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Received: December 1, 2011 / Accepted: January 12, 2012 / Published: February 20, 2012.
Abstract: The loess deposits comprise several paleosol layers reflecting alternation of drier and wetter climate during Quaternary. Such a situation occurs in north of Barlad, on The Sohodau’s Hill. Morphological study of the quarry paleosols from north of Barlad was accomplished based on field observations and macroscopic physic-chemical results. Three levels of paleosols with variable thickness were determined. These three fossils layers are interbedded by four loess deposits. The physical-chimical data provide important information for the paleosol genesis and depositional/climatic environments. The carbon content and C/N ratio indicate the strength of pedogenesis in the Pleistocene and trends of biomass accumulation.
Key words: Paleosols, loess deposits, pedogenesis, quaternary.
1. Introduction
Plateau of Barlad [1] consists in quaternary deposits on wide surfaces, which cover the older formations [2]. The loess deposits comprise several paleosol layers reflecting alternation of dryer and wetter climate during Quaternary. Aeolian origin of the loess from Romania was sustained for the first time by Ref. [3]. The bases of the loess and paleosols studies have been set at the beginning of the XXth century [4, 5]. These studies sustained aeolian’s loess origin (in the east part of Romanian Plain, the alluvia of the rivers which cross the plain were obvious sources in this case). So, these evidences have shown that the red layers from loess are paleosols and after a carefully analyze, these paleosols could be the reason of the climatic changes in Romania since the age of loess sedimentation. In the same period, Sevastos [6] studied the loess from Moldavia. It is considered that it was aeolian deposit formed by sedimentation of the dust brought by winds from Asiatic deserts or from the north European ice fields. Simionescu [7] showed that in Moldavia region between Siret and Prut rivers, the loess-like deposits have alluvial origin (there are formed in the same period with the melting of the north European ice-sheet). In the Europe and in parts of the North American midcontinent [8], the stratigraphic record is straightforward because, in general, loess deposits indicate glacials or stadials while palaeosols indicate interglacials or interstadials [9]. Loess also shows particle size variations at individual localities, even within the same depositional package. In China, Porter et al. [10] showed that mean diameters of the quartz fraction in loess varied significantly over the last glacial period. They interpret these data to indicate varying wind strengths over the period of loess deposition. These paleosols consist of fossil organic matter in contrast with upper and underlying materials.
2. Methods and Data
The Barlad sequence (location: 46°14′56′ N and 27°40′38′ E, altitude: 100 m) is on the Sohodau’s Hill, Plateau of Barlad, Eastern Romania (Fig. 1). The height of outcrop is 11.50 metres, while paleosol horizons exposed along the 50-m long cliff of a former quarry. Morphological study of the quarry paleosols from north of Barlad was accomplished based on field observations and macroscopic physic-chemical results. The flow of loess deposits is in fact the main rock of Paleosols from North Part of Barlad City (Romania)
Fig. 1 Geological map of the plateau Barlad showing the location of the study area.
soil formation for the actual soil cover. Within these deposits, it acknowledged several layers of dark colour, from rusty brown, in the upper side of the profile, to dark brown, into the basic outcrop. Due to the field researches, it can be concluded that these layers are in fact fossil soils or paleosols. Morphological traits of the fossil soils cover: their thickness, the genetic horizons, storage of the morphological status. It determined three levels of paleosols with variable thickness, i.e. 70 centimetres, 100 centimetres and 110 centimetres. These three fossils layers are interbedded by four loess deposits. The fossils layers are noted with S1, S2, S3 and L1, L2, L3, L4 are the loess deposits (Fig. 2). Description focused on the physical characteristics of the sediments, and on the relationship between lithostratigraphic units and overprinted pedostratigraphic units. Once descriptions were completed, two suites of samples were collected from representative lithostratigraphic units and paleosol horizons: bulk samples for geochemical and grain size. 36 bulk samples were collected.
Fig. 2 Overview of section at the Sohodau Hill Quarry, with horizon numbering. Loess units were indicated by “L” prefix; paleosols were indicated by “S” prefix.
Several geochemical and physical laboratory techniques were used to analyze the bulk samples. Organic carbon (wt.%) was determined by K2Cr2O7 oxidation by the Tyurin method [12]. Soil organic matter content (more accurately, the humus content) was calculated from the organic carbon results (wt.%) by the application of a conversion ratio equal to 1.732 as recommended by Zyrin et al. [11]. Carbonate content (wt.%) was determined by the volumometric Kozlovsky method and recalculated to CaCO3 equivalent [12]. After the initial carbonate estimate, the grain size analysis for all bulk samples was performed by wet sieving (> 63 μm) and by X-ray Sedigraph (< 63 μm) [13]. Samples that yielded high carbonate values (> 4% by CaCO3 equivalent) were pre-treated with 10% HCl prior to the 63 μm wet sieving, as recommended by Coakley et al. [13] to disaggregate particles cemented with secondary carbonate.
Regarding the degree of morphological differentiation, it determined the first fossil soil horizon as a moderate stage of development and, then, the next two horizons with advanced stage of development. Morphologically differentiated fossil soil horizons had been delineated based on observed characteristics measured on the soil profile: colour, texture and structure, quantity of humus, the presence or absence of carbonates.
3. Results
The paleosols of the clays quarry from north part of Barlad city include three horizontal paleosols layers. The clays quarry from north part of Barlad city includes three horizontal paleosol layers. These layers become thinner in the proximity of Barlad River’s plain.
These layers are embedded in the loess deposits. Genesis and evolution of the paleosols was highly conditioned to loess formation properties. According to Cazacu [14], from a systematically studied point of view, there are steppes paleosols as they have large thicknesses, high content of humus and macro elements which show that it was developed under the conditions of an abundant vegetation and relative humid warm climate. Therefore, the quantity, composition and humus type is specific to morphological characters. Also, its qualitative composition in paleosols guide towards the paleoclimatic and paleofloristic conditions during its genesis.
The age of the studied deposits from the quarry of interglacial stages corresponds to the second half of the Medium Pleistocene and Upper Pleistocene environment [15].
4. Discussions
Organic C content is from 0.06% to 1.55%. The vertical distribution of C in each profile fluctuates is always < 1.55% (Fig. 3). The values of C% and the C/N ratio depend on local climatic conditions.
Total of nitrogen content is in the range 0.039%-0.127% in paleosols. These values provide information about increasing moisture index parallel with the decreasing temperature.
Carbonates/nitrates ratio, by its values (10.2-17.8), shows the presence in these paleosols of a mull-calcic humus type (Fig. 3). This means that steppe vegetation produced an intense biological accumulation processes. Therefore, hard humic acids are closely related to clay and lead to the formation of a high quality humus.
In the fossil soils pH values are between 7.5-7.8, with a slightly alkaline soil reaction. In the upper and underlying deposits, the values of the pH are higher than 8.2.
Humus has higher values in the layers of fossil soils, compared to upper and underlying deposits. The presence of high quantities of humus stats represents an important contribution of plant material during soil formation (Fig. 4).
Grain-size analysis of silt for Barlad sequence produced varying ratios of coarse silt fractions (Fig. 4). This unit has high clay content (22%-47%) and coarse silt (23%-30%), but also has a high amount of coarse sand (5%-15%) to fine sand (21%-47%). Comparing the fine particle size from the upper and underlying deposits, it can be observed that these fine particle sizes facilitated the accumulation and preservation of organic matter over time.
Fig. 3 Vertical distribution of carbon content (C %) and C/N ratio.
Fig. 4 Vertical distribution of humus and grain size ratio.
5. Conclusions
The carbon content and C/N ratio are weathering indices, that are all greater in layers identified as buried soils, and their vertical distributions indicate the strength of pedogenesis in the Pleistocene and trends of biomass accumulation.
The Barlad sequences in particular offer a detailed record of Pleistocene environment, the peaks indicating environmental changes. However, the wavelength of the periodicity, which is estimated at approximately 103 years for these sequences, may depend on the rate of supply of inorganic materials.
The diagram of humus content obtained for the Barlad sequence, which have been formed and developed on similar climatic conditions, show good correspondence, although have need of more precise dating of the soils. The Barlad section, formed under cooler and drier conditions, shows a different pattern.
The periods which have been windier reveal that the grain size ratio of loess paleosols from Barlad quarry section shows that loess had a higher amount of sand and coarse silt than the intercalated paleosols, indicating stronger winds during periods of relatively high sedimentation rate.
The start of the Quaternary period brought changes both in terms of flora and fauna as to the soils. These facts reflect in the paleoclimatic and paleomedium changes caused by climate oscillations.
Acknowledgments
This work was supported by the European Social
Fund in Romania, under the responsibility of the
Managing Authority for the Sectorial Operational
Program for Human Resources Development
2007-2013 (grant POSDRU/88/1.5/S/47646) and
(grant POSDRU/107/1.5/S/78342). Also, the authors
wish to thank the reviewers for their extremely useful
comments.
References
[1] C. Martiniuc, Geomorfological zoning of the Romania,
Geographical Monography of the Romania, Academy Press, Bucharest, 1960, Vol. I, pp. 135-141. (in Romanian)
[2] L. Ionesi, Geology of Platform Units and North Dobrogea Orogene, Technic Press, Bucharest, 1994, pp. 56-70. (in Romanian)
[3] L. Mrazec, Comunication Concerning the Loess Deposits from Romania, Scientific Society Press, Bucharest, 1899, Vol. III, pp. 4-5. (in Romanian)
[4] G.M. Murgoci, The Climate and the Soils from the Quaternay Period of Romania, Agronomic Society Library Press, Bucharest, 1920, Vol. 3, pp. 13-16. (in Romanian)
[5] E. Protopopescu-Pache, Agrogeological research of the Romanian plain between Mostistea valley and olt, D.S.Com.Geol 1 (1923) 56-59. (in Romanian)
[6] R. Sevastos, Tectonic rate between Romanian plaine and Moldavian hills region, An. Inst. Geol. Bucharest 1 (1908) 311-360. (in Romanian)
[7] I. Simionescu, Contributions to the geology of the Moldova region between Siret and Prut rivers, Adamachi Foundation Bucharest 16 (1903) 2-4. (in Romanian)
[8] E.A. Bettis, D.R. Muhs, H.M. Roberts, A.G. Wintle, Last glacial loess in the conterminous U.S.A., Quaternary Science Reviews 22 (2003) 1907-1946.
[9] R.V. Ruhe, Depositional environment of late Wisconsin loess in the midcontinental United States, in Jr.H.R. Wright, S.C. Porter (Eds.), Late-Quaternary Environments of the United States, The Late Pleistocene, University of Minnesota, Minneapolis, 1983, Vol. 1, pp. 130-137.
[10] S.C. Porter, Z. An, Correlation between climate events in the North Atlantic and China during the last glaciation, Nature 375 (1995) 305-308.
[11] N.G. Zyrin, D.S. Orlov, Fiziko-khimicheskie Metodym Issledovaniya Pochv, Moscow State University Press, Moscow, 1980, p. 382. (in Russian)
[12] E.V. Arinushkina, Rukovodstvo po khimicheskomu analizu pochv, Moscow State Univ. Press, Moscow, Russia, 1970. (in Russian)
[13] J.P. Coakley, J.P.M. Syvitski, Sedigraph technique, in: Principles, Methods and Application of Particle Size, Cambridge University Press, New York, 1991.
[14] E. Cazacu, Biostratigraphical and paleoenvironemntal sutdy of the fossils sols from Elanul basin river, Ph.D. Thesis, Iasi University, Iasi, 2001. (in Romanian)
[15] C. Panaiotu, C.E. Panaiotu, A. Grama, C. Necula, Paleoclimatic record from a loess-paleosol profile in southeastern Romania, Physics and Chemistry of the Earth A (26) (2001) 893-898.
Abstract: The loess deposits comprise several paleosol layers reflecting alternation of drier and wetter climate during Quaternary. Such a situation occurs in north of Barlad, on The Sohodau’s Hill. Morphological study of the quarry paleosols from north of Barlad was accomplished based on field observations and macroscopic physic-chemical results. Three levels of paleosols with variable thickness were determined. These three fossils layers are interbedded by four loess deposits. The physical-chimical data provide important information for the paleosol genesis and depositional/climatic environments. The carbon content and C/N ratio indicate the strength of pedogenesis in the Pleistocene and trends of biomass accumulation.
Key words: Paleosols, loess deposits, pedogenesis, quaternary.
1. Introduction
Plateau of Barlad [1] consists in quaternary deposits on wide surfaces, which cover the older formations [2]. The loess deposits comprise several paleosol layers reflecting alternation of dryer and wetter climate during Quaternary. Aeolian origin of the loess from Romania was sustained for the first time by Ref. [3]. The bases of the loess and paleosols studies have been set at the beginning of the XXth century [4, 5]. These studies sustained aeolian’s loess origin (in the east part of Romanian Plain, the alluvia of the rivers which cross the plain were obvious sources in this case). So, these evidences have shown that the red layers from loess are paleosols and after a carefully analyze, these paleosols could be the reason of the climatic changes in Romania since the age of loess sedimentation. In the same period, Sevastos [6] studied the loess from Moldavia. It is considered that it was aeolian deposit formed by sedimentation of the dust brought by winds from Asiatic deserts or from the north European ice fields. Simionescu [7] showed that in Moldavia region between Siret and Prut rivers, the loess-like deposits have alluvial origin (there are formed in the same period with the melting of the north European ice-sheet). In the Europe and in parts of the North American midcontinent [8], the stratigraphic record is straightforward because, in general, loess deposits indicate glacials or stadials while palaeosols indicate interglacials or interstadials [9]. Loess also shows particle size variations at individual localities, even within the same depositional package. In China, Porter et al. [10] showed that mean diameters of the quartz fraction in loess varied significantly over the last glacial period. They interpret these data to indicate varying wind strengths over the period of loess deposition. These paleosols consist of fossil organic matter in contrast with upper and underlying materials.
2. Methods and Data
The Barlad sequence (location: 46°14′56′ N and 27°40′38′ E, altitude: 100 m) is on the Sohodau’s Hill, Plateau of Barlad, Eastern Romania (Fig. 1). The height of outcrop is 11.50 metres, while paleosol horizons exposed along the 50-m long cliff of a former quarry. Morphological study of the quarry paleosols from north of Barlad was accomplished based on field observations and macroscopic physic-chemical results. The flow of loess deposits is in fact the main rock of Paleosols from North Part of Barlad City (Romania)
Fig. 1 Geological map of the plateau Barlad showing the location of the study area.
soil formation for the actual soil cover. Within these deposits, it acknowledged several layers of dark colour, from rusty brown, in the upper side of the profile, to dark brown, into the basic outcrop. Due to the field researches, it can be concluded that these layers are in fact fossil soils or paleosols. Morphological traits of the fossil soils cover: their thickness, the genetic horizons, storage of the morphological status. It determined three levels of paleosols with variable thickness, i.e. 70 centimetres, 100 centimetres and 110 centimetres. These three fossils layers are interbedded by four loess deposits. The fossils layers are noted with S1, S2, S3 and L1, L2, L3, L4 are the loess deposits (Fig. 2). Description focused on the physical characteristics of the sediments, and on the relationship between lithostratigraphic units and overprinted pedostratigraphic units. Once descriptions were completed, two suites of samples were collected from representative lithostratigraphic units and paleosol horizons: bulk samples for geochemical and grain size. 36 bulk samples were collected.
Fig. 2 Overview of section at the Sohodau Hill Quarry, with horizon numbering. Loess units were indicated by “L” prefix; paleosols were indicated by “S” prefix.
Several geochemical and physical laboratory techniques were used to analyze the bulk samples. Organic carbon (wt.%) was determined by K2Cr2O7 oxidation by the Tyurin method [12]. Soil organic matter content (more accurately, the humus content) was calculated from the organic carbon results (wt.%) by the application of a conversion ratio equal to 1.732 as recommended by Zyrin et al. [11]. Carbonate content (wt.%) was determined by the volumometric Kozlovsky method and recalculated to CaCO3 equivalent [12]. After the initial carbonate estimate, the grain size analysis for all bulk samples was performed by wet sieving (> 63 μm) and by X-ray Sedigraph (< 63 μm) [13]. Samples that yielded high carbonate values (> 4% by CaCO3 equivalent) were pre-treated with 10% HCl prior to the 63 μm wet sieving, as recommended by Coakley et al. [13] to disaggregate particles cemented with secondary carbonate.
Regarding the degree of morphological differentiation, it determined the first fossil soil horizon as a moderate stage of development and, then, the next two horizons with advanced stage of development. Morphologically differentiated fossil soil horizons had been delineated based on observed characteristics measured on the soil profile: colour, texture and structure, quantity of humus, the presence or absence of carbonates.
3. Results
The paleosols of the clays quarry from north part of Barlad city include three horizontal paleosols layers. The clays quarry from north part of Barlad city includes three horizontal paleosol layers. These layers become thinner in the proximity of Barlad River’s plain.
These layers are embedded in the loess deposits. Genesis and evolution of the paleosols was highly conditioned to loess formation properties. According to Cazacu [14], from a systematically studied point of view, there are steppes paleosols as they have large thicknesses, high content of humus and macro elements which show that it was developed under the conditions of an abundant vegetation and relative humid warm climate. Therefore, the quantity, composition and humus type is specific to morphological characters. Also, its qualitative composition in paleosols guide towards the paleoclimatic and paleofloristic conditions during its genesis.
The age of the studied deposits from the quarry of interglacial stages corresponds to the second half of the Medium Pleistocene and Upper Pleistocene environment [15].
4. Discussions
Organic C content is from 0.06% to 1.55%. The vertical distribution of C in each profile fluctuates is always < 1.55% (Fig. 3). The values of C% and the C/N ratio depend on local climatic conditions.
Total of nitrogen content is in the range 0.039%-0.127% in paleosols. These values provide information about increasing moisture index parallel with the decreasing temperature.
Carbonates/nitrates ratio, by its values (10.2-17.8), shows the presence in these paleosols of a mull-calcic humus type (Fig. 3). This means that steppe vegetation produced an intense biological accumulation processes. Therefore, hard humic acids are closely related to clay and lead to the formation of a high quality humus.
In the fossil soils pH values are between 7.5-7.8, with a slightly alkaline soil reaction. In the upper and underlying deposits, the values of the pH are higher than 8.2.
Humus has higher values in the layers of fossil soils, compared to upper and underlying deposits. The presence of high quantities of humus stats represents an important contribution of plant material during soil formation (Fig. 4).
Grain-size analysis of silt for Barlad sequence produced varying ratios of coarse silt fractions (Fig. 4). This unit has high clay content (22%-47%) and coarse silt (23%-30%), but also has a high amount of coarse sand (5%-15%) to fine sand (21%-47%). Comparing the fine particle size from the upper and underlying deposits, it can be observed that these fine particle sizes facilitated the accumulation and preservation of organic matter over time.
Fig. 3 Vertical distribution of carbon content (C %) and C/N ratio.
Fig. 4 Vertical distribution of humus and grain size ratio.
5. Conclusions
The carbon content and C/N ratio are weathering indices, that are all greater in layers identified as buried soils, and their vertical distributions indicate the strength of pedogenesis in the Pleistocene and trends of biomass accumulation.
The Barlad sequences in particular offer a detailed record of Pleistocene environment, the peaks indicating environmental changes. However, the wavelength of the periodicity, which is estimated at approximately 103 years for these sequences, may depend on the rate of supply of inorganic materials.
The diagram of humus content obtained for the Barlad sequence, which have been formed and developed on similar climatic conditions, show good correspondence, although have need of more precise dating of the soils. The Barlad section, formed under cooler and drier conditions, shows a different pattern.
The periods which have been windier reveal that the grain size ratio of loess paleosols from Barlad quarry section shows that loess had a higher amount of sand and coarse silt than the intercalated paleosols, indicating stronger winds during periods of relatively high sedimentation rate.
The start of the Quaternary period brought changes both in terms of flora and fauna as to the soils. These facts reflect in the paleoclimatic and paleomedium changes caused by climate oscillations.
Acknowledgments
This work was supported by the European Social
Fund in Romania, under the responsibility of the
Managing Authority for the Sectorial Operational
Program for Human Resources Development
2007-2013 (grant POSDRU/88/1.5/S/47646) and
(grant POSDRU/107/1.5/S/78342). Also, the authors
wish to thank the reviewers for their extremely useful
comments.
References
[1] C. Martiniuc, Geomorfological zoning of the Romania,
Geographical Monography of the Romania, Academy Press, Bucharest, 1960, Vol. I, pp. 135-141. (in Romanian)
[2] L. Ionesi, Geology of Platform Units and North Dobrogea Orogene, Technic Press, Bucharest, 1994, pp. 56-70. (in Romanian)
[3] L. Mrazec, Comunication Concerning the Loess Deposits from Romania, Scientific Society Press, Bucharest, 1899, Vol. III, pp. 4-5. (in Romanian)
[4] G.M. Murgoci, The Climate and the Soils from the Quaternay Period of Romania, Agronomic Society Library Press, Bucharest, 1920, Vol. 3, pp. 13-16. (in Romanian)
[5] E. Protopopescu-Pache, Agrogeological research of the Romanian plain between Mostistea valley and olt, D.S.Com.Geol 1 (1923) 56-59. (in Romanian)
[6] R. Sevastos, Tectonic rate between Romanian plaine and Moldavian hills region, An. Inst. Geol. Bucharest 1 (1908) 311-360. (in Romanian)
[7] I. Simionescu, Contributions to the geology of the Moldova region between Siret and Prut rivers, Adamachi Foundation Bucharest 16 (1903) 2-4. (in Romanian)
[8] E.A. Bettis, D.R. Muhs, H.M. Roberts, A.G. Wintle, Last glacial loess in the conterminous U.S.A., Quaternary Science Reviews 22 (2003) 1907-1946.
[9] R.V. Ruhe, Depositional environment of late Wisconsin loess in the midcontinental United States, in Jr.H.R. Wright, S.C. Porter (Eds.), Late-Quaternary Environments of the United States, The Late Pleistocene, University of Minnesota, Minneapolis, 1983, Vol. 1, pp. 130-137.
[10] S.C. Porter, Z. An, Correlation between climate events in the North Atlantic and China during the last glaciation, Nature 375 (1995) 305-308.
[11] N.G. Zyrin, D.S. Orlov, Fiziko-khimicheskie Metodym Issledovaniya Pochv, Moscow State University Press, Moscow, 1980, p. 382. (in Russian)
[12] E.V. Arinushkina, Rukovodstvo po khimicheskomu analizu pochv, Moscow State Univ. Press, Moscow, Russia, 1970. (in Russian)
[13] J.P. Coakley, J.P.M. Syvitski, Sedigraph technique, in: Principles, Methods and Application of Particle Size, Cambridge University Press, New York, 1991.
[14] E. Cazacu, Biostratigraphical and paleoenvironemntal sutdy of the fossils sols from Elanul basin river, Ph.D. Thesis, Iasi University, Iasi, 2001. (in Romanian)
[15] C. Panaiotu, C.E. Panaiotu, A. Grama, C. Necula, Paleoclimatic record from a loess-paleosol profile in southeastern Romania, Physics and Chemistry of the Earth A (26) (2001) 893-898.