Landscape Dynamics in the Caspian Lowlands Since the Last Deglaciation Reconstructed From the Pedosedimentary Sequence of Srednaya Akhtuba, Southern Russia

Marina Lebedeva,Redzhep Kurbanov,Alexey Rusakov,Tamara Yanina,Evgeniy Varlamov,Alexander Makeev,Pavel Kust,Tatiana Romanis

doi:10.3390/geosciences8120492

Abstract

Surface Kastanozem of the Lower Volga area was first studied as a part of the pedocomplex, with the lower part (148–160 cm) formed in Early Khvalynian Chocolate clays (13–15 ka), the middle part (100–148 cm) in a mixed clay-loess sediment sand, and the upper part (0–100 cm) in loess. This resulted from local aeolian transport, with the source material derived from the rewinding of marine sediments. They are enriched in aggregates of Chocolate clays and glauconitic grains of a fine sand-course silt size and have similar contents of clay minerals. The high salinity of similar types evidences marine genesis for both Chocolate clays and source material for loess sediments. Clay fragments of a sand and silt size are responsible for the heavy texture and high gypsum content of loess. The study of soils with the focus on micromorphology and clay mineralogy allows the identification of the complex character of a shift from marine to sub-areal sedimentation. This shift was accompanied by short breaks in sedimentation, allowing the development of synlithogenic soil horizons of Late Khvalynian, after-Khvanynian, and Boreal time. The features of shallowly buried soil horizons confirm increased aridity after the last deglaciation. Surface Calcic Kastanozem is a full Holocene soil reflecting the present environment. However, it is deeply influenced by shallow buried soil horizons and Chocolate clays.

Highlights

The Caspian Lowland is a part of the extensive Ponto-Caspian basin that reflects fluctuations in the level of the Caspian and Black sea, glacial-interglacial cycling, and related fluctuations in fluvial activityGeosciences 2018, 8, 492; doi:10.3390/geosciences8120492 www.mdpi.com/journal/geosciencesGeosciences 2018, 8, x FOR PEER REVIEW activity and aeolian sedimentation
Morphology, micromorphology, grain size distribution show that the studied Kastanozem is formed in a pedocomplex consisting of a layer of show that the studied
Kastanozem is formed in a pedocomplex consisting of a layer of loess distribution show that the studied Kastanozem is formed in a pedocomplex consisting of a(down layer to of loess underlain by Chocolate clays below 148 cm

Summary

Introduction

The Caspian Lowland is a part of the extensive Ponto-Caspian basin that reflects fluctuations in the level of the Caspian and Black sea, glacial-interglacial cycling, and related fluctuations in fluvial activity. Geosciences 2018, 8, x FOR PEER REVIEW activity and aeolian sedimentation. The outcrops at the banks of the Volga River and its tributaries expose detailed Late Pleistocene pedosedimentary sequences, with marine, aeolian, and fluvial. Geosciences 2018, 8, 492 deposits intermixed with pedogenetic levels of interglacial and interstadial paleosols [1]. During the last deglaciation and degradation of permafrost, the Volga River basin collected meltwater and acted as a aeolian trap forsedimentation. Pleistocene pedosedimentary sequences, and fluvial deposits clays–light-brown and dark-brown dense layers of heavy clays with a platy-prismatic structure intermixed with pedogenetic levels of interglacial and interstadial paleosols [1]. During the that last contain manganese and gypsum deglaciation and degradation ofstaining

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