Pedostratigraphic Sequences Research Articles

Catastrophic flashflood and mudflow events in the pre-historical Lajia Ruins at the northeast margin of the Chinese Tibetan Plateau

Global change induced regional environmental variation and related catastrophic surface processes have greatly affected human life and social development during the last decades. These occurrences have also been highlighted by pre-historical catastrophes exposed by archaeological excavation in the Lajia Ruins at the northeast margin of the Tibetan Plateau, which has attracted considerable focus from both geologists and the world media. The cause of the disasters responsible for the destruction of the Lajia Settlement (14C age 4.15–3.85 ka BP) of the Qijia Culture remains controversial due to insufficient investigation of the Holocene sedimentary succession needed to establish a complete pedo-stratigraphic sequence and chronology, and thus to precisely constrain environment variation and related surface processes at that time. During our field investigations, a complete and continuous Holocene soil and sediment profile was identified in the northern part of the Lajia Ruins uniquely. Soil and sediment samples were taken systematically for physical and chemical analysis and optically stimulated luminescence (OSL) dating after detailed field observations and descriptions. The results demonstrate that the pedo-stratigraphic sequence includes Malan loess (L1-1, >11.50 ka BP) and transitional loess (Lt, 11.50–8.50 ka BP) in the bottom, a composite palaeosol (S0, 8.50–3.10 ka BP) in the middle, and recent loess (L0, 3.10–1.50 ka BP) and modern soil (MS, 1.50–0 ka BP) in the top. This pedo-stratigraphic sequence is comparable to those identified in the central part of the Loess Plateau. However, the mid-Holocene palaeosol (S0) is inserted by three layers of red clay (RC1, RC2, and RC3) and flashflood deposit (FFD), and thus subdivided into four sub-layers (S0-upper, S0-upper middle, S0-lower middle, and S0-lower). The red clays and the flashflood deposit are inferred to represent abrupt events of flashflood and mudflow that were dated to 3.96–3.65 ka by OSL and to 3.85–3.60 ka BP by AMS 14C methods. Indeed, the entire settlement, dwellings, pottery artifacts, and human skeletons in the Lajia Ruins are directly packed by these deposits. The Lajia Ruins is thus considered to be destroyed by enormous flashfloods and mudflows coming from the Ganggou and Lüjiagou gullies, which submerged the settlement at 14C 3.85 ka BP or OSL 3.96 ka. These disastrous events are related to climatic deterioration since 4.20 ka BP that has resulted in severe convective weather and strong rainstorms affecting the northeast margin of the Tibetan Plateau. With consideration of the badly deformed ground and dwelling floors in the Lajia Ruins by crisscrossing earthquake fissures, that are also infilled and packed by flashflood and mudflow deposits, it is concluded that great earthquakes occurred as the first hitting to the settlement at Lajia. The enormous flashfloods and mudflows may have been induced by multiple earthquakes and rainstorms simultaneously. These results bear important implications for a better understanding of pre-historic environmental change and human-land relationship evolution at the northeast margin of the Tibetan Plateau.

Paleoenvironmental reconstruction of an urban archaeological site: The Roman Salt mines of Vigo, northwest Iberia

AbstractPedostratigraphy applied to urban archaeological coastal sites, combined with coastal geomorphological and archaeological data, provide important information for interpreting the complexity of coastal urban areas and their environment. This paper applies this methodology in the case of the Roman salt mines of Vigo, northwest Spain, and presents geomorphological and geoarchaeological data (stratigraphy, physicochemical soil properties, mineralogy, radiocarbon dating) for the museum where these remains are located. A 2000 year pedostratigraphic sequence was reconstructed, showing coastal evolution from beach to marshland. This change, along with more favorable climatic conditions related to the Roman Warm Period and dynamics associated with late Holocene rising sea level, created suitable conditions for the establishment of a salt mine. Geoarchaeological work is essential in archaeological excavations of modern urban areas, as demonstrated at Vigo where the study of pedostratigraphy provides crucial information on past environmental changes and human activities. Pedostratigraphic records and archaeological remains should be considered part of the geological and cultural heritage of urban areas.

Pedological investigation of an early Bronze Age site in southern Italy

AbstractArchaeological excavations over the last 40 years in Campania (southern Italy) confirm intense human occupation since the early Bronze Age (EBA). A pedological analysis of a ∼9 m deep pedostratigraphic sequence at Palma Campania (Naples) provides insights into fertility, rates of soil formation, and environmental conditions over the past 10 kyr. Fourteen volcanic soils formed in parent materials from Vesuvius and Campi Flegrei volcanic eruptions were analyzed. Results show that soils differ markedly in terms of thickness, andic properties, chemical fertility, and degree of development. Chemical properties, along with specific soil micromorphological features (such as silt coatings, laminar structure, iron segregations), are interpreted in terms of pedogenetic processes and used to reconstruct past environmental conditions. The degree of soil development, evaluated on the basis of organic matter content and some andic properties, proved more indicative of climate and geomorphological stability than duration of pedogenesis. Since the excavation also revealed an extensive EBA paleosurface and soil, targeted analyses were carried out to gain a better understanding of the impact of human activities and domestic animals on soil properties.

A multi-index analysis of the extraordinary paleoflood events recorded by slackwater deposits in the Yunxi Reach of the upper Hanjiang River, China

Paleoflood investigations were carried out on the first river terrace along the upper reaches of the Hanjiang River, a major tributary of the Yangtze River in China. Several bedsets of paleoflood slackwater deposit (SWD) were found within the eolian loess-soil profiles in the Yunxi Reach of the upper Hanjiang River. The pedo-stratigraphic sequences were studied using a multi-index approach, including magnetic susceptibility, particle-size distribution, loess-on-ignition, chemical elements and micro-morphology. Both the sedimentary criteria and the analytical results show that the paleoflood SWDs were clearly differentiated from eolian loess and paleosol in the same profile by their abrupt vertical change in the pedo-stratigraphy. The studies indicate that these paleoflood SWDs were deposited from the suspended sediment load in floodwaters and hardly affected by the subsequent weathering and pedogenesis. We have identified four episodes of extraordinary paleoflood events occurred on the Hanjiang River during the last 18,000years. The paleoflood events were dated to 12,500–12,000aB.P., 7500–7000aB.P., 3100–3000aB.P., and 1000–900aB.P. respectively, by using the OSL method in combination with archeological dating of anthropogenic remnants, and with pedo-stratigraphic correlation with well dated profiles in the upper Hanjiang River. The flooding events are considered to respond to climate variability in relation with the monsoonal shift and coincide with the global climatic events recorded by other climatic proxies in different regions of the world. This study is of great significance for understanding the interactions between hydro-climatic systems and global change in sub-humid regions.

Upper Pleistocene loess-palaeosol records from Northern France in the European context: Environmental background and dating of the Middle Palaeolithic

In Northern France the loess cover from the Last glacial (Weichselian) is represented by a semi-continuous mantle up to 8 m in thickness in the best localities such as leeward slopes (E–NE exposures). In this large area, pedostratigraphic sequences from the last Interglacial-glacial cycle (Eemian-Weichselian) have been intensively studied, especially under the auspices of active rescue archaeological programmes that have provided hundreds of individual sequences from test-pits or excavations. In spite of variations in the thickness of the different stratigraphic units, driven by differences in geomorphological contexts, the pedostratigraphic sequences from the last Interglacial-glacial cycle exhibit a particularly constant pedosedimentary pattern, including well-identified pedological and periglacial marker horizons that can be followed towards the East in Belgium, in Germany and even in Central Europe. According to the newest data, it is shown that northern France loess-palaeosol sequences are well suited to record the response of Western European environments to rapid climatic changes (Dansgaard–Oeschger cycles). The main objective of this paper is to present a summary of the pedostratigraphic sequence from Northern France, supplemented by the data from the new reference sequence of Havrincourt and a global correlation scheme with surrounding areas. In Northern France, the synthesis of the observations carried out on ca. 100 sequences during the last 20 years allows the establishment of a highly detailed pedostratigraphic and chronostratigraphic scheme that represents a unique database for the discussion of the relations between Palaeolithic occupation and environment. In this context, a strong relationship between the intensity of human occupation and the climatic and environmental context is demonstrated. This relationship appears to be conditioned by the relative abundance of large mammal fauna, itself linked to vegetation density, as indicated by the extremely sparse biomass and the hiatus in human occupation that characterise Upper Pleniglacial loess.

Reconstruction of the pre-Merida glaciation, northwestern Venezuelan Andes

Valley glaciers have been well studied in the northwestern Venezuelan Andes over the last 20-year period but most reconstructions have been limited to the Last Glacial Maximum (LGM). Analyses have been confined to the mapping of moraine positions and the detailed analysis of pedostratigraphic sequences reaching back through the Middle to the Early Wisconsinan (Weichselian) Glaciation. Using bedding macrofeatures, fabric analysis (magnetic azimuths) with mirror images, clast inclination and microtextural evidence much has been learned about the lithology, source of ice, growth of an ice cap in the eastern cordillera and weathered state of surface paleosols. Analysis of two sections of pre-Mérida age, the only two such sections known in the Sierra de Santa Domingo (eastern cordillera), provides new information on lithology, source of the ice and weathered state of sediment of pre-Mérida age. The fabric in these sections is used to deduce the build-up of valley ice in the lower El Caballo Valley from an ice cap similar to one that developed later in Early Mérida time (~ 90 ka to ~ 65 ka). The presence of weathered tills in both sections suggests two glaciations perhaps correlative with the Illinoian and Kansan glaciations of North America. The weathered state of tills and outwash in both sections is assessed on the basis of geochemical (INAA) and mineral composition (XRD) and microtextural evidence determined by SEM/EDS.

Reconstruction of the Early Mérida, pre-LGM glaciation with comparison to Late Glacial Maximum till, northwestern Venezuelan Andes

Valley glaciers have been well studied in the northwestern Venezuelan Andes over the last 20-year period with most sourcing reconstructions limited to the Last Glacial Maximum (LGM) and confined to the mapping of moraine positions and the detailed analysis of pedostratigraphic sequences reaching back into the Middle Wisconsinan (Weichselian) Glaciation. Using bedding macrofeatures, fabric analysis (magnetic azimuths) with mirror images, clast inclination and microtextural evidence determined with the FE-SEM (Field Emission Scanning Electron Microscopy) and EDS (Energy Dispersive Spectroscopy), and micromorphology of the PED5 composite section of Early to Late Mérida age was analyzed to reconstruct the till succession and glacial dynamics. The fabric is used to reconstruct the build-up of valley ice in the lower Mucuñuque Valley, the icecap spreading over the upper catchments of neighbouring drainage basins toward the headwaters of the Mucuchache Valley over a time frame estimated to be < 90 ka and lasting to ∼ 60 ka. Microtextural analysis was invoked to determine if physical differences on quartz and garnet mineral surfaces could be determined between various diamictons such as subglacial, flow and meltout tills, and outwash. Sample identification was made optically and with EDS. The evidence supports the theory that a substantial ice mass – a virtual icecap – existed during the Early Mérida stade of the last glaciation with the ice mass originating and decaying from the upper Mucuñuque Catchment south over some 40° of arc. This is the first evidence for an icecap complex in the northwestern Andes. Comparison between Early and Late Mérida glacial styles indicates that, in the Mucuñuque–Mucuchache corridor of the Mérida Andes glaciation in the LGM was catchment restricted with no evidence of icecap growth.

Stratigraphy of near-valley head quaternary deposits and evidence of climate-driven slope-channel processes in southern Brazilian highlands

Abstract During the past 40 years colluvial and alluvial deposits have been used in Brazil as good indicators of regional landscape sensitivity to Quaternary environmental changes. In spite of the low resolution of most of the continental sedimentary record, geomorphology and sedimentology may favor palaeoenvironmental interpretation when supported by independent proxy data. This paper presents results obtained from pedostratigraphic sequences, in near-valley head sites of southern Brazilian highlands, based on geomorphologic, sedimentologic, micromorphologic, isotopic and palynologic data. Results point to environmental changes, with ages that coincide with Marine Isotopic Stages (MIS) 5b; 3; 2 and 1. During the late Pleistocene, although under temperatures and precipitation lower than today, the local record points to relatively wet local environments, where shallow soil-water saturated zones contributed to erosion and sedimentation during periods of climatic change, as during the transition between MIS 2 and MIS 1. Late Pleistocene events with ages that coincide with the Northern Hemisphere Younger Dryas are also depicted. During the mid Holocene, slope-wash deposits suggest a climate drier than today, probably under the influence of seasonally contrasted precipitation regimes. The predominance of overland flow-related sedimentary deposits suggests an excess of precipitation over evaporation that influenced local palaeohydrology. This environmental condition seems to be recurrent and explains how slope morphology had influenced pedogenesis and sedimentation in the study area. Due to relative sensitiveness, resilience and short source-to-sink sedimentary pathways, near-valley head sites deserve further attention in Quaternary studies in the humid tropics.

Registro de mudanças ambientais Pleistocênicas e Holocênicas em depósitos de cabeceira de vale: Campo Alegre, planalto norte catarinense (SC)

Low resolution of continental sedimentary record is a common source of skepticism about the application of geomorphology and sedimentology to Quaternary studies. However, when supported by independent proxy data, geomorphology and sedimentology favor palaeoenvironmental interpretation. This paper presents results obtained from pedostratigraphic sequences, in valley head sites of southern Brazilian highlands, based on geomorphological, micromorphological, sedimentological, isotopical and palynological data. Results point to environmental changes, which ages coincide with Marine Isotopic Stages (MIS) 5b; 3; 2 and 1. During the late Pleistocene, in spite of temperatures and precipitation lower than today, the local valley head record points to wetter local environments, where shallow soil-water saturated zones contributed to erosion and sedimentation during periods of climatic change. During the mid Holocene, slope wash deposits suggest a climate drier than today, under the influence of seasonally contrasted precipitation regimes and torrential overland flow on hillslopes. The predominance of overland flow-related sedimentary deposits suggests an excess of precipitation over evaporation influencing local palaeohydrology. This palaeohydrological condition seems to be recurrent and explains how slope morphology had influenced pedogenesis and sedimentation in the study area, in response to environmental changes.

REGISTRO DE MUDANÇAS AMBIENTAIS PLEISTOCÊNICAS E HOLOCÊNICAS EM DEPÓSITOS DE CABECEIRA DE VALE: CAMPO ALEGRE, PLANALTO NORTE CATARINENSE (SC)

Low resolution of continental sedimentary record is a common source of skepticism about the application of geomorphology and sedimentology to Quaternary studies. However, when supported by independent proxy data, geomorphology and sedimentology favor palaeoenvironmental interpretation. This paper presents results obtained from pedostratigraphic sequences, in valley head sites of southern Brazilian highlands, based on geomorphological, micromorphological, sedimentological, isotopical and palynological data. Results point to environmental changes, which ages coincide with Marine Isotopic Stages (MIS) 5b; 3; 2 and 1. During the late Pleistocene, in spite of temperatures and precipitation lower than today, the local valley head record points to wetter local environments, where shallow soil-water saturated zones contributed to erosion and sedimentation during periods of climatic change. During the mid Holocene, slope wash deposits suggest a climate drier than today, under the influence of seasonally contrasted precipitation regimes and torrential overland flow on hillslopes. The predominance of overland flow-related sedimentary deposits suggests an excess of precipitation over evaporation influencing local palaeohydrology. This palaeohydrological condition seems to be recurrent and explains how slope morphology had influenced pedogenesis and sedimentation in the study area, in response to environmental changes.

Using pedostratigraphic levels and a GIS to generate three-dimensional maps of the Quaternary soil cover and reconstruct the geomorphological development of the Montagnola Senese (central Italy)

Pedostratigraphic levels (PLs) are characteristic assemblages of soil genetic horizons, formed in materials having a similar degree of weathering, and maximum age that is estimated by correlation to benchmark soils. In a pilot area of central Tuscany several soil profiles were studied and correlated with four different PLs, attributed to the Holocene, Late and Middle Pleistocene, and Early Pleistocene. The assignment of the surveyed depth made it possible to reproduce the geographic distribution of different pedostratigraphic sequences. Pedostratigraphic sequences were then related to soil map units, to obtain their geographical distribution. The objective of this work was to use PLs in a GIS environment to generate a set of three-dimensional (3D) maps of the Quaternary soil cover, and to analyze the spatial distribution of each level during main intervals of the Quaternary. The results indicate the geographical distribution of PLs is likely related to tectonic activity throughout Pleistocene and human utilization of the land during the Holocene.

Comparison of isotope stages 1–61 with the Baoji-type pedostratigraphic section of north-central China

Until now, comparisons between terrestrial and marine proxy climatic records have been achieved successfully only for the last 1.2 Ma or back to oxygen isotope stage 36. The Baoji loess–paleosol section of north-central China possesses 37 field-identifiable paleosols and 37 loess units representing a time span of about 2.5 Ma. The Baoji section is judged by the authors to be the most complete pedostratigraphic sequence in north-central China. This section, coupled with recent success in correlating isotope records back to stage 63, or approximately 1.88 Ma, has enabled a more detailed comparison over a longer time span. Using magnetic reversals as markers, the records are shown to have nearly equal numbers of identifiable warm and cold periods during the last 1.8 Ma. In addition, although there are exceptions, data sets reveal similar patterns during the same time intervals, indicating climatic events on a global scale.

L'enregistrement des phénomènes pédo-sédimentaires et climatiques. L'exemple de la coupe des Tares (Dordogne)

Recent detained works On coUuvial deposits in South-West France intend to build a litho- and pedostratigraphic sequence of the last interglacial-glacial climatic cycle, as paleoclimatic interpretations from cave deposits soon available were for few years called in question again. Les Tares section (Dordogne) is nowadays the most complete one and is taken there as an example. The microscopic characteristics of paleosols are used for correlating this section with theses from the northern part of France. Thus, we can clearly show : — a complex of soils «lessivés» and washed deposits, related to the Eemian interglacial and the early glacial; — gelifluction deposits correlated with the whole or a part of the weichselian pleniglacials. A permafrost, associated with eolian silts deposits, occurs during a late episode, which is probably equivalent to the upper pleniglacial. — the complexity of the superficial soil, which is affected by reworking processes in a cold environment, we consider as the last cold stage of the tardiglacial. We point out the presence of hiatus, probably of a great importance, which are due on the one hand, to intense periglacial upturns, and on the other hand, to biological activity. These processes explain that only major climatic events are recorded, in particular long stabilization soil periods or very cold stages.

Chronology of weathered materials and soil age determination in pedostratigraphic sequences

Subdivision of weathered (soil) continuums on the basis of age relationships often proves to be a difficult and contentious issue. Geochronological separation of weathered materials is normally achieved by application of absolute and relative dating methods. Radiocarbon residence times, uranium series dating, zircon-fission track ages, and thermoluminescence techniques have, for example, been used to estimate the timing of weathering events. Because many weathered materials are not amenable to isotopic age determination, relative dating methodologies which employ sedimentologic and stratigraphic principles have been applied to advantage in the chronological ordering of weathering mantles. Particle-size grading downslope and provenance of litho- and pedo-relicts help identify soil-sedimentary sequences. Interpretation of soil—geomorphic relationships, lithologic discontinuities, and pedogenetic overprinting as well as concepts of relative and effective soil age, micromorphological analysis of soil fabric sequences and investigation of skeleton grain morphologies are useful in the reconstruction of weathered sedimentary environments. Surface textures and mineral grain shapes in particular seem to offer clues to mineral provenance and geochronology of weathered deposits.