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In recent years, Beijing has been shown to suffer one of the most serious air pollution problems of any major world city. The concentrations of particulate matter (PM) pollutants, PM 2.5–10 and PM 2.5 , are commonly used as air pollution indexes. We conducted a detailed environmental magnetism study to investigate possible sources of air pollution in Beijing, China, using 283 pairs of the PM 2.5 and PM 2.5–10 samples collected daily from July 2010 to June 2011. Rock magnetic measurements, including magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization, saturation isothermal remanent magnetization, hysteresis loops, first-order reversal curves (FORCs), and thermomagnetism, indicate that the main magnetic mineral is low-coercivity pseudo-single domain (PSD) magnetite. Scanning electron microscope (SEM) observations and energy dispersive X-ray spectroscopy (EDS) analyses on the PM indicate that the major magnetic phase is coarse-grained magnetite, which is most likely from automobile exhausts and braking system debris. Magnetic parameters of PM 2.5 and PM 2.5–10 show significant seasonal patterns that may be attributed to domestic heating enhancing magnetization of the PM during late autumn to early spring. Power spectral analyses and box–whisker plots indicate that the magnetic parameters have strong weekly variations that may be due to traffic emissions. These results indicate that magnetic parameters can be used as efficient proxies for monitoring Beijing's air pollution, and that the atmospheric environment may be improved by controlling vehicle emissions. [ABSTRACT FROM AUTHOR]

A high-precision time framework is critical for improving our understanding of three major events: the Late Ordovician mass extinction, the Hirnantian glaciation, and the Hirnantian isotopic carbon excursion (HICE). In the present study, we conducted detailed cyclostratigraphic analysis of a high-resolution (1–2-cm intervals) anhysteretic remanent magnetization series obtained from the Wanhe section in South China, covering the lower Katian through Hirnantian. Power spectra and derived average spectral misfit results show that the section records the ensemble of Milankovitch cycles with 405-kyr (long-eccentricity), 93–125-kyr (short-eccentricity), 33.8-kyr (main obliquity), and 17–22-kyr (precession) periods. The obliquity period of 33.8 ± 0.46 kyr indicates a precession constant k of 57.19 ± 0.53 arcsec/yr, a length of day of 22.37 ± 0.12 h, and an Earth–Moon distance of 375,330 ± 722 km (vs. 384,000 km today) during the Late Ordovician (445 Ma). The ratios of obliquity band power to total power reveal periodicities of 1.32 Myr for the s 4 – s 3 term and 173.4 kyr for the s 3 – s 6 term. Aided by the highly fluctuating magnetic susceptibility (MS), we recognized a series of 1.32-Myr obliquity-forced glacio-eustatic cycles with three intervals of sea-level rise and climate warming trend characterized by high MS values and two episodes of sea-level fall and climate cooling trend before the Hirnantian. The 405-kyr and subsequent 33.8-kyr calibrations produce an ~7.36-Myr floating astronomical time scale (FATS) for the studied succession, indicating that the estimated durations for the Hirnantian Stage, the worldwide Hirnantian glaciation, and the first and second phases of the Late Ordovician mass extinction were ~1225 kyr, ~830 kyr, ~440 kyr, and ~540 kyr, respectively. This work provides a reliable high-resolution time framework for further investigation of the major geological events occurred in the Late Ordovician, and improves our knowledge of Solar System behaviour and Earth–Moon history during that period. • An ~7.36 Myr ATS was constructed for the early Katian through Hirnantian. • The durations of Hirnantian Stage, glaciation and mass extinction were estimated. • Earth–Moon evolution was constrained for the Late Ordovician. • Obliquity forcing controlled the Late Ordovician glacio-eustasy. [ABSTRACT FROM AUTHOR]

The Cambrian is the first period of the Phanerozoic during which numerous major geological and biological events occurred. Understanding these events requires a high-resolution time scale. The Luoyixi section in Guzhang (Hunan Province, China) is the global stratotype section and point (GSSP) for the Guzhangian Stage. Here, magnetic susceptibility and δ13C data were used to conduct cyclostratigraphic analyses covering the upper Drumian through lower Guzhangian stages. The results of the power spectral analyses and average spectral misfit analyses indicate that the 25–25.53 m, 6.25–6.91 m, 1.90–2.03 m, and 1.08–1.19 m sedimentary cycles may represent long-eccentricity, short-eccentricity, obliquity and precession cycles, respectively. A ~1400 kyr floating astronomical time scale was constructed using the stable 405-kyr eccentricity cycles to calibrate the agnostoid trilobite zones. The obtained fundamental obliquity period (30.7 ± 0.7 kyr) implies 370,180 ± 1220 km (vs. 384,000 km for present day) for the Earth–Moon distance and 21.58 ± 0.18 h (vs. 23.93 h for present day) for the length of day during the middle Cambrian (500 Ma). • Reliable Milankovitch cycles were identified in the Middle Cambrian marine strata. • An ~1400 kyr ATS was constructed for the Drumian–Guzhangian transition. • The durations of the two complete agnostoid trilobite biozones were estimated. • Deep-time evolution of the Earth–Moon system was reconstructed. [ABSTRACT FROM AUTHOR]