Pleistocene Environmental Changes Research Articles

Alternation between terrestrial and aquatic plants dominated organic matter sources in the Tiaoshu wetland (south China) and its response to late Pleistocene environmental changes

Widely distributed wetlands in China play an important role in the global carbon cycle. However, the long-term response of wetland evolution and carbon storage in tropical southern China to climate change remains unclear. Here, we present a sediment core record from the Tiaoshu Wetland in the northern Leizhou Peninsula and multiple proxy indicators are investigated, with the aim of better understanding past vegetation and environmental changes. The following conclusions were drawn: (i) The organic matter deposited in the Tiaoshu Wetland was mainly derived from terrestrial C3 plants and aquatic plants growing in and/or around the catchment. The temporal variability in the relative proportions of organic matter contributed by various sources revealed paleoenvironmental changes in the study area, generally consistent with regional and global climate records. (ii) The peat formation pattern in the Tiaoshu Wetland is in contrast to some individual sites reported in subtropical China, suggesting that there may be different peat formation patterns in the tropical and subtropical regions of China, which may be closely related to specific hydrothermal conditions in different regions. In addition, by comparison with atmospheric CH4 concentrations, our results suggest potential relationships between the evolution of wetlands in tropical China and global atmospheric CH4 cycles.

Response of Mediterranean Sea bivalves to Pliocene–Pleistocene environmental changes

AbstractThe Mediterranean Sea is recognized as a hotspot of marine biodiversity. Analysing its past biodiversity can help in understanding species' response to climate change. We built a species‐level dataset of bivalve occurrences across the Zanclean–Calabrian interval, a time characterized by significant changes in climate, and by bivalve extinctions. The dataset includes more than 400 species distributed from the eastern to the western Mediterranean Sea. We measured changes in richness and turnover through time, for the entire dataset, and for different palaeoenvironments and combinations of tiering and feeding categories to test if specific environmental conditions and different lifestyles were correlated to species extinction or survival through time. We also compared niche breadth, geographical range size, and species abundance of extinct and extant species, to test which of these parameters potentially affected extinction risk. Our results confirm a loss of biodiversity between 3 Ma and the Early Pleistocene, although this loss was less intense and more gradual than previously estimated. We also found significant differences in niche breadth and geographical range size between extinct and extant species. Suspension feeders lost a higher proportion of species and suffered a higher reduction of geographical range compared to infaunal deposit feeders. Species loss was more protracted and higher on the shoreface than on the shelf, which is probably related to the reduction of shallow‐water vegetated environments and to the disaggregation of heterozoan carbonate ramp habitats with cooling and sea‐level drop at the onset of the northern hemisphere glaciation.

The Early-Middle Pleistocene Environmental Changes on the Diatom Proxies at the South Kunashir Island (Kurile Islands)

The article considers diatom biostratigraphy and ecological factors of the formation of diatom complexes that characterize the Pleistocene volcanic-sedimentary facies of shelf deposits of the Golovnin Formation. Dividing the Golovnin Formation is proposed according to diatom complexes into three biostratigraphic zones: Zone <i>Eupyxidicula zabelinae,</i> Zone <i>Thalassiosira antiqua</i>, Zone <i>Proboscia Proboscima barboi</i>. Three transgressive phases of formation of the Golovnin deposits were established under the paleoecological analysis of diatom associations. Early Pleistocene transgressions are named Kunashir I (2.12-2.0 Ma) and Kunashiri II (1.95-1.77 Ma). The Late Golovnin transgressions during 0.424-0.374 Ma and 0.337-0.300 Ma are correlated to the Marine Isotopic Stages 11 and 9 respectively.

Revisiting Late Pleistocene Loess–Paleosol Sequences in the Azov Sea Region of Russia: Chronostratigraphy and Paleoenvironmental Record

Loess-paleosol sequences are the most intensively studied terrestrial archives used for the reconstruction of Late Pleistocene environmental and climatic changes in the Azov Sea region, southwest Russia. Here we present a refined chronostratigraphy and a multiproxy record of Late Pleistocene environmental dynamics of the most complete and representative loess–paleosol sequences (Beglitsa and Chumbur-Kosa sections) from the Azov Sea region. We propose a new chronostratigraphy following the Chinese and Danubean loess stratigraphic models that refines the subdivision of the Last Interglacial paleosol (S1) complex in two Azov Sea sites, resolve the uncertainty of the stratigraphic position of the weakly developed paleosol (L1SSm) in Beglitsa section, and allow for direct correlation of the Azov Sea sections with those in the Danube Basin and the Chinese Loess Plateau. More importantly, it may serve as a basis for better constraining local and regional chronostratigraphic correlations, and facilitate the interpretation of climatic connections and possible forcing mechanisms responsible for the climatic trends in the region. In addition, a general succession of environmental dynamics is reconstructed from these two vital sections, which is broadly consistent with other loess records in the Dnieper Lowland and Lower Danube Basin, demonstrating similar climatic trends at Glacial–Interglacial time scales. Furthermore, our results have important implications for the chronostratigraphic representativeness of Beglitsa as a key regional loess section and for the reconstruction of the temporal and spatial evolution of Late Pleistocene climate in the Azov Sea region.

Phylogeography and evolutionary dynamism of marine gastropods from the Lord Howe Island Group

Context There has been considerable interest in the biogeography of the marine fauna of the Lord Howe Island Group (LHIG) lying ~580 km from continental Australia. Most phylogenetic studies of the group’s marine taxa have included few specimens, limiting their phylogeographic perspective. Aims This investigation was conducted to enhance understanding of the phylogeographic relationships of the LHIG, especially with temperate Australia. Methods The investigation used mitochondrial DNA sequences of the muricid subfamily Ergalataxinae, especially Tenguella, which has a broad distribution in the Indo-West Pacific, and two other gastropod genera, Cellana and Bembicium, each proposed to have endemic species in the LHIG. Key results Most species of LHIG Ergalataxinae have recent genetic connections with tropical landmasses, but Tenguella marginalba is closely related to temperate mainland conspecifics. The endemic taxa Cellana howensis and Bembicium flavescens respectively, have tropical and southern temperate affinities. Conclusions The most recent common ancestors (MCRAs) of LHIG specimens of each of B. flavescens, C. howensis and T. marginalba all date from long after the archipelago’s emergence. Implications The studied species may have arrived only recently on the archipelago. Alternatively, their estimated MCRAs may be due to recent demographic bottlenecks or selective sweeps influenced by Pleistocene environmental changes.

Demographic changes in Pleistocene sea turtles were driven by past sea level fluctuations affecting feeding habitat availability.

Pleistocene environmental changes are generally assumed to have dramatically affected species’ demography via changes in habitat availability, but this is challenging to investigate due to our limited knowledge of how Pleistocene ecosystems changed through time. Here, we tracked changes in shallow marine habitat availability resulting from Pleistocene sea level fluctuations throughout the last glacial cycle (120–14 thousand years ago; kya) and assessed correlations with past changes in genetic diversity inferred from genome‐wide SNPs, obtained via ddRAD sequencing, in Caribbean hawksbill turtles, which feed in coral reefs commonly found in shallow tropical waters. We found sea level regression resulted in an average 75% reduction in shallow marine habitat availability during the last glacial cycle. Changes in shallow marine habitat availability correlated strongly with past changes in hawksbill turtle genetic diversity, which gradually declined to ~1/4th of present‐day levels during the Last Glacial Maximum (LGM; 26–19 kya). Shallow marine habitat availability and genetic diversity rapidly increased after the LGM, signifying a population expansion in response to warming environmental conditions. Our results suggest a positive correlation between Pleistocene environmental changes, habitat availability and species’ demography, and that demographic changes in hawksbill turtles were potentially driven by feeding habitat availability. However, we also identified challenges associated with disentangling the potential environmental drivers of past demographic changes, which highlights the need for integrative approaches. Our conclusions underline the role of habitat availability on species’ demography and biodiversity, and that the consequences of ongoing habitat loss should not be underestimated.

Orbital Forcing of Late Miocene–Early Pleistocene Environmental Change in the Zhada Basin, SW Tibetan Plateau

AbstractMechanisms controlling the long‐ and short‐term variability of the Indian Summer Monsoon (ISM) and high‐elevation environmental change have largely been examined using low‐elevation or marine records with less emphasis on high‐elevation non‐marine records. We address this using a high‐resolution, long‐term record from upper Miocene–lower Pleistocene (~9.0–2.2 Ma) fluvio‐lacustrine strata in the Zhada Basin, southwestern Tibetan Plateau. Long‐term changes include the onset of lacustrine deposition, a decrease in mean grain size, and an increase in δ18Ocarb and δ13Ccarb values at ~6.0 Ma in response to basin closure following regional extension. This was followed by a return to palustrine/fluvial deposition, an increase in mean grain size, and a decrease in δ18Ocarb and δ13Ccarb values at ~3.5 Ma in response to tectonically driven long‐term ISM weakening. Spectral analysis reveals that high‐frequency variations in the δ18Ocarb record are dominated by 100 and ~20 kyr cycles from ~6.0–2.2 Ma. Wavelet and spectral analysis of the most densely sampled interval (4.23–3.55 Ma), tuned to the record of daily insolation (21 June at 35°N) confirms and highlights 100 and 20 kyr cycles. The tuned Pliocene δ18Ocarb record is coherent with the record of Northern Hemisphere insolation at precession periods but not at obliquity or eccentricity periods. Additionally, the tuned δ18Ocarb record is anticorrelated to the insolation record, indicating that stronger Northern Hemisphere insolation correlates with a stronger ISM. These results suggest that variations in daily insolation drove late Miocene–early Pleistocene high‐frequency ISM variability and environmental changes in the high‐elevation southwestern Tibetan Plateau.

Technological innovations at the onset of the Mid-Pleistocene Climate Transition in high-latitude East Asia.

The interplay between Pleistocene climatic variability and hominin adaptations to diverse terrestrial ecosystems is a key topic in human evolutionary studies. Early and Middle Pleistocene environmental change and its relation to hominin behavioural responses has been a subject of great interest in Africa and Europe, though little information is available for other key regions of the Old World, particularly from Eastern Asia. Here we examine key Early Pleistocene sites of the Nihewan Basin, in high-latitude northern China, dating between ∼1.4 and 1.0 million years ago (Ma). We compare stone-tool assemblages from three Early Pleistocene sites in the Nihewan Basin, including detailed assessment of stone-tool refitting sequences at the ∼1.1-Ma-old site of Cenjiawan. Increased toolmaking skills and technological innovations are evident in the Nihewan Basin at the onset of the Mid-Pleistocene Climate Transition (MPT). Examination of the lithic technology of the Nihewan sites, together with an assessment of other key Palaeolithic sites of China, indicates that toolkits show increasing diversity at the outset of the MPT and in its aftermath. The overall evidence indicates the adaptive flexibility of early hominins to ecosystem changes since the MPT, though regional abandonments are also apparent in high latitudes, likely owing to cold and oscillating environmental conditions. The view presented here sharply contrasts with traditional arguments that stone-tool technologies of China are homogeneous and continuous over the course of the Early Pleistocene.

Insights into subtropical Australian aridity from Welsby Lagoon, north Stradbroke Island, over the past 80,000 years

Terrestrial sedimentary archives that record environmental responses to climate over the last glacial cycle are underrepresented in subtropical Australia. Limited spatial and temporal palaeoenvironmental record coverage across large parts of eastern Australia contribute to uncertainty regarding the relationship between long-term climate change and palaeoecological turnover; including the extinction of Australian megafauna during the late Pleistocene. This study presents a new, high-resolution, calibrated geochemical record and numerical dating framework from Welsby Lagoon, a wetland from North Stradbroke Island that records key periods of late Pleistocene environmental change. Single-grain optically stimulated luminescence and radiocarbon dating are integrated into a Bayesian age-depth model for the sedimentary sequence spanning Marine Isotope Stage (MIS) 5 to the present. Scanning micro X-ray fluorescence (XRF) and bulk sediment XRF assays are used to infer past dust dynamics, with changes in the abundance of silica and potassium interpreted as proxies for aridity across local and regional sources. Variations in dust flux were contemporaneous with hydrological change, concordant with changes in vegetation cover on the island and, relate to deflation events at major dust source regions on the Australian continent. The Welsby Lagoon record supports the notion of a variable MIS4 within which an increased dust flux (71–67 ka), may be indicative of drier climate. Additionally, the record also shows a lower dust flux through the Last Glacial Maximum (LGM) than is evident in other Australian aeolian records. However, this low LGM flux is attributed to the wetland’s evolution, rather than a reduction in total dust flux.

Multiproxy evidence of middle and Late Pleistocene environmental changes in the loess-paleosol sequence of Bůhzdař (Czech Republic)

Loess-paleosol sequences preserve information that can be used to reconstruct paleoenvironments. A dense network of reliably analyzed sequences from different geographic locations is crucial to address ecological and climatic trends, which occurred during the Pleistocene. This paper focuses on a loess-paleosol sequence in Bůhzdař, situated 9 km NW of Prague, Czech Republic. Geochemical approaches (total organic carbon, XRF elemental analyses, XRD mineralogy, 13C and 18O stable isotopes) are combined with grain-size distributions and optically stimulated luminescence (OSL) to assess the climatic conditions at the time of formation of the strata. The oldest loess at this location was formed circa 200 ka ago (MIS 7), making it the oldest loess in Central Bohemia for now. The Bůhzdař loess-paleosol sequence was highly affected by several erosion events, Eemian paleosols (MIS 5e) being completely missing. The partly relocated paleosols situated at the lower part of the Bůhzdař sequence represent a period of increased humidity during late MIS 7 and MIS 6. Despite the fact that the Bůhzdař profile is not particularly thick (5 m), significant changes in paleoclimate reconstructions have been detected.

Amplitude, frequency and drivers of Caspian Sea lake‐level variations during the Early Pleistocene and their impact on a protected wave‐dominated coastline

AbstractThe Caspian Sea, the largest isolated lake in the world, witnessed drastic lake‐level variations during the Quaternary. This restricted basin appears very sensitive to lake‐level variations, due to important variations in regional evaporation, precipitation and runoff. The amplitude, frequency and drivers of these lake‐level changes are still poorly documented and understood. Studying geological records of the Caspian Sea might be the key to better comprehend the complexity of these oscillations. The Hajigabul section documents sediment deposited on the northern margin of the Kura Basin, a former embayment of the Caspian Sea. The 2035 m thick, well‐exposed section was previously dated by magneto‐biostratigraphic techniques and provides an excellent record of Early Pleistocene environmental, lake‐level and climate changes. Within this succession, the 1050 m thick Apsheronian regional stage, between ca 2·1 Ma and 0·85 Ma, represents a particular time interval with 20 regressive sequences documented by sedimentary and palaeontological changes. Sequences are regressing from offshore to coastal, lagoonal or terrestrial settings and are bounded by abrupt flooding events. Sediment reveals a low energy, wave‐dominated, reflective beach system. Wave baselines delimiting each facies association appear to be located at shallower bathymetries compared to the open ocean. Water depth estimations of the wave baselines allow reconstruction of a lake‐level curve, recording oscillations of ca 40 m amplitude. Cyclostratigraphic analyses display lake‐level frequency close to 41 kyr, pointing to allogenic forcing, dominated by obliquity cycles and suggesting a direct or indirect link with high‐latitude climates and environments. This study provides a detailed lake‐level curve for the Early Pleistocene Caspian Sea and constitutes a first step towards a better comprehension of the magnitude, occurrence and forcing mechanisms of Caspian Sea lake‐level changes. Facies models developed in this study regarding sedimentary architectures of palaeocoastlines affected by repeated lake‐level fluctuations may form good analogues for other (semi‐)isolated basins worldwide.

Climatic and landscape influences on the distribution and abundance of the Pleistocene small-mammal burrows of Ukraine

ABSTRACT In this publication, we consider the impact of the Pleistocene environmental changes (with a focus on soil formation and other factors) on the abundance and distribution of burrowing small mammals in the Ukrainian area. The general patterns of changes in nature and climate, such as direction, rhythm, zonality, regionality, and individuality of development, play a significant role in analysing the trends in the small mammal fauna change over time and laterally throughout the Pleistocene. These patterns became decisive in the formation and distribution of the small-mammal fauna in Ukraine, when the climatic conditions, accessibility to colonisation, determined by obstacles and distance from the centres of formation of previously existing species, served as restriction.

Late Pleistocene sediments, landforms and events in Scotland: a review of the terrestrial stratigraphic record

ABSTRACTLithostratigraphical studies coupled with the development of new dating methods has led to significant progress in understanding the Late Pleistocene terrestrial record in Scotland. Systematic analysis and re-evaluation of key localities have provided new insights into the complexity of the event stratigraphy in some regions and the timing of Late Pleistocene environmental changes, but few additional critical sites have been described in the past 25 years. The terrestrial stratigraphic record remains important for understanding the timing, sequence and patterns of glaciation and deglaciation during the last glacial/interglacial cycle. Former interpretations of ice-free areas in peripheral areas during the Last Glacial Maximum (LGM) are inconsistent with current stratigraphic and dating evidence. Significant challenges remain to determine events and patterns of glaciation during the Early and Middle Devensian, particularly in the context of offshore evidence and ice sheet modelling that indicate significant build-up of ice throughout much of the period. The terrestrial evidence broadly supports recent reconstructions of a highly dynamic and climate-sensitive British–Irish Ice Sheet (BIIS), which apparently reached its greatest thickness in Scotland between 30 and 27ka, before the global LGM. A thick (relative to topography) integrated ice sheet reaching the shelf edge with a simple ice-divide structure was replaced after the LGM by a much thinner one comprising multiple dispersion centres and a more complex flow structure.

The Early Pleistocene environmental change in the northwestern Osaka sedimentary basin, southwestern Japan

The Early Pleistocene environmental change in the northwestern Osaka sedimentary basin, southwestern Japan

Overdeepened glacial basins as archives for the Quaternary landscape evolution of the Alps

The Alps and the Alpine foreland have been shaped by repeated glaciations during Quaternary glacial-interglacial cycles. Extent, timing and impact on landscape evolution of these glaciations are, however, poorly constrained due to the fragmentary character of terrestrial archives. In this context, the sedimentary infills of subglacially eroded, ‘overdeepened’, basins may serve as important archives to complement the Quaternary stratigraphy over several glacial-interglacial cycles. In this thesis, the infills of deep subglacial basins in the Lower Glatt valley (N Switzerland) are explored to better constrain the Middle- to Late Pleistocene environmental change. Five drill cores gave direct insight into to the up to ~200 m thick valley fill at the study site and allowed for detailed analysis of sedimentary facies, age and architecture of the basin fills. A first focus is set on the sedimentology of coarse-grained diamicts with sorted interbeds overlying bedrock in the trough center, which mark the onset of deposition in many glacial bedrock troughs. Evidence from macro- and microsedimentology suggests that these sediments are emplaced subglacially and reflect deposition, reworking and deformation in response to repeated coupling and decoupling of the ice-bed interface promoted by high basal water pressures. Overlying these subglacial sediments, large volumes of sandy glacio-deltaic, fine-grained glacio-lacustrine and lacustrine sediments document sedimentation during glacier retreat from the basins. On these thick valley fill sequences the applicability and reliability of luminescence dating is investigated in a second step on the basis of experiments with several different luminescence signals, protocols and experiments to assess the signal stability. The valley fill of the Lower Glatt valley is then grouped into nine depositional cycles (Formations A-I), which are related to the Birrfeld Glaciation (~MIS2), the Beringen Glaciation (~MIS6), and up to three earlier Middle Pleistocene glaciations, tentatively correlated to the Hagenholz, Habsburg, and Mohlin Glaciations, according to the regional glaciation history. The complex bedrock geometry and valley fill architecture are shown to be the result of multiple erosion and infilling cycles and reflect the interplay of subglacial erosion, glacial to lacustrine infilling of overdeepened basins, and fluvial down-cutting and aggradation in the non-overdeepened valley fill. Evidence suggests that in the study area deep bedrock incision, and/or partial re-excavation, occurred mainly during the Beringen and Hagenholz Glaciation, while older structures may have existed. Together with the observation of minor, ‘inlaid’ glacial basins, dynamic changes in the magnitude and focus of subglacial erosion over time are documented.

Substantial biases affecting Combe-Grenal faunal record cast doubts on previous models of Neanderthal subsistence and environmental context

Abstract: This short contribution presents faunal data from new fieldwork at the Middle Palaeolithic site of Combe-Grenal (Dordogne, France). This important sequence continues to serve as both a reference sequence to which other Western European Middle Palaeolithic sites are often compared and the basis of several models of Neanderthal subsistence and environmental context. However, several researchers have highlighted the likelihood that skeletal part profiles were biased as a consequence of the incomplete recovery methods used during previous excavations at Combe-Grenal. A comparison of faunal remains recovered during new excavations with data from the original collections allows recovery bias induced by previous excavation protocols to be quantified. The unreliability of the original skeletal part profiles is confirmed by our study, while, more importantly and unexpectedly, radical biases in species frequencies were equally identified. These results cast doubts on several interpretive models held to account for variability in Mousterian industries, the evolution of Neanderthal hunting strategies, as well as Pleistocene environmental changes. Furthermore, Combe-Grenal provides an instructive example to archaeologists working on sites with less than ideal recovery methods of faunal material. In such cases, recovery biases may be so substantial than even basic faunal data, such as species lists, prove unreliable.

A cave response to environmental changes in the Late Pleistocene: a study of Budimirica Cave sediments, Macedonia

Budimirica Cave is a small cave located in the southern part of the Republic of Macedonia, in the Kamenica Valley, a tributary to the Crna Reka and part of the Vardar river drainage network. The response of the cave to Late Pleistocene environmental changes is interpreted based on a detailed study of cave sediments, with previous data being supplemented, reinterpreted and compared to the Ohrid Lake palaeoclimate record. The oldest exposed speleothems in the Budimirica sediment profile were deposited during the MIS 5a (radiometric age of ca 83 ka). Sands to clays in the overburden are characterized by cycles separated by short-lived interruptions in deposition. They were deposited from a number of repeated flood events likely during the MIS 4 stage, the Weichselian (Wurmian) Glaciation, correlating to aggradation in the Kamenica Valley. The top flowstone is correlated with a warmer climate excursion at 45–50 ka (MIS 3) recorded from the Ohrid Lake deposits. The whole section was extensively eroded during the MIS 2 stage, due to strong incision in the Kamenica Valley, indicated by knickpoint retreat. The erosion surface is overlain by a fossil-bearing breccia (with Ursus spelaeus) derived from frost shattering of the cave walls close to the entrance due to climate deterioration and enlargement of the entrance by slope retreat during the MIS 2 stage. Budimirica Cave sediments reflect changes in the Kamenica Valley, as well as the environmental changes during the last glacial-interglacial cycle, with clastic cave sediments deposited during glacial stadials, and erosion and flowstone deposition characteristic of the interstadials. They also allow reconstruction of the evolution of the Kamenica Valley during the Late Pleistocene, with a general trend of valley incision hindered by climate influenced river aggradation, but reinforced by river knickpoint retreat.

Extinction rates of the Meade Basin rodents: application to current biodiversity losses

Extinction rates for terrestrial rodent species from palaeontological sites in the Meade Basin of southwestern Kansas and an archaeological site in New Mexico are compared with extinction rates for modern rodents from locations affected by anthropogenic activities. Background extinction rates are defined as global extinctions occurring over proscribed intervals in the absence of significant environmental perturbations. Background rates for the Meade Basin are estimated at 0–~1.0 E/MSY (extinctions per million species years). Elevated rates from 1.4 to 6.25 E/MSY are associated with volcanic events and Late Pleistocene environmental change. These rates are considerably less than those for rodent extinction rates promoted by human activities during the Holocene, the latter ranging from 42.3 to 50,000 E/MSY.

Late Pleistocene (MIS2) environmental changes and palaeoclimatic dynamics around Aiding Lake in the Turpan Basin, Xinjiang Province, NW-China

Late Pleistocene (MIS2) environmental changes and palaeoclimatic dynamics around Aiding Lake in the Turpan Basin, Xinjiang Province, NW-China

Radiocarbon dates, microblades and Late Pleistocene human migrations in the Transbaikal, Russia and the Paleo-Sakhalin-Hokkaido-Kuril Peninsula

We compare late Pleistocene archaeological 14C databases from the Transbaikal, Russia and the Paleo-Sakhalin-Hokkaido-Kuril Peninsula (PSHK) to the appearance and disappearance of microblade technology for evidence of human migration. In the Transbaikal, we identify as many as three events at 24,830, 22,740, and ∼15,000 cal bp, respectively. On the PSHK, we see migration at ∼26,800, and likely again at ∼13,000 cal bp. We offer an explanation for the Last Glacial Maximum origin of northeast Asian microblades that reconciles several major points of current competing theories. The later migration signals in both areas are weaker and associated with terminal Pleistocene (Bølling-Allerød-Younger Dryas) environmental changes at the beginning of the Mesolithic Period in the Transbaikal and the Incipient-Jomon Period on PSHK. In the former, the second migration event may have been repopulation of an empty or sparsely inhabited area. In the latter, it appears to be population replacement when microblades completely disappear from the Peninsula without a reduction in the number of 14C dates.