Thermoluminescence dating of loess deposits at Paudorf, Austria

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T H E R M O L U M I N E S C E N C E DATING OF LOESS DEPOSITS AT P A U D O R F , AUSTRIA M. NolI, E. L c i t n e r - W i l d * a n d P. Hille htstitltt ti'ir Radittm,!brschtm S, mtd Kernpltysik, University ~/ Viemut, Boltzmamzgasse 3, A-IO90 Viemm, Attstria

The fine grain thcrmoh.minesccncc (TL) dating method was applied to an upper palacosol from a loess deposit in Paudorf, l,owcr Austria. This site is of special interest as there is some contrmcrsy about the time of formation of this soil horizon. The rest.Its of the present study strongly indicate that the soil formed during the WOrm I/II intcrstadial (deep sea 81so Isotope Stage 3). Although age underestimation duc to a long-term instability of lumincsccnce centres m gcneral cannot be ruled out, arguments are given for the credibility of the presented TL agc, which is also corroborated by the radiocarbon age of charcoal from the top part of the correlated palaeosol in Aigcn, Lower Austria.

INTRODUCTION In addition to the well known loess deposit at Stillfried, Lower Austria, a Ioess-palaeosol sequence at Paudorf, Lower Austria is of great interest because of man~ discussions about the time of formation of the upper palaeosol at this site. G6tzinger (1936) attributes this palaeosol to the WOrm I/I1 interstadial and since that time 'Paudorf" has been a synonym for the w a r m e r time period preceding the last glaciation (Fink, 1976). Fink (1976) revised the view of G6tzinger (1936) and concluded that the Paudorf palaeosol originated from an interglacial period (Eemian or older), mainly due

to the occurrence of a typical mollusc fauna which was investigated by Lozek (1976). In this interpretation a 14C age of 32,14(I _+ 860 BP ( G R N 2196) of charcoal from the top of a palaeosol at Aigen, Lower Austria, described as "'Paudorf palaeosol in typical d e v e l o p m e n t (i.e. as at the locus o'picus)'" by Fink (1976), was not considered (Vogel and Zagwijn, 1967). Therefore the formation time of the palaeosol has been a matter of speculation until now. The present study is an attempt to contribute to the solution of this open question by applying the fine grain thermoluminescencc (TL) dating method to the soil horizon and the loess layer underneath. In Fig. 1 the locations of the key loess

®

FIG. 1. :Map ol kox~cr Austria shinning the locations of the Iocss-palacosol sequence,, at Sliltlricd, Paudort and Aigen (after Binder, 1977).

]o

'.vhonl correspondence should bc addressed.

473

474

M. Noll et al. Ah

400 0 0 0

Bt C-Loess

350 000 -~- 300 000 - -

Paudorf-Palaeosol

250 000

:e:o:e:~=e.'o:e:~: p:e:o=e]e:e:e:e:~

200 0 0 0 150 0 0 0 - Loess

,..1 [.., 100000

/

50 000

_~o..,.~

o--'~-

/

-200-100 0

'

!

i

I to!

I

!

1

t

[Gy]

Dose

Pala¢osoI-Complex

Locss

I

tO0 200 300 400 500 600 700 800 900 1000

FIG. 3. Determination of the equivalent dose for the palaeosol in the temperature interval 310--319°C with the additive (o) and the partial bleach (o) methods. The partial bleach m e a s u r e m e n t s were performed after a 611 rain sunlight exposure. The errors given are let standard deviations of three individual m e a s u r e m e n t s for each point. From these experimental errors a relative m e a n error assumed to be constant for all data points of about 3% was calculated and used in the fit (see text),

FIG. 2. Simplified schematic profile of the Paudorf loess site (after Verginis, 1993).

sections discussed above are shown on a map of the northern part of Lower Austria. A schematic profile of the Paudorf loess-palaeosol sequence is sketched in Fig. 2.

EXPERIMENTAL

The fine grain polymineral fractions (4-11 ~m) of sediment samples from the middle of the palacosol and the loess layer under the soil were pretreated with dilute HCI and additionally with a mixture of tetrahvdrofuran + lO%v/v 6 M HCI to remove carbonates and organic material. The TL samples were prepared by settling the suspended grains on aluminium discs. The TL measurements were performed with a TL reader equipped with an EMI 9635QA photomultiplier, and Schott UG 11 and Schott KG3 heat-absorbing filters. The glow curves were recorded at a heating rate of 5°C sec- z in nitrogen atmosphere after a preheat of one minute at 230°C. Following a suggestion of Berger (1988), the additive and the partial bleach methods as described by Wintle and Pr6szynska (1983) were chosen for the determination of the equivalent dose to prevent sensitivity changes sometimes caused bv the bleaching procedure when the regeneration method is applied. Normal sunlight was used for bleaching. Laboratory irradiations were performed with a 1110mCi Amersham '~"Sr/'mY beta source mounted in a Daybreak irradiator. The equivalent dose was calculated over the temperature range of the glow curves, yielding good plateaus (300-400°C) at 10°C intervals. In Fig. 3 the equivalent dose determination for the palaeosol obtained by applying the additive and partial bleach methods is shown for the interval 310--319°C. For both methods

least-squares fits using a saturating exponential function and weights assuming constant relative errors of the measured TL values were applied. Figure 4 shows the equivalent dose plateaus determined with the two methods for the loess and the palaeosol. Fading tests over one month showed no significant fading (error limit 5%) of the TL signal during this period. The uranium, thorium and potassium contents of the sediment samples were determined with a NaI(T1) gamma spectrometer using a modified version of the method described by Meakins et al. (19791. A detailed description of this modification is given in LcitncrWild et al. (in preparation). For the estimation of the annual dose rate the contribution from cosmic radiation was considered and a saturation water content of W=0.40 + 0.10 was determined for both sediments

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250 _

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100

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50 I

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I

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I

2

4

6

8

10

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Temperature

interval

FIG. 4. T e m p e r a t u r e dependence of the equivalent dose evaluated at IO°C intervals in the temperature region 3(~-400°(': h,r the palaeosol and the underlying loess. Mean values in the plateau region are indicated. Data points for the partial bleach method in parentheses yielded unphysical T L values at the intersection point. 5, • Additive and partial bleach m e t h o d for the palacosol: 7 , 7 additive and partial bleach method for the loess laver.

475

TL [)atin~ ol l_ocs,, at Paudorf, Austria

complex formed during the warm substages of Isotope Stage 5. This divergence may be due to the different methods used for the TL dating. ZOller et al. (1494) recorded the glow curves using a filter with maximum transmission in the blue region and after a stronger thermal washing procedure. Z6ller et al. (1988) stated that this technique offers the opportunity to expand the TL datable range, but there are some indications that this extension is not always achievablc (Frechen et al., 1992). Berger (1994) recommended, together with some other suggestions, the use of a blue filter to avoid age underestimation. The data presented in our paper here were recorded in the ultraviolet region, therefore the possibility of an underestimation must be discussed. Consideration of a long-term instability of the luminescence centres (Debenham, 1985) with a mean lifetime of 15(I ka as suggested by Wintle (1990) would yield corrected TL ages of 48 ka for the palaeosol and 111 ka for the underlying loess. According to these corrections the palaeosol of Paudorf must still be attributed to Isotope Stage 3. Independent evidence to support a Stage 3 rather than, for example, a Stage 5e age for the Paudorf palaeosol comes from the work of Bronger (1976). He described the Paudorf palaeosol as a chernozem with a primary carbonate content. Bronger's results of a micromorphological investigation of this soil horizon contradict the assumption made by

and according to this value a mean water content of the samples of (20 + 10)% was presumed.

RESULTS

AND

DISCUSSION

The results of the TL age determination derived by the application of the additive and partial bleach methods for the determination of the equivalent dose are presented in Table 1. The values obtained by the additive dose method are confirmed by the values obtained with the partial bleach method. Figure 5 shows the mid-June insolation for the 47.5 °N latitude during the last 140 ka computed by applying the formulas and orbital parameters given by Berger (1978). SPECMAP deep sea 8~xO Isotope Stages (lmbrie et al., 1984) are given on the upper x-axis and the TL ages determined by the application of the additive method together with the lo- statistical errors are indicated in Fig, 5. It is evident that the age of the palaeosol lies within Isotope Stage 3. The age of the loess horizon within the limits of error can be attributed to the cold Isotope Stage 4 and coincides with a (local) decrease in summer insolation. The determined ages are in disagreement with the results of Z611er et al. (1994) for the same site. In their study the Paudorf palaeosol is interpreted as a soil

T A B L E 1. Results of the TL dating of lhc upper palaeosol and the t.ndcrl_~ing loess at Paudorl. Auslria Sample

Method

Equivalent

a Value

dose (Gy) Additi'.c Partial bleach Additi',e

156-+ 16 225-+2U

Partial bleach

216-+22

2.72+0.22

[)osc rate

Age

t)

(mGy a I)

(ka)

(I. 13_+(L04

3.S4-+(I.45

{111(}~, a

12.37_+11.51 1.77h_+UJ)t,4

2.42-+

S.2U_+0.45

22

l 271mi (1(~1!

(LII_+ILU3

2.Sh_+0.3n 77-+ 12

5

(x I 0 0 0 )

I

48

'

2

I

[]

44

1

3 I I I Palaeos.l I I I I [ I

46

[]

[] 0 0

42

oo

I

'

I I I

0 []

[] o []

o% o

0 D

0 o

I

[]

1

o

o

o o

[]

o 0

I

0

o 0

0 I I

o

ol

0

I

[] []

nl

I I I I ,

I 30

rn oO

I I I

I I I I I I

o

I I

I o I

4O

0

I'1

o

I I I I I I -

I I I I I I I I I

I

o o

38

Cosmic dose rate

41.1-+6 7S-+ 12

0.()7h-+(L()2S

.-

K

(",,)

42_+6 0.(U5_+ILI~21

Q

Th

(ppm)

162-+13

Palaeosol

Underlying loess

U

{ppm)

M

6

I I I I I I t I ! I I I

o

b I° ! []

o

n

0

b I0

13

121

0

Ii ~

I !

I l

[] 13

D

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,%o I !

n

0

0 []

[]

q~

0

I I

I

I

o

i

60

|

I

90

120

150

[kal FIG. 5. Mid-June insolation (for 47.5°N) for the last 14U ka. 8rs(-) Isotope St;tee', and "I+1. age,, hw the PaudoM palacosol and loess arc indicated.

476

M. Noll el al.

Kukla (1969) that the palaeosol represents a palaeosol complex, which is drawn from the interpretation of the different mollusc fauna at the upper and lower edge of the palaeosol, The assumption of a palaeosol complex is a necessary condition for the interpretation of Z611er et al. (1994). Bronger (1976) showed that the degree of weathering of the Wfirm chernozems and Braunerde chernozems in the Carpathian Basin "'is at least as high as in recent soils of the same type in this area". He concludes that these soils originate from warmer periods during the WOrm and that "'it seems to be neither necessary nor probable to associate the "Paudorf Soil" (Ioc. typ.) . . . with thc Ril3/W0.rm-interglacial". These fndings, together with the fact that our uncorrected TL ages are in a reasonable time relationship to the radiocarbon age of 32,140 + 860 BP ( G R N 2196) from the top part of the corresponding palaeosol at Aigen, are a good justification for the reliability of the determined formation time of the soil and loess layers, i.e. Isotope Stages 3 and 4.

Bronger, A. (1976). Zur quartfiren Klima- und Landschaftsentwicklung des Karpatenbeckens auf (paliio-)pedologischer und bodengeographischer Grundlage. Kieler

(;eogra/~/tisc/te Schrff'len,

45, 268 pp.

Debenham, N.C. (1985). Use of U.V. emissions in TL dating of sediments. Nuclear D'acks and Radiation Measurements, 10, 717-724. Fink, J. (ed.) (1976). Exkursionen durch den osterreichischen Tell des n6rdlichen Alpenvorlandes und den Donauraum zwischen Krems und Wiener Pforte, M!neihmgen der Kommission fi~r Quartdr/brschtmg der Osterreichischen Akademie der Wissenschften, 1, Frechen, M., BriJckner, H. and Radtke, U. (1992). A comparison of different TL-techniques on loess samples from Rheindahlen (F.R.G.). QuaternapT Science Reviews, !1, 1(19-113. G6tzinger, G. (1936). Ftihrer ftir die Quart~rexkursionen in Osterreich. I11. INQUA-Konferenz, Wien. lmbrie, J., Hays, J.D., Martinson, D.G., Mcintyre, A., Mix, A.C., Morley, J.J., Pisias, N.G., Prell. W.L. and Shackleton, N.J. (1984). The orbital theor 3 of Pleistocene climate: support from a revised chronology of the marine 8tsO record, hi: Berger. A., lmbrie. J., Hays, J., Kukla, G. and Saltzman, B. (eds). Milankovitch and CTimate, pp. 269-3(15. NATO ASI Series, Series C, Mathematical and Physical Sciences, 12OD. Reidel, Dordrecht. Kukla, J. (1969). Die zvklische Entwickh, ng und die CONCLUSIONS absolute Datierung der L6ss-Serien. In: Dcmek, J. and Kukla, J. (eds), Periglazialzone. LO[3 trod Paliiolithikum According to the TL ages of the Paudorf palaeosol der Tschechoslowakei, pp. 75-95. Tschcchoslowz, k. Akad. presented in this study, the conclusion of G6tzinger d. Wiss., Geogr. Inst. Brno, Brno. (1936) that the formation time of this pedogenic Leitner-Wild, E.. Hille, P., Aref-Azar: H. and Verginis, S. Characterization of palaeosols by mttltiparametcr analysis horizon was the WOrm I/II interstadial is confirmed. As (in prcTmration). discussed, the TL method applied may underestimate Lozek, V. (1976). Malakologie. In: Fink, J. (ed.), Exursioncn the ages due to the long-term instability of the durch den 6ster-reichischen Teil des n6rdlichcn Alpcnvof luminescence centres, Corrections for this effect, howhmdes und den Donauraum zwischcn Krems und Wiener ever, would still yield an age of the palaeosol in the time Pforte. Mitteihmgen der Kommission ,/fir QtmrtgilJ?,schung der Oster-reichischen Akademie der Wi.ssenscha/h'n. I. range of Isotope Stage 3, whereas for the underlying loess horizon the corrected age would be difficult to Meakins, R.L., Dickson, B.L. and Kelly, J.C. (1979). Gamma ray analysis of K, U, and Th for dose-rate explain. estimation in thermohnninescent dating. Archaeonletrv, 21, 79-$6. Vcrginis. S. (1993). L6Bakkumulation und Palfioh6den ACKNOWLEDGEMENT als lndikatoren for Klima-schwankungcn wfihrend des Pal:iiolithikums (Plcistoz/in). In: Neugebauer-Maresch, C. We th~,nk S. Verginis for his help in obtaining the sediment (ed.), Alsleinzeit im Osten Osterreich,s, pp. 13-30. Wissensamples. schaftliche Schrtftenreihe Nieder6sterreich 95/96/97. Vcrlag Nieder6stcrreichisches Pressehaus. St. P61tcn-Wein. Vogel. J.C. and Zagwijn, W.H. (1967). Groningcn radioREFERENCES carbon dates VI. Radiocarhon, 9, 63-111fi. Wintlc, A.G. (1990). A review of current research on TL dating of loess. Quaterna O' Science Reviews, 9, 385-397. Berger, A.L. (1978). Long-term variations of daily insolation and Quaternary climatic changes. ,lourmd of-the Almo- Wintlc, A.G. and Pr6szynska, H. (1983). TL dating of loess in Germany and Pohmd. PACT, 9, 547-554. spheric Sciences, 35, 2362-2367. Bergcr. G.W. (1988). Dating Quaternary events by lumines- Z611er, L., Strcmmc, H. and Wagner, G.A. (1988). Thcrmolumincszcnz-Daticrung an l,(~ss-Paliioboden-Scqcence. Geological Society of America. Specml l'aper 227, ucnzcn on Nicdcr-, Mitcl- und Obcrrhcin-Bundesrepublik 13-50. Dcutschhmd. (Twmical Geology (l.sotope (;eosciem'e SecBerger, G.W. (1994). Thermolumincsccncc dating of sedition). 73, 39-62. ments older than 11)0 ka. ()uaterml U (;eochronology Z(~,ller, L., Oches, E. and McCoy, W.D. (1994). Towards a (Quaternary Science Reviews) (this issue). revised chronostratigraphy of loess in Austria, with rcspcct Binder, H. (1977). Bemerkenswcrtc Molluskcnfaunen aus to key sections in the Czech Republic and in Htmgary. dem Plioz/,in und Pleistozim yon Niedcroslcrrcich. Beitrdge Quatermtt T Geochronology (Qttaterna O' Science Reviews1 ,Tttr Paliiontologie yon O.sterreich. V'ol. 3, pp. I-7S. lnstitut (this issue). for Pal~iontologie der Universitfit Wien.