Paleosols

L’érosion du littoral aquitain favorise, sur les plages du Nord Médoc, l’affleurement d’anciens niveaux de sols (dits paléosols) pléistocènes et holocènes sous jacents au cordon dunaire. Ils sont connus depuis le XIXe siècle, à la fois par les géologues, mais aussi par les archéologues. Aujourd’hui encore, ils font l’objet d’une surveillance attentive de quelques chercheurs et de passionnés d’histoire, dans le cadre du programme de recherche interdisciplinaire LITAQ, dirigé par Florence Verdin (CNRS, Institut Ausonius) et Frédérique Eynaud (Université de Bordeaux).
C’est ainsi que fut repéré, le dimanche 19 avril 2015, au moment du plus bas niveau de la marée, les restes d’un squelette de cerf sur la plage de l’Amélie Nord (Soulac-sur-Mer). Le lendemain, dans le cadre du projet LITAQ, une fouille de sauvetage fut programmée avant que l’ensemble des données ne soit emporté par l’Océan Atlantique. Le matériel faunique recueilli et les interprétations liées à ce dernier sont présentés dans cet article.

Slope and lowland sediment systems throughout southern Africa are dominated by the presence of colluvium with interbedded palaeosols and hardground duricrusts. These sediments correspond to phases of land surface instability and stability, respectively, during the late Quaternary. This study examines the stratigraphy and environmental interpretation of slope sediment records from specific sites in southern Africa for the period of marine isotope stages (MIS) 6 to 1 (~191 ka to present), informed by theoretical ideas of the dynamics of slope systems including sediment supply and accommodation space. Based on this analysis, phases of land surface instability and stability for the period MIS 6 to 1 are identified. The spatial and temporal patterns of land surface conditions are not a simple reflection of climate forcing, but rather reflect the workings of slope systems in response to climate in addition to the role of geologic, edaphic and ecological factors that operate within catchment-scale sediment systems. Considering these systems dynamics can yield a better understanding of the usefulness and limitations of slope sediment stratigraphies.

The Sausar belt on the southern flank of the Satpura Mountain Belt of Central India comprises several generations of granite gneisses and migmatites, and the metasedimentary rocks of the Sausar Group. A suite of ~3200-2450 Ma old rocks comprising of an older Tonalite-Trondhjemite-Granodiorite (TTG) gneiss and younger quartz-monzonite plutons (Tirodi Gneiss-I) constitutes the basement complex for the Sausar Group. The contact of Tirodi Gneiss-I and the Sausar Group records the geological history at Archaean-Palaeoproterozoic boundary. A paleosol horizon at this contact contains unusual minerals such as siderite, ankerite, uraninite, and alumino-silicate minerals. The geochemical data of the paleosol indicate a reducing environment of formation and oxygen deficient conditions in the atmosphere at the time of development of this paleosol at the Archaean-Palaeoproterozoic boundary. The Sausar Group is reported to contain coarse clastics, volcanics, glaciogenic sediments, cap carbonates, and fine clastics with manganese ore deposits. Geochemical data from the cap carbonate horizon above the glaciogenic unit and manganese bearing horizons above the cap carbonate confirm presence of reducing environment in the shallow ocean.

This report re-evaluates the depositional history, biostratigraphic “age,” and regional correlates of Chadron Formation rocks in North Dakota using a variety of data sources. A series of well-developed paleosols are herein recognized for the first time at the top of the Chalky Buttes Member across much of southwestern North Dakota. Those paleosols are contemporaneous with the Weta Paleosol Series of southern South Dakota developed on top of the Chamberlain Pass Formation, and together these paleosols indicate a period of nondeposition and geomorphic stability throughout the Great Plains region following a first phase of late Eocene deposition. Within the Williston Basin, that first phase of deposition begins with rocks dominated by group A heavy minerals (zircon > staurolite > aluminosilicates, tourmaline) that are overlain by rocks dominated by group B heavy minerals (epidote > garnet > zircon). Deposition of these group A and group B rocks would have occurred sometime in the early Chadronian (Ch1-Ch2: 36.9-35.8 Ma).

The second phase of late Eocene deposition in North Dakota consisted of local downcutting of stream channels that were infilled with rocks dominated by group D heavy minerals (hornblende > diopside > epidote). Two faunas are now known from these group D rocks: the late early Chadronian (Ch2: 36.6-35.8 Ma) Medicine Pole Hills local fauna, and the newly reported middle Chadronian (Ch3: 35.8-34.8 Ma) Stover Site local fauna (Adams County, North Dakota). This second phase of deposition occurred after the onset of paleosol development in North Dakota as indicated by the common presence of ferruginous aggregate grains within the opaque heavy minerals from the Stover Site sample that appear to be derived from erosion of paleosols developed on older Chalky Buttes Member rocks that contained group B heavy minerals. Deposition of group D rocks in North Dakota was contemporaneous with portions of those rocks infilling the base of the Red River Paleovalley in southern South Dakota (Ahearn and Crazy Johnson Members).

Deposition of the South Heart Member began gradually during the development of the paleosols within the Williston Basin, indicating those rocks are younger than the group A and group B rocks of the Chalky Buttes Member. Given the lack of biostratigraphic data from the South Heart Member and absence of those rocks within Bowman and Adams Counties where group D rocks of the Chalky Buttes Member are exposed, insufficient evidence is currently available to determine the relative timing of deposition of group D Chalky Buttes Member rocks and those of the South Heart Member. Overall, this study demonstrates that late Eocene deposition was more complicated than previously reported, though these patterns match those found elsewhere within the Great Plains region.

In 1961, the late Marlin G. Cline wrote a remarkable essay entitled, “The Changing Model of Soil” for the 25th Anniversary Issue of the Soil Science Society of America Proceedings. Cline was most impressed with how geomorphology was enriching pedology, and with the increasingly sophisticated views of soil time and of the processes of soil formation. We revisit Cline’s general objectives by re-evaluating the changing model of
soil from the perspective of the early 21st century, and by taking stock of the application of soil models to contemporary needs and challenges. Today, three ongoing changes in the genetic model of soil have far-reaching consequences for the future of soil science: (i) that soil is being transformed globally from natural to human-natural body, (ii) that the lower boundary of soil is much deeper than the solum historically confined to O to B horizons, and (iii) that most soils are a kind of pedogenic paleosol, archival products of soil-forming processes that have ranged widely over the life of most soils.
Together and each in their own way, these three changes in the model of soil impact directly human–soil relations and give structure and guidance to the science of anthropedology. In other words, human forcings represent a global wave of soil polygenesis altering fl uxes of matter and energy and
transforming the thermodynamics of soils as potentially very deep systems. Anthropedogenesis needs much better quantifi cation to evaluate the future of soil and the wider environment.

Archaeological investigations undertaken by the Proyecto Arqueológico Tlajinga Teotihuacán are focused on understanding urban expansion and household economies in this southern district of the city. Our geoarchaeological research addresses similar topics through examination of relevant microstratigraphic and botanical signatures as well as those relevant to reconstructing paleoenvironment. We investigated four different contexts at Tlajinga: the southern extension of the Street of the Dead, an obsidian working area outside Compound 17:S3E1, anthropogenic and natural layers below Compound 18:S3E1, and a soil profile at the San Lorenzo river. We employed micromorphological, pollen, and phytolith analyses as well as standard soil analytics to study the various deposits in these contexts. Our analysis demonstrates artificial lowering of the tepetate for continuing the axis of the Street of the Dead, microdebitage from obsidian working outside Compound 17:S3E1, and the preservation of in situ burning activities at Compound 18:S3E1. Further, we reconstruct alluvial infilling of the Street of the Dead with pedogenetic overprinting and present further evidence on the occurrence and variability of the Black San Pablo Paleosol and its agricultural significance.

A B S T R A C T As an important geological archive, paleosols have been widely used in reconstruction of paleoenvironmental and paleoclimatic conditions. In this study, we undertook detailed analyses of the clay mineralogy and carbon and oxygen isotopic compositions of pedogenic carbonates in a series of 13 paleosol horizons within a fluvial section of the Eocene (~52–44 Ma) Lulehe Formation in the Qaidam Basin. Pedogenic smectite and illite/ smectite (I/S) mixed-layer minerals are the predominant clay minerals in the paleosols, suggesting that the early Eocene paleoclimate of the Qaidam Basin was strongly seasonal with warm-wet summers. The high levels of pedogenic smectite production and high atmospheric pCO 2 reconstructed from soil carbonate nodule δ 13 C (mean −7.1 ± 0.8‰) are consistent with elevated temperatures during the Early Eocene Climatic Optimum (EECO). Coeval paleosol carbonate nodules yield estimated paleo-surface water compositions (δ 18 O psw) of −7.9‰ to −5.0‰ (VSMOW), which are significantly higher than the δ 18 O value of modern summer precipitation in the Qaidam Basin. The estimated temperature difference (~5.0 °C cooling) implies uplift of the study area by nearly 1000 m to its current average elevation of ~3000 m above sea level. This paleoelevation estimate agrees with modern meteoric water isotopes of Global Network of Isotopes in Precipitation (GNIP) sites in Asia in the same elevation range.

Interpretive cross sections based on detailed descriptions
of 33 outcrops and cores are used to better understand the relative
effects of tectonics, eustasy, tides, and climate on Upper Mississippian
(middle Chesterian) stratigraphy in the tectonically active, tide-dominated
Illinois basin. The cross sections show that five mixed carbonate–
siliciclastic, high-frequency sequences in the Bethel through Glen Dean
formations can be correlated around the outcrop belt through areas
with very different subsidence histories.
The sequence boundaries are marked by paleosols and incised valleys
and can be correlated basin-wide within a framework of distinctive
marker beds. Because of its updip position, lowstand systems tracts are
not preserved in the Illinois basin. The transgressive systems tracts
generally consist of one or two parasequences that are typically composed
of tidally influenced quartz sandstone filling incised valleys at
the base overlain by open-marine skeletal limestone, shallow-marine
shale, and heterolithic siliciclastic tidal-flat deposits. The maximum
flooding surface (MFS) for the sequences is picked at the base of the
deepest water limestone facies. Highstand systems tracts are composed
of 1 to 6 regressive parasequences that consist of basal offshore skeletal
limestone capped by laterally extensive shale and heterolithic siliciclastic
tidal-flat facies.
The basin-wide extent of the sequence boundaries and maximum
flooding surfaces across tectonic highs and lows suggests that the sequences
were produced by eustatic sea-level changes rather than local
tectonics or autogenic processes. The sequences were likely produced
by moderate- to high-amplitude (30–100 m) fourth-order (; 400 ky)
glacio-eustatic sea-level changes driven by the transition from the
greenhouse conditions of the Early Mississippian to the ‘‘icehouse’’
conditions of the late Paleozoic. The lateral extent and frequency of
component parasequences suggests that they were likely produced by
fifth-order sea-level changes (10–100 ky). The sequences may be bundled
into third-order composite sequences, but the third-order signal
is obscured by the magnitude of the fourth-order sea-level changes a
feature typical of ice-house stratigraphies.
The sequences can be used as time slices to identify spatial and temporal
variations in differential subsidence between the Cincinnati Arch
and the more rapidly subsiding Basin Interior. Episodes of high and
low differential subsidence occurred every two to three sequences.
These subsidence variations had a major impact on lithofacies distribution
and onlap and offlap geometries in sequences and parasequences.
The occurrence of some widespread seismically disturbed
beds suggests that active faulting occurred during deposition. Normal
faulting appears to have occurred during periods of high differential
subsidence and reverse faulting during periods of low differential subsidence.
Differential subsidence and related normal and reverse faulting
may have occurred in response to phases of thrust loading and
quiescence in the Appalachian orogenic belt to the east. Even in this
tectonically active setting, however, it is the eustatic signal that generates basin-wide, mappable stratigraphic sequences.

The Lower Permian (Wolfcampian) Abo Formation of south-central New Mexico was deposited by a silt-dominated fluvial system along the western half of the Orogrande basin a few degrees north of the equator in western Pangaea. Fluvial channel deposits consist primarily of: (1) inclined siltstone stratasets up to 4.5 m thick and 25 m wide interpreted as point bar deposits, and (2) symmetrically infilled siltstone stratasets up to 2.4 m thick and 14 m long that may represent avulsion crevasse channels. Both types of channels are dominated by climbing ripple cross-laminae and plane bed laminae, but trough cross-beds are also present, as are several types of soft-sediment deformation structures and desiccation cracks. Red silty mudstones interpreted as floodplain deposits comprise up to 70% of the formation and are interbedded with thin (<2 m) tabular siltstone beds of crevasse-splay/levee origin, as well as rare lacustrine carbonates (∼0.5 m thick) and structureless siltstones (<1 m thick) interpreted as loessites.Common pedogenic features in floodplain strata and on the tops of some fluvial channel beds include root traces, peds, and calcic nodules/tubules, whereas gypsum, gley colour mottling, and translocated clay and/or iron oxides are rare. Also present is an ichnofauna dominated by opportunistic arthropods that colonized the moist upper surfaces of recently deposited crevasse-splay/levee beds and the uppermost surfaces of fluvial channels following avulsion.The relative abundance of channel and crevasse-splay/levee deposits increases eastward in response to moderate asymmetrical subsidence of the basin, whereas calcic paleosols are more numerous on the more slowly subsiding western margin of the basin. A semi-arid to sub-humid palaeoclimate with seasonal precipitation favoured relatively deep rivers whose point bars were seasonally exposed, the formation of calcic and vertic soils, a sparse ichnofauna and flora, periodic desiccation of small carbonate lakes, and perhaps reworking of loess from the floodplain and/or upstream catchments.

Petrographic and calcrete carbon isotope data from seasonally waterlogged Upper Silurian (Přídolí) to Lower Devonian (Pragian) palaeo-V  ertisols of the Old Red Sandstone, South Wales, UK, are presented. The δ13C values mostly range from -9 to -12‰ (VPDB), suggesting the soils were inhabited by abundant vegetation that when oxidised (perhaps with microbial assistance) resulted in CO2-rich soils. Such soils would favour calcrete precipitation through equilibration of soil zone CO2 with the relatively lower atmospheric pCO2. However, reliably estimating palaeoatmospheric pCO2 calculated from these carbon isotope data is a challenge.

Se presentan los resultados del estudio parcial de los conjuntos de fitolitos localizados
en dos paleosuelos rubefactados de la Isla de Tenerife (Canarias), donde tales partículas
constituyen un depósito de microfósiles vegetales, desarrollados a nivel interno y
externo por antiguas plantas, cuya identificación y valoración permite conocer parte de
la paleoflora local en base a sus propiedades de diagnóstico taxonómico. Tal cualidad
deriva en la posibilidad de conocer las condiciones ambientales vinculadas a la
edafogénesis de este tipo de suelos. Las muestras fueron tomadas en dos perfiles de
suelos y sus registros de fitolitos nos han permitido valorar una metodología básica de
estudio paleoedáfico, aplicándola sobre los restos microscópicos depositados en este
tipo de suelos.
Las tareas de recogida de muestras, tratamientos de laboratorio y gabinete microscópico
verificaron la presencia de fitolitos en el perfil de la costa del Puerto de La Cruz (Los
Roques, 5 m.s.n.m.) y en el de las medianías de La Laguna (DECA-1, 400 m.s.n.m.).
Pese a no existir dataciones absolutas para ambos, trabajos anteriores permiten
enclavarlos en secuencias pleistocénicas de Würm II-IV, relacionándose con
condiciones climáticas propuestas como diferentes a las actuales, que propiciarían una
edafogénesis intercalada en la secuencia eruptiva aérea del edificio insular, bajo un
clima con mayores valores de humedad y temperatura. Los resultados confirman que
estos materiales pueden también calificarse como paleosuelos desde su contenido en
fitolitos, presentes en todos los niveles analizados (superficial, medio y profundo) y en
algunos casos en elevadas concentraciones (DECA-1). Dentro de los morfotipos
seleccionados como indicadores paleoambientales destacan las concentraciones de
fitolitos de células cortas Poaceae, donde prevalecen las gramíneas de tipo C3 frente a
C4 (familias Pooideae y Panicoideae respectivamente). Lo cual indica condiciones
climáticas más templadas y contrastadas que en la actualidad, al menos en las medianías
representadas por DECA-1 donde apenas existe rastro de palmáceas, como sí es habitual
en contextos edáficos holocénicos de Canarias. En el paleosuelo de Los Roques la
concentración de fitolitos de gramíneas es netamente inferior, aunque con mayor
representación de palmáceas e igual predominio de las gramíneas C3.

Plant fossils are rarely preserved within the Upper Permian of western Europe as the majority of continental deposits consists of siliciclastic redbeds. Because organic matter such as plant debris and palynomorphs is destroyed by oxidizing conditions, these red sedimentary facies were often considered as “devoid of life”. This paper presents new palaeobotanical data from the Upper Permian strata of Minorca (Balearic Islands, Spain). In addition, a rich and diverse “Thuringian” palynoflora was recovered from the Permian sediments, and several megafloral taxa are recorded. Additionally, a detailed sedimentological analysis of the studied section is provided. The Permian succession shows a general evolution from a ponded floodplain environment to sand-sheet rivers flowing across a semi-arid alluvial plain. Additionally, new palaeobotanical elements, added to the study of palaeosols, allow reconstruction of Late Permian plant growth within the terrestrial environment, as well as a palaeoenvironment reconstruction of the preserved sedimentary interval. At the transition between ponds and alluvial plain deposits, root systems surprisingly similar to those known in extant mangroves are described for the first time within Permian deposits. As there are no other palaeobotanical remains preserved in association, the type of plant that inhabited this environment remains conjectural.

While it is generally accepted that the initial Pleistocene human colonizers of the Americas likely entered the continents via the Pacific coast, formal models of their entry and dispersion into the continental interior are scarce. The ability to identify colonizer period archaeological sites for development of such models requires that researchers identify landforms of appropriate age and depositional character to target for large-scale archaeological survey. Well-preserved Upper Pleistocene and Early Holocene landforms are present across the Pacific Northwest. From coastal environs to the Palouse, these landforms represent a remnant landscape which initial colonizers explored at some point subsequent to the last glacial maximum. The types of landforms suitable for deposition and preservation of colonizer period archaeological sites include a broad array of settings, including: Coastal environments, characterized by relict Pleistocene-age landscape features shoreward of the submerged continental shelf; Continental ice-marginal and ice-distal depositional environments, where a variety of glaciomarine and long-standing glacial lakes formed behind the retreating Puget Lobe of western Washington State; Interior Scablands where cataclysmic outburst floods created scoured topographic lows that acted as local depositional basins—often holding paleo-lakes and marshes; and the Palouse loess within the Columbia Basin province, where eolian deposition has buried and preserved the Pleistocene and early Holocene landscape. Along the major drainageways, Upper Pleistocene to Early Holocene alluvial chronologies vary locally, but overall regional trends indicate that climate-controlled aggradation initiated between 12.0 to 11.0KBP, forming distinct terraces in the major river systems and their tributaries. Regional soil formation is evidenced by the Bishop Geosol which dates between 13.5KBP and 11.2KBP, present in a broad variety of depositional environments. Upper Pleistocene archaeology is sparse but present across the region; initial colonizers were broad-spectrum foragers whose toolkit included distinctive stemmed and shouldered bifaces, macroblade tools and crescents.

The Messak Settafet is a wide plateau located in the Libyan central Sahara (SW Fezzan); it is cut into the Nubian sandstone and interpreted as relic of a Tertiary peneplain, heavily affected by aeolian deflation. Notwithstanding degradation phenomena, discontinuous, thin soil bodies are locally preserved below the hamada. Several profiles, located in correspondence of different geomorphological units (the hamada, the endorheic depressions, and the southern escarpment), were described and sampled for micropedological analyses. Micromorphology outlined that the main characteristics of the residual B horizons from each geomorphological units are (i) high concentration of ferruginous nodules, (ii) multiple generations of clay illuviation, (iii) fragmentation and deformation of textural pedofeatures, and (iv) calcite mobilization and redeposition. According to horizon macro- and micromorphological characteristics, these pedologic bodies do not seem to be in equilibrium with the present-day climatic conditions and should be regarded as paleosols generated by processes regulated by large water availability and warm temperature, such as rubification, clay translocation, and calcite redistribution. The development of horizons acted mainly since the Early/Middle Pleistocene during subsequent pluvial periods and was interrupted by several erosional and aeolian input phases (arid periods). Pedological processes ended at the onset of the severe dry environmental conditions at the Mid-Late Holocene transition. The development of this kind of paleosols in the central Sahara is also discussed in comparison with pedogenetic processes occurring in temperate regions during interglacial and interstadial intervals.

Resumen: Se presenta el resultado de la investigación geoarqueológica conducida en el valle de Teotihuacan, con el objeto de establecer la distribución de asentamientos en diferentes periodos (Formativo, Clásico y Post-clásico) y su dinámica en la degradación ...

Fluvial, alluvial, lacustrine, and debris flow sedimentary rocks from the Keweenaw Peninsula (Michi-gan, USA) are geochemically characterized to examine weathering processes and provenance. These sedimentary rocks result from the erosion, weathering, and redistribution of effusive and plutonic igneous lithologies during periods of volcanic quiescence associated with the failed 1.1 Ga North Ameri-can Midcontinental Rift. Three units comprising the sedimentary/igneous-mixed Portage Lake Volcanics, coarseness and source-varied Copper Harbor Conglomerate, and the quartz-rich post-rift fill unit of the Jacobsville Sandstone were studied over a geographically-wide and lithologically-varied range of localities across the Keweenaw Peninsula, Michigan. Provenance indicators such as Ti/Zr and Ti/Al ratios and LaTh -Sc ternary diagrams reveal that the Portage Lake Volcanic conglomerates are near-source, and that the Copper Harbor Conglomerate is primarily derived from felsic uplifted basement and recycled orogen lithologies to the east. The Jacobsville Sandstone is a combination of pulses of sources from the top to the bottom of the stratigraphic section: (1) felsic arkosic arenites sourced from the erosion and uplift of basement orogenic volcanic and plutonic rocks (top), (2) felsic arkosic-subarkosic arenites sourced from the erosion of uplifted basement, recycled orogeny and reworking of primary sedimentary and metased-imentary rocks (middle), and (3) quartz arenites eroded from the cratonic interior (highly mature). This work can consequently aid in structuring a stratigraphic nomenclature for the Jacobsville Sandstone. Both petrographic data and weathering indices such as the chemical index of alteration (CIA) and the pale-osol hydrolysis metric (Al/Ca+Na+Mg+K) indicate low degrees of weathering during syn-rift deposition at 1.1 Ga, but increases with evolution of the rift in post-rift units toward the Late Mesoproterozoic/Early Neoproterozoic. Values for the CIA throughout the Mesoproterozoic from this and other localities have the same trend to that of proposed atmospheric CO 2 concentrations derived from paleosol data, demonstrating that characterizing the weathering trends of floodplain deposits can be a useful addition to deciphering past paleoclimatic conditions in the Precambrian geologic record.