Васильчук Ю.К., Гинзбург А.П., Сысолятин Р.Г., Токарев И.В., Королёва Е.С., Паламарчук В.А., Буданцева Н.А., Васильчук А.К. —
Криолитологическое строение и распределение стабильных изотопов кислорода и водорода в разрезе плейстоценовых отложений, вскрытых глубокой скважиной в пос. Чурапча, Лено-Алданское междуречье
// Арктика и Антарктика. – 2024. – № 3.
– С. 46 - 64.
DOI: 10.7256/2453-8922.2024.3.71544
URL: https://e-notabene.ru/arctic/article_71544.html
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Аннотация: Предметом исследования является криолитологическое строение плейстоценовых отложений, вскрытых глубокой скважиной в пос. Чурапча и распределение стабильных изотопов кислорода и водорода в текстурных преимущественно шлировых льдах. Район расположен в области сплошного распространения многолетнемёрзлых пород, вертикальная мощность которых здесь достигает 400–500 м. Среднегодовая температура пород колеблется в пределах –4,6 – –6,2°С, в долинах рек они повышены примерно до –2 – –1°С. Многолетнемёрзлые породы в районе Чурапчи отличаются относительно высокой льдистостью от 0,26–0,47 долей единицы. Лёд находится в породах в виде прослоев и формирует слоистую криотекстуру. В ходе полевых работ исследованы мерзлые керны, вскрытые буровой скважиной, глубиной 30 м. Бурение выполнялось с помощью крупногабаритной буровой установки ПБУ-2 на базе грузового автомобиля КАМАЗ. Использовалась колонковая буровая труба диаметром 146 мм. Отбор образцов осуществлялся из мерзлого керна Скважиной вскрыты многолетнемёрзлые отложения, имеющие в основном тёмно-бурые и серые цвета окраски, в особенности сизовато-серые оттенки характерна для тяжёлых суглинков и глин. Сезонно-талый слой имеет супесчаный состав, а ниже, на глубинах от 1,5 до 6,0 м отложения суглинистые. На глубинах 6,0–20,0 м наблюдается чередования слоёв суглинков и глин различной мощности, а ниже – резкая смена литологического состава на средний и мелкий песок (20,75 – 24,0 м), включающий большое количество слоёв органического вещества.
Распределение значений δ18O и δ2H изучено в текстурных льдах до глубины 17,7 м. В верхних 12 м изотопный состав заметно отрицательнее: значения δ18O варьируют от –29,44 до –34,35‰, а величины δ2H – от –213,5 до -253,6‰. В интервале 12–17,7 м значения δ18O варьируют от –25,94 до –28‰, а величины δ2H – от –195,3 до –214,3‰.
Abstract: The subject of the study is the cryostructures of Pleistocene sediments uncovered by a 30-m borehole in the Churapcha village and the distribution of stable oxygen and hydrogen isotopes in the schlieren ice and thin ice lenses. The research was located in the area of continuous permafrost distribution, the vertical thickness of which reaches 400–500 m here. The average annual temperature of rocks ranges from -4.6 to -6.2 °C, in river valleys the temperatures are increased to about –2 to –1°C. Permafrost sediments in the Churapcha area are characterized by relatively high iciness, from 26 to 47%. Ice is found in deposits as interlayers that form a layered (as well as lenticular and braided) cryostructure. During the fieldwork, frozen cores opened by a drilling hole at a depth of 30 meters were studied. Drilling was carried out using a large-sized drilling rig (PBU-2) based on a Kamaz truck. A core drilling pipe with a diameter of 146 mm was used. Sampling was carried out from the frozen core. The well-uncovered permafrost deposits, which have mainly dark brown and gray colors, especially bluish-gray shades characteristic of heavy loams and clays. The seasonally active layer has a sandy loam composition, and below, at depths from 1.5 to 6.0 m, the deposits are loamy. At depths of 6.0–20.0 m, alternating layers of loams and clays of different thickness are observed, and below there is a sharp change in the lithological composition to medium and fine sand (20.75–24.0 m), including a large number of layers of organic matter. The distribution of δ18O and δ2H values was examined in structured ice up to a depth of 17.7 meters. In the upper 12 m, the isotopic composition is significantly more negative: δ18O values vary from –29.44 to –34.35‰, while δ2H values range from –213.5 to –253.6‰. In the 12-17.7 m range, δ18O oscillates between –25.94 and –28‰, whereas δ2H ranges from –195.3 to –214.3‰. Analysis of data on the isotopic composition of structure ice in the yedoma deposits of Yakutia showed a close range of values with the ice of unit 1 from the borehole in Churapcha that we studied. The heavier isotopic composition of ice of unit 2 is probably explained by another source of water and the influence of isotopic fractionation during the interaction of clay particles with water. As for the contrast of the isotopic characteristics of unit 1 and unit 2, we note that such a ratio, when the isotopic composition in the upper unit is on average consistently 3-5‰ lower than in the lower unit, is quite rare in permafrost.
The water for the formation of segregation ice from the borehole could have been formed to a greater extent from melted winter snow and was less subject to evaporation. Contrasting values in the ice of the two studied units may indicate different water sources; for the ice in unit 1, the water source could have been, to a greater extent, winter precipitation (surface water formed from melted snow); the presence of a negative peak in the vertical distribution of isotopic values may indicate two-sided freezing (from above and below) and isotopic fractionation during freezing.
The deposits of unit 2 are represented by heavy loams, probably lacustrine. It can be assumed that the saturation of these deposits under these conditions occurred with lake water, which consisted of a mixture of precipitation from both winter and summer seasons and was characterized by higher values of the isotopic composition. Freezing of these loams could have begun already when the lake became shallow. In any case, for now the probable explanation for the heavier isotopic composition of unit 2 is isotopic fractionation in water during interaction with clay particles and a different water source than in unit 1.