Magnetic Susceptibility Record Research Articles

Cyclostratigraphy of late Cambrian marine sedimentary records and reconstruction of Earth-Moon system parameters

The Cambrian period is an important era in geological history, marked by numerous major geological and biological events. To better understand these events, it is important to establish a high-precision chronostratigraphic framework. An astronomical time scale can be created by the identified Milankovitch cycles in well-preserved stratigraphic successions. Duibian B section in Jiangshan (Zhejiang Province, China) is the global stratotype section and point (GSSP) for the Jiangshanian Stage, and this section provides well-preserved records covering the upper Paibian to lower Jiangshanian stages. In this study, we use high-resolution magnetic susceptibility record to conduct cyclostratigraphic analysis of the Duibian B section. Our results indicate that the 2.44 m, 0.84–0.73 m, 0.20–0.19 m, and 0.12–0.09 m sedimentary cycles may represent long-eccentricity, short-eccentricity, obliquity, and precession cycles, respectively. Using the stable 405-kyr eccentricity cycles, we constructed an ∼5.96 Myr floating astronomical time scale to calibrate agnostoid trilobite zones. In addition, we reconstructed the precession rate k from geological records, and our result provides an insight into the Earth-Moon distance and length of day in the late Cambrian (Paibian–Jiangshanian, ∼494.2 Ma). It enriches our understanding of the Earth-Moon evolutionary history in deep time.

Cosmogenic 3He anomaly K1 vs. the early Campanian isotopic event (ECE) as recorded in pelagic limestones of the Umbria-Marche succession (Italy)

In this paper, we report on a biostratigraphic, magnetostratigraphic, and stable isotope (δ13C and 3He) analysis across three pelagic limestone sections of the Campanian Scaglia Rossa Formation exposed in the classic Bottaccione Gorge at Gubbio (Umbria region), near the village of Furlo, and near the town of Apiro (both in the Marche region), all located in the Umbria-Marche basin of the northeastern Apennines of central Italy. These sections record the coincidental occurrence of an extraterrestrial 3He (3HeET) anomaly known as K1 and a negative shift in the δ13C record known as the early Campanian event. Cyclostratigraphic spectral analysis of the Furlo section based on a high-resolution magnetic susceptibility record in these pelagic limestones revealed that the regular orbitally forced Milankovitch cycles are somewhat disturbed or blurred through the interval of the coincident 3HeET K1 anomaly and the early Campanian event isotopic anomaly, suggesting a causal effect resulting from the enhanced influx of extraterrestrial material (i.e., interplanetary dust particles and a myriad of small meteorite impacts). This would have altered the transparency of the atmosphere, causing a short-lived climate change event.

Long-term vegetation history of a relict birch forest (Betula pubescens subsp. celtiberica (Rothm. & Vasc.) Rivas Mart.) in the Toledo Mountains (central Iberia). Conservation implications

Understanding ecosystem resilience requires long data series provided by palaeoecological studies, the best tool for reconstructing vegetation dynamics. Here, we analyzed a continuous and well-dated record of pollen, non-pollen palynomorphs, macrocharcoal remains, loss-on-ignition and magnetic susceptibility from one of the most singular peatlands in the Toledo Mountains (central Spain), in order to delineate the anthropogenic and/or climate impact on the peatland and the ecosystem’s response. La Ventilla mire is an isolated site of birch woodland dominated by Betula pubescens subsp. celtiberica (Rothm. & Vasc.) Rivas Mart. This mire, acting as a refugium for this species, is located in Cabañeros National Park and is recognized as ‘Special Area of Conservation’ according to Habitats Directive of the Natura 2000 network. We describe major patterns and trends in the development of this palaeorefugium since the mid-Holocene (∼6145 cal BP) and provide historical context for some natural and/or human-induced dynamics. Around 1500 cal BP, the lotic depositional environment with slow moving backwaters developed into a minerotrophic mire. Until the Middle Ages, macroclimate and autogenic succession appear to have been the main drivers of both local and regional development of vegetation. Between 1500 and 500 cal BP, an abrupt decline in birch cover started, coincident with the Visigothic period. The pronounced peaks in the coprophilous fungi record ca. 1000 and 150 cal BP reflect extensive pastoral activities in the area. This study shows how palaeoecological knowledge helps to explain present patterns in the composition of a valuable protected site, which may be used in prioritizing conservation.

Astronomically paced climate evolution during the Late Paleozoic icehouse-to-greenhouse transition

Late Paleozoic deglaciation is Earth's first icehouse-to-greenhouse transition with extensive vegetation, but the response of tropical climate to this transition has not yet been fully addressed. Here, cyclostratigraphic analysis was conducted on the magnetic susceptibility (MS) record of a deep marine carbonate succession in South China to construct the astrochronology of late Cisuralian (Early Permian), and decipher the evolutionary response to the climate transition in the MS and δ13Ccarb time series. The constructed astronomical time scale indicates an age of 272.83 ± 0.2 Ma for the Cisuralian–Guadalupian boundary in South China. Synchronizing global records demonstrates a complicated linkage between low and high latitudes, involving secular changes in atmospheric pCO2, ice volume, tropical climate and carbon cycling. In the final stage of the Early Permian icehouse (~290–288.2 Ma), the delivery of moisture from low to high latitudes was reduced in comparison with that in the icehouse apex. A more humid climate facilitated the development of tropical coal forests and more storage of 12C on land. In a full greenhouse condition (~281–272 Ma), the tropical responses to a rise in atmospheric pCO2 involved continental drying and ocean stagnation. On a shorter time scale, the nodes of 1.36 Myr obliquity cycles triggered ice-sheet expansion and enhanced tropical precipitation during an icehouse condition. With the gradual transition to an arid greenhouse, the insolation-climate relationship began to change at ~285.1 Ma, and the obliquity nodes became associated instead with terrestrial aridity and marine anoxia. These results bring into a focus pattern of shifting dynamics involving Earth's astronomical parameters and climate change for icehouse and greenhouse worlds in the Late Paleozoic Era.

Tracing glacial-interglacial water mass changes in the Gulf of Corinth (IODP Expedition 381) using iron-sulphur geochemistry and magnetic susceptibility

The Gulf of Corinth is a rapidly rifting basin that has been alternately connected to/isolated from the Mediterranean due to Quaternary global sea levels fluctuations. A recently retrieved sediment record from the Gulf of Corinth (IODP Expedition 381) shows variations in magnetic susceptibility, with relatively higher and more variable values in isolated/glacial sediments and lower, more stable values in connected/interglacial sediments. Using geochemical methods, we find that not the primary input of magnetic minerals, but diagenetic processes generated the magnetic susceptibility pattern. Easily reducible sulphides (most likely greigite) increase in high magnetic susceptibility (isolated/glacial) sediments, whilst magnetite shows no systematic relationship to magnetic susceptibility. After discounting several possible causes for the formation and preservation of greigite (bottom water redox conditions, high sedimentation rates, reactive Fe and organic matter availability), a decrease in sulphate concentrations in the Gulf of Corinth during isolated/glacial periods is the most likely explanation, supporting parallel microfossil evidence for a freshening of the water column. This sulphate limitation appears to stall sedimentary pyrite formation at the stage of ferrimagnetic monosulphides like greigite. Greigite formation as an indicator of paleosalinity variations has been observed in other depositional settings (e.g., Chesapeake Bay, the Baltic Sea, the Miocene Paratethys and the Black Sea), supporting our interpretation. Specific to the Gulf of Corinth, linking a proxy for basin connectivity to a high resolution (at least 40, and up to 7 year temporal resolution) magnetic susceptibility record over 750,000 years offers an opportunity to investigate, in detail, the tectonic evolution of this rift basin and its link to global sea level fluctuations.

Extracting Hierarchical Dynamical Structure From a Multistable Geological System—The Himalayan Paleomonsoon

AbstractThe author presents an iterative approach to describing a data set, such as a paleoclimatic proxy or a model output, in terms of automata of successively higher order. The automata reflect dynamics acting on successively longer timescales and larger spatial scales. The method uses the computed probability density function from reconstructed state space portraits, over successive overlapping windows in time, of the record of magnetic susceptibility of loess and paleosols at Luochuan, central China. Areas of consistently high probability across several time windows represent areas of metastability, which are used as the predictive and successor states of a succession of Markov Chains that characterize the variability of the strength of the East Asian paleomonsoon at different time scales. Seven metastable states are thus identified, forming four Markov Chains, which show a marked increase in complexity of behavior of the paleomonsoon system throughout the Quaternary. A higher‐order automaton is suggested by the sequence of Markov Chains, suggesting differing cycles of dynamic behavior in the Early and Late Quaternary.

Loess-palaeosol sequences in diverse environments: Aeolian accumulation identification and magnetic susceptibility models

The thick loess-palaeosol sequences of the Chinese Loess Plateau (CLP) are valuable continental archives of paleoclimatic and paleoenvironmental changes since at least the mid-Miocene. The magnetic susceptibility record of loess sequences is frequently used for palaeoclimatic reconstruction. However, the two magnetoclimatological models for the magnetic enhancement of loess-palaeosol sequences—the wind vigour model and the pedogenic model—are still debated, and neither model alone is sufficient to explain the magnetic susceptibility stratigraphy of loess deposits in diverse environments. Loess can be substantially altered by its environment of deposition and the macroscopic characteristics of loess may differ substantially from the well-documented sequences of the CLP, which complicates loess identification and its palaeoclimatic interpretation. In the present study, we summarize the attributes of loess deposits in different environments and review possible approaches for identifying aeolian accumulation. Loess-palaeosol sequences in various climatic contexts, from arid to subhumid, are summarized and categorized and the relationship between the magnetic susceptibility and effective precipitation is evaluated. A model comprising three cases is proposed to interpret the magnetic susceptibility of loess-palaeosol sequences in a variety of different environments. In case A (e.g., the Xinjiang loess, NW China), where physical weathering dominates and pedogenesis is weak, there is no relationship between the magnetic susceptibility and pedogenesis, and here the wind vigour model is applicable. In case B (e.g., the CLP), where, under predominantly oxidizing conditions, the magnetic susceptibility increases with pedogenic intensity, and an oxidizing-pedogenic model is applicable. In case C (e.g., Alaskan and Siberian loess), there is a negative relationship between magnetic susceptibility and pedogenesis due to the dissolution of detrital iron oxides under reducing conditions, and a reduction-pedogenesis model is applicable. In Case C, pedogenesis (or chemical weathering/dissolution) acts to largely obliterate the detrital magnetic susceptibility signal. Hence, contrary to the original interpretation of the magnetic susceptibility of Alaskan and Siberian loess, the wind vigour model is not applicable. Two thresholds of mean annual precipitation between the three cases are proposed, which enable the paleoclimatic interpretation of loess magnetic susceptibility records in different environments. • Approaches of identifying aeolian accumulation are reviewed. • Loess-palaeosol in 5 diverse environments are summarized. • A new mode of magnetic susceptibility for diverse loess-palaeosol.

OSL-dating of the Pleistocene-Holocene climatic transition in loess from China, Europe and North America, and evidence for accretionary pedogenesis

Loess deposits intercalated by paleosols are detailed terrestrial archives of Quaternary climate variability providing information on the global dust cycle and landscape dynamics. Their paleoclimatic significance is often explored by quantifying their mineral magnetic properties due to their sensitivity to local/regional hydroclimate variability. Detailed chronological assessment of such regional proxy records around the climatic transitions allow a better understanding of how regional records react to major global climatic transitions such as the Pleistocene-Holocene climatic transition. Logs of high-resolution magnetic susceptibility and its frequency dependence were used as paleoclimatic proxies to define the environmental transition from the last glacial loess to the current interglacial soil as reflected in nine loess-paleosol sequences across the northern hemisphere, from the Chinese Loess Plateau, the southeastern European loess belt and the central Great Plains, USA. The onset of increase in magnetic susceptibility above typical loess values was used to assess the onset of, and developments during, the Pleistocene-Holocene climatic transition. High-resolution luminescence dating was applied on multiple grain-sizes (4–11 μm, 63–90 μm, 90–125 μm) of quartz extracts from the same sample in order to investigate the timing of Pleistocene-Holocene climatic transition in the investigated sites. The magnetic susceptibility signal shows a smooth and gradual increase for the majority of the sites from the typical low loess values to the interglacial ones. The initiation of this increase, interpreted as recording the initiation of the Pleistocene-Holocene climatic transition at each site, was dated to 14–17.5 ka or even earlier. Our chronological results highlight the need of combining paleoclimatic proxies (magnetic susceptibility) with absolute dating when investigating the Pleistocene-Holocene climatic transition as reflected by the evolution of this proxy in order to avoid chronostratigraphic misinterpretations in loess-paleosol records caused by simple pattern correlation. The detailed luminescence chronologies evidence the continuity of eolian mineral dust accumulation regardless of glacial or interglacial global climatic regimes. Coupled with magnetic susceptibility records this indicates that dust sedimentation and pedogenesis act simultaneously and result in a non-negligible accretional component in the formation of Holocene soils in loess regions across the Northern Hemisphere. The luminescence ages allowed the modeling of accumulation rates for the Holocene soil which are similar for European, Chinese and U.S.A. loess sites investigated and vary from 2 cm ka −1 to 9 cm ka −1 . While accretional pedogenesis has often been implicitly or explicitly assumed in paleoclimatic interpretation of loess-paleosol sequences, especially in the Chinese Loess Plateau, our luminescence data add direct evidence for ongoing sedimentation as interglacial soils formed. • High-resolution magnetic susceptibility record as paleoclimate proxy. • High-resolution luminescence dating applied on multiple quartz fractions. • Initiation of magnetic susceptibility enhancement dated prior to ~11.7 ka. • Continuous dust accumulation during Pleistocene-Holocene transition and in Holocene. • Accretional Holocene soils in European, Chinese Loess Plateau and US loess sites.

One and a Half Million Yearlong Aridity During the Middle Eocene in North‐West China Linked to a Global Cooling Episode

AbstractThe Eocene record of substantial aridification near Tibet was reported to mimic the global climate cooling trend, overwriting the previously proposed dominant role of the Tibetan Plateau uplift in the aridification (Li et al., 2018, https://doi.org/10.1038/s41467‐018‐05415‐x). Here we present new paleoclimate data from the red clay sequence deposited between 40 and 50 Ma in Altun Shan at the northeastern edge of the Tibetan Plateau. After building an age model using a compilation of magnetostratigraphy and cyclostratigraphy, we demonstrate that our record of magnetic susceptibility in the Altun Shan red clay exhibits variations linked to eccentricity cycles. Our age model allows us to estimate the age of eight short geomagnetic events, cryprochrons, in Altun Shan. Further we show that the aridification interval in Altun Shan coincides with (i) a cooling event recorded in the global oxygen isotope record, (ii) a sea surface temperature record on the east Tasmanian plateau, and (iii) an aridity record in the surrounding sedimentary basins of Central Asia. The middle Eocene aridity and cooling reached its maximum 45.5‐44 Ma.

The Telychian (early Silurian) oxygenation event in northern Europe: A geochemical and magnetic perspective

Widespread marine red beds in the European Telychian (lower-Silurian) are one expression of an interval of unusually widespread oxic conditions in low palaeolatitude Silurian seas. This work examines in detail the geochemical and magnetic susceptibility record of cores from southern Poland, which also express the Telychian oxygenation event in grey-mudstones. The geochemical data provide an evaluation of redox conditions, palaeoweathering, sediment provenance, primary palaeoproductivity and upwelling. Sediment provenance is evaluated against possible sources on the East European Craton. The data suggest that the magnetic susceptibility is carried by both paramagnetic Fe-silicates and Fe-oxides. Magnetic data are supplemented by magnetic hysteresis and isothermal remanent magnetisations, and mineralogical data on selected samples. In Poland the oxygenation event is clearly expressed in larger Fe2O3 and magnetic susceptibility, caused by enhanced palaeoweathering, changes in sediment provenance and a redox influence on the preservation of Fe-oxides. A much briefer oxygenation event is detected in the upper Rhuddanian. Palaeoproductivity fluxes indicate that the Telychian oxygenation event was caused by a reduction in primary oceanic palaeoproductivity, possibly linked to a reduction in nutrient delivery to the margin of the East European Craton, inferred to be caused by increased aridity. The increased aridity stimulated enhanced delivery of Fe-enriched aeolian dust from soils, generating a magnetic susceptibility and Fe2O3 expression of the Telychian oxygenation event.

Magnetic Susceptibility Record in Paleozoic Succession (Rhenohercynian Massif, Northern Europe) – Disentangling Sea Level, Local and Diagenetic Impact on the Magnetic Records

This study uses an integrated approach, including sedimentology, geochemistry and hysteresis magnetic measurements on a million year Givetian sequence in the southern margin of the Ardennes carbonate platform (France) to test the reliability of magnetic susceptibility () records as inter-regional correlation tools in remagnetized settings. Furthermore, we aim to better understand the N-S depositional variations and sea-level fluctuations in the Ardennes. Sedimentological analyses revealed a complex platform evolution displaying a variety of shallow- and off-reef paleoenvironmental rocks, which ultimately allowed us to improve the sedimentological model of this area and to constrain the main sea-level fluctuations within the southern margin of the Ardennes platform. Comparison of the  curve of this succession with previously published time-equivalent records in the western margin of the platform indicates a clear correlation between the two areas, despite the distance between the locales, their different sedimentology background and the remagnetization affecting the entire region. In contrast, the comparison of these  profiles from the Ardennes (SW Rhenohercynian Massif, Belgian and France) with coeval data from the Rheinisches Schiefergebirge (NE Rhenohercinian Massif, Germany) do not show obvious correlations. Therefore, it is inferred that syn-sedimentary autogenic processes (e.g., vicinity to landmasses, wave agitation), which operate at small spatial and temporal scales affected the  signal and could cause the lack of correlation between  profiles.

A robust geochronology of the Yangtze River Delta based on magnetostratigraphy and cyclostratigraphy of sediment core ZKA2

Studying the evolution of sea-level fluctuations, climate oscillations and tectonic movements in the Yangtze River Delta requires a reliable chronology. Here, we present the results of a comprehensive study of the magnetostratigraphy and cyclostratigraphy of a 295-m-long sediment core (ZKA2) recovered from Nantong City, Jiangsu Province, China. Anisotropy of magnetic susceptibility (AMS) studies reveal that the petrofabrics are mainly primary. Based on rock magnetic and thermal demagnetization analyses, the major magnetic minerals in the studied sediments are magnetite, hematite and greigite, but only magnetite and hematite carry the primary remanence. The magnetostratigraphy reveals seven reversed polarity intervals, nine normal polarity intervals, and one interval of mixed polarity. Variations in natural gamma-ray activity reflect variable continental weathering in the sediment source regions and are paced by Earth orbital cycles. Notably, a prominent 405-kyr long eccentricity cycle and ~100-kyr short eccentricity cycle are evident, which allow us to constrain the basal age of core ZKA2 to ~3.1 Ma. The magnetostratigraphic and cyclostratigraphic results together enable us to define the depths of key chronostratigraphic and magnetostratigraphic boundaries. They include the Late/Middle Pleistocene boundary at ~18-m depth, the Brunhes/Matuyama boundary at ~88-m depth, and the Matuyama/Gauss boundary at ~254-m depth. According the new chronology, we find that although clear long eccentricity (~405 kyr) and short eccentricity cycles (~100-kyr) cycles are evident in the magnetic susceptibility record, they are not well matched with cycles of natural gamma-ray activity. This suggests the source and post depositional process of the magnetic particles is complicated, and it should be cautious to choose magnetic properties for cyclostratigraphic analysis.

Confirmation of a Late Miocene Subchron C4n.2n‐1r From the Eastern Qaidam Basin in the NE Tibetan Plateau

AbstractRefining reversal ages and improving reversal patterns for the geomagnetic polarity timescale are a major task for the paleomagnetic community. The Late Miocene is a period during which the geomagnetic field experienced frequent perturbations and which dramatic environmental changes occurred. Thus, improved (sub)chron definition during this period will enable to provide additional age control points for better understanding age of paleoenvironmental changes. A prior study of the Late Miocene C4n.2n magnetic polarity zone at Ocean Drilling Program Site 1092 in the sub‐Antarctic South Atlantic Ocean has revealed the potential existence of a subchron (C4n.2n‐1r). However, this subchron has not been incorporated into the geomagnetic polarity timescale yet because its existence has not been confirmed. Moreover, the low sediment accumulation rate of 1.32 cm/kyr at Site 1092 hampers a confident estimation of the age and duration of this subchron. Here we present a high‐resolution paleomagnetic data set covering C4n.2n from the Huaitoutala section in the eastern Qaidam Basin, Northwest China, with an average sediment accumulation rate of ~22 cm/kyr. Nine reversed declination/inclination data points define a subchron near the top of C4n.2n, similar to age of reported C4n.2n‐1r at Ocean Drilling Program Site 1092. Cyclostratigraphy of the magnetic susceptibility record of the Huaitoutala section suggests that the age and duration of the C4n.2n‐1r are 7.7612–7.7554 Ma and 5.8 ± 2.1 kyr, respectively. Confirming the existence of C4n.2n‐1r from a northern hemisphere terrestrial site suggests that two geomagnetic reversals bounding this subchron have global imprints and that this subchron can potentially serve as marker for stratigraphic correlation.

Chronostratigraphy, depositional patterns and climatic imprints in Lake Acigöl (SW Anatolia) during the Quaternary

A 601 m long sedimentary sequence was drilled in Lake Acigol, located in the lakes region of SW Anatolia, near the Denizli travertine from which the oldest hominin of Turkey was unearthed. Among all dating methods applied to the sedimentary sequence, paleomagnetism, through the recognition of geomagnetic chrons, was the most successful and led to a quasi linear age model, with the 601 m long sedimentary record covering the last 2.3 Ma. An attempt to use the atmospherically deposited 10 Be as a dating method was not very successful but provides interesting clues on this new method. Long-term lake level changes are depicted through lithological variations, in particular the carbonates and evaporites abundance. This change could be influenced by both long term cooling during the last 2 Ma and tectonic activity, which may in particular be responsible for a maximum water depth at around 1.8 Ma. Despite active tectonic influence, the sedimentary facies description and the magnetic susceptibility record (cleaned from tephra intervals) show that climate fluctuations (i.e., glacial-interglacial alternations) are likely recorded in the sedimentary succession, with warm periods marked by enhanced carbonate precipitation and cold and dry periods characterized by more detrital input linked to reduced vegetation cover and consequently more erosion in the catchment area. Preliminary pollen data, used to interpret magnetic susceptibility fluctuations, show that an average dry and open landscape prevailed around Acigol lake during the whole record.

Detection of Strong Precession Cycles from the Late Pliocene Sedimentary Records of Northeastern Tibetan Plateau

AbstractRecent studies demonstrate that aridification is sensitive to eccentricity forcing based on the northeastern Tibetan Plateau Cenozoic fluvio‐lacustrine stratigraphic records. However, it is unknown whether this is a bias associated with the fact that higher frequency periods normally have larger age model uncertainties, which tend to decrease spectral power of higher frequency orbital cycles (precession and obliquity) and enlarge lower frequency ones (eccentricity). Here we detect strong and well‐resolved (~23 and ~19 kyr) precession cycles in the magnetic susceptibility record of late Pliocene fluvio‐lacustrine sediments from the Qaidam Basin, northwestern China. We interpret the magnetic susceptibility as a proxy for the degree of chemical weathering in this region, based on the positive correlation between low‐frequency magnetic susceptibility and frequency‐dependent magnetic susceptibility. The different responses of magnetic susceptibility and a halite content proxy to orbital forcing suggest that aridification is more sensitive to eccentricity forcing than precipitation, but precipitation is more sensitive to precession forcing. This study indicates that different climatic aspects have different sensitivity to orbital forcing. Furthermore, a comparison of the magnetic susceptibility variations in the western Qaidam Basin and global ice volume proxy records suggests ice volume control of Qaidam Basin precipitation and chemical weathering at million‐year timescales.

Magnetostratigraphic dating of a drill core from the Northeast Plain of China: Implications for the evolution of Songnenpaleo-lake

Lacustrine sediments from the Northeast Plain of China are an ideal archive for recording the climatic history and variability of the East Asian monsoon during the Quaternary in mid-latitude East Asia. However, the lack of a high-resolution stratigraphy and high-precision geochronology of these sediments has limited our understanding of the mechanisms of Quaternary climatic and environmental changes in the region. In this study, we present a high-resolution magnetic susceptibility stratigraphy and precise paleomagnetic and optically stimulated luminescence (OSL) chronologies for core Qiananlingzi (QAL) from the Northeast Plain. Paleomagnetic data were obtained using alternating-field (AF) demagnetization with a peak AF of 80 mT and increments of 2.5−10 mT. In addition, OSL dating was conducted on coarse-grained quartz (90−150 µm) using the single aliquot regenerative dose (SAR) protocol. Correlation of the recognized polarity intervals of the QAL core to the geomagnetic polarity timescale was achieved by combining the magnetostratigraphic and OSL geochronologic data. The results indicate that the sedimentary sequence spans the interval from the Olduvai normal subchron to the end of the Brunhes normal chron. According to the lithology and the magnetic susceptibility record, the core can be divided into four intervals, from bottom to top: the Qian’an Formation (fluvial yellow-green, brown-red and grey-brown silty sand, interbedded with brown-black silty clay, with gravel layers in the lower part); the Lingzi Formation and Lindian Formation (lacustrine grey-green clay interbedded with grey-white silty sand, with fossil bivalves); and a loess-like soil (predominantly brown-yellow clayey silt, alternating with fluviolacustrine grey-white, brown and black clay). The magnetic susceptibilities (MS) of the sediments of the lower fluvial Qian’an Formation and upper loess-like soil strata are generally higher, indicating the neoformation of strongly magnetic minerals under predominantly oxidizing conditions. By contrast, lower MS values occur in the lacustrine sediments of the Lingzi Formation and Lindian Formation, which indicate a reducing environment. Overall, the MS record of the QAL core exhibits clear orbital-scale variations, with higher MS values in coarse-grained silt layers, and lower values in fine-grained clay layers. After the application of a 300 mT DC field, the isothermal remanence (IRM) is only 70%, and a hysteresis loop remained unclosed at 500 mT. These characteristics indicate the substantial presence of high-coercivity magnetic minerals in the intervals with low MS values. Thermomagnetic measurements ( χ - T ) curves show an abrupt decrease in the heating curve at 580°C, indicating that magnetite is the dominant magnetic mineral, and a further decrease above 580°C indicates the presence of hematite. After the application of an applied DC field of 300 mT, the IRM reached 90%, the hysteresis loop was closed, and the heating limb of the χ - T curve did not decrease significantly after 580°C, indicating that low-coercivity magnetic minerals contributed substantially to the magnetic properties within the intervals of higher MS. The lacustrine sediments of the core were dated to ~1180‒450 ka based on paleomagnetic and QSL dating, and interpolation of the age-depth relationship suggests that Songnen paleo-lake existed for ~730 ka. The grain-size record of the loess in the northeastern monsoon region shows no evidence of drought events at 450 ka, and records of MS and FeD/FeT from the deposits of the loess Plateau indicate a trend of increasing summer monsoon precipitation at this time. Therefore, the disappearance of the paleo-lake may be related to the multiple episodes of subsidence of the Yishu fault, which caused a diversion of the discharge of the Songhua River from the Songnen paleo-lake to the Sanjiang Plain. The high-resolution MS record and the precise chronology obtained in this study indicate that the lacustrine sedimentary sequence of QAL core can potentially resolve orbital-scale paleoclimate changes during the middle Pleistocene in mid-latitude East Asia. The Mid-Pleistocene Transition (MPT) is one of the most important climatic events in Quaternary paleoclimatology, and it is necessary to understand the response of different climatic systems to the MPT. Detailed environmental magnetic, sedimentological and geochemical studies of lacustrine sedimentary strata in the Northeast Plain in China should be carried out to explore the paleoclimatic record of the area, including the regional climatic response to the MPT.

Luminescence dating and palaeomagnetic age constraint of a last glacial loess-palaeosol sequence from Istria, Croatia

Loess and loess-like deposits with intercalated palaeosols are widely distributed in Croatia, particularly in the Pannonian basin in the east and along the Adriatic Coast in the west, which have provided invaluable evidences of Quaternary climate change. The timing, provenance and spatial distribution of such loess deposits have long been a major research interest. In the current study, a ∼8-m-thick loess-palaeosol sequence located near the town of Savudrija (Savudrija Section), on the northern-most cape of the Istrian Peninsula on the Adriatic Coast, is investigated. Multiple approaches of luminescence dating and palaeomagnetic age constraint are conducted to understand the timing of the regional aeolian activities and its implications for climate change. Seven samples were collected from the loess layers of the Savudrija section for comprehensive quartz optically stimulated luminescence (OSL) and feldspar post-IR infrared stimulation luminescence (IRSL) dating. The palaeomagnetic investigation was conducted on 82 oriented samples collected from the upper 6.7 m of the section. The quartz OSL ages of the upper four samples and the fading corrected pIRIR225 ages of the lower three samples were used to reconstruct the age framework of the section. The results demonstrate that the Savudrija loess-palaeosol sequence were formed between ∼70 ka and ∼9 ka, correlated to the time span from the last glacial to early Holocene. The variation of the magnetic susceptibility of the Savudrija section is strictly following the pattern that the palaeosol horizons generate high susceptibility values while the loess horizons show low susceptibility values. The palaeomagnetic age constraint is obtained by correlating the magnetic susceptibility record of the Savudrija section with other records, which gives the age range between 65 ka and 20 ka for the loess-palaeosol sequence (excluding the lowermost red soil). It broadly agrees with the luminescence chronology but conflicts in details, demonstrating that the correlation between the different magnetic susceptibility records is questionable. Furthermore, the magnetic susceptibility record suggests that the age of ∼70 ka of the red soil at the bottom of the section might be still ambiguous and needs further study.

Greigite formed in early Pleistocene lacustrine sediments from the Heqing Basin, southwest China, and its paleoenvironmental implications

The ferrimagnetic iron sulfide greigite (Fe3S4) occurs widely in sulfidic lacustrine and marine sedimentary environments. Knowledge of its formation and persistence is important for both magnetostratigraphic and paleoenvironmental studies. Although the formation mechanism of greigite has been widely demonstrated, the sedimentary environments associated with greigite formation in lakes, especially on relatively long timescales, are poorly understood. A long and continuous sequence of Pleistocene lacustrine sediments was recovered in the Heqing drill core from southwestern China, which provides an outstanding record of continental climate and environment. Integrated magnetic, geochemical, and paleoclimatic analysis of the lacustrine sequence provides an opportunity to improve our understanding of the environmental controls on greigite formation. Rock magnetic and scanning electron microscope analyses of selected samples from the core reveal that greigite is present in the lower part of the core (part 1, 665.8–372.5 m). Greigite occurs throughout this interval and is the dominant magnetic mineral, irrespective of the climatic state. The magnetic susceptibility (χ) record, which is mainly controlled by the concentration of greigite, matches well with variations in the Indian Summer Monsoon (ISM) index and total organic carbon (TOC) content, with no significant time lag. This indicates that the greigite formed during early diagenesis. In greigite-bearing intervals, with the χ increase, Bc value increase and tends to be stable at about 50 mT. Therefore, we suggest that χ values could estimate the variation of greigite concentration approximately in the Heqing core. Greigite favored more abundant in terrigenous-rich and organic-poor layers associated with weak summer monsoon which are characterized by high χ values, high Fe content, high Rb/Sr ratio and low TOC content. Greigite enhancement can be explained by variations in terrigenous inputs. Our studies demonstrate that, not only the greigite formation, but also its concentration changes could be useful for studying climatic and environmental variability in sulfidic environments.

Late Pleistocene dust dynamics and pedogenesis in Southern Eurasia – Detailed insights from the loess profile Toshan (NE Iran)

In southern Eurasia recurrent phases of aridization, dust source extension and enhanced Aeolian sedimentation alternated with moister intervals, promoting reduced deflation areas and dust accumulation in the context of late Pleistocene climate changes. Weathering and soil forming intensity in this greater region are, hence, mainly governed by fluctuations in the balance between dust supply and moisture availability.Among the hitherto known sections, the Toshan loess-soil sequence (LPS) represents a key site due to the quality of the record and the multitude of available data giving detailed insights into the timing and magnitude of dust accumulation and soil formation of the region. To elucidate these dynamics for much of the past 130.000 years bulk mineralogical and geochemical data are presented supplemented by a high resolution magnetic susceptibility record and by the results of a detailed micromorphological study of loess at Toshan.The last interglacial Luvisol/Phaeozem-like (∼MIS 5e) and the early glacial interstadial steppic palaeosols (∼MIS 5 c and a) are characterized by gradually increasing grain-size and decreasing degrees in decomposition of micaceous and mafic minerals. Pronounced feldspar weathering is detected in the last interglacial and modern soils only, which formed under reduced or absent dust deposition on penultimate and last glacial loess, respectively (postsedimentary). The overall pedosedimentary conditions correspond to large scale trends of increasing drought, dust accumulation and wind strength in southern Eurasia in relation to decreasing moisture availability towards the early Pleniglacial (∼MIS 4), causing soil formation under ongoing dust deposition (synsedimentary). Similar intervals of synsedimentary soil formation are recorded during the interglacial/interstadial-stadial transitions of the early glacial and during pleniglacial (∼MIS 4 to 2) interstadials. The latter are marked by gradual increases in magnetic susceptibility, colour and decreasing texture. Conversely, silicate weathering could not be detected, suggesting that grain-size fluctuations are a primary feature. Thus, windy and arid pleniglacial conditions in southern Eurasia were interrupted by intermittent phases of synsedimentary soil formation, in response to short-lived and relatively moist interstadials. Although the interrelation of these incipient soils, throughout southern Eurasia is afflicted with considerable restrictions, the oscillatory pattern of the Toshan LPS bears great similarity with millennial-scale oscillations recorded in limnic archives of western Asia.

Integrated stratigraphy of the Smirra Core (Umbria-Marche Basin, Apennines, Italy): A new early Paleogene reference section and implications for the geologic time scale

Pelagic sections of the Umbria-Marche Basin, in the Northern Apennines (Italy), have provided key geological archives for studying critical intervals of early Paleogene time. In addition to classical sections, the Smirra Coring project provides a new record of relatively undisturbed sediments (~120m from 4 overlapping holes) of the upper Scaglia Formation (Paleocene – middle Eocene). Here we present a new high-resolution integrated magneto-bio-stratigraphy of the ~93-m composite section drilled in Smirra Holes 1 and 2. The correlation of the magnetostratigraphy to published geomagnetic polarity timescales (GPTSs; CK95, GPTS2004, GPTS2012), as constrained by calcareous nannofossil biostratigraphy, reveals that the cores range from Chron C26r to C21n (Thanetian – Lutetian; ~60 to ~46Ma). Sedimentation rates range from ~0.6 to ~1cm/kyr and are comparable with those from coeval sections in the Umbria-Marche Basin. They point to significant discrepancies between existing time scales, which mainly involve the duration of Chron C23 and subchrons within C23n and C24n. Application of the average spectral misfit method on the magnetic susceptibility record reveals a strong signature of orbital forcing and allows an independent estimate of the sedimentation rates. This analysis offers additional insights into solving time scale issues, which mainly concern the duration of Chron C23n. Our results imply a significantly longer duration for C23n.2n, which would accommodate the presence of an extra third 405-kyr eccentricity related cycle in C23n. The Smirra record thus provides new constraints on the early Paleogene time scale, a key record for further cyclostratigraphic and astrochronological research, and a reference framework for paleo-climatic and -oceanographic studies.