Interaction between aggrading geomorphic surfaces and the formation of a late pleistocene paleosol in the palouse loess of eastern Washington state

Variable rates of loess deposition contributed to dramatic regional variation in a soil-stratigraphic unit, the Washtucna Soil, in the Palouse loess deposits in the Channeled Scabland of eastern Washington state. Throughout most of the Channeled Scabland, the morphology of the Washtucna Soil is that of a single buried soil, but it bifurcates into two well-developed and pedologically distinct buried soils in areas immediately downwind of the major source of loessial sediment. Regional loess stratigraphy confirms that the two well-developed soils formed during the same interval of time during which only one soil formed in areas that are distal to loess source areas. The variable and perhaps rapid rates of soil formation suggested by the stratigraphy resulted from an interaction between variable rates of loess deposition and the formation of superimposed calcic soils. Petrocalcic horizons with weak Stage IV morphology formed as the zone of carbonate accumulation moved up into former A and cambic horizons that had been profusely burrowed by cicadas. The development of cicada burrows in one phase of soil development that were subsequently engulfed by pedogenic carbonate under a rising land surface seems to have greatly accelerated the development of the petrocalcic horizons. Accelerated rates of formation of the petrocalcic horizons occurred when extrinsic (pulses of loess deposition) and intrinsic (engulfment of burrowed horizons) thresholds were exceeded. Stratigraphic evidence suggests that the soil formation that accompanied the rise in the land surface due to additional loess deposition may have occurred during the late Wisconsin glaciation when giant glacial outburst floods in the channeled Scabland triggered a new cycle of loess deposition.     

黄土的形成与气候旋回划分

根据黄土土壤特征的研究和黄土地层古土壤的识别和划分,结合磁化率测定,研究了黄土剖面冷干与温湿条件下发育的古土壤的分层和代表的气候旋回变化。资料表明,黄土具有土壤的结构和淀积成分,它是在相对冷干气候条件下发育的成熟的灰黄色古土壤,能够可靠地作为冷干气候的指示;250万年来的黄土地层至少可分为51层灰黄色古土壤与50层红褐色古土壤,代表了51个生物、气候、土壤旋回和亚旋回的变化。在50万年来的温湿气候阶段中,气候波动更频繁。     

15万年以来极地冰芯、黄土、深海沉积的对比研究与全球变化

由极地冰芯记录、中纬黄土记录和深海沉积记录的对比可得，１５万年以来全球变化的基本框架为：末次间冰期，从距今１４万年开始到约１２．５万年达鼎盛，可分为五个阶段，即冰芯中三次高温期夹两次低温期；黄土中三层古土壤夹两层黄土；深海沉积中三次高海面夹两次低海面。末次冰期，距今８万年到１万年，可分为三个阶段，早、晚冰段和中间的间冰段。早、晚冰段盛期气候寒冷程度相当，但晚冰段最低温持续期更长，造成海面比早期更低。中间的间冰段，至少可分为７个亚段，即４次暖期（４次弱成土古土壤）夹３次冷期。全新世与末次间冰期对比，总体气候变化较平缓。在上述基本框架中，近几年发现，在末次冰期存在许多短周期、高频快速变化事件。这些事件，温度变化幅度达７℃，变化速率为几年到几十年，对应的环境变化速率可能更快。这些事件的引发机理目前还不清楚，有待进一步研究。     

Palaeoclimatic record from a loess–soil profile in northeastern Bulgaria—I. Rock magnetic properties

A detailed record of mineral magnetic properties of a loess–palaeosol profile comprising seven loess horizons, six interbedded palaeosols and recent soil at the top in NE Bulgaria is analysed. A strong contrast between the soil and loess susceptibilities as well as other concentration-dependent hysteresis parameters is present, similar to the well-documented magnetic characteristics of the Chinese loess ( Hus & Han 1992 ; Maher & Thompson 1992 ; Heller & Evans 1995 ; Hunt et al. 1995 ). The magnetic enhancement of the palaeosol units is caused by very fine-grained pedogenic magnetite with superparamagnetic behaviour. Thermomagnetic analyses on bulk material suggest magnetite and maghemite as the main ferrimagnetic carriers in both soil and loess horizons. Their relative proportions are shown to reflect different palaeoclimatic conditions. Chernozem soils, which include recent soil S₀ and first and second palaeosols S₁ and S₂ developed under steppe vegetation, show a high degree of low-temperature oxidation of the pedogenic magnetite to maghemite. This material is characterized by coercive force H _c showing even higher values than those of the parent loess material. The older palaeosols (S₄ to S₆ ) were formed during more humid climatic conditions and therefore probably developed as forest types. Rock magnetic data suggest the existence here of only partly oxidized magnetite grains. The behaviour of the thermomagnetic curves, characterized by a kink at 200 °C, may be due to either a release of internal stress (built up as a result of partial low-temperature oxidation) or interactions between two phases.     

Integrating soils and geomorphology in mountains—an example from the Front Range of Colorado

Soil distribution in high mountains reflects the impact of several soil-forming factors. Soil geomorphologists use key pedological properties to estimate ages of Quaternary deposits of various depositional environments, estimate long-term stability and instability of landscapes, and make inferences on past climatic change. Once the influence of the soil-forming factors is known, soils can be used to help interpret some aspects of landscape evolution that otherwise might go undetected.The Front Range of Colorado rises from the plains of the Colorado Piedmont at about 1700 m past a widespread, dissected Tertiary erosion surface between 2300 and 2800 m up to an alpine Continental Divide at 3600 to over 4000 m. Pleistocene valley glaciers reached the western edge of the erosion surface. Parent rocks are broadly uniform (granitic and gneissic). Climate varies from 46 cm mean annual precipitation (MAP) and 11 °C mean annual temperature (MAT) in the plains to 102 cm and −4 °C, respectively, near the range crest. Vegetation follows climate with grassland in the plains, forest in the mountains, and tundra above 3450 m. Soils reflect the bioclimatic transect from plains to divide: A/Bw or Bt/Bk or K (grassland) to A/E/Bw or Bt/C (forest) to A/Bw/C (tundra). Corresponding soil pH values decrease from 8 to less than 5 with increasing elevation. The pedogenic clay minerals dominant in each major vegetation zone are: smectite (grassland), vermiculite (forest), and 1.0–1.8 nm mixed-layer clays (tundra). Within the lower forested zone, the topographic factor (aspect) results in more leached, colder soils, with relatively thin O horizons, well-expressed E horizons and Bt horizons (Alfisols) on N-facing slopes, whereas soils with thicker A horizons, less developed or no E horizons, and Bw or Bt horizons (Mollisols) are more common on S-facing slopes. The topographic factor in the tundra results in soil patterns as a consequence of wind-redistributed snow and the amount of time it lingers on the landscape. An important parent material factor is airborne dust, which results in fine-grained surface horizons and, if infiltrated, contributes to clay accumulation in some Bt horizons. The time factor is evaluated by soil chronosequence studies of Quaternary deposits in tundra, upper forest, and plains grassland. Few soils in the study area are >10,000 years old in the tundra, >100,000 years old in the forest, and >2 million years old in the grassland. Stages of granite weathering vary with distance from the Continental Divide and the best developed is grus near the sedimentary/granitic rock contact just west of the mountain front. Grus takes a minimum of 100,000 years to form.Some of the relations indicated by the soil map patterns are: (1) parts of the erosion surface have been stable for 100,000 years or more; (2) development of grus near the mountain front could be due in part to pre-Pennsylvanian weathering; (3) a few soil properties reflect Quaternary paleoclimate; and (4) a correlation between soil development in the canyons and stream incision rates.     

Geomorphology and late Quaternary of the Chaco (South America)

The Chaco is a large tropical plain located in the interior of South America, consisting of parts of Argentina, Paraguay and Bolivia. It is 840,000 km² in area and is characterized by forests, savannas and extensive swamps, which give it a marked climatic and biogeographic identity. It encompasses five huge alluvial fans built by the major rivers which cross the region: Salado, Bermejo, Pilcomayo, Parapetí and Grande. The fans are composed of several sedimentary units, deposited during different times of the late Quaternary under diverse climates. Two fluvial terraces appear at the apex of each fan; the older one is probably late Pleistocene in age, the second was formed in postglacial times. Humid climates, such as the present one, favoured the generation of soils and stable fluvial belts; drier climates led to widespread sedimentation along small ephemeral channels and large spill-outs. During two intervals, on in the late Quaternary glacial maximum and the late Holocene dry climates occurred in the region, leading to the formation of dune fields and loess mantles.     

青藏高原东北部残积母质土壤发育过程研究——以青海湖北部宁夏剖面为例

残积母质是青海湖地区重要的成土母质之一,目前对高原残积母质土壤的研究相对匮乏,特别是其形成发育的年代尚不明晰,限制了对高原残积母质土壤演变过程的认识及对区域气候环境演变的理解。为探究青藏高原东北部残积母质土壤的发育过程及其发育模式,以青海湖北部宁夏（NX）剖面作为研究对象,通过光释光（Optically stimulated luminescence,OSL）测年获得残积母质土壤发育年代,采用化学蚀变指数（Chemical index of alteration,CIA）、Rb/Sr和粉黏比等探究土壤发育程度,对比青海湖地区河湖相沉积和黄土的Zr/Nb、K₂O/Al₂O₃和TiO₂/Al₂O₃分析其物源。结果表明：NX土壤剖面在早全新世以来发育,其年代结果集中在10.02~8.67 ka,成土母质发育时间与流域内风沙强烈活动时期基本一致,为干暖气候背景下的产物;通过物源对比分析,NX剖面底部母质为母岩就地风化而成,上部为风尘加积发育,发育模式为混合母质风尘加积型;剖面整体处于弱化学风化阶段,土壤发育程度较弱。     

北亚热带江淮地区白浆化土壤的发生学特性

通过孢子花粉、石英砂颗粒和土壤微形态学分析,研究北亚热带江淮地区白浆化土壤的发生学特性。白浆化土壤下部土体经历了暖温带森林草原景观和亚热带草原景观,为高能化学环境。在母质沉积后,经历了褐土化过程或其他物质堆积,经过一定时期的沉积间断后,堆积新物质,随着气候的变化,成土环境演变为现代气候类型,属亚热带森林草原环境。淀积层也源于黄土状物质,风化程度更强,白浆层则为后期堆积物,不具备高能化学环境。淀积层在高能环境下,存在次生粘化和淀积粘化作用。     

青藏高原东缘山地古冰川沉积物磁化率特点及其影响因素分析

湖泊、黄土与古土壤、深海沉积物等连续沉积体的磁化率变化作为环境变化的替代性指标被广泛应用,然而对于非连续、能够反映特定时段气候变化的沉积体,如冰川沉积物的磁化率却较少涉及.本文通过对青藏高原东缘8 个典型冰川发育山地冰碛物磁化率进行研究,并与黄土、湖泊、深海沉积物以及不同区域的表土磁化率进行对比,采用质量磁化率和频率磁化率探讨冰碛物的磁化率特点及其影响因素.结果表明：青藏高原东缘山地的冰碛物质量磁化率呈宽幅波动,介于(3.01~1808.80)×10^-8 m³·kg^-1,平均值147.84×10^-8 m³·kg^-1;频率磁化率值较低、且波动幅度小,介于0~6.89%,平均值为1.37%.不同时空条件下冰碛物的磁化率特点不同,即不同地点同一冰期磁化率的差异显著;同一地点不同冰期冰碛物的磁化率变化不明显.影响冰碛物磁化率的主导因素是母岩的岩性条件,气候因素起次要作用.     

WEATHERING TRENDS IN FINE DEBRIS BENEATH A SNOW PATCH,NIWOT RIDGE,FRONT RANGE,COLORADO

Seven soil pits dug in a downhill sequence beneath Martinelli snow patch, Niwot Ridge, Front Range, Colorado, reveal that soils are coarse-grained with only limited evidence of silt translocation. Clay mineralogy within the pits exhibits a widespread and distinct change at a depth of ～15–20 cm. The most common characteristic of this change is a distinct increase in vermiculite in the lower layer, usually accompanied by a decrease in kaolinite and/or smectite. This pattern is interpreted to reflect decreased weathering intensity with depth. Microenvironments beneath the snow patch which exhibit high chemical weathering rates on coarse surficial debris also appear to experience high rates of clay production relative to referenced dry alpine sites, with specific clay mineralogies varying in a fashion commonly found in humid temperate environments. Data generated in this study appear to provide site-specific support for the regionally-developed Synthetic Alpine Slope Model. Spatial variations in eolian additions and meltwater produce complex patterns in chemical weathering of fines beneath large snow patches, although the nature of clay-mineral change is typical of humid, temperate, mid-latitude environments. [Key words: chemical weathering, alpine environments, clay mineralogy, Synthetic Alpine Slope Model.]     

新疆西风区黄土与古土壤磁化率变化特点

在东部季风区的黄土研究中,磁化率是反映季风区气候变化的重要替代性指标之一,但关于中国西风区黄土磁化率的研究至今仍然为空白。通过对新疆典型的西风区——伊犁地区现代土壤和两个典型剖面黄土与古土壤序列磁化率研究发现,两个剖面黄土与古土壤磁化率特征存在差别。地处荒漠草原地带的则克台黄土剖面中马兰黄土的磁化率值略高于弱成壤层,末次间冰期古土壤层的上部磁化率也低于黄土,与东部季风区相比黄土磁化率偏高;而位于草原地带的库尔德能布拉克剖面黄土磁化率为低值,古土壤为高值,表现出与东部季风区类似的变化特点。两个黄土剖面所反映的磁化率的区域差异在一定程度上揭示了气候对磁化率变化的控制作用,但另一方面也反映了该区磁化率物理意义的复杂性。提出虽然在西风区黄土记录研究中不能简单套用东部季风区的方法,但磁化率和碳酸盐含量在西风区可指示湿度变化。     

夏季风降水在我国西北地区不同粒级方解石记录上的反映

碳酸盐含量一直被作为指示干旱和季风变化的良好指标,但其发生与夏季风降雨的关系始终没有得到明确的科学证明。通过西北黄土覆盖区到物源区现代土壤、全新世古土壤S0和末次冰期最盛期黄土L1中不同粒级方解石含量的系统分析,揭示出中、粗粒级方解石含量少、变化小和无规律性,而＜2 μm粒级的细粒方解石含量高、变化大,且规律性强。现代土壤和古土壤S0淋溶层中的细粒方解石含量随降水量的增大而降低,黄土L1中方解石的含量变化则没有明显的规律性,与方解石总量和碳酸盐含量变化类似。这表明细粒方解石含量是导致方解石总量和碳酸盐含量变化的主体,代表了成壤时期形成的次生方解石,反映了成壤作用的强度和夏季风降水的变化。     

辽南滨海黄土粒度环境信息高分辨率研究

对辽南滨海黄土粒度研究证明 ,滨海黄土是在第四纪冰期寒冷气候下的产物 ,但是 ,由于滨海黄土所处靠近沿海的地理位置使得这种黄土的形成机制具有独特性。冰期时渤海湾西岸海面下降出露的冲洪积物和海底砂是滨海黄土除西北内陆地区以外的另一重要物源 ,搬运以风砂跃移方式进行。滨海黄土的粒度中包涵了丰富的有关渤海湾海面变化的信息。辽南滨海黄土剖面中的粒度拟合值、 2 - 3Ф粒级百分含量反映了渤海的海退、海侵过程和末次冰期蒙古高压的强弱 ,这种变化与滨海黄土 3个孢粉组合带所反映的古气候环境相吻合 ,同邻近地区的海面升降变化和深海岩芯氧同位素阶段也存在良好的对应关系 ,滨海黄土粒度的拟合度是本区古环境变化的重要的替代指标。     

Pollen-based reconstructions of Holocene vegetation and climatic change of Tibetan Plateau

A synthesis of Holocene pollen records from the Tibetan Plateau shows the history of vegetation and climatic changes during the Holocene. Palynological evidences from 24 cores/sections have been compiled and show that the vegetation shifted from subalpine/alpine conifer forest to subalpine/alpine evergreen sclerophyllous forest in the southeastern part of the plateau; from alpine steppe to alpine desert in the central, western and northern part; and from alpine meadow to alpine steppe in the eastern and southern plateau regions during the Holocene. These records show that increases in precipitation began about 9 ka from the southeast, and a wide ranging level of increased humidity developed over the entire of the plateau around 8-7 ka, followed by aridity from 6 ka and a continuous drying over the plateau after 4-3 ka. The changes in Holocene climates of the plateau can be interpreted qualitatively as a response to orbital forcing and its secondary effects on the Indian Monsoon which expanded northwards     

太白山高山带环境特征

对比国内外关于高山带景观划分的多种观点，采用气候树线以上部分为高山带的划分方法，重点讨论太白山高山带自然环境，包括第四纪冰川遗迹和现代冰缘作用影响下的高山、亚高山地貌，研究区内主要气候要素的分布状、特别气温和降水的时空分配分布格局，土壤有机质的空间分异，以及在这种环境条件下高山带的植物区系和植被分布格局。太白山高山带的各种环境要素之间密切相关，是表现特殊的自然综合体。在全球气候变化背景下，其自然环境特点及变化值得密切关主。     

Soils and landscape evolution of eolian plains: the Southern High Plains of Texas and New Mexico

Sheets of eolian sediment cover many areas of the earth's surface, sand seas, dune fields, and loess sheets being the best known examples of such features. Less well known are deposits of sandy, eolian sediment forming extensive plains. An excellent example of such a region is the semi-arid Southern High Plains (northwest Texas and eastern New Mexico). The level landscape of the area was created by deposition of multiple, extensive (≈ 80,000 km²) sheets of eolian sediment (Blackwater Draw Formation) over the past 1.4+ Ma. This deposit grades from sandy (southwest) to silty and clayey (northeast) and is up to 27 m thick. Surface soils (at least 30,000 and possibly 120,000 years old) are well developed (5YR hues, agrillic horizons, 1–2m thick with prismatic structure, Stage II–III calcic horizons) and are generally Paleustolls and Paleustalfs, with some Paleargids and Haplargids. Morphologic variation is due mainly to textural variation of the eolian parent material, although locally thickness of the parent material and wind erosion and cumulization are important factors, and locally slight variation in effective precipitation may be significant. The Blackwater Draw Formation contains as many as six well-developed buried soils, each formed in individual layers of eolian sediment, similar to or more strongly expressed (2.5YR hues, higher illuvial clay content) than the regional surface soils. The presence of the buried soils indicates that sedimentation was episodic and separated by long periods of relative landscape stability. Eolian processes also appear to have been important during the periods of stability and pedoenesis by providing clayey, calcareous dust that was added to the soil, promoting formation of the argillic and calcic horizons. The sedimentologic and pedologic uniformity of the deposit suggests that the regional environment has not varied significantly during the Quaternary except for periods of increased sedimentation or wind deflation. Underlying the Blackwater Draw Formation is an Upper Tertiary deposit (up to 36 m thick) of eolian sand, silt, and clay (Ogallala Formation). This deposit contains buried soils very similar to those in the Blackwater Draw Formation, suggesting that the geomorphic processes that created the Quaternary landscape of the Southern High Plains began to operate in the late Tertiary, perhaps as much as 11 million years ago.     

A preliminary study of the quantitative couplingbetween loess-paleosol sequences and summer monsoon changes

IntroductionRecentscientificresultsshowthatclimahcfactorsaredrivingforcestoenvironmentalchanges,whilesoils(Pajeosols)areoneofthebestrecorders.AlargeareaofloessdeposihonduringandsincetheQuartemareinChinaprovidesfairlyagood"soil"forst'UdythecouplingbetWeenloess-paloesolsequencesandspatio-temporalclimaticchanges.Temporally,high-resoluhonloess-paleosolsequencesontheLoessPlateau--NortheasternTibetanPlateauarethemostconhnuousandcompleteclimaticrecordsterrestrially,whichcorrelateverywellwiththose…     

则克台黄土粒度组分分离及其记录的末次冰期气候波动

北大西洋地区的末次冰期气候波动在全球具有广泛记录。伊犁地区作为西风区向季风区过渡的边缘带,对气候变化响应敏感,千年尺度气候波动如何影响该区域有待进一步解答。黄土作为恢复古气候的重要地质记录,有利于上述问题的研究。通过对伊犁则克台剖面黄土沉积进行粒度端元分析,结果表明：则克台黄土粒度可分为四个端元,分别为EM1（0.8 μm）、EM2（8 μm）、EM3（25.1 μm）和EM4（51.6 μm）。EM1代表成壤组分;EM2代表高空西风组分;EM3和EM4代表尘暴组分,但EM4组分更能够反映末次冰期西伯利亚高压在伊犁地区的扩张。EM2和EM4都能记录千年尺度气候的波动,但响应程度却不同：51.3~20 ka,EM4含量变化曲线记录的千年尺度气候事件更为明显;然而20 ka之后,千年尺度事件在EM2含量变化曲线中更为突出。这表明西风和西伯利亚高压都是千年尺度气候信号的重要扩散机制,且造成上述差异的原因很可能是太阳辐射驱动下的北半球冰量变化。     

Natural environmental changes and human impact reflected in sediments of a high alpine lake in Switzerland

From the high alpine Sägistalsee (1935 m a.s.l.), 13.50 m of continuously laminated sediments comprising the last 9050 years, were analyzed. Even though Sägistalsee is a high elevation site, human-induced environmental changes start as early as 4300 cal. BP and leave a clearly detectable signal in the mineralogy of the sediments, which is much stronger than the signal from natural environmental changes that occurred before this time. Variations in the physical and mineralogical sediment properties of this clastic sequence reflect erosional changes in the catchment, where almost pure limestone contrasts with carbonaceous, quartz-bearing marl, and shist. The calcite/quartz (Cc/Qz) ratio was found to be most indicative of these changes, which occurred around AD 1850 and at 650, 2000, 3700, and 6400 cal. BP. The first four are interpreted as erosion events, which are related to human-induced changes in the vegetation cover and land use. We associate them to the recent development of tourism and grazing, the medieval intensification of pasturing, Roman forest clearance, and Bronze Age forest clearance, respectively. The Cc/Qz-ratio increases significantly within less than 100 years during these events, reflecting the erosion of unweathered or poorly weathered soils. The time intervals in between are characterized by a gradually decreasing Cc/Qz-ratio and reflect the stabilization or formation of new soils. Only the change at 6400 cal. BP, which represents the initial gradual stabilization of the catchment, is related to the immigration of Picea abies.     

新疆阿尔泰山东段冰碛物光释光测年研究

冰川是塑造地表形态最积极的外营力之一,对冰川地貌的年代学研究是重建古冰川发展史的关键,也是研究气候变化的重要途径。冰碛物是冰川作用的直接产物,代表过去发生的冰川事件,对冰碛物进行准确测年能够为重建古冰川的进退、理解区域古气候变化提供年代学支撑。本文在新疆阿尔泰山东段采集了8个冰碛物样品以进行光释光测年,利用单片再生剂量法对90~125 μm的石英颗粒进行等效剂量的测定。通过等效剂量值频率分布特征及De（t）坪区图分析得出大部分冰碛物的光释光信号晒退不彻底,所以利用一阶动力学公式对持续激发的光释光信号晒退曲线（CW-OSL）进行多组分拟合拆分,得到快速、中速、慢速3种组分,依据分离出的快速组分确定等效剂量值。研究结果显示,距今32 ka以来阿尔泰山东段区域在MIS3阶段、MIS2阶段、8.2 ka左右、全新世大暖期及新冰期等5个时段有冰川发育,冰川发育与气候变化密切相关。