Cal Kyr BP Research Articles

Late Quaternary environmental changes of Lake Urmia basin (NW Iran) inferred from sedimentological and magnetic records

The ongoing changes affecting Lake Urmia (NW Iran) are revealed by the lake water level decrease (~7 m in the last 20 yr) that was attributed to natural and anthropogenic causes but the exact impact of these factors on the state of the lake is still not identified. Indeed, lack of detailed record of environmental evolution of the lake in the past limits the understanding of actual and future processes. Our project aims to obtain a high-temporal resolution record of environmental changes in the lake area for the last ~30 kyrs. Sediment cores have been obtained from the recently dried out part of the lake near Urmia City, and surface and ground waters have been measured for electric conductivity. This paper presents results of water and sediments analyses. Six 14C AMS dating on organic fractions provide a chronological framework and indicate that the record covers the last ~30 cal kyr BP. During this period, evaporitic conditions were prevailing in the lake. The electric conductivity of brines from the sediment highlights changes in the lake water salinity. The data indicate a lake-level low stand at ~30 cal kyr BP that was followed by a water level rise and establishment of lacustrine conditions for the next ~9 kyr, this phase representing the highest lake level recorded since that time to date. From the LGM, the lake experienced several fluctuations of the water level. The relatively long-term lacustrine condition established during the Early Holocene before the water level decrease between ~5.5 and 4.9 cal kyr BP. Sediments from the two dry events at ~30 cal kyr BP and at 5.5–4.9 cal kyr BP are characterized by the presence of greigite, which indicates anaerobic early diagenetic conditions in the sediment.

Climatic and environmental change in the western Tibetan Plateau during the Holocene, recorded by lake sediments from Aweng Co

Understanding the strength and extent of the Asian summer monsoon (including the East Asian summer monsoon and the Indian summer monsoon) in the Tibetan Plateau (TP) region is crucial for predicting possible changes in the regional eco-environment and water resources under global warming. Due to the lack of well-dated and high-resolution paleoclimate records, long-term monsoon dynamics are still not well understood in the western TP, which is currently influenced by both the Indian summer monsoon (ISM) and the westerlies. Here we present a multi-proxy lacustrine record covering the past 10,500 years from Aweng Co, an alpine lake at the northern limit of the modern ASM in western Tibet. Our results show that the western TP was mainly controlled by the ISM during the Holocene and the regional ecosystem/environment was sensitive to climate change. The climate was the wettest between 10.5 and 7.3 cal kyr BP, when terrestrial plants in the catchment were productive and the biomass of benthic algae was low possibly due to limited sunlight at the lake bottom due to high lake level. From 7.3 to 5.0 cal kyr BP the climate shifted towards drier conditions, resulting in a decline in terrestrial plant cover. Between 5.0 and 3.1 cal kyr BP, the climate became even drier, resulting in a further decline in vegetation cover in the catchment. Between 4.6 and 3.1 cal kyr BP, 100% endogenic dolomite precipitated from the lake water, possibly induced by high Mg/Ca ratios. After 3.1 cal kyr BP, the climate was the driest and frequent centennial-scale droughts occurred. The lake level was low and would have resulted in more light reaching the lake bottom, favoring the growth of benthic algae. The reconstructed lake level change of Aweng Co agrees well with the paleo-shoreline records in the southern TP, demonstrating that the ISM evolution played a key role in lake hydrological processes in this region. A comparison of paleoclimate records shows the ISM reached 34.5° N in the western TP during the Holocene.

Subglacial squeeze-up moraines adjacent to the Vaalajärvi-Ristonmännikkö glacially-induced fault system, Finnish Lapland

The Vaalajärvi-Ristonmännikkö glacially induced fault (GIF) system in central Finnish Lapland is attributed to multiple slip events (Mw ≈ 6.7–7.0 earthquakes), likely contributing to subglacial and postglacial sediment deformations. We applied light detection and ranging digital elevation models (LiDAR DEMs), electrical-sedimentary anisotropy (orientation) measurements and trenching to study the related geomorphology, particularly subglacial moraines on the hanging wall of the Ristonmännikkö GIF segment striking SW-NE direction. Transverse-to-ice-flow-oriented moraines and the Pulju moraines were found to cover the distal tails of the Early Weichselian rock-drumlins and they are interpreted as seismically induced crevasse infill landforms. The electrical-sedimentary anisotropy suggests squeeze-up origin rather than active ice oscillation end moraine formation processes. Based on our recent OSL-data, the squeeze-up moraines are also superimposed on a till-covered esker system yielding an age of 87 ka. Erosional V-shaped features with apices pointing up-ice were found on convex surfaces of the distal rock-drumlin tails and were attributed to subglacial mass-flows rather than glaciofluvial erosion or frozen bed fracturing mechanisms. The area lacks glaciofluvial/hummocky corridors, but a substantial outburst system on the streak of Ristonmännikkö GIF suggests an earthquake-triggered outburst of the former subglacial Lake Unari. Our recent 14C ages of paleolandslides suggest that the Vaalajärvi-Ristonmännikkö GIF terrain was ice-free already 11.3 cal kyr BP, but was subjected to lithospheric water discharge and landslide events at 2.9 and 10.6 cal kyr BP. The squeeze-up moraines most likely formed during the later phase of the Younger Dryas, between ca. 12.0–11.5 cal kyr BP. We propose that subglacial seismicity within a glacial isostatic adjustment (GIA) environment was a notable trigger for the squeeze-up and mass-flow features beneath the retreating Fennoscandian Ice Sheet (FIS) during the later phase of the Younger Dryas.

Stable isotope evidence of human diet in Mediterranean context during the Last Glacial Maximum

The Final Gravettian in Europe overlapped with the cold and dry climatic event of Heinrich 2 (ca. 27–23.5 kyr cal BP), which caused the contraction of human distribution over refuge regions in the southern peninsulas of Europe. Here, we consider the human subsistence in the northeast Iberian Peninsula, where an extensive range of small to large prey was available. Four human remains from the Serinyà caves were investigated using the stable isotope ratios of carbon, nitrogen, and sulfur of bulk collagen (δ13Ccoll, δ15Ncoll, δ34Scoll) and of phenylalanine and glutamine amino acids (δ15NPhe, δ15NGlu). Direct AMS dating of the human and animal remains from the Final Gravettian levels of Mollet III, Reclau Viver, and Arbreda at Serinyà confirmed their chronological position from 27.5 to 22.6 kyr cal BP and the occurrence of four different human individuals. The δ13Ccoll and δ15Ncoll values showed a large contribution of terrestrial prey to the dietary protein of the individuals. The δ34Scoll values were consistent with a subsistence based on the local continental resources, without detectable contribution of marine resource. The δ15NPhe and δ15NGlu values confirm that freshwater resources were not a substantial component of the diet of the considered individuals. Contrast in the isotopic amounts in bulk collagen could be interpreted as the result of different proportions of terrestrial prey in human diet at Serinyà. Altogether, the isotopic investigation reveals the importance of terrestrial over aquatic resources in the subsistence of the studied Final Gravettian individuals from the Serinyà caves in northeastern Iberia during the Last Glacial Maximum. It would be consistent with a scenario of a productive enough terrestrial ecosystem to sustain hunter-gatherer subsistence in this refuge region.

Reconstruction of the Persian Gulf SST variability over the last five millennia

Sea surface temperature (SST) variation in the Persian Gulf (PG) is investigated based on Mg/Ca ratio measured in the planktonic foraminifera Globigerina bulloides tests from a sediment core spanning the past 5000 years recovered from west of the Strait of Hormoz. The Mg/Ca SST data indicate a 3 °C fluctuation range with an overall temperature increase trend since the mid-Holocene. The average SST of the PG in the intervals of 5–4.2, 4.2–3, 3–1.8, 1.8–1 and 1 cal kyr BP to present, was 26.1, 26.8, 25.8, 26.3 and 26.7 °C, respectively. SST increase trend in the PG is attributed to seasonally opposing insolation changes led to northern hemisphere extra-tropics cooling and tropics warming. The short spells of decreased (increased) SST indicate a high correlation with an increase (decrease) in terrigenous silt deposited in the PG, representing humid (dry) climate conditions in the Middle East. Likely, northward migration of the Inter-tropical convergence zone during the warmer episodes of the mid to late Holocene results in a change to a drier climatic regime in S Iran. Although Arabian Sea SST has a considerable role in SST variations in the PG, however, SST of this landlocked water body is mainly controlled by a continental climate.

24.0 kyr cal BP stone artefact from Vale da Pedra Furada, Piauí, Brazil: Techno-functional analysis.

Current archaeological paradigm proposes that the first peopling of the Americas does not exceed the Last Glacial Maximum period. In this context, the acceptance of the anthropogenic character of the earliest stone artefacts generally rests on the presence of projectile points considered no more as typocentric but as typognomonic, since it allows, by itself, to certify the human character of the other associated artefacts. In other words, without this presence, nothing is certain. Archaeological research at Piauí (Brazil) attests to a Pleistocene human presence between 41 and 14 cal kyr BP, without any record of lithic projectile points. Here, we report the discovery and interpretation of an unusual stone artefact in the Vale da Pedra Furada site, in a context dating back to 24 cal kyr BP. The knapping stigmata and macroscopic use-wear traces reveal a conception centred on the configuration of double bevels and the production in the same specimen of at least two successive artefacts with probably different functions. This piece unambiguously presents an anthropic character and reveals a technical novelty during the Pleistocene occupation of South America.

Позднепалеолитический комплекс культурного горизонта 2Г стоянки Коврижка IV на р. Витим (Байкало-Патомское нагорье)

In 2016—2018 a living complex dated to ca. 18,6 kyr cal BP was excavated at Kovrizhka IV site, level 2G. This is an ocher colored area of 5.0 m in diameter, with a semi-circular hearth lined by four slabs, and a massive slab surrounded with large boulders and gneiss fragments. Slabs and boulders forming an arc were recorded on the periphery of the complex, and two pits (post-holes?) of 20 cm in diameter were found on the northern and southern outskirts. Based on use-wear analysis, 17 tools were identified as meat knives, scrapers and carvers for bone, antler and skins. Their number and composition indicate a short-term occupation. About 60% of artifacts in the collection are of quartz, hence it is assumed that access to pebble raw materials was seasonally limited. The three central stones in the hearth were heated to the temperature ranging from 250 to 380—440 °C. The source of ocher is hematite of two types: quartz-hematite association and rock with a significant content of calcite, chlorite, feldspar and mica. A comparison with the ore compositions of the known iron locations and archaeological sites showed that ocher was delivered from the north of Western and Eastern Baikal regions, situated more than 500 km away from Kovrizhka. The available evidence points to the existence of a winter dwelling. The closest analogies are known at the Transbaikalian sites of Studenoye–1 and 2, Ust-Menza–1 and 2, Sukhotino–4, etc.

Centennial-scale age offsets of plant wax n-alkanes in Adirondack lake sediments

Lacustrine sediments have the potential to preserve paleoenvironmental proxies such as terrestrial plant waxes at high temporal resolution. The temporal fidelity of plant wax records, however, can be up to several thousand years older than the corresponding sediment, based on compound-specific radiocarbon (14C) analysis. Unfortunately, the factors controlling 14C age offsets between plant waxes and sediments are not well understood. The aims of this study are to quantify and compare plant wax n-alkane 14C age offsets among lakes within the same region, and to determine if drainage and lake basin differences (e.g., size, relief, drainage basin morphology, fluvial inputs) influence these offsets. We collected sediments from five lakes in the Adirondack Mountains, NY, USA that lack petrogenic sources of n-alkanes, and range in drainage basin characteristics. Sediment age models were constructed for each lake using a combination of sediment 210Pb, 137Cs, and macrofossil 14C ages, and compared to 14C ages of long-chain (n-C27, n-C29, n-C31) alkanes sampled from Holocene and Late Glacial aged sediments. The n-alkane 14C ageinitial is a measure of the age offset in n-alkanes relative to the sediment they are deposited in. Across all lakes, the n-alkane 14C ageinitial ranged from penecontemporaneous to 2440 14C yr. This oldest n-alkane 14C ageinitial is significantly outside the distribution of all other samples; when excluded, the overall mean n-alkane 14C ageinitial was 400 ± 255 14C yr (n = 23). The largest n-alkane 14C ageinitial values were observed in the last 1 cal kyr BP (565 ± 180 14C yr (1σ), n = 12)) compared to sediments deposited between 1 and 13 cal kyr BP (220 ± 195 14C yr (1σ), n = 11)). These age offsets develop early after initial lake basin sedimentation and follow a similar pattern in all of the lakes despite differences in lake basin and catchment size, relief, and geomorphology. We speculate that 14C age offsets occur due to reworking of older n-alkanes stored in drainage basin sediments and soils and this mechanism is most effective in the last ∼1 kyr. Regardless, lakes in temperate forested metamorphic bedrock terrains have relatively small and stable n-alkane age offsets compared with lakes with extensive catchment soils or anthropogenic disturbance. By targeting lakes with minimal catchment soils, age offsets may be reduced, thereby minimizing attenuation or age distortion of climate signals in plant wax isotopic records.

The impacts of volcanic eruptions and climate changes on the development of Hani peatland in northeastern China during the Holocene

Abstract Peatland development is closely correlated with regional environment and climate changes. In this study, two sediment cores covering the past 13.8 cal kyr BP were collected from Hani peatland in northeastern China. The organic content, carbonate content, Rb/Sr and Zr/Rb ratios were obtained to discuss the peat development process and associated environment and climate changes. The results showed that there were two deposition events in Hani peatland during 11.2–9.3 cal kyr BP and 2–1.4 cal kyr BP, when the organic content and Rb/Sr ratio decreased sharply, the carbonate content and Zr/Rb ratio increased dramatically. The synchronous occurrence of these two events and nearby volcanic eruptions, combining with tephra observed in sediments, indicated that volcanic activities have some impacts on the peat development. Except for the two events, the organic content of peat sediments increased gradually from the early to mid Holocene, and was highest at 8–6 cal kyr BP, then decreased gradually from the mid to late Holocene. The comparison with regional vegetation and paleoclimate records, together with the chemical weathering intensity obtained from the Rb/Sr, suggested that the orbital scale peat development in Hani during the Holocene was closely coupled with regional climate changes, including both temperature and precipitation. In addition, the 0.5–2 ka band filtering results of organic content showed similar oscillations with the drift ice indices of the North Atlantic Ocean and the atmospheric Δ14C record, implying that the North Atlantic climate and solar activities could also leave footprints on peat development of Hani on millennial timescale.

The Origin of Terraces in Buried Valleys in the Northwest of the East European Plain

Abstract —The paper considers the origin of terraces that often complicate the slopes of abnormally deep buried valleys in the northwest of the East European Plain. The Izborsk–Maly valley (Pskov Region, Russia), which is half filled with Quaternary sediments, was chosen as the object of study. Since the upper part of the valley remains unfilled, it is possible to study in detail both geologic and geomorphologic structures of its terraced slopes being of particular interest in the context of the origin of buried valleys and the role of substrate in it. The four denudation-terrace levels that have been identified on the slopes of the Izborsk–Maly valley at absolute elevations of 53, 56–58, 70–72, and 75–77 m formed during the destruction of the preglacial karst landscape under the influence of Pleistocene glaciations. The formation of the terraces was probably linked with several stages of overdeepening of the valley and its expansion by the glacial erosion processes, which corresponded to at least two stages of the ice sheet advance in this area. The last stage may have been the beginning of the Late Valdai (Weichselian) glaciation or the activation of the edge of an ice sheet during its Luga phase (~15.7 cal kyr BP). Results of the study suggest that the Izborsk–Maly valley formed in subglacial conditions. The degree of glacial erosion was determined primarily by the coherence of Devonian carbonate-terrigenous rocks hosting the valley and the degree of the area transformation by karst processes. The cirque shape of slopes is the evidence of karst processes expression in pre-glacial time. Analysis of literature data shows that the origin of denudation terraces in the buried valleys in the northwest of the East European Plain has been paid little attention. The obtained data contribute to the study of this problem and provide insights into the origin of buried valleys.

Where did Christopher Columbus start?: The estuarine scenario of a historical date

On August 3, 1492, Christopher Columbus departed from the port of Palos de la Frontera, located in a small cove in southwestern Spain, and returned to this same port on March 15, 1493. On the basis of sedimentology, geochemistry, paleontology and dating of a long core (18 m) collected in this cove, thirteen facies are distinguished in the Neogene-Holocene evolution of its sedimentary infilling, with a transition from Miocene marine environments to Late Holocene marshes, going through an intermediate period that includes fluvial gravels, alluvial sediments and shallow coastal deposits that characterize the maximum of the Fladrian transgression in this area (~6.5 cal kyr BP). These data and others contributed by historical sources allow an approximate reconstruction of this cove at the end of the 15th century.

Petrology of green polished stone axes of the Jomon period from the Sannai‐Maruyama site, Japan, investigating the origin of source rock

AbstractNumerous green polished stone axes have been excavated from the Sannai‐Maruyama site, one of Japan's largest archeological sites in the Jomon period (5.9–4.2 cal kyr BP). The axes are composed of weakly metamorphosed fine‐grained volcaniclastic rock having a peculiar texture that includes numerous acicular actinolites growing in random directions within a quartz and albite matrix. Cobbles of Aotora stone found along the Nukabira River, Biratori town, southern Hokkaido, are the most likely raw material for these stone axes. Aotora stones have alternate bands of a soft dark‐green picritic layer and a hard SiO2‐rich pale‐green layer. The pale‐green layer has a texture similar to the stone axes. Basaltic and picritic volcanic rocks of the Sorachi‐Yezo Belt occupy the area along the Shidoni River, a tributary of the Nukabira River. Volcaniclastic rocks similar in texture, mineralogy, and bulk rock compositions to the Aotora stone are exposed in the area. These rocks underwent metamorphism under the actinolite‐pumpellyite facies conditions. Their protolith is submarine hyaloclastic rocks that are intercalated with laminated picrite detritus. The stone axes, pale‐green layers of Aotora stone, and those of the volcaniclastic rocks of the Shidoni River area all have high SiO2 (~ 55 wt%), Cr (~ 840 μg/g), and Ni (~ 370 μg/g). The rare earth element patterns with abundant light rare earth elements and depleted heavy rare earth elements of stone axes were also consistent with the pale‐green layers of the outcrop. These pale‐green layers, interleaved with dark‐green layers of picritic detritus, were the likely source rock of the stone axes. The high SiO2 content in the pale‐green layer caused the crystallization of quartz and albite in the matrix, which resulted in high‐quality raw material for making stone axes.

Environmental Genomics of Late Pleistocene Black Bears and Giant Short-Faced Bears

Analysis of ancient environmental DNA (eDNA) has revolutionized our ability to describe biological communities in space and time, by allowing for parallel sequencing of DNA from all trophic levels. However, because environmental samples contain sparse and fragmented data from multiple individuals, and often contain closely related species, the field of ancient eDNA has so far been limited to organellar genomes in its contribution to population and phylogenetic studies. This is in contrast to data from fossils where full-genome studies are routine, despite these being rare and their destruction for sequencing undesirable. Here, we report the retrieval of three low coverage (0.03x) genomes from American black bear (Ursus americanus) and a 0.04x genome of an extinct giant short-faced bear (Arctodus simus) from cave sediment samples from northern Mexico dated to 16-14 thousand calibrated years before present (cal kyr BP), which we contextualize with a new high coverage (26x) and two lower coverage giant short-faced bear genomes from ~22-30 cal kyr BP old Yukon fossils. We show that the Late Pleistocene black bear population in Mexico is ancestrally related to the present day eastern American black bear population, and that the extinct giant short-faced bears present in Mexico were deeply divergent from the earlier Beringian population. Our findings demonstrate the ability to separately analyse genomic-scale DNA sequences of closely related species co-preserved in environmental samples, which brings the use of ancient eDNA into the era of population genomics and phylogenetics.

New insight into the palaeoenvironmental dynamics as a background of the human history in the Nemunas River delta region, W Lithuania, throughout the Lateglacial and Early Holocene

A new reconstruction of the Lateglacial – Early Holocene paleoenvironmental dynamics as a background of the habitation history in the territory of the Nemunas River Delta (NRD) was based on the geological-geomorphological, grain-size, isotope (14C), pollen and diatom data supplemented by archaeological information obtained within the framework of the project „Man and Baltic Sea in the Meso-Neolithic: Relict Coasts and Settlements Below and Above Present Sea Level. ReCoasts&People“. The existence of extended proglacial lakes formed during the onset of the Lateglacial was succeeded by a period of low water estuaries or freshwater lagoons as early as 13.8 cal kyr BP. Simultaneously, groups of the Final Palaeolithic population, representing the classic Swiderian culture, inhabited the area. As shores of the Yoldia Sea and Ancylus Lake were situated further westwards (-11 to -24 – -29 m NN), wetlands and lake systems alongside with shallow boggy basins and fluvial streams predominated in the local landscape throughout the Early Holocene. Archaeological data suggest an episodic human activity in the territory while part of the archaeological sites might have been covered by sediments during the further intervals of the Holocene. Since the Early Holocene an extended peat bogs have become an important part of the landscape here.

Результаты полевых археологических исследований на стоянке финального палеолита Комудваны в 2021 году

The authors present the results of 2021 field archaeological research carried out in at the Komudwanу Terminal Paleolithic site located in the estuarine part of the Manya river (Oktyabrsky District of the Khanty-Mansi Autonomous Okrug). The research was directed to study the geomorphological and geological features in the vicinity of the site, to specify the stratigraphic position of the cultural layers and to get new archaeological materials. The terrace and cape sections of the site as well as the adjacent areas were examined, surface finds were searched, several excavation trenches and a test pit were established (total area 10 m2). High water level in the river Manya did not allow explorations of the floodplain area of the site. The detailed stratigraphy description of the terrace and cape sections has been made, which testify to simultaneity of the uncovered archaeological materials; the geomorphological and geological features of the site area and the estuarine part of the Manya river has been clarified; the derived data testify the presence of humans 15-14 cal kyr BP. In the excavation trench on the terrace-like area, the upper bone-bearing level (layer 4) was excavated over the area of 8 sq. m, the medial bone-bearing level (layer 5) was discovered for the first time; 29 bones, of which all definable bones were those of mammoth, and 10 lithic artifacts were found in the upper bone-bearing level. Stone assemblage includes a spall with utilization retouch, flakes, shatters and a chip. Komudvany is the northernmost Terminal Paleolithic site on the West Siberian Plain.

BARMAKY SITE IN THE CONTEXT OF EPIGRAVETTIAN OF THE MIDDLE DNIEPER BASIN

The Upper Paleolithic site Barmaky, 2nd cultural layer from Volyhnia-Lublin upland is the most western manifestation of Epigravettian of the Mid Dnieper basin. During several field campaigns the 147 m2 of cultural deposits with three pits and one chalk / marl concentration were studied (fig. 1). The silty-loess deposits of Barmaky, 2 accumulated about 19 kyr cal BP (table 1) under the permafrost conditions. The fauna assemblage is represented by: mammoths, bison, reindeer, red deer, horse, bear, wolf, wolverine, polar fox, fox and hare. More than 100 thousand artifacts were recovered during the last two field campaigns. In essential account (without chips, chunks, unidentifiable debitage), the artifacts assemblage is represented by: cores and pre-cores — 0.87 %; flakes — 45.23; blades — 17.34; bladelets — 14.27; micro-blades — 7.34; burin spalls — 8.08; tools — 6.79 % (table 2). The reduction sequences are based on the flaking of uni-, bidirectional sub-cylindrical and narrow flaking surface unidirectional cores for blades and bladelets (table 3; fig. 2). There is no evidence of micro-blade technology implication. The structure of tool-kit is characterized by the dominance of burins — about 50 %; microliths — 25 %; and truncated pieces — about 18 % (table 4). The rest of tool classes are represented by a few percentages each. Among them are the end-scrapers on blades with truncated base (fig. 3). The most part of burins are represented by pieces made on obliquely truncated blades (table 5; fig. 4). Also, the obliquely truncated blades dominate the truncated pieces assemblage (table 6; fig. 5). The most representative type of microliths is the micro-points with abruptly retouched straight back and obliquely retouched base (table 7; fig. 6). The points, pendants, bracelet fragment made on tusk and perforated fossil marine shells from local chalk deposits are available. The composition of microliths, burins and end-scrapers in Barmaky, 2 tool-kit is characteristic to the cultural layers beyond the dwelling structures on such base-camps as Mezhyrich (fig. 7). Also, the presences of pits and fauna composition are close to what expected from Epigravettian base-camps. The artifacts assemblage of Barmaky, 2 belongs to the Mizyn industry. Also, Barmaky, 2 is the earliest manifestation of Epigravettian in the Mid Dnieper basin.

Snail assemblages in Holocene floodplain research – an example from the southern Caucasus

Abstract. During the last decades, rivers and their deposits in different regions were intensively studied to better understand the late-Quaternary landscape evolution and former human activities. One proxy for paleoecological and paleoclimatic reconstructions is the analysis of gastropods (snails) from carbonatic river sediments. In the scope of this study, we investigated gastropod assemblages from a Holocene fluvial sediment–paleosol sequence at the upper Alazani River in the southeastern Caucasus. On the one hand, we aimed to derive reliable independent information about possible long-lasting human activity since the late Neolithic–Chalcolithic in the upper Alazani floodplain. This was formerly suggested by n-alkane biomarker vegetation reconstructions from the fluvial sediments. However, the reliability of that method is still debated. On the other hand, we aimed to obtain reliable information about a formerly suggested, possibly tectonic-driven, large-scale shift of the river course during the Late Holocene. In agreement with the n-alkane biomarkers, our results demonstrate that the studied site was free of the natural forests during the Early and Middle Holocene until ca. 4.5 cal kyr BP. Since this contrasts with a pollen-based vegetation reconstruction from a neighboring floodplain that was covered with forests during that time, the open vegetation in the upper Alazani valley was probably caused by continuous settlement activity as is also indicated by archeological finds in the sequence. Therefore, using our paleoecological proxies it is possible that we identified a settlement center in the upper Alazani floodplain that was populated from the late Neolithic–Chalcolithic. This center was not known thus far, since the settlement remains are covered by thick floodloam today that hindered their detection during archeological surface surveys. Therefore, our findings suggest that the area in the southern Caucasus region that was settled during the late-Neolithic–Chalcolithic period should have been larger than was known thus far. Furthermore, increasing contributions of wetland gastropods since ca. 4 cal kyr BP confirm a local shift of the river course towards the investigated site during the Late Holocene, possibly linked with ongoing tectonic activity. However, in contrast to former suggestions our gastropod assemblages indicate a slow rather than abrupt process. Our study demonstrates the high value of gastropod assemblages for geoarcheological and geomorphological research in floodplains with carbonatic river sediments at both a regional and local spatial scale.

The cryostratigraphy of the Yedoma cliff of Sobo-Sise Island (Lena delta) reveals permafrost dynamics in the central Laptev Sea coastal region during the last 52 kyr

Abstract. The present study examines the formation history and cryolithological properties of the late-Pleistocene Yedoma Ice Complex (IC) and its Holocene cover in the eastern Lena delta on Sobo-Sise Island. The sedimentary sequence was continuously sampled at 0.5 m resolution at a vertical Yedoma cliff starting from 24.2 m above river level (a.r.l.). The sequence differentiates into three cryostratigraphic units: Unit A, dated from ca. 52 to 28 cal kyr BP; Unit B, dated from ca. 28 to 15 cal kyr BP; Unit C, dated from ca. 7 to 0 cal kyr BP. Three chronologic gaps in the record are striking. The hiatus during the interstadial marine isotope stage (MIS) 3 (36–29 cal kyr BP) as well as during stadial MIS 2 (20–17 cal kyr BP) might be related to fluvial erosion and/or changed discharge patterns of the Lena river caused by repeated outburst floods from the glacial Lake Vitim in southern Siberia along the Lena river valley towards the Arctic Ocean. The hiatus during the MIS 2–1 transition (15–7 cal kyr BP) is a commonly observed feature in permafrost chronologies due to intense thermokarst activity of the deglacial period. The chronologic gaps of the Sobo-Sise Yedoma record are similarly found at two neighbouring Yedoma IC sites on Bykovsky Peninsula and Kurungnakh-Sise Island and are most likely of regional importance. The three cryostratigraphic units of the Sobo-Sise Yedoma exhibit distinct signatures in properties of their clastic, organic, and ice components. Higher permafrost aggradation rates of 1 m kyr−1 with higher organic-matter (OM) stocks (29 ± 15 kg C m−3, 2.2 ± 1.0 kg N m−3; Unit A) and mainly coarse silt are found for the interstadial MIS 3 if compared to the stadial MIS 2 with 0.7 m kyr−1 permafrost aggradation, lower OM stocks (14 ± 8 kg C m−3, 1.4 ± 0.4 kg N m−3; Unit B), and pronounced peaks in the coarse-silt and medium-sand fractions. Geochemical signatures of intra-sedimental ice reflect the differences in summer evaporation and moisture regime by higher ion content and less depleted ratios of stable δ18O and stable δD isotopes but lower deuterium excess (d) values during interstadial MIS 3 if compared to stadial MIS 2. The δ18O and δD composition of MIS 3 and MIS 2 ice wedges shows characteristic well-depleted values and low d values, while MIS 1 ice wedges have elevated mean d values between 11 ‰ and 15 ‰ and surprisingly low δ18O and δD values. Hence, the isotopic difference between late-Pleistocene and Holocene ice wedges is more pronounced in d than in δ values. The present study of the permafrost exposed at the Sobo-Sise Yedoma cliff provides a comprehensive cryostratigraphic inventory, insights into permafrost aggradation, and degradation over the last approximately 52 kyr as well as their climatic and morphodynamic controls on the regional scale of the central Laptev Sea coastal region in NE Siberia.

Depositional sequences of the Mekong river delta and adjacent shelf over the past 140 kyr, southern Vietnam

Two 40 m-long sediment cores BL01 and SC02 were drilled in the lower Mekong River Delta plain and compared to high-resolution seismic profiles from the adjacent shelf documenting the presence of two depositional sequences (SQ1, SQ2) for the past 140 kyr. SQ2 is a fourth-order sequence and covers a complete sea-level cycle of 120 kyr. SQ1 is a fifth-order sequence comprising a sea-level half cycle in the past 20 kyr. These two sequences are bounded by the sequence boundaries (SB1, SB2) and the topographic surface. The transgressive systems tract (TST2) of SQ2 was probably formed during the sea-level rise from the Marine Isotope Stage (MIS) 6 lowstand to the MIS 5e highstand, indicated by riverine-estuarine and shallow-marine sediments. The regressive systems tract (RST2) of SQ2 corresponds to the sea-level lowering from MIS 5e to 3 with deltaic and alluvial plain sediments prevailing. These sediments were then gradually exposed to tropical subaerial processes to generate the formation of patchy reddish-orange stiff sandy silt and clay. The overlaying sequence SQ1 contains the lowstand systems tract (LST1), TST1, and RST1. LST1 consists of deltaic sediments at the shelf edge deposited during the MIS 2 sea-level lowstand. TST1 includes retrograding-fluvial, estuarine, and shallow-marine sediments deposited during the deglacial sea-level rise 19–8 cal kyr BP and the maximum flooding period 8–6 cal kyr BP before the advance of the modern Mekong River Delta. RST1 comprises the modern delta-facies association formed during the past 8 kyr and is restricted to the water depth of 25 m.

Distinct periods of fan aggradation and incision for tributary valleys of different sizes along the Bailong River, eastern margin of the Tibetan Plateau

Understanding the mechanisms of fan incision/aggradation provides key insights into the dynamics of fan evolution and hazardous fan-forming processes. This paper focuses on the discrepancy in fan evolution for two nearby valleys of different catchment areas along the Bailong River. Specifically, we study fan evolution in the small-sized CJB valley (watershed area being 1.1 km2) using sedimentary analyses and 14C dating. Sedimentary logging of seven exposed profiles indicates that mudflows and debris flows are the primary fan-forming processes. Seven samples were taken from paleosols developed in mudflow sediments, and the humin fraction was extracted for 14C dating. These ages constrain the fan aggradation period to between 10 and 4.9 cal kyr BP, and then the incision period occurred after 4.9 cal kyr BP. As the mudflow sediments may contain organic matter from hillslope legacies, the fan aggradation period may be later than the 14C ages defined in this study. In any case, the time of fan incision/aggradation in CJB is younger than that of the GLP valley (watershed area being 20 km2) where fan aggradation occurred in 21.7–7 ka and incision occurred afterward. The fan aggradation period defined by the 14C ages in CJB is consistent with an alluvial fan of similar thickness in the southeastern Tibetan Plateau and two other fans along the Bailong River. This consistency may suggest a plausible climatic control on fan evolution for small-sized tributary valleys, while the inconsistency with the larger GLP valley may suggest different climate-response regimes for tributary valleys of different sizes. More research on similar types of alluvial fans and cross-validation of different dating methods is needed.