Search Results (9)

The results of a recent palynological study of the Kulikovo section (southeastern Baltic) allow us to elaborate on issues of the presence of pollen from the “thermophilous” trees (Picea, Alnus, Corylus, Ulmus, Quercus, Tilia, Fraxinus) in Lateglacial sediments. The research shows their continuous presence throughout the interval of 13.9–12.5 ka with a total contribution from 7% to 17%. Comparing the results with regional palynological data revealed certain similarities and patterns, which are not sufficiently explained by contamination by ancient redeposited material. These taxa belonging to the hemiboreal plant group were most probably part of the Lateglacial vegetation along with subpolar and boreal plants. This correlates well with regional paleoclimate reconstructions, assuming that, during the major part of the Lateglacial, July temperatures were comparable to modern average temperatures, which range from +16.5 to +18 °C. Inclusion of hemiboreal tree vegetation in paleoreconstructions will offer an updated picture of the dynamics of the natural environment and increase the accuracy of paleoclimatic reconstructions based on palynological data, allowing us to obtain more accurate temperature values of the climate of the past. Full article

We present a two-dimensional reconstruction of blocking frequency indices in the Atlantic-European region spanning the last 400 years. Our approach is based on a simple field reconstruction scheme similar to the principal component regression method. The particularity of our reconstruction scheme is that we select the blocking predictors using observed and reconstructed surface temperature and precipitation gridded data based on the correlation stability criteria. This approach avoids the problem of non-stationarity between predictand and predictors that commonly affects the quality of climate field reconstructions. First, we reconstruct the blocking field back to 1891 using observed gridded surface temperature and precipitation data. Then, the reconstruction is extended back in time to 1602 using seasonal-resolution paleo-reanalysis temperature and precipitation fields. The reconstruction is validated against various observed blocking frequency fields and climate reconstruction indices. The methodology presented in this study offers an opportunity for extracting paleo-weather signals from seasonal-resolution gridded datasets, which enables an improved understanding of the forcing of low-frequency variability for atmospheric blockings and related extremes. Full article

This study reviews the Meso–Cenozoic tectonic paleo-reconstructions for the East Asian and western North American continental margins, focusing on strike-slip tectonics. It follows previous studies by the present and other authors, which investigated the Cretaceous turn of geological evolution (CTGE). They largely studied significant changes in the Earth’s mineralization, magmatism and climate. The present study focuses on significant changes related to the Earth’s rotation velocity. This question is significant not only for fundamental science, but also for applied geology, because CTGE is marked by abundant ore and energetic resources. The results show domination of sinistral shearing on the NE-oriented Asian margin during the pre-early Cretaceous time that turned to significant development of dextral movements in the mid Cretaceous–Cenozoic time. On the NW-oriented American margin, significant development of sinistral movements in the pre-early Cretaceous time turned to domination of dextral shearing during late Cretaceous and Cenozoic. These tectonic changes indicate the transition of the Earth’s rotation from the accelerating towards decelerating regime after CTGE (135–120 Ma). This change may be caused by the transition of the Earth’ mass to, and then, away from the polar regions, the processes being related to melting and freezing of the ice caps. Full article

Based on the data of the plant macrofossil and palynological composition of the peat deposits, the evolution and current state of polygonal peatlands were analyzed at the southern limit of continuous permafrost in the Pur-Taz interfluve. Paleoreconstruction shows that peat accumulation began in the Early Holocene, about 9814 cal. year BP, in the Late Pre-Boreal (PB-2), at a rate of 1 to 1.5 mm year⁻¹. Intensive peat accumulation continued in the Boreal and early Atlantic. The geocryological complex of polygonal peatlands has remained a stable bog system despite the predicted warming and increasing humidity. However, a rather rapid upper permafrost degradation and irreversible changes in the bog systems of polygonal peatlands occur with anthropogenic disturbances, in particular, a change in the natural hydrological regime under construction of linear objects. Full article

Trace elements in freshwater bivalve shells are widely used for reconstructing long-term changes in the riverine environments. However, Northern Eurasian regions, notably the European Russian North, susceptible to strong environmental impact via both local pollution and climate warming, are poorly studied. This work reports new data on trace elements accumulation by widespread species of freshwater mussels Unio spp. and Anodonta anatina in the Severnaya Dvina and the Onega River Basin, the two largest subarctic river basins in the Northeastern Europe. We revealed that iron and phosphorous accumulation in Unio spp. and Anodonta anatina shells have a strong relationship with a distance from the mouth of the studied river (the Severnaya Dvina). Based on multiparametric statistics comprising chemical composition of shells, water, and sediments, we demonstrated that the accumulation of elements in the shell depends on the environment of the biotope. Differences in the elemental composition of shells between different taxa are associated with ecological preferences of certain species to the substrate. The results set new constraints for the use of freshwater mussels’ shells for monitoring riverine environments and performing paleo-reconstructions. Full article

The eccentric dipole (ED) is the next approach of the geomagnetic field after the generally used geocentric dipole. Here, we analyzed the evolution of the ED during extreme events, such as the Matuyama-Brunhes polarity transition (~780 ka), the Laschamp (~41 ka) and Mono Lake (~34 ka) excursions, and during the time of two anomalous features of the geomagnetic field observed during the Holocene: the Levantine Iron Age Anomaly (LIAA, ~1000 BC) and the South Atlantic Anomaly (SAA, analyzed from ~700 AD to present day). The analysis was carried out using the paleoreconstructions that cover the time of the mentioned events (IMMAB4, IMOLEe, LSMOD.2, SHAWQ-Iron Age, and SHAWQ2k). We found that the ED moves around the meridian plane of 0–180° during the reversal and the excursions; it moves towards the region of the LIAA; and it moves away from the SAA. To investigate what information can be extracted from its evolution, we designed a simple model based on 360-point dipoles evenly distributed in a ring close to the inner core boundary that can be reversed and their magnitude changed. We tried to reproduce with our simple model the observed evolution of the ED, and the total field energy at the Earth’s surface. We observed that the modeled ED moves away from the region where we set the dipoles to reverse. If we consider that the ring dipoles could be related to convective columns in the outer core of the Earth, our simple model would indicate the potential of the displacement of the ED to give information about the regions in the outer core where changes start for polarity transitions and for the generation of important anomalies of the geomagnetic field. According to our simple model, the regions in which the most important events of the Holocene occur, or in which the last polarity reversal or excursion begin, are related to the regions of the Core Mantle Boundary (CMB), where the heat flux is low. Full article

The present study examined the references in the works of ancient authors to the ancient city and the Roman fortress Pitiunt, the geological aspects of the formation of the coastline in the Pitsunda Cape area in the first centuries AD and the results of archaeological research of the monument performed from 1952 to 1974. The creation of the 3D reconstruction of the exterior of the Pitiunt fortress during its prosperity in the IV century AD, along with the churches which were the first monuments of religious architecture in northwestern Colchis (northwestern Colchis comprises parts of the territory of modern Russia, Georgia and Abkhazia) was carried out based on the excavation plans and the principles of fortification and temple architecture that were accepted in the late Roman times, paying special attention to the geological paleoreconstructions. Full article

Peat sediments represent important environmental and climatic archives, as well as recording information on the processes affecting the formation of these deposits; combined these data can be used for paleoreconstruction of peat-bogs. In this paper we characterize heavy mineral-rich sandy layers from two peat-bog sites in Mizerów and Strumień (Poland). In both cases, the most common identified mineral suite is: epidote, staurolite, tourmaline (dravite and schörl), garnet, spinel, Al₂SiO₅ polymorphs (sillimanite, kyanite, andalusite), amphibole (mainly hornblende), pyroxene (e.g., richterite, diopside), perovskite, topaz, cordierite, apatite, monazite, chromite, ilmenite, chlorite, iron oxides, rutile and siderite. This mineral suite is characteristic of a metamorphic aureole surrounding a magmatic body. Pyrite is likely authigenic in origin. Apatite and monazite were employed for U-Pb and CHIME dating, respectively. Based on the U-Pb age information composition and textural features of selected minerals, different provenance areas were indicated: the Tatra Massif, the Bohemian Massif, and the Silesian Basin area. Transport of the investigated mineral phases was linked to development of both the Odra (praOdra) and the Vistula valleys. Full article

The emplacement age of the Great Udzha Dyke (northern Siberian Craton) was determined by the U-Pb dating of apatite using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). This produced an age of 1386 ± 30 Ma. This dyke along with two other adjacent intrusions, which cross-cut the sedimentary units of the Udzha paleo-rift, were subjected to paleomagnetic investigation. The paleomagnetic poles for the Udzha paleo-rift intrusions are consistent with previous results published for the Chieress dyke in the Anabar shield of the Siberian Craton (1384 ± 2 Ma). Our results suggest that there was a period of intense volcanism in the northern Siberian Craton, as well as allow us to reconstruct the apparent migration of the Siberian Craton during the Mesoproterozoic. Full article