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Abstract A cooling trend during the Middle Ordovician may have resulted in significant biotic, atmospheric and hydrologic changes, but the exact timing and forcing of this climate event still remain largely ambiguous. Here, we present astronomically calibrated magnetic susceptibility (MS) and gamma ray (GR) data from the shale and carbonate successions of the Kalpin area in the Tarim Basin, NW China to study the Middle Ordovician climate. The spectral analyses of the 405-kyr calibrated MS and GR time series reveal periodicities close to 405 (calibrated), 100, 31 and 19 kyr, supporting a Milankovitch forcing for the sedimentary cyclicity. The eccentricity and obliquity amplitude modulation cycles show main periodicities of ~2.4 and ~1.2 Myr, respectively. A cooling event along with the middle Darriwilian isotope carbon excursion (MDICE) appears to have been initiated by the alignment of the eccentricity and obliquity amplitude minima at 4.07 Myr prior to the Darriwilian/Sandbian (D/S) boundary. This climate event was in pace with high-amplitude obliquity oscillations during a period when the 1.2 Myr obliquity amplitude modulation cycles controlled the global third-order eustatic sequences. The termination of this cooling event corresponding to a global third-order highstand was initiated by an eccentricity oscillation maximum at 0.63 Myr prior to the D/S boundary. Subsequent climate alleviation was dominated by eccentricity forcing until the earliest Sandbian. We suggest that although the climate changes have been primarily associated with the CO 2 level, a specific sequence of astronomical variations during the Middle Ordovician was responsible for the time when the critical threshold was crossed. Highlights • Onset and termination of a cooling event in the Middle Ordovician were dated. • Obliquity forcing dominated this cooling event. • 1.2 Myr obliquity modulation cycles controlled the third-order eustatic sequences. • Onset and termination of cooling event were controlled by astronomical forcing. [ABSTRACT FROM AUTHOR]

The Late Paleozoic Ice Age (ca. 335–260 Ma, LPIA) has long been considered as an analogy for the Cenozoic ice age since the Oligocene. The impact of astronomical forcing on the LPIA glaciation has been hampered due to the low-resolution (multi-million year scale) time framework. In the present study, high-resolution cyclostratigraphy based on magnetic susceptibility (MS), covering the Serpukhovian to late Moscovian icehouse climate, has been investigated in the Luokun section of South China. Power spectral analysis of the MS series reveals 3.44–4 m, 0.8–1.07 m, 0.3–0.32 m, and 0.17–0.19 m thick sedimentary cycles. Based on the available biostratigraphic constraints, calibrating the 3.44–4 m cycles to the 405 kyr eccentricity cycles indicates short eccentricity (136 and 100 kyr), short obliquity (34 kyr), and precession (19 and 15.9 kyr) orbital bands in addition to long eccentricity (405 kyr) band. We assigned the basal Serpukhovian and Moscovian stages in Luokun with the numerical ages from Geological Time Scale 2012 to construct two floating time scales ranging from 331.55 ± 0.5 Ma to 323.2 ± 0.5 Ma, and from 315.34 ± 0.35 Ma to 310.17 ± 0.35 Ma, respectively. The modulation of main obliquity ( s 4 – s 3 term) has a main periodicity of ∼1200 kyr. The modulation of ∼100 kyr eccentricity ( g 4 – g 3 term) shows a main periodicity of ∼2400 kyr with subordinate periodicities of ∼1620 and ∼1200 kyr for the Serpukhovian, and a main periodicity of ∼1600 kyr for the Moscovian. They may provide the geological evidence for a chaotic resonance associated with interactions between the orbits of Mars and the Earth in the Carboniferous. A duration of 7.68 ± 0.15 Myr was estimated for the Serpukhovian Stage. Eight higher accumulation rate events due to glacioeustatic drawdown were temporally constrained, and show close correspondence to far-field and near-field reconstructions of the LPIA glaciation. Glacioeustasy was paced with 405-kyr-long eccentricity and 1.2-Myr obliquity amplitude cycles during the Serpukhovian and Moscovian stages, likely indicating the nature in the warmer icehouse world similar to that of the Oligocene to Pliocene. [ABSTRACT FROM AUTHOR]

High-resolution (930 samples) magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) analyses were conducted on the ~ 49 m thick Middle Permian Maokou Formation at Dukou, South China. Spectral analysis of covariant MS and ARM series reveal Milankovitch cycles with eccentricity, obliquity, and precession. A 5.7 myr floating 405 kyr eccentricity cycle-calibrated astronomical time scale was constructed and used as a geochronometer for estimating the durations of the conodont zones. The results indicate that the durations of the Jinogondolella postserrata , J. altudaensis , J. prexuanhanensis , and J. xuanhanensis conodont zones were 490 kyr, 560 kyr, 820 kyr, and 750 kyr, respectively. The 405 kyr-calibrated MS and ARM series also show prominent ~ 1 myr cyclicity, which may correspond to the secular frequencies of Earth and Mars, s 4 –s 3 , in the Middle Permian. The early Capitanian time interval was synchronous with the Kamura cooling event, and the accentuated obliquity cycling may signal ice-sheet expansion. The modulations of the obliquity have a close relationship with third-order eustatic sequences of the Wordian and Capitanian stages, suggesting a glacioeustatic origin during the Middle Permian. [ABSTRACT FROM AUTHOR]

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]

Abstract: The Early Cretaceous Jehol Biota in northeastern China provides an evolutionary window for ‘feathered’ dinosaurs, primitive birds, insects and early flowering plants. It also provides critical information for the biodiversity changes of the Early Cretaceous terrestrial ecosystem. Here we report a time series analysis for the 11.2-m-thick, fossil-bearing lacustrine deposits at the Sihetun section in western Liaoning, northeastern China on the basis of high-resolution magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) measurements. A hierarchy of sedimentary cycle bands of 120–260cm, 50–67cm and 18–42cm was recorded in the MS and ARM series. With available radioisotope age constraints from the same section, sedimentary cycles of 120–260cm, 50–67cm and 18–42cm were interpreted as Milankovitch cycles of short eccentricity (130 and 95kyr), obliquity (36.6 and 46kyr), and precession (22.1, 20.9 and 18kyr), respectively. The 100kyr-tuned ‘floating’ astronomical time scale indicates that the duration of the 11.2-m-thick section is ~0.67Myr and the average depositional rate is ~1.70cm/kyr. The duration of the 1.8-m-thick, main fossil-bearing interval that contains 8 beds of ‘feathered’ dinosaur/primitive bird fossils can be estimated as short as 150kyr. The results suggest that climate fluctuations manifested in paleobotanical, sedimentological and geochemical records of the Yixian Formation may have been controlled by orbital forcing during Early Cretaceous. [Copyright &y& Elsevier]

Abstract: The first complete Early Turonian–Early Campanian lacustrine succession has been recovered from the SK-I south (SK-Is) borehole in the Songliao Basin (SLB), northeastern China. We conducted a detailed cyclostratigraphic study of natural gamma-ray (GR) log, thorium (Th) log, and magnetic susceptibility (MS) data from this core. Spectral analysis of the upper Quantou Formation (K2q3+4), Qingshankou Formation (K2qn), Yaojia Formation (K2y), and lower Nenjiang Formation (K2n1+2) reveals a hierarchy of meter- to decameter-scale cycling in the data. The wavelength ratios of the cycles in these stratigraphic units are ~20:5:2:1, corresponding with those of Milankovitch cycle periods of 405kyr (long eccentricity):100kyr (short eccentricity):37kyr (obliquity):20kyr (precession), indicating astronomical control on sedimentation. An astronomical time scale (ATS) was established by tuning interpreted 405kyr cycles to a 405kyr orbital eccentricity target curve, and to four SIMS U–Pb zircon radioisotope ages. This ‘absolute’ ATS provides precise numerical ages for stratigraphic boundaries, biozones, geological and geophysical events, and serves as a basis for correlation of strata and events between marine and terrestrial systems. The ages of the C33r/C34n geomagnetic polarity boundary in K2n2 and three short reversal events in K2y are estimated as 83.633Ma, 84.819–84.862Ma, 84.982–85.092Ma and 85.240–85.629Ma, respectively. Long-period amplitude modulations in the obliquity and eccentricity bands of the 405-kyr-tuned GR-Th series provide strong evidence that long-period orbital forcing influenced climate change and depositional processes in the SLB. The extracted amplitude modulations provide evidence that the orbits of Earth and Mars were not in secular resonance, and were undergoing chaotic interactions during this time, although the modulations do not match those of recent astronomical models. [Copyright &y& Elsevier]

The "hothouse" Triassic climate provides a key window to study megamonsoon systems. However, high-quality paleoclimate proxy records are rarely reported from the Tethys realm, where the seasonal meridional migration of the intertropical convergence zone (ITCZ) should be the most remarkable. Here, continuous and well-dated proxy records are used to study monsoon activity in the northeastern Tethys from the Middle Triassic lacustrine sediments (Ch7 black shale, Yanchang Formation) in the Ordos Basin (China). The proxies, including natural gamma-ray intensity, magnetic susceptibility, and element concentrations and ratios (U, K, Zr/Al, Zr/Rb and Sr/Rb), document a strong precession signal in the sediments. We propose that the periodic deposition of the Ch7 black shale occurred in response to intensifications in a monsoon-driven climate enhanced by the early Ladinian warming event. Climate variability in the Ordos Basin (~25°N) reflects the harmonics of ~100 kyr, ~20 kyr and ~10 kyr cycles and is highly coherent with solar insolation at 9° latitude, suggesting that this monsoon system might have been modulated by tropical solar insolation. The dominance of tropical climate processes in this mid-latitude monsoon region can be attributed to the dramatic dynamics of the ITCZ and intense monsoon circulation in the Tethys realm. • Deposition of Ch7 black shale was paced by the precession-controlled monsoon activity. • Warming event in the early Ladinian triggered Ch7 black shale deposition. • Semi-precession signal in the Ordos Basin responded to tropical insolation forcing. • Tropical insolation was the dominant driver of the Tethyan monsoon. [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]

[Display omitted] • A newly constructed astronomical time scale constrains the duration of the GICE to ∼ 0.82 Myr. • The duration of the Middle Ordovician stratigraphic gap in South China is ∼ 1.38 Myr. • Positive 13C carb excursions during the MDICE and GICE were associated with astronomical forcing. The Middle–Late Ordovician transition was one of the most critical periods throughout the Earth's history, and it involved paleoclimate changes and biological turnover. Here, we conducted cyclostratigraphic analysis on the magnetic susceptibility (MS) from the Kuniutan and Miaopo formations in the Zhenjin section and the Pagoda and Linhsiang formations in the Puxihe section in Yichang, South China. We constructed an astronomical time scale to understand the astronomically forced paleoclimate changes during this key interval. Spectral analyses on the MS series show that the thickness ratios of different sedimentary cycles in the studied sections are consistent with those of Milankovitch cycles during the Middle and Late Ordovician. The floating astronomical time scale of the studied sections was constructed based on astronomical tuning to 405-kyr eccentricity cycles, providing an estimated duration of ∼ 0.82 Myr for the Guttenberg isotopic carbon excursion (GICE). A high-precision and continuous astronomical time scale has previously been established in the Ordovician marine sediments in the Tarim Basin. The cyclostratigraphic correlation of sedimentary successions between the South China Block and Tarim Basin reveals that the duration of the Middle Ordovician gap in South China is ∼ 1.38 Myr. Alignment of the maxima of the ∼ 1.2-Myr obliquity cycle and the 405-kyr eccentricity cycle may have resulted in increased weathering inputs and prolonged periods of ocean anoxia, pacing the enhanced organic carbon burials and the positive isotopic carbon excursion during the middle Darriwilian isotope carbon excursion (MDICE) and GICE. [ABSTRACT FROM AUTHOR]

The Cryogenian nonglacial epoch (CNE) spans from the termination of the Sturtian snowball Earth (ca. 659 Ma) to the initiation of the Marinoan snowball Earth (ca. 649.2 Ma). The carbonate sequences formed in low latitudes record paleoclimatic and paleoceanographic changes during the CNE. Three negative carbon isotope (δ13C) excursions, named Rasthof, Tayshir and Trezona, are present at the bottom, middle, and top of the carbonate sequences, bracketing two intervals with highly positive δ13C values. Uranium isotope (δ238U) data from Mongolia reveal ocean redox changes linked to δ13C variations during the CNE, marked by the development of anoxic deep ocean to extensive oxygenation and subsequent deoxygenation. However, the timing and duration of these paleoceanographic events and δ13C excursions have not been adequately investigated. Here, we report new environmental magnetic results of the higher paleo-latitudinal, siliciclastic-dominated Datangpo Formation (Fm) in South China that may help constrain the age and correlation of the CNE geochemical events. We identified four segments of the Datangpo Fm based on the magnetic susceptibility (MS) profile and other environmental magnetic parameters, which are, in ascending order, the ascent segment (Da), lower stable-segment (Db), transition segment (Dc), and upper stable-segment (Dd). These segments are dated by the astronomical time scale as 659–655.6 Ma (Da), 655.6–653.3 Ma (Db), 653.3–652.3 Ma (Dc), and 652.3–649.2 Ma (Dd). Environmental magnetism analyses show that the highest magnetite concentration but lowest fine-grained magnetite contents are present in "Da", followed by "Dd" and "Db". These results suggest a sea-level fall and a potential decrease in oxygenation after the deposition of the transition segment (Dc), implying that a cooling climate started ∼4 Myr before the Nantuo glaciation (Marinoan snowball Earth). Ocean redox variations revealed by environmental magnetism in the Datangpo Fm are consistent with those reported from the low-latitudinal carbonate sequences. "Da" likely corresponds to the Rasthof δ13C excursion and "Dc" corresponds to the Tayshir δ 13C excursion; whereas "Db" and "Dd" probably correspond to the two intervals with positive δ 13C values. • Four segments of the Cryogenian nonglaciatial epoch in South China are identified and the time of each segment is constrained. • Environmental magnetism analyses show a climate cooling ∼4 Myr before the Nantuo glaciation (or Marinoan snowball Earth). • Siliciclastic depositions in South China are linked to carbonate depositions in low-latitude continents. [ABSTRACT FROM AUTHOR]

Recent studies of the upper Gaoyuzhuang Formation (Fm) (ca. 1600–1540 Ma) in north China have suggested that Earth underwent an oxygenation event associated with a negative δ13C carb excursion and this event may have led to the expansion of eukaryotic life. However, the duration of this negative δ13C carb excursion, which is crucial to understand its origin, remains uncertain. Here, we report a floating astronomical timescale based on Milankovitch cycles extracted from the carbonate-dominated strata of the Member 3 of the Gaoyuzhuang Fm in north China, in which the oxygenation event is recorded. High-resolution magnetic susceptibility, anhysteretic remnant magnetization and saturation isothermal remnant magnetization series were obtained from the stratigraphic sections in the Jixian and Yanqing regions. Rock magnetic experiments suggest that the magnetic parameters are dominated by the detrital materials whose flux was likely controlled by orbitally forced climatic changes. Our results for the first time reveal well-constrained eccentricity, obliquity, and precession cycles from the Gaoyuzhuang Fm and demonstrate that the ca. 1560 Ma negative δ13C carb excursion and associated transient oxygenation event indicated by I/(Ca + Mg) had durations of ~1.7 Myr and ~6.2 Myr, respectively. The ca. 1560 Ma δ13C carb excursion is comparable with the short-term Neoproterozoic excursions in respect of duration, rather than with the long-term ones such as the ca. 574–567 Ma Shuram excursion. The similarity may indicate a common mechanism in origin of the short-term excursions in the Mesoproterozoic and Neoproterozoic time, which deserve testing by more investigations. • Cyclostratigraphic analyses revealed Milankovitch cycles from the ca. 1.56 Ga Gaoyuzhuang Formation • Durations of the δ13C carb excursion and the oxygenation event in the ca. 1.56 Ga are 1.7 Myr and 6.2 Myr, respectively • The duration of this δ13C carb excursion are comparable to the short-term ones in the Neoproterozoic [ABSTRACT FROM AUTHOR]

The Shuram carbon isotope excursion (CIE) is the largest negative CIE in geological history that may have recorded dramatic changes in Earth's surface environments, yet its time, duration, and global synchroneity have been debated. In South China, the Shuram CIE has been correlated with the negative CIE of the upper Doushantuo Formation (named as EN3 or DOUNCE). It is previously suggested that the Shuram CIE in South China stratigraphically consists of the upper Member 3 and Member 4, with an ending age of ca. 551 Ma. Recent studies, however, demonstrated that the EN3 or DOUNCE shifts to near zero or positive carbon isotope (δ13C) values within carbonate rocks of the Doushantuo Member 3. To better understand the duration of this CIE and its spatial variability, we have conducted a high-resolution cyclostratigraphic study using magnetic susceptibility (MS) in two sections: the Zhengjiatang section that preserves a complete EN3 in carbonate rocks of the Doushantuo Member 3 and the Wuhe-Gaojiaxi (WG) drillcore in which the EN3 does not shift to positive δ13C values until the end of the Member 4 black shales. In both sections, power spectral analyses of the MS series of the carbonate rocks reveal periodicities that match well with those of the Milankovitch cycles at 570 Ma. The duration of the Shuram CIE is estimated to be 6.1 ± 0.2 Myr by counting the interpreted 405-kyr sedimentary cycles observed in the Zhengjiatang section. Taking the newly reported Re Os age of 567.3 ± 3.0 Ma as the approximate termination age, the Shuram CIE in the best-preserved section in South China is constrained between ca. 573.4 and 567.3 Ma. Regional correlation, however, shows a ≥ 1 Myr stratigraphic hiatus or unconformity at the top of the Doushantuo Member 3 that separates the Shuram CIE from overlying post-Shuram ẟ13C "excursions". Similar phenomena may exist in the Shuram CIE documented from stratigraphic successions in Oman, Australia, and the Death Valley region of western United States. The results invoke a reevaluation of the stratigraphic range of the Shuram CIE and suggest that the geochemical records documented from the black shales of the Doushantuo Member 4 and its globally correlative intervals may record paleoceanographic conditions millions of years after the Shuram CIE. Comparison of astrochronologically calibrated δ13C profiles reveals significant difference in the shape and amplitude of the Shuram CIE among the sections in South China and globally, which may have been caused by isotopic departure in local depositional environments and/or diagenetic overprints. • The Zhengjiatang section in South China preserves a complete Shuram excursion. • Astronomically estimated duration of 6.1 ± 0.2 Myr for the Shuram excursion. • Portion of the previously defined Shuram excursion may be post-Shuram. • The shape and amplitude of the Shuram excursion differ regionally and globally. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic susceptibility of Chinese loess–paleosol sequences has been extensively used as a reliable paleoclimatic proxy for reconstruction of the Asian summer monsoon system, and its enhancement is usually attributed to neoformation of fine-grained ferrimagnetic particles via pedogenesis, but there is little understanding of either the formation process of such magnetic particles or their actual form and grain sizes. To investigate these problems, scanning electron microscope observations were conducted on magnetic extracts from pristine loess and strongly-pedogenic paleosol samples from Xifeng on the Chinese Loess Plateau. Both magnetic extracts commonly contained coarse-grained detrital magnetite with grain size ranging from a few μm to several tens of μm. However, the magnetic extract from the mature paleosol sample additionally included coarse silicate particles with ultrafine ferrimagnetic inclusions, while that from the pristine loess sample did not. The size of the ferrimagnetic inclusions mainly ranged from tens to hundreds of nanometers. The temperature-dependent susceptibility and hysteresis loops of the paleosol sample, combined with the stratigraphic variations of rock-magnetic parameters, showed that the pedogenic maghemite inclusions should be a potential contributor to magnetic enhancements in Chinese paleosols. The fine-grained ferrimagnetic inclusions have been pedogenically formed by weathering of coarse-grained Fe-bearing silicate minerals. Our proposed magnetic enhancement mechanism is consistent with the accepted rock magnetic result that magnetic enhancement in Chinese paleosols is caused by pedogenic maghemite grains in superparamagnetic and single-domain size regions. The presence of ultrafine ferrimagnetic grains as inclusions within coarse silicate particles is also consistent with Han and Jiang''s (1999) significant experimental result that magnetic enhancement in Chinese paleosols is mainly contributed by the >0.5μm sediment fractions. [Copyright &y& Elsevier]

The marked negative carbon excursion from the upper part of the Member 3 of the Doushantuo Formation (DST3) in South China is generally considered as equivalent of the Shuram excursion. This negative carbon excursion has been identified in numerous sections globally. Due to the lack of chronologic constraints, however, its duration and global synchronicity are obscure and thus much debate still exists regarding to its origin.In order to constrain the duration of the negative carbon excursion from the upper part of DST3, a cyclostratigraphic study has been conducted on two sections around the Huangling Granite (HG), in the eastern Three Gorges region. One section is a segment of the Wuhe-Gaojiaxi (WG) core that was jointly collected by Northwest University and Tokyo Institute of Technology. The WG core is located on the southeast to the HG. The other section is located on the northwest to the HG, named the Zhengjiatang (ZJT) section. The DST3 of the WG core contains two parts in lithology. The upper part is ribbon grey dolomite and the lower is thick-bedded grey dolomite. The DST3 of the ZJT section is more complex in lithology, the top ~5-meter interval is predominated by light grey and pale red dolomite and intervals downward are thin-bedded grey calcite (~9-meter in thickness), thin-bedded purple calcite (18.5-meter in thickness), thin-bedded pink dolomite (~6-meter in thickness) and thick-bedded grey dolomite.The magnetic susceptibility (MS) sequences were achieved from the WG core at 1 cm interval and from the ZJT section at ~5 cm interval. These two MS sequences were comparable. After linear interpolation at 4 cm interval and detrending by subtracting 10% weighted averages, both the MS sequences were ready for cyclostratigraphic analyses, including power spectral analysis, Evolutionary Fast Fourier Transform (FFT) spectrograms, and Gaussian bandpass filtering.The spectral peaks of the MS sequence of the WG core revealed cycle periods of 588-243 cm, 108-78.1 cm, 37.9-24.3 cm, 20.6-15.5 cm and cycle periods of the ZJT section were 325-245 cm, 81.3-60.6 cm, 30.1-19.2 cm, 18.8-14.1 cm. They were consistent and interpreted to correspond to the Milankovitch cycles at ~570 Ma, i.e. eccentricity periods (E, 405 k.y. and e, 100 k.y.), obliquity period (O, 31.7 k.y.) and precession periods (P1, 20.2 k.y., P2, 19.2 k.y. and P3, 16.6 k.y.). The E-filter-output results suggested that duration of the entire negative carbon excursion from the upper part of DST3 in the region was ~6.1 m.y. (~15.2 E). [ABSTRACT FROM AUTHOR]