Paleosol Stratigraphy Research Articles

Structure of large flat-bottom depressions on loess interfluves of eastern Azov region (on the example of “Chervonaya Pad'”)

Geological and geomorphological structure of the “Chervonaya Pad’”, one of the largest orientated depressions of Eastern Azov region, was considered. The study is based on the results of the analysis of remote-sensing data and new geological data obtained during manual drilling and studying the coastal outcrops. Features of the morphological similarity between the neighboring large depressions and “Chervonaya Pad’” was revealed. It is evidence of the unity of their origin. This allows us to consider “Chervonaya Pad’” as a model object for research. The features of the geological structure and morphology of the “Chervonaya Pad’” show that the depression is a denudation form developed in the cover of loess deposits as a result of the impact of airflow on the surface. According to the paleosol stratigraphy, it was revealed that the main stage of the formation of the depression was in the end of the Middle Pleistocene.Based on the material obtained, the authors verify the existing hypotheses of the formation of the large flat-bottom depression relief of the Eastern Azov region. It is revealed that the previously proposed mechanisms for the formation of large depressions (thermokarst, erosion-suffusion, loess subsidence, estuary-lake) do not consistent with the actual data on the geological-geomorphological structure of the “Chervonaya Pad’”. The authors propose the hypothesis of the eolian-denudation (deflation) origin of large depressions of the Eastern Azov region.

Three-dimensional pore network characterization of loess and paleosol stratigraphy from South Jingyang Plateau, China

The deformation and failure of a loess slope are closely related to the loess collapsibility and permeability, which are primarily controlled by the pore geometrical structure. This is a microstructural investigation of loess and paleosol from Jingyang on the South Loess Plateau in China using X-ray micro-computed tomography to explore the three-dimensional pore structure by quantitative pore network parameters. The three soil types (L1, L2 and S2) exhibit complex pore structures and obvious anisotropy, as reflected by dense networks, wide pore size ranges and different pore throat radii and frequencies at different dip angles. From L1 to L2 to S2, the structure tends to become more compact, the pore size tends to decrease, and the connectivity tends to weaken; these differences chiefly depend on the particle composition. In soil with low clay content, the clay particles mainly act as connectors of silt and sand particles or adhere to their peripheries. With high clay content, the clay particles also combine with silt particles to form bulky aggregates, generating some large inter-aggregate pores and numerous fine intra-aggregate pores. Pore structure, which provides space for water movement, has a profound influence on the mechanical behavior of soil, and the relationship between permeability and pore structure is discussed. The results demonstrate the positive role that the pore (> 13 μm) proportion, pore connectivity and pore throat radius play in permeability. Both the pore throat radius and the permeability coefficient are greater in the vertical direction than in the horizontal direction, implying a large pore throat has a greater effect on water migration than that of multiple small pore throats.

Reconstructing Last Glacial Maximum and Younger Dryas paleolandscapes through subsurface paleosol stratigraphy: An example from the Po coastal plain, Italy

Paleosols are commonly used to reconstruct ancient landscapes and past environmental conditions. Through identification and subsurface mapping of two pedogenically modified surfaces formed at the onset of the Last Glacial Maximum (LGM) and during the Younger Dryas (YD) cold event, respectively, and based on their lateral correlation with coeval channel-belt sand bodies, we assessed the geomorphic processes affecting the Po coastal plain during the Late Pleistocene (30–11.5calky BP). The 3D-reconstruction of the LGM and YD paleosurfaces provides insight into the paleolandscapes that developed in the Po alluvial plain at the transitions between warm and cold climate periods. The LGM paleosol records a stratigraphic hiatus of approximately 5kyr (29–24calky BP), whereas the development of the YD paleosol was associated with a climatic episode of significantly shorter duration. Both paleosols, dissected by Apennine rivers flowing from the south, dip towards the north-east, where they are replaced by fluvial channel belts fed by the Po River. The LGM channel-belt sand body reflects the protracted lateral migration of the Po River at the onset of the glacial maximum. It is wider (>24km) and thicker (~15m) of the fluvial sand body formed during the YD. The northern margin of LGM Po channel-belt deposits was not encountered in the study area. In contrast, a spatially restricted paleosol, identified in the north at the same elevation as the southern plateau, may represent local expression of the Alpine interfluve during the YD event. This study highlights how 3D-mapping of regionally extensive, weakly developed paleosols can be used to assess the geomorphic response of an alluvial system to rapid climate change.

Paleosol architecture of a late Quaternary basin–margin sequence and its implications for high-resolution, non-marine sequence stratigraphy

Paleosol stratigraphy, a technique commonly applied in basin–margin settings to depict cyclic alluvial architecture on time scales of 10–100ky, can be consistent with regional accommodation trends at even higher temporal resolution (1–10ky), having strong implications for the sequence stratigraphy of late Quaternary, non-marine deposits. Three closely-spaced late Pleistocene paleosols (P1–P3), dating back approximately to 42–39, 35–31, and 29–26calkyr BP, respectively, form prominent stratigraphic markers across a lithologically homogeneous interfluve succession in the subsurface of Bologna, close to the Apenninic foothills. These paleosols are weakly developed (Inceptisols) and can be tracked continuously for 6km across the triangle-shaped interchannel zone between two gravel/sand-filled channel systems (Reno and Savena rivers). In particular, the thickest paleosol (P3) is a distinctive stiff horizon that can be traced into laterally extensive, erosional-based fluvial bodies. We infer the correlation between (P3) soil development (and channel downcutting) and the final stage of the stepwise Late Pleistocene sea-level fall that culminated at the marine isotope stage 3/2 transition around 29calkyr BP (low accommodation systems tract). A fourth laterally extensive Inceptisol, encompassing the Pleistocene–Holocene boundary (PH), represents the major phase of soil development since the Last Glacial Maximum and is inferred to be related to channel entrenchment at the onset of the Younger Dryas. With the exception of the Iron Age-Roman paleosol, which reflects a predominantly anthropogenic control, the Holocene paleosols are laterally discontinuous and invariably more immature (Entisols) than their Pleistocene counterparts. This trend of decreasing paleosol development (and correlatability) upsection is interpreted to reflect increasing (transgressive-equivalent) accommodation during sea-level rise, thus confirming the possible extension of models used to interpret the ancient rock record to short-term depositional cycles.

Loess–paleosol stratigraphy of Dukso area, Namyangju City, Korea (South)

As Korea lies between China, with a drier climate, and the wetter Japanese Islands, the Korean loess–paleosol stratigraphy constitutes an important record of variations in the East Asian monsoon climate. The loess–paleosol sequence consists of three loess layers (L1LL1, L1LL2, and L2) and three paleosols (L1SS1, S1, and S2) in the study area. L1LL1 accumulated near the surface, and is only about 5 cm in outcrop because it was removed for farming. L1SS1 is about 103 cm thick. Soil crack structures developed in the upper part of L1SS1 were formed by shrinkage or as seasonally frozen ground soil wedges during the early cold-dry stage of glacial period. L2 is 48 cm thick, with OSL ages of 167,000 and 186,000 yr. Magnetic susceptibilities of paleosols were higher than the loess layers. Fine quartz grains in the loess layers are characterized by rounded shape and pitted surfaces. Based on the presence of the AT tephra, OSL ages, soil color, soil crack structure, magnetic susceptibility, and median diameter, the loess–paleosol sequence of the Dukso section can be correlated with the Chinese loess–paleosol sequence between MIS 2 and 7.

A river erosion estimate on the Loess Plateau: a case study from Luohe River, a second-order tributary of the Yellow River

Based on fieldwork and terrace ages, which were determined using 14C, TL and paleosol stratigraphy, a general model was established for the development of the Yellow River terrace system. The ages for the terraces and valley flats of the Yellow River system are T 6—1.67–0.85 Ma BP, T 5—0.85–0.47 Ma BP, T 4—0.47–0.10 Ma BP, T 3—0.10–0.007 Ma BP, T 2—7.0–0.7 ka BP, T 1—0.7–0.3 ka BP, the higher valley flat—0.3–0.15 ka BP and the lower valley flat 0.15–0 ka BP, respectively. Each terrace or valley flat and corresponding paleo-valley represents a river erosion/deposition cycle. Using this model and selected geomorphic parameters of terraces and paleo-valleys from 10 typical cross sections of Luohe River, a tributary of the Yellow River, an attempt is made here to estimate paleo-river erosion since the Pleistocene on the Loess Plateau.

River response to an active fold-and-thrust belt in a convergent margin setting, North Island, New Zealand

High-resolution digital elevation data (TOPSAR 10-m grid) are used to reconstruct Late Quaternary growth histories of subtle folding in the Wairarapa fold-and-thrust belt, North Island, New Zealand. Outcrop data of deformed latest Miocene and younger strata are combined with observations of warped and faulted late Quaternary terrace surfaces to unravel the geomorphic and structural history of the Huangarua River valley. Optically stimulated luminescence (OSL) dating of loess that accumulated on these strath terraces and paleosol stratigraphy allow temporal correlation among the terraces and with glacial climate cycles since the Last Interglaciation. These data indicate that five intervals of strath cutting occurred, at ∼125, 60–70, ∼30, ∼15, and <10 ka. Strath beveling is largely independent of local folding or regional base-level change. We hypothesize that straths are cut when an increase in sediment supply, during cool climatic periods, brings river sediment load and river transport capacity into balance. In the Wairarapa, strath-cutting events appear to occur near the end of cool climatic cycles. This study shows that the identification of subtle departures from regional topographic trends becomes practical when a high-resolution DEM is available. After subtraction of an average valley gradient from the digital topography, the residual topography on the terrace treads reveals cross-valley and longitudinal tilting. Although rates of folding are slow and the magnitude of deformation is commonly limited to less than a few tens of meters, these topographic anomalies define fold axes that coincide with subsurface structures. When combined with time control, these anomalies serve to define the patterns and rates of fold growth over the past 125 kyears.

Characterization of the Chinese loess–paleosol stratigraphy by whiteness measurement

Changing color is one of the most striking features of loess–paleosol sequences in central China: the loess is light yellow and the interstratified paleosols are reddish-brown. Until a few years ago, conventional color description of loess sediments was made using a qualitative visual method, the Munsell system. To better understand the character of the color changes and to quantify results, whiteness and magnetic susceptibility were compared from four loess–paleosol sequences. Results show that the two parameters are highly correlated in the four sequences studied. Grain-size analysis and chemical extraction experiments indicate that the concentration and species of fine-grained iron oxides are major factors determining color changes in loess and paleosols. Whiteness and latitude values from the last glacial–interglacial sequence exhibit a linear relationship suggesting that whiteness will be a useful tool for reconstructing past atmospheric circulation, especially the East Asian summer monsoon. Whiteness and magnetic susceptibility in the Luochuan profile over the past 0.9 Myr display a strong correlation indicating that whiteness can be also used to reveal a long climatic history from Chinese loess–paleosol sequences.

Chinese loess record of monsoon climate during the last glacial–interglacial cycle

The thick loess–paleosol succession of central China contains a detailed record of changes in East Asian monsoon climate since the late Miocene Epoch. The alternating loess–paleosol stratigraphy closely resembles the marine oxygen-isotope record, implying that episodic dust deposition and pedogenesis are in phase with global ice-volume fluctuations and controlled by variations in solar radiation reaching the land surface. Deposits equivalent to marine isotope stages (MIS) 5 through 1 have been dated by 14C, 10Be, luminescence, and magnetic susceptibility and grain-size models. Malan Loess (MIS 4–2) decreases in thickness southeastward from >30 m in the western Loess Plateau to <5 m east of Xi'an. Downwind, Asian dust is found in Japan, the North Pacific Ocean, and the Greenland Ice Sheet, where it has a chemical signature that points to a primary source in western China. During glacial times, the mean dust flux in the central Loess Plateau reached 0.35 mm/year, whereas in interglacial times it fell to <0.1 mm/year. Times of high dust influx and reduced soil development coincided with strengthened winter monsoon conditions, which are inferred from variations in loess grain size. Times of decreased dust accumulation and strong pedogenesis, marked by high values of magnetic susceptibility, represent times of strengthened summer monsoon conditions. High-frequency fluctuations in dust influx during deposition of the Malan Loess include peaks that likely correlate with North Atlantic Heinrich events. The Younger Dryas oscillation is recorded in Chinese eolian and organic deposits by a shift from cool, humid late-glacial conditions to cold and dry conditions, followed by a return to milder, humid climate at the beginning of the Holocene. Warm, moist climate, associated with a strong summer monsoon, characterized the first half of the Holocene Epoch when a widespread paleosol complex developed on the Loess Plateau. Increased dust deposition during the middle to late Holocene marked a shift to cooler, drier conditions.

Climatic changes from the late Pliocene to middle Pleistocene in and around central Japan reconstructed from plant macrofossil assemblages

We used composition of plant macrofossil assemblages obtained mainly from theOsaka Group in central Japan to reconstruct the palaeoclimate between the late Pliocene (about 3.3m.y. B.P.) and the middle Pleistocene (about 0.4 m.y. B.P.). The warmest climate of the periodwas before 3.0 m.y. B.P. Cool-temperate elements increased and subtropical elements decreasedbetween 3 m.y. B.P. and 2.7 m.y. B.P., indicating the first climatic deterioration. The firstoccurrence of subarctic elements characterizes the Plio-Pleistocene boundary as a severe coldstage. After 1.1 m.y. B.P., climatic fluctuation occurred at less than 100,000 year intervals. Asevere cold stage occurred just after the Jaramillo event (about 0.8 m.y. B.P.). The warmest stagein the middle Pleistocene occurred at about 0.5 m.y. B.P. With it evergreen broad-leaved forestexpanded into central Japan. The climatic curves reconstructed from plant macrofossils parallel theclimatic changes reconstructed from loess - paleosol stratigraphy in Central China, radiolarianfaunal stratigraphy in the north Pacific deep sea drilling core, oxygen-isotope data in the NorthPacific, and pollen spectra in western Europe.

Quaternary paleosol stratigraphy and paleomagnetic record near Dreihausen, central Germany

Summary A succession of sediments and paleosols near Dreihausen in central Germany records a normal magnetic remanence throughout and appears to have formed during the Brunhes Chron. This sequence of sediments, and paleosols developed in bedrock, loess, colluvium, and residual regolith exhibits no clear evidence for secular variation swings or excursions, suggesting rather slow and intermittent sedimentation rates. The paleosols are primarily Alfisols with pronounced argillic horizons which formed during interglacial periods when climate was presumably warmer and certainly wetter than today. The distribution of higher clay in the older paleosol of Eemian age supports the hypothesis of strong interglacial paleoclimates relative to the present-day climate. Clay mineral transformations in these paleosols suggest a weathering sequence of illite → illite - smectite → vermiculite. Despite minor clay mineral transformations of this type, the data supports the interpretation of a mixed deciduous - coniferous forest during the Eemian Interglaciation.

Paleosol Stratigraphy of the Eskridge Formation; Early Permian Pedogenesis and Climate in Southeastern Nebraska

ABSTRACT At least five Aridisol- and Vertisol-like paleosols are developed within the Eskridge Formation (Lower Permian) in Richardson County, Nebraska; these soils are recognized by their prominent soil structure (peds, nodules and filled cracks), micromorphology (oriented clay fabrics, and iron cutans), and well-developed carbonate-enriched horizons. Eskridge paleosols represent significant decreases or cessations in terrestrial sedimentation during long-term subaerial exposure; direct evidence for drowning of three out of the five paleosols (by subsequent marine transgressions) indicates strong marine influence on the duration of pedogenesis. Stratigraphic fluctuations in the 13C and 18O values of Eskridge pedogenic micrites are potentially compatible with climatic fluctuations between wetter and drier conditions during the Permian, based on comparisons with isotope values from Cenozoic paleosols. Occurrence of fossil plants and coals, along with evaporites, as well as the different paleosol types, tends to support an interpretation of varying climate. Recognition of paleosols within the Eskridge improves the understanding of cyclic sedimentation and sea level change by recording several episodes of low terrestrial sedimentation and geomorphic stability; these episodes probably correspond to peak marine regressions.