The loess record in southern Tajikistan and correlation with Chinese loess

In the present study, the Chashmanigar loess–soil sequence in southern Tajikistan is studied; this loess section has a paleomagnetic basal age of about 1.77 Myr. Magnetic susceptibility, color reflectance and grain size were systematically measured for closely spaced samples from the section. Paleosols consistently have a finer grain size distribution, higher magnetic susceptibility, redder color reflectance and lower dust sedimentation rate than loess horizons, suggesting a colder, drier and dustier environment during glacial periods than in interglacial periods. The grain size record was tuned to variations in obliquity and precession of the Earth’s orbit. The resulting magnetic susceptibility, grain size and color reflectance time series all show well-expressed astronomical periodicities during the Pleistocene. The mid-Pleistocene climate transition, characterized by a shift of dominant climatic periods from 41 kyr to 100 kyr at about 1.0–0.8 Myr, is clearly documented in these proxy records. Comparison of the Chashmanigar loess record with the Lingtai loess section in China and the ODP site 677 δ¹⁸O record shows that during the entire Pleistocene, the climate cycles recorded by the Central Asian loess can be well correlated to the Chinese loess and deep-sea oxygen isotope records. It is suggested that alternations of loess and soil horizons both in Central Asia and China could be basically forced by global ice volume variations, although different wind systems have controlled the Pleistocene loess transport and sedimentation in the two areas.     

Palaeomagnetic studies within the Ballantrae Ophiolite; southwest Scotland: magnetotectonic and regional tectonic implications

The Early Arenig Slockenray Formation within the Ballantrae Ophiolite, southwest Scotland, displays a multivectorial magnetisation structure. Two components (S and M) are identified delineated by differing blocking temperature/ coercivity spectra. Component S is removed around 200°C/10 mT, and is regarded to be of recent viscous origin. Component M forms the characteristic formation magnetisation and resides in both magnetite and haematite. Extensive sampling of all exposed lithologies reveals an (in situ) non-Fisherian distribution of the characteristic magnetisation defining an envelope from SE moderate positive to SW shallow negative directions. A negative infra-formation conglomerate test identifies this component as a pervasive overprint.

A second conglomerate test performed in the overlying Benan Conglomerate of Llandeilo age, reveals dispersely directed magnetisation with a stability range equivalent to that of component M. This field test therefore defines a maximum remagnetisation window of 30 million years for the characteristic remanence. “Hard” viscous magnetisations are identified both in the Benan Conglomerate and at some sites within the Slockenray Formation.

Structurally corrected site mean results from the Slockenray Formation define a non-Fisherian distribution and form a small circle partial arc centred on a vertical axis (NW moderate positive to SW moderate positive directions). A combined palaeomagnetic fold and fault test suggests that acquisition of component M pre-dates both folding and faulting.

The resulting palaeolatitude of remanence acquisition (28.8°S) implies a tectonic position close to the southern Laurentian margin for the Ballantrae ophiolite in Arenig times.     

Palaeomagnetism of the loess/palaeosol sequence in Viatovo (NE Bulgaria) in the Danube basin

The results of a palaeomagnetic investigation of a 27 m thick loess/palaeosol sequence in Viatovo (NE Bulgaria) are presented in this paper. The sequence consists of topsoil S₀, seven loess horizons (L₁–L₇) and six interbedded palaeosols (S₁–S₆) overlying a red clay (terra rossa) complex. Magnetic viscosity experiments, IRM acquisition, AMS analysis and NRM stepwise alternating and thermal demagnetisation experiments of pilot samples were implemented for precise determination of the characteristic remanence and construction of a reliable magnetostratigraphical scheme. Analysis of IRM acquisition curves using the expectation – maximization algorithm of Heslop et al. [Heslop, D., Dekkers, M., Kruiver, P., van Oorschot, H., 2002. Analysis of isothermal remanent magnetization acquisition curves using the expectation – maximization algorithm. Geophys. J. Int., 148, 58–64] suggests that the best fitting is obtained by three coercivity components. Component 1 corresponds to SD maghemite/magnetite, while component 2 is probably related to the presence of oxidised detrital magnetites. The third component shows varying coercivities depending on the degree of pedogenic alteration of the samples and probably reflects the presence of detrital magnetite grains oxidised at different degree.

The relevance of the Viatovo section as a key representative sequence for the loess cover in the Danube basin is confirmed by the presence of geomagnetic polarity changes in the lower part of the sequence. The youngest one recorded in the seventh loess unit L₇ can be identified as corresponding to the Matuyama/Brunhes palaeomagnetic polarity transition. Two normal magnetozones were found in the red clay complex, probably corresponding to the Jaramillo and Olduvai subchronozones of the Matuyama chron.     

A metamorphic history from micron-scale Pb/Pb chronometry of Archean monazite

Ion microprobe measurements of Pb isotope ratios in monazites have been obtained, in situ, from thin sections using the Cambridge ISOLAB 120. Molecular interferences are sufficiently resolved at an RP of 6500 to allow ²⁰⁷Pb/²⁰⁶Pb dating of monazite with precisions as low as 4–5 Ma (2σ). The results presented here provide important information on the chronological history of the Late Archean metamorphism of the Wind River Range, Wyoming (USA).

Matrix monazites and monazite inclusions in garnets from a metapelite from the northern Wind River Range have been analysed by SIMS. In a previous study peak metamorphic conditions (T = 800°C; P = 8 ± 1 kb^*) were estimated using inclusion assemblages in garnets from this same sample. Isolated monazite inclusions in garnet yield ²⁰⁷Pb/²⁰⁶Pb age estimates of 2781 ± 6 to 2809 ± 10 Ma. Those along fractures yield lower ages (2603–2687 Ma) which are similar to TIMS and SIMS ages of matrix monazites. A single large (500 μm) monazite grain locally preserves growth zoning, but has a recrystallised core and a resorbed (recrystallised?) rim. Age estimates for these three regions are 2788 ± 9 Ma, 2663 ± 4 and 2523 ± 6 Ma, respectively. Thus the inclusion assemblages of Sharp and Essene^* may record peak metamorphic conditions at ca. 2.8 Ga, and indicate a phase of metamorphism that predates by over 100 Ma the emplacement of the Bridger Batholith, the major lithologic component of the northern Wind River Range.

The analysed monazite grains appear to preserve ca. 300 Ma history, even within a single grain. Monazite inclusions in garnet that are fully armoured may provide estimates for the time of garnet growth, even in high grade terranes where most chronometers are reset. The age pattern preserved by the large monazite grain cannot be simply related to diffusion controlled closure. Instead, a chronology is preserved which can be related to the petrographic setting of indicidual grains through in situ analysis.     

Loess in the Czech Republic: Magnetic properties and paleoclimate

Summary We have studied 454 oriented samples from seven loess outcrops in the Czech Republic for comparison and correlation of the magnetic properties with those of the loess profiles in China and Central Asia. Three sections at Sedlec (Prague), Zeměchy and Dolní Věstonice cover the time span of the last glacial-interglacial cycle. Loess from the middle Pleistocene period including pedocomplexes V and VI was studied at Sedlešovice (Znojmo) and Karlštejn. Loess of uncertain — possibly lower to middle Pleistocene age — was sampled at Sedlec near Mikulov. At Červeny Kopec (Red Hill, Brno) we investigated the oldest loess near the Matuyama/Brunhes (M/B) boundary. The characteristic remanence (ChRM) determined after magnetic clearning is of normal polarity throughout all sections except at Červeny Kopec. There, two polarity changes from reversed to normal were found within two sections initially thought to represent two successive stratigraphic intervals. However, the marked similarities between lithological, susceptibility, declination and inclination profiles lead us to suggest that the two polarity changes are in fact one and the same. The two sections are therefore laterally equivalent and both have recorded the M/B field reversal. The susceptibility variations were used to mutually correlate the Czech sections and to construct a composite profile across the present day loess outcrops in the Czech Republic. They also serve as a paleoclimate proxy which can be compared and correlated with the paleoclimatic records observed in the Chinese and Central Asian loess. The origin of the low field susceptibility variations was studied by measuring the frequency dependence of susceptibility which revealed that the enhancement within the pedocomplexes is controlled by the amount of fine-grained ferromagnetic minerals present.     

Interception losses of rainfall from Cashew trees

The rainfall interception losses from Cashew trees were quantified, based on the records of 105 selected storms within the range 25.0 mm, occurring in a humid tropical region at Kottamparamba, India.

The storage capacity of the Cashew trees was worked out as 0.8 mm and the throughfall coefficient as 0.391. The trees under observation were 15–20 years of age with a leaf area index of 1.0–1.25.

About 31% of the storm rainfall for storms 25.0 mm was intercepted by the Cashew trees and lost to the atmosphere.

The measured interception losses from the trees were compared with the estimated interception losses using the analytical model of Gash (1979). The predicted interception losses from the Cashew trees were within ± 10% for storms with total rainfall 10.0 mm and within ± 22% for storms with a rainfall of 10.1–25.0 mm.     

Magnetic indicator of global paleoclimate cycles in Siberian loess–paleosol sequences

The loess–paleosol sequences of China, Siberia, Alaska and many other regions, along with lake sediments and glaciers, provide the only accurate paleoclimatic terrestrial records for intervals of thousands to hundreds of thousand years. The frequency dependence (FD) of magnetic susceptibility (MS) in such sequences has become the leading parameter for analyzing climatic change and Milankovitch (astronomical) periodicity in Siberian sequences; it is always higher in soil horizons than in loess. The enhanced FD parameter in soils is associated with ferromagnetic minerals, mostly magnetite, produced during pedogenesis. The MS and FD parameters of 670 samples from five sections in Siberia are reported here. Inter-section correlation is used to produce a combined FD time series for the studied sections. Chronological control is established by absolute dating and stratigraphic correlation. Spectral analysis of the FD time series reveals the presence of Milankovitch signals at ～100 kyr (eccentricity), ～40 kyr (obliquity) and ～23 kyr (precession) and demonstrates that Siberian loess–paleosol sequences are excellent continental recorders of long-term paleoclimatic changes. This suggests that the FD parameter can potentially be used more widely for evaluation of climate periodicity in loess/paleosol sequences in other parts of the world.     

Palaeomagnetism of (late Vendian-earliest Cambrian) minor alkaline intrusions, Fen Complex, southeast Norway

Emplacement of the Fen central complex (603-565 Ma) within the Fennoscandian Shield in southeast Norway was preceded by the emplacement of numerous minor alkaline intrusions into the surrounding gneisses. A palaeomagnetic sample of 28 of these bodies has identified a predominant SSE negative remanence carried by magnetite in some bodies and hematite in others. A sporadic high blocking temperature component appears to record localised effects associated with the development of the Oslo rift and igneous province to the east, but no major magnetic overprinting by post-emplacement events is recognised. The stable magnetisation vectors for twenty sites comprise a coherent population with those for two sites reversed with respect to the remainder; they yield a mean direction ofD = 210°,I = 44° (₉₅ = 6.4°) and a palaeomagnetic pole at 324°E, 50°S (dpdm=4.9°7.9°). The difference between the pole position for this early phase of the Fen magmatism and that for the late metasomatic rødberg (322°E, 63°S) in the interior of the complex is interpreted in terms of continental movement during the late Vendian-earliest Cambrian interval of alkaline activity here. The defined direction of APW movement continues a motion recognised from other Vendian data but subsequent movements during Lower Cambrian times are unclear.     

Paleomagnetism of the Upper Silurian and Lower Devonian carbonates of New York State: evidence for secondary magnetizations residing in magnetite

Paleomagnetic directions for the Upper Silurian and Lower Devonian carbonates of the Helderberg escarpment (New York State) differ from expected Late Silurian and Early Devonian directions for cratonic North America. The mean direction (D = 165°, I = −10°; paleopole at 50°N 129°E) is similar to Late Carboniferous and Early Permian results. Negative fold tests, and a lack of reversals, suggest that the magnetization is secondary. However, low coercivities, low blocking temperatures, the thermomagnetic curves (T_C near 570°C) and the acquisition of isothermal remanent magnetizations all suggest that the remanence is carried by magnetite. If a detrital origin of these magnetites is assumed, the secondary nature of the remanence would argue for thermal resetting as a result of deep burial of the rocks. However, no evidence for such thermal resetting is seen in the alteration of conodonts. More likely perhaps is a chemical or thermochemical origin of the remanence; this would require the magnetites to be authigenic.     

Magnetostratigraphy of the lower member of the hadar formation (Ethiopia): Evidence for a short normal event in the mammoth subchron

Summary Rock magnetism and magnetostratigraphy of the lower part of the Hadar Formation (Afar, Ethiopia) is presented after analysis of multiple new collection of samples from over 84 horizons. The Hadar Formation is composed of lacustrine, lake margin, fluvial and flood plain sediments and known for important Pliocene vertebrate faunas including Australopithecus afarensis. Hysteresis measurements, thermomagnetic analysis, growth and decay of isothermal remanent magnetisation are used to unravel the complex magnetic mineralogy of the different representative lithologies. Ferrimagnetic minerals of magnetite or titanomagnetite in composition, in the stable pseudo-single domain (PSD) size range are found to be the main carriers of the remanence. In most sites the characteristic remanence was isolated using stepwise thermal demagnetisation. The overall mean direction for about 72 horizons (434 samples) is D=358·6°, I=7° (k=17·9, α₉₅=4°) implying some 14° of inclination shallowing, related to sediment compaction due to the very rapid sedimentation history of the site. Five successive polarity zones (N1-R1-N2-R2-N3) are identified and correlation with the lower Gauss chron of the astronomically calibrated geomagnetic polarity time scale (GPTS) is proposed using the existing⁴⁰Ar/³⁹Ar ages. This implies the existence of a short normal polarity event (N2), identified on six different sites, within the reversed Mammoth subchron, called the Kada-Hadar event. The age calculated for the Kada-Hadar event, using linear interpolation of the dated horizons, assuming a constant rate of sedimentation is 3.246 Ma and its duration is about 8 kyr.     

基于地磁场相对古强度变化的下蜀黄土年代序列及其古气候意义

分布于宁镇地区的下蜀黄土年代标尺研究薄弱.我们以镇江大港钻孔岩芯的下蜀黄土为例,探讨了下蜀黄土记录地磁场相对古强度的可靠性.岩石磁学的实验显示,下蜀黄土大体上符合估计相对古强度对沉积物的要求.以低频磁化率()作为天然剩磁(NRM300)的归一化因子,我们获得了下蜀黄土记录的地磁场相对古强度变化.通过与邻区和全球的单个及合成曲线的对比,我们发现大港钻孔岩芯的相对古强度记录展现出主要的全球偶极场的变化特征,因而可用于建立下蜀黄土的年代标尺.新的年代标尺表明,大港钻孔的磁化率年代序列与北方黄土无法直接对比,证实了该地点的下蜀黄土磁化率变化机制与北方的不同.大港钻孔下蜀黄土的沉积速率与磁化率相关,低风尘沉积速率对应低磁化率,是降水增加所导致的结果.沉积速率与磁化率年代序列显示,下蜀黄土记录的本区季风变化过程可分为4个阶段.阶段Ⅳ(819～700ka)对应中更新世转型阶段,东亚季风降水较少.阶段Ⅲ(700～412ka)对应中更新世的大间冰期,东亚季风降水最多.阶段Ⅱ(412～197ka)时东亚季风降水减少,较阶段Ⅳ略少.阶段Ⅰ(197～34ka)东亚季风降水最少.因此,中更新世气候转型后,长时间尺度东亚季风降水持续减少,可能受全球温度阶段性降低驱动.     

The metamorphic history of LL-group ordinary chondrites

A study of feldspar grain size and microprobe analysis of coexisting orthopyroxene, olivine, diopside, and metal in twenty equilibrated LL-group chondrites and clasts defines the conditions of metamorphism, indicates the relative position of samples within the parent body, and suggests an accretionary-metamorphic history.

Variation of mineral chemistry indicates a range of equilibrium temperature and parallels textural variation, providing two continuous relative temperature scales, based on mean feldspar grain size and the calcium content of orthopyroxene coexisting with diopside. Maximum equilibrium temperatures range from less than 600° up to 950°C. The total Tschermak's component in orthopyroxene indicates that maximum pressure was less than 1 kbar, and a pressure gradient correlates directly with temperature. A reduction sequence, evident from systematic variation of iron in ferromagnesian silicates and metal, correlates inversely with temperature.

The maximum permissible sampling depth for the formation of surface breccias (2/10 r) also limits pressure to less than 1 kbar. The LL parent body had a minimum radius of 200 km, determined using the permissible sampling depth and published cooling rates.

The data are broadly consistent with simple reheating of colder material within a completely accreted body. This model may have problems with volatile depletion, a required lack of impact sampling during metamorphism, and the timing of the event. The data are more consistent with accretion of colder material on a hot but cooling surface. Both models apparently require a recycling process during accretion to account for the reduction sequence.     

In situ cosmogenic ~(10)Be dating of the Quaternary glaciations in the southern Shaluli Mountain on the Southeastern Tibetan Plateau

It is generally considered that four-times ice age happened during the Quaternary epoch on the Tibetan Plateau. However, the research on the chronology of the four-times ice age is far from enough. The Shaluli Mountain on the Southeastern Tibetan Plateau is an ideal place for plaeo-glacier study, because there are abundant Quaternary glacial remains there. This paper discusses the ages of the Quaternary glaciations, based on the exposure dating of roche moutonnée, moraines and gla- cial erosion surfaces using in situ cosmogenic isotopes 10Be. It is found that the exposure age of the roche moutonnée at Tuershan is 15 ka, corresponding to Stage 2 of the deep-sea oxygen isotope, suggesting that the roche moutonnée at Tuershan is formed in the last glacial maximum. The expo- sure age of glacial erosion surface at Laolinkou is 130―160 ka, corresponding to Stage 6 of the deep-sea oxygen isotope. The oldest end moraine at Kuzhaori may form at 421―766 kaBP, corre- sponding to Stages 12―18 of the deep-sea oxygen isotope. In accordance with the climate charac- teristic of stages 12,14,16 and 18 reflected by the deep-sea oxygen isotope, polar ice cores and loess sequence, the oldest end moraine at Kuzhaori may form at stage 12 or stage 16, the latter is more possible.     

Testing post-IR-IRSL dating on Armenian loess-palaeosol sections against independent age control

Loess-palaeosol sections (LPS) in northern Armenia exhibit at least three alternating loess and pedocomplex units, indicative of an environment changing between erosional/depositional and stable conditions. The LPS they are located in a central key position between loess in Europe, central Asia and the Russian/Ukrainian Plains. Since an accurate chronology is crucial for any palaeoenvironmental reconstruction and correlation with other proxy records, we establish a post-IR-IRSL chronology for two loess sections in the Sevkar loess area and compare it with independent age control. This is mainly based on an ⁴⁰Ar/³⁹Ar age of a tephra encountered in the L-2 loess layer from the penultimate glacial, which is dated to 194.0 ± 8.5 ka. Further checks on the accuracy are provided by the expected stratigraphy and comparison with other palaeoenvironmental records. The comparison indicates that a fading correction is necessary for the older samples within the L-2 loess layer but when correcting for fading with fading rates measured in the laboratory, the ages are clearly overestimated. Therefore, it is tentatively suggested using a reduced fading rate by subtracting a fixed percentage of the measured fading rate as surrogate for a laboratory artefact. In our study, we reduce all fading rates by 1%/decade and yield fading corrected pIRIR ages which are in agreement with the independent age control. The resulting chronology reaches down to at least MIS8 and shows that loess deposition in northern Armenia occurred during global cold phases, whereas global warm phases are associated with landscape stability and soil formation.     

Age and isotope geochemistry of the Archaean Pongola and Usushwana suites in Swaziland, southern Africa: a case for crustal contamination of mantle-derived magma

The igneous rocks of the Pongola Supergroup (PS) and Usushwana Intrusive Suite (UIS) represent a case of late Archaean continental magmatism in the southeastern part of the Kaapvaal craton of South Africa and Swaziland.

U-Pb dating on zircons from felsic volcanic rocks of the PS yields a concordia intercept age of 2940 ± 22Ma that is consistent with a Sm-Nd whole rock age of 2934 ± 114Ma determined on the PS basalt-rhyolite suite. The initial ε_Nd of−2.6 ± 0.9 is the lowest value so far reported for Archaean mantle-derived rocks. Rb-Sr whole rock dating of the PS yields a younger isochron age of 2883 ± 69Ma, which is not significantly different form the accepted U-Pb zircon age.

An internal (cpx-opx-plag-whole rock) isochron for a pyroxenite from the younger UIS yields an age of 2871 ± 30 Ma and initial ¹⁴³Nd/¹⁴⁴Nd that lies off the CHUR growth curve by ε_Nd −2.9 ± 0.2. However, Sm-Nd whole-rock data for the UIS yield an excessively high age of 3.1 Ga that conflicts with firm geological evidence showing the UIS to be intrusive into the PS.

The negative deviations of initialε_Nd from the chondritic Nd evolution curve suggest significant contamination of the PS and UIS melts by older continental crust. A mixing process with continental crust after magma segregation is supported by a high initial ⁸⁷Sr/⁸⁶Sr ratio of0.703024 ± 24 for a clinopyroxene sample from a UIS pyroxenite, compared with an expected value of 0.701 for the 2.9 Ga mantle. We therefore interpret the linear array of data points for the UIS gabbros as a mixing line between 2.87 Ga old magma and older continental crust.

Parallel LREE-enriched REE patterns, negative Nb-Ti anomalies, a distinctive and uniform ratio of Ti/Zr 46 and a narrow span of initial Nd indicate a common source for both the PS and UIS suites which is different from primitive mantle.     

New contributions to Chinese Plio-Pleistocene magnetostratigraphy

A new collection of over 500 orientated hand-samples (of which 180 are red clays) from a 195 m loess/red clay section near Xian (109° 12′ E, 34° 12′ N), China, has been dated by magnetic stratigraphy. Biostratigraphic and previous magnetostratigraphic investigations gave a maximum age for the Chinese loess of 2.4 Ma, implying that the underlying Red Clay Formation is Pliocene in age. The present study yields a clearly defined magnetic polarity stratigraphy in good agreement with a polarity time scale developed by earlier workers. An interpretation of this magnetostratigraphy suggests a basal age for the loess series in this region of 2.5 Ma, and a minimum age for the base of the Red Clay Formation, which is also the base of the section, of 5.0 Ma.     

An analysis of the components of the luminescence signals of selected polymineral and quartz samples from loess in western China and southern Tajikistan,and their suitability for optical dating

Previous luminescence dating studies on loess from China and Tajikistan have focused on the establishment of the regional chronology of the loess sequences. In order to improve the precision and accuracy of optical ages derived from the loess of the last glacial period in these regions, we have examined the components of luminescence signals in three loess samples from western China and southern Tajikistan. Our results show that the polymineral IRSL and post-IR OSL, and quartz OSL signals from loess of the two regions are represented by three components, which display different bleaching and growth characteristics. While the composition of the polymineral IRSL signals is similar between samples with the same age from the two regions, in the case of quartz there is significant discrepancy in the proportion of the fast and medium components of the OSL signals. Greater difference is observed in the composition of the polymineral post-IR OSL signals for the loess from the two regions. The three components of polymineral IRSL signals yield almost identical equivalent dose values as that derived from the total IRSL signal. An apparent agreement in equivalent dose is observed between the fast component of the polymineral post-IR OSL and the quartz OSL for the loess of western China but not in the loess of the same age from southern Tajikistan. The fast component of the quartz OSL yields an equivalent dose 25% higher than that based on the total signal for the sample from the base of the Late Pleistocene loess in southern Tajikistan. This demonstrates the importance of signal selection for an accurate luminescence dating of Central Asian loess.     

Characteristics of the burial environment related to quartz SAR-OSL dating at St. Vincent Island, NW Florida, USA

St. Vincent Island, on the northwest Gulf coast of Florida, USA, preserves a well-developed beach ridge plain that began to form 4000 years ago based on inferred ages of pottery artefact assemblages. Seven vibra cores up to 2.88 m in length (uncompacted sediment) were retrieved from six ridges across the island. The single-aliquot regenerative-dose (SAR) procedure was used to obtain two optically stimulated luminescence (OSL) ages per core at different depths within each core.

The geographically youngest ridges gave ages of 370±50–1900±300 years, yielding an inter-ridge accumulation time of 150 years assuming uniform sediment accumulation. The oldest ridge sets yielded ages of 2700±400–2800±300 years. Dating results are evaluated in terms of equivalent dose (D_E) distributions and other characteristics in relation to aspects of the burial environment, including pedogenesis.     

Late cretaceous to early paleogene paleomagnetic results from Sikhote Alin, far eastern Russia: implications for deformation of East Asia

Welded tuffs in the Bogopol and Sijanov groups were sampled at 27 sites from 12 caldera formations in the Sikhote Alin mountain range around Kavalerovo (44.3°N, 135.0°E) for chronological and paleomagnetic studies. KAr age dates show that the welded tuffs erupted between 66 Ma and 46 Ma. All sites yield reliable paleomagnetic directions, with unblocking temperatures higher than 560°C. The high-temperature component at 12 sites and the medium-temperature component at 3 sites in the Bogopol Group show reversed polarity (D = 193.7°, I = −57.6°,₉₅ = 8.1°). The high-temperature component at 11 sites in the Sijanov Group showed both reversed and normal polarities and its mean direction reveals no detectable deflection from north (D = −2.9°, I = 59.6°,₉₅ = 11.2°). The combined paleomagnetic direction of the two groups yields a paleomagnetic pole of 250.5°E, 84.1°N (A₉₅ = 8.8°), which falls near Cretaceous paleomagnetic poles from Outer Mongolia, Inner Mongolia, the North China Block and the South China Block. The Sikhote Alin area appears not to have been subjected to detectable motion with respect to East Asia since about 50 Ma. This implies that the Sikhote Alin area behaved as an integral part of East Asia during the opening of the Japan Sea at about 15 Ma. However, significant separation between the paleomagnetic poles of East Asia and Europe during the Jurassic-Paleogene implies a major relative movement between these two blocks since the Paleogene.     

In situ cosmogenic 10Be dating of the Quaternary glaciations in the southern Shaluli Mountain on the Southeastern Tibetan Plateau

It is generally considered that four-times ice age happened during the Quaternary epoch on the Tibetan Plateau. However, the research on the chronology of the four-times ice age is far from enough. The Shaluli Mountain on the Southeastern Tibetan Plateau is an ideal place for plaeo-glacier study, because there are abundant Quaternary glacial remains there. This paper discusses the ages of the Quaternary glaciations, based on the exposure dating of roche moutonnée, moraines and glacial erosion surfaces using in situ cosmogenic isotopes ¹⁰Be. It is found that the exposure age of the roche moutonnée at Tuershan is 15 ka, corresponding to Stage 2 of the deep-sea oxygen isotope, suggesting that the roche moutonnée at Tuershan is formed in the last glacial maximum. The exposure age of glacial erosion surface at Laolinkou is 130–160 ka, corresponding to Stage 6 of the deep-sea oxygen isotope. The oldest end moraine at Kuzhaori may form at 421–766 kaBP, corresponding to Stages 12–18 of the deep-sea oxygen isotope. In accordance with the climate characteristic of stages 12, 14, 16 and 18 reflected by the deep-sea oxygen isotope, polar ice cores and loess sequence, the oldest end moraine at Kuzhaori may form at stage 12 or stage 16, the latter is more possible.