Paleoclimatic Indicators Research Articles

Mineral composition of lake Sabakty sediments as an indicator of paleoclimate, Southern Urals, Russia

Relevance. Reconstruction of climatic changes based on the lacustrine sediments of lakes makes it possible to identify climatic trends and events in the late Quaternary. The Urals is considered as one of the climatic divisions, therefore, studies of the conditions of lake sedimentation, including climatic ones, are relevant in this area. Aim. To study mineral composition as an indicator of paleoclimate of Lake Sabakty sediments. Object. Core of Lake Sabakty sediments (length is 298 cm). The age of the core is ~25 thousand years old. Materials and methods. Sampling was carried out taking into account seismoacoustic data, lithological description, as well as measurements of magnetic susceptibility and radiometric dating data. The granulometric analysis was carried out by laser granulometry using a Bluewave particle size analyzer (Microtrac, USA) combined with a sample loading and circulation system with an integrated ultrasonic dispersant. Mineral composition of the sediments was determined using the D2 PHASER X-ray diffractometer and the Merlin auto-emission scanning electron microscope. Results. The predominance of the siltstone fraction was established. The mineral composition is characterized by the predominance of allotigenic minerals in sediments (quartz, microcline, albite, mica, chlorite, mixed-layer clay minerals, hornblende, kaolinite) according to X-ray diffraction and electron microscopy. Autigenic minerals include biogenic silica (cristobalite, tridymite), pyrite, carbonates (calcite, dolomite), sulfates (gypsum, barite). Conclusions. The ratio of allogenic and autogenic components reflects the changes in the accommodation of the reservoir and the supply of clastic material associated with changes in climate humidity. Changes in climate humidity are reflected in changes in the contents of carbonate and sulfate minerals. At the beginning of sedimentation, Lake Sabakty was shallow and mineralized due to climate aridization, which probably included the global Bond 8 event (~26000–11700 BP). The study of the mineral composition of the sediments of Lake Sabakty allowed us to establish the events of climate aridization: ~10000 BP, ~7600 BP, ~6900 BP ~1900 BP and ~1400 BP. In Sabakty Lake, there is a bright episode of a decrease in climate humidity in the range of ~7300-5200 BP, which is marked by an increase in carbonate content up to 70% and the detection of gypsum at ~6900 BP.

Petro-chemical characterization and depositional setting of a late Permian high ash coal deposit, Central Mongolia

Pan global Permian coal measures are unique in the evolution of the Earth, not matched in any period before or since. Middle and late Permian coal-bearing strata are widely distributed in Mongolia. In particular, a large concentration of transtensive coal-bearing sub-basins is located in southern Mongolia, some of which are well documented. However, the late Permian coal measures developed along the shores of the Mongol-Transbaikalian Seaway in central Mongolia, the focus of this contribution, has received very limited attention. This study focuses on the c. 420 m thick coal-bearing middle part of a c. 2,600 m thick Permo-Triassic succession in the Bayanjargalan district. The study draws on data from 38 drillholes, 3 km of trenches, mapping, petrological analysis of sandstone samples, analysis of macroflora, fauna and trace fossils, 82 coal quality samples as well as washability and ash XRD analysis from a 3t coal bulk sample. The unstable and wedge-shaped architecture of the coal seams strongly suggest a syn-tectonic influence on their development. Paleoclimatic indicators suggest the peat mire ecosystem developed during relatively cold - temperate climatic conditions. Peat-forming plants such as Cordaites, Rufloria and Koretrophyllites probably benefited from moist air currents along the seaway. Plant-arthropod interactions are reported from two sites, in particular DT228 and DT246 oviposition lesions, the latter being almost twice the size of a previous report from North America. Results from 82 proximate analyses returned consistent very high ash yields of 46.95% (db) and 43.45% (adb) from the 3t bulk sample, which are unusual for Permian coals in Mongolia.

Peatland history under post-glacial climate changes in the southern Baikal region: Biogeochemical evidence from the Vydrino Bog (Tankhoi piedmont plain)

The paper presents new data and reviews previously obtained results on the late glacial to Holocene history of peatlands in the southern part of the Baikal region under conditions of regional climate changes. To better understand climate signals, we have combined vegetation and geochemical variation data in 4.6 m thick peat deposits in the Vydrino bog located on the Tankhoi piedmont plain south of Lake Baikal. The territory has been swamped since 13.1 cal ka BP when the peatland started developing as a fen upon a sedimentary substrate. The 13.1–9.5 cal kyr climate record included two events of warming separated by an excursion of dry cold climate. Warming continued till 9.0 cal ka BP and eutrophic peat formation occurred in favorable temperature and moisture conditions. Another warming episode between 9.0 and 8.4 cal ka BP ended up with the Holocene climate optimum while the bog became mesotrophic. About 7.3–6.5 cal ka BP, the temperature and moisture inputs were no longer optimal for fir and spruce forests in the Vydrino area, which led to dramatic changes in landscape and vegetation. The wet and warm climate gradually became drier and colder from 6.5 to 2.3 cal ka BP, with a brief warm excursion about 5.5–5.3 cal ka BP. The peat deposition was interrupted in a cold climate from ∼2.3 cal ka BP to ∼0.7 cal ka BP, and the bog became oligotrophic afterwards. The newly obtained data allowed us to compare the paleoclimatic indicators available for the south Baikal region to determine their compatibility and inconsistency. In addition, we provide a general view to the quality of the climate and environmental reconstructions in the Baikal region by comparison of the data on its peatland study.

Color Origin of Red Beds within the Danxia Basin, Southern China

Sedimentary facies color is an important paleoclimate indicator, but may be unreliable in thick continental red beds. The Danxia Formation is the landscape strata of the Danxia basin, and its color fluctuates between reddish-brown and reddish-purple vertically. This study examined the ferric oxides characteristics, distribution, and mineral composition of the Danxia Formation using a variety of analytical techniques, including optical microscopy, high-resolution scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and micro-Raman spectroscopy. The results indicate that the reddish-brown mineral is composed primarily of fine hematite with traces of goethite, while the reddish-purple mineral consists solely of fine hematite. These hematites exhibit a particle size range of submicron to micron and display various morphologies, including spherical, flake, and fibrous forms. Goethite particles are needle-shaped and often form star-shaped aggregates containing twins. Whole rock geochemical analysis reveals a strong positive correlation between iron and iron group elements, as well as phosphorus and rare earth elements. The findings suggest that the reddening of the Danxia Formation occurs during diagenesis, with fine hematite forming as a result of the alteration of iron-bearing detrital grains. In addition, vertical color variations in Danxia Formation are not attributable to the paleoclimate records, but rather the result of the differentiation of sediment sources. This study provides a novel viewpoint for examining the coloration of thick continental red beds in other regions.

Clays as indicators of paleoclimate and source rocks in The Chu-Sarysu Basin (Kazakhstan)

Newly formed smectite and palygorskite and their association are good proxies of a subtropical climate alternating dry and warm/ humid seasons during the late Cretaceous during the formation of the Chu-Syrasu basin. The association of fine-grain clays, smectite and fibres (palygorskite) and the occurrence locally of grains of albite, and natrolite, indicate they formed from water, slightly alkali-rich, and enriched in silica and magnesium. These clays may result partly from the alteration of volcanic rocks (glass) either in situ in case of volcanic emissions during sedimentation or close as smectite are euhedral and palygorskite well preserved. The flood plain may have been submitted during the hot season to drying, favouring the formation of brines which interacted with volcanic glass. Evaporation processes could have thus triggered the oversaturation with respect to smectite and palygorskite.
 Besides, muscovite as coarse grain particles, illite and chloritized biotites attest to a second source compatible with the coarse grain microcline and quartz, which can derive from granites. Source rocks could be, therefore, dual, with acid plutonic series (peraluminous granites probably) releasing coarse-grained detrital phyllosilicates (muscovite and biotite-chlorite) transported together with quartz and feldspars by rivers, and volcanic series, altered into newly formed clays (smectite and palygorskite).

Paleolakes of Eastern Africa: Zeolites, Clay Minerals, and Climate

The eastern branch of the East African Rift System hosts many shallow modern lakes and paleolakes, which can be sensitive recorders of changing climate conditions (complicated by tectonics) during the past few million years. However, many of such lakes are saline–alkaline (salty and high pH), and these conditions do not easily preserve pollen and other biologically derived paleoclimate indicators. Fortunately, some preserved minerals that formed in these extreme environments reflect subtle shifts in lake water chemistry (controlled by changes in climate conditions) and therefore provide a continuous record of local and regional climate change. We present two different mineral proxies (zeolites and clays) from two different paleolake basins (Olduvai Gorge, Tanzania, and Chew Bahir, Ethiopia) as examples.

Effect of Standing Water on Formation of Fan‐Shaped Sedimentary Deposits at Hypanis Valles, Mars

AbstractFan‐shaped sedimentary deposits are key indicators of paleoclimate on Mars. The largest example, a multi‐lobed deposit (>1,000 km2) at the outlet of Hypanis Valles, may have formed either subaerially or at the edge of a water body. We used a numerical model to test whether these contrasting basin boundary conditions would cause deposit geometries that are diagnostic and distinguishable from orbit. We compared depositional scenarios with either (a) fully subaerial conditions, (b) a constant water level, or (c) a falling water level. In the model, standing water generates deposits that are thicker, less extensive, and increase in dip angle from proximal to distal locations. Nonetheless, deposit geometries for all scenarios are consistent with orbital observations, which are inconclusive regarding a topset‐foreset break that would indicate standing water. Thus, it is possible that the Hypanis deposits formed subaerially, without a water body onlapping the Mars dichotomy boundary.

Holocene evolution of parabolic dunes, White River Badlands, South Dakota, USA, revealed by high-resolution mapping

AbstractThe White River Badlands (WRB) of South Dakota record eolian activity spanning the late Pleistocene through the latest Holocene (21 ka to modern), reflecting the effects of the last glacial period and Holocene climate fluctuations (Holocene Thermal Maximum, Medieval Climate Anomaly, and Little Ice Age). The WRB dune fields are important paleoclimate indicators in an area of the Great Plains with few climate proxies. The goal of this study is to use 1 m/pixel-resolution digital elevation models from drone imagery to distinguish Early to Middle Holocene parabolic dunes from Late Holocene parabolic dunes. Results indicate that relative ages of dunes are distinguished by slope and roughness (terrain ruggedness index). Morphological differences are attributed to postdepositional wind erosion, soil formation, and mass wasting. Early to Middle Holocene and Late Holocene paleowind directions, 324°± 13.1° (N = 7) and 323° ± 3.0° (N = 19), respectively, are similar to the modern wind regime. Results suggest significant landscape resilience to wind erosion, which resulted in preservation of a mosaic of Early and Late Holocene parabolic dunes. Quantification of dune characteristics will help refine the chronology of eolian activity in the WRB, provide insight into drought-driven landscape evolution, and integrate WRB eolian activity in a regional paleoenvironmental context.

Aridification in the Asian Interior Recorded by Mineral Assemblages in Tarim Basin since the Late Miocene and Its Link to Global Cooling

Understanding climate change during the relatively warm Pliocene, as compared to the present, offers significant potential for understanding future global consequences of rising atmospheric CO2. Sensitivity differences among various climate proxies lead to divergent interpretations of the driving mechanisms of inland aridification. Minerals as a paleoclimatic indicator with high water-sensitivity can provide effective support for reconstructing climate evolution and clearly understanding driving mechanisms in extremely arid regions. Here we present results of mineral analyses from lacustrine–fluvial Neogene sediments in the eastern Tarim Basin. Evaporite minerals are composed principally of calcite, dolomite, and gypsum, with minor amounts of ankerite and celestite. Clay minerals are dominated by illite and chlorite. We find that evaporite minerals and illite reflect regional climate change through time, and specifically determine the following: (1) climate in the Tarim Basin during the late Miocene was relatively humid, with alternating dry and wet periods from 6.86~5.58 Ma; (2) immediately following that interval, aridification increased rapidly, with reduced regional precipitation that accelerated the shrinkage of the lake; (3) from 4.4 Ma to 3.62 Ma, regional precipitation increased slightly but afterwards, aridification resumed: the climate there has been extremely dry since about 2.7 Ma. Our results show that the climate in the Tarim Basin has followed a global cooling trend since the late Miocene, and suggest that the effect of uplift in the Tibetan Plateau is a secondary influence.

The Effects of Hydrochloric Acid Pretreatment on Different Types of Clay Minerals

Clay minerals are common in geological samples and are useful paleoclimate and sediment provenance proxies. Acid pretreatment is the most common method for the separation and purification of clay minerals. Given that hydrochloric acid (HCl) can dissolve chlorite and distinguish it from kaolinite, the HCl digestion method is used to simplify the routine method of clay mineral analysis. However, there have been few studies of the effects of acid digestion on different clay minerals in the context of extracting paleoclimate indicators. In this study, we used illite, chlorite, kaolinite, and two types of smectite to assess the effects of pretreatment with different HCl concentrations at variable temperatures. Our results show that chlorite is the most soluble clay mineral in HCl and can be effectively dissolved in HCl with concentrations of >1 N. The variable crystal structure of smectite affects its solubility in HCl. Ca-rich smectite, which has more cation substitution of octahedral Al, can be dissolved with HCl. However, Na-rich smectite, which has less cation substitution for octahedral Al, is hardly dissolved in HCl of any concentration or at any temperature. Illite can be partly dissolved in HCl, and the threshold beyond which dissolution occurs is 5 N HCl at 70 °C. Kaolinite is relatively difficult to dissolve in HCl. Given that the HCl digestion method uses the peak intensity of the bulk sample X-ray diffraction (XRD) analysis, whereas the routine method uses the peak area of clay particles, we compared the results of clay mineral quantification and the paleoclimate proxy obtained using the two methods for synthetically prepared mixed and natural clay samples. The results obtained with the HCl digestion method are less accurate than those obtained with the routine method because of the dissolution of illite and smectite in HCl. Therefore, the HCl pretreatment method is not suitable for clay mineral analysis in paleoclimate studies. The present results provide reference data for future studies that employ the acid dissolution pretreatment of clay mineral samples to acquire and quantify paleoclimate proxies.

Paleoenvironment evolution of the Permian Lucaogou Formation in the southern Junggar Basin, NW China

The Early-Middle Permian is regarded as a critical period for the Junggar Basin in marine to continental transition. Lacustrine organic-rich shale successions were deposited in the Lucaogou Formation in the southern Junggar Basin (SJB) at that time. Although the paleoenvironment conditions of the Lucaogou Formation have been discussed from diverse perspectives, their spatial and temporal evolution remains controversial. This study systematically investigated 11 outcrop sections and cores in three sags from the SJB, namely the Chaiwopu Sag, the Fukang Sag, and the Jimsar Sag, respectively. Paleoclimatic indicators (i.e., CIA values and Sr/Cu ratios) show that the Lucaogou Formation was generally deposited under semiarid to arid conditions, among which the Jimsar Sag was more arid than the other two sags. Meanwhile, paleoredox indices (V/Cr, V/(V + Ni) ratios, and MoEF, UEF values) illustrate dysoxic-anoxic conditions prevailing during its deposition. Paleosalinity indicators (Sr/Ba and B/Ga ratios) suggest high salinity levels in the three sags, among which the Jimsar Sag exhibited the highest salinity. Our results suggest that, relative to the Chaiwopu and Fukang sags, the Jimsar Sag experienced a more arid, more restricted, and saltier condition during deposition of the Lucaogou Formation. There is a generally lake transgression trend, with relatively less arid climate and less salty water columns in the upper Lucaogou in all the three sags. This transgression may be related to the deglaciation of Gondwanaland, which cause an increase in global temperature and more rainfall. The SJB was composed of a cluster of lakes that were relatively independent and rarely connected with each other. However, lake level rising may have coalesced to form a giant paleo-lake when lake transgression took place.

Holocene and Upper Pleistocene stratigraphy of Xochimilco lake, central Mexico

The lacustrine system developed in the basin of Mexico has been of great interest in studies of various geological and social disciplines. Its sediments preserve the history of the environmental changes that occurred during the late Quaternary. Between 2016 and 2018, a set of lacustrine sediment cores were collected in the Xochimilco sub-basin, located south of the basin of Mexico. From these sedimentary sequences, a master sequence was constructed that represents the upper 66.5 m of the lacustrine deposits. For the establishment of its stratigraphic column, 15 lithotypes were defined from their sedimentary components in which the clastic components made up of silicates dominate, mostly silt and clay in size. The most abundant biogenic fraction is diatoms that frequently form oozes, and ostracods are a common component in most of the sequence, which locally form hashes. Interbedded with the clastic and biogenic lithotypes are volcaniclastic deposits. Eight lithological units were defined based on their dominant lithotypes. The time scale of the sequence is still uncertain for the oldest sediments; however, it is estimated that it covers the last 300000 to 350000 years. From this temporality, environmental oscillations of millennial scales are inferred. Diatom-rich laminated sediments represent the deepest phases in the lake. The deposits with higher biogenic and authigenic calcareous components indicate the phases of higher ionic concentration during which the lake was shallower. The detailed analysis of the stratigraphy and the description of the sedimentary components in Xochimilco allows to establish an initial interpretation of the variations in the depositional environments, and provides the base from which the detailed studies of paleoclimatic indicators will be supported.

Fast quantitative analysis of n-alkanes, PAHs and alkenones in sediments

The study of different organic biomarker classes is essential to elucidate global Earth dynamics since different biogeochemical processes play a role in regulating environmental and climatic conditions. However, multiproxy analysis generally consists of labor-intensive and time-consuming methodologies, which hamper the study of a large number of samples. Here, we develop and validate a fast analytical method to quantify different classes of organic biomarkers (PAHs, n-alkanes and alkenones) in sediments. This new method sequentally extracts and fractionates the target compounds using a pressure liquid extraction (PLE) system, which allows us to selectively obtain the analytes by reducing the time of analysis, sample handling and solvent usage. We show that our method provides reproducible results and high recoveries (>70%), and can be applied to a wide range of sedimentary environments, such as oceanic basins, continental slope and shelf, and lakes. Moreover, the method provides reproducible estimates of paleoclimatic indices, such as the carbon preference index (CPI), the average chain length (ACL) and the U37K'-derived sea-surface temperature (SST). Therefore, this new method enables fast quantitative multiproxy analysis of oceanic, coastal and lake sediments.

Evolution of the groundwater flow system driven by the sedimentary environment since the Last Glacial Maximum in the central Yangtze River Basin

• Fluctuations in the Yangtze River and sedimentary environment control GFS evolution. • Sedimentary evolution caused unconformable distribution of groundwater age in a GFS. • Continuous uplift of discharge base level favors preservation of ancient groundwater. • Holocene fine-grained sedimentary strata led to the stagnation of regional GFS. Understanding the circulation and evolution of groundwater and its control mechanism in the Jianghan Plain, which exhibits the complex sedimentary evolution and a progressively deteriorating groundwater environment, is highly imperative and challenging to promote the practical application of groundwater flow system (GFS) and protect the groundwater resources in the region. The aim of this work was to elucidate the evolution pattern of the GFS in the Jianghan Plain and its underlying mechanism. To this end, the grain size characteristics of sediments, geochronological information, stable isotopes in clay porewater, paleoclimate indicators, and existing groundwater age were analyzed to reveal the sedimentary environment of aquifer systems at the basin scale in the study area. It was found that the sedimentary environment changed from one of deep downcutting during the Last Glacial Maximum (LGM) to a fluvial facies that was rapidly infilled with coarse-grained sediments during the last deglaciation period (LDP), and then to a stable lacustrine facies with fine-grained sediments during the Holocene warm period (HWP). These changes were closely linked to the fluctuations of the Yangtze River. Consequently, the existing GFS pattern in the basin presents an unconformable distribution of groundwater age, indicating that it results from the temporal superposition of groundwater flow controlled by the historical sedimentary environment. Dramatic sea level fluctuations since the LGM have resulted in significant changes in the water level of the Yangtze River. This process has impacted the driving force of groundwater, resulting in the evolution of the GFS from a pattern of a fully developed regional GFS during the LGM to the present pattern of a multi-hierarchy nested GFS.

Cirque Floor Altitude of the Gangdise Mountains and its Controlling Factors

The cirque floor altitude (CFA) was used to indicate the patterns of paleoprecipitation, paleocloudiness, palaeoglaciation, and paleo-equilibrium line altitude (ELA). However, CFA is also affected by non-climatic factors, which limits its efficacy of being a paleoclimatic indicator. This study focuses on the Gangdise Mountains with an aim to investigate the controlling factors on CFA and test the CFA efficiency as an indicator of paleoclimate. A total of 1652 cirques were identified, and their CFAs were analysed in this study. The results show that the lowest CFA is in the eastern part of the Gangdise Mountains, followed by the western and central parts. This spatial distribution is in contrast with that of precipitation. This means that the development of the cirque is favoured by high precipitation. The high CFA values on southern and western slopes are due to effects of solar radiation and wind. The weak correlation between the cirque height and CFA and their different spatial distributions imply that cirque deepening is not the main factor affecting CFA. Various bedrocks of cirques manifest different CFA values, while the spatial patterns of the CFAs in the western, central and eastern parts can be partly explained by their bedrock types. The CFA values of the Gangdise Mountains are higher than those of the central Tibetan Plateau (TP). The CFA spatial distribution of the central TP is in contrast with that of precipitation, highlighting that precipitation is the primary control of the CFA. The relief and glacier type significantly control the CFAs. These findings lead to the conclusion that CFA is not always an actual indicator of paleoclimate on a large regional scale.

New model for seasonal ikaite precipitation: Evidence from White Sea glendonites

The mineral ikaite (CaCO3·6H2O) and its pseudomorphs (glendonite) are considered as important paleoclimate indicators in the geological record. Here we examine the youngest known glendonites, their host concretions, and bivalve shells fossilized within these host concretions from the White Sea, north-western Russia. We applied mineralogical, geochemical and isotopic methods to shed new light on the paleogeographic and geochemical environments during ikaite precipitation and ikaite-calcite transformation. We show that White Sea glendonites are so far the youngest known glendonites in the world (4.1 ± 0.4 cal thousand years before present). Ikaite precipitation occurred during the cold winter months, accompanied by the formation of extensive sea ice and presence of decaying organic matter, which resulted in a small negative Ce anomaly and negative δ13C values. Increasing temperature led to ikaite dehydration and subsequent cementation with aragonite or amorphous calcium carbonate, containing elevated concentrations of Ba and Sr. Needle-like cements within glendonites display small negative Ce anomalies and precipitated from pore waters derived from seawater. The high‑magnesium calcite forming the host concretion precipitated in the sulfate-reduction zone from pore waters derived from seawater. The geochemistry of these pore waters was modified by interaction with clastic components of the host sediments, resulting in δ18O values comparable to those of dissolved inorganic carbon (DIC) and almost flat Post Archean Australian Shale (PAAS)-normalized rare earth element patterns. Therefore, we show that glendonites can be used as a proxy for near-freezing bottom water temperatures at least seasonally during the cold winter months. Changes in the geochemical composition of carbonate phases within the glendonites and host concretions can be used to determine successive changes in the geochemical environment during their formation.

Reconstruction of Chemical Weathering Intensity and Asian Summer Monsoon Evolution in the Red River Basin Over the Past 36 kyr

AbstractThe Red River is located at the intersection of the Indian and East Asian monsoons. Understanding the evolution history of the monsoon in the Red River basin helps to comprehend the evolution of Asian Summer Monsoon. Herein, we present the high‐resolution major elements and Sr‐Nd isotopic ratios of the terrigenous sediment component for a well‐dated core retrieved from the northern South China Sea slope, aiming to identify the sediment provenance and reconstruct the silicate chemical weathering intensity since the past 36 kyr. The Red River was confirmed as the major sediment source through Sr‐Nd isotopic ratios. The silicate chemical weathering was affected by the rapid changes of sea level and monsoon, and thus it is difficult to indicate the regional paleoenvironment by the weathering degree. The principal component 1 composed of TFe2O3, Al2O3, K2O and MgO was shown to represent the fine‐grained sediment discharge, and employed as a proxy for the summer monsoon rainfall. Global cooling events/stages were identified through the proxies, including the Last Glacial Maximum, Heinrich events, Younger Dryas, and 8.2 ka, as well as the enhanced summer monsoon stages, including the Bølling/Allerød and early Holocene. Based on the comparison with the neighboring paleoclimate indicators, the region summer monsoon of the Red River basin was found to be governed by the Indian summer monsoon, and the summer insolation at low latitudes might be the primary forcing force on the orbital scale.

Geochemistry and granulometry as indicators of paleoclimate, weathering, and provenance of sediments for the past 1,00,000 years in the eastern Arabian Sea

• Climate during MIS1, 3, 5a & 5c was hot and humid with intense SWM than YD, LGM, MIS2, 4, 5b. • Source area has experienced moderate to intense chemical weathering. • Provenance of sediments was felsic rocks during warm periods and mafic rocks and dust during cold periods. • Sources of sediments are ∼50% basalt , 40–80% gneiss and 10–20% dust. • Climate of lower and higher latitudes suggests inter-regional teleconnections . Geochemical and granulometric investigation of a 408 cm long sediment core raised from the Eastern Arabian Sea was carried out to decipher the climate, weathering, dust flux and provenance of sediments during the past 100 ka. The diagnostic ratio of Cr/Ni (0.99 to 1.77), Rb/Al (6.01 to 17.14), Ti/Al (0.02 to 0.03), Fe/Al (0.94 to 1.61), Mg/Al (0.31 to 0.59) and silt% (38.68 to 66.37) indicate hot and humid climate with the intensification of south-west monsoon during marine isotope stage (MIS) 1, 3, 5a and 5c and cold and dry climate with the intensification of the northeast monsoon and high dust flux during Younger Dryas cooling, last glacial maximum, MIS 2, 4 and 5b. The clay% (20.42 to 53.92), Silica–Titanium Index (71.88 to 86.28), Ruxton Ratio (2.89 to 7.22), and Th/U ratio (0.98 to 4.11) indicate moderate to intense chemical weathering in the source area during warmer climate. Th(ppm) versus Sc(ppm), La/Th versus Th/Yb, Al 2 O 3 % versus Fe 2 O 3 %, Th/Sc versus Sc(ppm), La/Sc versus Sc/Th ratios and La-Th-Sc plot indicate intermediate/mixed sources for sediment provenance. Sand% (2.82 to 25.3), Si/Al (2.74 to 7.43), ΣLREE/ΣHREE (7.65 to 10.40), La/Sc (2.24 to 3.55) indicate felsic sources from Peninsular India during warm climates and ΣREE (103.98–201.17), Rb/Ga (1.36–4.33), Ni (70.42–137.3 ppm), Rb (55.39–138.90 ppm) indicate mafic sources from Deccan Traps and Arabian desert during cold climates. The synchronous relationship between the climate of lower and higher latitudes was observed, suggesting the global teleconnections of climate during the Late Quaternary.

Changes in prevailing surface-paleowinds reveal the atmospheric circulation transition during Early Cretaceous in North China

Eolian deposits, which record the geological history, have long been a hot topic in geoscience research for they are not only a sensitive indicator of paleoclimate, paleoecology, and paleoenvironment but also a basis for the reconstruction of the global paleocontinent and paleogeography. Upper Mesozoic eolian deposits, especially Lower Cretaceous eolian deposits, are widely developed in the North China Craton and show a transition of the paleocurrent from easterly to westerly. However, the driving mechanism and influence range of this transition remain unclear. In this study, we systematically investigated eolian deposits from the Lower Cretaceous in North China and conducted detailed sedimentological studies on the eolian deposits of the Lower Cretaceous Luohe Formation and Yijinhuoluo Formation in the Ordos Basin. Based on the data of approximately 850 dip-azimuths from large eolian cross-bedding foresets of 65 groups in 14 sections, we reconstruct the prevailing surface-paleowind directions and classify the paleowind belts of North China. The study demonstrates that the Yijinhuoluo Formation in the northeastern part of the Ordos Basin is the product of the easterly belt, whereas the eolian deposits of the Luohe Formation, which are widely developed in the basin, are a response to the westerly belt. In addition, combined with the paleo-current data from different regions of Northern China, this study exhibits that the true polar wander model cannot adequately explain the paleo-current variation; furthermore, it indicates that the transition of the Earth's surface atmospheric circulation in the same period may be the real driving mechanism. Influenced by the “great Jurassic east Asian aridification” and the Cretaceous “super greenhouse” during the Jurassic/Cretaceous transition period, the subtropical high belt was compressed from approximately 40°N in the Early Cretaceous to 30°N or even lower in the Middle Cretaceous. The migration of the subtropical high belt resulted in a change in atmospheric circulation in the study area, and the change in prevailing surface paleowinds during the same period was the sedimentary response to the atmospheric circulation transition. • Sedimentological characteristics of Luohe and Yijinhuoluo Formation are studied. • Variation law of the paleowind during the Cretaceous in Ordos Basin is found out. • The change of paleowinds during Early Cretaceous is caused by climate change.

Hydrochemistry and Diatom Assemblages on the Humpata Plateau, Southwestern Angola

Diatoms, a common siliceous alga, are effective paleoclimate and pollution indicators. They have been used in northern, eastern, and southern Africa as such because of well-documented ecologies of many taxa. In southwestern Africa, however, the country of Angola lacks similar modern assemblage studies. To close this gap, modern diatoms were sampled across four water bodies on the Humpata Plateau in southwestern Angola in the dry season of July 2019, with in-situ measurements of pH, conductivity, and total dissolved solids and laboratory analysis of cations and anions. This research concludes that bedrock determines local hydrochemistry. In addition, this exploratory study finds that diatoms in southwestern Angola can infer relative conductivities and trophic levels, but limited data hinder interpretations of diatom ecological preferences of pH, temperature, alkalinity, ions, and pollution, requiring further analyses. Such research is beneficial for both African diatomists interested in using accurate transfer functions across Africa to reconstruct paleoclimates as well as local communities and hydrologists interested in understanding water chemistry and pollution, given that these studied sites are vital water resources for local communities on the Humpata Plateau.