-level changes and regional tectonics that the sequences record. The Kanto coastal plain, eastern Japan is situated in a unique tectonic setting near the triple junction of plate boundaries and characterized by extensive development of the Last Interglacial raised marine terrace in contrast to the longer-term subsidence trend. In this article, we document the application of feldspar pIRIR dating to a 35-m-long sediment core collected from the marine terrace in the northeastern Kanto plain and examine how effective its chronology is for identifying depositional sequences related to the relative sea-level fluctuations since the Middle Pleistocene. The sediment core shows a succession of seven facies units, A to G, in ascending order, representing the shallow marine to shelf (units A to C), fluvial to brackish salt marsh (unit D), beach to shoreface (unit E), fluvial to aeolian (unit F), and loess (unit G) sedimentation. According to pre-tests, pIRIR at 225°C after prior infrared stimulated luminescence at 50°C (pIRIR225) was chosen as an optimal signal for dating. pIRIR225 is characterized by modest anomalous fading with an average g2days-value of 1.8%/decade. Fading-corrected pIRIR225 ages are consistent with the stratigraphy. Units A and B are dated as Marine Oxygen Isotope Stage (MIS) 7 and units C to F as MIS 5. However, uncertainties of individual age estimates do not allow further chronological correlation. Instead, using sea-level changes inferred from characteristic facies transitions as additional constraints, units C to F can be correlated to sub-stages in MIS 5. Unit E represents coastal progradation during the MIS 5c sea-level highstand, which refines the date of the marine terrace around the core site as MIS 5c and revises up the rate of the tectonic uplift accordingly. Our results exemplify a successful application of feldspar pIRIR dating for identifying depositional sequences formed in relations to 100-kyr glacial cycles, in which, with additional information of the sedimentary facies, higher-frequency sequences may be defined.