Dating Saharan dust deposits on Lanzarote (Canary Islands) by luminescence dating techniques and their implication for palaeoclimate reconstruction of NW Africa.

This a icle is published in: Geochemis y, Geophysics, and Geosys ems (2008) Volume 9, Numbe 2, 14 Feb ua y 2008, Q02Q07 doi:10.1029/2007GC001658 ISSN: 1525-2027 Da ing Saha an dus deposi s on Lanza o e (Cana y Islands) by luminescence da ing echniques and hei implica ion o palaeoclima e econs uc ion o NW A ica H. on Suchodole z*, M. Fuchs, and L. Zölle Depa men o Geomo phology, Uni e si y o Bay eu h, Uni e si ä ss asse 30, D-95440 Bay eu h, Ge many (*hans. onsuchodole z@uni-bay eu h.de) La a low dammed alleys (Vegas) on Lanza o e (Cana y Islands) ep esen unique sedimen aps, illed wi h au och honous olcanic ma e ial and alloch honous Saha an dus . These sedimen s and he in e cala ed palaeosoil sedimen s documen pas en i onmen al change o he las glacial-in e glacial cycles, bo h on Lanza o e and in NW A ica. A eliable ch onology mus be es ablished o use hese sedimen a chi es o palaeoclima e econs uc ions. Owing o he lack o o ganic ma e ial and he limi ing ime ange o he 14C- da ing me hod, luminescence da ing is he mos p omising me hod o hese sedimen s. Howe e , he lu io-eolian cha ac e o hese sedimen s is a majo p oblem o luminescence da ing, because hese sedimen s a e p one o insu icien ese ing o he pa en luminescence signal (bleaching) p io o sedimen a ion. To check o he bes age es ima es, we compa e he bleaching beha io o (1) di e en g ain sizes (coa se- e sus ine-g ain qua z OSL) and (2) di e en mine als ( ine-g ain eldspa IRSL e sus ine-g ain qua z OSL). The esul s show ha owing o i s bleaching cha ac e is ics, qua z is he p e e able mine al o luminescence da ing. On he basis o he ine- and coa se-g ain qua z OSL age es ima es, a ch onos a ig aphy up o 100 ka could be es ablished. Beyond his age limi o OSL qua z, he ch onos a ig aphy could be ex ended up o 180 ka by co ela ing he ega sedimen s wi h da ed ma ine sedimen a chi es. Keywo ds: luminescence da ing; Saha an dus ; Cana y Islands; insu icien bleaching; land/sea co ela ion; human occupa ion. 1. In oduc ion La a low dammed alleys (Vegas) on Lanza o e (Cana y Islands) ep esen sedimen aps, illed wi h au och honous olcanic ma e ial and alloch honous Saha an dus . These sedimen s a e ega ded as unique e es ial a chi es o he Qua e na y paleoclima e econs uc ion o no hwes A ica (H. on Suchodole z e al., Geomo phological in es iga ions o sedimen aps on Lanza o e (Cana y Islands) as a key o he in e p e a ion o a palaeoclima e a chi e o NWA ica, submi ed o Qua e na y In e na ional, 2008) (he eina e e e ed o as on Suchodole z e al., submi ed manusc ip , 2008a). The e ha e been many a emp s o econs uc he paleoclima e o his egion. Ma ine eco ds ha may ex end back o he Te ia y [e.g., Dupon , 1993; B unne and Maniscalco, 1998; Mo eno e al., 2001] ha e he ad an age ha hey p o ide con inuous eco ds wi h gene ally well-p ese ed p oxies. In con as , e es ial a chi es a e commonly discon inuous and ep esen only sho pe iods, which makes hei paleoclima e in e p e a ion di icul [e.g., Gasse e al., 1987; Cheddadi e al., 1998; Lancas e e al., 2002]. Howe e , despi e he limi a ion o in e p e a ion and hia uses, e es ial a chi es a e essen ial o in es iga ing paleoclima e on land, especially he egional pa e ns and he land-sea in e ac ion. On he Eas e n Cana y Islands, a ious e es ial a chi es ha e been used o econs uc paleoclima e, o example, dune sequences and hei in e cala ed paleosols [e.g., Rognon e al., 1989; C iado e al., 2004; O iz e al., 2006], calc e es [e.g., Alonso-Za za and Sil a, 2002], ca e sedimen s [e.g., Coello e al., 1999] and ma ine e aces [e.g., Meco e al., 2002]. Howe e , hese a chi es show hia uses and ep esen limi ed pe iods o he Qua e na y. Ou s udies om Lanza o e, whe e hick Saha an dus had accumula ed in olcanic alleys, e eal a gene ally con inuous eco d, eaching om he Holocene o he Middle Pleis ocene (Zo¨lle e al. [2003] and p esen s udy), which makes hese sedimen s an ou s anding e es ial a chi e o a paleoen i onmen al econs uc ion o Lanza o e and NW A ica. Fo paleoclima ic in e p e a ion o hese a chi es a sound ch onos a ig aphy is o c ucial impo ance. P e ious s udies on he Eas e n Cana y Islands used he 14C-da ing me hod [e.g., Pe i -Mai e e al., 1986] as well as U-Th ages [e.g., Hillai e-Ma cel e al., 1995], bu he esul s o bo h me hods su e om he ac ha he ages we e de e mined on land snail shells which may ep esen open sys ems. The e o e hese da es mus be ega ded as p o isional [Edwa ds and Meco, 2000]. The second sho all o bo h me hods is ha hey do no di ec ly da e he sedimen a ion p ocess, a d awback ha does no apply o luminescence da ing. Spo adic s udies om he Eas e n Cana y Islands using luminescence da ing we e p esen ed by Pomel e al. [1985] and Bouab and Lamo he [1997]. Since ou ini ial da ing esul s using in a ed s imula ed luminescence (IRSL) we e p omising [Zölle e al., 2003], and in mos pa s o he in es iga ed p o iles he e a e nei he o ganic ma e no land snail shells, we con inued o buil up ou ch onos a ig aphy using luminescence da ing. Luminescence da ing is based on he ac ha qua z and eldspa g ains accumula e ene gy in hei c ys al la ice a e bu ial, ha inc eases in esponse o ionizing adia ion o which he g ains a e exposed. This signal is discha ged when he g ains a e exposed o sunligh . Measu emen o his signal esul s in he equi alen dose (De). To de e mine he ime ha elapsed since he las bleaching, he De is di ided by he ionizing adia ion (dose a e, . D) o he da ed sedimen [Singh i and K be schek, 1996; Ai ken, 1998; Win le, 1998]. The ad an age o luminescence da ing is ha i di ec ly da es he las exposu e o sunligh , bu good op ical bleaching p io o bu ial is o majo impo ance. Pu e eolian sedimen s such as loess show e y good bleaching p io o sedimen a ion, and ha e been da ed success ully o many yea s [e.g., Be ge e al., 1992; Rousseau e al., 1998; Zölle e al., 2004]. I is only ecen ly ha he de elopmen o coa se-g ain da ing echniques using op ically s imula ed luminescence (OSL) acili a ed he da ing o poo ly bleached ma e ials, o example, lu ial, collu ial o playa sedimen s [e.g., Olley e al., 1998; Fuchs and Wagne , 2003; Bubenze and Hilge s, 2003]. Being awa e o he la gely collu ial cha ac e o ou sequences ( on Suchodole z e al., submi ed manusc ip , 2008), we ha e compa ed h ee di e en luminescence da ing echniques (IRSL o ine-g ained eldspa s and OSL o ine and coa se- g ained qua z) wi h di e en bleaching p ope ies o build up a eliable ch onos a ig aphy o ou a chi es. This me hodological compa ison should help o e alua e he eliabili y o he ‘‘p oblema ic’’ IRSL da es in he olde pa s o he p o iles, whe e hey a e he only nume ical da ing me hod a ailable. 2. S udy A ea Lanza o e (28°50’N-29°13’N, 13°25’W-13°52’W) belongs o he Cana y Islands/Spain and is si ua ed ~130 km wes o he sou he n Mo occan coas (Figu e 1). I is a olcanic island, composed o basic o ul abasic olcanic ocks. Volcanism s a ed a ound 15.5 Ma ago and has pe sis ed o ecen his o ical imes [e.g., Ca acedo e al., 1998]. Owing o i s limi ed al i ude (maximum 670 m amsl), Lanza o e does no ecei e p ecipi a ion om ising ade winds. I ecei es 100 mm (a lowe ele a ion) o 250 mm (a highe ele a ion) p ecipi a ion om bo eal win e cyclones. Mean annual empe a u e is 19.9°C [Jahn, 1988]. Lanza o e is cha ac e ized by a e y spa se, sh ubby and dispe se ege a ion domina ed by xe ophy ic and halophy ic species mani es ing a semi dese cha ac e . The island is si ua ed a he no he n inge o he Saha an dus plume o e he No h A lan ic Ocean. Dus is b ough o he island du ing wo di e en synop ic si ua ions: Du ing he i s si ua ion, dus is en ained by so called ‘‘Calima’’ winds: low-le el con inen al A ican T ade winds (Ha ma an) de lec ed owa d he wes by A lan ic cyclones especially du ing bo eal win e [C iado and Do a, 2003]. The second si ua ion occu s exclusi ely du ing bo eal summe , when dus is ad ec ed by he no he n b anch o he high-al i ude Saha an Ai Laye . Subsequen ly, he ma e ial sinks in o he lowe a mosphe e no h o he Cana y Islands and is inally anspo ed owa d he islands ia he No heas T ade wind [Koopmann, 1981; Bozzano e al., 2002]. Dus can be deposi ed he e du ing bo h d y and we condi ions [C iado and Do a, 2003; Menéndez e al., 2007]. 3. S udied Si es On Lanza o e, paleo- alleys o Miocence o Pliocene age we e dammed du ing he Ea ly and Middle Pleis ocene by la a lows and py oclas ic ma e ial. Locally hese alleys a e called egas. In ou s udies we used he ou c ops si ua ed in loam pi s exca a ed du ing he pas decades in he egas o Feme´s, Gua iza and Teguise (Valle de San José) (Figu e 1). All s udied p o iles we e chosen in a dis al posi ion om geomo phologically ac i e slopes. Hence we chose p o ile Gua iza III ins ead o Gua iza I and II [Zölle e al., 2003] o u he in es iga ions. Two egas (Gua iza and Teguise) a e si ua ed on he inges o he Fama a Massi in he no h o he island a a dis ance o ~6 km om each o he . Damming o hese alleys was ne e o al, so hia ae can be expec ed. The alley o Femeés is loca ed in he Los Ajaches Massi in he sou h o Lanza o e abou 30 km om he no he n si es, and damming was comple e un il oday [Zölle e al., 2006]. The s a ig aphies can be seen in Figu e 2. The sedimen s a e composed o in e bedded in si u and ewo ked collu ial ma e ial o igina ing om alloch honous Saha an dus and au och honous olcanic p oduc s. Pa s o hese sedimen s we e subjec o pedogenesis and a e consequen ly cha ac e ized by eddish colo and a e isol ex u e, whe eas o he laye s a e only sligh ly wea he ed and show a yellowish colo and a sil y g anulome y. Some beds we e o e p in ed by ca bona ic wa e s and hus con ain ca bona e nodules, calci ied oo channels, o a e ully de eloped as calc e e ho izons. Many laye s we e o e p in ed by wa e con aining Fe and Mn. Consequen ly, Fe and Mn s ains and conc e ions occu , he la ges in he ega o Teguise. In some ho izons, calci ied nes s o an hopho a bees a e common. Whe eas no coa se collu ial ma e ial is ound in he lowe pa s o he sequences, he uppe pa s consis o an h opogenic collu ium con aining pebbles and pa ly o icap id bones. In Femés, coa se olcanic allou is obse ed be ween ~220 and 400 cm. The s a ig aphy o his p o ile is sligh ly e ised compa ed o ha published by Zölle e al. [2003]. Consequen ly, in he case o di e ing dep hs bo h a e indica ed in Table 4 in sec ion 4.3 and Table 5 in sec ion 5.2. The p ope ies o he sequences a e lis ed in Table 1. These sedimen a y uni s eco d he landscape and paleoclima ic his o y om he Lowe Pleis ocene o he Holocene. The geomo phic sys em and i s sedimen a ion p ocesses a e desc ibed in de ail by on Suchodole z e al. (submi ed manusc ip , 2008a). 4. Me hods Fo luminescence da ing sampling ook place du ing he nigh , a e emo ing he ou e 30 cm o he p o ile o a oid any con amina ion wi h ligh exposed ma e ial. Sampling and sample p epa a ion a he Bay eu h luminescence labo a o y (Uni e si y o Bay eu h/Ge many) was done unde subdued ed ligh (wa eleng h 640 ± 20 nm). 4.1. Sample P epa a ion 4.1.1. Coa se-G ain Qua z Samples A e sie ing, he ac ion 63-200 mm was ea ed wi h HCl and H2O2 o des oy ca bona e and o ganic ma e , and was held in an ul asonic ba h o 30 min o des oy agg ega es. Hea y mine als (densi y > 2.75 g/cm3) and eldspa s (densi y < 2.62 g/cm3) we e sepa a ed in a li hium he e opoly ungs a e solu ion (LST). The qua z ma e ial was subsequen ly e ched in 40% HF o 45 min in o de o emo e any emaining eldspa as well as he alpha i adia ed ou e laye o he qua z g ains. The esul an ma e ial was ixed on aluminum cups (diame e 12 mm) using silicone oil. The numbe o g ains pe cup was be ween 200 and 600, ep esen ing small aliquo s acco ding o Fuchs and Wagne [2003]. 4.1.2. Fine-G ain Qua z Samples To emo e ca bona es and o ganic ca bon, he ac ion <63 mm was ea ed wi h HCl and H2O2. Subsequen addi ion o 0.05 M sodium py ophospha e and ea men in an ul asonic ba h o 30 min dispe sed clays and des oyed g ain agg ega es. Ex ac ion o he 4–11 mm ac ion was done in A e be g-se ling ubes up o 50 imes. The sepa a ed polymine al ac ion 4–11 mm was e ched o 4-5 days in p e ea ed 34% hexa luo osilicic acid o emo e any emaining eldspa s ( o me hodology, see Fuchs e al. [2005]). A e a sho IRSL es on wo aliquo s ha included adia ion (50 Gy) and IRSL measu emen o iden i y any possible emaining eldspa con amina ion, he ma e ial was pipe ed on o 9.6-mm aluminum discs. 4.1.3. Fine-G ain Polymine al Samples The polymine al ine sil ac ion was ex ac ed as desc ibed abo e o ine-g ain qua z samples and was di ec ly pipe ed on o aluminum discs (diame e 9.6 mm). Each disc had abou 1.6 mg o sil . 4.2. Measu emen s Fo measu emen s we used wo Risø-Reade s TL/OSL-DA-15 combined wi h a Tho n-EMI 9235QA pho omul iplie [Bø e -Jensen e al., 1999]. Sou ces used o adia ion a e lis ed in Table 2. The so wa e Analys 3.07b was used o analysis o he da a. 4.2.1. Fine- and Coa se-G ain Qua z OSL Measu emen pa ame e s o ine- and coa seg ain qua z samples a e lis ed in Table 3. Equi alen doses (De) we e de e mined using he single aliquo egene a i e dose p o ocol (SAR) [see Mu ay and Win le, 2000]. A sa u a ing exponen ial g ow h cu e was cons uc ed, using six egene a ion cycles a e one measu emen o he na u al OSL: ou measu emen s o egene a ed doses, one epea ed measu emen o he i s egene a ed dose o de e mine he ecycling a io and one 0-dose egene a ion cycle. The De was de e mined by sub ac ing he backg ound om he used OSL in eg al. A check o possible eldspa con amina ion was done by s imula ing he a i icially i adia ed samples wi h in a ed and de ec ing in he blue ange (390-450 nm). Depending on he a ailabili y o he p epa ed mine al ac ion, we ied o measu e a minimum o 30 aliquo s om he coa seg ained ac ion, and 6–7 aliquo s om he ineg ained samples. In indi idual cases, he numbe o measu ed aliquo s was below 30 o coa se-g ained samples. To de e mine a- alues o he ine-g ain samples, a-i adia ion was used. 4.2.2. Polymine al IRSL Measu emen pa ame e s o polymine al IRSL samples a e lis ed in Table 3. Fo De de e mina ion, he mul iple aliquo addi i e dose p o ocol (MAAD) ollowing Lang e al. [1996] was ou inely used. A e measu emen o h ee na u al and h ee a i icially i adia ed discs ( es dose o 50 Gy) o ob ain a ough app oxima ion o he equi alen dose, six dose g oups wi h i e discs each we e i adia ed and s o ed o 1 mon h a oom empe a u e. Subsequen ly, hey we e measu ed oge he wi h nine na u al discs o cons uc he addi i e g ow h cu e. The a- alue o some ep esen a i e samples was de e mined using an a-g ow h cu e wi h h ee dose g oups o h ee aliquo s each. Owing o limi ed labo a o y capaci y, we did no conduc es s o anomalous ading a e Auclai e al. [2003], bu used ins ead a simple p o ocol ollowing Lang e al. [1996]. We i adia ed i e discs wi h he highes i adia ion dose, s o ed hem o 3 mon hs a oom empe a u e be o e measu emen and compa ed hem o he measu emen s done a e 1 mon h o s o age. 4.3. Dose Ra e De e mina ion The dose a e ( . D) is he ene gy ha accumula es in a mine al and hus c ea es he luminescence signal. The dose a e is composed o he na u al adioac i i y (α-, β-, γ- adia ion) and he cosmic adia ion a ec ing he sample. Since he ou e im o coa se g ains a e e ched away using HF, α- adia ion in luences only he ine-g ain ma e ial. Thus, o ine g ains, he a- alue gi ing he e ec i i y o α- compa ed o β- adia ion mus be de e mined. We de e mined na u al adioac i i y by measu ing he concen a ion o he adioac i e elemen s U, Th and K using d y, g ound ma e ial. U and Th con en s we e calcula ed using hick sou ce α-coun ing (42 mm) a he Uni e si y o Bay eu h. Po assium concen a ions we e measu ed a he Bay eu h Cen e o Ecology and En i onmen al Resea ch (BayCEER), Bay eu h/Ge many using induc i ely coupled plasma sou ce mass spec ome y (ICPMS), and a he Uni e si y o Ma bu g/Ge many using an a omic adso p ion spec ome e (AAS). Dose a es we e calcula ed using he con e sion ac o s gi en by Adamiec and Ai ken [1998]. Cosmic dose a es we e e alua ed acco ding o P esco and Hu on [1994]. All dose a es a e lis ed in Table 4. 4.4. Wa e Con en Fo e e y sample he wa e con en was measu ed g a ime ically. Since he ou c ops ha e been open o many yea s and he sedimen s ha e been desicca ed, measu ed alues a e ob iously unde es ima ions compa ed o he paleo alues as al eady s a ed by Zölle e al. [2003]. Thus, using he g ain size dis ibu ion o a sample and he esul ing middle po e olume, we es ima ed po en ial minimal and maximal wa e con en s o a sample as desc ibed by Fuchs [2001]. Fo age calcula ion, an a e age alue was aken. The e o is assumed o be gene ally 0.1. Measu ed and co ec ed wa e con en s a e gi en in Table 4. 4.5. Age Calcula ion on Suchodole z e al. (submi ed manusc ip , 2008a) demons a e ha mos o he sedimen s illing he egas a e ewo ked and deposi ed by collu ial and lu ial p ocesses. These p ocesses a e p oblema ic o luminescence da ing because hey a e occu ing a he apidly and o en he ine ma e ial is anspo ed in he o m o agg ega es. Hence bleaching o hese sedimen s du ing collu ial anspo was p esumably no always comple e, hus esul ing in o e es ima ed De alues as de ec ed in o he s udies [e.g., Po a e al., 2001; Fuchs and Wagne , 2003]. Fo ine g ains, insu icien bleaching is no easily de ec able since e e y disc con ains housands o g ains gi ing a luminescence signal so ha De di e ences be ween he discs a e a e aged. Ins ead, o coa se g ains single aliquo and single g ain me hods o e he possibili y o de ec and co ec insu icien bleaching by looking a hei De sca e and he ype o De dis ibu ion (Gaussian, le -skewed, igh -skewed) [e.g., Olley e al., 1998; Leppe e al., 2000; Bailey and A nold, 2006; Fuchs and Wagne , 2003]. Since mos o ou De dis ibu ions a e posi i ely skewed which may indica e insu icien bleaching, we had o ind a way o ob ain he De co esponding o he las ewo king o he sedimen s. Di e en echniques we e de eloped on he basis o he assump ion ha he las bleaching e en is equi alen o he le maximum o a igh skewed De dis ibu ion. Howe e , some o hese echniques a e no applicable o ou De dis ibu ions o di e en easons: he app oach o Olley e al. [1998] aking he lowes 5% o he De dis ibu ion is no applicable owing o a ela i ely b oad ising limb o he De dis ibu ion esul ing in g ea ly unde es ima ed De. Acco dingly, his me hod is gene ally judged o be use ul only in case o young, poo ly bleached lu ial samples [Bailey and A nold, 2006]. The leading edge me hod de eloped by Leppe e al. [2000] was inapplicable since he quan i y o measu ed aliquo s was no su icien o ge a good Gaussian i h ough he ising limb o ou dis ibu ions [c . Fuchs e al., 2007]. The me hod o Fuchs and Lang [2001], using an empi ically de i ed h eshold o iden i y he well bleached p opo ion o an insu icien ly bleached sample is also no applicable in ou case. This is due o he ac ha o many samples he h eshold was al eady exceeded using he i s wo De om he so ed low o high De alue da a se . Thus we decided o use he app oach o Juyal e al. [2006], modi ied by Fuchs e al. [2007]. Basically, his is a simpli ied minimum age model o Galb ai h e al. [1999]. De = Demin + 2 * σmax + 4% whe e Demin is he minimal equi alen dose a e sub ac ion o he lowe 5% quan il (see below), σmax is he maximal e o occu ing in he da a om he lowe end o he i s maximum o he De his og am and 4% a e added as gene al ins umen a ion e o o he used Risø eade . A common p oblem is he mixing o younge ma e ial d opped h ough pedogenic c acks o oo channels as desc ibed by Ba eman e al. [2003]. We ha e obse ed his p ocess in he ega o Gua iza. This phenomenon would cause an unde es ima ion o he De and is isible as indi idual ou lie s no linked o he o m o he De dis ibu ion owa d lowe alues in many his og ams (Figu e 3). To neu alize his equen ly occu ing e ec , we decided o sub ac he lowe 5%quan il o he so ed De dis ibu ion om all samples p io o s a is ical ccalcula ions. Depending on he numbe o measu ed aliquo s, one o wo De had o be ejec ed. Fo ine g ains, insu icien bleaching is ha dly de ec able. Thus he a i hme ic mean o ob ained De om he measu emen s was aken o age calcula ion. IRSL ages by Zölle e al. [2003] we e ecalcula ed using co ec ed wa e con en s (see abo e) and new cosmic dose a es. 5. Resul s 5.1. Dose Ra es Resul s o dose a e ( . D) de e mina ion a e gi en in Table 4 wi h hei 1s e o s. U anium con en s calcula ed om hicksou ce α-coun ing ange om 1.46 o 3.1 ppm and ho ium alues om 5.0 o 10.7 ppm. Po assium con en s de e mined ei he by AAS o ICPMS ange om 1.7 o 4.1%. Ra he low dose a e alues gene ally occu in calca eous ho izons (e.g., BT 318, BT 319, BT 308). The occu ence o adioac i e disequilib ia in calca eous ho izons canno be excluded. Howe e , he U con en o calci e p esen s only a e y small p opo ion compa ed o he o al Ucon en , so ha desequilib ia in he U-decay chain a e no expec ed o ha e a signi ican in luence on he o al dose a e. Fu he mo e, Schä e and Zölle [1996] demons a ed om a Middle Palaeoli hic si e in Thu ingia/Ge many showing signi ican disequilib ia de ec ed by lowle el γ-spec ome y, ha using dose a es om U and Th based on α-coun ing is a good app oach i adioac i e disequilib ium has egene a ed mo e o less pe manen ly since deposi ion. Ca bona e p ecipi a ion pos e io o deposi ion may dilu e concen a ions o adioelemen s and hus lowe he dose a e. Howe e , ca bona e- ee laye s deposi ed o e ca bona e- ich beds indica e ha seconda y calci ica ion was mo e o less con empo aneous o sedimen a ion. The consequences o his e ec should no ha e played a majo ole al hough a sligh unde es ima ion o dose a es due o his e ec canno be excluded. 5.2. Equi alen Doses Equi alen doses o qua z OSL and eldspa IRSL measu emen s a e lis ed in Table 5 wi h hei 1σ e o s. Owing o hei own cha ac e is ics and accu acies, he applied luminescence me hods (coa se- and ine-g ain OSL, ine-g ain IRSL) a e discussed sepa a ely. 5.2.1. Qua z Coa se-G ain OSL measu emen s The po en ial o o al bleaching o he in es iga ed sedimen s was es ed by exposu e o he p epa ed coa se-g ain qua z ex ac s o 10 hou s o na u al dayligh (Bay eu h/Ge many, ~50°N, No embe 2005) wi h a subsequen OSL measu emen . This es was ca ied ou o samples BT 190, BT 195 and BT 196 which showed no OSL signal a e dayligh exposu e. Fu he mo e, a dose eco e y es was ca ied ou using he same samples as o he bleaching es . A e he bleaching o he samples hey we e gi en b- adia ions o 4.28 Gy (sample BT 195), 17.13 Gy (sample BT 196) and 38.55 Gy (sample BT 190). Subsequen ly, he OSL measu emen s o De de e mina ion we e pe o med wi h p ehea empe a u es o 220°, 240°, 260° and 280°C, wi h ou aliquo s o each empe a u e. In Figu e 4 he esul s o hese measu emen s can be seen, wi h a De pla eau be ween 220° and 280°C wi hin e o ba s. Thus, in spi e o a sligh o e es ima ion o gi en doses, o all u he De measu emen s a p ehea empe a u e o 240°C was applied. All qua z samples show ypical exponen ial sa u a ing g ow h. F om he g ow h cu es i can be seen ha sa u a ion, on a e age, is eached a ound 350 Gy bu can also be somewha highe o se e al samples. Thus highes De es ima ions abo e 300 Gy ha e o be ea ed wi h cau ion. Measu ed aliquo s we e excluded om u he analysis when es dose e o , paleodose e o , o ecycling a io e o we e >10%. The same applies o aliquo s gi ing a signal less han h ee imes he s anda d de ia ion o he backg ound. This was ue o abou 7% o he measu ed aliquo s. 5.2.2. Qua z ine-g ain OSL measu emen s Fine-g ain OSL De ange om 5.6 o 211 Gy. The equency dis ibu ion o he measu ed aliquo s pe sample yielded a s anda d de ia ion be ween 2 o 12%. Abou 3% o he measu ed aliquo s had o be emo ed owing o he exclusion c i e ia de ined abo e. All g ow h cu es show an exponen ial beha io , wi h sa u a ion a ained a ound 350 Gy (highes calcula ed De = 211 Gy). Typical measu emen s o a- alues ange be ween 0.03 and 0.05. Consequen ly, a mean alue o 0.04 was used o calcula ions. 5.2.3. IRSL ine-g ain measu emen s As can be seen om he IRSL g ow h cu es, sa u a ion o he in es iga ed eldspa s is a ained a ound 1800-2000 Gy. Hence all in es iga ed samples (highes De ~700 Gy) a e wi hin he da able dose ange. IRSL g ow h cu es om Lowe o Middle Holocene samples show an almos linea beha io , whe eas he olde ones a e clea ly sa u a ing exponen ial. Fi ing e o o he g ow h cu es was be ween 0.3 and 3.5%, gi ing lowe alues o highe doses. As al eady s a ed by Pomel e al. [1985], measu ed a- alues a e e y low wi h alues be ween 0.029 and 0.063, being in gene al highe in Teguise (a e age 0.06) han in Femés (a e age 0.04) and Gua iza (a e age 0.05). Owing o long a-i adia ion imes only some ep esen a i e a- alues we e de e mined, whe eas o he missing alues he mean o e e y p o ile was aken. Almos hal o he samples show signi ican anomalous ading up o 40%. 6. Discussion 6.1. Reliabili y o di e en luminescence me hods 6.1.1. Coa se-G ain OSL Ages Mos o ou coa se-g ain single aliquo his og ams a e igh skewed (mean skewness 1.24), indica ing insu icien bleaching du ing collu ial anspo . Se e al ou lie s owa d lowe doses we e also obse ed (Figu e 3). Owing o he s ong sca e o he equi alen doses, age e o s a e be ween 9 and 31%. The occu ence o collu ial ewo king du ing mos pe iods was also p o en by mic omo phological s udies [Saue and Zölle , 2006]. This occu s in all egas, howe e he his og am asymme y is gene ally lowe in Teguise compa ed o Femés and Gua iza III. This is explained by he lowe ca chmen a ea- alley bo om a io, which means a lowe p opo ion o (insu icien ly bleached) collu ial ma e ial o igina ing om he slopes ela i e o in si u eolian dus is ound in he ega bo om sedimen s ( on Suchodole z e al., submi ed manusc ip , 2008). Co espondingly, lowes e o s we e obse ed in he ega o Teguise. Using he app oach o Juyal e al. [2006], mos De alues a e now si ua ed a he uppe ising le limb o ou dis ibu ion (Figu e 3). He e we belie e ha he equi alen doses co esponding o he las bleaching e en should be loca ed. The gene al omission o he lowe 5% o measu ed aliquo s om all samples s ongly imp o ed ou De calcula ion in samples exhibi ing ou lie s owa d he lowe end o he dis ibu ion, and hus De o mos o hese samples all a he uppe ising limb o ou his og ams as well. In cases wi hou ou lie s, owing o he b oad ising limb, he esul ing shi owa d highe De is e y small. Thus his me hod appea s o be a jus i ied app oach o De de e mina ion. Fo wo samples, howe e , his app oach seems o ail: Sample BT 200 shows an excep ional De his og am wi h a le skewed dis ibu ion (Figu e 5a). Since he De o his sample is close o sa u a ion le el i is e y likely ha he aliquo s no mally o ming he igh (olde ) ail o he dis ibu ion we e al eady in sa u a ion and hus a e no p esen in he his og am. Addi ionally, he numbe o aliquo s is s ongly limi ed so ha a ising limb is no well de eloped. The a i hme ic mean De o his sample gi es a alue a he ising limb close o he i s maximum o he dis ibu ion (Figu e 5a). Howe e , owing o he non-Gaussian o m o he dis ibu ion his a i hme ic mean can only be a ough es ima ion. Caused by he limi ed amoun o aliquo s, he calcula ed De o sample BT 197 may be unde es ima ed and should be ega ded as a minimum age (Figu e 5b). Luminescence es s in es iga ing insu icien bleaching (due o i on s ains a ound he g ains) du ing aeolian anspo we e ca ied ou wi h ecen Saha an dus om he Cana y Islands (H. on Suchodole z e al., Luminescence bleaching cha ac e is ics o Saha an dus – A case s udy om Lanza o e, Cana y Islands (Spain), submi ed o Qua e na y Geoch onology, 2008) (he eina e e e ed o as on Suchodole z e al., submi ed manusc ip , 2008b). They show ha o coa se g ains inhe i ed doses wi h espec o dose a es om Lanza o e a e in he ange o only 0.1-0.2 ka and a e hus negligible. A sample om collu ial ma e ial o e lying a his o ic la a low da ing om 1736 AD (sample BT 204) yields an appa en coa se-g ain OSL age o abou 1.2 ka, hus indica ing an o e es ima ion <1 ka. These es s show ha coa se- g ain OSL basically o e s he equi ed condi ions o da ing Lowe Holocene o olde lu io- eolian sedimen s. The p oblem o a sligh o e es ima ion o gi en doses du ing he p ehea es s (see Figu e 4) mus be seen agains he backg ound o gene ally ela i ely la ge e o s o coa se-g ain OSL ages:owing o he unce ain y caused by insu icien bleaching, da ing e o s a e a he la ge, so ha he o e es ima ion e ec is smalle han calcula ed e o s. This shows, howe e , ha ou luminescence ages a e poin s o e e ence a he han p ecise da es. 6.1.2. Fine-G ain Qua z OSL Ages Compa ison o coa se and ine-g ain qua z OSL ages e eals ha he la e do no show signi ican age o e es ima ions as could be expec ed owing o insu icien bleaching. Young Holocene samples show, howe e , a egula o e es ima ion o abou 1 o 3 ka. (samples BT 189, BT 198, BT 310). O e es ima ion o he same magni ude is ound o ecen sample BT 204. Thus bleaching o ine g ains is no as comple e as o coa se-g ain OSL. This could be due o hei collu ial anspo as agg ega es. Since qua z OSL does no exhibi anomalous - Menéndez, I., J. L. Diaz-He nandez, J. Mangas, I. Alsonso, and P.-J. Sanchez-So o (2007), Ai bo ne dus accumula ion and soil de elopmen in he No h-Eas sec o o G an Cana ia (Cana y Islands, Spain), J. A id En i on., 71, 57–81. - Mo eno, A., J. Ta agona, J. Hende iks,M. Canals, T. F euden hal, and H. Megge s (2001), O bi al o cing o dus supply o he No h Cana y Basin o e he las 250 ky , Qua . Sci. Re ., 20, 1327–1339. - Mu ay, A., and A. Win le (2000), Luminescence da ing o qua z using an imp o ed single-aliquo egene a i e-dose p o ocol, Radia . Meas., 32, 57–73. - Olley, J., G. Cai cheon, and A. Mu ay (1998), The dis ibu ion o appa en dose as de e mined by op ically s imula ed luminescence in small aliquo s o lu ial qua z: Implica ions o da ing young sedimen s, Qua . Geoch onol., 17, 1033–1040. - O iz, J. E., T. To es, Y. Yanes, C. Cas illo, J. de la Nuez, M. Ibanez, and M. R. 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Coudeé-Gaussen (1987), Changemen s dans les ci cula ions a mosphé ique e océanique à la la i ude des Cana ies e du Ma oc en e les s ades iso opiques 2 e 1, Qua e nai e, 7(4), 197–206. - Rognon, P., G. Coude´-Gaussen, M.-N. Le Cous ume , J. C. Baloue , and S. Occhie i (1989), Le massi dunai e de Jandía (Fue e en u a, Cana ies): É olu ion des paléoen i onnemen s de 20.000 BP a` l’ac uel, In . J. F . Qua . Assoc., 37, 31–37. - Rousseau, D.-D., L. Zölle , and J.-P. Vale (1998), La e Pleis ocene clima ic a ia ions a Achenheim, F ance, based on magne ic suscep ibili y and TL ch onology o loess, Qua . Res., 49, 255–263. - Saue , D., and L. Zölle (2006), Mik omo phologie de Paläoböden de P o ile Femés und Gua iza, Lanza o e, Bay eu he Geowiss. A b., 27, 105–130. - Schä e , D., and L. Zölle (1996), Zu Cha ak e isie ung des weichselzei lichen F eiland undpla zes om Gamsenbe g bei Oppu g/Thü ingen, Tübinge Monog . U geschich e, 11, 235–246. - Singh i, A. K., and M. R. K be schek (1996), Luminescence da ing: A e iew and a pe spec i e o a id zone sedimen s, Ann. A id Zone, 35(3), 249–279. - T au mann, T., M. R. K be schek, A. Die ich, and W. S olz (2000), The basic p inciple o adioluminescence da ing and a localized ansi ion model, Radia . Meas., 32, 487–492. - Win le, A. G. (1973), Anomalous ading o he moluminescence in mine al samples, Na u e, 245, 143–144. - Win le, A. G. (1998), Luminescence da ing: Labo a o y p ocedu es and p o ocols, Radia . Meas., 27, 769–817. - Xie, J., and M. J. Ai ken (1991), The hypo hesis o mid- e m ading and i s ial on Chinese loess, Ancien TL, 9, 21–25. - Zölle , L., H. on Suchodole z, and N. Küs e (2003), Geoa chaeological and ch onome ical e idence o ea ly human occupa ion on Lanza o e (Cana y Islands), Qua . Sci. Re ., 22, 1299–1307. - Zölle , L., D.-D. Rousseau, K.-D. Jäge , and G. Kukla (2004), Las in e glacial, Lowe and Middle Weichselian—A compa a i e s udy om he Uppe Rhine and Thu ingian loess a eas, Z. Geomo phol., 48, 1–24. - Zölle , L., D. Faus , and H. on Suchodole z (2006), Pedos a ig aphie des Qua ä s au Lanza o e, Bay eu he Geowiss. A b., 27, 1–21. Tables Table 1: P ope ies o S udied Si es on Lanza o e Femés Gua iza Teguise La i ude N 28°55´32´´ 29°04´08´´ 29°04´52´´ longi ude W 13°45´19´´ 13°29´22´´ 13°30´55´´ Al i ude (m a.s.l.) 300 100 300 ca chmen a ea (km2) 5.07 10.1 3.8 alley bo om (% o ca chmen a ea) 18 16.1 35 ela i e ele a ion di e ence in he ca chmen a ea (m) 100 (SE slopes) – 200 (NW slopes) > 550 100 ime o olcanic damming 1.4 Ma1 170 ka2 1.2 Ma3 olcanic damming comple e? yes no no hickness o an h opogenic collu ial deposi s (cm) 55 420 80 1 Zölle e al. (2006) 2consis en he moluminescence and ESR da a (H. . Suchodole z e al., unpublished esul s, 2006) 3 Ins i u o Tecnológico y Geomine o de España [2008]. Table 2 : Kind and s eng hs o used i adia ion-sou ces. S eng hs a e gi en in Gy/min and e e ed o 21 Augus 2006, excep o he ex e nal 90S /90Y-sou ce which is e e ed o 15 June 2006. ype o i adia ion ype o sou ce coa se g ain ine g ain 90S /90Y (in e nal Risø- eade 1) 8.81 - 90S /90Y (in e nal Risø- eade 2) 2.57 2.52 Β 90S /90Y (ex e nal) - 7.85 Α Li lemo e 241Am (ex e nal) - 1.26 Table 3: Used measu emen -pa ame e s o OSL and IRSL OSL IRSL S imula ion- LEDs 470 ± 20 nm 845 ± 20 nm De ec ion- il e U-340 Hoya ( ansmission 290 - 380 nm) BG 39, GG 400, 2xBG 3 ( ansmission 390-450 nm) P ehea ( a e 10°/s) 240°C o 10 s 220°C o 120 s (age < 10 ka) 220°C o 300 s (age > 10 ka) Cu -hea ( a e 5°C/s) 160°C Tes dose Reade 1: 2.2 Gy Reade 2: 0.64 Gy Measu emen 20 s a 125°C 60 s a oom empe a u e Used in eg al 0.0 - 0.4 s 0 - 15 s Backg ound in e al 16 - 20 s 55 - 60 s Table 4: Luminescence da ing: Analy ical esul s Dose a es ( . D) a e gi en in Gy/ka. U- and Th-con en s we e calcula ed om he α –coun a e. Measu ed wa e con en s p esen he a io mois /d y weigh , he co ec ion was done using he clay con en s o he samples. The e o o wa e con en s is assumed o be 0.1. Sample dep h (cm) Sample α - coun a e (cpm) U-con en (ppm) Th-con en (ppm) K-con en (%) 1 om ICPMS 2 om AAS . D-β* . D-γ* . Dcosm Measu ed wa e con en Co ec ed wa e con en Femés 60 BT 310, (BN-D 207) 0.58* - - - 2.58 ± 0.13 1.12 ± 0.06 0.21 ± 0.011 1.1* 1.19 80 BT 311 0.48 ± 0.012 2.34 ± 0.058 8.00 ± 0.20 2.45 ± 0.072 - - 0.21 ± 0.010 1.13 1.24 100 BT 189 0.46 ± 0.009 2.25 ± 0.044 7.70 ± 0.15 3.19 ± 0.101 - - 0.20 ± 0.010 1.13 1.24 120 BT 312 0.36 ± 0.008 1.75 ± 0.039 6.01 ± 0.13 3.32 ± 0.102 - - 0.20 ± 0.010 1.13 1.24 140 BT 313 0.43 ±0.006 2.09 ± 0.029 7.16 ± 0.10 2.12 ± 0.062 - - 0.20 ± 0.010 1.14 1.22 170 BT 190, (BN-D 209) 0.47* - - - 3.25 ± 0.05 1.08 ± 0.05 0.19 ± 0.010 1.19* 1.25 190 BT 314 0.40 ± 0.008 1.96 ± 0.040 6.71 ± 0.14 1.91 ± 0.062 - - 0.19 ± 0.010 1.17 1.26 210 BT 315 0.44 ± 0.001 2.12 ± 0.004 7.25 ± 0.02 2.61 ± 0.082 - - 0.19 ± 0.009 1.20 1.27 225 BT 316 0.39 ± 0.010 1.87 ± 0.047 6.39 ± 0.16 2.66 ± 0.082 - - 0.19 ± 0.009 1.20 1.28 245 BT 317 0.41 ± 2.01 ± 0.047 6.87 ± 0.16 2.99 ± 0.092 - - 0.18 ± 0.009 1.19 1.30 0.010 270 BT 224 0.44 ± 0.008 2.13 ± 0.039 7.28 ± 0.13 2.89 ± 0.091 - - 0.18 ± 0.009 1.18 1.24 290 BT 318 0.30 ± 0.008 1.46 ± 0.039 5.01 ±0.13 1.78 ± 0.052 - - 0.18 ± 0.009 1.11 1.24 310 BT 319 0.30 ± 0.006 1.46 ± 0.027 5.01 ± 0.09 2.07 ± 0.062 - - 0.18 ± 0.009 1.11 1.23 330 BT 301 0.44 ± 0.009 2.12 ± 0.044 7.27 ± 0.15 2.24 ± 0.072 - - 0.17 ± 0.009 1.14 1.25 350 BT 302 0.43 ± 0.010 2.09 ± 0.048 7.16 ± 0.17 1.70 ± 0.052 - - 0.17 ± 0.009 1.18 1.28 380 (400*) BN-D 211 0.45* - - - 3.27 ± 0.05 1.09 ± 0.06 0.17 ± 0.008 1.15* 1.27 460 BT 191 0.47 ± 0.010 2.28 ± 0.050 7.16 ± 0.17 3.39 ± 0.101 - - 0.16 ± 0.008 1.12 1.26 480 BT 303 0.44 ± 0.007 2.11 ± 0.034 7.23 ± 0.12 2.83 ± 0.081 - - 0.15 ± 0.008 1.17 1.28 630 (670*) BN-D 213 0.45* - - - 3.12 ± 0.16 0.99 ± 0.05 0.14 ± 0.007 1.30* 1.3 Teguise 80 BT 306 0.52 ± 0.018 2.5 ± 0.087 8.57 ± 0.30 2.53 ± 0.082 - - 0.21 ± 0.010 1.05 1.16 90 BT 198 0.65 ± 0.013 3.12 ± 0.061 10.70 ± 0.21 2.49 ± 0.071 - - 0.21 ± 0.010 1.04 1.16 110 BT 235 0.52 ± 0.010 2.51 ± 0.048 8.60 ± 0.17 2.86 ± 0.092 - - 0.20 ± 0.010 1.09 1.27 135 BT 307 0.44 ± 0.016 2.11 ± 0.078 7.22 ± 0.27 3.19 ± 0.102 - - 0.20 ± 0.010 1.19 1.28 160 BT 199 0.46 ± 0.007 2.21 ± 0.033 7.57 ± 0.11 3.69 ± 0.111 - - 0.20 ± 0.010 1.13 1.31 185 BT 308 0.32 ± 0.006 1.56 ± 0.030 5.35 ± 0.10 2.24 ± 0.072 - - 0.19 ± 0.010 1.14 1.26 210 BT 309 0.39 ± 0.008 1.86 ± 0.039 6.38 ± 0.13 2.32 ± 0.072 - - 0.19 ± 0.009 1.17 1.24 250 BT 200 0.56 ± 0.010 2.69 ± 0.048 9.21 ± 0.17 2.90 ± 0.091 - - 0.18 ± 0.009 1.1 1.26 330 BT 236 0.40 ± 0.007 1.92 ± 0.034 6.57 ± 0.12 4.08 ± 0.121 - - 0.17 ± 0.009 1.14 1.26 450 BT 201 0.42 ± 0.009 2.05 ± 0.044 7.03 ± 0.15 3.73 ± 0.111 - - 0.16 ± 0.008 1.18 1.26 610 BT 202 0.43 ± 0.007 2.10 ± 0.034 7.19 ± 0.12 2.93 ± 0.091 - - 0.14 ± 0.007 1.09 1.27 Gua iza III 110 BT 193 0.39 ± 0.008 1.88 ± 0.039 6.44 ± 0.13 2.89 ± 0.091 - - 0.2 ± 0.010 1.09 1.24 250 BT 194 0.40 ± 0.009 1.96 ± 0.044 6.71 ± 0.15 2.53 ± 0.081 - - 0.18 ± 0.009 1.10 1.26 435 BT 195 0.51 ± 0.009 2.49 ± 0.044 8.53 ± 0.15 3.96 ± 0.121 - - 0.16 ± 0.008 1.07 1.21 470 BT 233 0.43 ± 0.006 2.06 ± 0.029 7.05 ± 0.10 2.51 ± 0.081 - - 0.15 ± 0.008 1.11 1.25 495 BT 196 0.48 ± 2.35 ± 0.044 8.03 ± 0.15 2.73 ± 0.081 - - 0.15 ± 0.008 1.08 1.25 0.009 550 BT 234 0.44 ± 0.006 2.11 ± 0.029 7.22 ± 0.10 3.22 ± 0.101 - - 0.15 ± 0.008 1.14 1.26 610 BT 304 0.39 ± 0.011 1.90 ± 0.053 6.51 ± 0.18 4.02 ± 0.122 - - 0.14 ± 0.007 1.13 1.28 660 BT 197 0.53 ± 0.009 2.58 ± 0.044 8.84 ± 0.15 2.99 ± 0.091 - - 0.14 ± 0.007 1.09 1.22 700 BT 305 0.50 ± 0.013 2.43 ± 0.063 8.32 ± 0.22 3.86 ± 0.122 - - 0.13 ± 0.007 1.11 1.23 Gua iza I 210 BN-D 219 0.46* - - - 2.58 ± 0.04 0.85 ± 0.04 0.18 ± 0.009 1.20 - Tahiche ecen BT 204 0.42 ± 0.009 2.04 ± 0.043 6.98 ± 0.15 2.00 ± 0.061 - - 0.21 ± 0.011 1.10 - * da a aken om Zölle e al. [2003] Table 5: Luminescence da ing: Equi alen doses and ages De´s a e gi en in Gy. Coa se g ain OSL-De´s we e calcula ed a e Juyal e al. [2006]. All ages a e gi en in ka. Measu ed a- alues a e gi en in s anda d, assumed a- alues in i alic le e s. Sample dep h (cm) Code IRSL-De a- alue IRSL IRSL age Anomalous Fading Fine-g ain qua z OSL-De a- alue ine g ain qua z OSL Fine-g ain qua z OSL age Coa se-g ain qua z OSL-De Coa se-g ain qua z OSL age Femés 60 BT 310 (BN-D 207) 18.3 ± 4.7* 0.04 ± 0.001* 4.9 ± 1.3 yes* - - - 20.5 ± 1.5 6.4 ± 0.7 80 BT 311 - - - - - - 38.0 ± 3.4 12.4 ± 1.6 100 BT 189 65.5 ± 0.8 0.04 ± 0.002 16.7 ± 1.5 yes 65.3 ± 4.9 0.03 ± 0.01 16.8 ± 1.9 47.9 ± 3.7 13.6 ± 1.6 120 BT 312 - - - - - - - 122 ±11.9 35.4 ± 4.7 140 BT 313 - - - - - - - 150 ± 10.8 56.0 ± 6.5 170 BT 190 (BN-D 209) 166 ± 12* 0.04 ± 0.002* 41.0 ± 3.8 no* - - - 165 ± 31.4 45.9 ± 9.7 190 BT 314 - - - - - - - 194 ± 22.6 55.9 ± 8.2 210 BT 315 - - - - - - - 164 ± 22.8 47.7 ± 7.8 225 BT 316 - - - - - - - 204 ± 25.1 54.8 ± 7.2 245 BT 317 - - - - - - - 193 ± 17.4 57.6 ± 7.2 270 BT 224 328 ± 2 0.04 ± 0.002 91.2 ± 8.1 no - - - 208 ± 16.6 64.8 ± 7.8 290 BT 318 - - - - - - - 213 ± 49.2 101.0 ± 24.9 310 BT 319 - - - - - - - 219 ± 65.7 93.3 ± 29.2 330 BT 301 - - - - - - - 237 ± 21.0 88.3 ± 11.1 350 BT 302 - - - - - - - 275 ± 46.8 125.0 ± 23.8 Figu e 4. Resul s o he dose eco e y es o coa seg ain samples measu ed wi h OSL, shown wi h e o ba s (2σ). E e y da a poin is he a e age o ou single measu emen s. Dashed lines below a g aph indica e he gi en paleodose. Mean a ios gi en/measu ed dose we e: 220°C, 1.08; 440°C, 1.09; 260°C, 1.1; 280°C, 1.07. Figu e 5. De his og ams o coa se-g ain OSL samples (a) BT 200 and (b) BT 197 wi h di e en De. Figu e 6. Vega s a ig aphies wi h ela i e kaolini e con en s adjus ed o nume ical ch onos a ig aphy and o ma ine Al and Fe con en s. Luminescence da es gi ing co ec sedimen a ion ages a e shown wi h hei e o ba s (in kiloannums), whe eas he minimum age o sample BT 197 no p esen ed. Shadowed a eas in he p o iles indica e gene ally unwea he ed/less wea he ed laye s isible in he ield and used o co ela ion be ween he egas. Ho izon dep hs in cen ime e s (no in scale) a e indica ed on he le side o he p o iles. Figu e 7. O e iew o measu ed luminescence ages wi h hia ae. Reliable and un eliable ages a e disc imina ed.