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Abstracts of Paleopedology Symposium and Poster Session at XY INQUA Congress in Durban, August 1999 Arnt Bronger Xiao-Min FANG (1), Ji-Jun LI (1), Subir BANERJEE (2), Yugo ONO (3), Lianqing NU (1), Maodu YAN (1) (1) Dept Geography, Lanzhou Univ., China. (2) Inst. Rock Magnetism, Univ. Minnesota, Minneapolis USA. (3) Graduate School of Environmental Earth Science, Hokkaido Univ., Japan. Lucretia GHERGARI, Bogdan ONAC, Corina IONESCU, Antoniu BODNARIUC, Liana ONAC & Tudor TAMAS Dept Mineralogy, Babes-Bolyai Univ., Cluj-Napoca, Romania. Norbert GÜNSTER & Armin SKOWRONEK Inst. Bodenkunde, Univ. Bonn, Germany. MAGNETIC PROPERTIES OF LOESS/PALAEOSOL SEQUENCE AND ITS VARIATION BY PEDOGENESIS Xiu Ming LIU Dept. Physical Geography, Macquarie Univ., Sydney, Australia.
QUANTITATIVE ESTIMATE OF PALAEOCLIMATE BASED ON MAGNETIC SUSCEPTIBILITY AND PHYTOLITH ASSEMBLAGE OF MODERN SOILS Houyuan LU Inst. Geology, Chinese Acad. Sciences, Beijing, China. Surface Paleosols of “loess islands” in the center of Russian Plain – Vladimir Opolie Alexander O. MAKEEV Soil Institute of Moscow University, Moscow, Russia Brad PILLANS Research School of Earth Sciences, Australian National Univ., Canberra,
Australia.
DEEP WEATHERING AND QUATERNARY COLLUVIATION IN SWAZILAND T SCHOLTEN & P FELIX-HENNINGSEN Inst. Soil Science and Soil Conservation, Justus-Liebig-Univ., Giessen, Germany. PALEOSOL SEQUENCES AS EVIDENCE OF LONG AND SHORT TERM CLIMATIC CYCLES Michael J SINGER (1) & Kenneth L VEROSUB (2) (1) Dept of LAWR and (2) Dept. of Geology, University of California, Davis, USA. USING PLANT DNA FROM PALAEOSOLS TO DETERMINE PALEOCLIMATE Michael J. SINGER (1) & Edouard JURKEVITCH (2) Dept. LAWR, Univ. California, USA. (2) Dept. of Plant Pathology and
Microbiology, Hebrew Univ. Jerusalem, Israel.
LOESSES - BURIED PALEOSOLS - GEOSOLS - WELDED PALEOSOLS - PEDOCOMPLEXES - INDICATORS OF A QUATERNARY PALEOCIMATIC RECORD? Arnt Bronger Recent small climatic fluctuations on a 102-103 year time scale can be correlated worldwide. These moraines result from glacier advances caused by a decline of mean annual temperature of only about 10C, suggesting that major climatic changes on a 105 year scale (glacial-interglacial cycles) and probably a 104 year scale (the approximate length of an interglacial) must be of similar age throughout the temperate climatic belt of the Northern Hemisphere. This concept is important for continental pedostratigraphic correlations, because only the more detailed loess-paleosol sequences can indicate the full paleoclimatic history on a 104-105 year scale. Knowledge of the genesis of paleosols is needed to establish loess-paleosol stratigraphies. Most paleosols, however, are truncated and largely recalcified by carbonate from overlying loess. Micromorphological studies distinguish primary and secondary carbonates and provide unequivocal evidence of clay illuviation. For the Brunhes chron the sequence of Karamaydan, Tadjikistan, is more detailed then corresponding sections at Luochuan, China and Central Europe and should therefore be regarded as a key sequence for reconstructing the climatic history of the Middle Pleistocene. The correlation with the deep sea oxygen isotope record allows a detailed chronostratigraphical subdivision of the Karamaydan sequence in the Brunhes epoch. For most of the Matuyama epoch the central and lower part of the sequence at Chashmanigar, Tadjikistan, show more pronounced paleosols that the equivalent part of the sequences at Luochuan and much more that in Central Europe. The primary and secondary minerals of the silt and clay fractions must be determined separately to evaluate the type and intensity of mineral weathering. The results show that there is little difference in the type and amount of pedogenic clay mineral formation between the Holocene soils and the paleosols of the Brunhes epoch at Karamaydan, and of most of the Matuyama epoch at Chashmanigar suggesting that the interglacial climates represented by the B or Bt horizons of the buried paleosols of young, middle and old Pleistocene age were all similar to that of the Holocene. A pedocomplex (PK) in one region can be the chronostratigraphical equivalent of several paleosols with intervening loess layers in another. The same is true for a composite geosol or a welded paleosol. For example, because the mid-Pleistocene "F6"-soil in Stari Slankamen, Yugoslavia, shows stronger pedochemical weathering and clay mineral formation than the Holocene soils in the same area, previously thought to have formed in a warmer climate. However, it corresponds chronostratigraphically with several interglacial soils (PKs VI and V) at Karamaydan, formed over a period of about 140 ka, with pedogenesis interrupted several times by loess formation. Thus the much stronger pedochemical weathering in the welded F6-soil is due not to climate but to a longer period of soil formation. Similarly, the "Yarmouth-Sangamon paleosol which represents about 700 ka" is an example of a composite geosol and should not be regarded any longer as a single pedostratigraphical unit: it is equivalent to PK IX-PK I at Karamaydan. GENERAL MONSOON INSTABILITY: EVIDENCE FROM SOIL FORMATION AND 150,000-YEAR CENTURY-SCALE LOESS—PALAEOSOL CLIMATIC RECORDS ON THE CHINESE WESTERN LOESS PLATEAU Xiao-Min FANG (1), Ji-Jun LI (1), Subir BANERJEE (2), Yugo ONO (3), Lianqing NU (1), Maodu YAN (1) (1) Dept Geography, Lanzhou Univ., China. (2) Inst. Rock Magnetism, Univ. Minnesota, Minneapolis USA. (3) Graduate School of Environmental Earth Science, Hokkaido Univ., Japan. Multi-climatic proxies (rock magnetic, carbonate, soil colour and grain size) from four late Pleistocene century scale loess—palaeosol records in the Lanzhou-Linxia region on the Chinese western Loess Plateau have shown that in the last glacial cycle, Asian summer monsoon experienced 27 episodic pulse enhancements spanning only ca.1–2 ka in high frequency domain and having at least 13 sub-Milankovitch cycles of progressive weakening in low frequency domain, and winter monsoon had at least 13 episodic cold surges. Soil formation is in surprisingly fast response to these warm pulses. In low resolution (10,000-year scale), both winter and summer monsoon changes match global climatic changes driven by global ice volume. But in high resolution (100–1000-year scale), winter and summer monsoon seem to vary broadly in pace (for winter monsoon) or by 1–2 ka lag(for summer monsoon) with North Atlantic rapid climatic changes, with the most identified cold surges and warm enhancements correlated to Heinrich events, major warm (Dansgaard-Oeschger) episodes and long-term cooling (Bond) cycles of North Atlantic climatic records, respectively. But in detail, both monsoons show different variations from North Atlantic climatic changes. This is particularly evident in the Holocene when both winter and summer monsoons had large fluctuations, but the North Atlantic region shows a fair stable Holocene in climate. These suggest that in one hand there have been strong links between Asian monsoon system and North Atlantic climatic system in much of the last glacial cycle, and in other hand Asian monsoon worked in its own way in some periods. However, present dating precision has limited our clarification of which system is the driving force. THE MIRRORING OF THE PALEOENVIRONMENT ON THE CLAY MINERALS IN QUATERNARY DEPOSITS FROM NORTH AND WEST OF ROMANIA Lucretia GHERGARI, Bogdan ONAC, Corina IONESCU, Antoniu BODNARIUC, Liana ONAC & Tudor TAMAS Dept Mineralogy, Babes-Bolyai Univ., Cluj-Napoca, Romania. The mineralogy of the Quaternary clay deposits from the North and the West of Romania (Oas-Gutai Mts. and Bihor Mts.) is presented. The clay deposits represent: a) Thin clay beds from two pitch deposits, one from Gutai Mts. and one from Bihor Mts.; b) Clay deposits from the alluvia of Valea Rea River (Oas Mts.); c) Various elluvial and delluvial formations; d) Soils generated both on alluvial deposits and magmatic and sedimentary rocks. The granulometry of the clay deposits shows the presence of clay-, silt- and siltic-arenitic stones. The source rocks for the clay minerals are Neogene volcanic and sedimentary rocks in Oas-Gutai Mts. and metamorphic and sedimentary rocks in Bihor Mts., as reflected by the allogenic minerals found in clay deposits: feldspars, quartz, amphiboles, pyroxenes. The clay minerals are: kaolinite, halloysite, illite, smectite, clorite, illite and interstratified illite/smectite, clorite/smectite. The clay’s mineral assemblages reflect the palaeoenvironmental conditions, as: pH (from acid to basic) and Eh (reducing or oxidizing), the drainage (good or weak) and biotic activity. CYCLIC SEDIMENTATION AND SOIL FORMATION DURING THE UPPER NEOGENE AND QUATERNARY IN THE WESTERN MEDITERRANEAN Norbert GÜNSTER & Armin SKOWRONEK Inst. Bodenkunde, Univ. Bonn, Germany. The variability of climate is mainly driven by orbitally controlled variations of the insolation (Milankovitch cycles). These are issued by rhythms of 100 ka (eccentricity), 41 ka (obliquity) and 19–21 ka (precession) and can generally be correlated with the oscillations of ∂O18 isotopic curves in marine sediments. Furthermore exist smaller amplitudes of 10–12 ka (Heinrich events) and of 2–3 ka (Bond cycles). A reliable indicator of this climatic cyclicity on continents is the alternation of erosion/sedimentation and pedogenesis. The first took place during geomorphodynamic activity under dry climatic conditions with an opened or without vegetation cover, the latter during geomorphodynamic stability under wetter climate with a closed vegetation. The Western Mediterranean has rich divided accumulation sites, where the above described alternation is recorded by multiple sediment soil sequences. So the Granada Basin (Southern Spain) was a sediment receiving area for several terrestrial sediments since the Tortonian: 240 samples of Pliocene and Pleistocene soils and sediments were analysed by pedological standard methods. The large subdivided sediment soil sequences with on the whole 85(!) different palaeosols substantiate a (in Europe probably exceptional) climo-cyclic resolution of the last 5.4 Ma in the Western Mediterranean. Based on the analytical results the following climo-ecological differentiation of the Pliocene and the Pleistocene can be realised. The Lower Pliocene is characterised by an alternation of stronger developed red soils and weaker developed reddish brown soils. In these the highest degrees of averaged soil forming intensities occur. Decreasing humidity leads to a pronounced weakening of the pedogenetic processes in the Middle and Upper Pliocene. The driest conditions are reached in the Upper Pliocene, testified by increasing quantities of smectite, wind transported silt and multiple pedogenic calcretes. Stronger weathered rubeficated palaeosols in the Lower Pleistocene deduce a climatic change to temporarily more humid phases, but also pedogenic(?) calcretes do exist as evidence for Lower Pleistocene dry periods. The Middle and Upper Pleistocene are determined by the symptoms of an increasing influence of dry—cold glacials or stadials. More or less intensive pedogenesis took place during warmer and wetter interglacials or interstadials. As a witness of periglacial conditions cryoclasts, geli-solifluction and ice wedge fillings could be identified. The Upper Pleistocene is represented by 10 fossil soils. Soil sequences in slope deposits and/or loesses with grey and grey-brown Ah-horizons, enriched with organic material, as well as cambic B-horizons show a parallelity to the middle european loess stratigraphy. Hence the pedogenetically effective climate was subtropical mediterranean since the Lower Pliocene, but with a consequent decrease of humidity until the Upper Pleistocene. MAGNETIC PROPERTIES OF LOESS/PALAEOSOL SEQUENCE AND ITS VARIATION BY PEDOGENESIS Xiu Ming LIU Dept. Physical Geography, Macquarie Univ., Sydney, Australia. Variations in magnetic properties, such as the susceptibility, in loess/palaeosol sequences from China, are widely recognised as a proxy indicator of Quaternary climatic evolution. However the link between magnetic susceptibility and climate is not consistent. In China and central Europe, the magnetic susceptibility of palaeosols is enhanced relative to the intervening loess, due to the formation of ultrafine ferrimagnetic material during pedogenesis. Conversely, in high latitude deposits, such as Alaska and Siberia, magnetic susceptibility minima coincide with palaeosols. This inverse relationship has been explained by the idea that susceptibility is reflecting the magnitude of an aeolian ferrimagnetic component of consistent mineralogy, the size of which is inversely related to average wind velocity. In order to understand the intrinsic linkage, magnetic measurements for samples from both Alaska and the Loess Plateau, China have been carried out, including frequency-dependent and temperature-dependant (-196oC to 700oC) susceptibility, hysteresis loops and thermomagnetic (Curie) curves and so on. The data suggest that there are differences in magnetic properties between Alaskan loess and palaeosols, not only in magnetic grain-size but also in magnetic mineralogy. This complicates the simple hypothesis of a wind velocity signal by introducing an additional factor in to the climatic signal. By analogy with magnetic variations between the central and southern parts of Chinese Loess Plateau, we argue that the low magnetic susceptibility values in the Alaskan palaeosol units are a reflection, at least in part, of post-depositional processes. QUANTITATIVE ESTIMATE OF PALAEOCLIMATE BASED ON MAGNETIC SUSCEPTIBILITY AND PHYTOLITH ASSEMBLAGE OF MODERN SOILS Houyuan LU Inst. Geology, Chinese Acad. Sciences, Beijing, China. In this study, magnetic susceptibility (MS) and opal phytolith were analyzed on the samples taken from modern surface soils, and were used as proxy indicators of physical and biological records. Totally, 371 MS samples and 153 phytolith samples, collected from many categories of modern soils in China were investigated. The purposes of this study are (1) to find a better relationship between MS of the modern soils and present day climate parameters such as temperature and precipitation, (2) to establish a better relationship between phytolith associations and vegetation types, and hence the relation with climate factors, and (3) to estimate palaeoclimate parameters based on MS and phytolith records of the loess palaeosol sequence in the loess plateau using the climofunctions obtained from the regression analysis of the modern analogues. The main results are presented as follows. (1) The MS of the modern soil samples in the loess plateau and its surrounding areas increases with annual mean temperature (MAT) and annual mean precipitation (MAP). A contrary relationship exists for the southern China where MAT exceeds 15¡æ and MAP exceeds 1100 mm, of which the MS of the modern soils decreases with increasing MAT and/or MAP. The parent soils may have played a more important role on the soils MS than for the climate conditions. (2) Distribution of phytolith associations in the modern soils is apparently influenced by local climate condition, 15 phytolith assemblages correspond to 15 types of grasslands. (3) Through the study of MS and phytolith of the modern soils and related meteorological data, I have established the quantitative relationships between MS and climate parameters, phytolith and climate parameters, respectively. The palaeoclimatic parameters since the last interglacial, estimated from both proxy records of Weinan loess section, are nearly consistent. (4) Using MS records from different loess sections, I have made estimates of MAT and MAP for the last 1.2 Ma and 150 ka, respectively. Spatial pattern of MAP distribution has been reconstructed also. Seasonal climatic variations in this region since the last interglacial has been investigated and discussed in detail. Surface Paleosols of “loess islands” in the center of Russian Plain – Vladimir Opolie Alexander O. MAKEEV Soil Institute of Moscow University, Moscow, Russia High flat interfluves - Opolies (from the Russian word polie – field) - are common for the periphery of Moscow/Riss II glaciation area north from the main loess area. They are contrasting in all landscape components (parent rocks, vegetation, soil cover) with surrounding territories - moraine plains and fluvioglacial lowlands. Because of loess mantles V. Dokuchaev called them loess islands. Vladimir Opolie is a typical loess island, 50-60 km in diameter, situated 200 km east of Moscow. It is an ancient denudation plain, with an elevation of 180-230 m asl surrounded by moraine plains from West, North and East and bordering vast fluvioglacial plain in the South. Vladimir Opolie is covered by loess mantle of 3-5 m thick, which has determined high soil fertility and subsequently ancient cultivation and lack of forest vegetation. The surface of Opolie is characterized by swell-and-swale topography. Oval depressions 0,5 m deep and 10-20 m wide occupy 20-30% of terrain, forming a regular network. They are the remains of a former thermokarst relief. Soils of Vladimir Opolie show textural differentiation. Clay content in the upper part is about 15% and in the lower part – about 30%. Such a differentiation resulted from two phases of eolian deposition of material from different sources (a fine textured part - ground moraine source; light textured layer - eolian dust from fluvioglacial fields). Microrelief has determined the structure of soil cover that is quite different from the soils of adjacent territories. Soils with buried humus horizon are formed only within depressions. Buried humus horizons are black lenses 20-30 cm thick situated at a depth of 30-40 cm within the light textured part of soil profile; towards the slopes of depressions they gradually ceases and never occur in soils of main surfaces. In reverse, the soils of inter-depression areas are characterized by presence of carbonate layer at a depth of 50-80 cm, that is deepening abruptly along the slope of depressions and never occur in soils with buried humus horizons. Carbonates occur in the form of grains of loess fraction, pseudomicellia and hard nodules of hydromorphic origin. Humus content in buried horizons is the highest in the profile and in contrast with surface horizons humus is highly enriched in humic substances. Periglacial environment during the final stages of loess sedimentation resulted in the formation of a system of thermokarst depressions where frost-meadow soils with black hydromorphic humus horizons had been formed. Permafrost and deep seasonal freezing produced pseudomorphs and frost cracks, complicating the lower boarder of buried humus horizons. The generally arid climatic conditions of that period caused evaporational concentration of free carbonates. Formation of a hydromorphic humus horizons and differentiation of carbonates was accompanied and succeeded by the final stages of loess sedimentation, burying former surface humus horizons. This is also evidenced by profile distribution of phytoliths with prominent maximum in a buried horizon. PALAEOMAGNETISM OF EARLY TO MID PLEISTOCENE PALAEOSOLS, AND EVIDENCE FOR DIACHRONOUS ARID CLIMATE SHIFTS IN NORTHERN AND SOUTHERN AUSTRALIA Brad PILLANS Research School of Earth Sciences, Australian National Univ., Canberra, Australia. In South Australia, in coastal sections near Adelaide, and on Kangaroo Island, the Brunhes/Matuyama (B/M) polarity transition (0.78 Ma) is identified in the strongly oxide-mottled Ochre Cove Formation. The Ochre Cove Formation is overlain by a calcareous grey-green aeolian clay, called Ngaltinga Clay, which in turn is overlain by calcareous sediments of the Christies Beach and Taringa Formations. The marked change from an oxide-dominated weathering regime to a carbonate weathering regime is estimated to have occurred at about 500 to 600 ka, and is interpreted as a major arid shift in regional climates. Similar arid shifts are inferred from the Murray Basin in southeastern Australia and Lake Lefroy in southern Western Australia, where changes from lacustrine clays to evaporites and dune sediments are estimated to have occurred between 400 and 700 ka, and about 500 ka, respectively. An increase in aeolian dust input to Tasman Sea sediments also occurs in the last 400 ka. In northeast Queensland soils developed on basaltic lava flows with ages 0.01, 0.89, 2.46, 2.64, 3.4 and 5.59 Ma show a trend of progressive soil thickness increase of c. 0.3 m/Ma. Reverse polarity magnetisation of pedogenic hematite in the lower B horizons of the soils on the four oldest flows indicates acquisition of the remanence prior to the B/M transition at 0.78 Ma. Preservation of reverse polarity implies that the pedogenic hematite has been unchanged by chemical weathering or physical disturbance by soil biota for at least 0.78 Ma. It is inferred that prior to 0.78 Ma soil weathering may have occurred to greater depth because summer rainfall was significantly higher than present, which is consistent with evidence from Lake Amadeus in central Australia indicating a change from lacustrine clays to evaporites and dunes at about 1 Ma. Between 600 and 900 ka, oxygen isotope fluctuations in deep sea cores show a pronounced change in frequency, from a 40 ka (obliquity dominated) to a 100 ka (eccentricity dominated) pattern. At the same time, glacial—interglacial amplitudes increased, with a marked enrichment of glacial 18O values consistent with larger continental based ice-sheets. From the evidence presented above, climatic responses to these global changes were not synchronous across the Australian continent. DEEP WEATHERING AND QUATERNARY COLLUVIATION IN SWAZILAND T SCHOLTEN & P FELIX-HENNINGSEN Inst. Soil Science and Soil Conservation, Justus-Liebig-Univ., Giessen, Germany. Soil formation and landscape development in most parts of Swaziland is associated with deep weathering and Quaternary colluviation. Geomorphologically Middleveld and Highveld of Swaziland belong to the Great Escarpment predominantly formed by erosion. The geological structure is characterized by high diversity of Archaic intrusive rocks, ranging from granite to gabbro, with average ages between 2500 and 3500 Ma. The prevailing parts of the weathering mantle in the Middleveld and Highveld of Swaziland, today affected by severe soil erosion, consist of thick soil-saprolite complexes of crystalline rocks. The saprolite of the magmatic and metamorphic rocks developed under a tropical humid climate during the Cretaceous and Early Tertiary. Subsequently, the old weathering mantle was widely denuded in phases of morphodynamic activity and further developed in more humid phases of higher morphodynamic stability during the Upper Tertiary and Quaternary. From thick sediment sequences in depressions and at flat lower slopes it can be assumed that in most areas the soil cover has been denuded during the Quaternary. Middle Pleistocene soil sediments in the Lowveld of Swaziland have been stratified by embedded Old Stone Age artifacts. This leads to the assumption that the saprolite was the parent material of younger soils after phases of denudation, although the soils developed therefrom are characterized by polygenetic characteristics as a consequence of gradual climatic changes, small-area denudation, substratum displacement, and sedimentation at slopes. Stone lines are a widespread feature of the soils, indicating a former erosion surface and the extent of redeposited sediments so that most soil profiles show an upper allochthonous part of varying thickness and an underlying autochthonous part grading into the saprolite. The soil units change within short distances due to the polygenetic nature of the soils and varying intensities of younger erosional processes. At present gully erosion in Swaziland accounts for an annual loss of some 2000–3000 ha of land. Subsequently, today's truncated landscape displays an association of soils of different ages and environments. More than 60% of Swaziland's soils are not autochthonous. Colluvial soil sediments produce a multi-layer profile in most soils. Therefore, deep weathering and Quaternary colluviation are important processes not only contributing to the development of the landscape at the Great Escarpment of Swaziland and comparable subtropical regions but also determining crop and livestock production. The presentation summarises first results of the polygenetic and polycyclic genesis of soil-saprolite-complexes from plutonic rocks in Swaziland and resulting soil-physical and soil-chemical properties. PALEOSOL SEQUENCES AS EVIDENCE OF LONG AND SHORT TERM CLIMATIC CYCLES Michael J SINGER (1) & Kenneth L VEROSUB (2) (1) Dept of LAWR and (2) Dept. of Geology, University of California, Davis, USA. Jenny created his soil forming equation postulating that soil properties are a function of parent material, biota, topography, climate and time. If we can isolate one of the factors by holding the others “constant” or “ineffective”, we can either develop an understanding of how the isolated factor influences soil formation, or we can solve the inverse problem by using soil properties to understand the factor. Using paleosols to understand paleoclimate is an example of solving the inverse problem. Boundary conditions for studying climate are that soils are freely drained and on a stable landscape. For those interested in global climate change, the factor of greatest interest is climate, in particular, macroclimate indicators such as mean annual air temperature and precipitation. Less emphasis is placed on microclimate. Mean annual precipitation does not provide information on extreme events or years that may be critical to soil properties. The importance of precipitation is in leaching and weathering. Mean annual air temperature controls soil temperature, which in turn control the rates of biological and chemical reactions. Temperature and precipitation also contribute to determining the type of vegetation that grows on soils. Among the soil properties that may be sufficiently sensitive to climate to use as indicators of climate are number and type of horizons, horizon thickness, type and amount of clay minerals, evidence of clay mineral translocation, organic matter content, organic matter composition, soluble-salt content and distribution, calcium carbonate content and distribution, and some magnetic properties of soils. Each property may indicate something about the climate. For example, the depth of carbonate leaching from calcareous parent materials in humid region soils is well correlated to mean annual precipitation. Organic matter content varies with both MAT and MAP as these two variables independently affect plant growth, decomposition processes and rates and rates of accumulation of decomposition products. Soluble salt accumulation is a function of depth to water table in arid or semi-arid climates. A major challenge to pedologists is to quantify the relationship(s) between each of the morphological, chemical and biological properties and climate. In the People’s Republic of China, the long continuous record of intercalated loess and paleosol layers have been studied to develop knowledge about global climate change. Does the Chinese loess/paleosol record meet the conditions necessary to isolate climate as a soil-forming factor? Are the measurements being made sufficiently sensitive to determine long and short-term variation in climate? Does study of continuously aggrading deposits meet the boundary condition of a stable surface? These and other questions need to be answered if soils and paleosols are to be used in climate studies. USING PLANT DNA FROM PALAEOSOLS TO DETERMINE PALEOCLIMATE Michael J. SINGER (1) & Edouard JURKEVITCH (2) Dept. LAWR, Univ. California, USA. (2) Dept. of Plant Pathology and Microbiology, Hebrew Univ. Jerusalem, Israel. Many methods including
extraction and identification of pollen and fossils are used to extract
information about palaeoclimate from palaeosols. Pollen and fossils are
frequently absent from palaeosols. Extraction and identification of preserved
DNA fragments associated with clay minerals offers a new 'direct' strategy
for quantification of palaeoclimate. This strategy is fraught with difficulties,
not the least of which is the lack of information on preservation of DNA
fragments in palaeosols. Other questions require answers before DNA can
be used to reconstruct palaeoclimate. These include the following. If plant
DNA is preserved, can it be extracted and can the plants be identified
that contributed to the DNA? If the plants can be identified, did they
grow in a sufficiently narrow temperature and precipitation range that
their identification could provide useful climate information? To answer
if DNA is preserved in palaeosols, we attempted to extract DNA from three
palaeosols in Israel. The palaeosols ranged in age from 40 ka to >5 Ma.
All were buried under younger soils and parent materials. The present mean
annual precipitation at the sample locations ranges from 200 to 700 mm.
Soil samples were taken by auguring horizontally into fresh exposures along
roads. Samples were collected from locations where no visible modern roots
were observed and deep enough within the exposure to preclude horizontal
wetting from the exposure face. No attempt was made to maintain aseptic
conditions. Palaeosol samples contained from 2 to 6% total carbon and 22
to 72% clay. The mean palaeosol sample pH was 8.3 and pH ranged from 7.6
to 8.6. Sample calcium carbonate content ranged from 0.2 to 33%. After
crushing and sieving to pass 2-mm diameter holes, samples were extracted
using standard techniques. Extracted DNA was purified using Elutip columns.
Before extracting palaeosol samples, modern soil samples from the same
locations were sampled and extracted. Sufficient DNA was obtained from
the modern soils that it could be easily visualised on Agarose gel, indicating
that the extraction and purification methods worked. Much smaller amounts
of DNA were obtained from the palaeosols. For example, based on spectrophotometer
absorbence at 260 nm, 250 nanograms of DNA were extracted from 80 g of
one 60 ka paleosol. In many extractions virtually no DNA was extracted,
indicating that the samples were not contaminated with modern bacterial
or fungal DNA. Purity of the DNA based on the A260/A280 ratio varied from
61 to 71%. We were not able to visualise the DNA on agarose gel stained
with ethidium bromide because of the low DNA concentrations. The polymerase
chain reaction was attempted using two primers designed to amplify plant
loci. No success was achieved with either of the primers. Although we were
unable to amplify the DNA or sequence it, we are confident that DNA is
preserved in palaeosols. Much additional work is needed to answer the other
questions, but we have initiated a new methodology that provides great
new opportunities for direct assessment of palaeoclimate.
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