Astronomical calibration of the Matuyama-Brunhes boundary: Consequences for magnetic remanence acquisition in marine carbonates and the Asian loess sequences

We have compiled 19 records from marine carbonate cores in which the Matuyama-Brunhes boundary (MBB) has been reasonably well constrained within the astronomically forced stratigraphic framework using oxygen isotopes. By correlation of the δ¹⁸O data to a timescale based on astronomical forcing, we estimate astronomical ages for each of the MBB horizons. In all but one record the MBB occurs within Stage 19.

Most magnetostratigraphic sections in Asian Loess place the MBB within a loess interval. Since loess deposition is presumed to be associated with glacial intervals, loess horizons should correspond to even-numbered oxygen isotope stages. A glacial age for the MBB is at odds with the results presented here, which firmly place the MBB within interglacial Stage 19. Inconsistency among the many loess sections and between the loess and the marine records suggests that the magnetic interpretation of loess sections may be more complicated than hitherto supposed.

The mean of the Stage 19 age estimates for the MBB is 777.9 ± 1.8 (N = 18). Inclusion of the single Stage 20 age results in a mean of 778.8 ± 2.5 (N = 19). The astronomical age estimate of the MBB compares favorably with an (unweighted) mean of 778.2 ± 3.5 (N = 10) from a compilation of ⁴⁰Ar/39^Ar results of transitional lava flows. Combining the two independent data sets yields a grand mean of 778.0 ± 1.7 (N = 28).

The new compilation shows virtually no trend in placement of the MBB within isotope Stage 19 as a function of sediment accumulation rate. We interpret this to mean that the average depth of remanence acquisition is within a few centimeters of the sediment-water interface.

Separating the cores into two geographic regions (an Indo-Pacific-Caribbean [IPC] Group and an Atlantic Group) results in a significant difference in the position of the mid-point of the reversal with respect to the astronomical time scale. The data presented here suggest a difference of several thousand years between the two regions. This observation could be caused by systematic differences between the two regions in sedimentation rate within the interval of interest, systematic differences in remanence acquisition, or by genuine differences in the timing of the directional changes between the two regions.     

黄土高原晚更新世黄土与古季风研究进展

黄土高原晚更新世黄土地层含有末次间冰期一次期东亚季风演变的大量信息，经外地学界十年来的探索，初步揭示了东亚季风演化的规律，本文对于这方面研究的现状作了综合评述。     

辽东海岸带黄土

本文论述了辽东海岸带黄土的成因,它主要由低空气流搬运的近源物质组成,其次为高空气流携带的内陆远源物质,主要物源地是辽东湾。冰期时,海平面下降,辽东湾干口渤海裸露成陆而发生沙漠化,海底沉积物经强劲的西北风作用,被搬运到东侧海岸带沉降下来,与大气环流系统自内陆携带而至的风尘物质混合在一起,形成海岸带黄土。     

The Coastal Zone Loess of the Liaodong Peninsula, Liaoning Province

This Paper discusses the origin of the Coastal Zone Loess on the Liaodong Peninsula, Liaoning Province.The loess is composed mainly of proximal materials transported by low-altitude air flow and less commonly ofinland distal materials carried by high-altitude air flow. The main provenance is the Liaodong Bay. When thesea level declined during glacial period, the bottoms of the Liaodong Bay and Bohai Sea emerged, wheredesertization occurred. As a result, submarine sediments were transported by strong northwesterly winds to theeastern coastal zone of the peninsula and deposited there. These materials mixed with the windblown dust car-ried by atmospheric circulation from the interior of the continent, forming the loess.     

黄土高原西部会宁地区66万年以来冰期—黄土旋回的孢粉记录

根据野外剖面观测及古地磁资料,将会宁黄土地层与兰州、洛川黄土地层进行对比。在孢粉分析的基础上,把该区约66万年以来的植被与气候演变历史划分为13个阶段,并将其与深海沉积氧同位素阶段及冰期旋回进行了对比。约66万年以来,该地植被变化于温性针阔叶混交林与荒漠草原之间,气候变化于温暖半湿润-寒冷干旱之间。     

黄土孔隙性分类判别的人工神经网络方法

运用人工神经网络的一典型模型——“反向传播”神经网络,对洛川黄土孔隙性的实测数据进行了分析,建立了洛川黄土孔隙性预测的计算机智能专家系统。结果表明,神经网络方法性能良好,可望成为黄土孔隙性分类、判别的有效辅助手段。     

Flow Characteristics of Large-Scale Liquefaction-Slip of the Loess Strata in Shibei Tableland, Guyuan City, Induced by the 1920 Haiyuan M8 1/2 Earthquake

Based on the dynamic triaxial liquefaction test of the loess samples which are taken from Shibei tableland, Guyuan City, Ningxia, China, the characteristics of dynamic strain, dynamic stress and pore water pressure are studied under cyclic loading. Triaxial shear test is conducted immediately after the sample reaches liquefaction point. During the test, the property of the liquefied soil is analyzed through fluid mechanics method, whereby the fluidity of the liquefied soil is represented by apparent viscosity.The results show that the fluidity of liquefied loess changes from "shear thickening" to "shear thinning" as the shear force continues, and the fluidity of liquefied loess is closely related to its structure. In addition, in the process of forming a new stable state, the apparent viscosity and deviant stress change with axial strain in a similar approach. When the sample reaches its stable state, it meanwhile shows a relatively stable apparent viscosity. According to the fluid mechanics and the law of conservation of energy, the slip distance of the liquefied soil is estimated, and the results are in good agreement with the field investigation results.     

试论加入WTO后我国海洋文化发展的法制意识趋势

在漫长的旧社会 ,由于各种原因 ,使得我国沿海地区居民的法制意识比较淡薄。我国加入WTO后 ,经济生活乃至社会生活将要严格遵守规则 ,从而也将促使我国沿海地区的法制意识增强。     

The carbon isotope composition of C<Superscript>3</Superscript> herbaceous plants in loess area of northern China

¹³C of 367 C₃ herbaceous plants was measured in loess area in northern China. Their δ¹³C values vary between −21.7%. and −30.0%., with a mean of −26.7%.. In the center of Loess Plateau (semimoist area) with annual precipitation of 400–600 mm, the δ¹³ C values of C₃ herbaceous plants range from −24.4%. to −28.5%., with a mean of −27.5%.. In the west of Loess Plateau (semiarid and arid area) with annual precipitation less than 400 mm, they range between −21.7%. and −30.0%., with a mean of −26.2%.. Annual precipitation is the main factor that makes δ¹³C values of C₃ herbaceous plants in the west greater than those in the central Loess Plateau. The composition of δ¹³C in C₃ plants increases with deceasing annual precipitation, and the mean change is −49%./100 mm.     

陇西民和黄土CaCO3和有机碳总量的含量变化及其气候指标的局限性

民和黄土地处黄土高原与青藏高原东北缘的交接部位,对气候反应较敏感,对该黄土1.87-0.70Ma BP段进行了CaCO3和有机碳总量（TOC）的采样分析。民和黄土CoCO3含量在5.89%-18.63%之间变化,平均11.41%;有机碳含量较低,在0.007%-0.452%之间,平均0.088%。民和黄土中的CaCO3含量明显高于兰州、洛川和西安等地,而有机碳含量则远低于上述地区。黄土中CaCO3和有机碳含量变化反映了该区1.87Ma BP以来气候变干冷的趋向。分别受复杂的CaCO3来源与类型、困难的采样、地区上的差异对比等和有机碳保存条件、沉积速率以及“埋藏效应”的影响,黄土中的CaCO3和有机碳的波动变化作为气候变化的替代性指标存在一定的局限性。文章最后指出,在实际应用中,黄土（特别是黄土高原西北部）中CaCO3和有机碳气候指标应结合其他环境指标共同使用,才能从中提取正确的古气候信息。