Properties of simulated cosmic matters after gamma-ray and neutron irradiation

Interstellar and circumstellar matter is known to be strongly irradiated by cosmic radiation and several types of cosmic ray particles. The effects of irradiation on simulated interstellar and circumstellar matter such as CaCO₃, MgCO₃, SiO₂ and Al₂O₃ are investigated. Especially, thermoluminescence (TL) spectra after γ-ray and neutron irradiation are compared carefully. It is shown that the thermoluminescence after neutron irradiation appears significantly in the wavelength of blue region. On the reflectance in infrared region, the irradiation effect appears scarcely.     

Relict nebkhas (pimple mounds) record prolonged late Holocene drought in the forested region of south-central United States

The origin and significance of pimple mounds (low, elliptical to circular dune-like features found across much of the south-central United States) have been debated for nearly two centuries. We cored pimple mounds at four sites spanning the Ozark Plateau, Arkansas River Valley, and Gulf of Mexico Coastal Plain and found that these mounds have a regionally consistent textural asymmetry such that there is a significant excess of coarse-grained sediment within their northwest flanks. We interpret this asymmetry as evidence of an eolian depositional origin of these mounds and conclude they are relict nebkhas (coppice dunes) deposited during protracted middle to late Holocene droughts. These four mounds yield optically stimulated luminescence ages between 2400 and 700 yr that correlate with well-documented periods of eolian activity and droughts on the southern Great Plains, including the Medieval Climate Anomaly. We conclude vegetation loss during extended droughts led to local eolian deflation and pimple mound deposition. These mounds reflect landscape response to multi-decadal droughts for the south-central U.S. The spatial extent of pimple mounds across this region further underscores the severity and duration of late Holocene droughts, which were significantly greater than historic droughts.     

Vertical variations of luminescence sensitivity of quartz grains from loess/paleosol of Luochuan section in the central Chinese Loess Plateau since the last interglacial

The provenance of loess in Chinese Loess Plateau, including origin, transport pathways and source areas, has long been one of the most important questions. In this study, the vertical variations of the luminescence sensitivity of quartz grains from the central Chinese Loess Plateau were investigated by using optically stimulated luminescence (OSL) techniques. Our results indicate that the luminescence sensitivity of quartz grains of paleosols can be much higher than that of loess beds. In addition, the quartz grains from the loess-paleosol sequence exhibit a temporal trend in the strength of luminescence sensitivity, characterized by higher values in soils and lower values in loess beds. The OSL sensitivity of quartz grains of the loess-paleosol sequence also shows very similar trend to the magnetic susceptibility and particle size fluctuations, implying that the luminescence sensitivity might be climatic dependent. The possible factors affecting the variations of luminescence sensitivity were discussed including particle size, natural radioactivity, and the provenance of eolian deposits. We suggest that the temporal variations of luminescence sensitivity can be attributed to the retreat-advance of deserts, the different contributions of glacial origin quartz particles associated with mountain processes, and wind patterns during glacial/interglacial cycles. Therefore, the secular variations of luminescence sensitivity of quartz grains are ultimately influenced by past climatic change through its controlling on sediment provenance changes.     

Late Quaternary paleoenvironments and paleoclimatic conditions in the distal Andean piedmont, southern Mendoza, Argentina

The Andean piedmont of Mendoza is a semiarid region covered by extensive and partially vegetated dune fields consisting of mostly inactive aeolian landforms of diverse size and morphology. This paper is focused on the San Rafael plain (SRP) environment, situated in the distal Andean piedmont of Mendoza (34° 30′S), and reports the sedimentology and OSL chronology of two representative exposures of late Quaternary deposits, including their paleoenvironmental and paleoclimatic significance. Eleven facies, including channel, floodplain, fluvio–aeolian interaction, and reworked pyroclastic and aeolian deposits, were described and grouped into two facies associations (FA1 and FA2). FA1 was formed by unconfined sheet flows, minor channelized streams and fluvial–aeolian interaction processes. FA2 was interpreted as aeolian dune and sand-sheet deposits. OSL chronology from the SRP sedimentary record indicates that between ca. 58–39 ka and ca. 36–24 ka (MIS 3), aggradation was governed by ephemeral fluvial processes (FA1) under generally semiarid conditions. During MIS 2, the last glacial maximum (ca. 24–12 ka), a major climatic shift to more arid conditions is documented by significant aeolian activity (FA2) that became the dominant sedimentation process north of the Diamante–Atuel fluvial system. The inferred paleoenvironmental conditions from the SRP sections are in broad agreement with regional evidence.     

The last interglacial sea-level high stand on the southern Cape coastline of South Africa

The continental margin of southern South Africa exhibits an array of emergent marginal marine sediments permitting the reconstruction of long-term eustatic sea-level changes. We report a suite of optical luminescence ages and supplementary amino acid racemization data, which provide paleosea-level index points for three sites on this coastline. Deposits in the Swartvlei and Groot Brak estuaries display tidal inlet facies overlain by shoreface or eolian facies. Contemporary facies relations suggest a probable high stand 6.0-8.5 m above modern sea level (amsl). At Cape Agulhas, evidence of a past sea-level high stand comprises a gravel beach (ca. 3.8 m amsl) and an overlying sandy shoreface facies (up to 7.5 m amsl). OSL ages between 138 ± 7 ka and 118 ± 7 ka confirm a last interglacial age for all marginal marine facies. The high stand was followed by a sea-level regression that was associated with the accumulation of eolian dunes dating to between 122 ± 7 ka and 113 ± 6 ka. These data provide the first rigorous numerical age constraints for last interglacial sea-level fluctuations in this region, revealing the timing and elevation of the last interglacial high stand to broadly mirror a number of other far-field locations.     

Luminescence dating of scoria fall and lahar deposits from Somma–Vesuvius,Italy

Luminescence dating has been applied to scoria and lahar deposits from Somma–Vesuvius, Italy. Samples include scoria from the AD472 and 512 (or 536) eruptions and lahar deposits. In order to find a stable luminescence signal which is less affected by anomalous fading, infrared stimulated luminescence (IRSL) signals at elevated temperatures after bleaching with IR at 50 °C (termed post-IR IRSL; pIRIR) were tested at different preheat and elevated stimulation temperatures. The fading rates of both IRSL and pIRIR signals reduced dramatically with increasing preheat and pIRIR stimulation temperatures. A pIRIR signal measured at 290 °C after a preheat at 320 °C (60 s) and an IR stimulation at 50 °C (100 s) was selected to calculate the equivalent dose (D_e). The gamma spectrometry results indicate that the U-series nuclides are not in equilibrium and there is a large ²²⁶Ra excess. The dose rates and ages were calculated by assuming a ²²⁶Ra excess (over its parent ²³⁰Th) at deposition, and that this unsupported excess then decayed to the present level. The resulting luminescence ages of the two scoria samples agreed with the expected ages, and the ages of the lahar deposits indicate that they are associated with the AD1631 eruption.     

Micro-hole and multigrain quartz luminescence dating of Paleodeltas at Lake Fryxell,McMurdo Dry Valleys (Antarctica), and relevance for lake history

Relict (perched) lacustrine deltas around the perennially ice-covered lakes in the Taylor Valley, Antarctica, imply that these lakes were up to 40 times larger in area than at present since the last glacial maximum (LGM). These deltas have been used to constrain ice-margin positions in Taylor Valley, and the boundaries of the proposed LGM ice-damned Glacial Lake Washburn. The timing of these high lake levels has depended on ¹⁴C chronologies of algal layers within relict lacustrine deltas. To provide additional geochronometric data for the post-LGM lake-level history, we applied photon-stimulated-luminescence (PSL) sediment dating to polymineral fine silt and sand-size quartz from 7 perched-delta and 3 active-delta sites of different elevations along 3 major meltwater streams entering Lake Fryxell. Our PSL dating of 4 quartz-sand samples from core tops in the seasonal ice-free moat of Lake Fryxell (elevation ∼18 m a.s.l.) and two core-top moat samples from the seasonal moat of Lake Vanda in nearby Wright Valley establish that adequate PSL clock zeroing (by daylight) occurs in regional, modern shoreline deposits. Minimum-age micro-hole PSL results from the moats are consistently near 100 a. Minimum-age micro-hole age estimates for the deltas range from ∼50 to 100 a near the present lake level up to 13.4 ± 1.3 ka at 240 m. These are systematically younger than the comparable, reservoir-uncorrected, ¹⁴C ages that range from 7 ka (cal yr BP) to 13 ka (cal yr BP) near lake level up to 20 ka (cal yr BP) at 220–240 m elevation. Our results indicate the occurrence of a dramatic discrepancy between PSL minimum-age and ¹⁴C age estimates that is presently unresolved.     

Post-IR IRSL290 dating of K-rich feldspar sand grains in a wind-dominated system on Sardinia

The reliability of a post-IR elevated temperature IRSL (290 °C; pIRIR₂₉₀) is tested on wind-blown, sand-sized (180–250 μm) K-rich feldspar grains. The pIRIR₂₉₀ ages were compared with quartz SAR-OSL data, other independent age controls and historical information. Three study areas along the coast of Sardinia (Italy) were selected: the south Alghero coast, the Bue Marino cave (E Sardinia) and the Alghero bay (NW Sardinia). Along the south Alghero coastline a thick dunefield system is widely recognised in the literature to represent the beginning of the last glacial phase (post 80 ka). From a single block sand-sized grains for quartz SAR-OSL and K-feldspar pIRIR dating were collected. The natural quartz SAR-OSL sample lies below the saturation limit of the dose response curve (D_e < 2xD₀) giving a reliable age of 76 ± 6 ka. The fading-uncorrected pIRIR₂₉₀ age of 73 ± 5 ka is in good agreement with the quartz result. A further test on older samples was carried out on the sedimentary succession at Bue Marino cave, which includes a sandy wind-blown unit, enclosed between two calcareous crusts. U-series dates of crusts constrain the aeolianite formation between ∼130 and ∼86 ka. The quartz SAR-OSL signals for aeolianite samples lies close to saturation and the resulting ages underestimate the independent age control. Instead, uncorrected pIRIR₂₉₀ ages on K-feldspar extracts point to a formation of the wind-blown unit between ∼100 and ∼80 ka, in good agreement with the U-series data. The bleachability of the pIRIR₂₉₀ signal was further investigated using samples from a modern coastal barrier system backing the Alghero bay. The dunefield was stabilized by plantation during the 1950s. The quartz SAR-OSL ages span from 2450 ± 170 years to 60 ± 13 years ago, consistent with the known coastal barrier stabilization. The pIRIR₂₉₀ ages indicate an offset up to ∼1000 years. We can conclude that the pIRIR₂₉₀ method on sand-sized K-feldspar grains shows great promise for samples at or beyond the quartz OSL age limit but should not be applied to Late Holocene or modern deposits.     

Toxicity-directed Fractionation of Tannery Wastewater Using Solid-phase Extraction and Luminescence Inhibition in Microtiter Plates

A four-step solid-phase extraction (SPE) method is presented for toxicity-directed fractionation of industrial wastewater. This fractionation procedure serves as a key step for identifying unknown organic toxicants in complex samples. Toxicity was determined as luminescence inhibition of Vibrio fischeri using microtiter plates. This method was compared to standard tests in glass cuvettes using both 37 standard chemicals and 24 wastewater fractions with EC₅₀ values covering five orders of magnitude. Results of both methods correlated well. 22 tannery wastewater samples were sequentially extracted using C₁₈e and polystyrene-divinylbenzene phases in combination with pH-changes. Final solid-phase filtrates showed low inhibition, so toxicity of inorganics could be neglected. Using 1/EC₅₀ values, the SPE eluates showed clearly different toxicity patterns. Even in eluates of the fourth extraction step, high toxic effects could be observed. In several cases, luminescence inhibition was increasing at the anaerobic treatment step compared to the corresponding untreated samples. After aerobic treatment, toxicity of most wastewater fractions was greatly diminished. HPLC/DAD analyses of the wastewater fractions showed a fair separation concerning compound polarity. However, the samples were still too complex to identify single compounds responsible for the detected toxicity. Therefore, a further clean-up step accompanied with toxicity testing is needed.     

Features of coated diamonds from the Snap Lake/King Lake kimberlite dyke, Slave craton, Canada, as revealed by optical topography

Confocal photoluminescence (PL) and local absorption spectroscopy were used to study the types and spatial distribution of point defects in coated diamonds, the input of which is about 30% in the Snap Lake deposit, Canada. Nitrogen concentration is on the level of several hundreds of ppm in the core, with a nitrogen-poor layer in its outer part, whereas in the coat it is usually several times higher as a result of fast growth. Nitrogen defects in the core are strongly aggregated with N3, B and B′-forms dominating, whereas A-defects are typical of the coat. The rounded shape of the coated diamonds is a result of the combined effect of partial dissolution of the octahedral core and the “abnormal” growth of the coat, which produces a fibrous structure. Analysis of PL and PL excitation spectra showed that structureless yellow-green PL of the coat is likely to be due to nickel-nitrogen complexes with their fine structure broadened in the strain fields. The presence of irradiation/annealing products such as vacancies V⁰ and nitrogen-vacancy complexes NV⁻, N₂V₂ shows that the diamonds studied have undergone post-growth ionizing irradiation with further low-temperature annealing in natural conditions.