重要环境与气候变化事件:深时古土壤的记录与响应

古土壤蕴含着其形成时期的表生环境特征,是研究过去环境变化的重要地质记录。受长期埋藏与成岩作用影响,深时古土壤形态特征与现代土壤存在差别,但仍保留明显区别于相邻岩层的土壤发生学特征。土壤发生层、根系痕迹、新生体、微形态等特征有助于辨识古土壤,而古土壤元素地球化学、成壤碳酸盐C、O同位素等是判断古土壤发育强度和重建古环境与古气候的重要方法。深时古土壤记录了前寒武纪大气组成与生物演变、泥盆纪乔木出现、二叠纪末的气候突变、白垩纪大气CO2波动、早始新世的高热气候及晚新生代高原隆升等重要环境与气候变化事件,在地球表层系统的"深时研究计划"中发挥着重要作用。目前古土壤学在埋藏与成岩作用影响、环境替代指标、古环境重建模型、时间分辨率等方面有待深入研究。     

四川盆地中生代古土壤发生学特征及古环境意义

古土壤形成于地质历史时期的地球表面,直接记录了其形成时地球陆地表层的环境信息.以四川盆地中生代古土壤为研究对象,通过古土壤的形态与微形态、矿物组成、颗粒组成以及地球化学等成土特征的观察与分析,开展土壤发生学特征概述与分类研究并探讨古土壤指示的环境意义.结果表明:(1)四川盆地中生代古土壤具有生物遗迹、成壤碳酸盐结核、土...     

辽宁朝阳凤凰山剖面古土壤序列土壤发育特征研究

通过对形态特征、矿质元素含量变化及分布特征、元素的淋溶(或聚积)状况、土壤发育指标等进行分析,探讨了辽宁朝阳凤凰山剖面古土壤序列的土壤发育特征和发育程度。研究结果表明,在凤凰山古土壤剖面中,自地表向下至19.85 m范围内,除现代土壤层S0(0～108 cm)外,还可划分出9个土壤地层,包括5层黄土(L1～L5)和4层古红土(S1～S4)。所有这些土壤地层都是发育在风积粉尘母质上的古土壤,形成时间介于71～423 ka B.P.之间。古土壤的发生与成土母质(粉尘)的沉积同步进行,发育成红色还是黄色的古土壤决定于不同的成土环境条件和粉尘沉积速率的相对大小。在凤凰山古土壤序列中,各层古红土比各层黄土质古土壤经受了更强的风化和淋溶作用,古红土发育程度明显强于黄土质古土壤。5层黄土质古土壤比较,土壤发育程度最弱的是L1层,最强的是L5层;比较4层古红土的发育程度,最弱的是S2层。纵观凤凰山古土壤序列,各个发育不同程度的古土壤交错排列,说明当地成土环境(气候)在423～71 ka B.P.间经过多次波动变化。     

四川盆地晚中生代古淋溶土发生学特征与形成因素研究

[目的]理解和揭示深时古土壤的形成与演化有助于了解地球宜居性的形成与演化、促进土壤发生学理论的发展.[方法]以四川盆地晚中生代侏罗系和白垩系地层发育的古土壤为研究对象,通过对典型剖面的形态与微形态、矿物组成、颗粒组成以及地球化学等发生学特征的观察与分析,开展深时古土壤发生学特征与分类研究,并基于母质、气候、生物、地形和...     

辽宁朝阳地区第四纪古红土特性及系统分类研究

为弄清北方古红土在中国土壤系统分类中的位置,对辽宁朝阳地区分布的第四纪古红土的特性和系统分类进行了研究。本文首先将古红土看做成土母质,按《中国土壤系统分类检索(第三版)》的原则和方法,讨论了供试古红土剖面的诊断层和诊断特性,并进行了分类检索;又从古红土本身的发生学特征出发,讨论了各古红土剖面的诊断层和诊断特性,并进行了分类检索。研究发现:现行的《中国土壤系统分类检索(第三版)》还不能给古红土一个合适的位置,要解决古红土在中国土壤系统分类中的位置问题,首要任务是建立关于古土壤的诊断标准。     

从古土壤看北京环境变迁

古土壤是在古自然环境条件下形的土壤,西胡林黄土剖面位于北京低山丘陵区,埋藏有七层古土壤,根据形态和微形态特征,可以划分出碳酸盐型古土壤、普通褐土型古土壤,淋溶褐土型古土壤和棕壤型古土壤。其地球化学特征和土壤学特性的研究表明,各古土壤类型之间和发生层之间存在着显著差异,通过古城磁测年和地层对比,确定古土壤的年龄。在研究古土壤性状的基础上,配合孢粉分析,可以勾画出北京低山丘陵区的环境变迁,北京地区自50万年前至1万前,交替经历了14次温湿、冷干的气候变化。     

黄淮海平原晚第四纪古土壤

本文运用孢子花粉,古生物化石和放射性碳断代等手段,从土壤剖面层段的特征,土壤年龄和环境变化方面证明,分布于黄淮海平原的变性土不是现代土壤,而是古土壤,该古土壤自晚新世晚期以来经历了三次沉积－成土作用旋回,其土壤发育程度较弱,且是由钙质结核土层,暗色土层,表土层和（或）淤土层组成的一个叠置型古土壤。     

西安少陵塬黄土—古土壤序列S_3剖面元素迁移及古气候意义

以西安少陵塬S3古土壤剖面为研究对象,通过地球化学分析并结合野外剖面观察,探讨该剖面的元素迁移、化学风化特征及其所揭示的气候变化等问题。结果表明:(1)少陵塬剖面S3黏化层具有3层结构,根据铁质胶膜发育、Ca CO3迁移等可以将S3剖面构型划分为黏化层(Bts1-Bts2-Bts3)、风化淋滤黄土层(BC)和Ca CO3结核淀积层(Bck);(2)Bts层Ca O与Ca CO3迁移程度最大,淋失率分别达到了-99.3%、-83.1%,Sr、Na2O和Mg O也发生了显著迁移,而Fe2O3、Al2O3和Rb则在黏化层略有富集,尤其Fe2O3和Al2O3在Bts3层有明显富集;(3)少陵塬S3古土壤介于初等风化向中等强度风化的过渡阶段,风化作用由BC→Bts2→Bts1→Bts3逐渐增强,Bts3已基本完成初期脱Ca、Na风化过程;(4)依据Ca CO3与Fe2O3的迁移富集特点确定,少陵塬剖面S3古土壤Bts3发育时的土壤为弱碱性,而Bts1和Bts2为碱性;初步确定少陵塬S3为黄褐土,S3发育时期西安地区的年均降水量为800 mm左右。     

黄土高原古土壤成土过程的特异性及发生学意义

中国西北地区 ,从中新世以来就有持续不断的风尘沉积。这种风尘沉积作用即使在气候较为湿热的古土壤发育时期也未中断。黄土上土壤发生的独特性在于成土过程与风尘沉积的同步性。这种独特的成土过程使得土壤剖面深厚而均匀 ,常呈复合性状。古土壤与下伏黄土 ,不再是土壤与母质的关系 ;古土壤的真正母质应是成土过程中不断添加的风尘物质。古土壤中并不存在埋藏A层 ,对古土壤进行A、B、C等发生学层次的划分值得商榷。由于富含碳酸钙风尘物质的不断添入 ,成土作用强度受到不断削弱 ,绝大多数古土壤的成土作用强度未达到棕壤的发育强度。     

新疆石城子遗址古代人类活动对土壤化学性质的影响

通过对新疆石城子遗址内古土壤和外部农田土壤剖面外观特征以及土壤碳氮磷等养分的对比分析,结果表明:古土壤剖面上含有古人类遗留的侵入体,而农田剖面上则无明显的侵入体。而且该地区人类活动对古土壤化学成分产生了明显的影响,其中土壤盐分、有机碳(SOC)、全磷(TP)和有机磷(OP)在各个历史时期均发生了明显的变化,人类活动还使土壤中元素含量的比值发生了明显变化,由有机磷占全磷比例(W_(OP)/W_(TP))和其他元素含量变化特征说明研究地点在近现代时期为耕作区,而在其他各个历史时期均为居民区。     

Paleosols of the southern coastal plain of Israel

Paleosols of the S coastal plain of Israel were studied in a characteristic sequence situated in the Ruhama badlands area. At the upper part of the sequence, there is a Loessial Arid Brown Soil (Calciorthids), characteristic of the mildly arid climate of the area. The soil has two calcic horizons and four clayey layers alternating with four calcareous layers which are beneath them. Physical, chemical, and magnetic‐susceptibility data and micromorphological evidence indicate that each clayey layer together with the calcareous layer beneath it forms a single pedogenic unit. These units are similar to modern Grumusolic soils (Xeric Paleargids or Xererthic Calciargids) that occur in the semiarid belt of the S coastal plain and develop on eolian‐dust parent material. The calcareous layers are in fact calcic horizons formed by leaching of the carbonates from the clayey layers and accumulated in the form of in situ carbonate nodules. The leaching of the carbonates is not complete; they were never completely leached in the past. This feature together with a typical brown color is also characteristic of the modern soils developed in the semiarid water regime of the area. The four superimposed paleosols represent four cycles. It is suggested that they were formed in two phases. During a dry environment, a short phase of rapid eolian‐dust accumulation prevailed, followed by a stable phase of soil development in a somewhat wetter climate. Dating by optically stimulated luminescence and previous dating by ¹⁴C in the area suggest that the upper two paleosol cycles belong to the Last Glacial period whereas the other two cycles are of an earlier age. The magnetic‐susceptibility values decrease with age and react different from temperate areas. Below the four cycles, two totally leached paleosols developed on sandy parent material occur. Both paleosols have a reversed magnetic polarity and are hence older than 780 ky BP. The upper one is a Brown Mediterranean soil, and the lower one is a Red Mediterranean soil. Thin‐section evidence suggests that they formed on terrestrial sand dunes.     

Near‐surface paleosols in coastal sands at the outlet of Hadera stream (Israel) in the light of archeology and luminescence chronology

Catenary changes, archeology, micromorphology, and magnetic mineralogy of paleosols in coastal sands, Israel, were investigated under chronostratigraphic control by available luminescence datings from adjacent sites. At the outlet of Hadera stream, eolianites (Hebrew: “kurkar”) underlie paleosols with Epipaleolithic (approx. 17–20 ky) artifacts at the top and occasional Mousterian (>40 ky) artifacts in the subsoil. The optically stimulated–luminescence/infrared stimulated–luminescence (OSL/IRSL) dates (>50–12 ky) from adjacent sites roughly agree with the archeological findings. The paleosols show a magnetically depleted Vertisol superimposed on a magnetically enhanced cumulative Chromic Luvisol (WRB) (USDA: Rhodoxeralf, Israeli class.: Hamra). The latter contain approx. 0.25 mm thick, isotropic clay infillings distinctly separated from the soil matrix. These infillings are tentatively interpreted as the result of strong environmental disturbances, such as surface desiccation, subsequent waterlogging, and enhanced dust deposition, presumably at the time of the Last Glacial Maximum. In addition to the massive accumulation of eolian dust, diverse pedogeomorphic changes lagging in time from the onset of climatic deterioration may have taken place in coastal settings. Recurrent desiccation cracks may have exposed subsurface materials repeatedly to sunlight, consequently resetting the luminescence signal. The eolianite sequences are thus distinct from loess/paleosol sequences from temperate climates and have to be treated more rigorously at a site‐specific level.     

Late Holocene paleopedological records contained in tephra from El Chichón volcano, Chiapas, Mexico

High rates of pedogenesis on unconsolidated volcanic materials imply the accelerated generation of the soil memory. The purpose of this research was to extract the high resolution (centennial scale) paleopedological records from the Late Holocene paleosols of the El Chichón volcano formed during the last 2000 years. We studied buried monogenetic Andosols on the dated tephras and a pedocomplex formed from a set of thin ash layers deposited on older Acrisol derived from shales. Particle size distribution, DCB-extractable Fe, oxalate-extractable Fe, Al and Si, sand and clay mineralogy, organic carbon content and stable C isotope composition in humus were evaluated and interpreted as the elements of the soil memory. However, some differences were found in properties of two buried soils, especially in the kind of A horizons. We attribute such differences of individual Andosols to be caused by ancient human impact because it has been demonstrated that humid conditions persisted during the last 1300 years. Thus the drought that was supposed to provoke the collapse of the Maya civilization at the end of I millennium A.D., should have been a short-term event, below the resolution of this paleopedological record. The Andic Acrisol pedocomplex demonstrated the domination of the humid tropical climate over longer time intervals (probably major part of the Holocene) with possible minor dry episodes.     

Late pleistocene paleosol sequences as an instrument for the local paleographic reconstruction of the Kostenki 14 key section (Voronezh oblast) as an example

A sequence of five paleosol units (with seven individual paleosol profiles) buried in the Late Pleistocene (20–40 ka) deposits was studied at the Kostenki 14 (K14) key section in Voronezh oblast with the use of a set of morphological, physicochemical, and instrumental methods. The upper-lying paleosols differed from the lower-lying paleosols in the less pronounced gley features, stronger aggregation of the soil material, more significant accumulation of carbonates, and higher percentage of calcium humates and fulvates. These features attested to the higher aridity of the paleoclimate and the development of the upper-lying paleosols under grassy vegetation. Within the studied paleosol sequence, the most developed profiles were typical of the soils that formed 27–32 ka ago during the Bryansk interstadial. The good aggregation, the presence of features left by the soil fauna activity, the high magnetic susceptibility, and the morphology of the secondary carbonates in the studied paleosols suggest that they were formed under meadow-steppe vegetation in well-drained positions and resembled modern cryoarid soils.     

The humus status of modern and buried volcanic soils in Mexico and its role in the paleogeographic interpretation of tephra-paleosol sequences

Chemical and optical characteristics of soil humus have been analyzed as “memory” components of the Pleistocene volcanic paleosols in Mexico. We have studied the A1 horizons of buried Andosols of the Nevado de Toluca series and of the modern Andosols formed under different bioclimatic conditions. Data on the organic matter of buried paleosols suggest that Andosols of the Nevado de Toluca series were formed in humid forest ecosystems. Optical characteristics of the humic acids and data on the molecular-mass distribution of the humus make it possible to assume that these soils were formed under pine forests rather than under fir forests.     

Upper Permian paleosols of the East European Platform: Diagnostics of pedogenesis and paleogeographic reconstruction

A vertical sequence of seven buried paleosols composing the Klimovsk pedocomplex was studied in the basin of the Sukhona River (Vologda oblast). These paleosols were formed according to the accumulative model of pedogenesis (pedosedimentation model). They had monogenetic profiles with eluvial-gley, structural, and carbonate-illuvial types of differentiation. The set of elementary pedogenic processes responsible for the development of these soils included gleyzation in the surface horizon and around the roots, the inter- and intrahorizon translocation and segregation of iron, structuring, humification, weathering, lessivage, the migration and segregation of carbonates, and the synthesis of palygorskite and analcime. The studied paleosol profiles make it possible to reconstruct seven pedogenetic stages; each of them lasted for about n × 10²–10³ years. The paleosols were formed on a flat lacustrine-alluvial plain with drying lakes and temporary streams. The stages of inundation and water stagnation on the surface alternated with the stages of drying of the territory. The climate was warm, with well-pronounced wet and dry seasons. Against this general climatic background, arid climatic epochs marked by the development of calcic paleosols alternated with humid climatic epochs marked by the development of noncalcareous paleosols.     

PaleoVertisols of the northwest Caucasus: (Micro)morphological,physical, chemical,and isotopic constraints on early to late Pleistocene climate

Physical and chemical properties, macro‐ and micromorphology, clay mineralogy, and stable‐isotope compositions of paleosols within a pedostratigraphic column (PSC) of early to late Pleistocene age, interstratified paleosols, and loess (NW Caucasus, S Russia) were examined to better understand the evolution of the pedogenic environment over this time period, separating the effects of postpedogenic diagenesis. The column includes eight paleosols and six intercalated loessic horizons. Most of paleosols represent Vertisols or vertic intergrades. Vertic features increase in the middle of the PSC, where the paleosols are more clayey in texture and reddish in color. The morphology of carbonate nodules and soft masses, morphology‐ and depth(age)‐related changes in stable C and O isotope compositions, soil color, redoximorphic features, clay mineralogy, and illuviated clay indicate periods of wetter pedoenvironment in the past and suggest the Pleistocene paleosols are polygenetic and were formed with several wet/dry stages under a climate generally similar to the modern environment in the N Caucasus (mean annual temperature approx. 9°C–12°C). Interpretation of the time sequence of climate/environmental change requires careful separation of pedogenic mineral phases from phases altered by later diagenesis. The early Pleistocene period of paleosol formation appeared to be wetter or more humid, resulting in more significant development of vertic features. The terrestrial ecosystem remained dominated by C3 vegetation throughout the formation of the PSC, with four small periods of change towards a greater proportion of C4 plants or increased moisture stress.     

Characterization of relict Late Pleistocene and Early Holocene paleosols buried in wedge-shaped structures on the southern coast of the Finnish Gulf

The physical and physicochemical properties and morphogenetic characteristics of the buried soddy gleyic and gleyed paleosols developed from the glaciolacustrine loamy sediments on the southern coast of the Finnish Gulf in the Late Pleistocene and Early Holocene (12–9 ka, calibrated) are considered. It is shown that the morphology and properties of these paleosols sharply differ from those of the enclosing gravelly sands deposited in the ancient basins. The latter substrates serve as the major type of soil-forming materials for the modern surface soils. The studied paleosols fill wedge-shaped structures dissecting the gravelly sediments. Their profiles are well preserved, though their normal horizontal orientation is disturbed; large soil blocks were displaced into the open wedges. The presence of these soils attests to the fact that the initial soil cover in the studied region was formed in the Late Glacial epoch soon after the retreat of the glacial sheet. The good degree of preservation of the paleopedogenic information recorded in the profiles of these paleosols is of great value for the paleoenvironmental reconstructions.