Ellwood, B. et al. (2004) Magnetic susceptibility applied as an age-depth-climate relative dating...

Magnetic susceptibility applied as an age–depth–climate relativedating technique using sediments from Scladina Cave, a Late

Pleistocene cave site in Belgium

Brooks B. Ellwooda,*, Francis B. Harroldb, Stephen L. Benoista, Paul Thackera,Marcel Ottec, Dominique Bonjeand, Gary J. Longe, Ahmed M. Shahine,

Raphael P. Hermannf, Fernande Grandjeanf

aDepartment of Geology and Geophysics, Louisiana State University, E235 Howe-Russell Geoscience Complex, Baton Rouge, LA 70803, USAbCollege of Natural and Social Sciences, University of Nebraska at Kearney, Kearney, NE 68849, USA

cUniversite de Liege, Service de Prehistoire, 7 Place du XX Aout, A1, B-4000, Liege, BelgiumdArcheologie Andennaise Asbl, 339d Rue Fond des Vaux, B-5300 Sclayn, Belgium

eDepartment of Chemistry, University of Missouri-Rolla, Rolla, MO 65409-0010, USAfInstitut de Physique, B5, Universite de Liege, B-4000 Sart-Tilman, Belgium

Received 28 April 2003; received in revised form 10 August 2003; accepted 26 August 2003

Abstract

Here we demonstrate that magnetic susceptibility (MS) data from Scladina Cave, Belgium, provide a time–depth–climaterelationship that is correlated to the marine oxygen isotopic record and thus yields a high-resolution relative dating method forsediments recovered from many archaeological sites. This methodology will help resolve one of the major problems facingarchaeologists, namely the difficulty of acquiring absolute dates with reasonable precision for the period from 40,000 to 400,000years or so. The problem is that dating techniques applicable to most materials within this age range are subject to significant errors.Relative dating techniques, such as magnetic secular variation or stable isotope methods, offer the potential to improve thisprecision, but both methods suffer from problems that make broad application to many sites impossible. However, for mostarchaeological cave sites, MS measurements of cave sediments offers the potential for intra-site correlation and paleoclimateestimation. This is possible in protected cave environments because the MS of cave sediments results from climate processes activeoutside caves, which cause variations in magnetic properties of the sediments that ultimately accumulate inside caves. Oncedeposited, these materials are often preserved and their stratigraphy provides a time–depth–climate signal that can be identified.Therefore MS data can be used as an independent methodology, alongside conventional methods such as sedimentology andpalynology, for relative age dates, and correlation within and between sites by tracing evidence of paleoclimatic change. Thiscorrelation has been used to infer an age of 90,000�7000 years for Neanderthal skeletal remains recovered from Scladina Cave, animportant Middle Paleolithic archaeological site in Belgium.� 2003 Elsevier Ltd. All rights reserved.

1. Introduction

We have been applying magnetic susceptibility(MS) measurements of micro-stratigraphic sedimentsample sets (continuous samples) recovered from well-

documented Pleistocene and Holocene archaeologicalsites in Europe and the United States (e.g. Refs. [6–11]).When applied to cave sites, MS relative dating appli-cations utilize the independent isotopic and cultural agesavailable from archaeological levels. The method isbased on the fact that pedogenesis produces magneticgrains, and that regional, long-term climate cycles(hundreds to thousands of years) control pedogenicvariations and thus the amount of magnetic material

* Corresponding author. Tel.: +1-225-578-3416;fax: +1-225-578-2302.

E-mail address: ellwood@lsu.edu (B.B. Ellwood).

Journal of Archaeological Science 31 (2004) 283–293

SCIENCE

Journal of

Archaeological

http://www.elsevier.com/locate/jas

SCIENCE

Journal of

Archaeological

http://www.elsevier.com/locate/jas

created. This material is then eroded and deposited incaves, with the resulting stratigraphy providing samplesfor MS measurement.

It has been possible to evaluate empirically the MSmethod for sediments deposited over the last 45,000years, because there are a number of cave sites welldated by 14C. These dates are easily incorporated intothe work. We have developed a composite referencesection (CRS) for southern Europe using MS data, usingavailable 14C dates from multiple sites and the graphiccorrelation method [6], and we have demonstrated thatthis CRS correlates well with independent climate indi-cators. An interesting result of this work is that there arew17.5 cycles represented in the CRS, indicating that theaverage cycle length is w2600 years, consistent withNeo-glacial climate cyclicity summarized by Mitchell[21] and shown by O’Brien et al. [26] for the GISP2 IceCore, and Ellwood et al. [10,28] for Konispol Cave,Albania, and Caldeirao Cave, Portugal. MS correlationsamong widely separated caves throughout Europe ispossible only because there is a slow, systematic influx ofpedogenically produced iron into these caves, thusproducing the time–depth climate correlation seen.

Sites that are older than about 45,000 years providea much more difficult problem because of the poorprecision of U series, thermoluminescence, ESR andother dating methods applicable to these sediments [30].Relative dating methods must have some age constraintsbefore they can be useful, but once such constraints areapplied to the data sets they can often provide veryprecise estimates of ages in the stratigraphic sectionbeing analyzed. To constrain the MS data from cavesites older than 45,000 years, and to use these data as aclimate proxy, we correlate MS to the already estab-lished marine oxygen isotope stratigraphic record [16]and provide an example from Scladina Cave in Belgium.We chose Scladina Cave for this application because ithas yielded well excavated human fossils and culturalcomponents, and a number of thermoluminescence anduranium–thorium dates. Furthermore, unlike our resultsfrom European caves with relatively high sedimentaccumulation rates (CRS of Ellwood et al. [6]), ScladinaCave has had a relatively slow rate of sedimentaccumulation, in line with rates observed for marinesediments.

1.1. Protected environments—caves and deep rockshelters

Many archaeological sites are very complex [12] andmay be affected by disruptive physical processes, such asin open air sites that are not well-protected environ-ments [36]. From our previous work, and the work ofothers [35], we believe that caves and deep rock sheltersare ideal for MS studies of paleoclimate, becausedeposited sediments are not strongly modified by

pedogenic effects after deposition (due to their isolationwithin caves), and thus should record climate as a resultof variable rates/intensities of soil formation outside ofcaves. However, even at open air sites where pedogenesisis active, like those evaluated by Ellwood et al. [8] inTexas, and by Ellwood et al. [7] in Portugal, use-ful intrasite correlations were established betweenexcavation units using MS data.

2. Methods and results

2.1. Magnetic susceptibility (MS)

All materials become magnetic when placed within aninducing magnetic field, and MS is an indicator of thestrength of this magnetism within a sample. MS is verydifferent from remanent magnetism (polarity), theintrinsic magnetization that accounts for the magneticpolarity recorded by some materials. In MS measure-ment, essentially all mineral grains are “susceptible” tobecoming magnetized in the presence of a magnetic field.In the very low inducing magnetic fields that we use,MS is largely a function of the concentration andcomposition (mineralogy and grain morphology) of themagnetizable material in a sample. MS has the advan-tage of being quickly and easily measured on smallsamples using commercially available devices such asbalanced coil induction systems (susceptibility bridges)that can be adapted for use in the field. In addition, MSis free of many of the problems associated with polarity(reversal) magnetostratigraphy. For example, it is poss-ible to measure the MS for small, unoriented, irregularlithic fragments and highly friable material.

2.2. Field and laboratory measurement

We collect continuous sample profiles (each samplecovering approximately 2 cm of the vertical section)from excavation units at each site sampled. Each sampleis then sieved and carefully weighed, and the <1 mmsediment fraction is measured three times usingthe susceptibility bridge in the Rock Laboratory atLouisiana State University. The MS is then calculatedand interpreted. We use only the <1 mm fraction toremove material from samples, such as bone and largecarbonate fragments, that are not climate controlledconstituents and that might otherwise dominate the MS.Mossbauer spectroscopy and reflectance spectra werethen determined for selected samples from the cave thatrepresent zones of high and low MS values. Extensivereflectance work from the cave is the subject of anotherpaper currently in preparation.

2.3. New Middle Paleolithic MS results from Belgium

We have sampled several sections within ScladinaCave, and measured the MS for these sections (Fig. 1).

B.B. Ellwood et al. / Journal of Archaeological Science 31 (2004) 283–293284

MS data were evaluated and overlapping data sets werecomposited to build the composite section in Fig. 2.Archaeological levels are given on the left, and MS dataare displayed as a bar log on the right. Availableabsolute dates are also given in Fig. 2 [27,28]. MS barlogs were constructed to simplify representation of theMS results. Bar logs of this type are routinely usedin magnetostratigraphic studies and can be comparedbetween excavation units and against other climateproxies such as oxygen isotopic data sets. The bar logs inthe diagram represent MS zones of relative high and lowMS values. Hatched areas represent higher MS, inter-preted to be times of warmer temperatures, while openareas represent lower MS and cooler times. Zones in thebar logs are differentiated based on midpoints betweentrends in the raw data toward decreasing or increasingMS (further discussed by Ellwood et al. [6]).

Following construction of the bar logs, we employedthe same method to assign bar logs to isotope stagenumbers of the marine isotope curve of Imbrie et al.

([16] Fig. 3) and used ages from Martinson et al. [19].During this process we developed two bar logs, a highresolution set representing �18O sub-stages and longerterm trends representing northern hemisphere glacialstages.

Next we assigned �18O sub-stage designations to theMS bar log in Fig. 2. These assignments are constrainedbased on available dates and the time–depth graph forthe Scladina data set (Fig. 4), where available absolutedates are plotted against depth within the section. OurFourier analysis of the Scladina Cave MS data indicateda cyclicity of w20,000 years (Fig. 5), equivalent toMilankovitch precessional climate cyclicity as alsorepresented by oxygen isotope sub-stage cyclicity [16].Given this equivalency, we then assigned dates to MSbar log tops and bottoms in Fig. 2. MS bar log tops andbottoms were then plotted in Fig. 4 and the solid, best fitline drawn. These results fit well with the assignment ofthe MS bar log variations to Isotope Stages 3a through5e and suggest that the MS data set in Scladina Cave

1.0E-08 1.0E-07 1.0E-06

Scladina Cave, Belgium Profile 1

1.0E-08 1.0E-07 1.0E-06

Magnetic Susceptibility (m3/kg)

1.0E-07

weatheredbase

Fig. 1. MS data for three sections from Scladina Cave, Belgium. These sections were combined and a composite section built and presentedin Fig. 2.

B.B. Ellwood et al. / Journal of Archaeological Science 31 (2004) 283–293 285

provide a proxy for climate. This result is consistent withpollen and other climatic indicators reported for thecave [27]. Sediment accumulation rates within ScladinaCave are clearly very low, on the order of 500–600 yearsper centimeter of sediment deposited (Fig. 2), so that it isdifficult to evaluate whether short hiatuses are present inthe data set. However, we believe that the excellent fit ofthe data to a linear trend (Fig. 4) preclude hiatuses oflong duration. The Scladina age–depth correlation indi-cates an age of 90,000�7000 years for the Neanderthalhuman remains at the site, and it brackets the principalMousterian occupation level between 105,000�7000and 112,000�7000 BP. These estimates are considerablymore precise than any previously derived (see discussionbelow).

2.4. Mossbauer spectroscopy and spectral reflectance

Mossbauer spectroscopy is based on the Mossbauereffect observed by Mossbauer [22] and is a techniquethat allows semiquantitative estimates of the Fe(II) andFe(III) mineralogy for individual sediment samples. TheMossbauer spectra reported here were obtained withabsorbers which contained w100 mg/cm2 of sedimentby using a constant acceleration spectrometer, whichutilized a rhodium matrix cobalt-57 source and wascalibrated at room temperature with �-iron foil. TheMossbauer spectra, see Fig. 6a, are characteristic ofpedogenic, iron-bearing, soils containing superparamag-netic iron(III) and/or isolated iron(III) ions, the iron(III)often referred to as “soil-iron” [17]. The iron(III) is

Fig. 2. The MS of Scladina Cave sediments, connected open points. The open points correspond to samples from several overlapping sections withinthe cave that were correlated with the archaeological levels shown on the left. MS measurements have then been used to construct the MS bar logwhich in turn is compared with the marine oxygen isotope results for the last w130,000 years [16,19]. For comparison with the MS results, the �18O,as a function of time, have been converted to a bar log that represents the times of relatively warm (hatched) and relatively cool (white) climates.The �18O isotope stage number assignments are based on the dates obtained by Otte et al. [27,28]. These ages have been used to construct theage–depth correlation shown in Fig. 4. The ages for the samples from the cave, in thousands of years, and their locations within the sequence areindicated, as are the lower Mousterian level and the location of the Neanderthal skeletal remains. The assigned ages for the top and the bottom ofthe MS warm zones have been based on the assumption that the top and bottom of each level are equivalent in age to the �18O ages of the isotopesub-stages.

present in small, inhomogeneous, poorly crystalline,particles with a diameter of the order of a few nan-ometers [24]; the average blocking temperature [20] ofthe superparamagnetic iron(III) particles is between 78and 4.2 K. The hyperfine parameters exhibited by themagnetically ordered iron(III) are characteristic of analuminum-containing goethite [25,29] with some impuremaghemite and/or magnetite [24]. The presence at 295 Kof an extensive amount of iron(III) in the sediments inthe form of small superparamagnetic iron(III) particlesfacilitates the measurement of the MS because themagnetization of the particles is easily aligned withthe small applied magnetic fields used for the MSmeasurements; there is little or no magnetocrystal-line anisotropy to overcome as there would be withlarger, single domain, or pseudo-single domain, crystals[20].

To support the Mossbauer data, reflectance spectrawere acquired with a Perkin–Elmer Lambda 35 UV/VISspectrometer. Because the iron minerals, especiallymaghemite, hematite and goethite, are important con-

tributors to the color of sediment samples we use visiblereflectance spectra (mainly in the 435–700 nm) to quan-titatively characterize color. Maghemite, goethite andhematite standards, produced by Toda ManufacturingCo., Japan, were used in calibration. It has been dem-onstrated that the concentration in natural samples ofthese iron minerals can be quantified with high precisionusing reflectance spectral data [4]. Maghemite andgoethite were identified as the primary iron minerals inthe sediments measured, with concentrations beinggreater in sediments deposited during warm climaticperiods (Fig. 6b). The warm sediment reflectance spec-trum exhibits the distinctive signature associated withsignificant amounts of both maghemite, i.e., a plateaufrom 495 to 525 nm, and goethite, �-FeOOH, i.e., adiagnostic peak at 435 nm. In contrast, the cool sedi-ment exhibits a much smaller amount of maghemite andgoethite.

In summary, the reflectance and Mossbauer spectraboth show the presence of maghemite and goethite,and indicate a pedogenic formation of these minerals.

Fig. 3. Marine oxygen isotope curve from Imbrie et al. [16]. Added bar logs represent times of relative warm (hatched) versus cool (open) climates.Dates for these boundaries are taken from Martinson et al. [19]. Isotope sub-stages are also graphically presented.

The reflectance spectra indicate that the amount ofmaghemite, the primary mineral responsible for theobserved MS is variable, a variation that represents

climatically imposed variations in the production ofmaghemite that has been eroded outside and depositedinside the cave.

Fig. 4. The age–depth correlation for Scladina Cave sediments. Absolute ages are represented as squares and the connecting lines represent thestatistical limits and ranges of the ages [3,27,28] obtained from various studies with 14C on charcoal, U/Th on calcite and with thermoluminescencespectra of calcite and flint. The assigned isotope stage numbers are given along the depth axis and the circles represent the age boundaries of the MSzones determined by comparison in Fig. 2 with the �18O isotope sub-stages [16,19]. The open and solid circles represent the top and bottom of thehigh MS zones, respectively. The solid diagonal line is the Line of Correlation and is the result of a linear regression analysis of the MS values asa time–depth function. The diagonal dashed lines are parallel to the regression line and represent an envelope that includes all the MS data. Notethat the statistical ranges of the absolute ages [3,27,28] all fall within this envelope. The position of the Neanderthal and Mousterian levels, their agesand errors which have been determined herein, are also shown.

0 5 10 15 20 25 30 35 40 45 50

Scladina Cave, Belgium

~25-17 Ka cyclicity

Cycles per 1 x 105 years

Fig. 5. The frequency power spectrum obtained from a fast Fourier transform of the MS for Scladina cave composite section shown in Fig. 2. Thedistribution of the climate cyclicity in MS is centered on a 17,000- to 25,000-year cycle.

3. Discussion

3.1. Magnetic susceptibility (MS) fortime–depth–climate correlation

MS works for climate correlation in a number ofenvironments because changing climate alters the mag-netic properties of sediments in many different settings.For example, it is well established for Chinese loesssequences that climate-driven pedogenic products in

these sediments yield a measured MS variation that hasbeen tied directly to the marine isotopic record of Imbrieet al. [16]. The Chinese loess MS data have beeninterpreted to indicate that MS variations provide auseful, easily measured representation of climate (earlywork summarized by Heller and Evans [15]). Basically,in Chinese loess, high MS occurs during warmclimates when pedogenesis is high and dominates overeolian influx, while low MS values are observed whentemperatures are cold and eolian influx dominates overpedogenic effects.

In unconsolidated samples found in protectedarchaeological cave sites from Europe, we have shownthat MS also works to represent climate there becauseclimate controls the magnetic properties of the sourcesediments, again primarily as a result of variations inpedogenesis versus eolian influxes (see Mullens [23])for an early summary and Maher [18] for a more recentsummary of magnetic products produced duringpedogenesis). In most contexts where we have worked,these sediments acquire an MS signature outside cavesand are then eroded and deposited inside caves, wheresediments are protected from further significant pedo-genesis. Pedogenic processes produce abundant mag-netic minerals such as maghemite and magnetite [10,31]during periods when climate is relatively warm and wet.This pedogenic activity increases the MS signature ofsediments.

Between temperature and the availability of moisture,the effect of temperature seems to be most significant indriving pedogenesis. For example, during very coldperiods the magnitude of pedogenic activity is low, evenwhen moisture is abundant. Then, as temperature rises,so does the bacterial activity required for the redoxreactions associated with pedogenesis [5]. Obviously,very low moisture will result in lower pedogenic rates,but even in desert regions, pedogenesis can be active andimportant.

In an archaeological context, the temperature/moisture climate problem has been addressed by thework of Guiot and others [13,14]. These researchersstudied two peat bog pollen sequences in France, dem-onstrating that temperature and moisture during the last140,000 years appear to be well correlated, and that, atleast for the long-term pollen and insect climate signalsthat they have analyzed, when temperature falls, rainfalldecreases and when temperature rises, rainfall increases.In Greece as well, it has been shown that temperatureand moisture are correlated, with warm periods gener-ally wetter than cool–cold times [2]. In summary, at leastfor the European sequences that we have examined, webelieve that moisture plays a secondary role in control-ling the MS trends observed in caves and that theclimate signature is dominated by temperature effects.While other processes may dominate at other latitudesor in other climatic zones, we would argue that it is still

Mössbauer Spectra

425 475 525 575 625 675 725 775 825 875 925 975

Wavelength (nm)

Spectral Reflectance

435 nm

495 nm525 nm

680 nm

Fig. 6. (a) The iron-57 Mossbauer spectra, obtained at the indicatedtemperatures, of a Scladina Cave sediment deposited during a warmclimatic period, a sediment which has a relatively high MS. (b) Thespectral reflectance spectra of sediments deposited during warm andcool periods at Scladina Cave.

the effects of changing climate that produces theobserved MS signatures. Clearly, climate is very import-ant in the development of MS variations in many typesof sediment.

In paleoclimate studies, MS, independent of othermeasurements, has been shown to be very sensitive tosubtle changes in total iron concentration of sediments[1]. Thus, the addition to sediments of pedogenicmaghemite or magnetite increases the MS. Furthermore,the authigenic production of maghemite and magnetiteproduced during pedogenesis appears to be relativelystable chemically [23], resulting in a stable MS signaturethat is preserved in sediments. The Mossbauer spectraand spectral reflectance work suggests the presence ofmaghemite in the Scladina samples, a result which isconsistent with our related work in other Europeancaves [11]. The nanometer size particles, which aresuperparamagnetic at 295 K, with a magnetizationorientation which is fluctuating rapidly on theMossbauer time scale at 295 K and slowly at 4.2 K (Fig.6a), indicate the presence of pedogenic maghemite.

3.2. Pedogenic and eolian effects on MS: competitionbetween climate-driven rates

The dominant climate-driven processes affecting sedi-mentary systems outside caves are pedogenesis andeolian deposition. These two factors are in competitionwith each other. During glacial times in Europe, eolianprocesses blanketed the region with wind-blown,relatively non-magnetic sediments (loess). Our measure-ments of loess sediment deposited during glacial timesresults in MS values that are in the low to mid 10�8

(m3/kg) range, similar to values observed for ScladinaCave during cold periods. During interglacial times,pedogenesis dominates and generates the magneticphases discussed above. The data sets from pedo-genically altered loess (paleosol) samples from Franceshow values in the low to mid 10�7 (m3/kg) range, againsimilar to those values observed at Scladina Cave duringwarm climate phases. The MS observed in sedimentsultimately deposited in caves represents a balance inrates between these two processes.

In fact, soils do not usually ‘erode’ with time. Instead,they grow or thicken on relatively flat surfaces andmaintain thin profiles on relatively steep slopes like thatinto which Scladina Cave was formed. As a result, sheetflow erosion, or other surfaces processes such as track-ing by animals, takes off only a small amount of surfaceor near-surface sediment, some of which may then bedeposited within caves. During cool periods these sur-face sediments are dominated by eolian components,which during the Pleistocene in this part of Europeare primarily loess and therefore have a relatively lowMS. During warmer, interglacial periods, the eoliancomponents undergo relatively rapid pedogenesis and

therefore sheet flow erosion will erode a surface sedi-ment that is relatively higher in maghemite and there-fore more magnetic. Essentially, climate drives therates at which pedogenesis or eolian influxes dominate.Given the sedimentation in Scladina Cave, erosion anddeposition of only a few grains of sediment per year is allthat is necessary to produce the sedimentary sequencesand associated MS values found in the cave.

3.3. MS outside caves is recorded and preserved insidecaves

As discussed above, erosion outside caves due towind, overland sheet flow, karstic weathering and otherprocesses often moves soil as sediment into caves, whereit is deposited and in some areas preserved. Excavation,exposure, observation and dating of sediments depositedin caves makes it possible to recover these strati-graphic sequences while carefully avoiding disturbed oranomalous sediments. Empirical comparisons betweensampled sections within individual caves ([11] and otherwork) and between caves within a region show a system-atically consistent MS result that has been correlated towell dated climatic fluctuations [6]. In addition, we haveshown from MS measurement at a number of open airand cave sites, that small-scale diagenetic effects, localdisturbances, or other within-site disruptions are notsufficiently extensive to destroy the correlation power ofthe curves produced. These previous MS results showgood agreement between the timing of known warm ortemperate periods for Europe [32] and the MS data sets.The excellent linear fit between ages and depths for theMS tops and bottoms that are assigned marine isotopiccurve ages also supports a climatic origin for the MSdata. In addition, careful evaluation of the MS data inFig. 2 illustrate, in some of the Scladina MS trends, theslow onset—fast finish shown for mid Pleistocene glacia-tion reported elsewhere [34]. For example, the transitionfrom interglacial Sub-stage 5a into glacial Stage 4(within Level 2B, Fig. 2) occurs gradually (representedin six samples) while the transition from glacial Stage 4to interglacial Sub-stage 3c is rapid, represented in onlytwo samples.

3.4. Utility of MS data sets

Sampling for MS in conjunction with archaeologicalexcavations provides data sets tied directly to excavationlevels, isotopic ages and diagnostic cultural associations.Because MS variations appear to be controlled primarilyby climate, and because the effects of climate areregional, affecting large areas, MS trends identified atone site or in one excavation unit appear at manysites/units within the region. These trends may be modi-fied locally, but in general the variations in MS trendsand magnitudes produced by changing climate provide

stratigraphic sequences that can be correlated betweenexcavation units that overlap in age.

We now conclude that MS can be used as an inde-pendent methodology, alongside conventional methodssuch as sedimentology and palynology, to correlatewithin and between sites by tracing paleoclimaticchange. Because MS data sets have been shown to be aproxy for climate fluxes, they can be used as a regional(possibly global) relative dating tool that avoids manydrawbacks of other methods, such as high sensitivity todiagenetic changes, poor pollen preservation, ambigu-ous isotopic ages and the need to make measurementsonly on unaltered calcium carbonate minerals in asample.

3.5. Relative climate variability: fine-scale paleoclimate

If one looks at climate variability for the past fewhundred thousand years, it is clear that there are signifi-cant relative short-term climate changes within other-wise long-term climatic intervals. This is well illustratedin the SPECMAP oxygen isotopic curve in Fig. 3,redrawn from Imbrie et al. [16]. �18O variations, whendivided into sub-stages, represent short-term climatefluctuations occurring within longer-term glacial orinterglacial intervals (Fig. 3). For example, a sub-stage,�18O Sub-stage 3c, is warmer than Sub-stage 3b, butmuch colder than Sub-stage 5d, also considered to be‘relatively’ cold. We may think of isotope Stage 3 asbeing a period of warmer climate (interpleniglacial; e.g.Straus [32]), but it is actually the middle of a long-term�18O stage that includes isotope Stages 2, 3 and 4 andrepresents overall glacial climatic conditions. This meansthat when either �18O or MS values are low, they maystill represent a relative ‘temperate’ event, even thoughabsolute values are actually lower than observed forother sub-stages that may represent relative ‘cold’.

Clearly there are different scales of fluctuationsrepresented in climatic data sets. The MS variations thatwe have presented elsewhere [6], covering the lastw44,000 years, display even finer-scale climate varia-bility than does the �18O sub-stage record [16]. This istrue, in part, because sediment accumulation rates incaves are generally higher than rates for deep-sea sedi-ments from which the �18O record was developed. Forexample, sedimentation rates calculated from our dataindicate a range for sediment accumulation rates atarchaeological sites in caves of 1 cm /10 years to 1 cm/500 years or more. Deep-sea sediments, from which theSPECMAP �18O record was derived [16], accumulategenerally in the range of 1 cm/500 to 2000 years or more.Therefore, finer scale climate variability can be expectedto be recorded in sediments from caves because sedimentaccumulation rates are generally higher.

In Fig. 7 we present a visual summary of the corre-lations between the marine oxygen isotope curve of

Imbrie et al. [16] and the Scladina Cave data set. A clearcorrelation exists between these data sets, indicating thatMS data of this type provide an excellent correlationto the marine isotope climate record and thereforeto climate changes. This works well in part becausethe Scladina Cave sediment accumulation rate is slowand more closely approximates deep-ocean sedimentaccumulation rates. Therefore, the Scladina MS signal ismore easily compared to the marine isotope record thanis the MS signal found in most other caves, making thesignal easier to interpret, and ideal for comparison toisotope records.

3.6. Relative dating using MS data from Scladina Cave

We can now illustrate how the variation in themagnetic susceptibility both is relevant to paleoanthro-pological issues and provides more precise ages thanpreviously available for the Neanderthal fossil remainsand cultural residues found in Scladina Cave. Fig. 4represents the time–depth relationships observed withinScladina cave and is the basis for the relative datesdetermined here. The assigned isotope stage numbers aregiven along the depth axis and the circles represent theage boundaries of the MS zones determined by compari-son in Fig. 2 with the �18O isotope sub-stage ages [16,19].The open and solid circles represent the top and bottomof the high MS zones, respectively. The solid diagonal

Fig. 7. Comparison of warm (hatched bar log segments) versus cold(open bar log segments) climatic trends for marine oxygen isotopicstages [16] and Scladina Cave. MS bar logs are hatched to the right;isotope bar logs to the left.

line is the line of correlation (LOC), and is the result ofa linear regression analysis of the MS values as atime–depth function. Relative dates can be determinedgraphically by projecting the depth position of theNeanderthal remains and the Mousterian occupationlevels through the LOC and into the age axis (Fig. 4).Ages can also be calculated from the time–depth linearregression analysis which produced a correlation coef-ficient (R2=0.977) indicating that the correlation isexcellent. The diagonal dashed lines are parallel to theregression line and represent an envelope that includesall the MS data. The partial skeletal remains of ajuvenile Neanderthal discovered in upper level 4A (Fig.2) in the cave [3,28,33] have been directly dated bygamma spectrometry to be 127,000+46,000/�32,000years old, i.e., with an age range of 78,000 years.Thermoluminescence dates have also been derived fromcalcite in stalagmitic deposits underlying (CC14) andoverlying (CC4) the human remains (Fig. 2). The CC14deposit has been found to be 110,000�13,000 years oldand the overlying CC4 deposit has been found to be100,000�12,000 years old, results which yield an agerange of 88,000 to 123,000 years for the human skeletalremains [3]. The age estimate derived herein from theScladina’s magnetic susceptibility time–depth corre-lation for the Neanderthal fossil remains is90,000�7000 years (Fig. 4). [Errors are based on pro-jecting the margins of the age envelope (dashed lines inFig. 4) to the age axis.] This age agrees, within one-sigma, with the ages reported earlier [3,28,33], but issubstantially more precise.

Similarly, the earlier Mousterian occupation ofScladina Cave has the range of its ages reduced dramati-cally (Fig. 4). Using the MS, we estimate that Scladina’soccupation Level 5 (Fig. 2) has an age ranging from105,000�7000 to 112,000�7000 years. This rangeis consistent with the thermoluminescence age of130,000�20,000 years obtained [28] for burned flintfound within Level 5 and provides an age range for theentire level rather than just a single age.

4. Conclusions

It is now clear that the MS data from caves canprovide a proxy that can be correlated to marine oxygenisotope stages and thus used as a relative dating tech-nique. However, useful chronology using the oxygenisotope data set is quite coarse. We believe that ulti-mately we will be able to develop a finer-scale dataset using the MS data from multiple cave sites withoverlapping ages, including caves where sedimentaccumulation rates are higher than those in ScladinaCave. When tied to the oxygen isotope record, a com-posite reference section from such sites should allowhigh correlations back to at least 300,000 years BP and

provide an excellent relative dating tool that can be usedto constrain other dating methods.

Acknowledgements

Support for the MS research was provided by NSFgrant BCS9903172 to Ellwood and Harrold. Grandjeanthanks the Belgian “Fonds National de la RechercheScientifique” for grant number 9.4565.95.

References

[1] S.K. Banerjee, Sediment reveals early Holocene climate change inChina. EOS, Transactions, American Geophysical Union 77(1996) 3 and 5.

[2] S. Bottema, The prehistoric environment of Greece: A review ofthe palynological record, in: P.N. Kardulias (Ed.), Beyond theSite: Regional Studies in the Aegean Area, University Press ofAmerica, Lanham, NY, 1994, pp. 45–68.

[3] D. Bonjean, L’Archeologie, in: M. Otte, M. Patou-Mathis, D.Bonjean (Eds.), Recherches aux Grottes de Sclayn 2, ERAUL 79,Liege, 1998, pp. 45–57.

[4] B.C. Deaton, W.L. Balsam, Visible spectroscopy—a rapidmethod for determining hematite and goethite concentration ingeological materials, J. Sedimentary Petrology 61 (1991) 628–632.

[5] B.B. Ellwood, B. Burkart, Test of hydrocarbon-induced magneticpatterns in soils: the sanitary landfill as laboratory, in: D.Schumacher, M.A. Abrams (Eds.), Hydrocarbon Migrationand its Near-Surface Expression: AAPG Memoir 66. Tulsa,Oklahoma, 1996, pp. 91–98.

[6] B.B. Ellwood, F.B. Harrold, S.L. Benoist, L.G. Straus, M.Gonzalez-Morales, K. Petruso, N.F. Bicho, Z. Zilhao, N. Soler,Paleoclimate and intersite correlations from Late Pleistocene/Holocene cave sites: results from Southern Europe,Geoarchaeology 16 (2001) 433–463.

[7] B.B. Ellwood, F.B. Harrold, A.E. Marks, Site identification andcorrelation using geoarchaeological methods at the Cabeco doPorto Marinho (CPM) locality, Rio Maior, Portugal, Journal ofArchaeological Science 21 (1994) 779–784.

[8] B.B. Ellwood, D.E. Peter, W. Balsam, J. Schieber, Magnetic andgeochemical variations as indicators of paleoclimate and archaeo-logical site evolution: examples from 41TR68, Fort Worth, Texas,Journal of Archaeological Science 22 (1995) 409–415.

[9] B.B. Ellwood, K.M. Petruso, F.B. Harrold, The utility of mag-netic susceptibility for detecting paleoclimatic trends and as astratigraphic correlation tool: an example from Konispol cavesediments, SW Albania, Journal of Field Archaeology 23 (1996)263–271.

[10] B.B. Ellwood, K.M. Petruso, F.B. Harrold, J. Schuldenrein,High-resolution paleoclimatic trends for the Holocene identifiedusing magnetic susceptibility data from archaeological exca-vations in caves, Journal of Archaeological Sciences 24 (1997)569–573.

[11] B.B. Ellwood, J. Zilhao, F.B. Harrold, W. Balsam, B. Burkart,G.J. Long, A. Debenath, A. Bouzouggar, Identification of the lastglacial maximum in the Upper Paleolithic of Portugal usingmagnetic susceptibility measurements of Caldeirao Cavesediments, Geoarchaeology 13 (1998) 55–71.

[12] W.R. Farrand, Discontinuity in the startigraphic record: snap-shots from Franchthi Cave, in: P. Goldberg, D.T. Nas, M.D.Petraglia (Eds.), Formation Processes in Archaeological Context:

Monographs in World Archaeology, No. 17, Prehistory Press,Madison, Wisconsin, 1993, pp. 85–96.

[13] J. Guiot, J.L. de Beaulieu, R. Cheddadi, F. David, P. Ponel, M.Reille, The climate in Western Europe during the lastglacial/interglacial cycle derived from pollen and insect remains,Palaeography, Palaeoclimatology, Palaeoecology 103 (1993)73–93.

[14] J. Guiot, A. Pons, J.L. de Beaulieu, M. Reille, A 140,000-yearcontinental climate reconstruction from two European pollenrecords, Nature 23 (1989) 309–313.

[15] F. Heller, M.E. Evans, Loess Magnetism, Reviews of Geophysics33 (1995) 211–240.

[16] J. Imbrie, J.D. Hays, D.G. Martinson, A. McIntyre, A.C. Mix,J.J. Morley, N.G. Pisias, W.L. Prell, N.J. Shackleton, The orbitaltheory of Pleistocene climate: support from a revised chronologyof the marine delta 18O record, in: A.L. Berger, J. Imbrie, J. Hays,G. Kukla, B. Saltzman (Eds.), Milankovitch and Climate, Part I,Reidel, Boston, 1984, pp. 269–305.

[17] W.L. Lindsay, Solubility and redox equilibria of iron compoundsin soils, in: J.W. Stucki, B.A. Goodman, U. Schwertmann (Eds.),Iron in Soils and Clay Minerals, D. Reidel Publishing Co,Dordrecht, 1988, pp. 31–62.

[18] B.A. Maher, Magnetic properties of modern soils and Quaternaryloessic paleosols: paleoclimatic implications, Palaeogeography,Palaeoclimatology, Palaeoecology 137 (1998) 25–54.

[19] D.G. Martinson, N.G. Pisias, J.D. Hays, T.C. Imbrie, N.J.Shackleton, Age dating and the orbital theory of the iceages: Development of a high-resolution 0 to 300,000-yearchronostratigraphy, Quaternary Research 27 (1987) 1–29.

[20] S. Mfrup, J.A. Dumesic, H. Topsfe, Magnetic microcrystals, in:R.L. Cohen (Ed.), Applications of Mossbauer Spectroscopy II,Academic Press, New York, 1980, pp. 1–53.

[21] J.M. Mitchell Jr, An overview of climatic variability and its causalmechanisms, Quaternary Research 6 (1976) 481–493.

[22] R. Mossbauer, Kernresonanzabsorption von gammastrahlung inIr191, Naturwissenschaften 45 (1958) 538–539.

[23] C.E. Mullens, Magnetic susceptibility of the soil and its signifi-cance in soil science—a review, Journal of Soil Science 28 (1977)223–246.

[24] E. Murad, J.H. Johnston, Iron oxides and oxyhydroxides, in: G.J.Long (Ed.), Mossbauer Spectroscopy Applied to InorganicChemistry 2, Plenum Press, New York, 1987, pp. 507–582.

[25] E. Murad, U. Schwertmann, The influence of aluminum substi-tution and crystallinity on the Mossbauer-spectra of goethite,Clay Minerals 18 (1983) 301–312.

[26] S.R. O’Brien, P.A. Mayewski, L.D. Meeker, D.A. Meese, M.S.Twickler, S.I. Whitlow, Complexity of Holocene climate asreconstructed from a Greenland ice core, Science 270 (1995)1962–1964.

[27] M. Otte, M. Patou-Mathis, D. Bonjean (Eds.). Recherches auxgrottes de Sclayn, Volume 2, L’Archeologie. ERAUL, Liege,1998, pp. 79.

[28] M. Otte, M. Toussaint, D. Bonjean, Decouverte de resteshumains immatures dans les niveaux mousteriens de la grotteScladina a Andenne (Belgique), Bull. et Mem. de la Societed’Anthropologie de Paris 5 (1993) 327–332.

[29] T.G. Quinn, G.J. Long, C.G. Benson, S. Mann, R.J.P. Williams,Influence of silicon and phosphorus on structural and magneticproperties of synthetic goethite and related oxides, Clay ClayMinerals 36 (1988) 165–175.

[30] W.J. Rink, H.P. Schwarcz, H.K. Lee, V. Cabrera Valdes, F.Bernaldo de Quiros, M. Hoyos, ESR dating of Mousterian levelsat El Castillo Cave, Cantabria, Spain, J Archaeological Science 23(1997) 593–600.

[31] H. Stanjek, J.W.E. Fassbinder, H. Vali, H. Wagele, W. Graf,Evidence of biogenic greigite (ferrimagnetic Fe3S4) in soil,European Journal of Soil Science 45 (1994) 97–103.

[32] L.G. Straus, The Upper Paleolithic of Europe: an overview,Evolutionary Anthropology 4 (1995) 4–16.

[33] M. Toussaint, M. Otte, D. Bonjean, H. Bocherens, C. Falgueres,Y. Yokoyama, Les restes humains neandertaliens immatures de lacouche 4A de la grotte Scladina (Andenne, Belgique), Academiedes Sciences de Paris 326 (1998) 737–742.

[34] E. Tziperman, H. Gildor, On the mid-Pleistocene transition to100-kyr glacial cycles and the asymmetry between glaciation anddeglaciation times, Paleoceanography 18 (1) (2003) 1001,doi:10.1029/2001PA000627.

[35] J.C. Woodward, G.N. Bailey, Sediment sources and terminalPleistocene geomorphological processes recorded in rocksheltersequences in North-west Greece, in: I.D.L. Foster (Ed.), Tracersin Geomorphology, John Wiley & Sons, Ltd, London, 2000,pp. 521–550.

[36] J.C. Woodward, J. Lewin, M.G. Macklin, Alluvial sedimentsources in a glaciated catchment: the Voidomatis Basin, north-west Greece, Earth Surface Processes and Landforms 17 (1992)205–216.

Ellwood, B. et al. (2004) Magnetic susceptibility applied as an age-depth-climate relative dating...

Documents

Transcript of Ellwood, B. et al. (2004) Magnetic susceptibility applied as an age-depth-climate relative dating...

Microclimatic characterization of a karstic cave: human impact on microenvironmental parameters of a prehistoric rock art cave (Candamo Cave, northern Spain)

CAVE CLIMATE - ZRC SAZU

Dylan the Papillon from Belgium wins Crufts - Collielife

Master List Argentina Australia Austria Belgium Brazil Canada

Mechelen, Belgium Slaughterhouse Industrial drainage system

Bobbins of Belgium

4 rescued from Thai cave; 9 remain

Panama Papers: Belgium

User's Guide - Toshiba Tec Belgium Imaging Systems

Stock market development and economic growth in Belgium

Printed in Belgium

Genetic analysis of cave bear specimens from Niedźwiedzia Cave, Sudetes, Poland

Extremely acidic, pendulous cave wall biofilms from the Frasassi cave system, Italy

Industry - Belgium - Loan 0014 - P037358 - Public Documents

Essai sidérurgie (Belgium)

Additional cranial remains from Vindija cave, Croatia

Hindu Forum Belgium asbl

Hospital supplements in Belgium: Price variation and regulation

Industrial relations in Belgium - Break Back Project

Belgium - Loan 0014 - P037358 - Bonds - Volume 1 - Public ...