First reliable chronology for the Early Khvalynian Caspian Sea transgression in the Lower Volga River valley

Abstract

During the late Quaternary, dramatic changes in relative sea level (~170 m) are known to have occurred in the Caspian Sea. However, all previous attempts at resolving the uncertainty associated with the timing of these transgressive/regressive events, primarily using radiocarbon, have produced inconclusive or controversial results. Here we present the first reliable chronology for the largest known transgression (Early Khvalynian). This was derived using optically stimulated luminescence (OSL) analysis of sand‐sized quartz, with support from infrared stimulated luminescence (IRSL) from K‐rich feldspar grains, all extracted from 16 sediment samples collected along the Lower Volga River. These samples were taken from loessic sediments, marine clays (known as Chocolate Clays) and the overlying modern soils exposed at three sections (Srednyaya Akhtuba, Raygorod, Leninsk) ~200 km upstream of the present‐day estuary. The differential bleaching rates of the quartz OSL and feldspar IRSL signals were used to evaluate the degree of resetting of quartz (and feldspar) signals; it was possible to conclude that all signals, and particularly quartz OSL, were sufficiently reset at deposition to allow accurate age estimation. Our results show unambiguously that the Early Khvalynian marine Chocolate Clays present at all three sections were deposited post‐LGM, between ~17 and ~13.1 ka ago. These age estimates are further constrained by those from the overlying Kastanozem soils (9.6–0.7 ka) and underlying loess‐soil series (32–19 ka), confirming a young (17–13 ka) age of the transgressive stage of the Early Khvalynian. Relative sea level during this period must have been well above the sampling altitudes of 11.7 m a.s.l. (Srednyaya Akhtuba), 11.3 m a.s.l. (Raygorod) and 4.7 m a.s.l. (Leninsk) to explain the absence of significant alluvial sand and to allow the deposition of the fine Chocolate Clays marker horizon.

Enviromagnetic study of Late Quaternary environmental evolution in Lower Volga loess sequences, Russia

“…Atelian does not strictly apply over all the Northern Caspian lowland and that at SA, site-specific influences such as local river migration might be reflected. Initial OSL ages from the chocolate clays are 13.4 ± 0.7 to 16.1 ± 1.4 ka, depending on their stratigraphic depth and have been obtained from all three sections (Kurbanov et al, 2020). These dates overlap with a single radiocarbon age of 14.0 ± 2.0 ka from SA (Kurbanov et al, 2020).…”

“…Initial OSL ages from the chocolate clays are 13.4 ± 0.7 to 16.1 ± 1.4 ka, depending on their stratigraphic depth and have been obtained from all three sections (Kurbanov et al, 2020). These dates overlap with a single radiocarbon age of 14.0 ± 2.0 ka from SA (Kurbanov et al, 2020). Existing OSL data of the continental deposits at RG and LN are currently unpublished, and the boundaries of the Atelian formation and MIS 3 and 4 are based on the established, yet unpublished, chronostratigraphy of the sections (Fig.…”

“…(color online) Map of the Caspian Sea region and surrounding areas with the study area located in the south of the Russian Plain (based on National Geographic World Map, Esri), the last glacial maximum ice sheet extent is depicted after Arkhipov et al (1995) (a), in the Lower Volga region of the Northern Caspian lowland (b). The three study sites Srednyaya Akhtuba, Leninsk and Raigorod are marked with stars (c) (from Kurbanov et al, 2020).…”

“…It should be considered that the loess was covered by a marine transgression for several ka (∼10 ka, Kurbanov et al, 2020), as the marine sand and clay overlying the loess deposits clearly reveal. A comparable setting is not known from any other loess site and appears to be unique for the Lower Volga profiles.…”

Chestnut Soils: A Comparison Study by Diffuse Reflectance and Attenuated Total Reflection FTIR spectroscopies with Fractionation

“…Samples of chestnut soils (WRB, 2006; Haplic Kastanozems) were taken at the Kachalino test site, Volgograd (lower Volga) region [8] were from two sections on the fallow (over 30 years; 49.06.42 N 44.09.43 E) and arable soil under the grain crop rotation (49.05.09 N 44.06.52 E). The wormwood-fescue association represents the vegetation cover of the deposit area.…”