ESR dating of the Wangsan fault,South Korea

The Wangsan fault is exposed at Kyeongju, Korea. The andesite is unconformably covered by Quaternary alternating conglomerate and sandstone deposits. The unconformity is cut by the thrust fault which displaces a hanging wall block of about 30 m. Exposed at the surface of this fault is a light gray and brown fault gouge, about 40–120 cm thick. In order to test the consistency of ESR ages from a single fault gouge zone, we collected six gouge samples systematically along and across the Wangsan fault. We found that six samples collected from the same gouge zone show consistent ESR date estimates (average 550 ka). Because fault rock is rare along faults in unconsolidated sediments due to low confining stress near the surface, we consider that this fault gouge has been moved up with the hanging wall block along the fault. The estimated average uplift rate of the hanging wall block is about 0.04 cm/year based on the age of the displaced Quaternary deposits (vertical separation; about 20 m) dated by OSL dating methods. The depth of the fault gouge at the time of reactivation, which was estimated from uplift rate and the ESR ages, is about 220 m. Therefore, we conclude that the results of ESR age estimates represent the time of reactivation of the fault gouge at a depth of 220 m in the past during fault movement, because later movements which occurred during uplift near the surface may not have zeroed ESR signals significantly for ESR dating of fault movements.     

Paleoseismic investigation along Nalagarh Thrust: Evidence of Late Pleistocene earthquake in Pinjaur Dun,Northwestern sub-Himalaya

The present article is the first time reporting of a paleoearthquake that occurred during Late Pleistocene time along the Nalagarh Thrust (NT) in the Pinjaur Dun in northwestern sub-Himalaya. Using CORONA satellite photographs, multi-spectral IRS satellite data, and aerial photographs, a prominent active fault has been identified at Nalagarh in Pinjaur Dun. This fault in the alluvial fan is located very close to the NT which borders the topographic front of the Tertiary rocks against Quaternary deposits. A trench excavation survey was carried out at Nalagarh for detailed paleoseismic studies across this thrust fault. Displacing all the lithologic units of the fan sequence, the fault plane has an average dip of 30° due ENE and a vertical displacement of 1.6 m and slip of ～2.5 m along the fault. The lithological units, consisting of alternating sand and gravel, show back tilting and asymmetrical tight folding. Based on Optically Stimulated Luminescence (OSL) ages, the oldest litho-unit in the trench is 85.83 ± 7.2 ka and the youngest is 67.05 ± 8.4 ka. The OSL age of the sample collected from the easterly exposure of the fault shows an age of 20 ka. The faulting and associated induced deformation features suggest occurrence of a Late Pleistocene large magnitude earthquake along NT in the Nalagarh region of the Pinjaur Dun following the deposition of the Quaternary sedimentary units. The Late Pleistocene fault substantiates the seismic potential of Pinjaur Dun and calls for more exhaustive study of paleoearthquakes in this fast developing industrial belt and highly populous mountainous region.     

The onset of dune formation in the Strzelecki Desert,South Australia

This study is concerned with the Late Quaternary climatic chronology of the Strzelecki Desert dunefields in central Australia. The sand ridges comprise layers of quartz sand, some of which include palaeosol horizons with carbonated rootlets providing excellent opportunity for dating of alternations of dune building and stability by using optically stimulated luminescence (OSL). Deduced from the OSL age of the oldest aeolian layer dated, we conclude that the onset of aridity dates back to at least ∼65 ka. Older phases of aeolian activity though, following a fluvial depositional phase 160 ka ago, cannot be excluded, although no aeolian layers giving evidence for this have been found in the two dunes dated here. Unconsolidated dune sands in the upper part of one section with Late Holocene (4 ka to modern) depositional ages indicate a reactivation of the dunefield in recent times.From the crosscheck of ¹⁴C ages of the carbonated rootlets with OSL results it is concluded that under the given environmental conditions radiocarbon dating of the calcareous rootlets is not able to provide reliable ages for the phase of soil development.     

A luminescence dating study of the sediment stratigraphy of the Lajia Ruins in the upper Yellow River valley,China

Pedo-sedimentological fieldwork were carried out in the Lajia Ruins within the Guanting Basin along the upper Yellow River valley. In the eolian loess-soil sections on the second river terrace in the Lajia Ruins, we find that the land of the Qijia Culture (4.20–3.95 ka BP) are fractured by several sets of earthquake fissures. A conglomerated red clay covers the ground of the Qijia Culture and also fills in the earthquake fissures. The clay was deposited by enormous mudflows in association with catastrophic earthquakes and rainstorms. The aim of this study is to provide a luminescence chronology of the sediment stratigraphy of the Lajia Ruins. Eight samples were taken from an eolian loess-soil section (Xialajia section) in the ruins for optically stimulated luminescence (OSL) dating. The OSL ages are in stratigraphic order and range from (31.94 ± 1.99) ka to (0.76 ± 0.02) ka. Combined OSL and ¹⁴C ages with additional stratigraphic correlations, a chronological framework is established. We conclude that: (1) the second terrace of the upper part of Yellow River formed 35.00 ka ago, which was followed by the accumulation of the eolian loess-soil section; and (2) the eolian loess-soil section is composed of the Malan Loess of the late last glacial (MIS-2) and Holocene loess-soil sequences.     

Late Quaternary highstands at Lake Chilwa,Malawi: Frequency,timing and possible forcing mechanisms in the last 44 ka

The extensive shoreline deposits of Lake Chilwa, southern Malawi, a shallow water body today covering 600 km² of a basin of 7500 km², are investigated for their record of late Quaternary highstands. OSL dating, applied to 36 samples from five sediment cores from the northern and western marginal sand ridges, reveal a highstand record spanning 44 ka. Using two different grouping methods, highstand phases are identified at 43.7–33.3 ka, 26.2–21.0 ka and 17.9–12.0 ka (total error method) or 38.4–35.5 ka, 24.3–22.3 ka, 16.2–15.1 ka and 13.5–12.7 ka (Finite Mixture Model age components) with two further discrete events recorded at 11.01 ± 0.76 ka and 8.52 ± 0.56 ka. Highstands are comparable to the timing of wet phases from other basins in East and southern Africa, demonstrating wet conditions in the region before the LGM, which was dry, and a wet Lateglacial, which commenced earlier in the southern compared to northern hemisphere in East Africa. We find no evidence that wet phases are insolation driven, but analysis of the dataset and GCM modelling experiments suggest that Heinrich events may be associated with enhanced monsoon activity in East Africa in both timing and as a possible causal mechanism.     

Cosmogenic 10Be and 36Cl ages from Late Pleistocene terminal moraine complexes in the Taylor River drainage basin,central Colorado,USA

Cosmogenic surface-exposure ages from boulders on a terminal moraine complex establish the timing of the local last glacial maximum (LGM) in the Taylor River drainage basin, central Colorado. Five zero-erosion ¹⁰Be ages have a mean of 19.5±1.8 ka while that for three ³⁶Cl ages is 20.7±2.3 ka. Corrections for modest rates (∼1 mm ka⁻¹) of boulder surface erosion result in individual and mean ages that are generally within 2% of their zero-erosion values. Both the means and the range in ages of individual boulders are consistent with those reported for late Pleistocene moraines elsewhere in the southern and middle Rocky Mountains, and thus suggest local LGM glacier activity was regionally synchronous. Two anomalously young (?) zero-erosion ¹⁰Be ages (mean 14.4±0.8 ka) from a second terminal moraine are tentatively attributed to the boulders having been melted out during a late phase of ice stagnation.     

Brittle reactivation of mylonitic fabric and the origin of the Cenozoic Rio Santana Graben,southeastern Brazil

In the Ribeira belt, southeastern Brazil, the Precambrian mylonitic fabric mainly formed during the Brasiliano/Pan-African orogeny (640–480 Ma) and was reactivated as fault zones in the Cretaceous and Cenozoic. The reactivation process led to the development of the System of Continental Rifts of southeastern Brazil, from the Paleogene to the Quaternary. We investigated the brittle reactivation of a mylonitic zone, which is part of a major mylonitic belt, Arcádia-Areal. We used geological and geomorphological mapping, resistivity survey, controlled source audiomagnetotelluric survey, and luminescence dating. Our results indicate that this shear zone was reactivated and formed a 15 km long and 2 km wide sedimentary-filled trough, the Rio Santana Graben. It is located on the northwest border of a major structure, the Guanabara Graben, in the State of Rio de Janeiro. The Rio Santana Graben forms an almost entirely fault-bounded, NE-elongated depression that was accommodated entirely within the Arcádia-Areal shear zone. The graben consists of two main depocenters separated by a relay ramp. The graben formed by means of multistage activity of several faults during at least two main periods. The first period formed silicified fault breccia and occurred during alkaline magmatism in the Paleogene. The second formed fault breccia and gouge in shallow conditions and occurred at least until the Quaternary. The NE-trending and NW-dipping Precambrian fabric was reactivated as dip-slip and strike-slip faults. These faults triggered clastic-sediment deposition at least 300 m thick. The upper part of the graben consists of Quaternary alluvial and colluvial sediment fill, which yielded maximum luminescence deposition ages from 49 to 13 ka in the center of the trough. An organic layer at the top of the Quaternary alluvial deposits yielded ¹⁴C ages at ～6000 years BP. The lower part of the graben may be composed of Paleogene to Neogene sedimentary deposits, which occur in other basins of the System of Continental Rifts of southeastern Brazil. We conclude that the Rio Santana Graben is an example of the direct control of a preexisting continental-scale rheological boundary on the geometry and location of fault systems and sediment deposition. Quaternary fault reactivation of the preexisting fabrics represents only the latest movement of a major structure.     

Moraine dam related to late Quaternary glaciation in the Yulong Mountains,southwest China,and impacts on the Jinsha River

The Yulong Mountain massif is tectonically active during Quaternary and contains the southernmost glacierized mountains in China, and all of Eurasia. Past glacial remnants remain preserved on the east and west sides of the Yulong Mountains. A ridge of moraine protruded into the Jinsha River at the Daju Basin, damming the river, and forming a lake at the head of the Jinsha River. Cosmogenic ¹⁰Be and ²⁶Al provide exposure age dates for the moraine-based fluvial terraces left behind after the dam breached, and for moraine boulders on both the eastern and western sides of the Yulong Mountains. Our results yield exposure ages for the terraces that range from 29 ka to 8 ka, and a downcutting rate of 7.6 m/ka. The preservation of the remaining dam for over 10,000 years suggests stability of the moraine dam and gradual erosion of the dam during drainage of the dammed lake. From the relationship between exposure ages and elevations of the fluvial terraces located in different walls of the Daju fault, we obtain a late Quaternary dip-slip rate of about 5.6 m/ka for the Daju fault. The exposure ages of 10.2 ka and 47 ka for moraine boulders located in the east and west sides of the Yulong Mountains, respectively, coincide with warm periods in the late Quaternary. This implies that precipitation provides the major control for glaciations on the Yulong Mountains, a domain of the southwest Asian monsoon.     

Nature and timing of large landslides in the Himalaya and Transhimalaya of northern India

Four large landslides, each with a debris volume >10⁶ m³, in the Himalaya and Transhimalaya of northern India were examined, mapped, and dated using ¹⁰Be terrestrial cosmogenic radionuclide surface exposure dating. The landslides date to 7.7±1.0 ka (Darcha), 7.9±0.8 ka (Patseo), 6.6±0.4 ka (Kelang Serai), and 8.5±0.5 ka (Chilam). Comparison of slip surface dips and physically reasonable angles of internal friction suggests that the landslides may have been triggered by increased pore water pressure, seismic shaking, or a combination of these two processes. However, the steepness of discontinuities in the Darcha rock-slope, suggests that it was more likely to have started as a consequence of gravitationally-induced buckling of planar slabs. Deglaciation of the region occurred more than 2000 years before the Darcha, Patseo, and Kelang Serai landslides; it is unlikely that glacial debuttressing was responsible for triggering the landslides. The four landslides, their causes, potential triggers and mechanisms, and their ages are compared to 12 previously dated large landslides in the region. Fourteen of the 16 dated landslides occurred during periods of intensified monsoons. Seismic shaking, however, cannot be ruled out as a mechanism for landslide initiation, because the Himalaya has experienced great earthquakes on centennial to millennial timescales. The average Holocene landscape lowering due to large landslides for the Lahul region, which contains the Darcha, Patseo, and Kelang Serai landslides, is ～0.12 mm/yr. Previously published large-landslide landscape-lowering rates for the Himalaya differ significantly. Furthermore, regional glacial and fluvial denudation rates for the Himalaya are more than an order of magnitude greater. This difference highlights the lack of large-landslide data, lack of chronology, problems associated with single catchment/large landslide-based calculations, and the need for regional landscape-lowering determinations over a standardized time period.     

Revised 14C dating of ice wedge growth in interior Alaska (USA) to MIS 2 reveals cold paleoclimate and carbon recycling in ancient permafrost terrain

Establishing firm radiocarbon chronologies for Quaternary permafrost sequences remains a challenge because of the persistence of old carbon in younger deposits. To investigate carbon dynamics and establish ice wedge formation ages in Interior Alaska, we dated a late Pleistocene ice wedge, formerly assigned to Marine Isotope Stage (MIS) 3, and host sediments near Fairbanks, Alaska, with 24 radiocarbon analyses on wood, particulate organic carbon (POC), air-bubble CO₂, and dissolved organic carbon (DOC). Our new CO₂ and DOC ages are up to 11,170 yr younger than ice wedge POC ages, indicating that POC is detrital in origin. We conclude an ice wedge formation age between 28 and 22 cal ka BP during cold stadial conditions of MIS 2 and solar insolation minimum, possibly associated with Heinrich event 2 or the last glacial maximum. A DOC age for an ice lens in a thaw unconformity above the ice wedge returned a maximum age of 21,470 ± 200 cal yr BP. Our variable ¹⁴C data indicate recycling of older carbon in ancient permafrost terrain, resulting in radiocarbon ages significantly older than the period of ice-wedge activity. Release of ancient carbon with climatic warming will therefore affect the global ¹⁴C budget.     

Progress towards single-grain optical dating of fossil mud-wasp nests and associated rock art in northern Australia

Here we report on investigations into optical dating of fossil mud-wasp nests as a means of constraining the ages of overlying and underlying rock paintings in northern Australia. We describe the application of a ‘dual-signal’ regenerative-dose approach, using the easy-to-bleach (‘fast’) and hard-to-bleach (‘slow’) components of optically stimulated luminescence (OSL) emitted by individual sand-sized grains of quartz extracted from two nests: a modern nest (<2 yr old) and a nest dated by ¹⁴C to about 30,000 calendar years (∼30 ka). For the modern nest, most of the palaeodoses obtained from both the fast and slow components are consistent with a zero age, while the ¹⁴C-dated nest yielded an age of 27.1±1.5 ka from those grains that yielded concordant palaeodoses from the fast and slow components (as measured by linearly modulated OSL). Our findings indicate that a dual-signal approach permits grains that were fully bleached by sunlight at the time of nest construction, and that have since remained concealed in the light-safe ‘core’ of a nest, to be distinguished from (a) grains that were incompletely bleached before nest construction, and (b) grains embedded in the continuously light-exposed, exterior portion of a nest. We conclude that reliable optical ages for small mud-wasp nests associated with ancient rock art may be obtained using the dual-signal approach and the light-safe grains.     

Quaternary glaciation of Mount Everest

The Quaternary glacial history of the Rongbuk valley on the northern slopes of Mount Everest is examined using field mapping, geomorphic and sedimentological methods, and optically stimulated luminescence (OSL) and ¹⁰Be terrestrial cosmogenic nuclide (TCN) dating. Six major sets of moraines are present representing significant glacier advances or still-stands. These date to >330 ka (Tingri moraine), >41 ka (Dzakar moraine), 24–27 ka (Jilong moraine), 14–17 ka (Rongbuk moraine), 8–2 ka (Samdupo moraines) and ～1.6 ka (Xarlungnama moraine), and each is assigned to a distinct glacial stage named after the moraine. The Samdupo glacial stage is subdivided into Samdupo I (6.8–7.7 ka) and Samdupo II (～2.4 ka). Comparison with OSL and TCN defined ages on moraines on the southern slopes of Mount Everest in the Khumbu Himal show that glaciations across the Everest massif were broadly synchronous. However, unlike the Khumbu Himal, no early Holocene glacier advance is recognized in the Rongbuk valley. This suggests that the Khumbu Himal may have received increased monsoon precipitation in the early Holocene to help increase positive glacier mass balances, while the Rongbuk valley was too sheltered to receive monsoon moisture during this time and glaciers could not advance. Comparison of equilibrium-line altitude depressions for glacial stages across Mount Everest reveals asymmetric patterns of glacier retreat that likely reflects greater glacier sensitivity to climate change on the northern slopes, possibly due to precipitation starvation.     

Genetic implications of a retransported loess profile near Córdoba,Argentina

This paper deals with a loess profile located southeast of Córdoba (64° 05′ 30 W to 31°30′ S) that was dated in Beijing University using the OSL method according to Simple Aliquot Regeneration Protocol. This study provides some inferences regarding climatic and environmental features, such as transport agents and probable sources of the materials.The profile, located inside Llanura Pampeana, is approximately 6.80 m in depth and comprises ages between 22.4 ± 3.2 and 9.9 ± 0.3 ka. Throughout the profile, and for all grain sizes, major minerals are quartz and feldspar, with micas, and opaques as subordinates. Illite and chlorite appear as traces, though the last one was not confirmed in the finest fraction analysis. Calcite is abundant in the uppermost sample and decreases downwards. In the base of the profile, and in the clay fraction, XRD showed illite, swellable clay minerals (smectite + mixed layers) and kaolinite traces. It was concluded that the profile would have been derived from the accumulation of sediments, along several events very similar in transport conditions, even though there are some indications that about 21 ka BP, water availability was slightly smaller than for the rest of the profile. This change was also established in some other places, allowing some regional correlations. According to the analyzed data, about 19 ka BP, water availability again increased.     

A multiple-approach radiometric age estimate for the Rotoiti and Earthquake Flat eruptions,New Zealand,with implications for the MIS 4/3 boundary

Pyroclastic fall deposits of the paired Rotoiti and Earthquake Flat eruptions from the Taupo Volcanic Zone (New Zealand) combine to form a widespread isochronous horizon over much of northern New Zealand and the southwest Pacific. This horizon is important for correlating climatic and environmental changes during the Last Glacial period, but has been the subject of numerous disparate age estimates between 35.1±2.8 and 71±6 ka (all errors are 1 s.d.), obtained by a variety of techniques. A potassium–argon (K–Ar) age of 64±4 ka was previously determined on bracketing lavas at Mayor Island volcano, offshore from the Taupo Volcanic Zone. We present a new, more-precise ⁴⁰Ar/³⁹Ar age determination on a lava flow on Mayor Island, that shortly post-dates the Rotoiti/Earthquake Flat fall deposits, of 58.5±1.1 ka. This value, coupled with existing ages from underlying lavas, yield a new estimate for the age of the combined eruptions of 61.0±1.4 ka, which is consistent with U–Th disequilibrium model-age data for zircons from the Rotoiti deposits. Direct ⁴⁰Ar/³⁹Ar age determinations of plagioclase and biotite from the Rotoiti and Earthquake Flat eruption products yield variable values between 49.6±2.8 and 125.3±10.0 ka, with the scatter attributed to low radiogenic Ar yields, and/or alteration, and/or inheritance of xenocrystic material with inherited Ar. Rotoiti/Earthquake Flat fall deposits occur in New Zealand in association with palynological indicators of mild climate, attributed to Marine Isotope Stage (MIS) 3 and thus used to suggest an age that is post-59 ka. The natures of the criteria used to define the MIS 4/3 boundary in the Northern and Southern hemispheres, however, imply that the new 61 ka age for the Rotoiti/Earthquake Flat eruption deposits will provide the inverse, namely, a more accurate isochronous marker for correlating diverse changes across the MIS 4/3 boundary in the southwest Pacific.     

Late Cenozoic fluvial dynamics of the River Tana,Kenya, an uplift dominated record

The Late Cenozoic development of the River Tana in Kenya has been reconstructed for its central reach near its confluence with the River Mutonga, which drains the Mount Kenya region. Age control for this system has been provided by K–Ar and Ar–Ar dating. Between 3.21 and 2.65 Ma a major updoming occurred, in relation to the formation of the Kenyan rift valley. The tilting related to this doming has been reconstructed from lava flows that preserve former river gradients. Linear projection of these trends to the current rift valley rim suggests a net updoming of the eastern Gregory Rift valley by at least ∼1 km during 3.21–2.65 Ma. In contrast, since 2.65 Ma the Tana system has been mainly subject to relatively minor epeirogenic uplift. Changing climatic conditions combined with continuing uplift yielded a typical staircase of strath terraces with at least 10 distinct levels. A more detailed reconstruction of the incision rates since 215 ka has been made, by correlating mineralogically fingerprinted volcaniclastic Tana deposits with dated tephras in a lake record. These volcaniclastic sediments were deposited during glacial periods, contemporaneous with lahars. The reconstructed incision rates for the three youngest terraces are ∼0.1–0.2 mm a⁻¹, thus considerably faster than the overall average rate of valley incision since the Mid-Pliocene, of 0.06 mm a⁻¹. A plausible uplift history has been reconstructed using the estimated ages of the Tana terraces and marine terraces on the Indian Ocean coastline. The result suggests an increase in the rate of incision by the River Tana at ∼0.9 Ma, an observation typical in most European river terrace staircases. The reconstructed Late Quaternary development of Tana valley indicates that a similar Quaternary uplift mechanism has operated in both Europe and East Kenya, suggesting a globally applicable process.     

Deglaciation and landscape history around Annapurna,Nepal, based on 10Be surface exposure dating

The High Himalaya is a key area for tectonic, geomorphological and climate studies, because of its extreme relief and location at the transition zone between areas with abundant monsoonal precipitation and the arid/semiarid Tibetan Plateau. We present ¹⁰Be surface exposure ages on 22 boulders from the Annapurna area in Nepal. The ages improve understanding of the Late Quaternary landscape history and the geomorphological processes operating in this part of the Himalaya.Although our study is reconnaissance in nature, it highlights the importance of catastrophic events, such as landslides and debris flows, for denudation of high mountains. Holocene exposure ages for the Dhampu–Chooya landslide (～4.1 ± 0.6 ka) and for 600 m of alluviation in Kali Gandaki Valley (～2.1 ± 0.6 ka), for example, indicate the frequent occurrence and extent of catastrophic events and their implications for natural hazards. We also offer an explanation for the differences in Late Quaternary glacial chronologies at closely spaced study sites in the Nepal Himalaya. Topographically controlled and spatially variable precipitation in the Himalaya determines the sensitivity of glaciers to changes in temperature and precipitation. Accordingly, some glaciers advanced in-phase with Northern Hemisphere ice sheets, whereas others reached their maximum extent at times of increased monsoonal precipitation during Marine Isotope Stage 3 and the early Holocene.     

Holocene climate change inferred from stratigraphy and OSL chronology of aeolian sediments in the Qaidam Basin,northeastern Qinghai–Tibetan Plateau

Paleoclimatic reconstruction based on aeolian sediments in the eastern Qaidam Basin (QB) has been hindered by the limited chronological data. Here we present 61 Optically Stimulated Luminescence (OSL) ages. On the basis of these OSL ages and the lithologic stratigraphy, we propose the ‘effective moisture index (EMI)’ for aeolian sediments to reconstruct the effective moisture change. Based on the EMI from twelve sections, the effective moisture change, moisture sources and relevant mechanisms for paleoclimatic change in the eastern QB are discussed. The results indicate that (1) aeolian deposition started at least before 12.4 ± 0.7 ka during the deglaciation, the paleosols developed at the early and mid-Holocene, and aeolian sand and loess accumulated at mid- and late Holocene; (2) effective moisture history was: hyper-arid at 12.8–11.6 ka, humid and variable at 11.6–8.3 ka, moderately humid and stable at 8.3–3.5 ka, and increasingly arid at 3.5–0 ka; (3) the effective moisture change was mainly controlled by the Asian summer monsoon (ASM), which mainly followed the change of Northern Hemispheric summer insolation, and the westerlies strengthened and increased the aridity in the QB when the ASM shrank.     

A method for coupled ESR/U-series dating of teeth showing post-depositional U-loss

An additional method of coupled ESR/U-series dating is developed for teeth showing post-depositional U-loss. The fundamental parameter for the dose rate calculation is the present-day ²³⁰Th-activity because of the geochemical immobility of thorium. Uranium and thorium concentrations are measured by thermal ionization mass spectrometry (TIMS). Due to the unknown uranium history an average saturation uptake of uranium is assumed leading to an average development of U-series activities. Therewith an internal dose rate and the age T can be calculated on condition that the modelled ²³⁰Th-activity at time T corresponds with the measured value. Using this new method, teeth, found in archaeological sites in France (Gramat, Bramefond), could be dated even though they show U-loss after U-uptake. Two teeth from Gramat could be dated to 128.3±8.6 and 130.5±10 ka. Two teeth from Bramefond have ages of 104.4±8.4 and 115.1±10.2 ka. Both sites can be ascribed to oxygen isotope stage 5.     

Late Quaternary erosion events in lowland and mid-altitude Tasmania in relation to climate change and first human arrival

The establishment of a chronology of landscape-forming events in lowland and mid-altitude Tasmania, essential for assessing the relative importance of climatic and human influences on erosion, and for assessing present erosion risk, has been limited by the small number of ages obtained and limitations of dating methods. In this paper we critically assess previous Tasmanian studies, list published radiocarbon ages considered to be dependable, present new radiocarbon and thermoluminescence (TL) ages for 25 sites around Tasmania, and consider the evidence for the hypotheses that erosion processes at low and mid altitudes have been: (1) purely climatically controlled; and (2) influenced both by climatic and anthropogenic (increased fire frequency) effects. A total of 94 dependable finite ages (calibrated for radiocarbon and ‘as measured’ for TL and optically stimulated luminescence (OSL) determinations) are listed for deposits comprising dunes, colluvium, alluvium and loess-like aeolian deposits. Two fall in the >100 ka period, 15 fall in the period 65–35 ka, and 77 fall in the period 35–0.3 ka. There was a sustained increase in erosion recorded in the period 35–15 ka, as reflected by a greater number of dated aeolian deposits during this period.We considered three possible biases that may have affected the age distribution obtained: the limitations of radiocarbon dating, sampling bias, and preservation bias. Sampling bias may have favoured more recent dune strata, but radiocarbon dating and preservation biases are unlikely to have significantly distorted the age distribution obtained.Long but intermittent aeolian deposition is recorded at two sites (Southwood B; c. 59–28 ka and Dunlin Dune; c. 29–14 ka) but there is no evidence of regional loess deposits such as found in New Zealand. The timing of increased erosion in Tasmania between 35 and 30 ka approximately coincides with the intermittent ten-fold increase of dust accumulation between 33 and 30 ka in the Antarctic Dome C ice core. The absence of widespread erosion before 35 ka, the abrupt increase of erosion around this time, the frequent association of erosion products with charcoal, the arrival of people in Tasmania at c. 40 cal ka, and the known use of fires by Aborigines to maintain areas of non-climax vegetation suggest that ecosystem disturbance by anthropogenic fires, in a drier climate than that presently prevailing, may have contributed to erosion in lowland and mid-altitude Tasmania after 35 ka. Thus the Tasmanian erosion record provides circumstantial support for the proposition that human dispersal in southeast Australia was accompanied by significant ecological change.     

Molybdenite Re–Os and albite 40Ar/39Ar dating of Cu–Au–Mo and magnetite porphyry systems in the Yangtze River valley and metallogenic implications

The area of the Middle–Lower Yangtze River valley, Eastern China, extending from Wuhan (Hubei province) to western Zhenjiang (Jiangsu province), hosts an important belt of Cu–Au–Mo and Fe deposits. There are two styles of mineralization, i.e., skarn/porphyry/stratabound Cu–Au–Mo–(Fe) deposits and magnetite porphyry deposits in several NNE-trending Cretaceous fault-bound volcanic basins. The origin of both deposit systems is much debated. We dated 11 molybdenite samples from five skarn/porphyry Cu–Au–Mo deposits and 5 molybdenite samples from the Datuanshan stratabound Cu–Au–Mo deposit by ICP-MS Re–Os isotope analysis. Nine samples from the same set were additionally analyzed by NTIMS on Re–Os. Results from the two methods are almost identical. The Re–Os model ages of 16 molybdenite samples range from 134.7 ± 2.3 to 143.7 ± 1.6 Ma (2σ). The model ages of the five samples from the Datuanshan stratabound deposit vary from 138.0 ± 3.2 to 140.8 ± 2.0 Ma, with a mean of 139.3 ± 2.6 Ma; their isochron age is 139.1 ± 2.7 Ma with an initial Os ratio of 0.7 ± 8.1 (MSWD = 0.29). These data indicate that the porphyry/skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system. Albite ⁴⁰Ar/³⁹Ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 Ma, i.e., 10–20 Ma later. Both mineralization styles characterize transitional geodynamic regimes, i.e., the period around 140 Ma when the main NS-trending compressional regime changed to an EW-trending lithospheric extensional regime, and the period of 125–115 Ma of dramatic EW-trending lithospheric extension.