Age determination of sediments from Pechora basin, Arctic Russia

The Vastiansky Kon' is the largest exposure of Quaternary deposits in the Pechora lowland, northern Russia. Morphologically the site belongs to the so-called Markhida Moraine; a complex, east-west trending zone of ice-marginal landforms deposited by the Kara Sea Ice Sheet during the last glaciation. The site exhibits a succession of sediments more than 100 m thick that, according to previous studies, covers the interval from the end of the Elsterian to the beginning of the Holocene. Unfortunately both the strong glaciotectonic deformation of the sedimentary succession and few absolute dates have made the chronological interpretation of the section difficult. The present paper reviews previous studies of the site published in Russian, and presents the results of a reinvestigation focusing on the post-Eemian stratigraphy. A marine Eemian clay more than 8 m thick is overlain erosionally by 20 m of fluvial deposits of Late Eemain or Early Weichselian age. The fluvial succession is overlain by a till and a marine clay, which, according to one interpretation, may represent an Early or Middle Weichselian advance of the Kara Ice Sheet followed by a transgression. The clay shows a transition into 15 m of estuarine and fluvial sediments overlain by more than 12 m of tundra-floodplain deposits. The whole succession has been upthrusted glaciotectonically by the last ice advance, which deposited a more than 12 m thick till on top of the section. Based on a number of subtill radiocarbon age-estimates from the site, in the range 25-32 ka BP, the youngest ice advance is considered to be of late Weichselian age, although a Middle Weichselian age cannot be excluded.

瓦斯塔恩斯基孔（Vastiansky Kon'）是俄罗斯北部伯朝拉低地规模最大的第四纪沉积（Quaternary deposits）出露点位。地貌上该遗址隶属于所谓的马尔希达冰碛（Markhida Moraine）——即末次冰期由喀拉海冰盖（Kara Sea Ice Sheet）堆积形成的、东西走向的复杂冰缘地貌带。该遗址出露的沉积序列厚度超100米，据既往研究，其覆盖了从埃尔斯特冰期（Elsterian）结束至全新世（Holocene）开始的地层区间。遗憾的是，沉积序列强烈的冰缘构造变形（glaciotectonic deformation）以及有限的绝对年代数据（absolute dates），使得该剖面的年代学解释（chronological interpretation）难度较大。本文综述了此前以俄语发表的该遗址相关研究成果，并呈现了针对埃姆间冰期（Eemian）后地层的重新调查结果。一层厚度超8米的埃姆海相黏土被晚埃姆间冰期或早韦克塞尔冰期（Weichselian）的20米河流沉积（fluvial deposits）侵蚀覆盖。该河流沉积序列之上依次覆有冰碛物（till）与海相黏土，据一种学术解读，这可能代表喀拉冰盖的早或中韦克塞尔冰期冰进，随后伴随海侵（transgression）事件。该海相黏土过渡为15米厚的河口与河流沉积（estuarine and fluvial sediments），其上又覆盖了超12米的苔原泛滥平原沉积（tundra-floodplain deposits）。整个沉积序列被末次冰进的冰缘构造作用抬升，末次冰进在该剖面顶部堆积了厚度超12米的冰碛物。基于该遗址获取的多组冰碛物下伏碳十四年代估算（radiocarbon age-estimates）数据（范围为25~32 ka BP），尽管无法排除中韦克塞尔冰期的可能性，但最新的冰进被认定属于晚韦克塞尔冰期。