Normal Chron Research Articles

New volcanological, 40Ar/39Ar dating and paleomagnetic record from Trindade Island and stratigraphic implications

Unrevealing the stratigraphy of volcanic systems is fundamental to understanding their eruptive history and requires a multiproxy approach for the accurate correlation and interpretation of deposits. We present new volcanological, 40Ar/39Ar ages and paleomagnetic data from the volcanic rocks of Trindade Island, located at ∼1.260 km from the Brazilian coast in the South Atlantic Ocean. The reconstruction of the volcanic history of Trindade Island is important because it is the youngest volcanic terrain in Brazil and part of a submarine chain that represents the most recent plume-induced alkaline manifestation beneath the South American plate. Our results suggest Trindade Island underwent two main phases of volcanism. The first phase (3.9–1.5 Ma) formed the Trindade Complex and Desejado Formation, with eruptive styles ranging from phreatomagmatic/Surtseyan to Vulcanian and of dominant phonolitic composition. The second phase (1.0–0.06 Ma) formed the nephelinitic monogenetic centers Morro Vermelho, Valado and Paredão Volcano Formations through dominant Hawaiian and Strombolian styles. The new ages imply a revised stratigraphy for the youngest units of Trindade Island, with partial overlap between them. The revised chronology integrated to the paleomagnetic directional data evidence that Trindade Complex formed during Gauss normal chron (D = 355.4°; I = −49.6°), Valado and Paredão Volcano during Brunhes normal chron (D = 14°; I = −42.3° and D = 9.2°; I = −35.2°, respectively), while Morro Vermelho records the late Matuyama-early Brunhes chron (D = 36.5°; I = −19.8°), with site-level mean paleodirections of normal and transitional polarity within the reverse Matuyama interval.

High precision multi-collector 40Ar/39Ar dating of moldavites (Central European tektites) reconciles geochrological and paleomagnetic data

Moldavites (Central European tektites) are genetically related to the meteorite impact event that produced the 24-km diameter Ries crater (Germany) during the Langhian, and representing one of the youngest large impact structures on Earth. Despite the numerous geochronological studies over the last decades and the potential implications for stratigraphic, paleontological and paleoclimatic studies, the age of the Ries impact is still debated. In this study, I investigate in detail moldavite samples by multicollector 40Ar/39Ar laser dating in order to address the age of the Ries impact. Data were obtained relative to the key Fish Canyon sanidine (FCs) and Alder Creek sanidine (ACs) reference materials, over a period of nearly two years, in four irradiations of different duration. Results, completed through the step-heating and the total fusion techniques, demonstrate an excellent intrasample and intersample reproducibility of moldavites and prove that analytical performances of moldavites in terms of uncertainties on the 40Ar*/39ArK ratios are in line with those achievable by the most widely used FCs and ACs reference minerals. Results from total fusion analyses yield a mean RACsMoldavite = 12.4952 ± 0.0038 (±2σ) and a mean RFCsMoldavite = 0.52106 ± 0.00014 (±2σ). Data also allow to define a direct mean RFCsACs = 0.041703 ± 0.000032 (±2σ) and an indirect (using moldavites as intermediary), more precise, mean RFCsACs = 0.041700 ± 0.000019 (±2σ). Using the internally consistent astronomically-calibrated ages for the ACs (1.1848 ± 0.0012 Ma) and the FCs (28.201 ± 0.046 Ma) reference minerals from the literature, the R-values yield indistinguishable ages for moldavites of 14.7495 ± 0.0045 (± 0.016 Ma, including all known source of errors) and 14.7486 ± 0.0039 Ma (± 0.025 Ma), respectively. The most recent astronomically calibrated age for FCs (28.176 ± 0.023 Ma) yields a slightly younger, but more precise, age of 14.7355 ± 0.0039 Ma (± 0.013 Ma). Results place definitively the age of the Ries impact in the reverse polarity chron C5ADr of the ATNTS2022, and suggest that the Ries impact preceded the switch from reversed to normal chron by at least 127 ± 15 ka.

U-Pb zircon age constraints on the vertebrate assemblages and palaeomagnetic record of the Guadalupian Abrahamskraal Formation, Karoo Basin, South Africa

The rich fossil record of the Permo-Triassic Beaufort Group of the main Karoo Basin serves as a reference sequence for tetrapod biochronology and provides a unique window into the evolution of terrestrial ecosystems between the Guadalupian and Middle Triassic. Absolute temporal constraints on the Beaufort Group have improved in the last decade with the application of U-Pb zircon geochronology but precise ages have not yet been reported for its basal Abrahamskraal Formation. Consequently, the age of the Eodicynodon Assemblage Zone and the lower boundary of the Tapinocephalus Assemblage Zone have remained less clear than younger Permian biozones. An improvement in temporal constraints also has implications for the correlation of palaeomagnetic logs reported from the Abrahamskraal Formation. In this paper we present new CA-ID-TIMS U-Pb geochronology from tuff beds that provide the first high-resolution chronostratigraphy for the upper two thirds of Abrahamskraal Formation. These ages constrain the base of the Tapinocephalus Assemblage Zone to be older than 264.4 Ma, and closely constrain the boundary between its two subzones to ca. 262 Ma. Combined with published ages from the overlying Teekloof Formation, our data show the Tapinocephalus Assemblage Zone is latest Wordian to late Capitanian in age. These complement previously published CA-ID-TIMS U-Pb ages for younger Beaufort rocks and suggest that the normal polarity interval observed in the middle Abrahamskraal Formation represents a normal (probably third) chron within the mixed-polarity Illawarra Superchron.

Magnetostratigraphic dating of the danangou and dongyaozitou mammalian faunas in the Nihewan Basin, North China

The fluvio-lacustrine sequences in the Nihewan Basin of North China are rich sources of mammalian faunas and Paleolithic sites, thus providing unique insights into our understanding of land mammal biochronology and early human settlements in East Asia. Among the Nihewan Fauna (sensu lato), the Danangou (DNG) and Dongyaozitou (DZ) faunas are two of the important Pleistocene and Pliocene mammalian faunas in the Nihewan Basin. Except for a biostratigraphy, precise age control on the DNG and DZ faunas remains unavailable. Here we report high-resolution magnetostratigraphy results that stringently constrain their ages. The results show that the DNG sequence recorded the Brunhes normal chron, the Matuyama reverse chron and the late Gauss normal chron, yielding the fossil-rich layers of DNG fauna with an age of ca. 1.95 Ma to 1.78 Ma during the Olduvai normal subchron. The DZ sequence was located at the late Gauss normal chron, yielding an age of ca. 3.04–2.58 Ma before the termination of the Kaena reverse subchron.

Vegetation and climate history during the Mammoth subchron from high-resolution pollen records in Yinchuan Basin, northwestern China

The Mammoth subchron was a significant geomagnetic reversed polarity event within the Gauss normal chron interval; however, the availability of high-resolution climate change records during this period is limited. We reconstructed the vegetation and climate history in the period using high-resolution pollen records from core PL02 (depths from 705.7 to 678.9 m) from the Yinchuan Basin, northwestern China. The results showed that the vegetation in the Yinchuan Basin was dominantly desert steppe during this period and that a gradual increase in arid conditions was superimposed by warm and humid and cold and dry conditions, but the climate was slightly wetter than that during the Quaternary. From 3.337 to 3.313 Ma, the study area climate was relatively warm and humid, and an especially warm and humid climate event from ~3.322 to 3.313 Ma was reflected by the highest pollen concentrations of trees, shrubs and herbs and a low percentage of herbs. From 3.313 to 3.287 Ma, the percentage of herbs and xerophytic shrubs (such as Chenopodiaceae, Artemisia and Nitraria) increased gradually, reflecting a relatively cold and dry climate. From 3.287 to 3.241 Ma, the herb taxa percentage decreased, and the climate became wetter relative to the previous stage. However, after ~3.241 Ma, the xerophytic plant abundance increased significantly, and the proportion of arboreal plants reached a minimum, indicating that the climate in the Yinchuan Basin became much drier than before. Moreover, the results suggested that the vegetation and climate change in the Yinchuan Basin might be related to global change.

Quaternary stratigraphic architecture and sedimentaryevolution from borehole GB014 in the westernXiong’an New Area

To scientifically utilize underground space and to explore the regional structural characteristics and processes of basin evolution of the North China Plain, we combine paleomagnetic and sedimentary analyses of sediments from borehole GB014, which extends 200 m deep, in the western Xiong’an New Area. Magnetostratigraphy and regional sedimentary characteristics were determined to establish a chronological framework. Sedimentary facies and sedimentary systems were reconstructed by considering the lithology, geophysical logs gamma ray ( GR ), and grain size, sediment color ( L *, a * and b *) and magnetic susceptibility measurements. To determine the remanence carriers and magnetic mineralogy of the sediments, rock magnetic measurements were performed on 8 representative samples from various depths. A total of 145 specimens were subjected to progressive thermal demagnetization up to a maximum temperature of 690 ° C, with intervals of 25−50 ° C below 585 ° C and 10−25 ° C above 585 ° C, using a Magnetic Measurements Thermal Demagnetizer (TD48) with a residual magnetic field less than 10 nT. Paleomagnetic measurements were made using a 2G Enterprises Model 760-R cryogenic magnetometer installed in a magnetically shielded space ( GR logs obtained at 20-cm intervals were used to analyze the sedimentary facies. For measurements of sediment color, 526 powder samples were air-dried and then disaggregated, passed through a 200-mesh sieve and measured using a Konica-Minolta SPAD503 spectrometer. The 526 powder samples were packed into 8-cm3 plastic boxes and used to obtain measurements of magnetic susceptibility ( χ ) using a Bartington Instruments MS2B sensor. Electronic scales with a resolution of 0.001 g were used to weigh the samples to enable the mass-specific susceptibility to be calculated. For grain-size measurements, 189 powder samples were pretreated with 10% H2O2 to remove organic matter and 10% HCl to remove carbonates. After standing for 24 h, the residues were dispersed with 10% (NaPO3)6 and ultrasonicated for 10 min. The grain size measurements were made using a Mastersizer-2000 laser analyzer (relative error The main findings are as follows: (1) Magnetite is the main carrier of the characteristic remanent magnetization in these sedimentary sequences, and the secondary carrier is hematite. (2) The borehole measurements recorded the Brunhes and Gauss normal chrons and the Matuyama reversed chron. The depths of the Matuyama/Brunhes and Gauss/Matuyama boundaries are 33.8 m and 135 m, respectively. (3) According to the chronological framework and sedimentary facies, five sedimentary units have been identified, from bottom to top: Unit V, with a depth of 200−146.6 m and sedimentary rate of 4.9 cm/ka, whose age is 3.90−2.81 Ma, is dominated by alluvial fan facies with coarse grain sediments. Unit IV, with a depth of 146.6−108.0 m and sedimentation rate of 2.76 cm/ka, whose age is 2.81−1.88 Ma, is dominated by flood plain facies with fine grain sediments. Unit III, with a depth of 108.0−57.6 m and sedimentation rate of 5.86 cm/ka, whose age is 1.88−1.02 Ma, is dominated by braided channel facies with coarse particle sediments. Unit II, with a depth of 57.6−35.8 m and sedimentation rate of 9.48 cm/ka, whose age is 1.02−0.79 Ma, is dominated by flood plain facies with fine grain sediments. Unit I, with a depth of 0−35.8 m and sedimentation rate of 4.53 cm/ka, whose age is 0.79−0 Ma, is dominated by flood plains interbedded with crevasse fan facies. At borehole GB014, evidence of two tectonic movements that occurred at 3.90−2.81 and 1.88−0.79 Ma have been preserved since the late Pliocene, and sediment provenance probably changed during 1.88−1.02 Ma. The piedmont area of Taihang Mountain hosts two widely deposited layers of coarse-grained sediments resulting from these two tectonic movements, and the Middle and Late Pleistocene sand layers are mainly related to the marine transgression in Bohai Bay and the enhancement of the East Asian monsoon system.

Magnetostratigraphic and archaeological records at the Early Pleistocene site complex of Madigou (Nihewan Basin): Implications for human adaptations in North China

The Nihewan Basin in North China contains the densest concentration of early Pleistocene Paleolithic sites outside Africa. This paper introduces a new archaeological site complex at Madigou (MDG) that was systematically excavated from 2011 to 2014 in the northeastern part of the Nihewan Basin. The site contains fossils and well-preserved stone artefacts in fluvio-lacustrine sediments. Our magnetostratigraphic results situate the MDG sedimentary sequence in the early Brunhes normal chron and the late Matuyama reverse chron, including the Jaramillo normal subchron. The MDG artifact layers are positioned within the pre-Jaramillo Matuyama chron, with an estimated age of ca. 1.2 Ma, close to the onset of Mid-Pleistocene climate transition. The MDG core and flake technology includes bipolar flaking of siliceous dolomite cobbles, and freehand flaking of chert and brecciated chert block fragments. Mammalian fauna and pollen compositions indicate that the MDG hominins lived in an open habitat varying from lightly-wooded grassland to an ecosystem dominated by sparse steppe near the shore of the Nihewan paleolake. Our combined results in the fields of archaeology, paleontology, palynology and magnetochronology suggest that innovations in technological behavior may correlate with adaptations to high environmental variability during the start of Mid-Pleistocene climate transition.

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.

Relative Paleointensity and Inclination Anomaly Over the Last 8 Myr Obtained From the Integrated Ocean Drilling Program Site U1335 Sediments in the Eastern Equatorial Pacific

AbstractFor understanding the fundamentals of the geodynamo such as the relation between paleointensity and polarity length and time‐averaged field (TAF) structure, continuous records of relative paleointensity (RPI) and inclination anomaly (ΔI) are desired; however, available records older than ~3 Ma are still very limited in time and space. We conducted a paleomagnetic study of the Integrated Ocean Drilling Program Site U1335 sediments in the eastern equatorial Pacific to obtain continuous RPI and ΔI records since ~8 Ma. Slow deposition, ~8.4 m/Myr or less, limits the resolution of the records but did allow for determination of long‐term variations. Rock‐magnetic measurements showed that biogenic magnetite dominates the magnetic mineral assemblages, and the proportion of biogenic to terrigenous magnetic minerals increases prior to ~4 Ma. The average paleointensity between ~4 and 8 Ma is approximately 30% lower than that from 0 to ~4 Ma. The apparent reduction of RPI at ~4 Ma reaches approximately ~50%, but ~20% of this is estimated to be artificial, induced by the increase in the proportion of biogenic magnetite. No relation between paleointensity and polarity length is recognized for the last ~8 Myr. The magnitude of ΔI is slightly larger during reversed polarity chrons (4.43° ± 1.47°) than normal polarity chrons (−0.69° ± 2.98°) over the last ~5 Myr, which agrees with the available TAF models of this time span. Prior to ~6 Ma, the sign of ΔI during the normal chrons might have switched to positive, and ΔI during reversed chrons might have been slightly larger than that after ~5 Ma.

Magnetic stratigraphy of the Danube loess: A composite Titel-Stari Slankamen loess section over the last one million years in Vojvodina, Serbia

In Europe, the most complete loess-paleosol sequences over the past million years are preserved in the Serbian part of the Danube River drainage basin. The similarity in stratigraphy and climatic cycles between the Serbian and the Chinese loess sequences suggests that the loess deposits in these two regions could play an important role in the study of intercontinental climatic correlations and linkage. However, previous magnetostratigraphic studies of the Serbian loess, mainly conducted using the alternating field (AF) demagnetization approach, show significant differences with the Chinese loess, especially the stratigraphic positioning of the Matuyama-Brunhes boundary (MBB). Here, we conduct a detailed magnetostratigraphic investigation of a composite Titel-Stari Slankamen loess section in the Vojvodina (northern Serbia), using thermal and hybrid demagnetization methods, aiming to establish new chronological constraints for the Danube Basin loess. Based on the analyses of the mineral magnetic properties, anisotropy of magnetic susceptibility, progressive thermal and hybrid demagnetization, the MBB was determined within S8, broadly consistent with the MBB position seen in the Chinese loess. Present evidence supports the hypothesis that the overall normal polarity in the upper part of L9, with a thickness of 2.1 m, was possibly caused by a combination of the remagnetization of remanence-carrying coarse-grained magnetite during the Brunhes normal chron and bioturbation during the forming of the overlying paleosol S8. Thus, our magnetostratigraphic results provide solid chronological evidence for the coherence of pedostratigraphy and climatostratigraphy for the loess deposits in the Danube Basin and China. The synchronous occurrence of the strongest developed paleosol S5 (corresponding to MISs 15–13) and the least weathered thick loess unit L9 (corresponding to MISs 24–22) in the two regions confirms that extreme climatic events during these two intervals are possibly common features of the climate in the Northern Hemisphere at those times.

Magnetostratigraphy of two deep boreholes in southwestern Bohai Bay: Tectonic implications and constraints on the ages of volcanic layers

Abstract The sediments of Bohai Bay Basin have recorded the processes of basin infilling and structural evolution, reflecting the destruction of the North China Craton during the late Mesozoic and the early Cenozoic. However, the absence of a reliable chronostratigraphic framework for the sedimentary sequences in the basin has precluded a comprehensive understanding of these processes. This is especially the case for southwestern Bohai Bay, the evolution of which has been affected by two Quaternary volcanoes, Dashan and Xiaoshan. In this study, we combine paleomagnetic and sedimentary analyses of the sediments from two boreholes (CK3 and G4) from southwestern Bohai Bay Basin in order to provide new insights into the sedimentary history and regional tectonic processes since the Pliocene. The main findings are as follows. (1) Magnetite and hematite are the main carriers of the characteristic remanent magnetization in these sedimentary sequences, with hematite the main component. (2) The two drill cores record the Brunhes, Olduvai and Gauss normal chrons, and the Matuyama and Gilbert reverse chrons. (3) Subsidence-related differences in the depths of the Matuyama/Brunhes (M/B) and Gauss/Matuyama (G/M) boundaries in boreholes across Bohai Bay, distributed within different structural units, reflect the fact that northern Bohai Bay is the regional subsidence center and that the development of the WNW-orientated structures of the basin has intensified during the Quaternary. (4) The trend of changes in the elevation of three marine layers is similar to that of the M/B and G/M boundaries across Bohai Bay. Based on magnetostratigraphic constraints of the boreholes, the ages of the second and third marine layers are assigned to Marine Oxygen Isotope (MIS) 3 and MIS 5, respectively. The WNW-orientated structures and ‘super interglacials’ resulted in the formation of transgressions in the Huanghua depression. (5) In borehole CK3, the ages of four volcanic layers at the depth intervals of 13.14–16.18 m, 33.37–48.02 m, 145.8–154.05 m and 222.16–233.80 m, are 10–18 ka BP, 80–90 ka BP, 2.2 Ma and 3.1 Ma, respectively. In borehole G4, the age of the volcanic layer at the depth of 46.4–55.8 m is 0.33–0.55 Ma. Comparative analysis of subsidence-related differences between the NEE and NE-orientated uplifts and depressions in western and southern Bohai Bay indicates that structural evolution in the vertical plane during the Quaternary was mainly controlled by the subduction of the Pacific Plate.

Plio-Pleistocene magnetostratigraphy of northern Bohai Bay and its implications for tectonic events since ca. 2.0 Ma

The sediments of Bohai Bay Basin in North China have recorded the processes of basin filling and structural evolution, which may have resulted from the destruction of the North China Craton during the late Mesozoic and early Cenozoic. However, the absence of a reliable chronostratigraphic framework for the sedimentary sequences in the basin has prevented a comprehensive understanding of these processes. In this study, we combine paleomagnetic and sedimentary analyses of the sediments from two new boreholes (NY05 and TZ02) from northern Bohai Bay to provide new insights into the sedimentary history and regional tectonic processes since the Pliocene. The main findings are as follows: (1) Magnetite and hematite are the main carriers of the characteristic remanent magnetization. (2) The boreholes record the Brunhes and Gauss normal chrons, and the Matuyama reversed chron. (3) Subsidence-related differences in the depths of the Matuyama/Brunhes (M/B) and Gauss/Matuyama (G/M) boundaries, sediment accumulation rates, and the sedimentary environments of the different tectonic units, enable us to identify that tectonic movements started in the Olduvai normal subchron and the development of the WNW-orientated tectonic features were intensified. (4) In the Huanghua depression, comparative analysis of subsidence-related differences between western and northern Bohai Bay indicates that the subsidence of the northern Bohai Bay may have been superimposed on the WNW-orientated tectonic activity and faulting associated with the collision between the Indian and the Eurasian Plates, in the context of localized subsidence.

Magnetostratigraphy of Plio–Pleistocene fossiliferous cave sediments in the Bubing Basin, southern China

Abstract Our understanding of the chronological sequence of Pleistocene land mammal faunas (including hominids) preserved in caves and fissures in the karstic terrain of subtropical southern China has been greatly impeded by the discontinuous nature of the strata yielding the fossils. A contributory issue is the lack of suitable elements for numerical dating, especially for the Early Pleistocene cave sediments. Here we present new magnetostratigraphic dating results for five cave sedimentary sequences in the Bubing Basin, Guangxi Zhuang Autonomous Region, which contain the typical Pleistocene Gigantopithecus fauna and Ailuropoda–Stegodon fauna of southern China. The five karstic caves are situated at elevations ranging from 252 m to 191 m above sea level. The integrated dating results reveal that the five cave sedimentary sequences span an age range from the late Gauss normal Chron to the early Brunhes normal Chron. The faunas are assigned to >2.6 Ma (Mohui–houshan Cave), 1.95–1.78 Ma (Mohui Cave), 0.99–0.78 Ma (Baolai Cave) and ∼0.7 Ma (Upper Wuyun and Ganxian Caves). Furthermore, by combining our new magnetostratigraphy work with previously published magnetostratigraphic, U–series and electron spin resonance dating results, a chronological sequence of the Plio–Pleistocene mammalian faunas from cave sites in southern China has been established. The chronological sequence contributes to an improved understanding of the evolutionary processes of Plio–Pleistocene land mammals, as well as of early humans in subtropical southern China.

Paleo-megalake termination in the Quaternary: Paleomagnetic and water-level evidence from south Bohai Sea, China

Asian marginal seas play an important role in moderating material and energy flux linkages between Asia and the Northwest Pacific, and thus have profound climatic and environmental effects. In this study, by combining paleomagnetic study with sediment grain-size analysis on the Lz908 borehole sedimentary sequence from the southern Bohai Sea, new insights into regional geomorphological process since the late early Pleistocene are obtained. The main results are as follows. (1) Paleomagnetic findings suggest that the sequence recorded the Brunhes normal chron and the late Matuyama reverse chron, including the Jaramillo normal subchron. (2) The sedimentary processes in the study area since 1327ka show a three-stage pattern, with depositional rates of 4.3, 17 and 107cm/ka during 1327–260ka (later part of the early and middle Pleistocene), 260–10ka (late middle and late Pleistocene), and the Holocene, respectively. (3) The sedimentary basin was a part of the Bohai Paleolakes (BHPL) prior to 260ka, whose water levels were consistently higher than 3m above the present-day level. After 260ka, seawater entered the Bohai basin, and relative sea level cyclically fluctuated with global sea-level changes. We therefore infer that the Miaodao Islands, which were the natural barrier of the BHPL blocking seawater entry, had partially subsided before 260ka, only allowing seawater to enter the basin during a global sea-level maximum. The BHPL terminated around 260ka, and the “barrier” subsided completely around ~130ka, causing the Bohai basin to become an inner shelf sea.

A complete skull of Crocuta crocuta ultima indicates a late Middle Pleistocene age for the Khok Sung (northeastern Thailand) vertebrate fauna

The locality of Khok Sung, Nakhon Ratchasima province, which corresponds to an ancient river terrace, has yielded the richest Pleistocene fauna of Thailand with a thousand of fossil vertebrate remains. This fauna has been previously dated between the Early Pleistocene and the Middle Pleistocene. We describe here a nearly complete hyaenid skull and associated mandible identified as belonging to spotted hyaena Crocuta crocuta ultima. The spotted hyaena C. c. ultima, which extended its maximum latitudinal distribution from northern China to Peninsular Thailand, is a characteristic component of Southeast Asian Middle Pleistocene faunas. These new biochronological data, coupled with a magnetostratigraphic study of the lithological section, provide a powerful multiproxy approach for the dating of Khok Sung fauna, pinpointing rather a late Middle Pleistocene age than the Early Pleistocene. In addition, the occurrence in the Khok Sung section of a short reverse excursion of the magnetic field within the Brunhes normal Chron can be tentatively identified as corresponding either to the “Iceland Basin” (188 ka) or to the “Pringle Falls” (213 ka) excursion, suggesting an even more precise dating of the locality. According to the presence of a spotted hyaena, the Khok Sung fauna may illustrate an open canopy habitat in a floodplain with abundant and diversified herbivores, close to the main river channel. This interpretation contrasts with the paleobotanical data which indicate wet and dry tropical forests and may instead describe the surrounding upland vegetation.

Magnetostratigraphy and luminescence dating on a sedimentary sequence from northern East China Sea: Constraints on evolutionary history of eastern marginal seas of China since the Early Pleistocene

Owing to the large and increasing population density in low-lying coastal regions, even small changes in sea level can have substantial societal and economic impacts. Alternations of terrestrial and marine sediments deposited in coastal areas or continental shelves are important and effective indicators of sea-level changes, and thus, have been widely studied in the marginal seas of China over the past 30 years. However, sea-level change results from not only eustatic factors but also tectonic activity. The Zhe-Min (or Zhejiang–Fujian) Uplift (ZMU) was such an important factor in geomorphology, and formed a barrier preventing entry of sea water into the northern marginal seas of China, but its Quaternary history is poorly known.In this study, a new borehole (ECS-DZ1) was drilled in the Zhoushan Islands, northern East China Sea to obtain information on the evolution of the ZMU during the Quaternary. Information from paleomagnetic and luminescence dating was combined with data on sedimentary changes. The main results are: (1) constrained by luminescence ages, the upper sedimentary units were extrapolated to have been deposited since ∼0.2 Ma; (2) paleomagnetic results suggest that the ECS-DZ1 borehole sequence spans from the pre-Olduvai Matuyama reverse chron to the Brunhes normal chron, approximately constraining the age of the basal sedimentary unit to ∼2.0 Ma; (3) a significant hiatus or erosion between two major sedimentary units possibly occurred between the late Early Pleistocene and Middle Pleistocene.As the Zhoushan Islands are within the ZMU and considering previous transgression studies around this region, it is inferred that the ZMU subsided at ∼2.0 Ma, allowing sea water to invade northward in the Yellow Sea basin. The ZMU might have been uplifted again no later than 1.0 Ma, causing a sedimentary hiatus or lacustrine development. After ∼0.2 Ma, the ZMU subsided completely, allowing large transgressions to develop across the northern marginal seas of China in the context of global sea-level changes.

Magnetostratigraphic dating of the Xiashagou Fauna and implication for sequencing the mammalian faunas in the Nihewan Basin, North China

The Nihewan Basin sedimentary sequences in northern China are rich in mammalian fossil and Paleolithic sites, thus providing insights into our understanding of Quaternary land mammal biochronology and early human settlements in East Asia. Here we present high-resolution magnetostratigraphic results that place stringent age controls on the Xiashagou (XSG) Fauna (that is, the well-known Nihewan Fauna sensu stricto) in the Nihewan Basin, northern China. Results show that the XSG sequence recorded the Brunhes normal chron, the Matuyama reverse chron and the late Gauss normal chron. The XSG Fauna resides in the Matuyama reverse chron (between the pre-Reunion Matuyama chron and the post-Olduvai Matuyama chron), yielding an estimated age of ca. 2.2–1.7 Ma. The Pliocene–Pleistocene boundary (Gauss/Matuyama boundary) is located in the lower part of the XSG section. The combination of our study and previously published magnetostratigraphic data suggest that the mammalian fossil sites in the eastern Nihewan Basin can be placed between the Gauss–Matuyama geomagnetic reversal and the Matuyama–Brunhes geomagnetic reversal (2.58–0.78 Ma), leading to a time range of ca. 2.6–0.8 Ma for the Nihewan mammalian faunas.

Magnetostratigraphic dating of the Hougou Paleolithic site in the Nihewan Basin, North China

The fluvio-lacustrine sedimentary sequences in the Nihewan Basin, northern China, are important for studying Quaternary land mammal evolution and Paleolithic settlements in the high-latitude temperate East Asia. Here we report new magnetostratigraphic results that constrain age of the Hougou Paleolithic site in this basin. Magnetite and hematite were identified as carriers of the characteristic remanent magnetizations, with the former being dominant. Magnetic polarity stratigraphy shows that the Hougou sequence recorded the very late Matuyama reverse chron and the Brunhes normal chron. The age of the Hougou Paleolithic site was estimated to be 395 ka based on an averaged rate of sediment accumulation. The combination of our magnetostratigraphy and previously published chronological data for early Paleolithic or human sites in the high-latitude northern China may document a persistent colonization of the hostile high-latitude areas of the eastern Old World during the middle- early Pleistocene.

Evidence for the earliest Pleistocene hominid activity in the Nihewan Basin of northern China

The Nihewan Basin in North China contains the densest concentration of early Pleistocene Paleolithic sites outside Africa. This paper introduces a new archaeological site complex at Madigou (MDG) that was systematically excavated from 2011 to 2014 in the northeastern part of the Nihewan Basin. The site contains fossils and well-preserved stone artefacts in fluvio-lacustrine sediments. Our magnetostratigraphic results situate the MDG sedimentary sequence in the early Brunhes normal chron and the late Matuyama reverse chron, including the Jaramillo normal subchron. The MDG artifact layers are positioned within the pre-Jaramillo Matuyama chron, with an estimated age of ca. 1.2 Ma, close to the onset of Mid-Pleistocene climate transition. The MDG core and flake technology includes bipolar flaking of siliceous dolomite cobbles, and freehand flaking of chert and brecciated chert block fragments. Mammalian fauna and pollen compositions indicate that the MDG hominins lived in an open habitat varying from lightly-wooded grassland to an ecosystem dominated by sparse steppe near the shore of the Nihewan paleolake. Our combined results in the fields of archaeology, paleontology, palynology and magnetochronology suggest that innovations in technological behavior may correlate with adaptations to high environmental variability during the start of Mid-Pleistocene climate transition.

Stratigraphy of the Fort Selkirk Volcanogenic Complex in central Yukon and its paleoclimatic significance: Ar/Ar and paleomagnetic data

Brunhes, Matuyama, Kaena, and Mammoth age basaltic lava flows (Tertiary–Quaternary Selkirk Volcanics) were sampled in west-central Yukon. The mean characteristic remanent magnetization (ChRM) direction of the flows sampled in this and previous studies has a declination of 348.7° and an inclination of 70.8° (n = 42, k = 99.6, α95 = 2.2°) (all on lower hemisphere). The time range represented in this study (ca. 3.25 to ca. 0.004 Ma) is great enough to have confidently averaged secular variation. Sediment associated with the basalt has a mean declination of 7.6° and inclination of 78.8° (n = 5, k = 5.6, α95 = 35.7°). A new 40Ar–39Ar date on the reversely magnetized basal basalts at Ne Ch’e Ddhäwa places the eruption in the Mammoth subchron of the Gauss Normal Chron. The newly dated basal basalt at Ne Ch’e Ddhäwa precedes the initial continental glaciation in Yukon and is older than the Fort Selkirk vent (Lower Mushroom), which was previously thought to be the oldest eruption at Fort Selkirk Volcanic Complex (FSVC). This basal flow at Mushroom is dated at 1.82 ± 0.03 Ma and the uppermost flow is reproducibly dated at 1.36 ± 0.04 Ma. Till on the flanks of a subglacial volcanic mound called Ne Ch’e Ddhäwa (informal) is older than previously thought; its reverse magnetization indicates an Early Pleistocene age rather than the Reid glaciation, which falls during the Brunhes Normal Chron. The paleomagnetism of Tertiary–Quaternary Selkirk Volcanics outcrops outside the FSVC was studied for the first time. The ChRM direction of basalt at the northern edge of the northern Cordillera volcanic province agrees with FSVC directions, suggesting that this flow reflects the same period of volcanism. This suggests that an Eocene K–Ar date, previously thought to be unreliable, may well be correct.