Towards Efficient Detection of Small Near-Earth Asteroids Using the Zwicky Transient Facility (ZTF)

We describe ZStreak, a semi-real-time pipeline specialized in detecting small, fast-moving near-Earth asteroids (NEAs) that is currently operating on the data from the newly-commissioned Zwicky Transient Facility (ZTF) survey. Based on a prototype originally developed by Waszczak et al. (2017) for the Palomar Transient Factory (PTF), the predecessor of ZTF, ZStreak features an improved machine-learning model that can cope with the $10\times$ data rate increment between PTF and ZTF. Since its first discovery on 2018 February 5 (2018 CL), ZTF/ZStreak has discovered $45$ confirmed new NEAs over a total of 232 observable nights until 2018 December 31. Most of the discoveries are small NEAs, with diameters less than $\sim100$ m. By analyzing the discovery circumstances, we find that objects having the first to last detection time interval under 2 hr are at risk of being lost. We will further improve real-time follow-up capabilities, and work on suppressing false positives using deep learning.Comment: PASP in pres

Towards Efficient Detection of Small Near-Earth Asteroids Using the Zwicky Transient Facility (ZTF)

We describe ZStreak, a semi-real-time pipeline specialized in detecting small, fast-moving, near-Earth asteroids (NEAs), which is currently operating on the data from the newly commissioned Zwicky Transient Facility (ZTF) survey. Based on a prototype originally developed by Waszczak et al. (2017) for the Palomar Transient Factory (PTF), the predecessor of ZTF, ZStreak features an improved machine-learning model that can cope with the 10× data rate increment between PTF and ZTF. Since its first discovery on 2018 February 5 (2018 CL), ZTF/ZStreak has discovered 45 confirmed new NEAs over a total of 232 observable nights until 2018 December 31. Most of the discoveries are small NEAs, with diameters less than ~100 m. By analyzing the discovery circumstances, we find that objects having the first to last detection time interval under 2 hr are at risk of being lost. We will further improve real-time follow-up capabilities, and work on suppressing false positives using deep learning

Dwindling vanadium in seawater during the early Cambrian, South China

Elemental vanadium (V), an essentially redox-sensitive metal in seawater, has had a significant impact on the understanding of the evolution of the atmosphere-ocean system throughout the history of the Earth. In fact, the geochemical cycle of V in early Cambrian seawater may have had an influence on the Chengjiang Biota in South China; however, it has not yet been well established. Given the authigenic vanadium accumulation is sensitive to the redox conditions of seawater, here, to constrain the geochemical cycle of V in seawater during the early Cambrian, the Mo, U and total organic carbon (TOC) distributions with high-resolution samples from both the outer shelf and slope facies (e.g., the Duoding and Longbizui sections), are applied to evaluate the redox conditions of ambient seawater. The Mo-U relationships indicate that the redox conditions of the mid-depth seawater evolved in a systematic way in South China, transitioning from an Fe-Mn reduction zone to anoxic/intermittently euxinic states and then to oxic conditions during the early Cambrian. As a consequence, the authigenic V enrichment, constrained by the marine redox conditions, was mainly controlled by the Fe-Mn particulate shuttle and the reduction and adsorption of organic matter in anoxic/euxinic conditions. However, the decoupling among V, Mo, U and TOC under anoxic/euxinic conditions suggests a dwindling vanadium concentration in the early Cambrian seawater of South China. The scavenging efficiency of V from seawater is much higher than those of Mo and U under anoxic/euxinic conditions. Ultimately, these trace elements (e.g., Mo, U, and especially V) in seawater could effectively be regulated and adjusted to a reasonable level under the widespread anoxic/euxinic conditions. The drawdown of trace elements in seawater might provide an earlystage preparation of the marine environment for the subsequent Chengjiang Biota

Enrichment of Niobium and Titanium from Kaolin Using an Acid-Alkali Leaching Process

Niobium is a strategic resource because it is useful in a wide number of applications and its global distribution is uneven. It has been reported that kaolin clay from the bottom of the Xuanwei Formation, the Late Permian sequences in southwest China, contains Nb. In this paper, the major, trace, and mineral compositions of kaolin clay were characterized using XRF, ICP-MS, and XRD. The results show that it is mainly composed of kaolinite, anatase, and rutile, with a chemical composition of Al2O3 34.38pct, SiO2 39.97pct, TiO2 8.79pct, Fe2O3 3.24pct, and Nb 491g/g. A process including calcination treatment and acid-alkali leaching with HCl and NaOH was employed to separate Al, Fe, and Si in a leaching solution and to enrich Nb and Ti in the residue. The experimental results indicated that the reaction temperature played a vital role for Al and Fe extractions from acid leaching, while the concentration of alkali was the key factor for Si extraction. Under the optimal conditions, the contents of Nb and Ti in the final product were 4280g/g and 80.5pct, respectively

Reconstruction of early Cambrian ocean chemistry from Mo isotopes

International audienceThe Neoproterozoic–Cambrian transition was a key time interval in the history of the Earth, especially for variations in oceanic and atmospheric chemical composition. However, two conflicting views exist concerning the nature of ocean chemistry across the Precambrian–Cambrian boundary. Abundant geochemical evidence suggests that oceanic basins were fully oxygenated by the late Ediacaran, while other studies provide seemingly conflicting evidence for anoxic deep waters, with ferruginous conditions [Fe(II)-enriched] persisting into the Cambrian. Here, two early Cambrian sedimentary platform and shelf-slope sections in South China were investigated to trace early Cambrian ocean chemistry from Mo isotopes. The results reveal that early Cambrian sediments deposited under oxic to anoxic/euxinic conditions have δ98/95Mo values ranging from −0.28‰ to 2.29‰, which suggests that early Cambrian seawater may have had δ98/95Mo values of at least 2.29‰, similar to modern oceans. The heaviest and relatively homogeneous δ98/95Mo values were recorded in siltstone samples formed under completely oxic conditions, which is considered that Mn oxide-free shuttling was responsible for such heavy δ98/95Mo value. Further, combined with Fe species data and the accumulation extent of Mo and U, the variation of δ98/95Mo values in the two studied sections demonstrate a redox-stratified ocean with completely oxic shallow water and predominantly anoxic (even euxinic) deeper water having developed early on, which eventually became completely oxygenated. This suggests that oceanic circulation at the time became reorganized, and such changes in oceanic chemistry may have been responsible for triggering the “Cambrian Explosion” of biological diversity

Cadmium isotopic evidence for the evolution of marine primary productivity and the biological extinction event during the Permian-Triassic crisis from the Meishan section, South China

International audienc

Age and metal source of orogenic gold deposits in Southeast Guizhou Province, China: Constraints from Re–Os and He–Ar isotopic evidence

The orogenic gold deposits in Southeast Guizhou are an important component of the Xuefeng polymetallic ore belt and have significant exploration potential, but geochronology research on these gold deposits is scarce. Therefore, the ore genetic models are poorly constrained and remain unclear. In the present study, two important deposits (Pingqiu and Jinjing) are investigated, including combined Re–Os dating and the He–Ar isotope study of auriferous arsenopyrites. It is found that the arsenopyrites from the Pingqiu gold deposit yielded an isochron age of 400 ± 24 Ma, with an initial 187Os/188Os ratio of 1.24 ± 0.57 (MSWD = 0.96). An identical isochron age of 400 ± 11 Ma with an initial 187Os/188Os ratio of 1.55 ± 0.14 (MSWD = 0.34) was obtained from the Jinjing deposit. These ages correspond to the regional Caledonian orogeny and are interpreted to represent the age of the main stage ore. Both initial 187Os ratios suggest that the Os was derived from crustal rocks. Combined with previous rare earth element (REE), trace elements, Nd–Sr–S–Pb isotope studies on scheelite, inclusion fluids with other residues of gangue quartz, and sulfides from other gold deposits in the region, it is suggested that the ore metals from Pingqiu and Jinjing were sourced from the Xiajiang Group. The He and Ar isotopes of arsenopyrites are characterized by 3He/4He ratios ranging from 5.3 × 10−4 Ra to 2.5 × 10−2 Ra (Ra = 1.4 × 10−6, the 3He/4He ratio of air), 40Ar*/4He ratios from 0.64 × 10−2 to 15.39 × 10−2, and 40Ar/36Ar ratios from 633.2 to 6582.0. Those noble gas isotopic compositions of fluid inclusions also support a crustal source origin, evidenced by the Os isotope. Meanwhile, recent noble gas studies suggest that the amount of in situ radiogenic 4He generated should not be ignored, even when Th and U are present at levels of only a few ppm in host minerals. Keywords: Re–Os geochronology, Arsenopyrite, He–Ar isotopes, Pingqiu, Jinjing, Southeast Guizhou Province, Chin

Determination of low bromine (Br) and iodine (I) in water with low-to high-salinity content using ICP-MS

A newly developed method for the determination of bromine (Br) and iodine (I) in low- to high-salinity aqueous samples by ICP-MS was established. Matrix related isobaric interferences ((ArK)-Ar-40-K-39 and (ArArH)-Ar-40-Ar-38-H-1 on Br-79) have been quantitatively estimated in the kinetic energy discrimination (KED) operation mode and the standard (STD) mode; it was shown that such interferences can be efficiently eliminated using the KED mode with He as a collision reaction gas. In addition, samples with high salt concentrations were analysed after pre-treatment using H-form cation-exchange resin with low dilution factors (10 or 20), rather than the high dilution factors (>200) reported in previous studies. The values for the total procedure blank of Br and I from this process were 0.784 and 0.015 mu gL(-1), respectively. The Br and I limits of detection (LOD) and spiked recoveries for this ICP-MS method were 0.1104 and 0.0013 mu g L-1 and 98.9-100.9% and 98.0-102.9%, respectively. The present method was successfully applied for the rapid and direct determination of Br and I in seawater and other aqueous samples. (C) 2018 Elsevier B.V. All rights reserved