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Chen Jun Wan Hongtao Department of Earth Sciences Nanjing University Nanjing Jiangsuand Lu HuayuKey Lab. of Loess Quaternary Geology Chinese Academy of Sciences Xi an Shaanxi Liu Xinzhu 《《地质学报》英文版》1996,70(3):290-302
The chemical leaching method is used for a systematic analysis of distribution characteristics of acid-soluble and acid-insoluble REE and other trace elements from the Luochuan loess deposits. The study shows that the acid-insoluble phase in loess and palaeosol is a stable component of old aeolian dusts and is characteristic of the provenance; the acid-soluble phase is the unstable component in the weathering pedogenic process and reflects rock-forming features after accumulation of aeolian dusts. The acid-insoluble REE and acid-soluble Sr and Pb can be used as geochemical indicators respectively to trace the provenance characteristics and the weathering pedogenic process. 相似文献
3.
Rock-magnetic proxies of climate change in the loess-palaeosol sequences of the western Loess Plateau of China 总被引：5，自引：0，他引：5
Christopher P. Hunt Subir K. Banerjee Jiamao Han Peter A. Solheid Eric Oches Weiwei Sun Tungsheng Liu 《Geophysical Journal International》1995,123(1):232-244
Results of the first detailed study of the climate proxy record in the loess-palaeosol sequence at Xining-one of the few palaeoclimate sites in the currently arid western Loess Plateau of China-illustrate the importance of making many types of rock-magnetic measurements other than susceptibility. A multiparameter approach yielded confirmation that here, as elsewhere in the Loess Plateau, the susceptibility enhancement in palaeosols was caused primarily by ultrafine magnetite and maghaemite. Nevertheless, magnetic enhancement was caused not exclusively by changes in relative grain size, but also by variations in concentration and mineralogy of the magnetic fraction.
The effects of concentration variations were removed through normalization of susceptibility and anhysteretic remanence with saturation magnetization and saturation remanence, respectively. the resulting signal was ascribed more confidently to variation in magnetic grain size, which in turn was interpreted as a better proxy of pedogenesis than simple susceptibility. Variations in magnetic mineralogy were also determined to constrain interpretations further. the data were then used to discuss climate history at Xining. Finally, results from Xining were compared with other western sites and contrasted with eastern sites.
In summary: (1) data is presented from a new Loess Plateau site which also appears to yield a global climate signal; (2) a demonstration is made of a more rock-magnetically robust way to separate concentration, composition and grain-size controls on susceptibility and other magnetic parameters; and (3) models are provided for inter-regional comparisons of palaeoclimate proxy records. 相似文献
The effects of concentration variations were removed through normalization of susceptibility and anhysteretic remanence with saturation magnetization and saturation remanence, respectively. the resulting signal was ascribed more confidently to variation in magnetic grain size, which in turn was interpreted as a better proxy of pedogenesis than simple susceptibility. Variations in magnetic mineralogy were also determined to constrain interpretations further. the data were then used to discuss climate history at Xining. Finally, results from Xining were compared with other western sites and contrasted with eastern sites.
In summary: (1) data is presented from a new Loess Plateau site which also appears to yield a global climate signal; (2) a demonstration is made of a more rock-magnetically robust way to separate concentration, composition and grain-size controls on susceptibility and other magnetic parameters; and (3) models are provided for inter-regional comparisons of palaeoclimate proxy records. 相似文献
4.
渭北黄土台塬全新世地层高分辨率研究 总被引：5，自引：0，他引：5
在野外观测研究的基础上 ,对陕西扶风新店村全新世黄土剖面作了详细的地层划分。通过磁化率、粒度、TOC、全铁和碳酸盐含量测定分析 ,进一步揭示渭北黄土台塬全新世季风气候变化的规律。同时 ,阐明了“全新世大暖期”的气候有明显的波动变化 ,尤其是在 6 0 0 0— 5 0 0 0 a B.P.发生了一个干旱气候事件 ,形成黄土堆积 ,使得全新世古土壤分裂成为两层 ,表现为多周期土壤。从 3 10 0 a B.P.开始至今气候变得干旱 ,风尘堆积旺盛 ,形成了现代黄土和表土层 相似文献
5.
黄土高原稳定同位素与古环境研究 总被引：2，自引：0，他引：2
黄土高原黄土地层已被证明是大陆上最完好的记录了过去环境信息的载体。通过黄土地层的碳,氧同位素作为气候替代指标研究古植被,降雨量,古环境温度及古季风演化方面取得了长足的进展,本文拟就主要研究成果作一综述,并对今后的研究方向做一前瞻。 相似文献
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对汉江上游进行野外实地详细调查,在湖北省郧县尚家河台地前沿发现了典型的全新世黄土-古土壤沉积剖面,通过粒度、磁化率、吸湿水和烧失量分析表明,黏粒、细粉砂、磁化率、吸湿水和烧失量在古土壤层S0出现高值,在L1、Lt、L0为低值;而粗粉砂、细砂粒和粗砂粒在S0为低值,在L1、Lt、L0为高值。这些指标的变化说明了全新世以来的气候和成壤环境的变化特征,即在古土壤S0形成时期,气候温暖湿润,成壤作用非常强烈;黄土堆积时期气候相对干旱,成壤作用较弱。 相似文献
8.
Subaerial unconformities are used widely for palaeoenvironmental and palaeogeographic reconstructions, sequence stratigraphy and petroleum reservoir assessments. Recognition and interpretation of these unconformities, particularly those with associated palaeosols, may be problematic in Lower and Middle Palaeozoic carbonate successions because of the collective effect of limited land plant development, superficial similarities between some pedogenic and marine features, and overprinting by later diagenesis. The isolated Judy Creek reef complex in the Lower Frasnian Swan Hills Formation in west‐central Alberta, Canada, contains two subaerial unconformities, R0.5 and R4, which formed as a consequence of relative sea‐level falls of at least regional scale. Deposits beneath these unconformities have distinctive palaeosol and palaeokarst features. The lower unconformity, R0.5, occurs at the top of a progradational reefal phase of stromatoporoid rudstones–floatstones and peloidal packstones–grainstones and has been recognized in at least one other isolated Swan Hills reef complex (Snipe Lake). Palaeosol–palaeokarst profiles beneath this unconformity extend as deep as ca 2 m below the unconformity. These profiles are characterized by the presence of small rhizoliths, laminar calcretes, ferroan dolomite glaebules, desiccation cracks, breccias, green shale and solution vugs. The upper unconformity, R4, occurs at the top of a backstepping phase of reef growth and has been correlated widely between isolated reefs and carbonate banks on both the western and eastern shelves of the Central Alberta Basin. Palaeosol–palaeokarst profiles, extending as deep as ca 9·5 m beneath the R4 unconformity, are distinguished by abundant, sub‐horizontal desiccation cracks filled with green shale, occurring in peloidal wackestones–packstones. Comparison of the R0.5 and R4 profiles indicates that the major intrinsic controls on the development and modification of the profiles are parent‐material lithology, particularly the prior degree of induration and particle size; the low topographic relief at the top of the reef interior; and limited vegetation of the exposed reef top due to unfavourable growth conditions and geographic isolation. In addition to climate, the major extrinsic controls are the extent of relative sea‐level fall, estimated to be 2·5 to 3 m and 13 to 14 m associated with the R0.5 and R4 unconformities, respectively, and the degree of shoreface erosion during the ensuing marine transgression, estimated to be up to 3 m. This study highlights the complex interplay of mainly physical and chemical processes influencing the formation of subaerial unconformities in carbonate environments during the Devonian, before major evolutionary innovations among vascular land plants led to more intense pedogenesis. 相似文献
9.
Ewarara is a small layered ultramafic intrusion which forms part of the Giles Complex. The flat‐lying body displays both sub‐horizontal and vertical layering, which appear to have different origins. Petrographically the intrusion consists of a lower olivine bronzitite unit and an upper pyroxenite unit. These display a small cryptic variation with the upper layer being the more iron‐rich. Many of the primary igneous textures have been destroyed by deformational effects but the intrusion retains many features of a body formed by gravity accumulation of crystals precipitating from a magma. Crystallisation of the magma is believed to have occurred near the base of the crust. 相似文献
10.
The S1 pedocomplex, correlated to Oxygen Isotope Stage 5 of the ocean cores, has been traced west of the Loess Plateau on to the extreme northeastern margin of the Qinghai-Xizang (Tibetan) Plateau in China. Detailed micromorphological analysis of closely spaced thinsections from the pedocomplex at this site provides the basis for reconstruction of the sequence of pedosedimentary processes and associated palaeoenvironmental changes occurring during this time interval. The six pedosedimentary stages identified are interpreted in terms of temporal variations in depositional rates, size of particles transported and availability of moisture for pedogenic alteration, as determined by changing balances in dominance of winter and summer monsoonal forces. Two main ‘soil-forming intervals’ are identified: the more extensive of the two in terms of resultant pedological features reflects pedogenic alteration at a relatively ‘stable’ land surface under a semi-arid climate during the later part of pedosedimentary stage 2. The other main period corresponds to pedosedimentary stages 4 and 5, when leaching and bioturbation processes were active at aggrading surfaces, leading to development of an accretionary unit without clear differentiation of horizons. Pedosedimentary stages 1, 3 and 6 were characterised mainly by rapid rates of coarse loess accumulation, with synsedimentary modification restricted to surface slaking and crust formation, and minor localised redistribution of calcite. 相似文献