Geo log i cal Quar terly, 2021, 65: 46 DOI: http://dx.doi.org/10.7306/gq.1615
Cor re la tion of Eemian sec tions in Lith u a nia and Belarus based on palaeomagnetic, ra dio iso tope and palaeobotanic data
Vaida EIRIEN#1, *, Al ex an der KARABANOV2, Valentinas BALTR¤NAS1, Bronislavas KARMAZA1, Valentas KATINAS1, Violeta PUKELYT#1, Tatyana RYLOVA2 and Svetlana DEMIDOVA2
1 Na ture Re search Cen tre, In sti tute of Ge ol ogy and Ge og ra phy, Akademijos 2, 08412 Vilnius, Lith u a nia
2 Na tional Acad emy of Sci ences of Belarus, In sti tute for Na ture Man age ment, Skoriny 10, 220114 Minsk, Belarus
eirienÅ, V., Karabanov, A., Baltrñnas, V., Karmaza, B., Katinas, V., PukelytÅ, V., Rylova, T., Demidova, S., 2021. Cor re la - tion of Eemian sec tions in Lith u a nia and Belarus based on palaeomagnetic, ra dio iso tope and palaeobotanic data. Geo log i - cal Quar terly, 65: 46, doi: 10.7306/gq.1615
As so ci ate Ed i tor: Wojciech Granoszewski
Eemian (Murava, MerkinÅ) de pos its at five ex posed sec tions (Zaslavl, Zhukevichi, Ponemun, SnaigupÅlÅ, and Netiesos) lo - cated in Lith u a nia and Belarus are de scribed. Pre lim i nary palaeomagnetic re sults show a re cord of the Brunhes ep och nor - mal mag netic field and a short-term re ver sal – the Blake Event – is rec og nized in three of the five sec tions. The Blake Event re corded in the Netiesos sec tion is char ac ter ized by a pat tern con sist ing of three short re versed po lar ity in ter vals sep a rated by two short nor mal po lar ity in ter vals. The di rec tional changes of dec li na tion, in cli na tion, and MS (mag netic sus cep ti bil ity) are clear. ESR dat ing (112.5 ±10.8 and 112.1 ±25.9) and 230Th/U dates ob tained from this sec tion (108.8 ±12.0/9.9 ka for the L/L tech nique and 100.2 ±10.3/8.6 ka for the TSD tech nique) sug gest that (Blake and post-Blake) palaeomagnetic ex cur - sions are pres ent in this sec tion. Palaeobotanical anal y sis and iso tope dat ing of the Netiesos sec tion sug gest that the Blake Event oc curred dur ing the cli ma tic op ti mum.
Key words: Eemian Inter gla cial, Blake Event, ra dio iso topes, pol len, Belarus, Lith u a nia.
INTRODUCTION
The Qua ter nary ge ol ogy of Lith u a nia and Belarus is sim i lar, as the ar eas of both neigh bour ing coun tries be long to the zone of con ti nen tal glaciations and the thick ness of the Qua ter nary cover var ies from 10 up to 300 m (GuobytÅ and Satkñnas, 2011; Karabanov and Matveev, 2011). The stra tig ra phy and cor re la tion of sed i men tary lay ers and sec tions have been among the most im por tant and con tro ver sial re search sub jects in Lith u a nia and Belarus for many years. The Qua ter nary strati - graphic sub di vi sion de vel oped in the mid-1990s was mainly based on lithostratigraphy (pe trog ra phy and min er al ogy) and biostratigraphy (pol len, macroplant re mains, di a toms, mam - mals and molluscs) data (Lindner and Sanko, 2008; eirienÅ et al., 2015). Some palaeomagnetic stud ies were also per formed, but no broader strati graphic gen er al iza tions were made (e.g., Pevzner and Gaigalas, 1976; Sanko and Moiseev, 1996; Sanko et al., 2004; Baltrñnas et al., 2013, 2015; Bitinas et al., 2014, 2015). Dur ing the last few de cades, there have been few new
bore holes and there is lit tle hope of find ing new sec tions which could al ter or sup ple ment the ex ist ing strati graphic charts. Con - se quently, much at ten tion was paid to the ap pli ca tion of new meth ods and meth od olog i cal ap proaches, and the im prove - ment of dat ing.
Im por tant is sues in clude the age and du ra tion of the last inter gla cial pe riod, as well as palaeomagnetic in ves ti ga tions, which are still few in this re gion. In ves ti ga tions of the Earth’s geo - mag netic field re ver sals and ex cur sions plays an im por tant role in Qua ter nary stra tig ra phy: in cor re lat ing sec tions and un der - stand ing as pects of the global cli mate and sur face pro cesses.
Iden ti fi ca tion of the re ver sal bound aries can be used to pro vide ac cu rate time planes for geo logic cor re la tions. The pat tern of such re ver sals dur ing the past five mil lion years has been well es tab lished. How ever, many ques tions re gard ing the du ra tion, struc ture, and tim ing of the re ver sals re main prob lem atic.
This study cor re lates palaeo-events/sec tions within the re - gion, us ing the re sults of palaeomagnetic, palaeobotanical, and ra dio iso tope stud ies to es tab lish their re la tion ship to con tem po - ra ne ous global en vi ron men tal changes. Five sec tions rep re sent - ing the last inter gla cial of the Late Pleis to cene lo cated in west ern and cen tral Belarus and south ern Lith u a nia were stud ied. The re sults ex tend our un der stand ing of palaeoenviron mental changes in the re gion dur ing the Late Pleis to cene Eemian Inter - gla cial (Murava Inter gla cial in Belarus and MerkinÅ Inter gla cial in Lith u a nia) and help es tab lish their wider re la tion ships.
* Cor re spond ing au thor, e-mail: vaida.seiriene@gamtc.lt
Received: April 14, 2021; ac cepted: August 24, 2021; first pub lished on line: September 14, 2021
REGIONAL SETTING
The sites in ves ti gated oc cur as ex po sures of gen er ally sim i - lar lithologies. The main dif fer ence is that the sec tions in south - ern Lith u a nia are sit u ated in side the area of the Last Gla ci ation and as so ci ated with sub se quent pro cesses of ero sion and sed i - men ta tion, while the sec tions in Belarus oc cur out side the limit of the Last Gla ci ation (Fig. 1).
The Zaslavl, Zhukevichi and Ponemun sec tions are in Belarus, ex tend ing south and south east out side the limit of the Last Gla ci ation. The Zaslavl sec tion is in the kame-sandur land - scape of the Minsk El e va tion formed dur ing the Oshmyany phase of the Dnie per (Pripyat) Gla cial. The Zhukevichi and Ponemun sec tions are within the Neman (Nemunas) River val - ley on the high est ero sional ter race. The geomorphological en - vi ron ment and geo log i cal set ting of all these sec tions have been closely stud ied, with palaeobotanical data de scribed in many pa pers (e.g., Karabanov and Elovicheva, 1997; Sanko et al., 2002; Lindner and Sanko, 2008; Karabanov et al., 2017).
Here we pro vide a pre lim i nary study of palaeomagnetic data.
The SnaigupÅlÅ and Netiesos sec tions are lo cated in the Nemunas River val ley, Lith u a nia, within the sec ond and fourth raised ter races above the floodplain ex tend ing to the north of the limit of the Last Gla ci ation. They are well stud ied, and geo - log i cal, palaeobotanical, geo chem i cal, palaeomagnetic and geo chron ol ogi cal data has al ready been pub lished (Baltrñnas et al., 2013, 2015). Here we pro vide new palaeomagnetic and geo chron ol ogi cal re sults from the Netiesos sec tion with ref er - ence to the Blake Event.
METHODS
Palaeomagnetic in ves ti ga tions. The palaeomagnetic data de scribed in this pa per in clude de ter mi na tion of the ani so -
tropy of mag netic sus cep ti bil ity (AMS) and in ves ti ga tions of remanent mag net is ation. The palaeomagnetic mea sure ments were per formed at the Palaeomagnetic Lab o ra tory of the In sti - tute of Ge ol ogy and Ge og ra phy, Na ture Re search Cen tre, Lith - u a nia, us ing equip ment man u fac tured by AGICO (Czech Re - pub lic) and MOLSPIN Ltd. (United King dom). The sam ples for palaeomagnetic re search were col lected from all the sec tions:
23 sam ples from Zaslavl, 44 from Zhukevichi, 44 from Ponemun, and 73 from Netiesos. Sam pling was un der taken through the whole ver ti cal thick ness of each sec tion at 2–10 cm in ter vals. Sam ples were taken by press ing sed i ments into spe - cial plas tic con tain ers (Natsuhara Giken Co.).
The ani so tropy of mag netic sus cep ti bil ity (AMS) was mea - sured along fif teen dif fer ent di rec tions (Jelinek, 1977) with a MFK1-B kappabridge (AGICO). The anal y sis of the AMS data was per formed us ing Anisoft 4.2 soft ware.
Af ter the AMS anal y sis, sam ples with the same ori en ta tion were used for the remanent mag net is ation stud ies. The nat u ral remanent mag net is ation (NRM) of sam ples was mea sured us ing a JR-6 spin ner mag ne tom e ter (AGICO). Mag netic dec li na tion and mag netic in cli na tion were then de ter mined and plot ted for each sam ple. All the sam ples were sub jected to stepwise al ter - nat ing field (AF) demonetarisation with an AF demagnetizer (MOLSPIN Ltd.). The re sults of the de mag neti sa tion were ob - tained and shown as ste reo graphic pro jec tions, Irm/Inrm, x, y and z pro jec tions. The char ac ter is tic di rec tions were cal cu lated us ing prin ci pal com po nent anal y sis (Kirschvink, 1980). The anal - y sis of the NRM was per formed us ing Remasoft 30 soft ware.
Mag netic sus cep ti bil ity (MS) mea sure ments. Mass mag netic sus cep ti bil ity (m3/kg) was mea sured us ing a kappabridge MFK-1B (AGICO). The anal y sis of the ani so tropy of mag netic sus cep ti bil ity (AMS) was ap plied to al low re con - struc tion of sed i ment in flow into the ba sin and its trans port. An AMS mea sure ment of one sed i ment spec i men re sults in an el - lip soid of mag netic sus cep ti bil ity (K) de fined by the length and Fig. 1. Study area in Lith u a nia and Belarus and lo ca tion of the sec tions in ves ti gated
1 – Zaslavl (N54°01’27.6’’, E27°15’02.4”, 219 m a.s.l.); 2 – Zhukevichi (N53°36’04.4”, E24°00’03.9’’, 112 m a.s.l.); 3 – Ponemun (N53°39’00.0”, E23°52’51.9’’, 93 m a.s.l.); 4 – SnaigupÅlÅ (N54°01’52.1’’, E23°59’57.8’’, 93 m a.s.l.); 5 – Netiesos (N54°10’39.4’’, E24°03’04.4’’, 88.2 m a.s.l.); the co or di nates (WGS 84 co or di na tion sys tem) and al ti tudes (ap prox i mate po si tion of the tops of sec tions in ves - ti gated, in metres above mean sea level) are given
ori en ta tion of its three prin ci pal axes, Kmax>Kint>Kmin, which are the eigenvectors of the sus cep ti bil ity ten sor (Tarling and Hrouda, 1993; Jezek and Hrouda, 2004). The long axis of the mag netic sus cep ti bil ity el lip soid Kmax de fines the mag netic lineation; Kmin (short axis) de fines the mag netic fo li a tion. Ac - cord ing to an ex pected model, the mag netic lineation should co in cide with the sed i men tary flow di rec tions, while Kmin is per - pen dic u lar (90°) to the di rec tion of the flow (CaÔón-Tapia, 2004). Many stud ies have shown that mag netic fab ric pro vides a re li able strain in di ca tor (cf. Gra ham, 1966; Henry, 1973;
Hrouda and Janak, 1976; Hrouda et al., 1978; Hrouda, 1979, 2002; Ferre et al., 2004).
The 230Th/U dat ing tech nique. These in ves ti ga tions were car ried out in the lab o ra tory of St. Pe ters burg State Uni ver sity.
For 230Th/U dat ing of the bur ied or ganic-rich de pos its of the Netiesos sec tion us ing a new ver sion of isochron ap proach, the fol low ing was done (Maksimov and Kuznetsov, 2010;
Kuznetsov and Maksimov, 2012; Baltrñnas et al., 2015): (1) radiochemical anal y sis of iso topes of U and Th in the same sam ples via leach ing (L/L-tech nique) and to tal sam ple dis so lu - tion (TSD-tech nique); (2) com par i son of the ex per i men tal iso to - pic data and iden ti fi ca tion of sam ples be long ing to closed geo - chem i cal sys tems; (3) isochronous cor rec tion dat ing in di vid u - ally by each of the tech niques (L/L and TSD) for dif fer ent com bi - na tions of sam ples; and (4) de ter mi na tion of the fi nal isochronous age based on the great est sim i lar ity of isochron-cal i brated dates in the same com bi na tion of sam ples treated us ing the L/L and TSD tech niques. The radiochemical anal y sis of or ganic-rich de pos its in cludes the 5 steps de scribed by Kuznetsov and Maksimov (2012).
RESULTS
Zaslavl sec tion. The Zaslavl sec tion AMS mea sure ments sug gest two di rec tions of flow of sed i men tary ma te rial: di rec tion I (A) with a dec li na tion of 273° and in cli na tion of 15° and di rec - tion II (B) with a dec li na tion of 34° and in cli na tion of 9° (Fig. 2).
The mag netic po lar ity scale of the sam pled part of the sec tion is the fol low ing: depth in ter vals from the bot tom to 3.13 m and from 2.60 to 1.0 m rep re sent nor mal mag netic po lar ity, while the depth in ter val from 2.60 to 3.13 m rep re sents re versed po lar ity.
The lat ter could be linked to the Blake geo mag netic in ver sion (Fig. 2 and Ap pen dix 1: ta ble 1*).
A se ries of thermoluminescent dates from the de pos its of the Zaslavl sec tion was ob tained by L.T. Voskovskaya at Mos - cow State Uni ver sity ac cord ing to the method de vel oped by A.I.
Shlyukov (Sanko et al., 2017). The ab so lute age of the lake sed i ments de pos ited dur ing the tran si tion from the Pripiatian (Saalian) Late Gla cial to the Muravian (Eemian) Inter gla cial turned out to be 128,000 ±11,000 (TLM-429). Five more thermoluminescence dates ob tained from the de pos its (be - tween the peat and loess units) in di cate an Early Poozerian (Weichselian) depositional age. At the same time, it should be noted that there is no reg u lar pat tern in the dis tri bu tion of thermoluminescence dates – the low er most sam ple (TLM-430) has a date of 70,000 ±5,000 years, while the over ly ing sam ple yielded an older age of 130,000 ±10,000 years (TLM-433), while a sim i lar jux ta po si tion of youn ger and older dates was ob - served in the re main ing part of the sec tion (Sanko et al., 2017).
2. Zhukevichi sec tion. AMS mea sure ments of 44 ori ented sam ples from the Zhukevichi sec tion show two di rec tions of sed i men tary ma te rial ori en ta tion. All sam ples have a gen eral di -
rec tion of 14° with a 5° dip an gle. Di rec tion I is 8° with a low dip an gle. The sec ond di rec tion (II) az i muth (i.e. from west to east) is 86° with a low dip an gle. Di rec tion II was de tected only in the lower part of the sec tion (Fig. 3 and Ap pen dix 1: ta ble 2).
The mag netic po lar ity re cord in the Zhukevichi sec tion shows nor mal mag netic po lar ity from the bot tom to the top. The Blake geo mag netic ex cur sion was not iden ti fied in this sec tion.
3. Ponemun sec tion. The re sults of AMS mea sure ment of 42 ori ented sam ples from the Ponemun sec tion show two di rec - tions of the flow of sed i men tary ma te rial. The data of two sam - ples was not re li able and was re moved from the sta tis ti cal anal - y sis. All sam ples have a sed i men tary flow di rec tion of 55° with a 1° dip an gle. Di rec tion I – all sam ples have the gen eral di rec tion of 50° with a low dip an gle. Di rec tion II – an az i muth di rec tion of 140° (from the north west to the south east) with a low dip an gle.
Di rec tion II was de tected only in the mid dle part of the sec tion (Fig. 4 and Ap pen dix 1: ta ble 3).
The Ponemun sec tion showed nor mal po lar ity from the bot - tom to top of the seg ment sam pled; the Blake geo mag netic ex - cur sion was not iden ti fied.
4. Netiesos sec tion. More de tailed palaeomagnetic in ves - ti ga tions were per formed on that part of the Netiesos sec tion where the Blake ex cur sion had pre vi ously been de tected (Baltrñnas et al., 2013). The Blake Event was con strained by 18 sam ples in a 38 cm thick ness in ter val (Fig. 5 and Ap pen dix 1:
ta ble 4)
The pres ent study re veals that the Blake Event in the Netiesos sec tion re solves into 5 in ter vals of dif fer ent po lar ity: 3 of re versed po lar ity and 2 of nor mal po lar ity. The high est com - pat i bil ity of isochron-cal i brated dates for the Netiesos sec tion cal cu lated us ing the L/L and TSD tech niques was de ter mined for a com bi na tion of three sam ples. With the help of the cor rec - tion in dex f (in ter cept of isochrons on the or di nates axis in the plot of 230Th/232Th vs. 234U/232Th ac tiv ity ra tios), the con tri bu tion of the pri mary con tam i na tion with tho rium was de ter mined (Baltrñnas et.al., 2015). Ap ply ing the cor rected an a lyt i cal data, the isochron-cal i brated ages were cal cu lated: 108.8
±12.0/9.9 ka for the L/L tech nique and 100.2 ±10.3/8.6 ka for the TSD tech nique (Baltrñnas et al., 2015).
DISCUSSION
Re ver sals and ex cur sions of the Earth’s geo mag netic field are com mon. Dur ing the Qua ter nary Pe riod, 27 well-doc u - mented geo mag netic field in sta bil i ties have been iden ti fied as short-lived ex cur sions, 14 of those oc curred dur ing the Matuyama Chron and 13 dur ing the Brunhes Chron. Dur ing the Qua ter nary Pe riod, they oc cur nearly three times as of ten as full po lar ity re ver sals (Singer, 2014). How ever, geo mag netic ex cur - sions are much more dif fi cult to de tect and eval u ate than are the po lar ity bound aries them selves. Mag ne ti za tion di rec tions dur ing an ex cur sion may re cord a com plete po lar ity re ver sal, but more of ten they do not. Such ex cur sions can be used as time mark ers if they can be uniquely iden ti fied, but high-res o lu - tion re cords of these phe nom ena are quite scarce, as they are short-lived and dif fi cult to de tect.
The Geo mag netic In sta bil ity Time Scale (GITS) is based on the di rect dat ing of tran si tional po lar ity states in lava flows us ing the 40Ar/39Ar method, in par al lel with astrochronological age mod els of ma rine de pos its from which ox y gen iso tope and mag netic re cords have been ob tained (Singer, 2014). The geo - mag netic in ves ti ga tions of Singer et al. (2014) have shown that
Vaida eirienÅ et al. / Geo log i cal Quar terly, 2021, 65: 46 3
* Supplementary data associated with this article can be found, in the online version, at doi: 10.7306/gq.1615
Fig. 2. Re sults of the palaeomagnetic in ves ti ga tions of the Zaslavl sec tion
A – li thol ogy and data of palaeomagnetic char ac ter is tics; B – char ac ter is tic remanence (ChRM) di rec tions; C – di rec tional re sults of the ani - so tropy of mag netic sus cep ti bil ity (AMS) of the sec tions in ves ti gated; small sym bols rep re sent spec i men eigenvectors, large sym bols rep re - sent mean eigenvectors: K1 = Kmax (long axis), K2 = Kint (in te ger axis), K3 = Kmin (short axis) (Ap pen dix 1: ta ble 1); D – part of the Zaslavl sec tion within which the Blake subchron was re corded
five 40Ar/39Ar in cre men tal heat ing ex per i ments on the Am ster - dam Is land lava yield a pla teau age of 120 ±12 ka, whereas ages from two sites in the Calderon flow, New Mex ico, are 112 ±23 and 101 ±14 ka, to gether giv ing a weighted mean of 104 ±12 ka. The age of 120 ±12 ka from Am ster dam Is land, though im pre cise, cor re lates with the Blake ex cur sion. By con - trast, the 104–105 ka age ob tained from both Lipari Is land and the Calderon flow, New Mex ico, in di cates that these lavas re - cord a youn ger pe riod of dy namo in sta bil ity, most prob a bly as - so ci ated with the post-Blake ex cur sion. These ra dio met ric ages are con sis tent with the as tro nom i cal ages of two palaeo intensity min ima in the PISO-1500 global stack. These find ings in di cate that the Blake and post-Blake ex cur sions are both global fea - tures of the past geodynamo be hav iour (Singer et al., 2014).
Sier et al. (2015) sum ma rized nu mer ous in de pend ent age es ti mates for the Blake Event avail able from a num ber of stud -
ies and point out that they gen er ally in di cate a youn ger age than that of sapropel S5. In a sta lag mite in north ern Spain the Blake Event is U/Th-dated and spans the in ter val from 119.3 ±0.8 to 112.0 ±1.9 ka (in clud ing their B3 part of the event) and post - dates the iso tope sig nal peak cor re lated to MIS 5e (Osete et al., 2012; Sier et al., 2015).
Our pre vi ous study of the Netiesos site in south ern Lith u a - nia (Baltrñnas et al., 2013) re veals that the dat ing of the base of the Blake Event ob tained from the ESR dat ing of fresh wa ter molluscs is 112.5 ±10.8 and 112.1 ±25.9 ka (Gaigalas and Molodkov, 2002), whereas the top of the se quence pro duced U/Th dates of 108.8 ±8.7 and 105.7 ±10.0 ka (Gaigalas et al., 2005). The 230Th / U dates ob tained in our pres ent study (108.8
±12.0/9.9 ka for the L/L tech nique and 100.2 ±10.3/8.6 ka for the TSD tech nique) em pha size that.
Vaida eirienÅ et al. / Geo log i cal Quar terly, 2021, 65: 46 5
Fig. 3. Re sults of the palaeomagnetic in ves ti ga tions of the Zhukevichi sec tion
A – li thol ogy and data of palaeomagnetic char ac ter is tics; B – char ac ter is tic remanence (ChRM) di rec tions; C – di rec tional re sults of the ani so tropy of mag netic sus cep ti bil ity (AMS) of the sec tions in ves ti gated; small sym bols rep re sent spec i men eigenvectors, large sym bols rep re sent mean eigenvectors: K1 = Kmax (long axis), K2 = Kint
(in te ger axis), K3 = Kmin (short axis) (Ap pen dix 1: ta ble 2); other ex pla na tions as in Fig ure 2
The Caours tufa-se quence, north ern France, pro duced a set of U/Th (TIMS) dates of ~120 ka (Antoine et al., 2006) that re late to the base of the Blake Event (123 ±3 ka; Sier et al., 2015). In the Rutten core, the Neth er lands, lu mi nes cence dates of 109 ±6 and 112 ±11 ka are from within the Blake Event (Sier et al., 2015). The iden ti fi ca tion of the Blake Event at these two sites and cor re la tion to find ings in the ma rine core in di cate that NW and cen tral Eu rope en tered inter gla cial en vi ron men tal con - di tions ~5000 years later than south ern Eu rope (Sier et al., 2015).
The pres ent study re veals that the Blake Event in the Netiesos sec tion con sist ing of three short re versed po lar ity in - ter vals sep a rated by two short nor mal po lar ity in ter vals (Fig. 5).
The di rec tional changes are clear. The change of the po lar ity in the Blake Event is re corded in other re gions (e.g., Fang et al., 1997; Osete et al., 2012; Sier et al., 2013; Govin et al., 2015).
How ever, there are re cords of an other post-Blake ex cur sion
age of 104–105 ka (Singer et al., 2014; Govin et al., 2015). It is pos si ble that in the Netiesos sec tion these two (Blake and post-Blake) palaeomagnetic ex cur sions are close to each other due to the small thick ness of de pos its.
As can be seen from the ev i dence de scribed, the palaeomagnetic Blake Event is reg is tered in the Netiesos and SnaigupÅlÅ sec tions in Lith u a nia and in the Zaslavl sec tion in Belarus. In the Netiesos sec tion, it (Blake) oc curred dur ing the MerkinÅ (Eemian) Inter gla cial M3a (Quercus-Ulmus) pol len zone, which is con sis tent with the be gin ning of the cli ma tic op ti - mum of the inter gla cial phase. Dur ing that time, oak and elm for ests spread in the area. In the Zaslavl sec tion, the Blake Event is set in the lower part of the sec tion, in the Zsl-1 lo cal pol - len zone (Carpinus–Tillia), which is cor re lated with the Murava (Eemian) Inter gla cial re gional Mr-6 pol len zone (Karabanov and Yelovicheva, 1997; Karabanov et al., 2017). This is the sec ond part of the cli ma tic op ti mum re flect ing the wide spread oc cur - Fig. 4. Re sults of palaeomagnetic in ves ti ga tions of the Ponemun sec tion
A – li thol ogy and data of palaeomagnetic char ac ter is tics; B – char ac ter is tic remanence (ChRM) di rec tions; C – di rec - tional re sults of the ani so tropy of mag netic sus cep ti bil ity (AMS) of the sec tions in ves ti gated; small sym bols rep re sent spec i men eigenvectors, large sym bols rep re sent mean eigenvectors: K1 = Kmax (long axis), K2 = Kint (in te ger axis), K3 = Kmin (short axis) (Ap pen dix 1: ta ble 3); other ex pla na tions as in Fig ure 2
Vaida eirienÅ et al. / Geo log i cal Quar terly, 2021, 65: 46 7
Fig. 5. Re sults of the palaeomagnetic in ves ti ga tions of the Netiesos sec tion
A – li thol ogy and data of the palaeomagnetic char ac ter is tics: I – pre vi ously in ves ti gated sec tion, II – newly in ves ti gated frag ment of the sec - tion; B – char ac ter is tic remanence (ChRM) di rec tions; C – di rec tional re sults of the ani so tropy of mag netic sus cep ti bil ity (AMS) of the sec - tions in ves ti gated; small sym bols rep re sent spec i men eigenvectors, large sym bols rep re sent mean eigenvectors: K1 = Kmax (long axis), K2 = Kint (in te ger axis), K3 = Kmin (short axis) (Ap pen dix 1: ta ble 4); D – part of the Netiesos sec tion within which the Blake subchron was re corded;
other ex pla na tions as in Fig ure 2
rence of de cid u ous horn beam-lime for ests with ha zel un der - brush and abun dant al der for ests. In the SnaigupÅlÅ sec tion, the Blake Event is linked to the sec ond part of cli ma tic op ti mum of the inter gla cial Corylus–Carpinus–Ulmus pol len zone (Baltrñnas et al., 2015). De spite the sim i lar ity of the pol len suc - ces sion of Lith u a nia and Belarus, their com par i son also re - vealed re gional dif fer ences (Rylova et al., 2020). At the be gin - ning of the inter gla cial, Si be rian spruce (Picea obovata Ledeb.) was sig nif i cantly less com mon in the for ests of Belarus than in Lith u a nia; mean while, elm (Ulmus), oak (Quercus.) and Eu ro - pean ash (Fraxinus ex cel sior L.) were pres ent in Belarus for - ests, which at that time did not yet grow in Lith u a nia. Later, dur - ing the cli ma tic op ti mum, such thermophilous trees as lin den (Tilia) and horn beam (Carpinus) were more wide spread in Belarus for ests, mean while the spruce (Picea) was more nu - mer ous in Lith u a nia. At the end of the inter gla cial, larch (Larix) spread in Belarus, while in Lith u a nia it was ab sent.
The Blake geo mag netic ex cur sion was not iden ti fied in the Zhukevichi and Ponemun sec tions. In the Zhukevichi sec tion, this was pos si bly caused by a hi a tus in the sec tion, as ac cord - ing to pre vi ous in ves ti ga tions 30% of the suc ces sion is free of pol len (Sanko et al., 2002). There fore, the Blake Event may not be re corded by sed i ment. In the Ponemun sec tion, de ter mi na - tion of the ab so lute age of the se quence showed the end of the inter gla cial phase (70/80 – 110 thou sand years), which in di - cates a youn ger age than the Blake Event (Yelovicheva, Zubovich, 2007), and so it was not fixed there. How ever, it can - not be ruled out that the Blake Event may have not been re - corded in these sec tions for other rea sons, such as post-depositional remagnetization, lock-in depth, dat ing bias, etc.
Sier et al. (2015) noted that the Char ac ter is tic Remanent Mag ne ti za tion (ChRM) di rec tions with south ern dec li na tion and pos i tive in cli na tion re ported in the Netiesos sec tion (Baltrñnas et al., 2013) should also be in ter preted as excursional fol low ing the def i ni tions of Merril and McFadden (1994). Thus, it seems that the Blake Event of the Netiesos sec tion in NE Eu rope spans the en tire Eemian, sim i lar to the new re sults for the Eemian in NW Eu rope and those for cen tral Eu rope (Sier et al., 2015). Un for tu nately, the de pos its of the very end of the inter - gla cial are miss ing in the Netiesos sec tion ac cord ing to palaeobotanical data (KondratienÅ, 1996), and the li thol ogy of the sec tion (peat ac cu mu la tion) sug gests a break in sed i men ta - tion. Data from the SnaigupÅlÅ sec tion (Baltrñnas et al., 2015) sup port the sug ges tion that the sed i ments of the Blake Event ac cu mu lated dur ing the cli ma tic op ti mum. How ever, dat ing of the or ganic de pos its of the SnaigupÅlÅ sec tion by the 230Th/U method yielded an age of 127 ±18/14 ka for the L/L tech nique (LUU-833L/L) and 132 ±22/16 ka for the TSD tech nique (LUU-833TSD), which is older than that of the Netiesos sec tion.
There fore, ad di tional in ves ti ga tions are needed to prop erly de - ter mine the age of the base and the top of the Blake Event in the SnaigupÅlÅ sec tion. Mean while, in the Zaslavl sec tion, the Blake Event cov ers the sec ond part of cli ma tic op ti mum, but the low er most part of the inter gla cial is miss ing in the sec tion and a se ries of thermoluminescent dates ob tained by Sanko et al.
(2017) are ques tion able, fluc tu at ing be tween older and youn ger dates.
Cor re la tion be tween the sec tions re veals vary ing com plete - ness of their inter gla cial in ter vals, as well as prob lems in cor re - lat ing lo cal pol len zones with re gional pol len zones, es pe cially with the Eemian Inter gla cial pol len zones es tab lished in West - ern Eu rope. There fore, it would be ben e fi cial to re-ex am ine the meth od ol ogy of cor re la tion of palaeo geo graphi cal his to ries for
cen tral and north ern Eu rope. Cor re la tion be tween the ter res trial re cords and ocean se quences shows that Eemian for ests flour - ished up to MIS 5d in south-west ern Eu rope, while a much shorter du ra tion of Eemian Inter gla cial con di tions in north west - ern Eu rope is in ferred (Kukla et al., 2002).
Ac cord ing to Helmens (2014), MIS 5 is char ac ter ized by three long for ested in ter vals (broadly cor re spond ing to MIS 5e, 5c, 5a) both in tem per ate and north ern bo real Eu rope. These mild pe ri ods were in ter rupted by two short, rel a tively cold and dry in ter vals (MIS 5d and 5b) caused by the gla ci ation in Fennoscandia. The di vi sion be tween the Eemian (MIS 5e) and the Early Weichselian (MIS 5d-a) is not use ful, as it is not rel e - vant from a cli mate point of view (Helmens, 2014). This pre - sump tion is con sis tent with our data from the Netiesos sec tion (Baltrñnas et al., 2013) in di cat ing the rel a tively warm char ac ter of stage 5d and no glacigenic de po si tion up to stage 4. Rel a - tively high tem per a tures were re corded for the Early Weichselian pe riod in the Medininkai sec tion in Lith u a nia (Seiriene et al., 2014) and north ern Fennoscandia (Valiranta et al., 2009). Sim i larly, in ves ti ga tions in North ern Eur asia and the Voka sec tion of the Gulf of Fin land sug gest that inter gla cial cli - ma tic con di tions may have per sisted un til the end of MIS 5a (Molodkov and Bolikhovskaya, 2010, 2011).
CONCLUSIONS
Pre lim i nary palaeomagnetic in ves ti ga tions of five Eemian (Murava, Merkine) Inter gla cial sec tions have dem on strated a con sis tent de tec tion of the Brunhes nor mal mag netic field with a short-term re ver sal – the Blake Event – re corded in three sec - tions: Netiesos, SnaigupÅlÅ, and Zaslavl.
The Blake Event in the Netiesos sec tion is char ac ter ized by a three short re versed po lar ity in ter vals sep a rated by two short nor mal po lar ity in ter vals. ESR dat ing (112.5 ±10.8 ka and 112.1
±25.9 ka) and 230Th/U dates ob tained from this sec tion (108.8
±12.0/9.9 ka for the L/L tech nique and 100.2 ±10.3/8.6 ka for the TSD tech nique) sug gest that two (Blake and post-Blake) palaeomagnetic ex cur sions may be pres ent in this sec tion, in close prox im ity due to a slow ssedimentation rate.
The ab sence of the Blake Event in the re main ing two sec - tions was pos si bly caused by in com plete ness of the inter gla cial sec tions stud ied and a very small strati graphic thick ness (~36–50 cm) formed dur ing this re ver sal.
The com plex ity of in ter re gional cor re la tion of pol len zones of the Eemian Inter gla cial sec tions stud ied and the ra dio genic age dates of the palaeomagnetic Blake Event ob tained from some sec tions sug gest that the Blake Event took place dur ing the cli ma tic op ti mum of Eemian Inter gla cial. Fur ther palaeo - magnetic re search and pre cise dat ing re sults are needed for more pre cise de ter mi na tion of its du ra tion.
Our re search sup ports the in fer ence of a dif fer ent on set and du ra tion of the last inter gla cial in West ern and East ern Eu rope.
The ev i dence sug gests a much shorter du ra tion of Eemian con - di tions in East ern Eu rope than in SW and W Eu rope, al though the stages of for est de vel op ment are sim i lar.
Ac knowl edge ments. We are grate ful for the con struc tive com ments by Laimdota Kalnina and an anon y mous re viewer.
The re search was sup ported by the Re search Coun cil of Lith u - a nia (TAP LB 10/2013) and Belarusian Re pub li can Foun da tion for Fun da men tal Re search (No. X19MC-021). The au thors ex - press sin cere thanks to Dr. V. Kuznetsov and Dr. F. Maksimov (St. Pe ters burg State Uni ver sity) for re sults of 230Th/U dat ing of inter gla cial or ganic de pos its in the Netiesos sec tion.
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