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Paleomagnetic Inclination Shallowing in Badong Formation Red Beds, Middle Triassic of South China Block
HAN Lu, HUANG Baochun, ZHAO Qian, XUE Yi, LI Nengtao, Umar Farooq Jadoon
Acta Scientiarum Naturalium Universitatis Pekinensis    2022, 58 (3): 469-480.   DOI: 10.13209/j.0479-8023.2022.031
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Paleomagnetic and rock magnetic studies are conducted on Middle Triassic Badong Formation red beds from the South China Block (SCB). The anisotropy of high-field isothermal remanent magnetization (hf-AIR) method indicates that the characteristic remanent magnetization (ChRM) is significantly affected by inclination shallowing with a flattening factor f = 0.63. Rock magnetic analysis indicates that hematite is the main magnetic carrier with a subordinate contribution from magnetite. Anisotropy of magnetic susceptibility (AMS) and hf-AIR results both show a typical depositional fabrics without significant distortion from tectonic stress. The ChRM, carried by detrital hematite, has a unique negative polarity and passes the fold test at the 95% confidence level. The ChRM yields a common mean direction with that previously reported from the same section. The ChRM yields a tilt-corrected mean direction of Ds = 222.1°, Is = ?27.2° (α95 = 8.7°) and a corresponding paleomagnetic pole at 48.1°N, 215.5°E (A95 = 8.4°). Combined with high quality published data (Q≥5) for the Middle Triassic, the mean paleomagnetic pole for the SCB is corrected to 48.5°N, 207.6°E with A95 = 10.7° by using a flattening factor f = 0.63. Comparing this inclination shallowing-corrected mean paleomagnetic pole with Early Triassic pole for the North China Block, which has also inclination shallowing-corrected by the hf-AIR method, it shows that paleolatitudes of these two blocks at their eastern reference points are exactly compatible. This further confirms that the South and North China blocks experienced a scissors-like rotational collision during the Mesozoic times, as proposed by previous researches. 
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Paleomagnetic Inclination Shallowing in Lower Triassic Liujiagou Formation from Qinshui Basin, North China Block
ZHOU Tinghong, HUANG Baochun, JIA Shufei, LIANG Yalun, ZHANG Donghai, ZHAO Qian, ZHANG Ye, YAN Yonggang
Acta Scientiarum Naturalium Universitatis Pekinensis    2018, 54 (3): 521-534.   DOI: 10.13209/j.0479-8023.2017.100
Abstract893)   HTML9)    PDF(pc) (1526KB)(348)       Save

A combined paleomagnetic, rock magnetic and magnetic fabrics study is conducted on the redbeds of Early Triassic Liujiagou Formation from Qinshui Basin, North China Block (NCB). The E/I (elongation/inclination) method indicates that the characteristic remanent magnetizations (ChRM) was significantly affected by inclination shallowing with a flattening factor f=0.6. Rock magnetic analysis indicates that hematite and magnetite are the main magnetic carriers. Anisotropy of magnetic susceptibility (AMS) result shows typical depositional fabrics in water. The chRM has been successfully isolated from 15 sites with tilt-corrected mean direction of Ds=318.8°, Is=30.9° (α95=6.9°) and a corresponding paleomagnetic pole at 49.3°N, 5.5°E (A95=6.7°). The pole after E/I correction is 53.5°N, 18.0°E. Combining with published high quality Early Triassic pole (Q≥4) for NCB, the mean Early Triassic pole for NCB before and after inclination shallowing correction is 55.3°N, 357.1°E (A95=5.5°) and 60.8°N, 13.4°E (A95=5.8°), respectively. The paleolatitude of NCB is obviously higher at Early Triassic after inclination shallowing correction with ~10° increase. Furthermore, the corrected Early Triassic paleolatitude of NCB seems to be different from that of South China Block (SCB) at the east, which may result from the inclination shallowing error in Early Triassic limestone rocks of SCB instead of the real separation between the two blocks.

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Relationship between Shrubs Distribution and Slope: A Case Study in Mountains of the Beijing-Tianjin-Hebei Region
WANG Tao;HAO Qian;LIU Hongyan
   2015, 51 (4): 685-693.   DOI: 10.13209/j.0479-8023.2015.091
Abstract982)      PDF(pc) (1019KB)(397)       Save
Shrublands in the Beijing-Tianjin-Hebei region were selected to unveil relationships between the area percentage of shrubland and the slope angle. Gridded data of vegetation and slope angle were correlated for the whole region as well as different climatic regimes with piecewise regression analysis. The results show that there is a tipping point on the fitted curve between percentage of shrubs and slope angle, instead of a monotonous linear fit. On gentle slopes, percentage of shrubs increases with the increase of slope angle, which might be caused by the decrease of human cultivation. On steep slopes, there are divergent patterns, percentage of shrublands except that dominated by Vitex negundo var. heterophylla and Zizyphus jujuba var. spinosa decreases with the increase of slope angle, which might be caused by resource limitation. Percentage of this shrubland type does not show trend of decline with slope angle increase, which might be caused by its distribution on low elevations and its adaptation to varied habitats. In addition, the tipping point mostly fixes around 15 degree of slope angle when the region is taken as a whole; it changes under different climatic regimes.
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Modified CISK-Rossby Waves and Low-Frequency Oscillations
CHEN Jianzhou,ZHAO Qiang
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract743)      PDF(pc) (571KB)(362)       Save
A baroclinic semi-geostrophic model with the full, three-dimensional Coriolis acceleration and CISK mechanism is established, f ′ and the non-dimensional parameter η are introduced to represent the nontraditional Coriolis terms and CISK heating, respectively. The modified CISK-Rossby wave solutions of the model are obtained. Dynamics analyses and numerical calculations further confirm that the modified CISK-Rossby waves are very important physical processes in leading to the low-frequency oscillations (LFO) in the tropics.
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Response Time Characteristics of Proton-implanted KNbO3 Crystals
LI Qi,XIA Zonghuang,WANG Xuemei,ZHAO Qiang,SHEN Dingyu,LU Xiting,WANG Feng,CHEN Zhijian,GONG Qihuang,SHEN Dezhong
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract668)            Save
The experimental investigation on the intensity-dependent photorefractive response of the proton-implanted KNbO3 crystals is presented. The decay time constant was measured. The results revealed that two gratings existed simultaneously, one was caused by the photorefractive effect, and the other was contributed from the proton-implantation. The experimental results also reflect that low dose implantation hardly influence the photorefractive decay time.
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Baroclinic Mesoscale Semi-balanced and Quasi-balanced Dynamic Models
ZHAO Qiang,LIU Shikuo
Acta Scientiarum Naturalium Universitatis Pekinensis   
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The physical characteristics of mesoscale are analyzed, and results show that the unbalanced forced motion is the fundamental cause, which lead to evolution of some important mesoscale weather systems. The mesoscale dynamics equations are the basis of the theoretical studies of mesoscale atmospheric dynamics. There fore, according to the characteristics of the mesoscale motion, the formal scaling analysis and the asymptotic theory are used to simplify the governing atmospheric dynamics equations which are based on fluid dynamics and thermodynamics, so they can describe the basic characteristics of the mesoscale motion more accurately. These procedures are essential for the development of the mesoscale dynamics. The semi-balanced and quasi-balanced models based on nonlinear balance equation are derived;they are in analogy with the semi-geostrophic and quasi-geostrophic models, respectively, and may be used as basis for the theoretical studies of the mesoscale atmospheric dynamics. The uasi-balanced model is also used to study the mesoscale balanced vortex system, and the conclusion has shown that the mesoscale vortex system is mainly controlled by the gradient wind, and the development of its wind and pressure fields are described by an evolution equation.
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