Climate change dynamics in Northern Eurasia over the last 200 ka: Evidence from mollusc-based ESR-chronostratigraphy and vegetation successions of the loess–palaeosol records

Abstract

The time span of the past 200 ka has been marked by many large-scale global and regional climate changes, between warmer and cooler conditions. As is usually the case when studying the past, palaeoenvironmental data become scarcer with increasing age. Therefore, every detailed palaeoenvironmental record may be of special interest to Quaternary geologists in terms of palaeoenvironmental reconstructions, correlations and general stratigraphy of the Quaternary.

In this paper we present a long palynological record of terrestrial flora and an ESR-dated marine record of global-scale climatic variation obtained from a loess–palaeosol sequence in the East European Plain and continental margin of Northern Eurasia for the time span starting from the penultimate glacial period correlating with Marine Isotope Stage (MIS) 6. These records show that in combination they have a potential of assigning warm/cold climate related deposits to the chronostratigraphically organised sequence of the late Pleistocene palaeoenvironmental events.

Introduction

Long and continuous terrestrial proxy climate records throughout the time interval since the penultimate (Dnieper/Saale, MIS 6) glaciation are rare. A few most complete loess–palaeosol sections are situated in the glacial and extraglacial zones of the East European Plain. At present, these are among the longest and palynologically best studied sections (Bolikhovskaya, 1995). However, each of those is seriously limited in age control, especially beyond the limits of radiocarbon dating. Since our first joint paper (Bolikhovskaya and Molodkov, 1999), the palynostratigraphical record derived from long continuous loess–palaeosol sequences was calibrated for age by correlation to the mollusc-based ESR-chronostratigraphical record in which warm-climate-related events were dated by ESR on subfossil mollusc shells taken directly from the transgressive marine sediments. This integrated palyno-chronostratigraphic approach allowed us to constitute precious palaeoclimatic references helping to link at least the most prominent palaeoenvironmental events that had occurred in Northern Eurasia over the last 600 ka (Bolikhovskaya and Molodkov, 2002, Molodkov and Bolikhovskaya, 2002).

In the present study, we attempted to link marine mollusc-based age analysis from the two last glacial intervals and an interglacial between them with the palaeoclimatic data derived from the pollen-based vegetation signals of terrestrial environment from the East European loess province. The linkage of these two independent climatic records is our first attempt to insight palaeoenvironmental changes during the last two glacial periods where radiometrically dateable materials typically are scarce both in terrestrial and marine sediments.

The development of the loess–palaeosol formation (LPF) within the East European loess province has been closely related to ice sheet dynamics. Therefore, the long continuous loess–palaeosol sequences located in the glacial and extraglacial zones of this area, when thoroughly analysed palynologically, can provide the most detailed middle-late Pleistocene climatic records ever retrieved in this palaeoenvironmentally important geographical region. The best known sections here are the Likhvin-Chekalin (Upper Oka), Strelitsa (Upper Don), Arapovichi (Middle Desna), Molodova and Ketrosy (Middle Dniester), and Otkaznoe (Middle Kuma) (Fig. 1), because they provide evidence of almost complete and continuous deposition and contain enough pollen to construct a record of climate-driven vegetation changes since the penultimate glaciation (Bolikhovskaya, 1995).

However, time control in a long-term continental record is often poor. For a reliable understanding of the climate changes in the past, it is fundamental to integrate the long and continuous continental record in a physically dated time stratigraphic framework. For this purpose we use two independent sources of palaeoenvironmental data: electron spin resonance (ESR) chronology of warm-climate-related marine deposits and terrestrial record of vegetation response to climatic variability and palaeoenvironmental events.

Marine deposits of Northern Eurasia are palaeoenvironmentally the most important for Quaternary studies, as they are located in a climate-sensitive area, are characterized by a wide distribution, continuous sedimentation, and by usually well-preserved fossil material. Among the latter, mollusc shells are often found in uplifted coastal marine deposits. Dating of these fossils from transgressive deposits can provide an independent chronology of global ice volume and sea level/climate change. In other words, the raised mollusc-rich marine deposits can be considered to be a proxy indicator of global climate change that should be reflected both in marine and terrestrial records.

The palynological data of reference sections of the glacial–periglacial and extraglacial zones, reflecting the succession of vegetation following changes of moisture and heat supply in the Pleistocene, can provide the most complete record of climatic conditions on land, the assessment of the stratigraphic position of sediments, intra- and inter-regional correlations of geological bodies and palaeogeographical events. The structure of this record can be directly compared with the climate-dependent curve of deep-sea oxygen isotopy.

Together, this multi-proxy data from the continental and marine records should provide important evidence about the remote linkage between marine and terrestrial sedimentary environments: mollusc-rich raised marine deposits in the coastal areas of Northern Eurasia can be readily correlated to key palynological signatures of interglacial deposits in the complete terrestrial record and used as the basis for determining their chronostratigraphical position and their age. Besides, in such a way it is possible to demonstrate the presence of a chronological hierarchy of palaeoenvironmental events in the late middle and late Pleistocene sedimentary sequence that would allow us to interpret this observation in terms of climate changes. Such an integrated approach is of great importance for establishing event-to-event land-sea correlations, for understanding relatively long-term large-scale naturally induced climate changes, and for linkage of terrestrial and ESR-dated marine sequence to the standard measure of Pleistocene climate change like the global marine isotope stage sequence.