Phys. Chem. Earth (A), Vol. 24, No. 9,
pp. 773-777, 1999
0 1999 Elsevier Science Ltd All rights reserved 1464-1895/99/$ - see front matter
Pergamon
PII: S1464-1895(99)00113-l
The Paleo- and Petromagnetic record in the Polish and Ukrainian Loess-Paleosol Sequences J. Nawrocki’, V. Bakhmutov2, A. Bogucki3 and L. Dole&i4 ‘Department of Geophysics, Polish Geological Institute, Rakowiecka 4,00-975 Warsaw, Poland E-mail:
[email protected] 21nstitute of Geophysics, National Ukrainian Academy of Sciences, Palladin av.32,252680 Kiev-142, Ukraine 3Department of Geography, Lvov University, Doroszenki 41,290OOO Lvov, Ukraine 4Department of Physical Geography and Paleogeography, Maria Curie-Sklodowska University, Akademicka 19,20-033 Lublin, Poland Received 24 April 1998; revised I September 1998; accepted 3 November 1998 quantitative paleorainfall reconstruction (Maher & Thompson, 1995). Preliminary magnetic susceptibility studies of the Polish and western Ukrainian loess-paleosol sequences (Nawrocki et al., 1996) showed that the correlation of susceptibility data with paleoclimate is more complex than for the Chinese sections. The major causes of the complexities are the relatively thin loess units and the diverse geochemical processes that affected the loess surface during interglacial
Abstract. 718 samples from five loess-paleosol sections located in the Black Sea region, the western Ukraine and Poland (Lublin Upland) were the subject of a paleomagnetic and petromagnetic study. Strong magnetic enhancement is observed in the cambisols, chemozems and iluvial horizons of the forest (podzolic) and leached brown type (brownerde) soils. Distinct magnetic depletion or dilution occurs in the gley soils and the leached horizons of podsols and brown type soils. Magnetic enhancement in the section from Black Sea region was not simply dependent on paleotemperature. Soils Tom the interstadial periods could be magnetically enhanced to the same degree as soils which were formed during interglacials. In the Polish and Ukrainian loess-palesol sequences, paleorainfall could be a significant factor controlling the susceptibility signal in addition to paleotemperature. The degree of warming of paleoclimate can be expressed by the amount of secondary maghemite that was formed in the studied paleosols. All sections were deposited after the BrunhesMatuyama paleomagnetic reversal. No remarkable paleomagnetic event was encountered. However, very distinct directional changes associated most probably with the secular variations were observed in the Polish and western Ukrainian sections. These changes can serve as a correlation tool for comparison with stratigraphic petromagnetic data. 0 1999 Elsevier Science Ltd. All rights reserved
1. Introduction Fig. 1. Sketch map of the loess dlstrlbntmn and max~mmn extent of the main glaciations in Central Europe (after Hohl, 1980) The loess sections studied here are marked with circles.
The concentration of magnetic minerals in sediments, expressed by magnetic susceptibility or other petromagnetic parameters, can reflect climatic conditions in which they were deposited. Magnetic susceptibility of the loesspaleosol sequences have been used for their stratigraphic correlation with deep-sea sequences (Beget et al., 1990; Kukla et al., 1988; Heller & Evans, 1995; Rutter & Chlachula, 1995; Forster & Heller, 1994). In the Chinese loess plateau magnetic susceptibility has been used for correspondence
and interstadial times. This paper presents further paleoand petromagnetic data Tom the Polish and Ukrainian loess-paleosol sequences. About 700 oriented samples were taken from five outcrops located in the Black Sea region, western Ukraine and SW Poland (Fig. 1). The most southern section Primorskoje is exposed in the Black Sea cliff, about 50 km south from Odessa. The outcrop at Jezupol near Halicz is located on the right slope of the
lo: Jerzy Nawrocki
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J. Nawrocki et al.: Polish and Ukrainian Loess-Paleosol
Dniestr River valley. Loesses at Bojanice and Obrowiec are exposed in the brick-yards and jointly with the ravine section at Zadebce belong to the abundant patches deposited along the Polish/Ukrainian border, near the Bug River valey. 2. Results and discussion 2.1. Magnetic susceptibility and magnetic carriers The magnetic susceptibility values measured in the samples t?om loess and gleyed horizons was lower than 300 SI units. In the paleosols I?om western Ukraine and Poland susceptibility values did not exceed 600 SI units. Susceptibility values up to 3 times higher (up to 2000 SI units) were measured in the paleosols from Primorskoje situated in a Black Sea cliff, A plot of volume magnetic susceptibility versus saturation isotermal remanent magnetization (SIRM), acquired in the field of 3 T (Fig. 2a), shows that the susceptibility of loesses and probably
Sequences
indicate that susceptibility here depends on the content of fine-grained ferrimagnets. The IRM and thermomagnetic curves (Fig. 2c,d) point to the presence of magnetite as a main carrier of the IRM in the measured paleosols and loesses of the Primorskoje section. A decrease of the IRM measured on the soil samples after heating could indicate that maghemite is also present here. Maghemite (y-FezOX) as a metastable phase during heating inverts to a less magnetic hematite (aFezOX). The decrease of the IRM is more conspicuous in the red-brown cambiosols of subtropic type (see Gozhik et al., 1995) than in the chemozem and initial brown earth (braunerde) type paleosol. According to Maher (1998) maghemitisation is common in the soil profiles and may play an important role in the persistence of the tine-grained ferrimagnets, protecting the inner magnetite core from dissolution. The ampliude of the IRM decrease after heating (i.e. the amount of maghemite ?) reflects most probably the degree of soil oxidation and consequently could reflect the degree of warming in the interglacial and interstadial periods. Loesses from Primorskoje contain also some hematite with maximum unblocking temperatures higher than 600 ’ C (Fig. 2d). This mineral was also observed in Polish and western Ukrainian loesses (see Nawrocki et al., 1996). A hysteresis loop measured on a paleosol sample from the Bojanice section has a ,,wasp-waisted” shape, but a hysteresis loop for pure loess from that section is not waspwaisted (opcit.). These observations could also indicate that two different gram size populations of magnetite are present in the paleosol ( see Tauxe et al., 1996). 2.2. Differentiation of selected petromagnetic parameters along lithostratigraphic columns In the Primorskoje section relatively high susceptibility values are characteristic of the cambisols and chemozems. PRLMORSKOJE.
Fig. 2. (a) Low-field magnetic susceptibility versus saturation isotennal remanent magnetization (acquired in the field of 3 T) in Polish and western Ukrainian loess and paleosol samples (b) Low-field magnetic susceptibdity versus ARM intensity in loess and paleosol samples 6om Primorskoje section. ( c) IRM curves obtained for loess and paleosol samples from Primorskoje section. (d) Thermomagnetic curves for loess and paleosol samples from Primorskoje section. Numbers in parentheses express the ratio of the RM acquired m the field of 1 T after heating to 7OO’Cto IRA4acqurred m the same field before heating.
also gleyed paleosols from Poland and western Ukraine depends primarily on concentration of ferrimagnets, although a certain influence of grain size diferentiation can not be excluded. The situation is different in the case of cambisols, chemozems and illuvial horizons of paleosols t?om that area, where the increase of magnetic susceptibility is not accompanied by a proportional increase of the SIRh4. This phenomenon is most probably related to the high content of paramagnetic or (and) superparamagnetic particles in these soil horizons. On the other hand, a good correlation between magnetic susceptibility and anhysteretic remanent magnetization (ARM) achieved for the soil samples Tom the ‘Primorskoje section (Fig. 2b) could
Fig. 3. Low-field magnetic susceptibility, ARM mtensity and me&an destructive field changes as a function of depth at Prlmorskoje section. Cl4 and TL ages after Gozhiket al. (1995).
Surprisingly the magnetic susceptibility signal in the interstadial chemozem that occurs between 1.5 and 2.7 m of
J. Nawrocki et ul.: Polish and Ukrainian Loess-Paleosol Sequences profile (Biilling interstadial ?) corresponds to that of the interglacial cambisols (Fig. 3). The ARM plot for the with the corresponds directly Primorskoje section susceptibility curve. OBROWlEC 0
K (XIO-as,““I&) 100 200 300 400
NRM FU&@, 20 40 60 80
0
175
devoloped during the climatic optimum of oxygen-isotope substage 5e (Fig. 4a). The IRh4 values noted in the unweathered loess and paleosols are very similar. There is a negative correlation between the Rh40RM and the intensity decay (after AF cleaning in the field of 23 mT) plot prepared for the Bojanice section (Fig. 4a,b). This fact indicates that RM/IRM ratio reflects rather changes in magnetite grain size than relative changes of paleointensity. On the other hand, the upper part of the RM/IRM plot drawn for the Obrowiec sections could reflect real changes of paleointensity because correlation of this parameter with the intensity decay after AF cleaning is very weak (Fig. 4b). The maximum values of RMiIRM, which occur in the loesses from oxygen-isotope stage 3, could be correlated with the paleointensity maximum noted at the same time in the deep-sea and lake sediments (e.g. Stoner et al.. 1995). Therefore it can not be excluded that after grain size correction the relative paleointensity determination in loesses from Poland and western Ukraine will be possible. 2.3. Stratigraphic correlation
Fig.
4.
(a) IRM
(the natural NRM
(the natural
changes
during
remanent of
ages have
(b) Scatter
prepared
for
plots
depth
after
susceptiblhty, and
at Obrowiec
NRM and
loto segments
of RMiIRM
BOJ~WX
to
BOJ~WC~ sectmns
by Butrym and
of Rhl
decay (III 23 mT)
related
versus NRM
ratlo
m 23 mT)
demagnetlzatmn
been detemuned
loesses from
the oxygewsotope
magnetx
magnetzatmn)
curves were subdivided
stages. TL
laboratory). 23 mT
magnetwatmn
as a functmn
Susceptibility Isotope
mtenslty, low-field
remanent
to the oxygen(UMCS
mtensity
Obrowec
Lublin decay III
accumulated
stage 3.
In the western Ukrainian and Polish sections a significant decrease of magnetic susceptibility was noted in the gleyed paleosols (Fig. 4a; e.g., the Bojanice section - from 4.8 to 5.6m). leached horizons of the forest (podzolic) soils (Fig. 5a; e.g., the Jezupol section - upper part of 5e segment) and leached horizons of leached brown type (braunerde) soils (Fig. Sa; e.g., the Zadebce section - upper parts of segments 9 and 11). in which accumulation horizons were usually eroded. High values of susceptibility occur in chemozem soils and illuvial horizons of interglacial podzolic or leached brown paleosols (especially Eemian). The magnetic susceptibility of chemozems that formed during oxygenisotope substage 5c is usually higher than the magnetic susceptibility of the Eemian paleosols which were
Stratigraphic subdivision of investigated sections into segments correlated with the deep-sea oxygen-isotope stages is based on the results of Cl4 and TL dating, plus lithostratigraphic and magnetic susceptibility studies. The shape of magnetic susceptibility curves was taken into account especially in the case of western Ukrainian and Polish sections (Fig. 5a). In the loesses which accumulated during oxygen-isotope stage 3, several (6 to 8) minor oscillations of magnetic susceptibility are visible. These oscillations can be related to subordinate climatic changes that occured during the Vistulian glaciation. In spite of stratigraphic arguments based on the results of geological and magnetic susceptibility studies, correctness of stratigraphic correlations should be verified by an intependent method. Unfortunately all investigated sections are younger than the Brunhes/Matuyama paleomagnetic boundary. Samples from Primorskoje were thermally demagnetized up to 25O’C and subsequently treated with alternating field demagnetization (AF) of 25 mT. They revealed only normal polarity directions. AF demagnetization of samples from Polish and western Ukrainian sections did not provide any paleomagnetic excursion which may be used for correlation. Only in one sample from Zadebce section was a full reversal of direction observed (Fig. 5b). On the other hand, very distinct directional changes, associated most probably with secular variation, are observed in all sections from this area. These changes can serve as a control tool for stratigraphic correlation of the studied sections. In Fig. 5b declination and inclination plots were divided into equivalents of oxygen- isotope stages as were the magnetic susceptibility plots. A very good correlation of directional changes is noted in the sediments attributed to the oxygenisotope stages 4, 6 and 8. Weak correlation is also observed in the segments of sections from warming periods (e.g. 3 and 5~). Such correlation was not expected in the case of strongly reworked and magnetically enriched interglacial sediments (e.g. illuvial horizon of the Eemian paleosol).
J. Nawrocki et al.: Polish and Ukrainian Loess-Paleosol Sequences
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NNW
SSE Primorskoje
JEZUPOL
OBROWIEC
BOJANICE
Fig. 5. Correlation of magnetic susceptibility (a) and inclination-declination plots (b) prepared for selected Polish and Ukrainian loess sections. Susceptibihty, declination and inclination curves were subdlvided into segments related to the oxygen-isotope stages. Declmatton and inclmation values were determined after AF demagnetlzatlon
3. Conclusions From the above the following
conclusions
can be drawn:
(1) In the Polish and Ukrainian loess-paleosol sequences strong magnetic enhancement is seen in the cambisols, chemozems and illuvial horizons of the forest (podzolic) and leached brown type (braunerde) soils.
(2) Magnetic depletion or dilution is seen in gleyed soils and horizons and leached horizons of the podsols and brown type soils. (3) Magnetic enhancement in the Primorskoje section (Black Sea region) was not a simple function of paleotemperature. Chemozems horn the interstadial cycles could become magnetically enhanced to the same degree as
J. Nawrocki et nl.: Polish and Ukrainian Loess-Paleosol cambisols from interglacials. Thus rainfall could be as important a factor controlling the magnetic susceptibility as temperature. (4) In the Polish and western Ukrainian loesses trends of paleosecular variation can serve as a control tool of their stratigraphic subdivision and correlation
Acknow/edgenten& The ARM and h4DF analyses were carried out at the Paleomagnetic Laboratory of GeoForschungsZentrum Potsdam We thank Norbert Nowaczyk for it. Our thanks are also extended to Chriistoph Gelss and anymous reviever for their critical review of this manuscript.
Beget, J., Stone, D.B., and Hawkins, D.B., Paleoclimatic forcing of magnetic susceptibility variations in Alaskan loess during the late Quatemary, Geology, 18, 40-43, 1990. Forster, T., and Heller, F., Paleomagnetism of loess deposits from the Tajik depression (Central Asia), Earth Planet. Sci. Lett., 128. 501-512, 1994. Gozhik, P., Shelkoplyas, V., and Khristoforova, T., Development stages of loessial and glacial formations in Ukraine (Stratigraphy of loesses in Ukraine), Annales UiUCS Sec. B, 50, 65-74, 1995. Heller, F., and Evans, M., Loess magnetism, Rev. Geophys., 33, 21 I-240, 1995.
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Hohl, R., (ed.), Die Entwicklungsgeschichte der Erde, 703 pp., VEB F.A. Brockhaus Verlag, Leipzig, 1980. Kukla, G., Heller, F., Liu, X.M., Xu, T.C., Liu, T.S., and An, Z.S., Pleistocene climates in China dated by magnetic susceptibility, Geology, 16, 81 l-81 4, 1988. Maher, B., and Thompson, R., Paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the Chinese loess and paleosols, Quat. Rex, 44, 383-391, 1995. Maher, B.. Magnetic properties of modem soils and Quaternary loessic paleosols: paleoclimatic implications, Paleogeogr., Paleoclimatol., Paleoecol., 102, 215-237, 1998. Nawrocki, J., Wojcik. A., and Bogucki, A.. The magnetic susceptibility record in the Polish and western Ukrainian loess-palaeosol sequences conditioned by 25, 161-169, 1996. paleoclimate, Boreas, Rutter, N.W., Chlachula, Magnetic susceptibility and remanence record of the Kurtak Loess, Southern Siberia, Russia, Terra Nostra, 2. 235, 1995. Stoner, J.S., Channell, J.E.T., and Hillaire-Marcel, C., Late Pleistocene relative geomagnetic paleointensity from the deep Labrador Sea: Regional and global correlations, Earth Planet. Sci. Lett., 134, 237-252, 1995 Tauxe, L., Mullender, T.A.T., and Pick, T., Potbellies, wasp-waists, and superparamagnetism in magnetic hysteresis, J. Geophys. Res., 101, 571-583, 1996.
