Palaeoclimatic Signal Research Articles

Organic matter enrichment in Asia's palaeolake controlled by the early and middle Eocene global warming and astronomically driven precessional climate

The sediments deposited in continental lake systems record sensitive palaeoclimate signals and provide better perspectives for understanding rapid palaeoclimate changes and their implications. To better understand the terrestrial record and climate-driven organic matter enrichment mechanism in a low-latitude region, which have rarely been investigated, we studied the Eocene terrestrial records from the Beibuwan Basin, South China Sea (SCS). Cyclostratigraphic analysis was conducted to assess the orbital forcing. Milankovitch-scale astronomical signals were determined by spectral analyses, evolutionary Fast Fourier transform, and sedimentation rates estimation of the natural gamma ray logging data in the depth domain. A floating astronomical time scale (ATS) was constructed based on astronomical tuning that converts the depth domain to the time domain by sedimentation rates. The ATS was calibrated using published dating result of 35.2 Ma from the Eocene to the Oligocene. This ATS constrains the ages of two organic-rich lacustrine petroleum source intervals of the Eocene Liushagang Formation in the Beibuwan Basin at ∼49-47 Ma and ∼40.9–40.2 Ma, respectively. A comparison of the timing of these two source rocks with a published global benthic carbon and oxygen isotope series shows that they correspond to Eocene positive carbon isotope excursions. This finding suggests that organic carbon burial in Eocene lacustrine basins responded to early and middle Eocene Climatic Optimum (i.e., EECO and MECO). We used geochemical data based on X-ray fluorescence core scans for further investigation of the effect of orbital forcing on organic matter enrichment. The high Rb/Sr, K + Ti + Rb and Sr/Ca geochemical ratios and stable Mo and U/Th values all correspond to the precessional minimum, suggesting that the orbital precessional minimum is responsible for a warm and humid climate, and brackish and hypoxic water conditions. Thus, four schematic hypotheses were proposed to explain the effect of the precessional monsoonal climate on organic matter enrichment. This study provides a terrestrial record that documents the mid-Eocene global warming event well and provides evidence that the orbital precessional climate controlled organic matter enrichment in Asia's palaeolake.

Using environmental tracers to evaluate the preservation of palaeoclimate signals in aquifers of the London Basin, UK

The concept of aquifer basins as palaeoclimate archives has existed for some decades, yet few detailed studies comparing aquifer types have been carried out. To assess the potential of a particular aquifer as an archive, its hydrogeochemical characteristics must be thoroughly investigated, ideally in comparison to an adjacent aquifer which can be shown to substantially preserve its ice-age endowment at depth. The London Basin (UK) presents such an opportunity, containing two main aquifers of contrasting type: the Chalk, a fractured microporous limestone, and the Lower Greensand, a porous sandstone. Despite intensive exploitation of both, evidence for Devensian (late-glacial) water remains at depth, though this differs between aquifer type. To understand the reasons for this, a suite of environmental tracers has been applied. In addition to hydrochemistry, stable isotopes (δ18O, δ2H), carbon isotopes (δ13C-DIC, 14C-DIC) and noble gases (He, Ne, Ar, Kr and Xe), two tracers new to the basin (CFCs and 14C-DOC) have been used. In effect the Lower Greensand appears to be the ‘reference aquifer’, preserving recharge from prior to the Last Glacial Maximum (LGM), while the Chalk contains mixed water, with no remaining trace of the undiluted pre-LGM end member even at depth in remote parts of the confined basin. Whereas both aquifers had in the past given maximum 14C-DIC model ages ≥ 30kyr (the effective limit of that method), in the present study the use of 14C-DOC has reduced this to 23.4 kyr (Lower Greensand) and 17.2 kyr (Chalk). Similar contrasts in maximum stable isotope depletions (−8.2 ‰ and −7.8 ‰ δ18O) and noble-gas-derived recharge temperature minima (2.6° and 4.1 °C) were also observed. CFCs were found at all Chalk sites, with traces detectable even at 40 km from outcrop, so some climate signal degradation appears inevitable throughout the Chalk aquifer of the basin. A correlation between 14C activity and excess 4He suggests that deep saline water in the Lower Greensand could be ≥ 50kyr old. The use of 14C-DOC in particular appears to be key to understanding how reliable these individual aquifers are as palaeoarchives.

Environmental change and carbon-cycle dynamics during the onset of Cretaceous oceanic anoxic event 1a from a carbonate-ramp depositional system, Abu Dhabi, U.A.E.

We report the first high-resolution sedimentological and geochemical record of the negative carbon-isotope excursion (CIE) at the onset of the early Aptian oceanic anoxic event (OAE) 1a from a carbonate-ramp depositional environment, analysed from a well core from c. 2500 m depth, 100 km offshore Abu Dhabi, United Arab Emirates. Time-series analysis of stable oxygen isotope values and concentrations of Si, Al, and Ti resulted in durations of the C3 and C4 segments of the CIE that support relative completeness of the C3 segment and high sediment preservation rates of c. 13 cm/kyr of the studied sedimentary sequence. Stable oxygen-isotope ratios of bulk carbonates are interpreted to indicate two episodes of cooling, separated by rapid warming during the peak of the negative CIE. The contributions of diagenesis and seawater pH on the bulk oxygen-isotope record will have affected the palaeoclimatic signal and are critically discussed. A major shift in oxygen isotope values at the peak of the negative CIE in the C3 segment coincides with relatively carbonate-poor, marly deposits, time-equivalent with other, global evidence for a reduction of carbonate saturation of sea-surface water. According to our chemo- and cyclostratigraphic calibration, this episode of low carbonate saturation of seawater reflects a pulse of major volcanic CO2 release from the Ontong-Java large igneous province that was sufficiently short to have escaped internal buffering by the dynamics of the ocean lysocline.

Forward modelling of the completeness and preservation of palaeoclimate signals recorded by ice-marginal moraines.

Glaciers fluctuate in response to climate change and record these changes by building sedimentary landforms, including moraines. Therefore, glacial landscapes are a potentially valuable archive of terrestrial palaeoclimate change. Typically, a cooling climate causes glaciers to expand and a warming climate causes glaciers to shrink. However, the glacier response time and the influence of mountainous topography on glacier dynamics complicates this behaviour, such that moraines are not always a straightforward indicator of glacier change in response to climate change. We used a glacial landscape evolution model to simulate the response of a hypothetical mountain glacier to simple changes in climate and the resulting formation and preservation of moraines. These results show that the rate of climate change relative to the glacier response time determines the geometry, number, and position of moraines. Glaciers can build distinct moraines in the absence of climate change. The distance from the maximum ice extent may not represent the chronological order of moraine formation. Moraines can be preserved after being overrun and eroded by subsequent glaciations, but moraine sequences may also contain gaps that are unidentifiable in the field.

Test of high sampling density OSL dating of aeolian samples from the south margin of the Tengger Desert using the global standardised growth curve (gSGC) method

Chronostratigraphic records in the drylands of north China provide basic archives to reveal the dynamic connections between climate changes and the behaviour of aeolian systems. However, the interpretation of aeolian chronostratigraphy is not straightforward and may be associated with significant uncertainty due to a number of external and localised forces. Taking into account this complexity of aeolian systems, excluding preservation and sampling bias from palaeoclimatic signals requires that the interpretation of chronostratigraphic records be based on as many dates from as many sites as possible. Optically stimulated luminescence (OSL) dating provides a direct way to date aeolian sediments. However, the determination of equivalent dose (D e ) using the commonly applied single-aliquot regenerative dose (SAR) protocol is relatively time-consuming for samples with burial doses exceeding 50 or 100 Gy. In this study, the global standardised growth curve (gSGC) method is applied to multi-grain aliquots of coarse quartz from various sites covering a wide region of the south margin of the Tengger Desert in north China to rapidly determine D e for a large number of aliquots and samples. The large between-aliquot variability in the shape of the dose response curve (DRC) is significantly reduced using a least-squares normalisation procedure. The results of a leave-one-out cross-validation (LOOCV) protocol demonstrates that D e values determined using the gSGC and SAR methods are very consistent with each other up to at least 200 Gy and 400 Gy, for the 90–150 μm and 63–90 μm fractions, respectively. It suggests that the gSGC protocol can be used as an efficient procedure for D e determination of a large number of aeolian samples from multiple sites. This in turn provides a better constraint for the interpretation of Late Quaternary aeolian chronostratigraphic records in drylands of north China.

Low-Calcium Cave Dripwaters in a High CO2 Environment: Formation and Development of Corrosion Cups in Postojna Cave, Slovenia

Speleothems have proven to be one of the most reliable terrestrial archives for palaeoclimate research. However, due to the complexity of karst systems, long-term monitoring and high-resolution analyses of the cave atmosphere and water geochemistry have become essential to better constrain the factors that control calcite growth and how geochemical palaeoclimate proxies are encoded into speleothems. While calcite precipitation incorporates the palaeoclimate signals into the speleothem fabric, certain conditions in caves can favour dissolution, which may form hiatuses or even destroy these signals. In extreme cases, in-cave dissolution by dripwater can form cup-shaped features (i.e., corrosion cups), which were the main focus of this study. The study site in Postojna Cave, Slovenia was investigated through cave climate monitoring and drip and cup water sampling, which took place during 2017–2021. We found that the cups are fed by low-calcium drips as the consequence of the thin rock overburden above the cave. Due to the specific configuration of the airflow pathways, the study site accumulates high levels of CO2 (>10,000 ppm), which shifts low-calcium dripwater into undersaturation. This causes dissolution on the rock surfaces and speleothems on the cave floor. The results of this study have broader significance in addressing the suitability of cave environments and speleothems used in paleoclimate research.

Separating provenance and palaeoclimatic signals from particle size and geochemistry of loess-palaeosol sequences using log-ratio transformation: Central European loess belt, Czech Republic

Loess-palaeosol sequences represent the most complete terrestrial archives of Quaternary climatic cyclicality. Particle size and geochemistry are widely used proxy data in palaeoclimatologic analysis of loess-palaeosol sequences. The palaeoclimatologic signals hidden in the texture and chemical composition of the Czech loess-palaeosol sequences, which are part of the European loess belt, are modulated by temporal changes in the interplay of oceanic and continental macroclimates and by the diverse bedrock geology of the Bohemian Massif.Innovative tools of compositional data analysis, including log-ratio transformation and scalar-on-function regression, can substantially enhance the information value of large granulometric and geochemical datasets, when compared to classical statistics of raw data. Particle size distribution and bulk-rock geochemistry of 389 and 542 samples, respectively, from four Czech loess-palaeosol sequence sections representing the last glacial-interglacial cycle were analysed in this study. Centered log-ratio transformation was applied to the key elemental proxies and their spatial (between sections) and stratigraphic (within section) distribution. Centered log-ratio transformed densities of key elements were then plotted against particle size distribution to assess the particle size control on element concentrations.Nearly all loess-palaeosol sequence samples exhibit a bimodal particle size distribution with medium/coarse silt and coarse clay fraction representing the main modes. The dominant silt fraction is completely allogenic. The clay component is partly allogenic, transported by high altitudes air stream, and partly authigenic (neoformed in situ by pedogenic processes). However there is only a minor variation in particle size between the sections, the centered log-ratio transformed density functions reveal that the particle size control on the distribution of major and trace elements is highly site-specific. The provenance signal is recorded especially in coarser-grained fractions transported for a short distance from the source area by near-surface wind. The proportion of the authigenic clay fraction, the alteration of feldspars, micas and low alkali contents indicated by high Rb/K ratio and high values of Rb/Sr and Sr/Ca ratios, which indicate the intensity of carbonate leaching, reflect the intensity of chemical weathering, which is highest in the podzols. Precipitation rates were likely the main microclimatic factor that controlled the compositional differences. The loess-palaeosol sequences in areas with higher present-day annual precipitation show higher contents of clay minerals, higher degree of loessification (cementation) and subsequent pedogenic changes.

Unravelling Middle to Late Jurassic palaeoceanographic and palaeoclimatic signals in the Hebrides Basin using belemnite clumped isotope thermometry

Clumped isotope based temperature estimates from exceptionally well-preserved belemnites from Staffin Bay (Isle of Skye, Scotland) reveal that seawater temperatures throughout the Middle-Late Jurassic were significantly warmer than previously reconstructed by conventional oxygen isotope thermometry. We demonstrate here that this underestimation by oxygen isotope thermometry was likely due to a) using the incorrect calcite thermometry equation for belemnite temperature reconstructions and b) by incorrectly estimating the seawater δ18O (δ18Osw) for the Hebrides Basin. Our data suggests that the fractionation factor for oxygen isotopes in belemnites from seawater was closer to that of slow-growing abiogenic calcites than that of other marine calcifying organisms. Our clumped isotope temperatures are used to reconstruct δ18Osw trends across the Callovian–Kimmeridgian in the Hebrides Basin. The δ18Osw varied significantly in the Hebrides Basin throughout this interval, possibly as a result of changing currents through the Laurasian seaway. Trends in temperature and δ18Osw are compared to published palaeoceanographic studies to shed light on changing palaeoceanography in the Tethyan and Boreal realms throughout the Middle–Late Jurassic.

Smoothed millennial-scale palaeoclimatic reference data as unconventional comparison targets: Application to European loess records

Millennial-scale palaeoclimate variability has been documented in various terrestrial and marine palaeoclimate proxy records throughout the Northern Hemisphere for the last glacial cycle. Its clear expression and rapid shifts between different states of climate (Greenland Interstadials and Stadials) represents a correlation tool beyond the resolution of e.g. luminescence dating, especially relevant for terrestrial deposits. Usually, comparison of terrestrial proxy datasets and the Greenland ice cores indicates a complex expression of millennial-scale climate variability as recorded in terrestrial geoarchives including loess. Loess is the most widespread terrestrial geoarchive of the Quaternary and especially widespread over Eurasia. However, loess often records a smoothed representation of millennial-scale variability without all fidelity when compared to the Greenland data, this being a relevant limiting feature in integrating loess with other palaeoclimate records. To better understand the loess proxy-response to millennial-scale climate variability, we simulate a proxy signal smoothing by natural processes through application of low-pass filters of δ18O data from Greenland, a high-resolution palaeoclimate reference record, alongside speleothem isotope records from the Black Sea-Mediterranean region. We show that low-pass filters represent rather simple models for better constraining the expression of millennial-scale climate variability in low sedimentation environments, and in sediments where proxy-response signals are most likely affected by natural smoothing (by e.g. bioturbation). Interestingly, smoothed datasets from Greenland and the Black Sea-Mediterranean region are most similar in the last ~15 ka and between ~50–30 ka. Between ~30–15 ka, roughly corresponding to the Last Glacial Maximum and the deglaciation, the records show dissimilarities, challenging the construction of robust correlative time-scales in this age range. From our analysis it becomes apparent that patterns of palaeoclimate signals in loess-palaeosol sequences often might be better explained by smoothed Greenland reference data than the original high-resolution Greenland dataset, or other reference data. This opens the possibility to better assess the temporal resolution and palaeoclimate potential of loess-palaeosol sequences in recording supra-regional climate patterns, as well as to securely integrate loess with other chronologically better-resolved palaeoclimate records.

Multidisciplinary approach for palaeoclimatic signals of the non-marine carbonates: The case of the Sarıkavak tufa deposits (Afyon, SW-Turkey)

Non-marine carbonates such as travertine, tufa and speleothem are quite sensitive for climatic fluctuations. This study presents the new dating and the first pollen records from Afyon (Sarıkavak) tufas, SW-Turkey, together with lithofacies descriptions, geochemical and petrographic results obtained from drilling cores (SL-2, SL-6 and SL-7). The data extensively provides insight into palaeoenvironmental and palaeoclimatic changes during the Middle-Late Pleistocene period. According to core samples, these fluvial tufa occurrences formed in high-gradient and stepped fluvial conditions have been defined as barrage-dammed and terraced-slope systems in the investigated area. The depositional lithofacies are moss tufa included macrophytes, bryophytes and vertical stems, phytoclastic tufa, peloidal tufa, micritic tufa, microbial tufa, intraclastic tufa, extra-formational tufa, lime-muddy clay and paleosol level, in respectively. The new U/Th radiometric dating and stable isotopes are evaluated together with previously published results. In regard to new radiometric data, tufa deposits occurred predominantly during the Marine Isotopic Stages, at 313.3 ± 21 (MIS 9), 295.8 ± 63 (MIS 8-9), 230.8 ± 42 (MIS 7d-e), 228.8 ± 12 (MIS 7d), 215.7 ± 17 (MIS 7c) and 188.2 ± 16 (MIS 6-7a) ka, respectively. The climatic changes occurring between glacial and interglacial periods (such as during the Middle –Late Pleistocene) might probably influenced the precipitation of tufas in the area. In addition, the less negative and the more positive carbon isotopic values (between −0.8 and + 1.3‰ V-PDB) could be related to the progressive downstream CO2 degassing from host rocks, enhanced by high-velocity current conditions, changes in the soil-CO2 contribution and photosynthesis. The changes of δ18O values (between −8.3 and −10.1‰ V-PDB) are most probably related to variable effects of evaporation in depositional environment. Palynofloral data, gives important clues about the paleovegetation and paleoclimate of the region. This field survey has been conducted the first time in this area. Both carbon values and palynological findings show that drought conditions were dominantly present in the Pleistocene period, but in some processes drought conditions decreased depending on the amount of rainfall. The increasing amount of gymnosperm pollens is more likely to appear in more humid conditions due to the decreasing of drought condition in this time interval.

Late Jurassic–Early Cretaceous climate change record in clay minerals of the Norwegian-Greenland Seaway

The humid climate of northwestern Europe during the Late Jurassic–Early Cretaceous was punctuated by a widespread arid phase. There are few well constrained and complete sections that document this climate shift from semi-humid to arid, and back to more humid conditions. Detrital clay minerals formed in soils and derived through weathering may be used as palaeoclimatic proxies, and here, clay mineral assemblages from several well-constrained sections from the Norwegian Continental Shelf are presented as a N-S transect of the Norwegian-Greenland Seaway. Palaeoclimate signals in most of the clay mineral sections are complicated by diagenetic overprinting. Yet, towards the Boreal realm of the Norwegian-Greenland Seaway there is a discernible palaeoclimatic signal in the clay mineralogy of Well 16/3–4. At ~30°N, kaolinite is known to have reappeared in the clay mineralogical record in the upper part of Calpionellid Zone B (early-mid Berriasian). However, we find an absence of kaolinite at ~40°N in Well 16/3–4 from the North Sea until the late Berriasian, suggesting that initiation of the first humid phase in the Early Cretaceous Norwegian-Greenland Seaway was diachronous.

Åland churches as archives of tree-ring records sensitive to fluctuating climate

Abstract Tree-ring chronologies provide high-resolution late Quaternary palaeoclimatic data. An important aim of tree-ring research is to extend the chronologies back in time, before the period covered by old living trees. Tree-ring material from historic buildings offers an opportunity to develop long chronologies that, in some regions, may cover the period of the past millennium. Such materials have remained in conditions favourable to preservation and can be used to date the construction timber by means of dendrochronology. Apart from dating, tree-ring data may prove valuable in interpreting past climatic conditions. Here we analyse the data of 111 Scots pine (Pinus sylvestris L.) tree-ring series from the Åland Islands in south-western Finland. In so doing, we illustrate the variation of wetness and drought in the region over a historical time frame (1057–1826). Non-climatic trends were removed from these series using alternative types of detrending procedures. Tree-ring chronologies constructed from the same raw data but using different types of detrending methods agreed on annual to subcentennial scales. The chronologies produced using regional curve standardization (RCS), preferably combined with implementation of a signal-free approach, were comparable with previously published sedimentary and tree-ring evidence from the same region. While non-RCS methods are effective in removing non-climatic information from the chronology, they also resulted in removal of the long-term variation (low-frequency), which did, at least in our data, represent the palaeoclimatic signal common to different types of proxy records. These records, including our data and those of gridded reconstructions developed previously as the Old World Drought Atlas, agreed in indicating dry conditions over the pre-1250 period and around the mid-15th century. The Åland chronology is characterized by notable fluctuations in the availability of tree-ring samples; the periods with low sample replication probably pinpoint years when large construction projects were suspended on these islands.

A new species of permineralized palm stem from the Maastrichtian–Danian sediments of Central India and its palaeoclimatic signal

ABSTRACTA new species of permineralized palm stem, Palmoxylon deoriensis Khan, Mandal et Bera, sp. nov. is described from the Late Maastrichtian (late Cretaceous) – Danian (early Paleocene) sediments of the Deccan Intertrappean Beds of Deori village in Dindori District, Madhya Pradesh, Central India. The fossil specimen is a stem, characterized by the presence of cortical, sub-cortical and central zones with dermal, sub-dermal and inner central zones. The common anatomical features observed in the dermal, sub-dermal and inner central zones are the presence of regularly dispersed fibrovascular bundles, reniforma type of dorsal fibrous sclerenchymatous part (dcap), usually one metaxylem vessel element in each fibrovascular bundle (fvb), both tabular and radiating parenchyma around fvb, leaf-trace bundles distinguished by their protruded tongue-like vascular part with protoxylem vessel elements and highly compact ground tissue with thick-walled parenchyma cells, and the absence of fibrous and diminutive vascular bundles as well as centrifugal differentiation of fibrous part of fvb. These anatomical characters reveal its affinities with the extant Cocos-type palm taxa belonging to the family Arecaceae. Presence of mostly one, large (diameter > 183 μm) metaxylem vessel in each fvb and absence of lacunar ground tissue in the present fossil specimen indicate that palms thrived under a tropical, terrestrial environment during the deposition time (Late Maastrichtian–Danian).

Messor barbarus ants as soil bioturbators: Implications for granulometry, mineralogical composition and fossil remains extraction in Somosaguas site (Madrid basin, Spain)

Few studies have inquired about the relationship between myrmecological activity and the granulometry and mineralogy of sediments of a palaeontological site. The objectives of this article are to determine the sedimentological or mineralogical distinctions produced by ants of the species Messor barbarus when excavating their nests and extracting grains and vertebrate fossil remains from the Miocene palaeontological site of Somosaguas (Madrid, Spain), to evaluate the degree of taphonomic influence this myrmecological activity has on the fossil remains, and to decide whether or not it can be used as a tool for palaeontological prospection. Results show that Messor barbarus does not alter fossil remains when examined under a 10× binocular magnifying glass. Ants preferentially extract from the ant nest grains of medium sizes (0.25–2 mm) compared to the non-ant-modified soils, and also extract a higher quantity of feldspars. These significant granulometric and mineralogical modifications should be considered when carrying out compositional, sedimentological or stratigraphical studies, since these can become biased and alter geological interpretations as provenance or palaeoclimatic signal. Grain size selection could be due to Messor barbarus' physical capacities or the use of clay particles as cementing elements in nests. Mineralogical distinction may be related to feldspars' embayments and pits filled with finer material (mainly smectites), making transportation and pheromone impregnation easier.Results show that the ant mounds had increasing concentrations of fossil remains the nearer they were from the main excavation area, therefore the study of ant mounds in potentially fossiliferous zones can indeed be used as a new method of palaeontological prospection.

Cretaceous coastal lagoon facies: Geochemical insights into multi-stage diagenesis and palaeoclimatic signals

Shallow-water Cretaceous, carbonate platform archives have only rarely been explored through their elemental signature. Yet, facies-sensitive geochemical records can shed light onto the specific dynamics of shallow/proximal settings, where changes in depositional conditions are pronounced. Changes stemming from early and later diagenetic processes must be considered, since they may alter the original geochemical signals, but still contribute to a better understanding of the evolution of ancient shallow carbonates.Here, the elemental record of a variety of carbonate materials from two middle Cenomanian coastal lagoon settings is examined. The two selected sections (Lousa and Lampas, W Portugal) provide a varied record of lithofacies, including matrix micrite, corresponding to diverse palaeoenvironments (marine, marine lagoon, restricted lagoon and subaerial exposed intervals), along with dolomitized beds and atypical darkened grey carbonate horizons. Sparry carbonate veinlets that intersect these materials are included for comparison. Based on the characteristic elemental composition of each carbonate material, and by means of a stepwise statistical approach, dolomitization was determined to be a rather early feature occurring exclusively along shallow to frequently exposed intervals. In contrast, carbonate veinlets were identified as the latest diagenetic event. Matrix micrite and darkened beds present the lowest degree of geochemical differentiation, though certain key elemental contrasts allow for their comparison. Accordingly, the atypical case of darkened beds was attributed to an early blackening process in which low contents of organic matter and non-carbonate mineral phases played a decisive role. Matrix micrite samples—presenting a rather narrow range of elemental fluctuations—were linked to previously identified palaeoenvironmental settings by means of stratigraphically constrained cluster analysis. Specific combinations of elemental trends identified for each established cluster reflect variations in palaeoclimatic regimes throughout the studied interval. Furthermore, the degree of connectivity between open waters and coastal lagoons emerged as predictive of the distribution of major and trace elements in ancient shallow carbonates.This study explores the depositional and diagenetic controls forcing elemental distribution across dynamic shallow carbonate settings, as is the case of coastal lagoons. Complex and atypical elemental fingerprints, established by means of statistical analysis, provide arguments to reconstruct the evolution of the examined carbonate materials. Our findings are highly pertinent, as they: (i) provide a rich dataset not only regarding Lusitanian Basin deposits, but also for coeval settings where basin evolution and diagenesis are pivotal; (ii) underline the insight to be gained from time series analyses of raw elemental data collected from carbonate facies; and (iii) place a suite of numerical analyses within a logical hierarchy for stratigraphic facies analysis, fully supported by independent data.

Groundwater and Global Palaeoclimate Signals (G@GPS)

Groundwater sources supply fresh drinking water to almost half of the World's population and are a main source of water for irrigation across world. Characterization of groundwater resources, surface groundwater interactions and their link to the global water cycle and modern global change are important themes in hydrogeological research, whereas little attention has been given to the relation between groundwater and past climate variations. A groundwater system's history is vital to assess its vulnerability under future and potentially adverse climatic changes. The scientific initiative Groundwater and Global Palaeoclimate Signals (G@GPS) investigates major recharge periods of large groundwater aquifers worldwide. We describe the findings for a major basin on each permanently inhabited continent and one with coastal influences in Australia. As palaeo-signals in groundwater are inherently low-resolution records, they can only be related to considerable amounts of recharge. Long periods with substantial groundwater recharge ought to be well identifiable in terrestrial records. Correlation with regional and global climate records may give ideas of the conditions under which such large amounts of recharge were initiated.

Changes in northeast African hydrology and vegetation associated with Pliocene-Pleistocene sapropel cycles.

East African climate change since the Late Miocene consisted of persistent shorter-term, orbital-scale wet-dry cycles superimposed upon a long-term trend towards more open, grassy landscapes. Either or both of these modes of palaeoclimate variability may have influenced East African mammalian evolution, yet the interrelationship between these secular and orbital palaeoclimate signals remains poorly understood. Here, we explore whether the long-term secular climate change was also accompanied by significant changes at the orbital-scale. We develop northeast African hydroclimate and vegetation proxy data for two 100 kyr-duration windows near 3.05 and 1.75 Ma at ODP Site 967 in the eastern Mediterranean basin, where sedimentation is dominated by eastern Sahara dust input and Nile River run-off. These two windows were selected because they have comparable orbital configurations and bracket an important increase in East African C4 grasslands. We conducted high-resolution (2.5 kyr sampling) multiproxy biomarker, H- and C-isotopic analyses of plant waxes and lignin phenols to document orbital-scale changes in hydrology, vegetation and woody cover for these two intervals. Both intervals are dominated by large-amplitude, precession-scale (approx. 20 kyr) changes in northeast African vegetation and rainfall/run-off. The δ(13)Cwax values and lignin phenol composition record a variable but consistently C4 grass-dominated ecosystem for both intervals (50-80% C4). Precessional δDwax cycles were approximately 20-30‰ in peak-to-peak amplitude, comparable with other δDwax records of the Early Holocene African Humid Period. There were no significant differences in the means or variances of the δDwax or δ(13)Cwax data for the 3.05 and 1.75 Ma intervals studied, suggesting that the palaeohydrology and palaeovegetation responses to precessional forcing were similar for these two periods. Data for these two windows suggest that the eastern Sahara did not experience the significant increase in C4 vegetation that has been observed in East Africa over this time period. This observation would be consistent with a proposed mechanism whereby East African precipitation is reduced, and drier conditions established, in response to the emergence of modern zonal sea surface temperature gradients in the tropical oceans between 3 and 2 Ma.This article is part of the themed issue 'Major transitions in human evolution'.

Sediment grain size and surface textural observations of quartz grains in late quaternary lacustrine sediments from Schirmacher Oasis, East Antarctica: Paleoenvironmental significance

In this study we report the sediment grain size parameters and surface textural observations (using scanning electron microscopy (SEM)) of quartz grains from sediments of Sandy Lake, Schirmacher Oasis, East Antarctica. The sediment core spans the last 43 cal ka B.P. The statistical parameters of grain size data (sorting, skewness, kurtosis, mean grain size, D10, D50, D90 and SPAN index) indicate that the sediments are primarily transported by melt-water streams and glaciers. However, during the last glacial period, sediments seem to be transported due to wind activity as evident by the good correlation between rounded quartz data and dust flux data from EPICA ice-core data. The mean grain size values are low during the last glacial period indicating colder climatic conditions and the values increase after the last glacial maximum suggesting an increase in the energy of the transporting medium, i.e., melt-water streams. The sediments are poorly sorted and finely skewed and show different modes of grain size distribution throughout the last 43 cal ka B.P. SEM studies of selected quartz grains and analyses of various surface textures indicate that glacigenic conditions must have prevailed at the time of their transport. Semi-quantitative analyses of mineral (quartz, feldspar, mica, garnet and rock fragments & other minerals) counts suggest a mixed population of minerals with quartz being the dominant mineral. Higher concentration of quartz grains over other minerals indicates that the sediments are compositionally mature. The study reveals the different types of physical weathering, erosive signatures, and chemical precipitation most of them characteristic of glacial environment which affected these quartz grains before final deposition as lake sediments. The palaeoclimatic signals obtained from this study show similarities with ice-core and lake sediment records from Schirmacher Oasis and other ice-free regions in East Antarctica.

Modelled glacier equilibrium line altitudes during the mid-Holocene in the southern mid-latitudes

Abstract. Glacier behaviour during the mid-Holocene (MH, 6000 years BP) in the Southern Hemisphere provides observational data to constrain our understanding of the origin and propagation of palaeoclimate signals. In this study we examine the climatic forcing of glacier response in the MH by evaluating modelled glacier equilibrium line altitudes (ELAs) and climatic conditions during the MH compared with pre-industrial time (PI, year 1750). We focus on the middle latitudes of the Southern Hemisphere, specifically Patagonia and the South Island of New Zealand. Climate conditions for the MH were obtained from PMIP2 model simulations, which in turn were used to force a simple glacier mass balance model to simulate changes in ELA. In Patagonia, the models simulate colder conditions during the MH in austral summer (−0.2 °C), autumn (−0.5 °C), and winter (−0.4), and warmer temperatures (0.2 °C) during spring. In the Southern Alps the models show colder MH conditions in autumn (−0.7 °C) and winter (−0.4 °C), warmer conditions in spring (0.3 °C), and no significant change in summer temperature. Precipitation does not show significant changes but exhibits a seasonal shift, with less precipitation from April to September and more precipitation from October to April during the MH in both regions. The mass balance model simulates a climatic ELA that is 15–33 m lower during the MH compared with PI conditions. We suggest that the main causes of this difference are driven mainly by colder temperatures associated with the MH simulation. Differences in temperature have a dual effect on glacier mass balance: (i) less energy is available for ablation during summer and early autumn and (ii) lower temperatures cause more precipitation to fall as snow rather than rain in late autumn and winter, resulting in more accumulation and higher surface albedo. For these reasons, we postulate that the modelled ELA changes, although small, may help to explain larger glacier extents observed by 6000 years BP in South America and New Zealand.

Plio-Pleistocene floras of the Vildštejn Formation in the Cheb Basin, Czech Republic — A floristic and palaeoenvironmental review

Plant fossil assemblages (foliage, fruits and seeds, pollen, wood) from the Pliocene and early Pleistocene deposits in W Bohemia (the Vildštejn Formation of the Cheb Basin, Tachov/Cheb–Domažlice/ Graben) are newly analysed using several palaeoenvironmental methods with the aim to reconstruct palaeovegetation and palaeoclimatic changes. Floras of four subsequent stratigraphic levels show a decrease of exotic elements in the Pliocene and a massive immigration of boreal elements in the early Pleistocene. Vegetation changes start with broad-leaved deciduous and mixed mesophytic forests and continue towards light forests of the mentioned types in areas of zonal to extrazonal habitats. This vegetational change is characterised by an immigration of dry herbaceous and sclerophyllous elements. Wetland communities from higher positions in the profiles stepwise loose exotic components and point to cool–temperate conditions similar to the present conditions. Palaeoclimatic signals show warmer and more humid conditions for the Pliocene levels (about 15°C of mean annual temperature, 5°C of mean temperature of the coldest month and 25°C of mean temperature of the warmest month, more than 900mm of mean annual precipitation). Early Pleistocene proxy data indicate the beginning of a cooler phase at the Plio-Pleistocene boundary (about 7°C of mean annual temperature and decreasing trend of precipitation), but conditions not colder than those of the present day in the NW part of the Bohemian Massif.