Paleovegetation Reconstruction Research Articles

Pollen analysis in reconstruction of paleo vegetation on the southwestern part of the Yamal Peninsula

The aim of this study is to explore the pollen palynomorphs from the bottom sediments of an unnamed tundra lake whilst attempt to reconstruct the past vegetation and paleoecological conditions for the southwestern part of the Yamal Peninsula. 34 pollen (11 boreal, 18 arboreal) and 5 spore palynomorphs were identified. Pollen spectra characterized by a predominance of arboreal pollen (Betula sect. Nanae, Betula sect. Albae, Alnus). It was found in the range of ~6000-5100 cal. yr BP during the Holocene optimum birch forest and shrubby vegetation with bogs has been developed in the lake’s catchment area. The tundra biome was dominant, however, around ~5800 cal. yr BP, the indicator of the taiga biome increases to maximal values. Since the beginning of the Subatlantic period (~2200 cal. yr BP), local vegetation began to evolve into the modern southern tundra with shrubs (dwarf birch, alder, willow), and sedge-sphagnum bogs in lowlands.

A Review on Diagnostic Phytoliths for the Application in Paleovegetation Reconstruction and Environmental Archaeology in East Asia

A Review on Diagnostic Phytoliths for the Application in Paleovegetation Reconstruction and Environmental Archaeology in East Asia

Phytolith-reconstructed Holocene vegetation dynamics from a subalpine peat deposit in the mid-subtropical zone of China

With the improvements in our knowledge of the phytolith morphology of different Poaceae subfamilies and even different species, phytolith records in paleosols provide valuable information on past vegetation in situ, especially for herbaceous plants. Nevertheless, the reliability of phytolith records for the reconstruction of forest vegetation needs to be further verified, and it needs to be assessed before they can be used in palaeoecological contexts. In this study we analyzed the topsoil phytolith assemblages of 39 sampling sites and established a modern soil phytolith reference dataset for five plant communities in the mid-subtropical zone of China. We then used the phytolith reference dataset to analyze a stratigraphic sequence of fossil phytolith assemblages from the same region. The results show that the topsoil phytolith assemblages and phytolith indices (Ic and Iph) vary substantially among different plant communities, and that there is a good correlation with the aboveground vegetation composition. This shows that modern soil phytoliths are reliable analogues for reconstructing the paleovegetation. The results of a paleovegetation reconstruction based on the modern phytolith reference dataset show that the SWGT region has experienced substantial vegetation changes during the Holocene—from evergreen and deciduous broadleaved mixed forest to evergreen broadleaved forest, and finally to evergreen broadleaved forest with occasional shrub and herbaceous communities. The phytolith-based Holocene vegetation types are consistent with those reconstructed by a pollen record from the same stratigraphic profile. Moreover, the phytolith reconstruction also records changes in the understory herbaceous plants and C3/C4 grasses, which supplements the results of the pollen-based paleovegetation reconstruction. Overall, our results confirm the reliability of phytolith analysis for interpreting the entire vegetation landscape and forest composition in the mid-subtropical zone of China. They also provide a new perspective for the application of phytoliths to the study of forest dynamics in this region.

The vertical distribution of modern pollen in the southeastern edge of the Tibetan Plateau, China

The tropical mountainous area of the southeastern Tibetan Plateau (TP) is a hotspot of ecological environment research because of its rich biodiversity. However, limited knowledge regarding modern pollen rain within this area has impeded further investigation of eco-environmental evolution using the pollen record. We collected 62 modern pollen samples from lowland tropics to the subalpine region (740–3550 m a.s.l.) in Medog County, located in the southeastern TP, and performed pollen analysis. Cluster analysis, redundancy analysis, variance partitioning analysis, and boosted regression trees were employed to investigate the relationship between pollen and vegetation/climate. Additionally, Hill numbers (N0, N1, N2) and specificity–occupancy plots were utilized to explore plant diversity. The results indicate that modern pollen rain in Medog reflects well the current characteristics of the vegetation, encompassing both primary and secondary features. Pollen of Cyclobalanopsis, Tsuga and Abies, which are dominant components of the primary vegetation above 2100 m a.s.l., can serve as indicator species for paleovegetation reconstructions. Mean annual precipitation is the most important climatic determinant affecting pollen distribution. Pollen indices reveal that the plant diversity in this study area has a bimodal pattern of ‘relatively high–low–highest–low’ with increasing altitude. The plant diversity above 2100 m a.s.l. is mainly decided by primary vegetation, whereas below 2100 m a.s.l. it can be explained by the intermediate disturbance hypothesis. Furthermore, it is advisable to exercise caution when dealing with arboreal pollen evenness in open mountainous environments due to the increased potential pollen source area caused by valley wind.

Phytolith analyses of tropical plants and topsoil from western Peninsular Malaysia and their implications for paleoenvironmental reconstruction

The underrepresentation of many important rainforest species in pollen records still hinders accurate paleovegetation reconstructions in tropical Southeast Asia. In this study, we conducted a modern phytolith study of 141 plant and 15 surface soil samples around the forests of Jerai Hill in western Peninsular Malaysia to evaluate the potential of phytolith assemblages as a proxy for indicating tropical vegetation types. In the plant samples, including many Dipterocarpaceae species, tracheary annulate/helical phytoliths occur most commonly, followed by silicified epidermis, silicified stomata, elongate entire, sclereid, trichomes, irregular. A few diagnostic phytoliths with unique morphological features are found in dicotyledonous trees, palms, and ferns, such as spheroid ornate (sph_orn) and spheroid echinate (sph_ech). In contrast, the phytolith assemblage of surface sediment is dominated by sph_orn, sph_ech, and spheroid psilate. This suggests that similar to pollen, the contribution from dominating forest vegetation rich in Dipterocarpaceae species is obscure in phytolith deposits. However, phytolith analysis highlights the representation of monocotyledons and a few dicotyledonous trees. The more sensitive indication of Poaceae short-cell phytoliths than pollen for parent plants implies that their ratio to forest indicator phytoliths might be a valuable proxy of landscape openness. Additionally, the statistical analysis confirms that phytolith assemblages in the heath forest are slightly different from those in the lowland dipterocarp forest, exhibiting their potential to indicate various vegetation types.

Holocene vegetation and climate reconstructions from pollen records in the Mu Us Sandy Land, China

Knowledge of changes in vegetation and climate during the Holocene is important for improved assessments of future climate change and for mitigating climate warming. Owing to the relative difficulty in obtaining high-resolution sedimentary records and identifying pollen, few paleovegetation reconstructions are available from the Mu Us Sandy Land, China. This study analyzes a naturally-exposed fluvio-lacustrine section in the hinterland of the Mu Us Sandy Land. Based on a chronological framework constructed by AMS 14C, a pollen-based random forest model was used to quantitatively reconstruct changes in Holocene climate and normalized difference vegetation index (NDVI) changes. The relationships between NDVI, pollen and precipitation, as well as pollen assemblage characteristics were combined to reconstruct the evolution of the Holocene vegetation in the Mu Us Sandy Land. Our results show that the climate was cold and humid, and the dominant vegetation type was Ephedra shrub-encroached steppe between 11.2 and 8.3 ka BP; the climate reached an optimum, and vegetation evolved into Artemisia–Taraxacum-type–Thalictrum steppe from 8.3 to 2.6 ka BP; and finally, the climate gradually deteriorated and vegetation became an Artemisia–Chenopodiaceae steppe after 2.6 ka BP. In comparisons with other climate records, we found that the Mu Us Sandy Land climate optimum occurred synchronously at 8.3–2.6 ka BP, and the pattern of climate change is closely consistent with the East Asian summer monsoon. We suggest that millennial-scale Holocene climatic change in this region was mainly driven by the influences of high-latitude ice volume and summer solar radiation on the East Asian summer monsoon.

Relative pollen productivity estimates for alpine meadow in the Qinghai-Tibet Plateau and their potential significance for paleovegetation reconstruction

Alpine meadow is a common vegetation type in the Qinghai-Tibet Plateau. The Extended R-Value (ERV) model was then used to estimate the Relevant Source Area of Pollen (RSAP) and the RPPs of five major plant taxa in the study area. Log-likelihood curves indicated that the combination of the Prentice-Sugita-Sutton model with sub-model 3 provided the best results, with an estimated RSAP of 1235 m. The RPPs of other plant taxa were lower than for Cyperaceae (=1); the RPPs for Asteraceae and Polygonaceae were similar (0.798 ± 0.162 and 0.772 ± 0.121); and those for Rosaceae (0.182 ± 0.076) and Ranunculaceae (0.084 ± 0.102) were much lower. The leave-one-out method and a comparison of the RPPs with the results of previous studies for the study area demonstrated that our RPPs are stable and credible and can be used as a modern reference for pollen-based paleovegetation reconstruction in the Qinghai-Tibet Plateau.

Relative pollen productivities of major woody plant taxa in deciduous broadleaved forest in the Ziwuling Mountains of the central Chinese Loess Plateau

Accurate estimates of relative pollen productivity (RPP) values are fundamental to the use of fossil pollen records to quantitatively reconstruct paleovegetation. Based on a pollen dataset from moss polster and related vegetation data for 34 sites in the central part of the Ziwuling Mountains (central Chinese Loess Plateau, with a temperate–warm temperate climate), we estimated the relevant source area of pollen (RSAP) and the RPP values of 8 major woody plant taxa in deciduous broadleaved forest, using the Extended R-Value (ERV) model. The best results were obtained with ERV sub-model 2 and the inverse distance (1/d) method to distance weight the vegetation data. The RSAP was estimated to be 855 m and the rank order of the RPP values for the 8 major woody plant taxa is as follows: Betula (2.083 ± 0.091), Syringa (1.367 ± 0.087), Quercus (1 ± 0, the reference taxon), Pinus (0.791 ± 0.036), Ulmus (0.643 ± 0.062), Carpinus (0.621 ± 0.122), Malus (0.035 ± 0.015), and Acer (0.035 ± 0.025). Repeatability tests using the leave-one-out and K-fold methods showed that the RPP values of all 8 major woody plant taxa have a good reproducibility, which indicates that the RPP values are consistent in the study area. Comparison of the RPP values of the major plant taxa from deciduous broadleaved forest in temperate and warm temperate regions shows that the RPP values for the same pollen taxon may differ significantly between different areas. For example, the RPP for Pinus in areas with dominantly natural vegetation is much lower than for areas where the vegetation has been substantially altered by human activity. We suggest that differences in vegetation/landscape characteristics (including community structure and species composition/abundance) are the major causes of the difference. Therefore, changes in the regional landscape should be considered when choosing suitable RPP values for quantitative paleovegetation reconstruction.

Phytolith and simulation evidence for precipitation-modulated vegetation dynamics along the East Asian monsoon margin

An improved understanding of past interactions between terrestrial vegetation and various forcings, such as climate change, human impact, and paleofire, is crucial for assessing impacts of future global change on terrestrial ecosystems. This study seeks to find the key factor or factors that have driven Holocene vegetation change along the East Asian monsoon margin. Several high-resolution pollen records are reviewed and new phytolith-based paleovegetation reconstructions and physical geochemical datasets are presented from a peatland in northeastern China. Using 108 modern topsoil samples as a training set, canopy cover and vegetation composition are estimated for the period since 5100 cal. yr BP. Variation partitioning analysis (VPA) is used to determine the relative importance of climate change, human impacts, and paleofire disturbance. The generalized dynamic vegetation model LPJ-GUESS is forced with climate anomaly output from an atmospheric general circulation model to simulate vegetation dynamics during the mid-Holocene and the pre-industrial era. The proxy-based estimates are compared to modelling output. Results indicate that regional tree cover varied from 10% to 40% during the past five millennia. The single-core, phytolith-based reconstructions are generally consistent with stacked tree pollen z-scores calculated from different records along the East Asian monsoon margin, implying that mid-Holocene tree cover decrease was persistent and almost synchronous over extensive areas. VPA demonstrates that long-term monsoon marginal vegetation successions were mainly caused by climate effects. Numerical modelling suggests that since the mid-Holocene the retreat of forests along the monsoon margin was primarily associated with precipitation deficits. Our investigation highlights that the precipitation associated with the East Asian monsoon system has exerted a stronger influence than the westerlies on the monsoon margin climate and vegetation change. With ongoing global change, close attention to variations in precipitation patterns and amounts should be especially helpful in efforts aimed at ecological monitoring, change prediction, and restoration.

Climatic and vegetational dynamics in southern Brazil between 47.8 and 7.4 cal ka BP: a palynological analysis

Vegetation and climate changes in southern Brazil are described based on the palynological analysis from marine core SIS 188, collected on the continental slope, which records the interval between 47.8 and 7.4 cal ka BP. The pollen record indicates that the grasslands dominated the landscape in southern Brazil throughout the studied period. During the last glacial period, the forests were reduced. Between 32.8 and 20.2 cal ka BP, there is an increase in grassland and reduction of arboreal palynomorphs, coinciding with colder and drier climatic conditions of the Last Glacial Maximum (LGM). From 30 to 25.2 cal ka BP, an increase in the sedimentation rate and concentration of most pollen indicators is observed. This change could be related to low sea level, which exposed the continental shelf to eolian erosion and fluvial inputs that transported sediments and palynomorphs to the ocean. A significant decrease in sedimentation rate is recorded between 19.5 and 12.6 cal ka BP, probably related to sea-level rise during deglaciation. During deglaciation and beginning of the Holocene, the increase in arboreal pollen indicates the expansion of forests, reflecting warmer and wetter climate. Heinrich event 1 is marked by a peak in the percentages of the arboreal vegetation at 15.9 cal ka BP. Around 8.5 cal ka BP, there seems to be another interval of higher moisture, indicated by the composition of the palynological association, formed by pteridophytes Blechnum, Huperzia, Polypodiaceae, Pteridaceae and Cyatheaceae. These results show that the palynological record from the SIS188 marine core is sensitive to global climatic changes and can provide a reliable paleovegetational reconstruction for the continental environment. Keywords: Pelotas Basin, paleoclimate, palynomorphs, palynology, Quaternary.

Relationship between modern pollen assemblages and vegetation in the Bashang typical steppe region of North China

Accurate knowledge of the relationship between modern vegetation and the corresponding surface pollen assemblages is the key to the quantitative reconstruction of paleovegetation and paleoclimate. The pollen assemblages of steppe regions are affected by many factors and distinguishing the pollen assemblages of different plant community types, especially Artemisia and Poaceae communities is a major difficulty in modern pollen studies in these regions. In this study we used RDA analysis to analyze modern vegetation and pollen percentage data from 119 sampling sites in different plant communities in the Bashang region of North China, which has a typical steppe vegetation. We used the results to quantitatively determine the distinguishing features of various plant community types and the relationship between the percentages of the dominant pollen types and the corresponding vegetation cover. The major results are as follows: 1) there is a clear distinction between Artemisia and Poaceae communities; in the Artemisia community, Artemisia pollen percentages are typically > 50%, and Poaceae pollen percentages are typically < 3%. In the Poaceae community, Poaceae pollen percentages are typically > 3%, and Artemisia pollen percentages are typically < 40%. 2) The Artemisia, Chenopodiaceae, Poaceae and Asteraceae are the most common vegetation types and their pollen percentages are the four most abundant types in the pollen assemblages. Their respective pollen percentages and vegetation cover show varying degrees of correlation and representativeness. Artemisia and Chenopodiaceae pollen are over-represented; that is, when the vegetation cover of Artemisia and Chenopodiaceae is < 5%, or even zero %, Artemisia and Chenopodiaceae pollen percentages can still reach 30–40%. By contrast, Poaceae and Asteraceae are under-represented in the pollen assemblages, and even where they have a high vegetation cover, their pollen percentages are rarely > 10%.

Fuzzy model-based reconstruction of paleovegetation in Ethiopia

ABSTRACT We introduce a new method to compute plant distribution in Ethiopia under paleoclimatic conditions using fuzzy logic. Using a published map of the potential vegetation for Ethiopia we decipher the boundary conditions for the main vegetation units shown, reflecting modern climatic conditions for temperature and precipitation in this region. Fuzzy logic using these climatic values on a GIS platform then derived the computational map of the potential vegetation. Comparing it with the original map shows a general correspondence of about 90%. By changing the underlying climate parameters, we then used this model for hypothetical paleoclimatic conditions to simulate the vegetational response on these changed climate settings. Finally, vegetational response maps for Ethiopia are presented for two scenarios: (i) a colder and drier condition (such as the Last Glacial Maximum) and (ii) a warmer and wetter condition (such as the last interglacial) than today.

Paleovegetational Reconstruction and Implications on Formation of Oil Shale and Coal in the Lower Cretaceous Laoheishan Basin (NE China): Evidence from Palynology and Terpenoid Biomarkers

In some cases, the oil shale deposited in shallow lakes may be genetically associated with the coal-bearing successions. Although paleovegetation is an important controlling factor for the formation of oil shale- and coal-bearing successions, few studies have focused on their joint characterization. In this study, a total of twenty-one oil shale and coal samples were collected from the upper member of the Lower Cretaceous Muling Formation (K1ml2) in the Laoheishan Basin, and investigated for their bulk geochemical, maceral, palynological, and terpenoid biomarker characteristics, in order to reconstruct the paleovegetation and reveal its influence on the formation of oil shale and coal. The K1ml2 is subdivided into lower, middle, and upper units. The studied oil shale samples from the lower and upper units display a high ash yield (Ad), low total organic carbon (TOC) and sulfur (S) contents, and limited hydrocarbon generation potential. The studied coal samples from the middle unit are characterized by low Ad, and high TOC and low S values, and show significant hydrocarbon generation potential. The paleovegetation during the formation of the lower unit was dominated by mire vegetation, such as shrubs (e.g., Lygodiaceae, Schizaeaceae), tree ferns (e.g., Dicksoniaceae/Cyatheaceae), and coniferous trees (e.g., Podocarpaceae). In the middle unit interval, the paleovegetation was represented by highland vegetation (Pinaceae and Araucariaceae) and peat-forming coniferous plants (e.g., Podocarpaceae, Cupressaceae/Taxodiaceae). Various vegetation, such as herbs (e.g., Osmundaceae), shrubs (e.g., Schizaeaceae), and coniferous trees (e.g., Podocarpaceae) was prosperous during the upper unit interval. Coniferous trees could provide abundant hydrogen-rich materials (e.g., resins) to the mire/lake, which may elevate the hydrogen content in peat/lake sediments, and finally result in higher hydrocarbon generation potential in the coal than in the oil shale. Therefore, the influence of paleovegetation on the formation of oil shale and coal should be fully considered when studying oil shale- and coal-bearing successions. The results also provide guidance for further exploration studies on oil shale and coal in northeast China.

The reconstruction of an abandoned historical reservoir network in a continental temperate climate region using a multi-method approach

Reservoirs represent a specific environmental component in many parts of the Earth, especially where water supply is limited. As is the case of the Moldavian hilly area, due to its dryness, the inhabitants created an extensive network of reservoirs since the medieval period, in the proximity of the settlement network. Over time, many dams were abandoned, while others have been relocated with impressive dynamics at a historical scale. In this paper, by analyzing old maps, LiDAR high-res DEMs, ERT surveys, and sediments, we have reconstructed the reservoir network's expansion in the last century at a regional scale and investigated the main geomorphologic characteristics of dams and associated landforms. In Jijia catchment (3386 km2) we found a total number of 1351 dams, of which 832 abandoned. 495 reservoirs were recognized on different topo maps dating from the 20th century, while 337 have been identified on DEMs. Two reservoirs were investigated in detail by field surveys, ERT surveys, profile digging, sediment analysis, and micro-sedimentological study, confirming lacustrine deposits according to the topographic reconstructions based on high-resolution LiDAR DEMs. These sedimentary lacustrine archives can substantially contribute to detailed paleoclimatic, paleohydrologic, and paleovegetation reconstruction in the study area.

Phytolith morphotypes of woody plants and their preservation in soil in the warm temperate humid zones of China

Studies of the morphotypes, production and preservation of phytoliths in soils provide a theoretical basis for paleovegetation reconstruction. However, there is a lack of systematic studies of the phytoliths of woody plants in the warm temperate humid zones, which greatly limits the application of phytoliths in paleovegetation reconstruction in this environmental context. In this study we analyzed the phytoliths of 211 plant samples (81 leaf samples, 73 branch samples, 57 bark samples) and 30 topsoil samples from the warm temperate humid zones of China. The results demonstrate that while most of the leaf samples contained phytoliths, only a few of the branch and bark samples did so. In terms of phytolith concentration, the sample types were ordered as follows: bark samples > leaf samples > branch samples. In this study the phytoliths in woody plants were classified into10 categories and 22 sub-categories, and the results of detrended correspondence analysis (DCA) showed that elongate dentate and blocky morphotypes were closely associated with Picea; elongate cavate and margin-cuneiform morphotypes were closely associated with Larix; acute bulbosus and hair base morphotypes were associated with Morus, Broussonetia and Diospyros; and elongate psilate, elongate attenuate, and sclereid morphotypes were associated with Quercus, but these types are not unique to Quercus. The topsoil woody phytolith assemblages contained four types of broad-leaved phytolith (tabular, tabular sinuate, sclereid, epidermal phytolith), and three types of coniferous phytolith (blocky, elongate dentate, elongate tabular). The ratio of the total of broad-leaved phytoliths to the sum of broad-leaved phytoliths and coniferous phytoliths is useful for discriminating broad-leaved forest from coniferous forest. Overall, the results confirm the usefulness of phytoliths as indicators of woody plants in the warm temperature humid region in China, and they demonstrate the potential of woody phytolith assemblages for paleovegetation reconstruction.

The disparity in the abundance of C4 plants estimated using the carbon isotopic composition of paleosol components

Long-term paleovegetational records from continental settings help in comprehending regional and global forcing on the abundance of C3-C4 plants in the past. The carbon isotopic composition of soil carbonates (δ13CSC), soil organic matter (δ13CSOM), organic matter occluded in soil carbonate nodules (δ13CNOM) and biomarkers in paleosol organic matter (long-chain fatty acid; δ13CFAME) are often used to estimate changes in the past-vegetational composition. However, it has been observed that depending on the type of proxy, the estimated abundance of C3-C4 plants varies, which can lead to uncertainty in paleovegetational records. Hence, the present study aims to comprehend the factors affecting the δ13CSC, δ13CSOM, δ13CNOM and δ13CFAME values within a paleosol. In this context, available δ13CSC, δ13CSOM, δ13CFAME and newly measured δ13CNOM values from the late Quaternary sequences of the Ganga Plain, India has been used. The abundance of C4 plants calculated from the δ13CSC and δ13CFAME values is ~2% to 89% higher compared to the δ13CSOM and δ13CNOM values-based estimates. Even with a common source of organic matter, the δ13CSOM values indicate a higher abundance of C4 plants (~2% to 50%) compared to the estimates from δ13CNOM values. We suggest that the disparity is due to the variation in the response of proxies to perturbations in the paleovegetational regime, growing season condition, and isotopic fractionation during decomposition and incorporation of organic matter into the soil. For example, the organic matter is incorporated into the soil throughout the year and represents average annual biomass, whereas SC precipitates under warmer and often drier condition when the ratio of C4 to C3 plant respiration is higher. Additionally, preferential degradation of 13C enriched labile compounds and C4 plants derived organic matter may lower the δ13CNOM values resulting in an under estimation of C4 plants in a mixed C3-C4 environment. The higher abundance of C4 plants estimated from the δ13CFAME values is due to the isotopic fractionation (13C enrichment of ~2‰ to 7‰) during incorporation of plant-derived long-chain fatty acids into the soil. The disparity in the abundance of C4 plants estimated from δ13CSOM and δ13CNOM values is due to the difference in the preservation of SOM and NOM. Contrary to the NOM (which is in a closed system), SOM in open system within the soil matrix is subjected to 13C enrichment due to the long-term humification of organic matter. Various factors such as grain size and pedogenesis that are inherent to the depositional environment also control the δ13C values of paleosol components. Considering the uncertainties associated with the δ13C values of paleosol components, reporting the absolute abundance of C4 plants would be uncertain. Therefore, we recommend presenting the relative change in abundance of C3-C4 plants during paleovegetational reconstruction.

표층퇴적물의 현생화분을 이용한 고식생 및 정량적 고온도 복원을 위한 연구방법 소개

표층퇴적물의 현생화분을 이용한 고식생 및 정량적 고온도 복원을 위한 연구방법 소개

Morpho-tectonic control on the distribution of C3-C4 plants in the central Himalayan Siwaliks during Late Plio-Pleistocene

The Siwalik deposits of the Himalayan foreland basin (HFB) preserve the Late Miocene-Pleistocene record of the Himalayan tectonics, monsoonal variation and the expansion of C4 plants. Previous vegetation reconstructions emphasized the Late Miocene expansion of C4 plants with an implicit assumption that the vegetation thrived in the floodplain of lowland rivers. The coarsening-upward sequence of the Siwalik Group suggests deposition in an alluvial fan setting in which the Lower and Middle Siwaliks are deposits of distal region whereas the Upper Siwaliks represents a proximal region of the fan. The modern alluvial fans forming in the Himalayan foothills show a significant difference in elevation (ca. 300 m) and vegetational composition between their proximal and distal regions. In the HFB, the elevation difference is expected to be more pronounced due to the surface uplift of Siwalik deposits along the Himalayan Frontal Thrust (HFT). The increased elevation would have affected the vegetation distribution in the Upper Siwaliks which implies that the vegetation in the proximal part of the fan might not represent lowland floodplain. However, the vegetation composition is less understood from the Upper Siwaliks region due to the scarcity of conventional proxies in these younger foreland deposits.In this context, δ13C values of bulk soil organic matter (SOM), n-alkane and n-alkanoic acid in the paleosols were measured from Late Mio-Pleistocene Siwaliks at Surai Khola (Nepal) to comprehend the impact of elevation on vegetation distribution in the HFB. The results suggest most commonly observed expansion of the C4 plants at ca. 7 Ma, and a unique second phase of expansion of C3 plants post-3 Ma. The higher δD values of n-alkane and n-alkanoic acid suggest that the climate was drier in the last 4 Myr; most likely driven by the onset of the Northern Hemisphere Glaciation (NHG). The growth of C3 plants was favored due to cool climatic conditions induced by a higher elevation in the proximal part of the fan. Water-bearing conglomerates in the Upper Siwaliks may have helped the C3 plants to thrive in a relatively drier climate. This multi-proxy paleovegetation reconstruction demonstrates a morpho-tectonic control on the abundance of C3-C4 plants in the Siwaliks with the possible influence of NHG.

Reliability of the Artemisia/Chenopodiaceae pollen ratio in differentiating vegetation and reflecting moisture in arid and semi-arid China

The reliability of the ratio between Artemisia and Chenopodiaceae pollen percentage (i.e. A/ C) in differentiating vegetation and reflecting moisture conditions in arid and semi-arid regions has been disputed and this hindered its potential application in palaeoclimate reconstructions. In this paper, we investigated the A/ C ratios of lake-centre surface sediment from 45 lakes in the Inner Mongolia Plateau and the Qaidam Basin in arid and semi-arid China, and numerically studied the relationships of A/ C ratios with vegetation and moisture. We found that the A/ C ratio of lake-centre surface sediments can be used as an effective index to differentiate desert and steppe and also can be used as a valid indicator to infer mean annual precipitation (MAP) in the Inner Mongolia Plateau and the Qaidam Basin in arid and semi-arid China. Moreover, the A/ C ratio from lake-centre surface sediments is more reliable and robust than that of soil-surface samples in differentiating vegetation and reflecting moisture conditions, and this might be attributed to its larger pollen source area and regional representation. In addition, the ( A − C)/( A + C) index helps to overcome the inherent weakness of non-linearity of the A/ C ratio and may be useful in paleo-vegetation reconstruction. These findings provide useful references for pollen-based vegetation and climate reconstructions of lake cores in arid and semi-arid China.

Translocation of Phytoliths Within Natural Soil Profiles in Northeast China.

Phytoliths are a reliable paleovegetation proxy and have made an important contribution to paleoclimatic studies. However, little is known about the depositional processes affecting soil phytoliths, which limits their use for paleoclimate and paleovegetation reconstructions. Here, we present the results of a study of the vertical translocation characteristics of phytoliths in 40 natural soil profiles in Northeast China. The results show that phytolith concentration decreases within the humic horizon of the soil profiles and that ∼22% of the phytoliths are translocated below the surface of the studied soils. In addition, we find that the translocation rate of phytoliths varies markedly with phytolith type and that phytolith size and aspect ratio also have a significant effect. Phytoliths with length >30 μm and with aspect ratio >2 and those with length <20 μm and aspect ratio <2 are preferentially translocated compared to those with length >25 μm and aspect ratio <2. Our results demonstrate that differential translocation of phytoliths within soil profiles should be considered when using soil phytoliths for paleoclimate and paleovegetation reconstruction.