青海喇家遗址地层划分及齐家文化废墟覆盖层成因分析     

王海燕  庞奖励  黄春长  周亚利  炊郁达  查小春  郭永强  张玉柱  尚瑞清  王兆夺 《地理科学》2020,40(5):853-862

对喇家遗址进行了全面的野外考察,在其北部发现完整连续的全新世黄土-古土壤地层剖面。通过系统采样、粒度和磁化率等多种指标测试,结合OSL技术测年断代,建立了完整的土壤地层序列。深入分析土壤沉积物性质与地表过程,揭示了覆盖齐家文化废墟的沉积物的成因。研究结果表明：喇家遗址土壤沉积物地层层序自地表向下依次为：现代土壤（MS,0~1.50 ka B.P.）→全新世晚期风成黄土（L₀,1.50~3.10 ka B.P.）→全新世中期古土壤（S₀,3.10~8.50 ka B.P.）→全新世早期过渡性风成黄土（L_t,8.50~11.50 ka B.P.）→晚更新世晚期马兰黄土（L₁,>11.50 ka B.P.）。其中全新世中期黑垆土古土壤（S₀）被3组红色粘土质泥流（RC₃、RC₂和RC₁）和山洪沙土（FFD）沉积层穿插分隔为4个亚层（S_0上、S_0中上、S_0中下和S_0下）。这证明黑垆土发育过程中,在OSL年龄3.96~3.65 ka,对应于¹⁴C年龄3.85~3.60 ka B.P.出现一个山洪泥流盛行期,来自于盆地北侧沟谷的大规模暴雨山洪泥流,在大红山前古洪积扇前沿溢出沟槽、扩散覆盖了黄河第二级阶地面的土地。其中与大地震相伴随的第一期暴雨山洪泥流过程,摧毁了喇家遗址齐家文化聚落,造成居室内人群的死亡。  相似文献   

A magnetic investigation of a Late Quaternary loess/palaeosol record in Siberia   总被引：10，自引：0，他引：10  

J. Chlachula  M. E. Evans  & N. W. Rutter 《Geophysical Journal International》1998,132(1):128-132

A Late Quaternary loess/palaeosol sequence at Kurtak in the Yenisey River valley, southern Siberia, has been studied magnetically. The 34  m section (340 samples) exhibits variations in magnetic susceptibility which can be correlated with oxygen isotope stages 1–7. A detailed sampling of stage 5 (a further 209 samples) permits the identification of substages 5a–e. The susceptibility variations themselves are in the opposite sense to that found in the classic sections of the Chinese Loess Plateau, but are in agreement with the 'wind-intensity' model which has been put forward to explain similar findings in loess sequences in Alaska. Published results for the susceptibility of magnetite imply volume fractions of ≈0.2 per cent in glacial stages 2 and 4, dropping to ≈0.05 per cent in stages 1, 3 and 5. These fluctuations match the aeolian flux variations observed in core V21–146 from the north Pacific. Even though the warmer intervals are characterized by lower susceptibilities, the observed frequency dependence of susceptibility indicates that new magnetic material is produced as a result of pedogenesis during interglacial and interstadial times.  相似文献   

Geochemical studies on Kashmir loess profiles     

G. S. Lodha  K. J. S. Sawhney  H. Razdan  D. P. Agrawal  N. Juyal 《Journal of Earth System Science》1987,96(2):135-145

Major and trace element concentrations of a few representative loess profiles in Kashmir valley are studied using EDXRF spectroscopy. Principal component analysis for pattern recognition has been employed to study association between elemental concentration variations in various horizons. The present study reveals that elements related to clay illuviation (K, Rb, Fe, Ti, Mn) and plant activity (Cu, Zn) are generally higher in B horizon of the palaeosols whereas Ca and Sr have a high concentration in the loess layers. Such an elemental concentration variation provides us with an objective index for identification and confirmation of palaeosols. There is further a close association in the movement of (i) K, Rb, (ii) Fe, Ti, Mn, (iii) Cu, Zn and (iv) Ca, Sr. These clusters of elements are also present in modern soils, suggesting that the soil characteristics in palaeosols have been preserved. Concentration of iron and titanium is also observed to be higher in loess profiles on Pir Panjal mountain flank which is dominated by basic rocks, compared to profiles on Himalayan flank, suggesting that the loess in Kashmir might have been derived from the nearby rocks in a localized way.  相似文献   

Spatial variability of palaeosols across Cretaceous interfluves in the Dunvegan Formation, NE British Columbia, Canada: palaeohydrological, palaeogeomorphological and stratigraphic implications     

Paul J. McCarthy  A. Guy Plint† 《Sedimentology》2003,50(6):1187-1220

A basic sedimentological and palaeopedological framework is now in place for non-marine sequence models. The variability of interfluve palaeosols has not, however, been systematically documented, nor have the stratigraphic implications of that variability been incorporated into sequence models. Interfluve palaeosol variability in the deltaic Dunvegan Formation, NE British Columbia, Canada, is investigated, for which a detailed allostratigraphic and palaeogeographic framework has been developed, based on abundant well (> 2300 logs) and outcrop (> 60 sections) control. Regionally extensive valley fills and interfluves have been mapped in coastal plain deposits over an area of about 50 000 km². This palaeogeographic framework permits interfluve surfaces exposed in outcrop to be located in terms of distance from the margins of coeval valleys. The micromorphological, geochemical and mineralogical characteristics of five representative sequence-bounding palaeosols located from 250 m to more than 15 km from coeval valley margins are described. These interfluve palaeosols are similar to modern Alfisols and all record (i) aggradation on an alluvial/coastal plain; (ii) a subsequent static and/or degradational phase related to valley incision, non-deposition and soil thickening; and (iii) a final aggradational phase related to valley filling and renewed sedimentation across the coastal plain. Within this overall template, however, variations in palaeosol thickness, redoximorphic features, illuvial clay content and geochemistry suggest developmental control by hydrological characteristics that were influenced by both the nature of the underlying alluvial sediments and distance from the valley margin. The presence of mature interfluve palaeosols with complex developmental histories suggests that landscape dissection may have been related to terrace development associated with valley incision. Palaeosols closer to valley margins are thicker, contain more illuvial clay and display characteristics suggesting better drained conditions relative to those palaeosols that developed further from valley margins. Subsequent deposition on interfluves also reflects distance from valleys, with those sites close to valleys accumulating cumulic soils with evidence of brackish groundwater, whereas far from valleys (> 10–15 km), groundwater was fresh and clastic supply minimal, encouraging peat formation. Variations in drainage and palaeotopography during landscape dissection resulted in different palaeosol development styles on interfluve surfaces that can be shown, on the basis of physical correlation, to have the same geomorphic age. These observations support the concept of the soil-forming interval as a basis for pedostratigraphic correlation in ancient terrestrial deposits. Palaeosol variability on interfluves is to be expected, and recognition and documentation of this variability is an important prerequisite to palaeogeomorphological, palaeoclimatic and sequence stratigraphic interpretations.  相似文献   

A lock-in model for the complex Matuyama-Brunhes boundary record of the loess/palaeosol sequence at Lingtai (Central Chinese Loess Plateau)   总被引：1，自引：0，他引：1  

S. Spassov  F. Heller  M. E. Evans  L. P. Yue  T. von Dobeneck 《Geophysical Journal International》2003,155(2):350-366

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Palaeoclimatic implications of the magnetic record from loess/palaeosol sequence Viatovo (NE Bulgaria)   总被引：1，自引：0，他引：1  

Diana Jordanova  Jozef Hus  Raoul Geeraerts 《Geophysical Journal International》2007,171(3):1036-1047

Loess-palaeosol deposits in the lower Danube area represent the southeastern edge of the loess cover in Europe. Detailed rock magnetic investigations of the loess/palaeosol sequence in Viatovo in NE Bulgaria reveal that magnetite and maghemite of very fine superparamagnetic grain size are responsible for the magnetic enhancement of palaeosol units. A detailed palaeoclimatic record is obtained through high-resolution measurements of magnetic susceptibility, frequency dependent magnetic susceptibility and CaCO₃ content. Magnetic proxies indicate a more warm and humid climate during the development of the older palaeosol units (S₄–S₆).  相似文献   

Variability of unsaturated Bromide fluxes as measured through a layered volcanic vadose zone in New Zealand          下载免费PDF全文

G. F. Barkle  Th Wöhling  R. Stenger 《水文研究》2014,28(25):6080-6097

The measured drainage fluxes through a layered volcanic vadose zone exhibited high spatial variability as a consequence of heterogeneous flow conditions. The drainage flux variability was quantified using automated equilibrium tension lysimeters, installed in close‐proximity and resulted in high variability in the Br masses recovered from a conservative tracer experiment. The primary cause of the heterogeneous flow was attributed to textural changes occurring at the interface between volcanic layers, resulting in development of funnel‐flow patterns, and further enhanced by the existence of hydrophobic conditions. The Br recoveries in individual automated equilibrium tension lysimeters were used to determine the corresponding variable sizes of the surface areas contributing drainage to the lysimeters. The tracer experiment confirmed the existence of unsaturated lateral transport occurring at the sloping interface of the coarse Taupo Ignimbrite material with the silty Palaeosol layer at approximately 4.2 m depth. This study demonstrates that measurements of both flux and solute concentrations at multiple locations are essential when heterogeneous flow is suspected to be present, to be able to determine reliable estimates of contaminant leaching through the vadose zone at the plot scale. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The value of pocket penetration tests for the high‐resolution palaeosol stratigraphy of late Quaternary deposits     

Alessandro Amorosi  Luigi Bruno  Bruno Campo  Agnese Morelli 《Geological Journal》2015,50(5):670-682

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Rinded iron‐oxide concretions: hallmarks of altered siderite masses of both early and late diagenetic origin     

DAVID B. LOOPE  RICHARD M. KETTLER  KARRIE A. WEBER  NATHAN L. HINRICHS  DEREK T. BURGESS 《Sedimentology》2012,59(6):1769-1781

Iron‐bearing concretions are valuable records of oxidation states of subsurface waters, but the first concretions to form can be altered drastically during later diagenetic events. Distinctive concretions composed of heavy rinds of iron oxide that surround iron‐poor, mud‐rich cores are common along bases of fluvial cross‐bed sets of the Cretaceous Dakota Formation, Nebraska, USA. Concretion rinds thicken inward and cores contain 46 to 89% void space. Millimetre‐scale spherosiderites are abundant in palaeosols that developed in floodplain facies. Evolution of rinded concretions began when intraformational clasts were eroded from sideritic soils, transported, abraded and deposited in river channels. Alteration of siderite and formation of rinds occurred much later, perhaps in the Quaternary when sandstone pore waters became oxic. Dakota concretions are analogous to ‘rattlestones’ in Pleistocene fluvial channels of The Netherlands, and their rinded structure is analogous to that of iron‐rich concretions in the aeolian Navajo Sandstone of Utah. In all three deposits, rinded concretions formed when pre‐existing, siderite‐cemented concretions were oxidized within a sand matrix. Unlike fluvial examples, siderite in the Navajo Sandstone was autochthonous and of late diagenetic origin, having precipitated from carbon dioxide and methane‐enriched waters moving through folded and jointed strata. Iron‐rich rinds formed in all these strata because concretion interiors remained anaerobic, even as oxygen accumulated in the pore waters of their surrounding, permeable matrix. Iron oxide first precipitated at redox boundaries at concretion perimeters and formed an inward‐thickening rind. Acid generated by the oxidation reaction drove siderite dissolution to completion, creating the iron‐poor core. Iron‐oxide rinds are indicators of the former presence of siderite, a mineral that forms only under reducing conditions, during either early or late diagenesis. Siderite is vulnerable to complete oxidation upon exposure, so the distinctive rinded concretions are valuable clues that aid in deciphering diagenetic histories and for recognizing methanic floodplain palaeoenvironments and wet palaeoclimate.  相似文献   

The Chinese loess in Xifeng, II. A study of anisotropy of magnetic susceptibility of loess from Xifeng   总被引：1，自引：0，他引：1  

Xiuming Liu  Tongchun Xu  Tungsheng Liu 《Geophysical Journal International》1988,92(2):349-353

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