Abstract
Research subject . The article presents the results of investigating calcite lenses with a cone-in-cone structure from Middle Devonian clay terrigenous deposits in the Middle Timan. Methods. The investigation of petrographic thin-sections was carried out using a polarizing microscope Nikon eclipse LV100 ND equipped with a Nikon DS Fi2 camera. Polished sections etched with HCl were examined using a scanning electronic microscope JSM-6400 Jeol with a power dispersive spectrometer ISIS Link and a wave spectrometer Microspec. The decomposition of carbonates and the measurement of isotope carbon composition in the mode of continuous helium stream were carried out using a ThermoFisher Scientific analytical complex. Results. It is established that the investigated calcite bodies consists of mosaic block crystals having a drusy structure. Calcite is characterized by abnormally low values S 13 C carb - up to -23.5 %o. Clay films and soapstone inclusions were studied in detail. The formation mechanism of the saw-tooth profile of the upper bound of these inclusions was determined, which consists in the local substitution of alumosilicates with calcite under the maintenance of their relic layered texture. Conclusions. A new version of the crystallization model of carbonate body genesis with a cone-in-cone structure is proposed.
Highlights
The article presents the results of investigating calcite lenses with a cone-in-cone structure from Middle Devonian clay terrigenous deposits in the Middle Timan
The investigation of petrographic thin-sections was carried out using a polarizing microscope Nikon eclipse LV100 ND equipped with a Nikon DS Fi2 camera
Polished sections etched with HCl were examined using a scanning electronic microscope JSM-6400 Jeol with a power dispersive spectrometer ISIS Link and a wave spectrometer Microspec
Summary
При исследовании средне- и верхнедевонских терригенных отложений на Цилемской площади. Обнаружено два слоя эллипсоидальных (длиной до 20, толщиной до 14 см) сидеритовых конкреций в кровле и на. 1 – глинистый алевролит; 2 – алевритистый аргиллит; 3 – слой глины иллитового состава; 4 – двойные слои-линзы, сложенные туфом основного состава сверху и кальцитом с текстурой конус-в-конусе снизу; 5 – микроконкреционные слои перерывов осадконакопления; 6 – слои линзовидных конкреций; 7 – слои эллипсоидальных конкреций; 8 – раковины конхострак; 9 – остатки панцирных рыб; 10 – крупные фрагменты углефицированных наземных растений. 0.5, 1.1, 2.4, 3.2 м от подошвы пачки, и в средней части (1.6 м от подошвы) – горизонт сидеритовых линзовидных конкреций (длиной до 16, толщиной до 3.5 см). В 0.8 м от подошвы залегает горизонт линзовидных сидеритовых конкреций В кровле пачки обнаружен горизонт линзообразных тел из туфа и кальцита с текстурой конус-в-конусе. Образцы для дальнейших исследований отбирались с обязательной маркировкой кровли и подошвы слоя
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