Paleoclimatic Evolution Research Articles

Characteristics and paleoclimate significance of authigenic ferrimagnetic minerals in the Xuancheng red earth, southern China

Soil magnetic records in Quaternary red earth (QRE) deposits contain a valuable record of paleoclimate information, providing insights into controls on Earth’s climate system in the past and potentially helping to predict its response to perturbations in the future. Here, analysis of the environmental magnetism and mineralogy of the Xuancheng QRE (Anhui Province, South China) shows that magnetic variation was strongly linked to production of authigenic ferrimagnetic minerals such as maghemite. Fine-grained maghemite formed during the weathering-related transformation of iron-bearing illite to vermiculite, generating aggregates of vermiculite or mixed-layer illite-vermiculite. Enclosure of authigenic ferrimagnetic minerals by illite and vermiculite-group minerals inhibits their chemical weathering, but this protective effect can be lost due to intensified weathering, allowing the authigenic ferrimagnetic minerals to transform into more stable antiferromagnetic minerals. Upsection within the Xuancheng QRE, the content of authigenic ferrimagnetic minerals gradually increases, as revealed by SIRM and SIRM/χ, indicating a decrease in weathering intensity as the regional climate evolved from warm and wet in the middle Pleistocene to relatively cooler and drier today. Thus, this study improves our understanding of the relationship between soil magnetic properties and paleoclimate evolution in QRE deposits.

Characterization of the Major Elements and Paleoenvironmental Significance of the Shiyang Profile in the Weinan Basin, China

The enrichment and migration patterns of different chemical elements record paleoclimatic information in loess formations. The chemical elemental measurements of 245 samples from the Shiyang profile in the Weinan Region were compared with the geochemical characteristics of typical wind-formed profiles, and the paleoclimatic evolution was discussed. The results showed the following: (1) the standardized curves of the cumulative concentrations of SiO2, Al2O3, and CaO along with the Upper Continental Crust (UCC) in the Shiyang profile exhibited significant similarities with typical wind-formed profiles. This strongly suggests that the Shiyang profile has a wind-formed origin. (2) The mean value of the chemical index of alteration (CIA) of the Shiyang profile is 62.06, indicating that the Shiyang profile has been in the stage of primary chemical weathering. (3) The ratios of K2O/Al2O3, TiO2/Al2O3, and Fe2O3/Al2O3 in the Shiyang profile are comparable to those found in typical wind-formed profiles, suggesting a common source area and supporting the premise that the Shiyang profile is of wind-induced origin.(4) The regional climate has undergone a series of transitions: from a dry and cool phase in the early Holocene to warm and humid yet unstable conditions in the middle Holocene, and returning to dry and cool during the late Holocene.

Lithium isotope systematics in an endorheic saline lacustrine system: Insights from Qinghai Lake, China

The study of lithium isotopic (δ7Li) signatures in sedimentary deposits has become a powerful tool to infer past silicate weathering regimes, thus informing our knowledge of the geological carbon cycle and paleoclimate evolution. Sediments from Qinghai Lake, the largest saltwater lake in China (4625 km2), offer an unparalleled archive for investigating the climatic history of the Qinghai-Tibet Plateau. However, prior to leveraging the δ7Li proxy in this context, it is imperative to unravel the mechanisms of lithium (Li) isotope fractionation and elemental cycling within the lake's aqueous and sedimentary systems. In this study, we collected and analyzed samples of Qinghai Lake's water, sediments, and recharge waters (rivers, groundwater, and rainfall) to investigate the processes controlling the δ7Li value recorded in Qinghai Lake sediments.Our data reveal subtle variances in Qinghai Lake water Li concentration ([Li]), ranging from 652 to 873 ng/g, suggesting interactions with iron oxides or suspended matter. The δ7Li signature, however, exhibits remarkable uniformity across the lake at 32.1‰ (±0.4‰). Near the estuary of the Buha River, there is a swift homogenization of [Li] and δ7Li, stabilizing within just 3 km of the inflow. Lake sediments exhibit δ7Li values ranging from 1.5‰ to 6.6‰, exceeding those of the upper continental crust (∼0‰ ± 4‰), yet approximately 30‰ lower than those in lake waters. This significant discrepancy between the δ7Li of lake water and sediments is likely due to the preferential incorporation of 6Li over 7Li during the neoformation of clay minerals.Lithium mass balance modeling for Qinghai Lake, incorporating inputs from river and groundwater (∼46.5 t/a with δ7Li ∼18.3‰) and outputs via clay mineral uptake (∼44 t/a with δ7Li ∼5.1‰), indicates that the lake's Li system is currently out of steady state. The model predicts a gradual rise in the lake's Li inventory, estimated to achieve steady state within 1.2 ka and the δ7Li value of lake water will increase until reaching ∼45‰ assuming constant climate conditions.

Impact of the Tibetan Plateau on Global High-Frequency Temperature Variability

Abstract The Tibetan Plateau’s (TP) topography has long been recognized for its impact on climate. However, recognition of the influence of the TP on global weather variability remains insufficient. Therefore, this study used numerical simulations to demonstrate the influences of the TP and its mechanical and thermal forcing on global high-frequency temperature variability and eddy kinetic energy (EKE). Despite local influences, the TP influenced the high-frequency temperature variability in far-flung regions like North America. In summer, the TP’s influence on high-frequency temperature variability showed dipole patterns in Eurasia and tripole patterns in North America, which were mainly induced by TP thermal forcing. In winter, the TP’s influence on high-frequency temperature variability was dominated by mechanical forcing and was less significant for remote regions than in summer. Mechanical forcing dominated EKE in both summer and winter. Furthermore, the horizontal temperature advection dominated the TP’s influence on high-frequency temperature variability for both its thermal effect in summer and its mechanical effect in winter, wherein EKE, as the dynamical factor, determined the horizontal temperature advection rather than the thermodynamical factor, the temperature gradient. Our findings suggest that the TP, via its mechanical and thermal forcing, may have an impact on temperature-related weather extremes around the world. Significance Statement The Tibetan Plateau (TP), being one of the world’s largest topographies, has been demonstrated to influence both paleoclimatic evolution and contemporary climate variability. However, the effect of TP on global weather variability has not been thoroughly studied. Therefore, this study looked into the effect of the TP on global high-frequency temperature variability. The TP’s overall, mechanical, and thermal effects on high-frequency temperature variability and EKE were specifically demonstrated. To get insights into dynamics, the physical processes underpinning the TP’s influence on high-frequency temperature variability were further clarified. This study contributes to a better understanding of the effects of large-scale topography on global high-frequency temperature variations, as well as relevant weather extremes.

Characteristics of Nanoparticles in Late Pliocene Paleo-Mountain Fire Relics in Jinsuo Basin, Yunnan Province and Their Implications for Paleoclimate Evolution

Wildfires significantly affect climate and environmental changes, closely tied to extreme weather responses. Vegetation combustion emits greenhouse gases (CO2, CH4, CO), warming the climate. Climate shifts, in turn, impact vegetation growth, altering combustible material types and quantities, thus affecting wildfire intensity, duration, and frequency. Wildfires profoundly affect ecosystems, influenced by factors like atmospheric oxygen and climate. Their combustion gases impact climate and vegetation growth. Recent advancements in studying ancient wildfires include analyzing nanoparticles as key indicators. This study discovered six types of nanoparticles in ancient wildfire remains, with sizes ranging from 50 nm to 500 nm and diverse compositions including elements such as C, O, Mg, Al, Ti, Fe, S, Ca, and P. These findings indicate that wildfires generate a variety of nanoparticles, offering new insights into ancient fire events. Elemental analysis revealed low magnesium but high calcium and aluminum levels, suggesting a warm, humid paleoclimate during these fires. The presence of high Ti-O ratios and carbon-rich nanoparticles points to ground fires with incomplete combustion. This research underscores the significance of nanoparticles in understanding the history and characteristics of ancient wildfires.

Early Paleogene plant biomes of the Pacific side of Eurasia

Major plant biome changes in East Asia during the early Paleogene are studied using the Integrated Plant Record vegetation analysis for the first time based on paleobotanical records. The paleobotanical record employed for the reconstruction comprises 110 paleofloras covering the early Paleocene to early Eocene, a time-span of ca. 17 Myr. Our data indicate the presence of more forested conditions over East Asia during the early Paleogene than at present. The early Paleogene vegetation cover in the study area fundamentally differed from modern and was much more homogeneous compared to the modern one. Mixed mesophytic zonal vegetation dominated on the Pacific side of Eurasia during the early Paleogene. Thermophilous mixed mesophytic forests were distributed even at very high latitudes, but at the same time, ecotone between the mixed mesophytic / broadleaved evergreen forests and broadleaved evergreen forest were confined to regions south of 50°N. The proportions of sclerophyllous plants are low in general, even in the mid-latitudes. The localities with open woodlands are all located south of ca. 45°N. The observed vegetation patterns and their changes throughout the early Paleogene in many cases can be correlated with climate patterns and the overall continental paleoclimate evolution as reconstructed from the paleobotanical record. The higher-than-present spatial homogeneity of early Paleogene vegetation coincides with shallow temperature gradients and a significantly more humid regional rainfall pattern over East Asia during the early Paleogene.

Geochemical constrains for unravelling the condition of sedimentation, provenance, paleoclimate variation, and metallogenic implication of the cretaceous deposits of Mayo Oulo Basin (North Cameroon, Africa)

The sediments from the Mayo Oulo intracontinental Basin, along the N–S cross section between the Gadavou and Lombel localities in central part of the basin, were investigated through major and trace elements geochemistry associated with palynological analysis to determine their condition of sedimentation, paleoclimate evolution and metallogenic implication along the Cretaceous sequence from the N–S cross section of the central part of this basin. From bottom to top of this sequence there are various types of facies with various concentrations of carbonate. Based on their major oxides compositions, the sediments were classified as Shales associated with Fe-shales, Fe-sands, Wacke and Litharenite. The CIX (Chemical Index of Alteration, 62.65 to 98.14) and PIX (Plagioclase Index of Alteration, 65.00 to 99.13) sediments underwent a various chemical weathering; little chemical weathering in the middle to the upper part of the sequence and moderate to high chemical weathering in the lower part. The discriminant function-based multidimensional tectonic diagrams indicate mainly and respectively arc-collisional and Island arc-active continental margin settings which are consistent with the Precambrian geological history of the study area. The SiO2 vs. Al2O3+K2O + Na2O, C-values, associated with trace elements plots such as Sr/Ba, and Rb/Sr, and palynological content (continental or terrestrial species exclusively, dominated by Gymnosperm pollens such as. Inaperturopollenites sp., Araucariacites sp. and Classopollis sp, associated with spores such as Cicatricosisporites sp) indicate mainly arid to semi-arid climate with periodic humid to semi-humid conditions. The Sr/Ba values ranging from 0.084 to 6.408 suggest a fluctuating and sometimes high salinity (Hypersaline milieu). The rare earth elements data show high LREE/HREE ratios (2.86–13.31); high negative and positive Eu anomaly (Eu/Eu∗ = 0.33 to 1.38) and no Ce anomaly (Ce/Ce∗ = 0.94 to 1.02); these features, together with mixed major and trace element ratios and plots such as, Al2O3/TiO2 ratios (14.31–54.26); Th/Co ratios (0.30–14.58); Ce vs La/Yb, Zr vs TiO2 and La/Sc vs Th/Co plots, indicate that the sediments are derived mainly from felsic to intermediate or mafic rock composition. Ni/Co (1.86–3.59) and U/Th (0.03–0.76) ratios are consistent with oxic conditions from bottom to top of the sequence. The Al/Si ratio shows positive correlation with CIA, Th, Zr, Hf, Na, K and negative correlation with Ca and Mg. The positive correlation with K, Hf, Na, Zr, and Th from detrital origin and negative correlation with Ca and Mg from chemical origin could suggest the geochemical composition control of grain size. According to the ternary Al–Fe–Mn diagram metallogenic classification, the studied samples are essentially terrigenous and partially weakly metalliferous, close to those from the Babouri –Figuil and Mamfe Basins (Cameroon) and contrary to those from the Sob area (Polar Urals). No marine or transitional fossil species are recorded. The presence of numerous tetrads to dyads indicate a lacustrine or swampy environment surrounded by vegetation.

Glacial activity and paleoclimatic evolution records in the Cosmonaut Sea since the last glacial maximum

This research explored the origin and paleoenvironmental significance of sediments from the Cosmonaut Sea, Antarctica, focusing on the period since the Last Glacial Maximum (LGM, 26,000 cal a BP). Sediment samples from core ANT37-C5/6-07 were subjected to AMS14C dating, clay-mineral assemblage analysis, grain size evaluation, and geochemical testing. Results indicated illite as the dominant clay mineral (average 46%), followed by kaolinite (22%) and smectite (21%), with chlorite (11%) being the least abundant. Comparison with previous studies suggested that these sediments are largely derived from weathered material from Prydz Bay and Enderby Land coastal regions. The study of mineral ratios, geochemical elements, and sediment grain size, alongside δ18O values from the East Antarctica EDML ice core, revealed that the ice sheet in the study area retreated around 18600 cal a BP, melted more markedly during 16800-15000 cal a BP, tended to expand during 14800-13500 cal a BP, and then the ice sheet remained in a state of retreat until it expanded again around 5000 cal a BP. It is largely synchronous with the phased changes in the Antarctic climate since the LGM (26ka) of the Cosmonaut Sea. Notably, the sediment record aligns with major paleoclimatic events, including Heinrich Stadial 1 and the Younger Dryas in the northern hemisphere and the Antarctic cold reversal, reflecting a climatic ‘seesaw’ effect. These findings suggest that the sedimentary record in the Cosmonaut Sea is a sensitive indicator of climatic conditions, highlighting a history of glacial movements and revealing East Antarctica’s climatic fluctuations. Additionally, the research indicates that the regional ice sheet is more sensitive to climatic changes than previously believed, underscoring its instability.

Sedimentary Environment, Tectonic Setting, and Uranium Mineralization Implications of the Yimin Formation, Kelulun Depression, Hailar Basin, China

The sandstone-type uranium deposit of the Kelulun Depression is the first industrially valuable uranium deposit discovered in the Hailar Basin. This study performed a systematic examination of 17 sandstone samples from the Yimin Formation in the Kelulun Depression based on various analytical techniques. The findings of the current study were synthesized with previous research to investigate the impact of the redox conditions and the tectonic background of the source area, as well as the paleoclimatic evolution of the Yimin Formation on uranium mineralization. The elemental Mo, U/Th, V/Cr, Ni/Co, and V/(V + Ni) ratios indicate that the paleowater was in an oxygen-rich environment during the deposition of the Yimin Formation. Additionally, the C-value, Sr/Cu, Al2O3/MgO, and Rb/Sr ratios indicate that the Yimin Formation was formed in a paleoclimate characterized by arid-to-semi-arid conditions. The geochemical characteristics of the observed elements indicated that the sediment source of the Yimin Formation was mainly felsic rocks from the upper continental crust, the weathering of the rock was weak, and the tectonic background was a passive continental margin. Coffinite is distributed in the form of cementation and stellates within or around pyrite crystals, and uranium-titanium oxide is mostly distributed in an irregular granular distribution in the biotite cleavage fractures of the study area. In summary, the findings of this study reveal that the tectonic settings, provenance, uranium source, paleoclimate, and oxygen-rich paleowater of the Yimin Formation have important geological significance for the large-scale uranium mineralization of the Kelulun Depression.

Geochemical and palynological records of the Early‐Middle Jurassic in the Turpan‐Hami Basin, NW China: Implications for paleoenvironment and paleoclimate change

The Early‐Middle Jurassic is one of the crucial coal‐forming geologic periods in the world and an important target for hydrocarbon exploration in the Turpan‐Hami Basin, China. The paleoenvironment and vegetation reconstruction of the Early‐Middle Jurassic have been investigated using elemental geochemistry and palynological analysis to reveal paleoclimate evolution. A total of 48 genera of pteridophyte spore and 35 genera of gymnosperm pollen were identified, and 5 palynological assemblages were longitudinally divided, which showed significant differences in geochemical behaviours. The paleoenvironment was a transition from suboxidation to anoxia and then to an oxidation environment under freshwater conditions. The paleowater in the northern Taibei Sag was deeper than that in the southern part during the Middle Jurassic, which coincided with the sedimentary background of the sublacustrine fan in the north and the shallow braided river delta in the south. The paleovegetation evolved from mixed lowland–upland forest in the Hettangian‐Toarcian, to lowland fern forest in the Aalenian‐Bajocian, to upland conifers forest in the early Bathonian, to upland Cheirolepidiaceae forest in the late Bathonian‐Callovian. The Toarcian and Bathonian‐Callovian arid climate and the Hettangian‐Pliensbachian and Aalenian‐Bajocian warm‐humid climate were responses to the continued global warming events and the intensification of the East Asian monsoon circulation, respectively. The influence of the Bathonian‐Callovian aridification event on the sedimentary response in the southern Taibei Sag will be delayed due to the gradual southward migration of the depositional centre.

Pollen and spore records constrained by millennial prodelta evolution: a case study of the Huanghe (Yellow River) delta

Pollen and spore records in prodeltaic sediments hold significant potential for reconstructing paleoecologic and paleoclimatic evolution. However, uncertainties in these reconstructions arise from millennial-scale prodelta evolution, which dominates stratigraphic development and consequently influences sedimentary processes and/or pollen provenance. Here we explore the intricate relationship between pollen/spore records and prodelta stratigraphic evolution, using established seismic stratigraphy and ten sediment cores (five new, five from literature) within both the proximal and distal (mud belt) parts of the Huanghe (Yellow River) prodelta. In the proximal region, dominant lobate stratigraphic development, accompanied by shifts in river mouth and depocenter, leads to variations in pollen assemblages and contents within individual cores and differences in vertical pollen distribution across core sites. Transport distance appears to be a key factor, with arboreal pollens, particularly saccate ones (e.g., Pinus), positively correlating with the distance from the river mouth in their percentages within a single delta lobe, while non-arboreal and non-saccate arboreal pollens show higher percentages within shorter transport distances, despite longer distances leading to decreased total pollen concentrations. Likely due to the total pollen concentration after extended long-distance transport, this pattern is not observable in the distal mud belt. Subsurface stratigraphy in this mud belt reveals a complex pollen provenance characterized by Artemisia-Ulmus-Chenopodiaceae-Pinus, with non-arboreal pollens in dominance. Therein, non-arboreal pollens are not consistent with deposition from long-distance transport, and Ulmus pollens are uncommon in the western Bohai Sea. Interestingly, surface sediments in the mud belt display a different assemblage, characterized by Pinus-Artemisia-Quercus, consistent with the nearby Luanhe River prodelta, suggesting recent pollen supply from nearby sources, possibly due to the recent abandonment of the mud belt. Additionally, an energetic longshore transport/erosional regime reduces pollen content at the mud-belt margins and create pollen sinks (with the highest concentration) in the mud patch (accumulation area) within the erosion-dominated region adjacent to the mud belt. Our findings confirm that stratigraphic evolution, alongside hydrodynamic conditions and pollen provenance, governs pollen assemblages in deltaic/prodeltaic sediments. They can provide insights for palynological and pollen-based paleoclimatic and paleoecologic studies in other deltas.

Editorial preface to special issue: Neogene-Quaternary changes of the Indo-Pacific Warm Pool encompassing oceanic, hydrologic and carbon cycles, and their implications for future change

The Indo-Pacific Warm Pool (IPWP) is the primary supplier of heat and moisture to the global atmosphere, and exerts a significant impact on tropical and worldwide climate variability. This special issue expands our understanding of the paleoceanographic and paleoclimatic evolution of the IPWP since Neogene times with implications for understanding future change. It contains fifteen research articles addressing two primary themes: (1) Ocean-atmosphere coupled processes via the ocean water-column, sea surface, atmospheric evaporation/precipitation; and (2) Sediment source-to-sink and biogeochemical carbon-cycles, and their interactions with oceanographic, hydrological, tectonic and other factors. These contributions improve our understanding of thermocline temperature, salinity, oxygenation, hydrography, carbon cycle, biological productivity, and sedimentary response in the IPWP across Neogene and Quaternary time scales, as well as aiding in the forecast of future climate responses in the context of current global warming. The special issue will capture the attention of geologists, climatologists, and anybody else interested in global climate change.

A revised model for Neogene Zagros foreland sedimentation in the Lurestan arc based on new geochemical data

AbstractThe Zagros foreland basin is an important sedimentary archive for the tectonic and paleoclimatic evolution of the Zagros Mountains and the entire Neotethyan Arabia–Iran collision zone. By combining new geochemical high‐resolution whole rock XRF data with clay mineralogy and soluble salt geochemistry we propose an evolution of the sedimentary environment in the Lurestan arc from the Serravallian to the early Pleistocene, closing a gap in understanding the complex exhumation history of the central Zagros mountain belt. An increase in ultramafic sedimentary input indicates a shift from provenance 1 to provenance 2 by ophiolite exhumation at ca.10 Ma in the Imbricated Zagros north of the Lurestan arc. Our data further indicates that the sedimentary environment of parts of the Lahbari Mb within the Lurestan arc represents a piedmont deposition of fine‐grained alluvial fans and siltstones with aeolian contribution deposited under hyper‐arid climate conditions. These represent provenance shift 3 and were likely sourced from evaporites of the underlying Gachsaran Fm and fluvial deposits of the Lower Aghajari Mb (provenance 1 and provenance 2), uplifted by the Mountain Front Flexure at around 5.6 Ma. Combining XRF whole rock data with clay mineral data refines formation conditions of the clay minerals in the foreland basin such as palygorskite, which is revealed to be authigenic in origin in the Lower Aghajari Mb. as a function of varying Mg‐content due to variations of erosion of the ultramafic and mafic rocks in the Imbricate Zagros belt. Palygorskite in the Lahbari Member is likely both inherited from the Neogene Gachsaran evaporites as well as of authigenic origin.

The Jurassic climate change in the northwest Gondwana (External Rif, Morocco): Evidence from geochemistry and implication for paleoclimate evolution

The present work deals with Jurassic deposits belonging to the External Rif chain. It is well known that the Jurassic time was a crucial period in the earth's history as witness of significant climate changes. This work aims to provide a preliminary reconstruction of the regional Jurassic paleoclimate of the northwest Gondwana hinterland and its global paleogeographic context. We used diverse geochemical proxies to unravel paleoclimate of the Jurassic sediments accumulated in the Atlantic and Tethysian hyperextended passive margins bordering the northwest Gondwana. We reconstituted their paleo-humidity, paleo-precipitation, paleo-weathering, paleo-productivity, paleo-floral landscape distribution in the Gondwanaland, the paleo-redox, paleo-oxygenation and paleosalinity of the bordering oceanic sinks. The obtained results indicate that the early Jurassic climate was cool with low rainfall and productivity, while the middle Jurassic was characterized by a semi-moist warm climate with high chemical weathering and subsequent seaward terrigenous supply. The Uppermost Jurassic climate was warm, semi-moist to moist with a return to an arid cold climate marked by high rainfall amount which yielded more terrigenous material to the bordering Tethysian and Atlantic hyperextended passive margins around the northwest Gondwana hinterland. The result of this research reveals, among others, the control of the first-order geodynamic processes on the Jurassic mid-latitude climate change, such as plate tectonics reorganization, oceanic seafloor spreading, and subsequent volcanic activity. The latter may triggered a climate shift from early Jurassic dry “cool” to middle-late Jurassic wet warm “greenhouse” climate conditions around the northwest Gondwanaland. Besides, the Jurassic climate change may have been also controlled by successive mega-monsoons that occurred through the Inter-Tropical Convergence Zone (ICZ) over margins and oceanic realms bordering the northwest Gondwanaland.

Calcareous Nannofossils and Paleoclimatic Evolution Across the Eocene‐Oligocene Transition at IODP Site U1509, Tasman Sea, Southwest Pacific Ocean

AbstractThe Eocene‐Oligocene transition (EOT; ∼34 Ma) was one of the most prominent global cooling events of the Cenozoic, coincident with the emergence of continental‐scale ice‐sheets on Antarctica. Calcareous nannoplankton experienced significant assemblage turnover at a time of long‐term surface ocean cooling and trophic conditions, suggesting cause‐effect relationships between Antarctic glaciation, broader climate changes, and the response of phytoplankton communities. To better evaluate the timing and nature of these relationships, we generated calcareous nannofossil and geochemical data sets (δ18O, δ13C and %CaCO3) over a ∼5 Myr stratigraphic interval recovered across the EOT from IODP Site U1509 in the Tasman Sea, South Pacific Ocean. Based on trends observed in the calcareous nannofossil assemblages, there was an overall decline of warm‐oligotrophic communities, with a shift toward taxa better adapted to cooler more eutrophic conditions. Assemblage changes indicate four distinct phases caused by temperature decrease and variations in paleocurrents: late Eocene warm‐oligotrophic phase, precursor diversity‐decrease phase, early Oligocene cold‐eutrophic phase, and a steady‐state cosmopolitan phase. The most prominent shift in the assemblages occurred during the ∼550 kyr‐long precursor diversity‐decrease phase, which has relatively high bulk δ18O and %CaCO3 values, and predates the phase of maximum glacial expansion (Earliest Oligocene Glacial Maximum–EOGM).

Astronomically forced paleoclimate and sea-level changes recorded in the continental margin of the South China Sea over the past ~23 m.y.

AbstractThe Earth has witnessed the emergence of continental-sized ice sheets, starting with Antarctica and gradually extending to both hemispheres over the past 40 million years. These ice accumulations have had a dramatic impact on both paleoclimate and sea level, substantially influencing sediment deposition in the continental margins. However, understanding sediment accumulation on an orbital scale in continental margins remains limited because of the scarcity of high-resolution, chronologically constrained sedimentary records. Here, we conducted a highly resolved cyclostratigraphic analysis based on natural gamma radiation (GR) series in depth domain at the continental margin of the South China Sea. We established a 22.8 m.y.-long high-resolution astronomical time scale spanning from the Miocene to the Quaternary by tuning the GR records to the global deep-sea benthic foraminifera carbon isotope curves and the 405 k.y. eccentricity cycles. The m.y.-scale sea-level changes since the Miocene were reconstructed through the sedimentary noise modeling of the 405-k.y.-tuned GR series. These reconstructions aligned with regional and global sea-level changes. The phase correlation between the filtered 1.2 m.y. cycles of sea-level change curves (dynamic noise after orbital tuning and ρ1 median models) from δ13Cbenthic and tuned GR series and the 1.2 m.y. obliquity amplitude modulation cycles revealed a shift from an anti-phase to an in-phase relationship across the middle Miocene climate transition (ca. 13.8 Ma), suggesting extensive expansion of the Antarctic ice sheet played a key role. In addition, a shift from an in-phase to an anti-phase relationship during the late Miocene (ca. 8 Ma and 5.3 Ma), indicating ephemeral expansion of the Arctic ice sheets or the changes in carbon cycle involving the terrestrial and deep ocean carbon reservoirs, might be the primary driver of eustatic changes. Furthermore, obliquity forcing and changes in meridional gradients in insolation that transported poleward flux of heat, moisture, and precipitation increased ice accumulation in both pole ice sheets and nonlinearly transferred high-latitude signals to low-latitude regions. This phenomenon is supported by the observation of strong obliquity signals in low latitude during global climate cooling interval. Our results suggest that m.y.-scale sea-level variations respond to astronomically induced climate change and ice sheet dynamics of both poles. This work contributes a highly resolved low-latitude geological archive to the future reconstruction of paleoclimate evolution on a global scale.

Geochemical and mineralogical proxies from the Messinian mudrocks (Catanzaro Basin, southern Italy): Paleoweathering and paleoclimate evolution during the onset of the Messinian salinity Crisis

The bulk mineralogy and geochemistry of mudrock samples from a representative section of the Calcare di Base Formation outcropping in the Catanzaro Basin (Calabria) were studied using X-Ray Diffraction and X-Ray Fluorescence techniques. Phyllosilicates are the main mineralogical constituents followed by quartz, calcite, feldspar, hematite and gypsum in the lower part of the studied succession, whereas calcite is the main mineralogical component in the upper part. The geochemical composition reveals that SiO2, Fe2O3, Al2O3, CaO and MgO are the most abundant oxides on average. The chemical weathering indices, such as the CIA (Chemical Index of Alteration) and its modifications, show low-medium values and thus suggest weak-moderate source area(s) weathering conditions, under a mainly dry/arid paleoclimate environment. The low kaolinite amounts confirm a low-moderate degree of weathering processes. The studied samples originate from an environment in which non-steady-state weathering conditions prevailed and active tectonism allows erosional processes. This trend suggests a paleoclimate characterized by persistent dry (arid) conditions alternating with relatively wet (humid) conditions. The studied mudrocks are characterized by recycling effects as recorded in the Al–Zr–Ti plot. The provenance of the studied samples is mainly related to a felsic source such as the rocks composing the Sila Massif.The composition of the studied samples was compared to that of similar samples from the Calcare di Base formation of the Rossano Basin to reconstruct the paleoclimate scenario of the Mediterranean area during the Messinian Salinity Crisis. The analogies between the mudrocks investigated in this work and the argillaceous marls from the Calcare di Base formation of the Rossano Basin suggest that they formed in the same (i) non-steady-state weathering and (ii) dry/arid paleoclimatic conditions. All the evidences allow to hypothesize that semi-closed basins, even if distant and not necessarily synchronous from each other, may have developed in a comparable way due to similar local climate condition, geochemistry of the body water and river run-off. The geochemical and mineralogical proxies from the mudrocks of the Calcare di Base Formation may open a new scenario for the understanding of paleoclimatic condition during the Messinian Salinity Crisis.

High-resolution climate variability across the Piacenzian/Gelasian boundary at land-based marine sequences of Monte San Nicola (Sicily, Mediterranean)

The Piacenzian – Gelasian transition is a time of profound changes in the Earth's climatic regime, epitomized by the definitive establishment of large ice caps in the Northern Hemisphere and the beginning of the “ice ages” at ca. 2.6 Ma. This event is sharply documented in δ18O records globally by a prominent triplet of severe glacial events (MIS 100, 98 and 96) that approximate the base of the Gelasian Stage. We have reconstructed a multi-species planktic and benthic foraminiferal δ18O and δ13C record from the Monte San Nicola section (Sicily) across the Piacenzian/Gelasian boundary, with the purpose of better constraining in time the main marker criteria for recognition of the Gelasian GSSP (Global Boundary Stratotype Section and Point) and investigating in detail the paleoclimatic and paleoceanographic response of the central Mediterranean to the definitive onset of the Northern Hemisphere Glaciation. Our results confirm the reliability and usability of the criteria originally proposed for defining the Gelasian GSSP, and significantly improve their chronology and chronostratigraphic positioning. Beyond an obvious alternation of obliquity-driven glacial-interglacial cycles, our isotopic record unraveled a pervasive climate variability in the suborbital time domain, the origin of which is still ambiguous. Altogether data presented in this paper provide the first high resolution isotopic records shedding new light both on the stratigraphic and paleoclimatic evolution of the Central Mediterranean area at the beginning of the Northern Hemisphere Glaciation.

Paleoweathering and Detrital Provenance of Balangbaru Shale, in South Sulawesi

Sulawesi Island, known for its geological complexity, offers a unique opportunity for researchers to investigate further into sedimentary basins particularly in South Sulawesi area. The Cretaceous Balangbaru Shale is one of the rocks that has an extensive distribution in South Sulawesi especially in the western part. Due to limitation of geological information related to this formation we performed the paleodepositional investigation to elucidate the paleoweathering, geochemistry characterization, and detrital provenance of the Balangbaru Shale. Indeed, previous studies have demonstrated that fine-grained sedimentary rocks can serve as valuable archives of geochemical information, enabling the reconstruction of paleoclimate evolution during the deposition period. Employing XRF quantitative analysis, we examine the dispersion of major elements within eight distinct layers of the Shale. Additionally, comprehensive whole-rock analyses enable us to ascertain the abundance of major elements and subsequently deduce detrital SiO2 and biogenic SiO2 content, thereby comprehending the inorganic geochemical composition of the Balangbaru Shale.The present study seeks to address the limited understanding of the geochemical properties of the Balangbaru Shale, specifically pertaining to paleoweathering intensity and detrital provenance. Acknowledging the scarcity of recent data available on the subject matter, this research aims to bridge the limitation data gap by conducting an in-depth investigation into the geochemical characteristics of the Balangbaru Shale by employing major oxides concentrations (SiO2, Al2O3, Fe2O3, K2O, P2O5, MgO, CaO, Na2O, MnO, TiO2, Cr2O3) and trace elements (Sr, Cu, Ba, Th, Ni, V, Th, U) into the equations such as C-value, chemical index alteration (CIA), plagioclase index of alteration (PIA), weathering index of parker (WIP) and ratio of Rb/Sr, U/Th, Sr/Cu, Sr/Ba. Furthermore, the major oxides ratio of Al2O3/TiO2 and TiO2/Zr were performed to specify the sediment provenance and the source-area rock compositions of the Balangbaru Shale. The obtained data reveals a moderate to high degree of weathering intensity in the detrital source environment of the Balangbaru Shale, suggesting warm to humid climate conditions in the source region. Additionally, the analysis of the detrital fraction indicates the possible origin of the Balangbaru Shale from felsic rocks. Overall, these findings contribute significantly to the understanding of paleoenvironmental conditions associated with the Balangbaru Shale, shedding light on its geological history.

Influence of Asian Topography on the Arctic Stratospheric Ozone

AbstractEvaluating the impact of topography on stratospheric ozone is a crucial step toward achieving a deeper comprehension of the role of topography uplift in driving paleoclimatic evolution and stratospheric dynamics and chemistry. This paper quantitatively estimates the contribution of Asian topography to Arctic stratospheric ozone by topography experiments in the Whole Atmosphere Community Climate Model version 6. The results indicate that Asian topography exerts an especially robust influence on Arctic stratospheric ozone during winter. Compared to the flattened topography, Asian topography significantly increases the ozone by 15% in the lower Arctic stratosphere, accompanied by the highest accumulation of total ozone appearing in the polar region north to the North American continent. The intensified residual mean circulation transport is principally responsible for the increase in ozone, and Asian topography has a stronger impact on the vertical residual mean transport than on the meridional residual mean transport. Further examination demonstrates that the robust strengthening of planetary waves caused by Asian topography significantly contributes to the enhancement of the residual mean circulation. Specifically, the upper Arctic stratosphere experiences a 42.7% increase in the amplitude of planetary waves with wavenumber 1, which means the weakened polar vortex. The diagnosis of the mean Lorenz energy cycle further indicates that Asian topography decreases the zonal mean kinetic energy and increases the eddy kinetic energy in the stratosphere. Therefore, the enhancement of residual mean circulation transport and the weakening of the polar vortex both work together to promote the accumulation of Arctic ozone.