Paleosol Layers Research Articles

Effect of Magnetotactic bacteria on the susceptibility in Chinese loess–paleosol sequences

A simulated experiment of Magnetotactic bacteria (MB) effect on susceptibility in the samples from the 5th to 6th loess layers (L 5–S 5–L 6) in Xifeng and Duangjiapo sections was performed. It is demonstrated that MB can increase the susceptibility of the samples and promote newly produced magnetic minerals from paleosol layers under the suitable condition. The tiny magnetic particles and arranged as a chain in the minerals less than 30 μm were found in the paleosol sample of Duangjiapo section.

The Cyborg Astrobiologist: scouting red beds for uncommon features with geological significance

The `Cyborg Astrobiologist' (CA) has undergone a second geological field trial, at a red sandstone site in northern Guadalajara, Spain, near Riba de Santiuste. The Cyborg Astrobiologist is a wearable computer and video camera system that has demonstrated a capability to find uncommon interest points in geological imagery in real-time in the field. The first (of three) geological structures that we studied was an outcrop of nearly homogeneous sandstone, which exhibits oxidized-iron impurities in red and and an absence of these iron impurities in white. The white areas in these ``red beds'' have turned white because the iron has been removed by chemical reduction, perhaps by a biological agent. The computer vision system found in one instance several (iron-free) white spots to be uncommon and therefore interesting, as well as several small and dark nodules. The second geological structure contained white, textured mineral deposits on the surface of the sandstone, which were found by the CA to be interesting. The third geological structure was a 50 cm thick paleosol layer, with fossilized root structures of some plants, which were found by the CA to be interesting. A quasi-blind comparison of the Cyborg Astrobiologist's interest points for these images with the interest points determined afterwards by a human geologist shows that the Cyborg Astrobiologist concurred with the human geologist 68% of the time (true positive rate), with a 32% false positive rate and a 32% false negative rate. (abstract has been abridged).

Lipid distributions in loess-paleosol sequences from northwest China

Molecular stratigraphic analyses using GC/MS have been performed on the top section of the Jiuzhoutai loess-paleosol sequences near Lanzhou in northwest China, with a record extending from the second-last interglacial through the present interglacial. The various molecular fossils identified from the second-order loess and paleosol layers include C14–C35n-alkanes, C8–C30n-alkanoic acids, C12–C30n-alkanols and C23–C33n-alkan-2-ones. The CPI (carbon preference index) values and the ratio of C29/C31n-alkan-2-ones display alternations between loess deposits and paleosols. They show a significant correlation with the loess magnetic susceptibility, an indicator of the East Asian summer monsoon. The observed variations of the ketone indices in relation to the change of lithology are proposed to result from microbial re-working of higher plant inputs in the paleosols.

Geochemical study of boron isotopes in the process of loess weathering

In this paper the boron contents and boron isotopic composition of acid-soluble phases in loess and paleosol samples are determined for the first time. The boron contents of acid-soluble phases in the Luochuan loess section (S0–S2) vary within the range of (0.8–2.7)×10−6 and their δ11 B values vary from −1.8‱ to +18.6‱, mostly within the range of 0−+10‱. The boron contents and δ11 B values of paleosol layers are higher than those of loess layers, especially in the loess layer S1. Varying chemical weathering intensity and loess adsorption capability are the main factors leading to the variations of boron contents and δ11B values of acid-soluble phases in the loess section. The variation of chemical weathering intensity in response to the variation of climatic conditions seems to be the main factor leading to the variations of boron contents and δ11B values of acid-soluble phases in the loess section.

Palynomorphs in the first paleosol layer in the Yangtze Delta and their paleoenvironmental implication

The relatively abundant palynomorphs were recovered from the samples of the first paleosol layer of core CY in Shanghai for the first time. A total of 55 genera and families of spore, pollen and phytoplankton were identified. According to the characteristics of the palynological assemblages, the depositional conditions in the development period of the paleosols were discussed and the microfossil evidence to study the origin of the paleosols in the Yangtze Delta area was provided as well. The research results show that paleosols should be freshwater deposits. The palynological assemblage sequence in the first paleosol layer reveals fluctuations of freshwater palynomorphs, mainly Concentricystis, and terricolous herbs pollen, reflecting the alternations of deposition and exposure in the development period of the paleosols. Concentricystis developed prosperously in the period of flood, while terricolous herbs grew on the emerged land in the period of exposure. The variations in the palynological assemblages suggest that the depositional conditions were various during the formation of the paleosols, and resulted in obvious stage characteristics of the paleosol’s development. The dinoflagellate cysts occur in low abundance in the palynological assemblages of the first paleosol layer of core CY, indicating that the area where core CY lies was influenced by seawater in the depositional period of the parent materials of the paleosols.

PALEOPEDOLOGICAL INVESTIGATION OF THREE AGRICULTURAL LOESS SOILS ON THE LOESS PLATEAU OF CHINA

Paleopedology is important for a proper understanding of the agrochemical and agroenvironmental behavior of surface (nonburied) paleosols. A long agricultural history on the Loess Plateau of China has caused extensive destruction of natural vegetation cover and resulted in profound modification of the original soils. Chinese soil scientists have called them agricultural loess soils and termed them Lutu soil, Zhong Heilutu soil, and Qin Heilutu soil, with variations of profile properties from the southeast to the northwest. The present paleopedological investigation was conducted in three typical profiles at three locations along a south-north transect across the Loess Plateau. New data and evidence of mineralogy, micromorphology, palynology, soil properties, and radiocarbon dating indicate that the so-called agricultural loess soils are Holocene paleopedosedimentary complexes combined with human disturbance, which consist of a paleosol layer developed in the middle Holocene and a cover layer of human disturbed fresh loess developed in the later Holocene. The pedogenetic types of the paleosols varied from Ustalfs to Argiustolls and Haplustepts (in the U.S. system) along the S-N transect, with paleo-bioclimatic pattern of the middle Holocene. The cover layers (Ap horizons) are newly deposited loess of the later Holocene, 10 to 25% of which in the south area was caused by human activities such as application of plaggen manure and irrigation with sediment-rich water. It has also has been affected by modern pedogenesis, and, therefore, it could be classified as a kind of Entisol or anthropogenic soil.

The summer monsoon evolution recorded by carbon isotope of organic matter from the Yuanbao loess section during the Last Interglaciation

Based on the carbon isotope record of organic matter from the Yuanbao loess section, northwestern China, five enhanced summer monsoon events were observed at this area during the Last Interglaciation. Such events were also recorded by the paleosol layers, pollen assemblage and magnetic susceptibility. It is suggested that the enhanced summer monsoon leads to the shift of vegetation type, which results in the change of δ13C value of organic matter in the paleosol layer. It appears that the δ13C of organic matter is a good indicator for the summer monsoon variation. Among these five events, the first, second and the fifth reached their maximum smoothly, but the other two had experienced a less cold stage before reaching their peaks, which suggests that the mechanisms of such events may be different.

Palynomorphs in the first paleosol layer in the Yangtze Delta and their paleoenvironmental implication

Palynomorphs in the first paleosol layer in the Yangtze Delta and their paleoenvironmental implication

Characterization of Argentine loess and paleosols by Mössbauer spectroscopy

We have used Mossbauer spectroscopy to investigate iron-bearing mineral samples of loess and paleosols from a geologic section at La Plata, Argentina, 34° 54′ 14″ S and 58° 2′ W. Hematite is by far the dominant iron-bearing magnetic component in initial loess and paleosol samples. The samples were also subjected to magnetic separation. The magnetically enriched loess fractions show a remarkable increase in the content of magnetite. The enhancement of non-magnetic Fe3+ and a decrease of Fe2+ mineral phases in the paleosol layer seem to be a consequence of the process of pedogenesis which also caused a dissolution of magnetic iron oxides by weathering. The increase of magnetite in the silt fraction suggests that the wind could have been the main carrier of magnetic minerals, causing the major differences in the magnetic parameters between loess and paleosols in the Argentine loess plateau.

Luminescence and radiocarbon dating of a dune series at Cape Kiwanda, Oregon, USA

The coastal dunes of the Pacific Northwest Coast of North America are dynamic systems in a seemingly constant state of change. The cycles of stabilization and re-activation may be connected to changes in climate. There has been much discussion and speculation about the source of these sands and the timing and nature of the episodic events that have shaped the present dune landscape. Holocene development of these dune systems is based primarily on the evidence of previous and present episodes of stabilization and re-activation. One of the best locations for dating these events is the dune system of Cape Kiwanda, where a parabolic dune is eroding on a broad front making six paleosols visible. Eight sediment samples for OSL analysis were taken from the eroding west face of the parabolic dune at Cape Kiwanda, seven being associated with the six exposed paleosols, and the eighth from the base of the dune. Four wood and/or charcoal samples for radiocarbon dating were taken from the paleosols. OSL dating of separated quartz was done using a single-aliquot regeneration technique. The dates cover a time period from a few hundred to around seven thousand years. Radiocarbon dating of charcoal from paleosol layers embedded in the dunes provided separate time markers. The results from the two dating methods are in agreement and provide valuable information about the dynamics of this coastal dune system.

Paleo-environmental study on the growth of magnetotactic bacteria and precipitation of magnetosomes in Chinese loess-paleosol sequences

405 samples were collected from L5-S5-L6 in consideration of obvious variations in susceptibility of the geological sections, which are section Xifeng in Gansu Province and section Duanjiapo in Shaanxi Province for study of magnetotactic bacteria (MB) and magnetosomes (MS) in Chinese loess-paleosol sequences. MB in each sample were observed by TEM after being cultured under 8–18°C., room temperature (RT), 25°C., 26°C and 30°C conditions. In general, MB are distributed widely in loess-paleosol sequences, fewer in loess layers with predomination of vibriod in shape. However, there are more MB in paleosol layers with morphological varieties such as roddish, vibriod and occasionally approximately coccus. The magnetosomes (MS) in MB of paleosol are usually arranged in chains along the cells. It was also found that MB growth and MS formation are associated with the environment in which MB live. It can be inferred from the distributions of MB and MS that the paleoclimates fluctuated during the formation of loess-paleosol sequences in the Chinese Loess Plateau. The climate became gradually warmer but displayed more frequent fluctuations from the northwest to the southeast of the Plateau.

Stratigraphy, chronology, and sedimentology of ignimbrites from the white trachytic tuff, Roccamonfina Volcano, Italy

We describe the stratigraphy, chronology, and grain size characteristics of the white trachytic tuff (WTT) of Roccamonfina Volcano (Italy). The pyroclastic rock was emplaced between 317 and 230 Ma BP during seven major eruptive events (units A to G) and three minor events (units BC, CD, and DE). These units are separated by paleosol layers and compositionally well-differentiated pyroclastic successions. Stratigraphic control is favored by the occurrence at the base of major units of marker layers. Four WTT units (1 to 4) occur within the central caldera. These are not positively correlated with specific extracaldera units. The source of most of the WTT units was the central caldera. Units B and C were controlled by the western wall of the caldera, whereas units D and E were able to overcome this barrier, spreading symmetrically along the flanks of MC. The maximum pumice size (MP) of units increases with distance from the caldera, whereas the maximum lithic size (ML) decreases. MP and ML of the marker layer of unit D (MKDa–MKDp) do not show any systematic variations with respect to the central caldera. In contrast, the thickness of surge MKDa decreases with distance from the source, and MKDp accumulates to the north of MC probably controlled, respectively, by mobility-transport power and by wind blowing northwards. The grain size characteristics of the WTT deposits are used for classifying the units. There is no systematic variation of the grain size as a function of stratigraphic height either among units or within single units. Large variation of components in subunit E1, with repetitive alternation of pyroclastic flow to surge through fallout vs. surge deposits, suggests that the process of eruption took place in a complex or piecemeal fashion. Pumice concentration zones (PCZ) occur at all WTT levels on the volcano, but they are much thicker and pumice clasts are much larger within the central caldera. These were probably originated by the disruption of lava (flow or dome) to pumice fragments and fine ash due to sudden depressurization and interaction with lake waters of the molten lava. Local basal PCZ are, in some cases, similar to the lapilli-rich “layer 1P” that has been described elsewhere, and may have been deposited from currents transitional between pyroclastic surge and flow. Other basal PCZ formed in response to small undulations in the substrate, or can be originated by fallout. Lenticular PCZ within ignimbrite interiors and tops are interpreted to record marginal pumice levees and pumice rafts, some of which were buried by subsequant pyroclastic flows. Lithic concentration zones (LCZ) also occur at various stratigraphic height within the extracaldera ignimbrites, whereas intracaldera LCZ are absent, probably due to the fact that ignimbrite currents are strongly energetic and erosive near vent. LCZ at the top of basal inversely graded layers are formed by mechanical sieving or dispersive pressure in response to variable velocity gradients and particle concentration gradients (a segregation process). Coarse LCZ and coarse lithic breccias (LB), that reside in the interior or tops of pyroclastic flows and that occur in medial to distal areas, are interpreted to be the result of slugs of lithic-rich debris introduced by vent collapse or rockslides into the moving pyroclastic flows along their flow paths. These LCZ become mixed to varying degrees due to differential densities and velocities relative to the pyroclastic flows (desegregation processes).

Reconstruction of Microenvironmental Changes in the Kopasz Hill Loess Area at Tokaj (Hungary) Between 15 and 70 ka BP

We collected 11 Kopasz Hill loess profiles for paleoecological and geochronological analysis. The loess accumulation and development formed during the last (Weichselian) glacial period between 70 and 15 ka bp. We found that the majority of the loess profiles were composed of three typical loess strata and two well-developed paleosol horizons. Based on vertebrate remains, the lowest loess layer formed between 70–50 ka bp, during the first cool and dry climatic phase of the last glacial period, when forest steppe vegetation dominated in the Kopasz Hill area. On the surface of the lowermost layer, a paleosol developed between 50 and 40 ka bp as an indication of a more humid and warmer climatic phase. This paleosol layer was buried by a new loess layer that developed between 40 and 32 ka bp. The upper paleosol horizon developed between 32 and 26 ka bp. Molluscs preferring a mild climate were found in this layer, suggesting that this phase was wet and relatively temperate. A number of fired macrocharcoal remains can be found on the top of this paleosol layer. Charcoal samples from nine sites were dated by radiocarbon analyses. These results reflect the presence of a charcoal-rich horizon that developed 28–26 ka bp. Ca. 26 ka bp, loess formation resumed. We analyzed 14 samples from 6 sites by the 14C method. Based on 14C data, the uppermost part of loess profiles developed between 26 and 15 ka bp.

Five million year 10Be record in Chinese loess and red-clay: climate and weathering relationships

10Be measurements in bulk samples, in different size fractions, in selective chemically leached fractions of several representative loess-paleosol sequences and in the underlying red-clay sediments from the Chinese Loess Plateau, back to ca. 5 Ma, were made using the AMS (accelerator mass spectrometer). Our data support but considerably extend the earlier studies of Shen and Beer and their colleagues in the upper 0.75 Ma Luochuan loess-paleosol sequences. The effect of climatic change is dramatically expressed by 10Be concentrations: (1) in the red-clay sediments, for which we estimate model accumulation rates of 5.8 and 8.7 m Ma −1 for the upper sequences in Lingtai and Baoji, respectively; (2) in the paleosols where soil maturation processes are manifest in the 10Be distribution within different size fractions, accompanied by downward movement to zones of high authigenic mineral concentration; and (3) in loess samples which, at deposition, had an appreciable endowment of 10Be from the dust source regions. On the basis of leaching experiments, we estimate that, on average, the paleosol layers lost about 3±3% of their initial 10Be content to the underlying layers by transport with water. Finally, we estimate that the relative average zonal precipitation rate during glacial periods was ∼(2-3)×the average interglacial value. The estimates of the initial 10Be concentrations and dust composition are consistent with the measured values for the recent atmospheric dust falls sampled from the Loess Plateau and the Shandong Peninsula.

Volcanic glass found in Late Quaternary Chinese loess: A pointer for future studies?

Abstract In a preliminary investigation of Chinese loess from Shandong Peninsula, trace amounts of volcanic glass have been found in the top of Malan loess and in the top of paleosol layers at two sections. Chemical compositions of the glass shards are compared with those of widespread tephras from Mt Changbai and Japanese volcanoes. There was only enough glass to make tentative suggestions as to the source eruptions. The volcanic glass in the top of Malan loess has a similar chemical composition to that of the ca. 22,000-25,000 BP Aira-Tanzawa (AT) tephra erupted from southern Japan, and the glass in the top of one paleosol has a similar chemical composition to that of the ca. 75,000-95,000 BP Kikai-Tozurahara (K-Tz) tephra, also from southern Japan. These possible identifications are consistent with the stratigraphic positions of the glass within the loess. The results suggest that tephrochronology has potential for dating Quaternary deposits in north-eastern China.

The role of maghemite in the enhancement of magnetic signal in the Chinese loess-paleosol sequence: An extensive rock magnetic study combined with citrate-bicarbonate-dithionite treatment

We have conducted a rock magnetic study of selected Chinese loess samples before and after citrate-bicarbonate-dithionite (CBD) treatment. Our study is more extensive than previous ones and reveals new details of the magnetic carriers which are related to paleoclimate change. Three pairs of paleosol S1 (the top paleosol layer in the Lishi Formation) and loess L2 (underlying S1) from three localities (Xining, Xifeng, and Jixian) were investigated by using a variety of magnetic methods. After the paleosols were treated with CBD, which removes all maghemite grains and the finest grains of magnetite, magnetic susceptibility decreased from 77 × 10 −8 to 20 × 10 −8 m 3/kg in Xining, from 165 × 10 −8 to 30 × 10 −8 m 3/kg in Xifeng, and from 180 × 10 −8 to 25 × 10 −8 m 3/kg in Jixian, anhysteretic remanent magnetizations (ARM) were reduced to less than one tenth of the original values in the three sites, and saturation magnetization ( J s) decreased by about 60% in Xining and 70% in Xifeng and Jixian. These reduced values in the paleosols after CBD treatment are similar to those of the corresponding underlying loess samples, which, however, did not show significant decrease after CBD treatment. Room-temperature frequency dependence of susceptibility, high-temperature dependence of susceptibility, and low-temperature SIRM demagnetization of the paleosol and loess samples before and after CBD treatment confirm that in addition to superparamagnetic (SP) particles (magnetite and/or maghemite), the CBD removable magnetic carriers also include maghemite of grain sizes larger than SP.

Paleosols of sandy lands and environmental changes in the western part of northeast plain of China western during holocene

Two-three paleosol layers were formed in the western part of the Northeast Plain. China during Holocene. These paleosol layers interlaid with eolian fine sand layers. Dated by14C dating, archeology and TL and analyzed by statistics, the formation periods of paleosols are divided from the results. The periods are 11,000–7000 5500–4500, 3500–2800 and 1400–1000 a B. P. respectively.

Mineral composition of Loess-Paleosol samples from the Loess Plateau of China and its environmental significance

34 samples of loess-paleosol from the Luochuan and Xifeng sections in the Loess Plateau, northern China were separated into sand, silt and clay fractions and analyzed for their mineral compositions. The results indicate that there is almost no difference between loess and paleosol in mineral composition. Major mineral species are quartz, mica, feldspar and chlorite, accounting for about 88–92% of the total; other minerals are kandite, smectite, vermiculite and a few heavy minerals. The calcite, magnente and hematite were not taken into consideration because of their removal in the process of sample preparation. The main difference with respect to the mineral composition of samples collected from different sections and different stratigraphic levels lies in the amount and grain size of minerals hosted. Comparisons between the Luochuan section and the Xifeng section, between paleosol and loess and between the upper part and the lower part of some paleosol layers show that the formers contain less feldspar but more mica and vermiculite and are finer in grain size, indicating the co-occurrence of both biochemical weathering process responsible for mineral change and physical weathering process leading to grain-size change during the soil-forming processes. This result favours such an explanation of the soil-forming mechanism that loess deposition and paleosol development occurred synchronously, though the rate of soil formation was greater than that of loess deposition, thus leading to soil development.

Evaluation of 14C Ages of Organic Fractions of Paleosols from Loess-Paleosol Sequences Near Xian, China

The 14C dating of organic fractions from paleosol layers containing <2% carbon in loess-paleosol sequences from the loess plateau in China has yielded results that are quite often much younger than the true age of the sediments. Percolation of modern organic materials from agricultural activities, and binding of these materials within the weathered clays of the paleosols has meant that conventional pretreatment techniques for 14C dating would not isolate a reliable chemical fraction. The total sequence from Bei Zhuang Cun, in Shaanxi Province, reflects the climatic history of the area for ca 30,000 years, ranging from the interstadial of the last glacial period to the postglacial period. Analysis of solvent extracts of organic material from this site indicates that they are mainly composed of carbohydrate residues originating from the relatively recent agricultural activity. Validity of the humic components for dating will be discussed.