Lithologically-re lated rare earth el e ment vari a tions the Mio-Plio cene Poznañ For ma tion (Po land)
Jacek RETKA1, *
1 Polish Geo log i cal In sti tute – Na tional Re search In sti tute, Rakowiecka 4, 00-975 Warszawa, Po land
Retka, J., 2018. Lithologically-re lated rare earth el e ment vari a tions the Mio-Plio cene Poznañ For ma tion (Po land). Geo log i - cal Quar terly, 62 (1): 146–154, doi: 10.7306/gq.1388
As so ci ate Ed i tor – Stanis³aw Z. Mikulski
Con cen tra tions of rare earth el e ments (REEs) were de ter mined in 129 clay sam ples col lected from the Mio-Plio cene Poznañ For ma tion in Po land. The REEs oc cur in a rel a tively wide range from 58.2 to 1,709 mg/kg. Low North Amer i can Shale Com - pos ite (NASC)-nor mal ized to tal REE con tents with heavy rare earth el e ment (HREE) de ple tion were noted in most of the sam ples ana lysed. Small vari a tions were de tected in the REE con tents in the lithologies dis tin guished. Red clays are char ac - ter ised by slightly lower REE con cen tra tions rel a tive to green and grey clays. All the Poznañ For ma tion clays ex hibit a neg a - tive Eu anom aly when nor mal ized to the av er age of chondrites. Val ues in crease ac cord ing to the fol low ing se quence: grey clays < red clays < green clays. The NASC-nor mal ized REE con cen tra tion curves show a pos i tive Eu anom aly. The LaNASC/YbNASC ra tio in di cates HREE de ple tion. A small vari a tion in this ra tio was ob served in the se quence green clays > grey clays > red clays. The vari abil ity of the REE con tents of the Poznañ For ma tion de creased from west to east.
Key words: Poznañ For ma tion, rare earth el e ments, clay lithotypes.
INTRODUCTION
The Mio-Plio cene Poznañ For ma tion (Po land), for merly called the Poznañ Se ries, is sit u ated in cen tral and north ern Po land and was formed in a large al lu vial-lac us trine in land ba - sin (Piwocki and Ziembiñska-Tworzyd³o, 1997). The thick ness of these de pos its gen er ally ranges from 40 to 60 m (Kozydra and Wyrwicki, 1970). The con tent of clay min er als is in the range of 35–90% (usu ally 50–60%). Their com po si tion is mainly dom i nated by smectites (beidellite-nontronite) and S/I (smectite-illite) mixed-layer min er als with sub or di nate illite and kaolinite. In the Poznañ For ma tion, these clay min er als show a di verse compositional spec trum. In the north ern and north - east ern part, illite and beidellite pre vail, with a pre dom i nance of beidellite. In the cen tral part, the dom i nant com po nents are illite and beidellite, and the amount of beidellite is no ta bly re - duced. To wards the coastal part of the ba sin, more sandy sed - i ments oc cur in which the share of illite and I/S mixed-layer min er als in creases. In the south ern part of the area, the con tri - bu tion of kaolinite also in creases. In the fore land of the Sudetes this min eral is dom i nant (Wiewióra and Wyrwicki,
1974, 1976; Wichrowski, 1981; Brañski, 1994, 2002; Nieæ and Ratajczak, 2004).
Col our is used to dis crim i nate be tween the three litho - stratigraphic lev els (units): grey clays, green clays, and red (bright red) clays (Wyrwicki, 1974; Nieæ and Ratajczak, 2004).
This is re lated to the pres ence of var i ous iron min er als (Kozydra and Wyrwicki, 1970). The red-, rus set-, and yel low-mot tled colour ing of red clays con tain ing 6–14% Fe2O3 is in duced by the pres ence of he ma tite and goethite. Finely dis persed iron sulphides give a grey ish-blue or green ish col our to the green clays. In the lower part of the grey clays, thin lig nite (brown coal) interbeds also oc cur.
For hun dreds of years the clay raw ma te ri als of the Poznañ For ma tion have found wide ap pli ca tions. Cur rently, be cause of the rel a tively easy ac cess to the de pos its and their sub stan tial thick ness, these clays are used in build ing ce ram ics (Brañski, 1994, 2012; Piwocki, 2002; Wyrwicki, 2002). An other ap pli ca - tion for the clays of the Poznañ For ma tion is their use for the pro tec tion and res to ra tion of the en vi ron ment (Brañski, 1994, 1998, 2002). Low per me abil ity and high mal lea bil ity, as well as good and very good sorp tion ca pac ity, and the ion ex change prop er ties of clays be long ing to the beidellite and polymineral types make them suit able as an in su la tor ma te rial in land fills (£uczak-Wilamowska, 2013).
The rare earth el e ments (REEs), also called lanthanides, are a fam ily of fif teen el e ments from lan tha num to lutetium (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu)
* E-mail: jacek.retka@pgi.gov.pl
Received: April 19, 2017; accepted: October 4, 2017; first published online: October 31, 2017
(Henderson, 1984). Ac cord ing to rec om men da tions by the In - ter na tional Un ion of Pure and Ap plied Chem is try (IUPAC), scan dium and yt trium are also in cluded in the REE group (Connelly et al., 2005). The REEs, due to their sim i lar chem i cal and geo chem i cal prop er ties, are a co her ent se ries. REEs are usu ally di vided into two con ven tion ally termed groups:
– light REE (LREE) from La through to Eu;
–heavy REE (HREE) from Gd through to Lu.
There is also a third dis crim i nated sub group, me dium REE (MREE) from Sm through to Ho, which partly over laps the LREE and HREE (Migaszewski et al., 2016). Rare earth el e - ments are highly dis persed and com monly oc cur in min er als that are very du ra ble and re sis tant to weath er ing (Kabata-Pendias and Pendias, 1999). There are more than 250 min er als con tain ing REE, in clud ing ~70 min er als in which REEs have a more spe cific role, for in stance monazite-(Ce), (Ce, La, Nd, Th)[PO4], bastnäsite-(La) (La, Ce)[F, CO3], cheralite Ca0.5Th0.5[PO4]2 and xeno time Y[PO4]. The REEs have been pro duced from ~20 min er als, but only some of them are mined and pro cessed (Paulo, 1999).
The mean REE con tent in clay sed i ments var ies in a wide range from 79 to 259.7 mg/kg (Kabata-Pendias and Mukherjee, 2007). It var ied in clay sed i ments pri mar ily due to its li thol ogy, gen e sis and age. In the Cre ta ceous and Plio cene sed i ments of cen tral Por tu gal (kaolinite, illite and smectite de pos its), the to tal con tent of La, Ce, Sm, Eu, Tb, Yb and Lu var ies from 190 to 323 mg/kg (Prudencio et al., 1989). The REE con cen tra tions in the Eocene Oshosun For ma tion (south west ern Ni ge ria) – black and grey shale, and also clay – were in the range of 176.76–374.31 mg/kg (Ajayi et al., 2006). In Plio cene red loess clays from the Chi nese Loess Pla teau, a SREE is lower – in range of 131–198 mg/kg (mean of 146 mg/kg) (Ding et al., 2001). A sim i lar range of REE con tent (139–252 mg/kg) was re - corded in Cre ta ceous Shale taken from the vi cin ity of Corelato Perticara in the south ern Apennines (Cavalante et al., 2014). In the Up per Cre ta ceous smectite, illite, and ka olin and mixed-layer illite-smectite clay interbeds from west ern Por tu gal (Aveiro and Taveiro re gions), the to tal con cen tra tion of La, Ce, Nd, Sm, Eu, Tb, Yb, and Lu var ied from 66.1 to 272 mg/kg (Marques et al., 2011). Much higher REE con tents were noted in the older clay de pos its. Stud ies of the Havensville and Eskridge shales from Kan sas and Oklahoma dated from the Lower Perm ian (ma rine) – en com pass ing mont mo ril lo nite, kaolinite, and illite – showed the pres ence of SREE in the range of 5.4–1,732 mg/kg (Cullers et al., 1975). In Pre cam brian clay-rich strata from the Buwambo ka olin de posit (cen tral Uganda), in which kaolinite is the dom i nant min eral, the REE con tents ranged from 70.18 to 2,186 mg/kg (Nyakairu et al., 2001). Un like in sed i men tary clay de pos its, it has been ob - served that (some) re sid ual clays con tain higher lev els of REEs, up to sev eral thou sand mil li grams per ki lo gram, mark ing these clay rocks as po ten tial REE ore de pos its (Foley et al., 2014; Yuan et al., 2014). For in stance, in the Xuanwei For ma - tion the to tal REE con cen tra tions were in a wide range of 89.0 to 9,965 mg/kg (Zhang et al., 2016).
The pur pose of the pres ent study con ducted in the Mio-Plio - cene Poznañ Clay For ma tion was to:
–de ter mine cur rent REE con cen tra tions in the Poznañ clays;
–to de scribe vari a tions of REE con tents in dif fer ent parts of the al lu vial-lac us trine ba sin;
–to es tab lish the re la tion ships be tween the REE con tents and the dif fer ent lithologies.
SAMPLES AND METHODS
129 sam ples were col lected from 18 clay de pos its:
Bojanice, Brzostów, Budy Mszczonowskie, Chwalimierz II, Cienia I, Fordon, Gozdnica, Kunice III, Mirostowice Dolne, Niet¹¿kowo I, Rudak I, Sierakowice, Stopka II, S³owiany, Soœnica, Szyd³ów II, Tadeuszów-Rudzienko, and Witaszyce (Fig. 1 and Ta ble 1). Sam ples were col lected from ver ti cal pro - files in all de pos its, ex cept for the Witaszyce de posit.
Af ter acid di ges tion (us ing a mix ture of HNO3, HClO4, HF), the REE (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) con cen tra tions were de ter mined us ing in duc tively cou pled plasma-qua dru ple mass spec trom e try (ICP-QMS; model ELAN DRC II, Perkin Elmer). Due to polyatomic in ter fer ences in the multi-el e ment tech nique (ICP-QMS), math e mat i cal cor rec tions were ap plied to elim i nate spec tral in ter fer ences. In ad di tion, to mini mise ma trix ef fects, sam ples were di luted ten fold prior to mea sure ment. The anal y sis was per formed in the pres ence of an in ter nal stan dard (Rh and Re) so lu tion. Qual ity con trol in - cluded dou ble di ges tion of se lected sam ples and dou ble sam - ple mea sure ments. The rel a tive stan dard de vi a tion (RSD) val - ues were <3% for most of the sam ples ana lysed. The es ti mated limit of quan ti fi ca tion of La, Ce, Pr, and Nd was 0.5 mg/kg, and for Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu it was 0.05 mg/kg.
The mea sured con cen tra tions of REE in the Poznañ For - ma tion were nor mal ized to av er age chondrite and to North Amer i can Shale Com pos ite (NASC) (Gromet et al., 1984; Piper and Bau, 2013). For all sam ples the value of the eu ro pium anom aly – the en rich ment or de ple tion of the eu ro pium con tent in min er als rel a tive to the con tent of other REEs – was cal cu - lated. In or der to in ves ti gate the en rich ment or de ple tion in light rare earth el e ments (LREEs) and heavy rare earth el e ments (HREEs) of var i ous clay lithologies in the Poznañ For ma tion, La/Yb and La/Sm ra tios were cal cu lated. To de ter mine these ra tios, their nor mal ized con tent in the clays tested was used.
Sta tis ti cal pa ram e ters (mean, geo met ric mean, me dian, min i mum, and max i mum val ues) were de ter mined us ing Statistica. This soft ware was also used to de velop his to grams and de ter mine REE, Eu/Eu*, La/Yb, and La/Sm ra tios.
RESULTS AND THEIR COMPARISON WITH DATA FROM OTHER FORMATIONS
REE con tents in the Poznañ For ma tion range from 58.2 to 1,709 mg/kg, with a mean of 176 mg/kg, a geo met ric mean of 150 mg/kg, and a me dian of 140 mg/kg (Ta ble 2). The mean con tents of in di vid ual el e ments were as fol lows (in mg/kg): La (32.0), Ce (80.6), Pr (8.40), Nd (32.4), Sm (6.53), Eu (1.38), Gd (4.98), Tb (0.73), Dy (4.1), Ho (0.75), Er (2.02), Tm (0.26), Yb (1.68), and Lu (0.25). The REE con cen tra tions var ied sub stan - tially in clays of dif fer ent de pos its. The high est mean con tent was found in clays from the Soœnica de posit (geo met ric mean of 260 mg/kg), and the low est in the Chwalimierz II de posit (geo - met ric mean of 78.5 mg/kg; Ta ble 2). The great est REE con - cen tra tion vari abil ity was noted in the Soœnica de posit, and the small est in the Stopka II de posit (Ta ble 2).
The Poznañ For ma tion is char ac ter ized by a high vari abil ity of REE con tents. This is par tic u larly ev i dent in re la tion to Cre ta - ceous and Plio cene de pos its from cen tral Por tu gal and Cre ta - ceous shales from the south ern Apennines (Prudencio et al., 1989; Marques et al., 2011; Cavalante et al., 2014). It was Lithologically-re lated rare earth el e ment vari a tions the Mio-Plio cene Poznañ For ma tion (Po land) 147
found that REE con cen tra tions de ter mined in dif fer ent de pos its (ex cept for Brzostów and Witaszyce) of the Poznañ For ma tion ex am ined by Duczmal-Czernikiewicz (2012) is in line with their av er age con tents in clays and shales. An av er age REE con tent sim i lar to that of the Poznañ clays was re ported from coal-bear - ing de pos its in Arkagalinskoe and Dolinskoe, where it is 172.07 mg/kg (Koporulin et al., 2007). In the Poznañ For ma - tion, the max i mum SREE con tent (~1,700 mg/kg) is nearly the same as that found in the Lower Perm ian shale lay ers of Havensville and Eskridge (Kan sas and Oklahoma) (Cullers et al., 1975). How ever, the min i mum con tent of the Poznañ clays is nearly 10 times higher.
The REE con cen tra tions nor mal ized to av er age chondrite ex hibit an en rich ment of these el e ments (from sev eral times to
>100 times). The NASC-nor mal ized REE con cen tra tion pat - terns in di cate that most of the sam ples ana lysed are de pleted in HREEs (Fig. 2). The curves for all the de pos its ex hibit a slight en rich ment in Ce and de ple tion in Tb, Ho, and Tm (Fig. 3). The
high est de ple tion of HREEs is seen in the Mirostowice Dolne, Witaszyce and Soœnica de pos its and the low est in the Chwalimierz II and Kunice III de pos its.
NASC-nor mal ized REE con cen tra tion curves show en rich - ment in La, Ce, Pr, and Nd, es pe cially in the Mirostowice Dolne, Soœnica and Witaszyce de pos its, and de ple tion of these el e - ments in the Chwalimierz II and Kunice III deposits.
The study shows that the value of eu ro pium anom a lies in the Poznañ clays is higher than in Por tu guese Paleogene and Mio cene clays, in which the Eu/Euchondrite* ra tios range from 0.48 to 0.69, and is also higher than in the loess from the Liyang Plain in south ern China (0.63–0.67) (Mao et al., 2011; Lisboa et al., 2015). The value of eu ro pium anom a lies in Poznañ For ma - tion clays is com pa ra ble or even lower than in sig nif i cantly older Perm ian clays from de pos its in Iran where Eu/Euchondrite* ra - tios range from 0.79 to 1.34 (Mahjoor et al., 2009).
It was found that the Lachondrite/Ybchondrite ra tio in the Poznañ For ma tion in di cates LREE en rich ment. The value of Fig. 1. Study area with Mio-Plio cene clay de posit lo ca tions
Lithologically-re lated rare earth el e ment vari a tions the Mio-Plio cene Poznañ For ma tion (Po land) 149
this ra tio is higher than in the Por tu guese Paleogene and Mio - cene clays (5.4–11.9; Lisboa et al., 2015), and in Iran’s Perm ian clays (7.1–10.8; Mahjoor et al., 2009).
The anal y sis of the cal cu lated La/Sm ra tio nor mal ized to av - er age chondrite and NASC shows a LREE en rich ment in the Poznañ For ma tion, al though in case of the lat ter this ra tio is low.
By com par i son, the value of this ra tio (chondrite-nor mal ised) in the Por tu guese Paleogene and Mio cene de pos its was in the range of 2.0 to 3.4 (Lisboa et al., 2015).
The study of the Poznañ For ma tion clay lithologies shows that red clays have slightly lower REE con cen tra tions in re la tion to the other two lithologies (Ta ble 3). Green clays are abun dant T a b l e 1 List of clay de pos its of the Poznañ For ma tion stud ied and their lo ca tion, num ber of sam ples col lected, and li thol ogy
No. De posit Lo ca tion No.
of sam ples Li thol ogy
1 Bojanice Krzemieniewo mu nic i pal ity,
Leszno dis trict 6 red, grey, blu ish clays
2 Brzostów Jaraczewo mu nic i pal ity, Jarocin dis trict 7 red, ol ive, green ish clays 3 Budy Mszczonowskie Radziejowice mu nic i pal ity,
¯yrardów dis trict 7 red, green ish clays
4 Chwalimierz II Chwalimierz mu nic i pal ity,
Œroda Œl¹ska dis trict 6 red clays
5 Cienia I Opatówek mu nic i pal ity, Kalisz dis trict 7 red, blu ish clays
6 Fordon Bydgoszcz 7 red, grey, ol ive-grey clays
7 Gozdnica ¯agañ dis trict 8 grey, green clays
8 Kunice III Legnica dis trict 7 red, green ish clays
9 Mirostowice Dolne ¯ary mu nic i pal ity, ¯ary dis trict 8 grey, blu ish, green ish clays 10 Niet¹¿kowo I Œmigiel mu nic i pal ity, Koœcian dis trict 8 red, grey, yel low-brown clays
11 Rudak I Toruñ 8 red-brown, green ish, green ish-yel low clays
12 Sierakowice Soœnicowice mu nic i pal ity, Gliwice dis trict 8 red clays
13 S³owiany Boles³awice dis trict 7 red yel low-grey clays
14 Soœnica K¹ty Wroc³awskie mu nic i pal ity,
Wroc³aw dis trict 7 brown-light grey clays
15 Stopka II Koronowo mu nic i pal ity, Bydgoszcz dis trict 7 green ish, yel low-brown clays
16 Szyd³ów II Tu³owice mu nic i pal ity, Opole dis trict 7 red clays
17 Tadeuszów-Rudzienko Dobre mu nic i pal ity, Miñsk dis trict 7 dark grey, green ish clays
18 Witaszyce Jarocin mu nic i pal ity, Jarocin dis trict 7 green ish clays
T a b l e 2 De scrip tive sta tis tics for the to tal REE con tents (mg/kg) of the sam ples
No. De posit Mean Geo met ric mean Me dian Min i mum Max i mum Stan dard de vi a tion
1 Bojanice 230 195 161 110 455 148
2 Brzostów 149 138 126 85.4 279 67.3
3 Budy Mszczonowskie 148 144 135 107 226 42.9
4 Chwalimierz II 79.0 78.5 78.3 67.3 91.6 9.38
5 Cienia I 161 158 172 94.3 190 32.9
6 Fordon 187 174 163 110 366 85.3
7 Gozdnica 162 155 138 118 256 50.9
8 Kunice III 101 96.6 85.1 73.9 164 33.4
9 Mirostowice Dolne 295 270 227 166 545 139
10 Niet¹¿kowo I 140 132 129 81.4 282 60.8
11 Rudak I 140 135 140 86.0 213 38.5
12 Sierakowice 159 146 143 83.7 277 68.4
13 S³owiany 125 119 137 58.7 165 37.8
14 Soœnica 429 260 200 125 1709 579
15 Stopka II 131 131 128 122 147 8.67
16 Szyd³ów II 154 153 151 138 176 15.5
17 Tadeuszów-Rudzienko 130 121 122 82.9 240 56.9
18 Witaszyce 244 227 249 107 376 92.8
in REEs from 82.9 to 376 mg/kg. Their av er age con tent is 173 mg/kg (geo met ric mean: 159, me dian: 155 mg/kg), while the REE con tents in grey clays range from 83.9 to 545 mg/kg and the mean is 177 mg/kg (geo met ric mean: 158, me dian:
142 mg/kg). In red clays the REE con cen tra tions vary from 58.7 to 1,709 mg/kg and the av er age value is 178 mg/kg, while the
geo met ric mean (140 mg/kg) and the me dian (133 mg/kg) are much lower.
In all clay lithologies, sam ples with REE con tents that vary from 100 to 150 mg/kg are most com mon (Fig. 4).
The REE con cen tra tion curves of the green, grey, and red clays nor mal ized to the chondrite av er age and to NASC do not Fig. 2. REE con cen tra tion curves for all the clays ex am ined
nor mal ized to chondrite and to NASC
Fig. 3. The NASC-nor mal ized REE con cen tra tion curves from all the clay de pos its
show any sig nif i cant dif fer ences. It has been doc u mented that all the Poznañ For ma tion lithologies ana lysed ex hibit a neg a tive Eu anom aly when chondrite-nor mal ized and a pos i tive Eu anom aly when nor mal ized to NASC.
The re sults ob tained for the Lachondrite/Ybchondrite ra tio in the three lithologies (Ta ble 4) in di cate that the green clays have slightly higher val ues. A ra tio di ver sity was noted in each li thol - ogy, with green clays > grey clays > red clays, ac cord ingly. The es ti mate of the Lachondrite/Smchondrite ra tio shows the high est value in grey clays.
INTERPRETATION OF RESULTS
The re sults were also ana lysed in terms of REE vari abil ity in the Poznañ For ma tion within the sed i men tary ba sin. The far ther to the east of Po land, the REE con cen tra tions were less di - verse. A much greater vari a tion in REE con tents was ob served in the west ern part of the ba sin. The high est REE con cen tra - tions were found in the Soœnica and Mirostowice Dolne de pos - its, and the low est in Chwalimierz II and Kunice III, which are lo - cated in the vi cin ity of the REE-rich Soœnica de posit. Clays con - tain ing the larg est amounts of REEs are from de pos its in the Lubuski re gion (Mirostowice Dolne, Gozdnica, and S³owiany).
These are ge net i cally linked to the west ern part of the Pre cam - Lithologically-re lated rare earth el e ment vari a tions the Mio-Plio cene Poznañ For ma tion (Po land) 151
T a b l e 3 Geo met ric mean REE con tents (mg/kg)
in the Poznañ For ma tion lithologies
El e ment Green clays Grey clays Red clays
La 29.8 30.0 26.2
Ce 73.8 72.9 63.9
Pr 7.42 7.40 6.62
Nd 28.4 27.9 25.0
Sm 1.20 1.10 1.05
Eu 5.61 5.45 5.02
Gd 4.31 4.17 3.76
Tb 0.63 0.61 0.56
Dy 3.60 3.50 3.28
Ho 0.67 0.65 0.61
Er 1.86 1.81 1.70
Tm 0.23 0.24 0.23
Yb 1.52 1.58 1.52
Lu 0.23 0.24 0.23
To tal REE 159 158 140
LREE 146 145 128
HREE 13.1 12.8 11.9
Fig. 4. His to grams, mean REE con tents (mg/kg), and REE con cen tra tion curves nor mal ized to the chondrite av er age and to NASC in green, grey, and red clays
brian Bo he mian Mas sif (Sudetes) which mainly en com pass meta mor phic and mag matic rocks. Gen er ally, the clays con - tain ing the small est amounts of REEs are from the group of Wroc³aw de pos its (Kunice III, Chwalimierz II). These were also sup plied by the Bo he mian Mas sif (Sudetes), but from its cen tral part, which is made up of rocks of var i ous rocks of var ied pe trol - ogy e.g. Pre cam brian shale and gneiss, and Up per Cre ta ceous sand stones. Clays from Sierakowice and Szyd³ów II (in the vi - cin ity of Opole and Gliwice), char ac ter ized by av er age REE con tents, were fed mainly from the west ern ar eas of the Carpathians fold belt. Clays from the Kujawski (Stopka II, Fordon, Rudak I) and Mazowsze (Budy Mszczonowskie, Tadeuszów-Rudzienko) re gions were sup plied from dif fer ent ar eas of the East Eu ro pean Craton, with rel a tively low REE con cen tra tions. De pos its lo cated in the cen tral part of the ba sin (Niet¹¿kowo I, Bojanice, Brzostów, Witaszyce, Cienia I) probably had mixed sources, but also favourable conditions to increase REE accumulation.
In the Poznañ For ma tion clays, as in all sed i men tary rocks, the con tents of rare earth el e ments de pends on clastic ma te rial com po si tion and its or i gin, i.e. the REE con tents in the source rocks. This study has shown that in the Poznañ For ma tion clays, no mat ter what clay li thol ogy, the high est REE con tents oc cur in the west ern part of the ba sin, in which a much greater vari a tion in REE con tents was also ob served. This part of the ba sin was sup plied from the Bo he mian Mas sif (Sudetes), where the crys tal line rocks, post-mag matic min er al isa tion, as well as sed i men tary rocks oc cur. Lower and less vari able REE con tents were ob served in the cen tral and east ern parts of the ba sin, which were fed by the Carpathians and the East European Craton that consist of sedimentary rocks.
The char ac ter is tic colours of the clay lithologies of the Poznañ For ma tion is re lated to the pres ence of var i ous iron
min er als. The red clays com prise Fe in the form of ox ides and hy drox ides – he ma tite and goethite. De po si tion of clays un der ox i dising con di tions (red clays) fa cil i tated REE mo bil ity from min er als and their scav eng ing by authigenic iron oxyhydroxides was rel a tively small. In these clays the iron con cen tra tion was the high est, while the me dian REE con tent was the low est (133 mg/kg) and they char ac ter ize the high est share of sam ples con tain ing REEs in the range of 50–100 mg/kg. The green clays show sig nif i cantly lower Fe con tents (in the form of sul - phide – py rite). In con trast, the me dian REE con tent was the high est (155 mg/kg) and the high est num ber of sam ples with REE con tents in the range of 150–200 mg/kg. Sed i men ta tion of clays un der re duc ing con di tions (green clays) con strained the re lease of REEs from allochthonous min er als (plagioclase, pyroxene, hornblende, and zircon, in which REEs were probably dispersed).
The el e vated Lachondrite/Ybchondrite ra tio, which in di cates LREE en rich ment, sug gests that the pres ence of REEs in clays is as so ci ated with plagioclase de bris (in which LREE en rich - ment com pared to py rox enes and am phi boles is char ac ter is tic), also other feld spars, and es pe cially clay min er als (Tay lor et al., 1983; McLennan, 1989; McLennan et al., 1993). Small dif fer - ences for each li thol ogy was found in the se ries of green > grey
> red clays.
CONCLUSIONS
The REE con tents in the Poznañ For ma tion ranged from 58.2 to 1,709 mg/kg, with a mean of 176 mg/kg, a geo met ric mean of 150 mg/kg, and a me dian of 140 mg/kg. Clays from the Poznañ For ma tion are char ac ter ized by REE con tents sim i lar to those from other clay deposits.
T a b l e 4 Sta tis ti cal pa ram e ters for Eu/Eu*, La/Yb, and La/Sm in the Poznañ For ma tion
Lithotype Ra tio Mean Geo met ric mean Min i mum Max i mum
Green clays Eu/Euchondrite* 0.84 0.84 0.70 0.90
Eu/EuNASC* 1.26 1.25 1.05 1.34
Grey clays Eu/Euchondrite* 0.80 0.80 0.58 0.97
Eu/EuNASC* 1.19 1.19 0.87 1.45
Red clays Eu/Euchondrite* 0.83 0.83 0.56 0.93
Eu/Eunasc* 1.24 1.24 0.83 1.39
Green clays Lachondrite/Ybchondrite 11.3 11.0 6.27 22.3
LaNASC/YbNASC 1.98 1.93 1.10 3.90
Grey clays Lachondrite/Ybchondrite 11.0 10.7 5.23 15.6
LaNASC/YbNASC 1.92 1.87 0.92 2.73
Red clays Lachondrite/Ybchondrite 10.2 9.68 4.76 23.9
LaNASC/YbNASC 1.78 1.69 0.83 4.19
Green clays Lachondrite/Smchondrite 3.57 3.49 1.70 5.25
LaNASC/SmNASC 1.31 1.28 0.62 1.93
Grey clays Lachondrite/Smchondrite 3.71 3.61 1.75 5.19
LaNASC/SmNASC 1.36 1.33 0.64 1.91
Red clays Lachondrite/Smchondrite 3.49 3.42 1.99 4.82
LaNASC/SmNASC 1.28 1.26 0.73 1.77
Lit tle di ver si fi ca tion of REE con tents was found in the dif fer - ent Poznañ For ma tion clay lithologies. Red clays had slightly lower REE con cen tra tions com pared to green and grey clays.
To tal REE val ues for green and grey clays can be con sid ered similar.
Dif fer ent REE con cen tra tions were found in dif fer ent de pos - its. The high est mean con tent was in Mirostowice Dolne (geo - met ric mean – 270 mg/kg), and the low est in Chwalimierz II (geo met ric mean – 78.5 mg/kg).
Poznañ For ma tion de pos its are char ac ter ized by the en - rich ment of REE as com pared to the chondrite pat tern, vis i ble in the graphs of their nor mal ized av er age con tent. At the same time these clays are char ac ter ized by im pov er ish ment in REE com pared to the NASC pat tern. All lithotypes of the Poznañ For ma tion show neg a tive chondrite-nor mal ized Eu anom a lies.
NASC nor mali za tion exhibited a positive Eu anomaly.
The Lachondrite/Ybchondrite ra tio in di cates LREE en rich ment.
Small dif fer ences among the lithologies was found in the pat - tern: green > grey > red clays.
Ac knowl edge ments. The REE anal y sis in the Poznañ For - ma tion clays was pos si ble by cour tesy of Prof. I. Bojako wska and Dr. P. Brañski. The au thor is grate ful for be ing given ac cess to the sam ples and to the ma jor and trace el e ment re sults from the pro ject “Vari abil ity of the con tent of trace se lected traces el - e ments in Poznañ se ries clays in sed i men ta tion ba sin”
(61.3207.0901.00.0). The pres ent study is based on the au - thor’s doc toral dis ser ta tion “Ocena zmiennoœci geochemicznej pierwiastków ziem rzadkich w i³ach serii poznañskiej w aspekcie ich litotypów” (in Pol ish) un der the supervision of Prof.
I. Bojakowska de fended at the Pol ish Geo log i cal In sti tute – Na - tional Re search In sti tute. I would like to thank all the re view ers (Z.M. Migaszewski, V. Lisboa and P. Brañski) sin cerely for their ef forts in pre par ing the re vised ver sion of this pa per.
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