During the late Quaternary, dramatic changes in relative sea level (~170 m) are known to have occurred in the Caspian Sea. However, all previous attempts at resolving the uncertainty associated with the timing of these transgressive/regressive events, primarily using radiocarbon, have produced inconclusive or controversial results. Here we present the first reliable chronology for the largest known transgression (Early Khvalynian). This was derived using optically stimulated luminescence (OSL) analysis of sand‐sized quartz, with support from infrared stimulated luminescence (IRSL) from K‐rich feldspar grains, all extracted from 16 sediment samples collected along the Lower Volga River. These samples were taken from loessic sediments, marine clays (known as Chocolate Clays) and the overlying modern soils exposed at three sections (Srednyaya Akhtuba, Raygorod, Leninsk) ~200 km upstream of the present‐day estuary. The differential bleaching rates of the quartz OSL and feldspar IRSL signals were used to evaluate the degree of resetting of quartz (and feldspar) signals; it was possible to conclude that all signals, and particularly quartz OSL, were sufficiently reset at deposition to allow accurate age estimation. Our results show unambiguously that the Early Khvalynian marine Chocolate Clays present at all three sections were deposited post‐LGM, between ~17 and ~13.1 ka ago. These age estimates are further constrained by those from the overlying Kastanozem soils (9.6–0.7 ka) and underlying loess‐soil series (32–19 ka), confirming a young (17–13 ka) age of the transgressive stage of the Early Khvalynian. Relative sea level during this period must have been well above the sampling altitudes of 11.7 m a.s.l. (Srednyaya Akhtuba), 11.3 m a.s.l. (Raygorod) and 4.7 m a.s.l. (Leninsk) to explain the absence of significant alluvial sand and to allow the deposition of the fine Chocolate Clays marker horizon.

中文翻译：

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伏尔加河下游河谷早期哈瓦里尼亚海里海侵的可靠年代学

在第四纪晚期，里海发生了相对海平面（〜170 m）的剧烈变化。但是，所有先前解决这些与海侵/回归事件的时间相关的不确定性的尝试，主要是使用放射性碳，均未得出结论性或有争议的结果。在这里，我们介绍了最大的已知海侵（早期Khvalynian）的第一个可靠的时间顺序。这是通过对沙子大小的石英进行光激发发光（OSL）分析得出的，并得到了富钾长石晶粒的红外激发发光（IRSL）的支持，这些都是从伏尔加河下游收集的16个沉积物样品中提取的。这些样品取自黄土沉积物，海洋粘土（称为巧克力粘土）和在三个部分（Srednyaya Akhtuba，列宁斯克的雷哥罗德（Raygorod，Leninsk）），距今河口上游约200公里。石英OSL和长石IRSL信号的差异漂白速率用于评估石英（和长石）信号的复位程度；可以得出结论，所有信号，特别是石英OSL，在沉积时都已充分复位，以进行准确的年龄估算。我们的结果清楚地表明，所有这三个断面中存在的早期哈瓦林海洋巧克力粘土是在LGM后约17至约13.1 ka之前沉积的。这些年龄估计值进一步受到上覆的卡斯坦诺西姆土壤（9.6–0.7 ka）和下伏的黄土-土壤序列（32–19 ka）的估计的约束，这证实了Khvalynian早期海侵阶段的年龄较小（17–13 ka）。 。在此期间，相对海平面必须已经远远高于11的采样高度。