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- Title
Paleosols as Markers of Stratigraphic Unconformities in the Upper Visean Rocks of the Mstikhino Section, Kaluga Oblast: Geochemistry, Mineralogy, and Biogenic Structures.
- Authors
Alekseeva, T. V.; Malyshev, V. V.; Alekseev, A. O.
- Abstract
The results of study of the Aleksinian–Venevian deposits of the Visean Stage exposed in a Mstikhino limestone open pit are presented. The samples for study were collected layer-by-layer and were studied using a complex of mineralogical–geochemical methods. Six unconformities are distinguished, which correspond to the main sedimentation breaks in a marine epicontinental basin. The deposits composing the unconformities are specified as paleosols and are divided into four pedotypes. Most profiles are thin and have a two-units structure: a variously subaerially transformed marine limestone (calcrete or karst) and a terrigenous layer also exogenically altered. The latter forms at the transgression stage and can represent the deposits of fresh temporally ephemeral lakes, marine shallow basins, or limestone eluvium. The following signatures of subaerial alteration of the top of limestones are revealed: the formation of platy and brecciated structures, a striking relief, the changes in physical properties (decrease in bulk density, the change in color and hardness), and the presence of rhizoliths. Carbonates exhibit dissolution and reprecipitation. The chemical composition is characterized by increased contents of Si, Al, Fe, K, and heavy metals. The terrigenous layers (carbonate or carbonate-free) in most cases are the coastal-marine pioneer soils. They contain organic matter; biota is presented by rhizoliths, plant detritus, and plant spores. Ferrugination is a morphologically striking and analytically supported feature. According to Mössbauer spectroscopy, the Fe-bearing phases include oxides: goethite and hematite in various proportions. The lower terrigenous level of the Mikhailovian Horizon (MHT1) is determined as a swamp paleosol (histosol) formed on a clastic carbonate-free substrate, which represents the bottom deposits of a freshwater lake, which was further shoaled and swamped. The diverse vegetation included bryophyte-like plants and lycopod trees. The complex of the characteristics indicated that the climate of the Mikhailovian period at the studied territory fluctuated, exhibiting dominant humid conditions and the amount of precipitation of 800–1000 mm/year. More arid periods with dominant Calcisol were also present. The comparison of our results with previously published data on a soil cover of the Moscow sedimentary basin in the Early Carboniferous showed its lateral diversity. At the same time, the paleosol of the MHT1 period is found in other open pits of Kaluga oblast. It is morphologically recognizable, has a specific mineral composition, and can be considered a significant stratigraphic unit (Geosol).
- Subjects
KALUGA (Kaluzhskaia oblast', Russia); MOSCOW (Russia); MINERALOGY; CALCRETES; LAKE sediments; PALEOPEDOLOGY; SEDIMENTARY basins; PLANT spores; GEOCHEMISTRY
- Publication
Stratigraphy & Geological Correlation, 2022, Vol 30, Issue 6, p475
- ISSN
0869-5938
- Publication type
Article
- DOI
10.1134/S086959382206003X