Paleoclimatic Implications Research Articles

Recognition of Milankovitch cycles during the Oligocene–Early Miocene in the Zagros Basin, SW Iran: Implications for paleoclimate and sequence stratigraphy

Milankovitch cycles during the Phanerozoic affected paleoclimate, the onset/termination of glacial/interglacial periods, sea-level changes, and thus the distribution of different facies in sedimentary basins. The effects of astronomical forcing have been recorded as astronomical frequency signals in sedimentary sequences through geological history. In this research, for the first time, the signal of Milankovitch cycles and orbital obliquity modulation cycles from the Oligocene–Early Miocene Asmari Formation at one of the oil fields in the Dezful Embayment of the Zagros Basin, Iran, have been identified, through wireline logs. Based on that, ten ~1.2 orbital obliquity modulation cycles have been recognized and correlated with global third-order sequences and δ18O events. The number of cycles during the Oligocene–Early Miocene in the Asmari Formation is equivalent to obliquity of the La2004 orbital solution. Additionally, the optimal sediment accumulation rates, depositional duration of this formation, and foraminiferal biozone durations have been calculated. The result of this study shows that sediment accumulation rates varied in the range 2.9 to 3.2 cm/kyr. The foraminiferal biozones are diachronous in this area. Based on the identified 405 kyr long-eccentricity cycles in the three studied wells, three astronomical time spans of 11.5 Myr, 9.42 Myr, and 9.02 Myr were obtained for the Asmari Formation in Wells A, B, and C, respectively.

Clay mineralogy of the Stari Slankamen (Serbia) loess-paleosol sequence during the last glacial cycle — Implications for dust provenance and interglacial climate

Clay minerals in loess-paleosol sequences carry important information on dust source and the paleoenvironments of the areas of loess distribution. The loess-paleosol sequences in the Serbian part of the Carpathian Basin are among the most complete Quaternary terrestrial sedimentary sequences in Europe. However, relatively little is known about the origin and temporal variations of clay minerals in these deposits and their paleoclimatic implications. Here we present the results of high-resolution XRD clay mineral analysis of the Stari Slankamen loess-paleosol sequence through the last glacial cycle. The roughly constant composition of the clay minerals within the loess unit and most of the paleosol suggests that the clay minerals are of detrital origin and that pedogenic transformation has only occurred in the lower part of paleosol S1, which corresponds to the climatic optimum of Marine Isotope Stage (MIS) 5e. This provides a basis for addressing several important issues regarding the Carpathian Basin loess, including its provenance, glacial dust activity, and the interglacial climate. The smectite-rich characteristic of the glacial loess provides a diagnostic indicator for confirming local sources for the Carpathian Basin loess deposits, and that these sources made little contribution to the dust deposited in Greenland during the last glacial. The first application of illite crystallinity and the chlorite ratio to the Carpathian Basin loess-paleosol sequence suggests that they are more sensitive indicators than the clay mineral proxies previously used in European loess studies. The enhanced precipitation during MIS 5e indicated by the new proxies and the transformation of clay mineral potentially provide new insights into understanding the regional climatic response to future global warming.

Chronology and paleoclimatic implications of lacustrine sediments at Inexpressible Island, Ross Sea, Antarctica

Lacustrine sediments from ice-free areas of Antarctica record both paleoecological and paleoclimatic information. Four sediment profiles (IIL1, IIL3, IIL4 and IIL9) were collected at Inexpressible Island, Ross Sea, to establish a robust late-Holocene chronology using accelerator mass spectrometry (AMS) 14C dating and geochemical and lithological analyses. The IIL1 and IIL4 sediments were strongly affected by penguin guano, and their bottom (oldest) ages were dated to 1659 and 4820 yr BP, respectively, using a Mixed Marine SoHem mode. By contrast, the organic matter of IIL3 and IIL9 sediments were predominantly sourced from aquatic microbial mats with the bottom ages of these two cores at 3179 and 2945 yr BP, respectively, based on a SHCal13 mode. The mass accumulation rates of the four sediment profiles inferred from this chronology showed peaks during ~1400–800 yr BP, corresponding to greater mean grain size and higher sand fraction ratios in the IIL3 and IIL9 profiles, suggesting a strengthened hydrodynamic effect in this period. Our results indicate a relatively warm period occurred in the study area, in accordance with an ‘optimum’ warming in the Ross Sea region. From a regional view, this warm period was also consolidated with climatic records from the western Ross Sea, most likely corresponding to a well-recognized climate perturbation known as the Medieval Climate Anomaly (MCA) in many parts of the world.

Early-Mid Holocene climatic changes inferred from colors of eolian deposits in the Mu Us Desert

Climatic changes of the early-mid Holocene in the monsoon margin of northwest China have long been debated. The extensive eolian deposits of the desert/loess transition in central China provide important terrestrial archives of paleoclimate change, especially the evolution of the East Asian Summer Monsoon (EASM). As yet, however, due to the specific geographical location of the region, relatively few eolian sedimentary records have been reported since the Holocene. Here we investigated paleoclimatic implications of color parameters and grain size end-member (EM) components in three eolian sand-paleosol sequences. The chronology framework of the stratigraphic sections was established using 11 radiocarbon dates from organic material and 9 optically stimulated luminescence (OSL) ages from quartz. We reconstructed the early-mid Holocene climate changes in the southeastern margin of the Mu Us Desert by combining magnetic susceptibility (MS) and total organic carbon (TOC) analyses. Similar to the loess-paleosol sequence in central China, the lightness was significantly negatively correlated with TOC, MS and fine EM and all were controlled primarily by effective moisture. However, the redness and blueness were more influenced by the sand’s parent materials rather than from weak pedogenesis and therefore reflected eolian activity. This was supported by the significant positive correlation between redness and blueness and coarse EM that represented components transported by saltation and creep from near-source areas during dust outbreaks in cold and dry climate condition. Our multi-proxy analysis indicated that during the Younger Dryas and early Holocene, the Mu Us Desert was dominated by cold and dry climate conditions with frequent strong eolian activities. During 8.5–3.7 ka BP, the climate shifted to warm and humid that effectively fixed dunes and the paleosol was widely developed confirming the occurrence of the Holocene climate optimum. In addition, these alterations during the Holocene were primarily controlled by the EASM that was driven by summer insolation in the Northern Hemisphere, as well as changes in high latitude ice-sheets area and the ocean–atmosphere interaction patterns in the Atlantic and Pacific Oceans on different scales.

Paleoceanographic and paleoclimatic variability in the Western Mediterranean during the last 25 cal. kyr BP. New insights from contourite drifts

The Western Mediterranean Deep Water (WMDW), on its way out toward the Atlantic Ocean, has favored the formation of contourite drifts in the Alboran Sea (SW Mediterranean) since the opening of the Strait of Gibraltar. Resolving the nature of these deposits is crucial for reconstructing the WMDW variability at a millennial scale, deciphering its bottom current paleo-velocity, and establishing paleoclimatic implications over the last 25 cal. kyr BP. Two sediment cores retrieved from elongated separated and plastered contourite drifts formed along its path are investigated by means of multi-sedimentological data (terrigenous grain-size, sortable silt, terrigenous and carbonate sediment fluxes, bioturbation and ichnofabric changes), geochemical data (Zr/Al and Si/(Si + Al) ratios), chronostratigraphic data (δ18O, and 14C data) as well as statistical analyses (grain-size end-member modelling and spectral analysis). Integration of these data confirms the contouritic nature of Alboran drift deposits. The high-resolution paleocurrent records of the WMDW inferred from the sortable silt of contourite sequences led us to define two regimes in terms of WMDW flow energy. Regime 1 (weak to moderate velocity) defined by paleo-velocities of ⁓4 to 23 cm s−1 is dominant during the last 24 cal kyr BP. Regime 2 (strong velocity) is characterized by estimated paleo-velocities of about ⁓36 cm s−1 during Heinrich Stadial 2. The spectral analysis of bottom current proxies (sortable silt and Zr/Al ratio) matches four cyclic climatic signals (1900 yr, 2300 yr, 4000 ye and 6100 yr), corroborating the occurrence of millennial-scale cyclicity. These cycles are related to atmospheric climate variability, in turn linked to variations in solar activity. Our results, when combined with published data from a neighboring NW Mediterranean contourite drift, provide for a better regional understanding of the WMDW millennial-scale dynamics.

Lithofacies and petrography of Miocene Murree Formation, Peshawar basin, NW Pakistan: implications for provenance and paleoclimate

The Miocene Murree Formation is an enormous sedimentary deposit and is considered as foreland basin sediments of Himalayas, extending EastWest throughout the foothills of Himalayas. Lithofacies analysis was performed to establish the depositional environment, the following lithofacies were identified: clast-supported massive gravel (Gcm), sandstone with planar cross lamination (Sp), sandstone trough cross lamination (St), sandstone with horizontal lamination (Sh), sandstone with ripple cross lamination (Sr), sandstone with low-angle cross lamination (Sl) and mud and silt massive with roots bioturbation (Fr). These lithofacies depict shallow channel depth, deposition on the distal part of point bar, natural levees and flood plain of a meandering river. The modal composition data indicates that the Murree sandstone is arkosic to lithic wacke. The mineralogical and textural data suggests that sandstone is compositionally submature to immature and texturally immature to submature. The debris of rock fragments proposes diverse sources for Murree Formation. The ternary plots of detrital quartz type of the current study designate plutonic provenance. The high percentage of unstrained monocrystalline quartz (Qnu) relative to undulatory monocrystalline quartz (Qu) and polycrystalline quartz (Qp) proposes plutonic source area for Murree Formation. The paleoclimate plot discloses semi-humid–humid environment.

A synthesis of the Devonian wildfire record: Implications for paleogeography, fossil flora, and paleoclimate

The Devonian is known for the earliest dispersal of extensive wildfires, but the spatiotemporal diversification pattern and process have not been studied in detail. We synthesize a total of 65 global wildfire occurrences based on fossil charcoals and geochemical (biomarker) evidence from 10 paleogeographic areas across 10 time bins (Lochkovian–late Famennian). Stratigraphically, the highest number of wildfire occurrences is found in the Late Devonian, especially the late Famennian. Paleogeographically, Devonian wildfire evidence is highly concentrated in the eastern Euramerican region that consists of the Appalachian Basin, Avalonia, and Baltica along the Acadian landmass. These data collectively define a unique diversification pattern, here coined as the ‘Famennian Wildfire Explosion’ (FWE). This possible global wildfire spread, based on our diversity analysis of the plant fossil record in eastern Euramerica, is tightly corresponding to the paleogeographic distribution of lignophytes, but not to other common groups of Late Devonian woody plants (e.g., lycopodiopsids, spermatophytes, pteridophytes-monilophytes). Those lignophyte trees and shrubs include 34 species of Aneurophytales, Archaeopteridales, and Spermatophytes in the eastern Euramerican area that represent the primary forest component as the major fuel source of the FWE. By comparing our wildfire and fossil plant diversity with available paleoclimate data (e.g., global atmospheric oxygen level, paleohumidity), we suggest that the FWE in eastern Euramerica is unique due to a combination of occurrences (i) in a relatively low paleolatitudinal zone and (ii) in arid and warm temperate climate zones, but it shows (iii) a relatively weak correlation with the rapidly increasing atmospheric oxygen level.

Updating the significance and paleoclimate implications of magnetic susceptibility of Holocene loessic soils

Mass specific magnetic susceptibility variation with depth along soil profiles developed on loess parent material is one of the most frequently used physical parameter in local, regional and global correlations of loess deposits. It is also utilized as a paleo-precipitation proxy, defined either as absolute difference between susceptibilities of the enhanced B-horizon and parent loess C-horizon; or relative enhancement, using ratios of magnetic parameters. In the present study we compare and analyze the applicability of various approaches in establishment of the empirical relationships between pedogenic magnetic enhancement of Holocene soils from Bulgarian lower Danube area, published data from cCentral and Eastern Europe, and the Chinese loess, and climate parameters – mean annual precipitation (MAP) and mean annual temperature (MAT). Unlike previous studies, which compile data from soils, developed on various parent materials, using maximum magnetic susceptibility of the B-horizon and mean of the C-horizon, we strictly utilize soils, developed on loess material only and consider minimum susceptibility signal in the underlying loess unit. The data analysis shows that minimum magnetic susceptibility of the parent loess exhibits strong relation to climate’s parameters as well. We show that by using minimum magnetic susceptibility of the C-horizon to correct for the detrital input, pedogenic enhancement shows significant multiple correlation with both MAP and MAT. This relationship is different for Chinese and European sites but it is not retained for sites, located at low river terraces, Black sea coast and soils having increased coarse silt and sand content. Grouping the sites according to present day vegetation cover reveals the presence of uniform linear relationship between pedogenic susceptibility enhancement and climate parameters mostly for locations with steppe vegetation, while mixed steppe-forest and forest sites reveal more scattered and steeper relation to MAT and MAP variations.

Grain size variation in two lakes from margin of Asian Summer Monsoon and its paleoclimate implications

A wealth of research has demonstrated that polymodal grain/particle size distributions (GSD or PSD) in lake sediments can be mathematically decomposed to serve as a more precise tool for paleoenvironmental reconstructions. However, linking grain size subcomponents to specific environmental parameters is sometimes ambiguous, as grain size in lake sediments depends on local characteristics of individual lakes. In view of this, illustrative case studies with widespread practical significance are needed. Here, GSD datasets of two lake sediments from the Asian Summer Monsoon (ASM) marginal zone were decomposed and compared with nearby surficial lacustrine/eolian sediments with clear geological origins, to study the dominant sedimentary processes-grain size regimes of these two representative lakes. The decomposition and comparison clarify the geologic properties of certain grain size parameters and minimizes extraneous signals. Based on this information, we interpret certain size fractions as regional climate indicators associated with ASM intensity changes. We also consider centennial-timescale climate variability during the last half of the Holocene, and discuss the driving forces controlling centennial moisture variability in the studied area.

Late Pleistocene-Holocene paleoclimatic implications in the Mixteca Alta, Oaxaca, Mexico, by using rock magnetism and micromorphological techniques

Paleosols and sediments in the Yanhuitlán Basin were analyzed to reconstruct the environmental conditions and human-environmental interactions for generating a terminal Pleistocene-Holocene paleoclimate record in the south of Mexico. Magnetic concentration, mineralogy and grain size domains were compared with micromorphological studies to infer variations in the transportation of clastic minerals, oxide and redox conditions in the materials and anthropogenic activities. In general, conditions for the terminal Pleistocene (?–11,700 BP) were humid and transitional until the establishment of drier conditions at the end of the Pleistocene. For the early Holocene (11,700–8200 BP), the conditions were wetter and controlled by seasonal precipitation; in the middle Holocene (8200–4200 BP), the climate indicated drier conditions. Finally, in the late Holocene (4200–0 BP), the climate suggests more humid conditions but oscillating to dry stages accompanied by anthropogenic activities, manifested by an increase in sedimentation rates at the end of the period, charcoal oscillations and poor soil development.

An Upper Pleistocene macroflora indicates warm and dry climate during an interglacial in central Brazil

This study is the first report of the fossil macroflora of the Paleolagoa Seca, an Upper Quaternary fossil locality of lacustrine origin in central Brazil. Here we present an analysis of well-preserved fossil leaves collected from an argillite level dated at ca. 43,000 cal yr BP and discuss the paleoclimatic implications of this record. We reconstructed paleotemperature and paleoprecipitation using Leaf Margin Analysis (LMA) and Leaf Area Analysis (LAA), respectively, and used mineralogical (XRD and IR) and palynological analyses of the fossiliferous level to assess a complete picture of the past landscape. To test the ability of LMA and LAA models available for Southern Hemisphere to correctly predict Mean Annual Temperature (MAT) and Mean Annual Precipitation (MAP) for the Paleolagoa Seca, we applied several calibration models to the leaf dataset of a modern Cerrado forest and then compared predictions with modern climate data. Six LMA calibration models presented consistent MAT results and all four LAA calibration models provided satisfactory estimations of the modern MAP. The botanical identification of the fossil leaves and the pollen record indicated a mosaic of open savanna, dry forests and gallery forest around the Paleolagoa Seca. The reconstructed MAP for the Paleolagoa Seca ranged between 647 and 948 mm depending on the LAA equation, which is at least 500 mm lower than the current MAP. The reconstructed Mean Annual Temperature (MAT) ranged between 22.6 and 26.3 °C, indicating a higher-than-present MAT, which we relate to a combination of high summer insolation and low humidity. Comparison with other local fossil macrofloras, including from nearby localities, and with other paleoclimatic records suggests that the observed dry conditions at Paleolagoa Seca were related to interhemispheric climate forcing and to a weakening of the South American Summer Monsoon (SASM).

Provenance and paleoclimatic implications of loess deposits in Shandong Province, eastern China

AbstractThe loess deposits in Shandong Province in eastern China potentially provide valuable insights into past environmental changes. However, their precise provenance and paleoclimatic implications are unclear. We studied three loess sections located in the piedmont of the Central Shandong Mountains (PCSM) and in an offshore island in Bohai Gulf. Both the glacial loess and interglacial paleosol units are characterized by a coarse grain size, indicating a proximal sediment source. Using the “grain size–transport distance” model established for the Chinese Loess Plateau (CLP), the estimated source-sink distance is ~200–300 km for the PCSM loess and ~100–200 km for the coastal loess. This suggests that fluvial deposits of the Yellow River system in the North China Plain and sediments on the adjacent continental shelf are the major provenance for the Shandong loess. In contrast to the CLP, the Shandong loess does not show a consistent pattern of coarse grain size and low magnetic susceptibility values in glacial loess compared with interglacial paleosols, likely due to frequent changes in dust sources caused by diversions of the Yellow River and local hydroclimatic conditions. Nevertheless, the loess-paleosol alternations in the Shandong loess are a product of global glacial–interglacial cycles.

Late Pennsylvanian Calcareous Paleosols from Central New Mexico: Implications for Paleoclimate

We document calcareous paleosols from Upper Pennsylvanian (lower Virgilian) strata of the Burrego Member of the Atrasado Formation in the Cerros de Amado of Socorro County, New Mexico. The Burrego paleosols are an excellent example of a scarce, climate-sensitive lithology in the Pennsylvanian strata of New Mexico. These paleosols contain mostly stage II to III carbonate horizons, and their overall morphology suggests deposition and pedogenesis under subhumid, seasonally dry conditions. This conclusion is consistent with paleobotanical and other data that indicate such climate conditions were widespread on Late Pennsylvanian Pangea. The mean value of the oxygen-isotope ratios from Burrego paleosol carbonates compares well with the values from Virgilian paleosols of the San Juan, the eastern Midland and Chama basins of New Mexico-Texas, suggesting similar conditions of temperature and paleoprecipitation. Application of the diffusion-reaction model to the mean carbon-isotope composition of the carbonate suggests a paleo-pCO2 of approximately 400 ppmV, which is also consistent with estimates from correlative carbonate deposits that formed farther east in Late Pennsylvanian Pangea.

Sedimentology and Mineralogy of Surface Formations of the Mossendjo Area (Republic of Congo): Paleoenvironmental and Paleoclimatic Implications

Studies undertaken at several sites in the Congolese basin and in the Chaillu massif are helping to reinterpret the sedimentological formations known as cover formations, which are widely exposed in Central Africa. This article presents the results of granulometric, morphoscopic, mineralogical and chemical analyzes obtained at three sites in the Chaillu. Gronulometric analysis indicates that the sands at the three sites are rated medium to high. The cumulative curves are essentially sigmoidal with regular and spreading slopes. This facies indicates that the deposition took place due to a banal and moderate variation in the competence of the carrier current. The morphoscopy of the quartz grains shows that they are mainly angular and shiny. These data reflect a relatively close source and transport by water. The synthesis of lithological, granulometric, petrographic and geochemical analyzes allowed us to highlight three episodes of deposits in the Mossendjo area: the first is characterized by a channel-type fluvial system marked by deposits from the hospital borehole and from the station; the second, which is alluvial, corresponds to the clogging of the channel. These two alluvial phases are overcome by a third, fluvial, channel-type episode, the end of which is marked by the establishment of the yellow formation. The vertical and lateral organization at the outcrop of this yellow formation has the same characteristics as those described earlier and in the sub-region where it was attributed to the wind-generated cover formation. This study thus highlights the existence of a wet phase during which two fluvial systems of non-contemporary channel types developed which overlap.

Age and paleoclimatic implication of middle to upper Miocene plant‐bearing strata in the southern Kanazawa area, Ishikawa Prefecture, Central Japan, based on refined Neogene palynostratigraphy in the Hokuriku district

Abstract13–8 Ma (middle to late Miocene) is a key period for understanding how the unique vegetation was established in Japan. Palynostratigraphy is useful for estimating the ages of plant‐bearing strata deposited in shallow‐marine and non‐marine environments, but has low temporal resolution for this key period in Japan. We compiled Neogene and early Quaternary palynological records for the Hokuriku district of Central Japan to clarify palynostratigraphic events that may improve the temporal resolution. Our results showed that palynoassemblages changed considerably during 10–6.4 Ma in the Hokuriku district, following a relatively stable period during 13–10 Ma. We found that evergreen Quercus abundance increased at 11.5–10 Ma. We used these palynostratigraphic signatures, along with other biostratigraphic markers, to infer the ages of the Miocene plant‐bearing Saikawa and Koderayama Formations in the southern Kanazawa area of Ishikawa Prefecture in the Hokuriku district. The ages of the Saikawa and Koderayama Formations were inferred as ~13 and 10–6.4 Ma, respectively. The palynoflora of the Koderayama Formation shows floristic similarity to that of present south China, implying that the unique flora of Japan established after the age of the Koderayama Formation.

Post-glacial Permian debris flow deposits and their paleoclimatic implications (Mariana Pimentel paleovalley, southern Paraná Basin)

The end of the Late Paleozoic Ice Age was followed by a global warming climate. This climate transition is characterized by, beyond other aspects, a decrease in the intensity of physical weathering, characteristic of arid conditions, and an increase in the intensity of chemical weathering. In the southern Paraná Basin, the post-glacial onset and intense record of “Pedra-Areia” diamictite within the Mariana Pimentel paleovalley was likely controlled by warming climate conditions and mark a period of intense rainfall and slope instability. To test this hypothesis, we have performed facies and sequence stratigraphy analysis on cores located within the Mariana Pimentel paleovalley, and U–Pb-Hf investigations to acquire sediment provenance information. Diamictite deposits were produced by debris flow processes, which transported regolith from the valley wall to the bottom, eroding and incorporating mud and peat when reaching the bottom of the valley. The local source of sediment is explained by the sedimentological characteristics of the diamictite and zircon provenance studies. These deposits are preserved within the transgressive system tract and the abundant deposition was controlled by increasing temperature and humidity, and thus the increase in chemical weathering on the walls, forming the regolith. The development of more humid and warmer climatic conditions, contrasting with the cold and dry climate of the glacial period, was an important control over diamictite deposition.

Oligocene Desmanthus (Leguminosae) from the Qaidam Basin in northeastern Tibetan Plateau, China, and its implications for paleoclimate and paleoelevation

ABSTRACT Fossils are critical for understanding the environmental changes and uplift history of the Tibetan Plateau during the Cenozoic. As the largest inland basin located at the northeastern plateau, Qaidam Basin has been regarded as the key region to understand the climatic changes in the plateau during the Cenozoic. Herein, fossil legumes from the Oligocene Shangganchaigou Formation in northwestern Qaidam Basin have been reported and are assigned to Desmanthus cf. virgatus (L.) Willd. based on morphological comparison. Current materials represent the first megafossil record of this genus in the world. The living analogues of current fossils now live in regions with mean annual temperature values (MAT) ranging from 13.4 to 29.1°C and mean annual precipitation values (MAP) ranging from 36 to 2874 mm while the MAT and MAP of current northwestern Qaidam Basin is −1.03°C and 60.5 mm, respectively, and indicate that the Oligocene Qaidam was much warmer than today. We calculate that current fossils could grow no higher than 2492 m considering the climatic condition of the Oligocene Qaidam. The difference between estimated and modern elevation of the fossil site suggests that the elevation of the research area has increased by at least ≈1000 m since the Oligocene.

Geochemistry of Sediments from the Lopare Basin (Bosnia and Herzegovina): Implications for Paleoclimate, Paleosalinity, Paleoredox and Provenance

AbstractA combined inorganic and organic geochemical study was carried out on marls and mudstones collected from the Lower Miocene Lopare Basin, Bosnia and Herzegovina. A total of 46 samples collected from two boreholes, Pot 1 (depth of 193 m) and Pot 3 (depth of 344 m), showed that element abundances like boron (B), lithium (Li), strontium (Sr), uranium (U), chromium (Cr), nickel (Ni), magnesium (Mg), sodium (Na) and calcium (Ca) are much higher than average than in the upper continental crust (UCC). Chemical composition indicates at least two sources: (i) Mesozoic ophiolites occurring in the north of the investigated area, and (ii) dacito‐andesitic pyroclastics (Mesozoic to Cenozoic). Lopare Basin sedimentation was influenced by strong evaporation resulting in a partly hypersaline lake, which formed during a warm climatic period, probably during the Miocene Climatic Optimum. A brief episode of humid climate conditions resulted in the basin filling‐up and deposition of felsic sediments enriched in thorium (Th). Organic geochemistry shows that the majority of studied sediments contains predominantly immature to marginally mature algal organic matter (OM). The biomarker patterns are generally in agreement with the geological history of the Lopare Basin and inorganic and mineralogical data. Conversely, the molecular distribution of n‐alkanes as reliable climatic and δ‐MTTC as paleosalinity indicators do not support this conclusion.

Depositional and erosional signatures in sedimentary successions on the continental slope and rise off Prydz Bay, East Antarctica– implications for Pliocene paleoclimate

The Prydz Bay region of Antarctica is the immediate recipient of ice and sediments transported by the Lambert Glacier, the single largest outflow from the East Antarctic Ice Sheet. The continental slope and rise provide records covering multiple glacial cycles and containing paleoclimatic information. Marine geological and geophysical data collected from the continental shelf and adjacent slope of Prydz Bay, Antarctica, including seismic reflection data, bathymetry, and core records from ODP drilling sites, reveal the history of glacial sediment transport and deposition since the early Pliocene times. Seismic facies are interpreted in terms of episodes of slope progradation, contourite, turbidite, trough-mouth fan, and mass transport deposition. Two seismic units with estimated age of early to late Pliocene and late Pliocene to recent have been analyzed in detail for the area immediately offshore the Lambert Glacier and Prydz Bay and the adjacent Mac. Robertson margin. The upper slope is dominated by episodic mass transport deposits, many of which accumulated to form a trough mouth fan since Early Pliocene times. The trough mouth fan contrasts with the adjacent steep (4–6°) continental slope of the Mac. Robertson margin, where glacigenic sediments have been transported down slope as high-velocity turbidity currents via submarine channels. The distal region exhibits evidence for contrasting effects of high-energy, traction-dominated versus lower-energy, fallout-dominated suspension flows. The counter-clockwise Coriolis force modifies the erosion and deposition patterns of turbidity currents creating an asymmetric channel-levee architecture. Since the early Pliocene, turbidite sedimentation surpassed the amount of sediment reworked and transported by westward-flowing contour currents along the base of slope. On the continental rise, contourites and sediment waves were deposited in response to enhanced bottom-water formation, which is consistent with climatic cooling since late Pliocene times. This study, based on existing seismic reflection and ODP data, highlights the need for a future scientific ocean drilling proposal on the Prydz Bay continental slope and rise in order to more accurately determine the timing of the important events that have influenced the evolution of this margin.

Major element and REE compositions of Pliocene sediments in southwest Japan: Implications for paleoweathering and paleoclimate

The history of the East Asian monsoon and the relationship between the development of the monsoon climate, tectonics and global climate are complicated and controversial. Earlier studies have indicated that the East Asian monsoon fluctuated in the Asian interior during the Pliocene. Thus, the chemical weathering record in coastal regions of East Asia can be the key to elucidating its evolution as well as the Kuroshio Current variability. The present study clarifies the chemical weathering conditions in southwest Japan based on the concentrations of major elements and rare earth elements (REEs) in lacustrine muddy sediments. The chemical weathering was moderate between 4.4 and 3.8 Ma. Between 3.8 and 3.4 Ma, chemical weathering significantly intensified, as indicated by the high values of the chemical index of alteration that reached a maximum of 98, as well as the high concentrations of REEs and light REEs against heavy REEs and kaolinite-rich clay mineral compositions, despite the wide variation in source rock compositions and grain sizes. The degree of chemical weathering remained moderate during the early Pleistocene. The intense chemical weathering on land in southwest Japan from 3.8 to 3.4 Ma may have been regulated by alternating periods of warm and humid climate brought by the invasion of the Kuroshio Current and the intensification of the East Asian summer monsoon.