Anna Świerczewska, Zbyszek Paul, Michał Banaś & Antek K. Tokarski

K-Ar DAT ING OF BEN TON ITE DIAGENESIS

IN ACCRETIONARY-WEDGE TURBIDITES:

CASE STUDY FROM WEST ERN OUTER CARPATHIANS

AGH Uni ver sity of Sci ence and Tech nol ogy, Fac ulty of Ge ol ogy, Geo phys ics and En vi ron men tal Pro tec tion, Mickiewicza 30, 30-059 Kraków, Po land; e-mail: swiercze@agh.edu.pl

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Pol ish Geo log i cal In sti tute, Re search and De vel op ment Unit, Carpathian Branch, Skrzatów 1, 31-560 Kraków, Po land; e-mail: zbigniew.paul@pgi.gov.pl

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In sti tute of Geo log i cal Sci ences, Pol ish Acad emy of Sci ences, Re search Cen tre in Kraków, Senacka 1, 31-002 Kraków, Po land; e-mails: ndbanas@cyfronet.krakow.pl, ndtokars@cyf-kr.edu.pl

Œwierczewska, A., Paul, Z., Banaœ, M.& Tokarski, A. K., 2015. K-Ar dat ing of ben ton ite diagenesis in accretionary-wedge turbidites: case study from West ern Outer Carpathians. Annales Societatis Geologorum Poloniae, 85: 177–185. Abstract: Six teen ben ton ite lay ers of Eocene–Oligocene age were sam pled at thir teen sites in accretionary-wedge turbidite se quences, in the three in ner most nappes of the West ern Outer Carpathians. K-Ar dat ing was car ried out for five of these lay ers to ob tain the max i mum burial ages. All of the ages ob tained are older than the strati graphic ages of the host strata. This re la tion ship is due to sig nif i cant con tam i na tion of the bentonites with non-authigenic min er als. This con tam i na tion re sulted from rapid sed i men ta tion dur ing synsedimentary fold ing, which is a com mon fea ture in accretionary wedges. It fol lows that the K-Ar dat ing of ben ton ite lay ers in the turbidite se quences of accretionary wedges should be largely re stricted to the very dis tal fa cies of turbidites or to pelitic in ter ca la tions within the turbidites.

Key words: Bentonites, illite-smectite, K-Ar dat ing, accretionary-wedge turbidites, West ern Outer Carpathians. Manu script re ceived 7 June 2014, ac cepted 7 November 2014

IN TRO DUC TION

The main aim of the pres ent study is the re con struc tion of the de vel op ment of the ther mal struc ture in the Pol ish seg ment of the West ern Outer Carpathians (WOC). This struc ture is fairly well rec og nized from ex ten sive stud ies of illite-smectite claystones (Dudek et al., 2000, 2004; Ko-tarba, 2003, Œwierczewska et al., 2003, 2007a, b; Œwier-czewska 2005). The ther mal struc ture is largely the re sult of fold ing and sub se quent thrust ing (Œwierczewska, 2005). How ever, no at tempt was made to date the max i mum palaeotemperatures which af fected the WOC strata. This pres ents a se ri ous gap in the knowl edge of the ther mal de vel op ment of the WOC and in con se quence, ham pers the un der -stand ing of WOC tec ton ics. There fore, the main ob jec tive of the re search re ported was to close this gap. The re sults of this re search have been only partly suc cess ful, as the au -thors were able to date the max i mum palaeotemperatures for only a few of the sam ples ana lysed (Œwierczewska et al., 2012). In this con tri bu tion, the au thors ex plain the pos si ble rea sons for this fail ure. The Eocene and Oligocene strata were cho sen by the au thors as the ob ject of study for two rea sons. Within the WOC, (1) ben ton ite lay ers are most nu -mer ous in strata of this age range (Wieser, 1985) and (2) the

bentonites that are Eocene and Oligocene in age have been stud ied most ex ten sively (Van Couvering et al., 1981; Wie-ser, 1985 and ref er ences therein; Cieszkowski et al., 2006 and ref er ences therein).

Dur ing the burial of siliciclastic strata, mixed-layer illite-smectite (I-S) forms in the course of pro gres sive smec- tite diagenesis. This trans for ma tion starts at a tem per a ture of about 70–80°C (e.g., Jennings and Thomp son, 1986). The trans for ma tion of smectite to illite is a oneway re ac -tion, in volv ing K en rich ment within the newly formed diagenetic I-S. In claystones, the de gree of trans for ma tion from smectite to illite, ex pressed by % S in IS can be cor re -lated with the max i mum palaeotemperature, which af fected the claystones. There fore, I-S is use ful for dat ing of the ma-ximum burial of siliciclastic strata (e.g., Clauer et al., 1997; Œrodoñ and Clauer, 2001; Œrodoñ et al., 2006b, 2009). How ever, there are some fac tors, which can mo dify the re -la tion ship be tween the de gree of trans for ma tion from smectite to illite, ex pressed by % S in I-S, and the es ti mated palaeotemperature. First of all, the de gree of transfor ma tion from smectite to illite de pends also on the avail abil ity of K in the diagenetic sys tem. For ex am ple, in a

bentonite-claystone se quence, the trans for ma tion from smectite to illite can be more ad vanced in claystone, be cause of a lo cal source of po tas sium (Altaner et al., 1984; Šucha et al., 1993). Fur ther more, a lon ger du ra tion of burial may re sult in the co-ex is tence of diagenetic I-S, which show dif fer ent ages (“mixed ages” of Œrodoñ et al., 2002).

The claystones stud ied for the re con struc tion of the WOC ther mal struc ture con tain K-bear ing min er als, both detrital and authigenic. The oc cur rence of the for mer ex -cludes the claystones from the K-Ar dat ing of diagenesis. There fore, the au thors de cided to use bentonites for the dat -ing. How ever, bentonites also may con tain non-authigenic K-bear ing min er als of both de tri tal and vol ca nic or i gins. The con tam i na tion of bentonites by K-bear ing non-authi-genic min er als, es pe cially by the 2M1 polytype of illite, re

-sults in the ages mea sured be ing a mix ture of pre-diagenetic and diagenetic KAr ages. There fore, only bentonites de -void of non-authigenic K-bear ing min er als are ap pro pri ate for K-Ar dat ing of the max i mum burial.

GEO LOG I CAL SET TING

The Pol ish seg ment of the WOC is com posed of five north-verg ing, root less nappes, from north to south: the Skole, Sub-Silesian, Silesian, Dukla and Magura nappes (Fig. 1). The nappes con sist largely of Lower Cre ta ceous to lower Mio cene flysch se quences. To the north, the WOC are thrust over the Carpathian Foredeep, filled with Neo -gene strata (e.g., Oszczypko, 2006 and ref er ences therein). To the south, the WOC are sep a rated from the In ner Carpathians by the Pieniny Klippen Belt, a nar row zone of ex -treme short en ing and wrench ing (Birkenmajer, 1986; Plašienka and Mikuš, 2010). Al though de bates on sev eral is sues still con tinue, there is broad agree ment that the main tec tonic fea tures of the WOC were formed largely dur ing the Palaeogene–Neo gene, ow ing to the south ward-di rected subduction of the oce anic or suboce anic crust at the south -ern mar gin of the Eu ro pean plate be low the con ti nen tal crust of the ALCAPA (Alps-Carpathian-Pannonian) unit

Fig. 1. Ge ol ogy of study area and lo ca tion of ben ton ite sites sam pled. A. Geo log i cal sketch map of cen tral Eu rope, show ing lo ca tion of area stud ied. B. Pol ish sec tor of the West ern Outer Carpathians (mod i fied af ter ¯ytko et al., 1989, and Œwierczewska, 2005) show ing lo ca -tion of ben ton ite sites sam pled; S – Silesian Nappe sites; D – Dukla Nappe sites; M – Magura Nappe sites. C. Cross-sec -tion through the Carpathians (af ter Oszczypko, 2006, mod i fied); CF – Carpathian Foredeep.

(for re view see: Picha et al., 2005; Fig. 1A). Dur ing those times, the WOC were an orogenic wedge, whereas the Pieniny Klippen Belt acted as a back-stop, in wards of which the Podhale Flysch fore-arc ba sin was lo cated, filled mainly with Oligocene flysch strata (Gedl, 2000).

MA TE RIAL

Bentonites were re ported from nu mer ous sites in the sed i men tary se quences in the Pol ish seg ment of the WOC (Cieszkowski et al., 2006 and ref er ences therein). They oc -cur in all five nappes, ex clu sively in thin-bed ded turbidites or hemipelagic claystones (Wieser, 1985; cf. Œl¹czka et al., 2005). In the pres ent ac count, the au thors use the term “ben -ton ite” in a gen eral sense. It de notes a rock, which shows the fol low ing fea tures: (1) it is very fine-grained, (2) it is noncar bon ate rock, and (3) it is very light in col our, strik -ingly dif fer ent from the host strata. More over, some of the stud ied “bentonites” swell in wa ter.

When choos ing sam pling sites, the au thors were restric- ted by two fac tors. One was the oc cur rence of ben ton ite lay -ers within the strata, which had been sub jected to a palaeo-tem per a ture of more than 100°C. The re sults of pre vi ous studies of the Carpathian bentonites (Šucha et al., 1993; cf. Cieszkowski et al., 2006) showed that such a tem per a ture is

nec es sary for the ini ti a tion of the trans for ma tion of smectite to illite in bentonites. It fol lows, that only strata af fected by tem per a tures of more than 100°C may con tain bentonites with diagenetic IS, ap pro pri ate for KAr dat ing of the max -i mum palaeotemperature af fect -ing the strata. Fol low -ing th-is re quire ment, the au thors de cided to leave out the Skole and Subsilesian nappes (cf. Œwierczewska, 2005) and re strict the sam pling to par tic u lar parts of the Silesian, Dukla and Magura nappes (Fig. 1, Tab. 1). Sec ondly, the au thors were re stricted by the quan tity of ma te rial nec es sary for all pro -jected lab o ra tory stud ies. There fore, thick and con tin u ous bento nite lay ers were sam pled.

Ac cord ing to Wieser (1985), in the Eocene and Oligo-cene strata of the nappes stud ied, ben ton ite lay ers oc cur at sev eral isochronous lev els. There are six such lev els in the Magura Nappe, three lev els in the Dukla Nappe and five lev els in the Silesian Nappe. The sam pling was most wide -spread in the Magura Nappe, where the Eocene Beloveža and Zembrzyce beds were sam pled in the west ern part of the nappe, and the Eocene Beloveža Beds were sam pled in the cen tral part of the nappe. In the Dukla Nappe, only the Oli-gocene Cergowa Beds ex posed in two tec tonic win dows were sam pled, whereas within the Silesian Nappe, the sam -pling was re stricted to the Oligocene Krosno Beds and the tran si tional beds be tween the Menilite and Krosno beds in the east ern most seg ment of the nappe. All sam ples were

co-Fig. 2. Typ i cal ex po sures of ben ton ite lay ers (ar rowed). A. Ben ton ite layer in the Cergowa Beds, site D1 (ham mer is 32 cm long). B. Ben ton ite lenses in the Zembrzyce Beds, close to sites M3 and M4. C. Ben ton ite layer in the Beloveža Beds, site M1 (note gradational up -ward tran si tion of ben ton ite into claystone). D. Ben ton ite lay ers in the Beloveža Beds, close to sites M1 and M2).

llected in mudstone/claystone se quences within thin- and me dium-bed ded turbidites (Fig. 2).

The sam ples dis cussed were col lected at thir teen sites: five in the Magura Nappe, two in the Dukla Nappe and six sites in the Silesian Nappe (Fig. 1, Tab. 1). Fiveteen ben ton -ite lay ers were sam pled al to gether. These lay ers ranged from 1 cm to more than 1 m thick, but lay ers 10 to 15 cm thick were the most com mon. Most of the ben ton ite lay ers pinch and swell along the strike (Fig. 2A). Most of these lay ers are also bed ding-par al lel, but some dis play a wavy ap pear ance (Fig. 2B). The ben ton ite lay ers are easy to dis tin guish, for they show a dis tinct col our dif fer ence, com -pared to the host strata (Fig. 2). Those in the Magura and Dukla nappes are creamy, light grey and light ol ive, whereas those within the Silesian Nappe show a light blu ish col our. All ben ton ite lay ers sam pled dis play sharp bot tom sur -faces. The top sur faces of these lay ers are ei ther sharp (Fig. 2A, B) or gradational into claystone (Fig. 2C). The bento -nites ob served at sites M2 and M4 swell in wa ter. In the

layer ex posed at site M2, three sam ples were col lected, whereas only sin gle sam ples were taken from all of the other ben ton ite lay ers. Al to gether, seventeen ben ton ite sam -ples were col lected.

At one of the sites sam pled (M3), the fis sion-track age had been de ter mined for zir cons (Van Couvering et al., 1981) and at an other site (S6) the pe trog ra phy of the ben -ton ite had been stud ied (Koszarski et al., 1960).

METH ODS

The clay frac tion (<0.2 µm) was sep a rated from all of the bentonites sam pled and from the claystones, as so ci ated with the ben ton ite lay ers, sam pled at sites M1, M2, M7, D2, as well as from claystones ex posed close (<200 m) to sites S1–S6 (Fig. 1, Tab. 1), us ing the pro ce dure of Jack son (1975). Fol low ing this pro ce dure, the Na-ex changed form of the mixed-layer min er als was ob tained. For 17 ben ton ite

M1 Glinka Bystrica Thrust Sheet

PA-457/T1

49°27.464' 19°13.591' Beloveža Beds Eocene 1 to 3 bulk

PA-457/1/T1 3 bulk

M2 Glinka Bystrica Thrust Sheet

PA-458/U

49°27.423' 19°13.170' Beloveža Beds Eocene 10 to 15

upper

PA-458/L lower

PA-458/C bulk

M3 Cisiec Raèa Thrust Sheet PA-459/T 49°34.118' 19°06.146' Zembrzyce Beds Eocene 1 bulk M4 Cisiec Raèa Thrust Sheet PA-459/1 49°34.168' 19°06.198' Zembrzyce Beds Eocene >100 middle M7 Zbludza Bystrica Thrust

Sheet PA-452/T 49°35.081' 20°21.387' Beloveža Beds Eocene 5 bulk Dukla Nappe

D1 Rzeka Bia³a Grybów Sub-Nappe

PA-465/B

49°37.157' 20°56.786' Cergowa Beds Oligocene 10 bulk

PA-465/1 15 bulk

D2 Grybów-Czerwony Potok

Grybów

Sub-Nappe PA-466/B 49°36.534' 20°56.119' Cergowa Beds Oligocene 10 bulk Silesian Nappe

S1 Rabe

Central Carpathian Depression

PA-479 49°18.928' 22°15.959' Krosno Beds Oligocene 5 bulk S2 Wetlina Fore Dukla Unit PA-477 49°09.755' 22°27.505' transitional beds* Oligocene 15 bulk S3 Nasiczne

Central Carpathian Depression

PA-474 49°09.202' 22°34.543' Krosno Beds Oligocene 40 bulk

S4 Chmiel

Central Carpathian Depression

PA-475 49°13.674' 22°35.043' Krosno Beds Oligocene 5 bulk

S5 Zatwarnica

Central Carpathian Depression

PA-476 49°14.160' 22°33.684' Krosno Beds Oligocene 10 bulk S6 Berechy Górne Fore Dukla Unit PA-473 49°08.275' 22°34.288' transitional beds* Oligocene 10 bulk * – “tran si tional beds” re fer to tran si tional strata be tween the Menilite and Krosno beds (cf. Œl¹czka, 1993)

sam ples, three grain-size frac tions (<0.02, 0.02–0.05 and 0.05–0.2 µm) were sep a rated by high-speed centrifugation. Ori ented airdry and glycoled prep a ra tions of the clay frac -tion were an a lyzed by X-ray dif frac -tion (XRD), us ing a Phi- llips diffractometer, equipped with a Cu tube and a graph ite mono chro ma tor, and an ARL X’TRA diffractometer, equipped with a Si(Li) solidstate de tec tor. To iden tify the min -eral com po si tion of bentonites 11 bulk rock sam ples (Fig. 3; Tab. 2) were also an a lyzed by XRD.

The de gree of trans for ma tion of smectite to illite, ex-pressed as the per cent age of smectite in the mixed-layer illite-smectite (% S), was de ter mined on the ba sis of the me- asurement of the po si tion of the di ag nos tic re flec tions in the glycolated sam ples. Re flec tions in the range 5–8, 15–17 and 33–35°2Q were used (Œrodoñ, 1980, 1981, 1984; Dudek and Œrodoñ, 1996). The max i mum palaeotemperatures were cal cu lated, us ing the de gree of trans for ma tion of smectite to illite in the claystones (Šucha et al., 1993). The cor rec tion of 10°C, sug gested by Clauer et al. (1997), was im ple -mented. Fol low ing Clauer et al. (1997) and Œrodoñ et al. (2002), the K-Ar dat ing of the ben ton ite clay frac tion was car ried out for three clay frac tions (<0.02, 0.02–0.05 and 0.05–0.2 µm) of five sam ples (Tab. 3), iden ti fied by XRD as be ing the most pure among the 17 ana lysed. A Sherwood Model 420 flame pho tom e ter was used for the de ter mi na -tion of the K2O con tent in all of the ben ton ite sam ples stud

ied. The fol low ing stan dards were used: 76a Burnt Re frac -tory NIST Stan dard Ref er ence (1.33% K2O) and 70a Po tas

-sium Feld spar NIST Stan dard Ref er ence Ma te rial (11.80%

K2O). The au thors used the Ar mea sure ment tech niques,

described by Œrodoñ et al. (2006a).

Most anal y ses were per formed in the lab o ra to ries of the In sti tute of Geo log i cal Sci ences, Pol ish Acad emy of Sci -ences, Kraków. Only bulk rock XRD anal y ses were done in the lab o ra tory of the Fac ulty of Ge ol ogy, Geo phys ics and En -vi ron ment, AGH Uni ver sity of Sci ences and Tech nol ogy, Kraków.

Fig. 3. Rep re sen ta tive ran dom XRD pat terns of wholerock ben -ton ite sam ples from the Magura (PA-457/T1, PA-459/T), Dukla (PA-465/1) and Silesian (PA-473) nappes. Q – quartz, Ch – chlorite, I-S – illite-smectite, I – illite, Mu – mus co vite, 2M1 polytype of illite, Pl – al bite, C – cal cite, D – do lo mite, K – kaolinite.

Ta ble 2 % S mea sure ments and or der ing (R) in I/S ob tained from shales and bentonites, and min eral com po si tion of bentonites

Site

Claystone Bentonite

% S in I/S Sample % S in I/S R other minerals in fraction <0.2 µm

other minerals identified in bulk rock Magura Nappe

M1 Glinka 28 PA-457/T1 22 R>1 I/S, I, Ch Q, C, Pl, Ch, I, 2M1, I/S PA-457/1/T1 20 I/S, I, Ch

M2 Glinka 30 PA-458/L 24 R1/ R>1 I/S, I, Ch Q, C, Pl, Ch, I, 2M1, I/S M3 Cisiec 35–70* PA-459/T 40 R0 I/S, I, K, Q Q, C, Pl, I, 2M1, I/S, K M4 Cisiec 35–70* PA-459/1 70 R0 I/S, I (tr), Q (tr),

M7 Zbludza 18 PA-452/T 20 R>1 I/S, I, Ch

Dukla Nappe

D1 Rzeka Bia³a 22 PA-465/B 20 R>1 I/S, I, Ch

PA-465/1 22 R>1 I/S, I, Ch Q, Pl C, D,Ch, I, 2M1, I/S D2 Grybów-Czerwony

Potok 12 PA-466/B 20 R>1 I/S, I, Ch?, K(?) Q, Pl, Ch, I, 2M1, I/S Silesian Nappe

S1 Rabe 21 PA-479 19 R1/R>1 I/S, I, Ch, Q (tr) Q, C, Ch, 2M1, Pl, I/S

S2 Wetlina 26 PA-477 23 R1 I/S, I, Ch Q, Pl, F, 2M1, D

S3 Nasiczne 23 PA-474 12 R>1 I/S, I, Ch, Q (tr) Q, C, D, Ch, I, 2M1, I/S S4 Chmiel 35 PA-475 32 R0/R1 I/S, I, Ch(tr), K Q, C, D(tr), 2M1, Pl, Py(tr), I/S S5 Zatwarnica 23 PA-476 33 R0/R1 I/S, I, Ch(tr), K Q, C, Ch, D(tr), 2M1 S6 Berechy Górne 26 PA-473 16 R1/R>1 I/S, I, Ch, Q (tr) Q, C, D, Ch, I, 2M1, I/S * – based on Œwierczewska (2005); Q – quartz, Ch – chlorite, I-S – illite-smectite, I – illite, Mu – mus co vite, 2M1 polytype of illite, Pl – al bite, C – cal cite, D – do lo mite, K – kaolinite.

RE SULTS

The bulk-rock ben ton ite sam ples con tain sig nif i cant amounts of nonclay min er als (Tab. 2; Fig. 3). Quartz oc -curs in all sam ples. Al bite is com mon, while car bon ates, mostly in the form of cal cite, oc cur in most sam ples. Only two sam ples, col lected at sites D2 and S2, are de void of cal -cite. Do lo mite was iden ti fied in six sam ples. Illite and I-S were ob served in all sam ples, whereas kaolinite was iden ti -fied in only one sam ple (site M3). The 2M1 polytype of illite

was iden ti fied in all sam ples, on the ba sis of its char ac ter is -tic re flec tions in the 19–35°2Q range (Moore and Reynolds, 1997). Chlorite is com mon in all ben ton ite sam ples, ex cept for those col lected at sites M3 and M4.

The min eral com po si tion of the clay frac tion <0.2 µm is very sim i lar in all ben ton ite sam ples stud ied (Fig.4; Tab. 2). I-S and dis crete illite oc cur in all sam ples, whereas kaolinite was ob served only in four sam ples (sam pling sites M3, D2, S4 and S5) and traces of quartz were noted in five sam ples. Chlorite is com mon in all ben ton ite sam ples, ex cept for those col lected at sites M3 and M4.

The XRD anal y sis re sults of I-S com po si tion in the claystones and bentonites are sum ma rized in Ta ble 2. The Oligocene claystones, sam pled in the east ern most seg ment of the Silesian Nappe, con tain I-S with 21–35% S, whereas the com po si tion of I-S in bentonites var ies there from 12 to 33% S. The Dukla Nappe Oligocene claystones were sam -pled in two tec tonic win dows. The sam ple from the Grybów Tec tonic Win dow con tains I-S with 12% S, whereas in the Kru¿lowa Tec tonic Win dow the smectite con tent in I-S is 22%. The Eocene claystones sam pled in the west ern seg -ment of the Magura Nappe (sites M1 and M2) con tain I-S with 28–30% S. On the other hand, in the same parts of this

nappe, in the vi cin ity of sites M3 and M4 these claystones show 35–70% S in I-S (Œwierczewska, 2005). The Eocene claystone sam pled in the cen tral seg ment of the Magura Nappe (site M5) con tain I-S with 18% S.

The com po si tion of IS in most of the bentonites sam -pled is largely sim i lar to that of I-S in the as so ci ated clay-stones. The only ex cep tion is the ben ton ite layer, more than 100 cm thick, sam pled at site M4. The lat ter ben ton ite shows a sig nif i cantly lower de gree of trans for ma tion from smectite to illite (70% S) than the de gree of this trans for ma -tion in a ben ton ite layer, 1 cm thick, sam pled at site M3 (40% S), 200 m from site M4.

K-Ar DAT ING RE SULTS

Five Eocene and Oligocene ben ton ite sam ples, two from the Dukla Nappe and three from the Magura Nappe, were se lected for KAr dat ing (Tab. 3). The dat ing was per formed for the bentonites with the clay frac tion, least con -tam i nated by de tri tal min er als. The larg est con -tam i na tion oc curs in the ben ton ite sam ples from the Silesian Nappe and, there fore, these bentonites were ex cluded from the K-Ar dat ing.

The K-Ar ages ob tained for par tic u lar frac tions of the ben ton ite sam ples dis cussed show sig nif i cant scat ter. The ages of the Oligocene bentonites range from 50.6 to 74.4 Ma, while those of the Eocene bentonites vary from 60.2 to 102.9 Ma. In four ben ton ite sam ples, the fin est frac tion shows the youn gest age and the coars est frac tion dis plays the old est age. In three sam ples (PA-457/T1, PA-458/L, PA-465/1), the K-Ar ages in crease sys tem at i cally with coarsening of the grain size.

PA-457/T1 < 0.02 5.53 58.4 491.1 60.7 1.1 34–38 Eocene (Priabonian) 0.02–0.05 5.55 49.9 573.3 70.4 0.9 0.05–0.2 5.47 40.7 634.8 78.9 2.9 PA-458/L < 0.02 5.41 50.2 476.8 60.2 1.2 37–50 Eocene (Ypresian-Priabonian)* 0.02–0.05 5.4 28.6 523.4 66.1 2.4 0.05–0.2 5.42 67.5 588.9 74 0.8 PA-459/1 < 0.02 2.70 71.7 373.2 93.6 1.6 34–38 Eocene (Priabonian) 0.02–0.05 2.88 59.4 352.7 83.1 3.0 0.05–0.2 3.66 68.6 557.6 102.9 1.7 Dukla Nappe PA-465/1 < 0.02 5.88 54.0 478.3 55.6 0.8 24–30 Oligocene NP24** and NP25** 0.02–0.05 5.95 65.5 516.0 59.3 0.8 0.05–0.2 5.96 70.4 651.3 74.4 0.7 PA-466/B < 0.02 6.61 60.6 488.4 50.6 0.6 24–30 Oligocene NP24** and NP25** 0.02–0.05 6.64 78.2 640.9 65.8 0.7 0.05–0.2 6.78 75.6 588.7 59.3 0.5

DIS CUS SION

The I-S com po si tion of the claystone beds as so ci ated with the bentonites stud ied in di cates that the max i mum palaeotemperatures, which af fected the bentonites, were 110 to 170°C. These tem per a tures in volved a con sid er able de gree of smectite-to-illite I-S trans for ma tion (12–70% S) in all of the sam pled bentonites (Tab. 2). Such a de gree of trans -for ma tion is suf fi cient -for the K-Ar dat ing of ben ton ite dia-gen e sis. How ever, all K-Ar ages ob tained are older than the strati graphic ages of the cor re spond ing host strata (Tab. 3). The au thors be lieve that this re la tion ship has re sulted from the ma jor con tam i na tion of the bentonites ana lysed by non-diagenetic min er als. Such con tam i na tion is ev i dent in the results of the XRD ben ton ite bulk-rock anal y ses and in some XRD clayfrac tion anal y ses (Fig. 3; Tab. 2). More -over, the con tam i na tion of the WOC bentonites by non-diagenetic min er als was al ready re ported (Koszarski et al., 1960; Van Couvering et al., 1981; Cieszkowski et al., 2001). Nev er the less, it ap peared pos si ble that the con tam i -na tion was largely re stricted to the coarser frac tions of the bentonites (cf. Cieszkowski et al., 2001).

In all ben ton ite sam ples an a lyzed, the age of the 0.05– 0.2 µm frac tion is much older (10–20 Ma) than that of the frac tion <0.02 µm (Tab. 3). This re la tion ship shows that a de ple tion in some Kbear ing de tri tal min er als took place sys -tem at i cally, with re spect to the de crease in grain size. This can be re lated to the re moval of mica flakes, the oc cur rence of which was also re ported in bentonites from the Silesian and Magura nappes (Koszarski et al., 1960; Leszczyñski and Malata, 2002). Nev er the less, the K-Ar ages ob tained show that not all of the Kbear ing nonauthigenic min er als were re moved dur ing sep a ra tion of the clay frac tion from the sam ples dated. It ap pears, there fore, that the ages ob tained are in flu enced by the pres ence of dis crete de tri tal illite. It is pos si ble that in some bentonites an a lyzed, small amounts of dis -crete illite may be a prod uct of the diage netic al ter ation of kaolinite. The illitization of kaolinite may oc cur par al lel to the illitization of smectite (cf. Œrodoñ et al., 2009). In sum -mary, the au thors be lieve that not all of the bentonites stud ied were suit able for K-Ar diagenetic dat ing, be cause they are con sid er ably con tam i nated by non-diagenetic min er als.

Not all of the WOC bentonites are con tam i nated by non-diagenetic min er als. Non-con tam i nated bentonites were re-ported from the Eocene strata of the sub-Silesian Nappe (Cieszkowski et al., 2006; Fig. 1). Un for tu nately, these bento nites are not suit able for the KAr dat ing of diagenesis, be -cause they show an in suf fi cient de gree of smectite-to-illite trans for ma tion in I-S. These bentonites oc cur ei ther in the very dis tal fa cies of turbidites or in the pelitic in ter ca la tions within the turbidites. The re la tion ship be tween the oc cur rence of non-con tam i nated vs. con tam i nated bentonites and the type of host strata was de scribed from the Cam pos Ba sin (off shore Brazil) by Caddah et al. (1998). In that area, the con tam i nated bentonites are as so ci ated with turbidites, whereas noncon tam -i nated ones oc cur -in pel-it-ic se quences. It fol lows that w-ith-in turbidite se quences, the bentonites oc cur ring in pelitic in ter ca -la tions or in the more dis tal turbidite fa cies are po ten tially more suit able for the KAr dat ing of diagenesis than those oc -cur ring in the more prox i mal turbidite fa cies.

Nu mer ous ben ton ite lay ers oc cur within the Oligocene flysch se quence, fill ing the forearc Podhale Flysch Ba sin (Fig. 1). The bentonites mostly are not con tam i nated by non-authigenic min er als (Œrodoñ et al., 2006b). Unfortuna-tely, the de tailed sedimentological set ting of the bentonites is not known. The au thors be lieve that dif fer ence in the de -gree of con tam i na tion be tween the WOC bentonites and the Podhale Flysch Ba sin bentonites re sults from dif fer ent tec tonic pro cesses, ac tive in the re spec tive re gions dur ing sed i men ta tion of the ben ton itebear ing strata. This dif fer en ti a -tion is, in turn, due to the very dif fer ent tec tonic set tings of the two re gions.

Dur ing the Eocene–Oligocene, the WOC were an ac -tive accretionary wedge, the for ma tion of which in volved a ma jor in crease in the rate of de po si tion (Poprawa et al., 2006) and the on set of synsedimentary fold ing (Œwierczewska and Tokarski, 1998). This fold ing as well as the co -eval and sub se quent thrust ing re sulted in the for ma tion of the WOC thrust-and-fold belt (Fig. 1C). In con trast, dur ing Oligocene times, the Podhale Flysch Ba sin was a fore-arc ba sin, in which sed i men ta tion was con trolled largely by sea- level changes (Starek et al., 2013). The Oligocene flysch se -quence fill ing the ba sin was de formed into open folds. The fold ing largely post-dated the flysch de po si tion

(Ludwi-Fig. 4. Rep re sen ta tive XRD pat terns of clay frac tion of bento-nites (Q – quartz, Ch – chlorite, I-S – illite-smectite, I – illite, ar – ox a late crys tal lized dur ing the sep a ra tion of clay frac tion). A. XRD pat terns of pow dered and un-ori ented clay frac tion of bento-nites from sites M4 (PA-459/1) and S6 (PA-473). B. XRD pat terns of ori ented eth yl ene-gly col-sat u rated <0.2 µm clay frac tions of bentonites from sites M1 (PA-457/T1) and M4 (PA-459/1).

seg ment of the WOC. The most im por tant is the dis cov ery of sev eral ben ton ite lay ers in the east ern most part of the Silesian Nappe (Fig. 2, Tab. 1), in which up to now only a sin gle oc cur rence of these rocks was re ported.

CON CLU SIONS

The K-Ar diagenesis dat ing of WOC bentonites should be re stricted to the bentonites af fected by palaeotempera-tures of more than 100°C.

Bentonites in the Eocene–Oligocene turbidite sequen-ces in the WOC accretionary wedge mostly are contamina-ted by non-diagenetic K-bear ing min er als and there fore are largely un suit able for the K-Ar dat ing of diagenesis. The K-Ar dat ing of bentonites in the turbidite se quences of accretionary wedges should be largely re stricted to the ex -treme dis tal fa cies of turbidites or to pelitic in ter ca la tions within the turbidites.

The de gree of con tam i na tion of bentonites by non-dia-ge netic min er als may de pend on the tec tonic set ting of the ben ton ite-bear ing bas ins.

The dis cov ery of sev eral ben ton ite lay ers in a part of the Silesian Nappe, in which only a sin gle oc cur rence of such rocks had been re ported up to now, rep re sents a sig nif i cant ad di tion to the in ven tory of bentonites within the Pol ish segment of the West ern Outer Carpathians.

Ac knowl edge ments

This re search was sup ported by the Min is try of Sci ence and Higher Ed u ca tion (Grant No. NN307 057434). The bulk-rock XRD anal y ses were funded by AGH Stat u tory Grant 11.11.140. 322. Many thanks are due to Marek Wendorff (AGH) for im prov -ing the Eng lish of the manu script. We wish to thank Dušan Pla-šienka and Jan Œrodoñ for con struc tive re views.

REF ER ENCES

Altaner, S. P., Hower, J., Whit ney, G. & Aronson, J. L., 1984. Model for K ben ton ite for ma tion: ev i dence from zoned K-bentonites in the dis turbed belt, Montana. Ge ol ogy, 12: 412– 415.

Birkenmajer, K., 1986. Stages of struc tural evo lu tion of the Pie-niny Klippen Belt, Carpathians. Studia Geologica Polonica, 88: 7–32.

Caddah, L. F. G., Alves, D. B. & Mizusaki, A. M. P., 1998. Turbidites as so ci ated with bentonites in the Up per Cre ta ceous of the Cam pos Ba sin, off shore Brazil. Sed i men tary Ge ol ogy, 115: 175–184.

Cieszkowski, M., Œrodoñ, J., Waœkowska-Oliwa, A. & Leœniak, T., 2006. Bentonitized tuffites in the lower Eocene de pos its of the Subsilesian unit (West ern Outer Carpathians, Po land): Li

-of illite fun da men tal par ti cles sep a rated from illite-smectite. Clay Min er als, 32: 181–196.

Dudek, T., Rauch, M. & Œwierczewska, A., 2004. Illite-smectite as an in di ca tor of tem per a tures in the east ern part of the Silesian nappe (Outer Carpathians). Pol ish Min er al og i cal So -ci ety, Spe -cial Pa pers, 24: 145–148.

Dudek, T. & Œrodoñ, J., 1996. Iden ti fi ca tion of illite/smectite by X-ray pow der dif frac tion tak ing into ac count the lognormal dis tri bu tion of crys tal thick ness. Geologica Carpathica, Se -ries Clays, 5: 21–32.

Dudek, T., Œwierczewska, A., Zuchiewicz, W. & Ozimkowski, W., 2000. Paleotemperatures in the Skole nappe (Outer Car-pathians) in ferred from diagenetic evo lu tion of illite/smectite; the pi lot re sults. Mineralia Slovaca, 32: 303–304.

Gedl, P., 2000. Podhale biostratigraphy and palaeoenvironment of the Podhale Palaeogene (In ner Carpathians, Po land) in the light of palynological stud ies. Part II. Sum mary and sys tem -atic de scrip tions. Studia Geologica Polonica, 117: 155–303. Jack son, M. L., 1975. Soil Chemical Analysis – Ad vanced Course.

2nd ed., Uni ver sity of Wis con sin, Mad i son, USA, 895 pp. Jennings, S. & Thomp son, G. R., 1986. Diagenesis of Plio–Pleis

to cene sed i ments of the Col o rado River Delta, South ern Cal i -for nia. Jour nal of Sed i men tary Pe trol ogy, 56: 89–98. Koszarski, L., Wieser, T. & ¯ytko, K., 1960. The tuffites from the

Krosno beds at Berechy Górne in the Bieszczady Moun tains (Mid dle Carpathians). Kwartalnik Geologiczny, 4: 495–509. [In Pol ish, with Eng lish sum mary.]

Kotarba, M., 2003. Historia diagenezy illitu/smektytu w ska³ach ilastych Karpat Zachodnich (przekrój Kraków–Zakopane). Un pub lished Ph.D. The sis. In sti tute of Geo log i cal Sci ence, Pol ish Acad emy of Sci ences, Kraków, 198 pp. [In Pol ish.] Leszczyñski, S. & Malata, E., 2002. Sed i men tary con di tions in the

Siary Zone of the Magura Ba sin (Carpathians) in the late Eocene–early Oligocene. Annales Societatis Geologorum Poloniae, 72: 201–239.

Ludwiniak, M., 2010. Multistage de vel op ment of the joint net -work in the flysch rocks of west ern Podhale (In ner West ern Carpathians, Po land). Acta Geologica Polonica, 60: 283–316. Moore, D. & Reynolds, R. C. Jr., 1997. X-Ray Dif frac tion and the Iden ti fi ca tion and Anal y sis of Clay Min er als, 2nd Edi tion. Ox ford Uni ver sity Press, New York, 378 pp.

Oszczypko, N., 2006. Late Ju ras sic–Mio cene evo lu tion of the Outer Carpathian fold-and-thrust belt and its foredeep ba sin (West ern Carpathians, Po land). Geo log i cal Quar terly, 50: 169–194.

Oszczypko-Clowes, M. & Œl¹czka, A., 2006. Nannofossil bio-stra tig ra phy of the Oligocene de pos its in the Grybów tec tonic win dow (Grybów Unit, West ern Carpathians, Po land). Geo-logica Carpathica, 57: 473–482.

Picha, F., Stranik, Z. & Krejèi, O., 2005. Ge ol ogy and hy dro car -bon re sources of the Outer West ern Carpathians and their fore land, Czech Re pub lic. In: Golonka, J. & Picha, J. (eds), The Carpathians and their fore land. Ge ol ogy and hy dro car bon re sources. Amer i can As so ci a tion of Pe tro leum Ge ol o -gists, Mem oir, 84: 49–175.

Plašienka, D. & Mikuš, V., 2010. Geo log i cal set tings of the Pie-niny and Šariš sec tors of the Klippen Belt be tween Litmanová

and Drienica vil lages in east ern Slovakia. Mineralia Slovaca, 42: 155–178. [In Slo vak, with Eng lish sum mary.]

Poprawa, P., Malata, T., Oszczypko, N., S³omka, T., Golonka, J. & Krobicki, M., 2006. Tec tonic ac tiv ity of sed i ment source ar eas for the West ern Carpathian bas ins – con strains from anal y sis of sed i ment de po si tion rate. Przegl¹d Geologiczny, 54: 878–887. [In Pol ish, with Eng lish sum mary.]

Œl¹czka, A., 1993. The Ge ol ogy of the Ex ter nal Carpathians: the clas sic lo cal i ties re vis ited. In: Kaminski, M. A., Geroch, S. & Kaminski, D. G. (eds.), The Or i gins of Ap plied Micropa-laeontoloogy: The School of Józef Grzybowski. Grzybowski Foun da tion Spe cial Pub li ca tion no. 1, Alden Press, pp. 225– 237.

Œl¹czka, A., Kruglov, S., Golonka, J., Oszczypko, N. & Popadyuk, I., 2005. Ge ol ogy and hy dro car bon re sources of the Outer Carpathians, Po land, Slovakia and Ukraine: Gen eral ge ol ogy. In: Golonka, J. & Picha, J. (eds), The Carpathians and their fore land: Ge ol ogy and hy dro car bon re sources. Amer i can As -so ci a tion of Pe tro leum Ge ol o gists, Mem oir, 84: 221–258. Œrodoñ, J., 1980. Pre cise iden ti fi ca tion of illite/smectite

interstratifications by Xray pow der dif frac tion. Clays and Clay Min -er als, 28: 401–411.

Œrodoñ, J., 1981. X-ray iden ti fi ca tion of ran domly interstratified illite/smectite in mix tures with dis crete illite. Clay Min er als, 16: 297–304.

Œrodoñ, J., 1984. X-ray pow der dif frac tion iden ti fi ca tion of illitic ma te ri als. Clays and Clay Min er als, 32: 337–349.

Œrodoñ, J. & Clauer, N., 2001. Diagenetic his tory of Lower Pala-eozoic sed i ments in Pomerania (north ern Po land), traced across the Teisseyre-Tornquist tec tonic zone us ing mixed-layer illite-smectite, Clay Min er als, 36: 15–27.

Œrodoñ, J., Clauer, N., Banaœ, M. & Wójtowicz, A., 2006a. K-Ar ev i dence of a Me so zoic ther mal event over-print ing burial diagenesis of the Car bon if er ous Up per Silesia Coal Ba sin. Clay Min er als, 41: 669–690.

Œrodoñ, J., Clauer, N. & Eberl, D. D., 2002. In ter pre ta tion of K-Ar dates of illitic clays from sed i men tary rocks aided by mod el -ling. Amer i can Min er al o gist, 87: 1528–1535.

Œrodoñ, J., Clauer, N., Huff, W., Dudek, T. & Banaœ, M., 2009. K-Ar dat ing of Or do vi cian bentonites from the Bal tic Ba sin and the Bal tic Shield: im pli ca tions for the role of tem per a ture and time in the illitization of smectite. Clay Min er als, 44: 361–387.

Œrodoñ, J., Kotarba, M., Biron, A., Šucha, V., Clauer, N. & Wój-towicz, A., 2006b. Diagenetic his tory of the Podhale-Orava Ba sin and the un der ly ing Tatra sed i men tary struc tural units (West ern Carpathians): ev i dence from XRD and K-Ar of illite-smectite. Clay Min er als, 41: 751–774.

Starek, D., Soták, J., Jablonský, J. & Marschalko, R., 2013. Large-vol ume grav ity flow de pos its in the Cen tral Carpathian Pale-ogene Ba sin (Orava re gion, Slovakia): ev i dence for hy per-pycnal river dis charge in deep-sea fans. Geologica

Carpa-thica, 64: 305–326.

Šucha, V., Kraus, I., Gerthofferová, H., Peteš, J. & Sereková, M., 1993. Smectite to illite con ver sion in bentonites and shales of the East Slo vak Ba sin. Clay Min er als, 28: 243–253.

Œwierczewska, A., 2005. The in ter play of ther mal and struc tural his to ries of the Magura Nappe (Outer Carpathians) in Po land and Slovakia. Mineralogia Polonica, 36: 91–144.

Œwierczewska, A., Dudek, T., Œrodoñ, J. & Malata, T., 2003. Zapis historii tektonicznej p³aszczowiny skolskiej w diage-nezie minera³ów ilastych. In: Chudzikiewicz, L. & Œwier-czewska, A. (eds), VI Karpackie Warsztaty Tektoniczne, Sesja Zimowa, Kraków 28.02–1.03.2003. Galicia Tec tonic Group, Instytut Nauk Geologicznych PAN, Kraków, pp. 37–39. [In Pol ish.]

Œwierczewska, A. & Tokarski, A. K., 1998. De for ma tion bands and the his tory of fold ing in the Magura Nappe, West ern Outer Carpathians (Po land). Tectonophysics, 297: 73–90. Œwierczewska, A., Tokarski, A. K., Dudek-Wing, T., Hurai, V. &

Rauch, M., 2007a. Ther mal struc ture of the Outer Carpathians (Po land, Slovakia and Ukraine) based on illite-smectite geo-ther mom e ter. In: Venera, Z. (ed.), CzechTec 07, April 11–14, 2007, Tepla, Czech Re pub lic, Pro ceed ings and Ex cur sion Guide. Czech Geo log i cal Sur vey, Prague, pp. 85–87. Œwierczewska, A., Tokarski, A. K., Dudek-Wing, T., Rauch, M. &

Hurai, V., 2007b. The ther mal struc ture of the Pol ish and Slo -vak seg ments of the Outer Carpathians based on the illite-smectite geothermometer. Przegl¹d Geologiczny, 55: 307. [In Pol ish.]

Œwierczewska, A., Tokarski, A. K. & Paul, Z., 2012. An at tempt at chronostraigraphic and burial dat ing of bentonites within the Cre ta ceous/Paleogene se quence in the Outer Carpathians (Po -land). Mineralia Slovaka, 44: 107.

Van Couvering, J. A., Aubry, M.-P., Berggren, W. A., Bujak, J. P., Naeser, C. W. & Wieser, T., 1981. The Terminal Eocene Event and the Pol ish con nec tion. Palaeo ge ogra phy, Palaeo-cli ma tol ogy, Palaeo ec ol ogy, 36: 321–362.

Wag ner, R., (ed.) 2008. Tabela stratygraficzna Polski. Karpaty. Pañstwowy Instytut Geologiczny, Warszawa. [In Pol ish.] Wieser, T., 1985. The Teschenite For ma tion and other ev i dence of

mag matic ac tiv ity in the Pol ish Flysch Carpathians and their geotectonic and strati graphic sig nif i cance. In: Wieser, T. (ed.), Fun da men tal re searches in the west ern part of the Pol -ish Carpathians. Guide to Ex cur sion 1. CBGA XIII Con gress, Cra cow, Po land 1985. Wydawnictwa Geologiczne, War-szawa, pp. 23–36.

¯ytko, K., Zaj¹c, R., Gucik, S., Ry³ko, W., Oszczypko, N., Gar-licka, I., Nemèok, J., Eliáš, M., Menèik, E. & Stráník, Z., 1988. Map of the tec tonic el e ments of the West ern Outer Carpathians and their fore land 1:500 000. In: Poprawa, D. & Nemèok, J. (eds), Geo log i cal At las of the West ern Outer Carpathians and their Fore land, 1989. Pañstwowy Instytut Geologiczny, Warszawa.