Impacts of the ancient Maya on soils and soil erosion in the central Maya Lowlands

Many studies across the central and southern Maya Lowlands of Belize, Guatemala, Honduras, and Mexico have produced records of land degradation, mostly sedimentation and soil erosion, during the ancient Maya period from before 1000 BC to the Maya Collapse of c. AD 900. This paper provides new data from two sites (Blue Creek and Cancuén), synthesizes more than a decade of the authors' research in Guatemala, Belize, and Mexico, and synthesizes other findings from this region. These research projects analyzed more than 100 excavations in upland and depression sites, cored lakes and wetland sediments, and studied sediments in the field and laboratory using radiocarbon dating, a battery of soil chemistry tests, stratigraphic analysis, magnetic susceptibility, elemental analyses, and artifact identification. Our objective was to date when sedimentation and soil erosion occurred, identify stable surfaces, and correlate them with the state of knowledge about past land use. These findings indicate three general epochs of accelerated soil erosion and identified two major paleosols. The three waves of soil erosion occurred in the Preclassic period (c. 1000 BC to AD 250), the Late Classic (AD 550 to 900), and in the last several decades. The major paleosol (‘Eklu'um’) in these sites is a well-developed Mollisol or Vertisol that started forming in the early Holocene and was buried in either the Preclassic or Classic periods (AD 250 to 900). At some sites the Eklu'um paleosol lies beneath sediments with a fainter paleosol, which in turn lies buried below Classic period and later sediments. This picture shows higher than expected soil erosion linked to the region's first pioneer farmers in the Preclassic and less than expected soil erosion in the Late Classic when population peaked and land use was the most intensive. In other regions like Cancuén, Guatemala, however, most soil erosion occurred during the Maya Late Classic (AD 550–830). Erosion here was intense but short-lived: depressions record 1–3 m of aggradation in two centuries. A third epoch of accelerated soil loss and aggradation arose with the rapid land use changes brought by new pioneers during the last several decades.     

New insights on the loess/paleosol Quaternary stratigraphy from key sections in the U.S. Midwest

Three key Quaternary loess/paleosol sections were examined in the Missouri Valley (Iowa), Eustis Ash Pit (Nebraska), and in the Wittsburg Quarry (Arkansas) to gain insights into the sedimentation, environment and climate change of the U.S. Midwest. Four loess units are present separated by three well-developed paleosols. Crowley's Ridge Loess (Oxygen Isotope Stage (OIS) 8) is pre-Illinoian in age, and is the oldest loess unit investigated. A well-developed paleosol, interpreted as Yarmouth Soil (OIS 7), is found in this loess in all three sections. Overlying the Yarmouth Soil is Loveland Loess (OIS 6) which has been pedogenically altered by the Sangamon Soil (OIS 5). It has luvisolic properties but a more clayey pedogenic texture than modern luvisols and has no clear eluvial horizon. The overlying Roxana Silt (OIS 4) is pedogenically altered. At Wittsburg and Missouri Valley, the Farmdale Soil (OIS 3) is developed in the Roxana Silt. Based on pedogenic features, we correlate this paleosol to that developed in the Gilman Canyon Formation at Eustis. In Missouri Valley and Eustis sections, the paleosol has chernozemic properties and therefore, the gleyic features observed at Missouri Valley are interpreted as later alterations. Overlying the Farmdale Soil is the widespread Peoria Loess (OIS 2).     

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。     

Micromorphology of a Mousterian paleosol in aeolianites at the site Habonim, Israel

A paleosol with Mousterian tools in aeolianites at the Habonim site (Carmel Coastal plain, Israel) is a complex pedosedimentary sequence which records a succession of soil-forming episodes and stages of coastal dune instability. We identified three strong soils and one accretionary soil within Mousterian pedocomplex via micromorphological techniques, coupled with FTIR and SEM/EDAX. In the lowermost, red sandy soil (hamra) in Unit IV, decalcification led to the formation of micritic coatings, disrupted by faunal churning, while rubefication resulted in red ferric segregations. Illuviation of ferruginious clay in the form of clay coatings is lacking, probably due to its strong incorporation into the matrix. Redox features were intensified in the pseudogley of the next stage (Unit III). Polyphase calcitic features here indicate that illuviation of clay pre-dates illuviation of micrite and its later recrystallization into sparitic calcite. Further deterioration of drainage conditions and increased accumulation of fine particles led to the formation of vertisol (Unit II). Paleovertisol is characterized by a maximum of clay, stress-originated microfabric, abundant Mn precipitates and calcitic pseudomorphs. The peak of landscape instability occurred later and is recorded in the upper Unit I, in which micromorphological signs of colluvial and aeolian processes are juxtaposed with various ferric accumulations, associated with gleying. The final episode occurred at a time of climatic instability, devegetation, and probably, a simultaneous groundwater rise in the littoral zone.     

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。     

Characteristics of silica-rich pedofeatures in a buried paleosol

Whitish and whitish-light brown milky-like textural pedofeatures and impregnations were found in the voids and the matrix of buried paleosols older than 2.7 million years in a site in Sardinia, Italy. The pedofeatures were described and analysed using micromorphology, X-ray diffraction and microprobe techniques, and their spatial distribution correlated with field evidence. The suite of analyses showed that the main components of the pedofeatures were more or less ordered silica phases. As well as forming a matrix cement, these pedofeatures also occurred as coatings and infillings in pores. Significant amounts of alumina and, less, Mg, Ca and Fe were also present in the pedofeatures, possibly in the form of silicate coatings and inclusions/impurities, or alumino-silicates of the adjacent soil matrix. A number of hypotheses are drawn on the possible mechanisms of formation of these silica-rich pedofeatures, including the possibility of prolonged weathering of volcanic materials and the resulting formation of colloids and more or less ordered silica phases, with successive dehydration and progressive ordering of phases during the at least 2.5 million years.     

Paleosols from the groups of burial mounds provide paleoclimatic records of centennial to intercentennial time scale: A case study from the Early Alan cemeteries in the Northern Caucasus (Russia)

Buried soil chronosequences under a series of Early Alan kurgans (burial mounds) in the Vladikavkazkaya depression of the Northern Caucasus, Russia, were studied to derive a high-resolution paleoclimatic record from the variations of the selected paleosol properties. Haplic Chernozems occur under kurgans and on the actual land surface. Three kurgan cemeteries, Brut 1, Brut 2 and Beslan, dated from the end of the second to the beginning of the seventh centuries AD have been studied. The cemeteries are situated close to each other under similar lithological and geomorphological conditions but differed in the paleosols' preservation. The Brut 2 site has been recently altered due to annual ploughing and intensive irrigation for more than 30 years. The background soils and paleosols of the Brut 2 site have been compared with synchronous soils of non-irrigated Brut 1 and Beslan sites to detect pedogenic properties that are less changed by irrigation and thus comprise the “soil memory”. Stronger black color of humus horizon, increase of humus content and decrease of humus δ¹³C values; clear signs of biological activity, absence of morphological and analytical signs of solonetz properties; diffused carbonate white soft spots in the Bca horizon and decreasing carbonate content are thought to be related to the comparatively humid climatic conditions in the region. On the contrary, relatively low humus content, tongue-like lower boundary of humus horizon, increase of humus δ¹³C values, morphological signs of solonetz properties together with high content of exchangeable Na, relatively large and clearly shaped carbonate white soft spots in the paleosols of the Brut 2 site, as well as increase of density, thickness of the carbonate pseudomicellium and high carbonate content in the upper part of profiles in the paleosols of the non-irrigated Brut 1 site are assumed to be xeromorphic features, indicating comparatively drier climatic conditions. The paleosols of the earliest chronointerval of burial (the end of the second to the beginning of the third centuries AD) demonstrate clear xeromorphic properties which indicate a relatively dry climate with a mean annual precipitation 50–100 mm less than today. The estimated duration of the period with such climatic conditions is thought to be not less than 100 years. In addition, those paleosols have some weak signs of humid conditions indicating that between the end of the first and the middle of the second centuries AD the climate was getting more moist, mean annual precipitation became equal or slightly higher than today. The paleosols buried in the first half of the fifth century AD again demonstrate the gradual enhancement of xeromorphic properties reflecting the next stage of droughts. Thus, the period with favourable humid climate when the Early Alan culture flourished in the Northern Caucasus was relatively short (about 400 years). Studying the detailed chronosequence in the non-irrigated Brut 1 site the records of intercentennial time scale soil properties variability produced by comparatively “fast” pedogenic processes typical for the steppe zone i.e., humus formation and accumulation, bioturbation, carbonate accumulation and transformation and solonetzization, have been provided.     

Environment of the East Carpathian Foreland during periods of Palaeolithic man's activity

Several Palaeolithic sites have been discovered in the Halyč Prydnistrov'ja (East Carpathian Foreland) during the last 20 years; thereby this region becomes important when studying the development of Palaeolithic cultures in Eastern Europe. The cultural layers are associated with different horizons of paleosols in loess profiles. Palaeolithic materials were found in four stratigraphic horizons: two of them are of Middle Palaeolithic and two others of Upper Palaeolithic. Palaeogeographical and stratigraphical studies of loesses were the basis of reconstructions of the past landscapes. The palaeopedological study as well as pollen analysis give information about the past environment. Moreover, the molluscan fauna indirectly shows the character of vegetation cover. Relatively open deciduous or mixed forests were the environment of the older Middle Palaeolithic phase of settlement, open forests with patches of steppe and meadow habitats characterized the younger one. Open vegetation dominated during the Upper Palaeolithic. The qualities of local relief as well as local climate and environment in the East Carpathian Foreland and especially in the Dniester River valley were favourable for Palaeolithic hunters.     

Late Quaternary environmental change inferred from phytoliths and other soil-related proxies: Case studies from the central and southern Great Plains,USA

This study investigates stable carbon isotopes (δ¹³C), opal phytolith assemblages, burnt phytoliths, microscopic charcoal and Sporormiella spores from modern soils and paleosols in Kansas and Oklahoma. Grass and dicot phytoliths in combination with δ¹³C are used as proxies for reconstructing the structure of grasslands and woodlands. Burnt grass phytoliths and microscopic charcoal are evaluated as proxies for reconstructing paleofire incidence. Concentrations of the fungal spore Sporormiella are used as a proxy for assessing large herbivore activity. These proxies were tested on various modern grassland communities of the central and southern Great Plains, including areas with bison, cattle, and small herbivores, and areas under different fire frequencies.     

Paleoclimatic implications of micromorphic features of Quaternary paleosols of NW Himalayas and polygenetic soils of the Gangetic Plains — A comparative study

Micromorphological examination of the paleosols (50–10 ka) developed in alluvial fan deposits of the NW Himalayas and the bordering polygenetic soils (mainly Holocene) of the Gangetic Plains has been used to differentiate the pedosedimentary features indicating climatic changes during late Quaternary time. The paleosols within rapidly aggrading sediments of the alluvial fans of the Dehradun valley resulted in response to the reduced rate of sedimentation and climatic changes and correspond to the MIS3 and MIS2 stages. Distinctive micromorphic features of these paleosols provided the details of the prevalent pedogenesis in response to the paleoclimatic changes during 50 ka. Microfabrics of these paleosols show reorganization of the pedality from massive and/or subangular blocky to platy and prismatic structures, strong to very strong mobilization of the plasma, different types of textural pedofeatures along with faunal activities. These pedofeatures are indicative of cold-humid climate with subsequent change to even colder but drier conditions during the last Glaciation. Comparison of the micromorphological characters of the paleosols of the NW Himalayas and the polygenetic soils of the Gangetic Plains show the same degree of soil development indicating 5–10 ka pedogenic intervals in alluvial fans of the Dehradun Valley. However, the difference in their pedofeatures is attributed to different pedogenic environments. The paleosols of the Dehradun Valley show predominance of the illuvial features with superposed impure silty clay on earlier clay pedofeatures and banded clay fabric features without any pedogenic calcium carbonate. The bordering Gangetic Plains are covered with polygenetic soils developed on stable surfaces and are < 13.5 ka. These surficial soils developed during the period marked by deglaciation and correspond to MIS1 stage. These are defined by the juxtaposition of different illuvial pedofeatures along with pedogenic calcium carbonate. This study suggests that formation of the paleosols in NW Himalayas was mainly controlled by warmer intervals during the last glaciation and the movement along the adjacent thrusts. While fluctuating climate punctuated with humid–semiarid–humid conditions played a major role during the formation of soils on the Gangetic Plains in Holocene that favoured illuviation, calcification and dissolution of pedogenic carbonates in the polygenetic soils.