Geo chem i cal and fau nal prox ies in the Westphalian A (Langsettian) ma rine ho ri zon of the Lublin Coal Ba sin
Ewa KRZESZOWSKA1, *
1 Silesian Uni ver sity of Tech nol ogy In sti tute of Ap plied Ge ol ogy, Akademicka 2, 44-100 Gliwice, Po land
Krzeszowska, E., 2017. Geo chem i cal and fau nal prox ies in the Westphalian A (Langsettian) ma rine ho ri zon of the Lublin Coal Ba sin. Geo log i cal Quar terly, 61 (4): 751–764, doi: 10.7306/gq.1374
The up per most Westphalian ma rine ho ri zon (Dunbarella ho ri zon) is es pe cially im por tant for cor re la tion of Car bon if er ous de - pos its in the Lublin Coal Ba sin and in other bas ins of the North west Eu ro pean Car bon if er ous Ba sin. The Dunbarella ho ri zon is char ac ter ized by cy clic sed i men ta tion and con se quent fau nal spec trum vari abil ity, typ i cal for Westphalian ma rine ho ri zons of north west ern Eu rope. Palaeontological study of the Dunbarella ho ri zon showed the pres ence of macrofauna rep re sent ing dif fer ent palaeoenvironments, from ma rine to brack ish (non-ma rine) and fresh wa ter con di tions. The ver ti cal sea level fluc tu - a tions and changes in sea wa ter sa lin ity re sult ing in palaeontological re cord changes do not link with geo chem i cal prox ies.
TOC, re dox-sen si tive trace el e ment con cen tra tions, and V/Cr, Ni/Co and V/(V + Ni) ra tios gen er ally sug gest that the Dunbarella ho ri zon sed i ments were de pos ited un der pre dom i nantly oxic con di tions (with lo cal ex cep tions dur ing the ini tial phase of the Dunbarella ingression; Kopina 1 bore hole).
Key words: in or ganic geo chem is try, palaeoredox con di tions, Dunbarella ho ri zon, Lublin Coal Ba sin.
INTRODUCTION
The North west Eu ro pean Car bon if er ous Ba sin (NWECB) is a large sed i men tary ba sin ex tend ing from Ire land in the west to Po land in the east. It de vel oped north of the Variscan Rheno - -Hercynian belt (Kombrink, 2008). Ge ol ogy of the NWECB has been ex ten sively stud ied by many au thors be cause of its eco - nomic im por tance the Penn syl va nian coal -bear ing (mainly Westphalian) se ries (e.g., Calver, 1968; Leeder, 1988; Narkie - wicz, 2007; Kombrink, 2008). Now a days, the most pro spec tive area for coal de pos its of the NWECB is the Lublin Coal Ba sin (LCB) lo cated in Po land, in the east ern part of the ba sin.
The most im por tant part of the coal-bear ing Car bon if er ous se ries of LCB is the Lublin For ma tion (Penn syl va nian, Westpha lian A and B) con tain ing the main multi-seam coal de - pos its (Porzycki and Zdanowski, 1995).
Only one coal mine op er ates in the LCB, and it en com - passes ~0.8% of the to tal coal ba sin area. Cur rently, due to the in ves tor in ter est, in ten sive geo log i cal re search of the de pos its has been con ducted. Within the Lublin Coal Pro ject, the Prai rie Min ing Lim ited Com pany has fo cused on the de vel op ment and op er a tion of a new coal mine in the Lublin Coal Ba sin. One of the most im por tant stages of the geo log i cal re search is the
iden ti fi ca tion of the Dunbarella ma rine marker ho ri zon that can be found in the lower part of the Lublin For ma tion. There fore, it con sti tutes the most im por tant sec tion for cor re la tion and ex plo - ra tion of the de pos its in the LCB. Fur ther more, since the Dunbarella ma rine marker ho ri zon has its equiv a lents in other coal fields of the Northwest Eu ro pean Car bon if er ous Ba sin, it is a sig nif i cant marker ho ri zon for the whole re gion. The iden ti fi ca - tion of this fau nal ho ri zon is es sen tial for the rec og ni tion of coal de pos its in the LCB.
Palaeontological stud ies of the Dunbarella ho ri zon have been pre sented by many au thors. So far, de tailed palaeonto - logical study is the only method for its iden ti fi ca tion (Musia³ et al., 1995; Musia³ and Ta bor, 2001; Krzeszowska, 2015 and ref - er ences cited therein).
Lat er ally ex ten sive ma rine ho ri zons that oc cur within paralic se quences (e.g., Dunbarella ma rine ho ri zon) are gen er ally re - garded as re li able cor re la tive strati graphic mark ers in the Penn - syl va nian coal fields. These ho ri zons are rep re sented typ i cally by goniatite-bear ing black shales char ac ter ized by high U and Mo lev els, and in ter preted as de pos ited dur ing times of an oxia (Fisher and Wignall, 2001; Kombrink, 2008; Kombrink et al., 2008; Pearce et al., 2010). En rich ment in re dox-sen si tive trace el e ments, and high TOC and S con tents al low iden ti fi ca tion of the ox y gen-re stricted en vi ron ments (e.g., Kombrink, 2008;
Fisher and Wignall, 2001; Zatoñ et al., 2009; Pearce et al., 2010; Racka et al., 2010; Marynowski et al., 2012).
There fore, the main goals of the study were to (1) de ter mine the palaeoredox con di tions of the Dunbarella ma rine ho ri zon, (2) com pare the geo chem i cal data with the palaeontological re cord, and (3) test, whether in or ganic geo chem is try can be used for iden ti fi ca tion and cor re la tion of the Dunbarella ma rine ho ri zon.
* E-mail: Ewa.Krzeszowska@polsl.pl
Received: April 9, 2017; accepted: July 9, 2017; first published online: August 27, 2017
GEOLOGICAL SETTING
The Lublin Coal Ba sin is lo cated in south-east Po land. The Lviv-Volhynia Coal Ba sin is its con tin u a tion in Ukraine. It is sit u - ated at the con tact zone of two ma jor geo log i cal units: the Pre - cam brian East Eu ro pean Plat form and the Early Pa leo zoic West Eu ro pean Plat form. The LCB is an ex tended prov ince stretch ing from south-east to north-west, 20 to 40 km wide and 180 km long (Fig. 1). The sub-Car bon if er ous base ment con sists of Pro tero - zoic crys tal line rocks and Lower and Up per Pa leo zoic de pos its.
The Car bon if er ous strata, which lie dis cor dantly on the older sub strate, are rep re sented by Mid dle Mis sis sip pian to Lower Penn syl va nian de pos its (Fig. 2). They are over lain by a se - quence of Permo-Me so zoic and Ce no zoic rocks. The thick ness of the over bur den var ies from 350 to >1200 m (e.g., Porzycki and Zdanowski, 1995; Zdanowski, 1999).
The main hard coal-bear ing se ries of the LCB, as well as the other bas ins of the NWECB, con sists of the Westphalian de pos its (rep re sent ing mostly the Lublin For ma tion in the LCB).
These are paralic de pos its with mul ti ple ma rine fauna ho ri zons (mainly in the Westphalian A), which pass into brack ish and then into con ti nen tal de pos its. The ma rine ho ri zons are im por -
tant marker ho ri zons within a mo not o nous mudstone-claystone se quence of flu vial or lac us trine sed i ments. They form rel a tively thin (up to sev eral metres in thick ness) de pos its be ing a re cord of ma rine or brack ish sed i men tary con di tions (Leeder, 1988;
Suess et al., 2007). The Dunbarella ma rine ho ri zon, which is the sub ject of this study, is the most im por tant marker ho ri zon in the LCB (in Po land). It marks the bound ary be tween the Westphalian A and B and be tween paralic and limnic sed i men - ta tion (Musia³ et al., 1995; Krzeszowska, 2015). This marker ho ri zon cor re lates with the Clay Cross Ma rine Band (Eng land), the Katharina ho ri zon (Ger many and the Neth er lands) and the Quaregnon ho ri zon (Bel gium). These are very im por tant cor re - la tion ho ri zons in north west ern and cen tral Eu rope due to their very large ex tent, their com mon pres ence, and the fact that they are lo cated within a se quence very rich in coal re sources (Calver, 1968; Musia³ et al., 1995; Kombrink, 2008; Krzeszo - wska, 2015). A dis tinc tive fea ture of this ho ri zon is cy clic sed i - men ta tion and as so ci ated vari abil ity of the fauna spec trum typ i - cal of the Westphalian ma rine fauna ho ri zons (Krzeszowska, 2015). The cy clic sed i men ta tion and con se quent fau nal spec - trum vari abil ity in the pro files of ma rine ho ri zons have been re - ported from the bas ins of north west ern and cen tral Eu rope (Calver, 1968; Kombrink, 2008).
Fig. 1. Lo ca tion of the Lublin Coal Ba sin (LCB) within the North west Eu ro pean Car bon if er ous Ba sin (NWECB) The dashed white line in di cates the pres ent-day con tours of the NWECB;
RHB – Rhenohercynian Ba sin, CAB – Cen tral Armori can Ba sin (Kombrink, 2008, re drawn af ter Ziegler, 1989)
MATERIALS AND METHODS
The ma te rial stud ied co mes from core sam ples from the Kopina 1, Borowo, Kulik and Syczyn 7 bore holes, lo cated in the cen tral part of the Lublin Coal Ba sin (Figs. 3 and 4). The study is based on data from 41 sam ples taken from the Dunbarella ma - rine marker ho ri zon.
The Dunbarella ho ri zon is com posed of grey claystones, lo cally sandy claystones or mudstones with thin car bon ate and sid er ite interlayers (Fig. 5).
Sam pling for the geo chem i cal study fol lowed a de tailed palaeontological study of the ho ri zon (Krzeszowska, 2015). Sam ples (claystones and sandy claystones) rep re sent ing 0.2 m in ter vals of the pro files with dif fer ent fau nal re cord were se - lected for the geo chem i cal study (Fig. 5).
The sam ples rep re sent in ter vals of the Dunba - rella ho ri zon char ac ter ized by the fol low ing fea tures (af ter Calver, 1968):
– abun dant typ i cal ma rine fauna rep re sented mainly by bi valve and same goniatites and gas tro pods, with vary ing oc cur rence of brachi o pods (mainly Lingula),
– abun dant brack ish fauna or fauna with high sa lin ity tol er ances, rep re sented mainly by bi - valves, with vary ing oc cur rence of brachi o - pods (mainly Lingula),
– abun dant fauna rep re sented mainly by brachi o pods (Lingula),
– fresh wa ter fauna or in de ter mi nate re mains of fresh wa ter fauna,
– few fau nal spec i mens, in clud ing pri mar ily brachi o pods and bi valves or in de ter mi nate re mains.
Sam ple prep a ra tion and an a lyt i cal pro ce dures were per formed by the AcmeLab An a lyt i cal Lab o ra - tory (cur rently Bu reau Veri tas Com mod i ties Can ada Ltd), Van cou ver, Can ada, and the Oil and Gas In sti - tute – Na tional Re search In sti tute (Kraków, Po land).
Ma jor and trace el e ments (U, TH, Mo, V, Cr, Co, Ni, Zn, Cu, Pb, Fe and Al) were ana lysed us ing in duc - tively cou pled plasma mass spec trom e try (ICP/MS) fol low ing 4-acid di ges tion (HF + HClO4 + HCl + + HNO3). Con tents of to tal sul phur (S) were ob tained us ing a LECO analyser. To tal or ganic car bon (TOC) was de ter mined by Rock-Eval py rol y sis. Ta ble pro - vid ing chem i cal data, in clud ing meth ods and de tec - tion lim its for each sam ple (Ap pen dix 1*).
RESULTS AND DISCUSSION
TOC-Fe-S RELATIONSHIPS
The re la tion ship be tween TOC (to tal or ganic car bon) vs. Fe vs. S has been ex ten sively used to as sess palaeoredox con di tions in ma rine sys tems (e.g., Berner and Raiswell, 1984; Raiswell and Berner, 1986; Leventhal, 1987; Raiswell and Al-Biatty, 1989;
Szczepanik et al., 2007; Algeo and Maynard, 2008; Zatoñ et al., 2009; Racka et al., 2010; Marynowski et al., 2012;
Wójcik-Tabol, 2015).
To tal or ganic car bon, and to tal sul phur (S) and iron (Fe) con tents are gen er ally low in the Dunbarella ho ri zon (Fig. 6, Ta - ble 1 and Ap pen dix 1). In creased TOC, S and Fe con tents were ob served mainly in the lower part of the ho ri zon in the Kopina 1 bore hole (sam ples K2, K3 and K4).
Fig. 2. Di vi sions of the Car bon if er ous suc ces sion in the Lublin Coal Ba sin and its cor re la tion with the North Amer ica Re gional Stage (sim pli fied) (af - ter Porzycki and Zdanowski, 1995; Dusar, 2006; Heckel and Clay ton, 2006;
Rich ards, 2013)
* Supplementary data associated with this article can be found, in the online version, at doi: 10.7306/gq.1374
De gree of pyritization (DOP) is of ten ap plied to de ter mine the palaeoredox con di tions (Hatch and Leventhal, 1992;
Cruse and Ly ons, 2000; Rimmer, 2004; Algeo and Maynard, 2008). DOP is de fined as the py rite iron/py rite iron + re ac tive iron (%Fepy rite/%Fepy rite+re ac tiveFe) (Berner, 1970) ra tio. Rais well
et al. (1988) have sug gested that sed i ments with DOP less than 0.46 in di cate aer o bic con di tions, DOP val ues be tween 0.46 and 0.75 in di cate dysoxic or re stricted con di tions, and DOP val ues >0.75 sug gest anoxic (in hos pi ta ble) con di tions for the sed i ment de po si tion.
Fig. 3. Lo ca tion of the sam pled bore holes: Kopina 1, Kulik, Borowo, Syczyn 7 car ried out un der the Lublin Coal Pro ject (http://www.pdz.com.au)
Cal cu la tion of DOP val ues re quires de ter mi na tion of re ac - tive iron, but Algeo and Maynard (2004, 2008) pro posed mak - ing a rough as sess ment us ing DOPt val ues (in place of true DOP). DOPt is based on the ra tio of py rite Fe (based on to tal S) to to tal Fe. This in dex can be used in place of true DOP, if py rite S com poses the bulk of to tal S, and re ac tive Fe com - poses the bulk of to tal Fe (Algeo and Maynard, 2008). Al - though DOPt val ues are sys tem at i cally lower than true DOP val ues, there is a strong re la tion ship be tween the two pa ram e - ters, and DOPt can be used as an es ti ma tor of true DOP (Algeo and Maynard, 2008).
DOPt val ues for aer o bic con di tions are typ i cally <0.3 for re - stricted con di tions be tween 0.3 and 0.6, while for in hos pi ta ble con di tions it is usu ally >0.6 (Algeo and Maynard, 2008).
In this study, DOPt val ues (in place of true DOP) have been ana lysed. DOPt val ues for most of the sam ples are low in di cat - ing aer o bic or re stricted con di tions (Fig. 7 and Ta ble 1). The sam ples from the lower part of the ho ri zon in the Kopina 1 bore - hole (K2, K3, K4) show higher DOPt val ues which in di cate anoxic con di tions.
REDOX-SENSITIVE TRACE ELEMENT
Re dox-sen si tive trace el e ment (TEs) con cen tra tions (such as U, V, Mo, Cr, Co, Ni, Cu, Zn and Pb) have been fre quently used as in di ca tors of re dox con di tions in mod ern and an cient sed i men tary sys tems (e.g., Calvert and Pedersen, 1993; Jones
and Man ning, 1994; Wignall, 1994; Algeo, 2004; Rimmer, 2004;
Tribovillard et al., 2006; Algeo and Maynard, 2008; Pearce et al., 2010; Racki et al., 2012; Wójcik-Tabol, 2015). The most use ful trace el e ments for palaeoenvironmental anal y ses are U and Mo, be cause they:
– dem on strate con ser va tive be hav iour un der oxic con di - tions and have long res i dence times in sea wa ter, – ex hibit nearly con sis tent con cen tra tions in sea wa ter
glob ally,
– are pres ent in low con cen tra tions in plank ton, so en rich - ments in sed i ments gen er ally co mes from sea wa ter, es - pe cially un der ox y gen-de pleted con di tions (Algeo and Tribovillard, 2009).
TEs com monly ex hibit con sid er able en rich ment in lam i - nated, or ganic-rich fa cies, es pe cially those de pos ited un der euxinic con di tions (Algeo and Maynard, 2008). On the other hand, in fer ences re gard ing palaeoenvironmental con di tions based on trace el e ment con cen tra tions are com monly un re li - able if sin gle el e ment dis tri bu tions are used, be cause their con cen tra tions are in flu enced by many fac tors and mech a - nisms (Tribovillard et al., 2006). Many au thors con sider not only the con cen tra tion of el e ments but also the de gree of en - rich ment or de ple tion of a trace el e ment to re con struct palaeo - environ mental con di tions (e.g., Wedepohl, 1991; Rimmer, 2004; Brum sack, 2006; Tribovillard et al., 2006; Kombrink, 2008; Algeo and Tribovillard, 2009). The method of geo chem i - cal nor mal iza tion and cal cu la tion of en rich ment fac tors (EFs) is as fol lows:
Fig. 4. Lo ca tion of the Dunbarella ho ri zon within the sim pli fied Car bon if er ous pro files of the Kopina 1, Borowo, Kulik and Syczyn 7 bore holes (LCB) (af ter Krzeszowska and Kokowska-Paw³owska, 2017: fig. 2 ibi dem, sim pli fied)
Fig. 5. Mol lusc/brachi o pod dy nam ics and sam pling lo ca tion within the Dunbarella ma rine marker ho ri zon (LCB)
A – Kopina 1, B – Borowo, C – Kulik, D – Syczyn 7; af ter Krzeszowska (2015: fig. 5 ibi dem)
Fig. 6. Ver ti cal dis tri bu tion of TOC, S and Fe within the Dunbarella ma rine ho ri zon in the Lublin Coal Ba sin
T a b l e 1 Ma jor palaeontological and geo chem i cal data for sam ples from the Dunbarella ho ri zon
Bore -
hole Sam ple Depth (m b.s.l.)
Ma jor palaeontological data Ma jor geo chem i cal prox ies Ge nus
dom i nated Main ge nus ac com pa ny ing
TOC S Fe
DOPt Uaut EFU EFmo V/Cr Ni/Co V/(Ni=V)
% % %
anipoK 1
K43 916.4 No fauna
<1
1.58 3.90 0.41 0.00 1.51 0.95
<2
<5
0.58-0.67
K47 916.8 Edmondia
Sanguinolites Lingula 1.56 3.24 0.48 1.73 1.10
K49 917.6 Posidonia
Edmondia Sanguinolites
Dunbarella Anthracoceras
1.63 3.24 0.50 0.27 1.88 1.24
K38 918.8 Re mains of fresh wa ter fauna 0.72 3.53 0.20
0.00
1.40 0.23
K34 919.4 No fauna 0.94 3.78 0.25 1.41 0.17
K32 920.0 Lingula 1.05 3.35 0.31 1.39 0.21
K19 922.6
No fauna 1.84 0.20 6.17 0.03 1.11 0.58
K8 924.6 <1 0.48 3.38 0.14 1.12 0.32
K4 926.2 Posidonia
Euchondria Dunbarella
Dunbarella Anthracoceras
Gastrioceras
3.46 1.72 2.69 0.64 5.60 2.76 20.93 6.74
K3 926.4 5.93 6.60 8.42 0.78 1.87 1.88 2.37
<5
K2 926.8 Carbonicola
Naiadites
Curvirimula
Anthracosia 4.67 4.65 6.47 0.72 1.20 1.57 1.81
oworoB
B40 922.2 Re mains of fresh wa ter fauna <1 0.42 3.37 0.12 0.57 1.40 0.32
<2 <5 0.60-0.69
B038 923.0 No fauna 0.74 3.96 0.19 0.60 1.41 0.40
B033 925.4 Edmondia
Sanguinolites Posidonia
Anthracoceras 1.92 0.90 3.82 0.24 0.38 1.57 0.49
B24 926.4 Posidonia Edmondia
Sanguinolites
<1
1.63 3.66 0.45 0.00 1.43 0.43
B015 928.0 Lingula Posidonia 0.94 3.68 0.26 0.27 1.66 0.32
B14 928.4
Posidonia
Dunbarella Polidevcia Anthracoceras
1.20 3.92 0.31 0.03 1.39 1.43
B10 928.6 1.29 3.74 0.34
0.00
1.22 0.29
B6 929.0 0.56 3.80 0.15 1.14 0.35
B2 929.4 0.84 3.32 0.25 1.17 0.27
B01 929.6 0.37 3.31 0.11 1.34 0.43
Fig. 7. Ver ti cal vari abil ity of the es ti mate of de gree of pyritization (DOPt) within the Dunbarella ma rine ho ri zon. The bound aries for aer o bic, re stricted and in hos pi ta ble con di tions (based on DOPt)
were es tab lished ac cord ing to Algeo et al. (2008)
Tab. 1 cont.
Bore -
hole Sam ple Depth (m b.s.l.)
Ma jor palaeontological data Ma jor geo chem i cal prox ies Ge nus
dom i nated
Main ge nus ac com pa ny ing
TOC S Fe
DOPt Uaut EFU EFMo V/Cr Ni/Co V/(Ni=V)
% % %
kiluK
Q45 951.8 Re mains of fresh wa ter fauna 1.09 0.39 3.11 0.13 0.53 1.56 0.34
<2 <5 0.57-0.70
Q04 952.6 Lingula 1.17 1.27 3.74 0.34 0.00 1.30 0.40
Q38 953.4 Lingula
<1
1.65 4.07 0.41 0.27 1.62 0.76
Q28 955.0
Edmondia
Posidonia Dunbarella Sanguinolites Anthracoceras
Lingula
1.45 3.57 0.41
0.00
1.46 0.61
Q24 955.6 1.36 3.90 0.35 1.50 0.63
Q02 956.8 Polidevcia,
Phestia Lingula
Posidonia Dunbarella Anthracoceras
0.78 3.58 0.22 1.35 1.07
Q15 957.4 Polidevcia,
Phestia
Posidonia Dunbarella Anthracocera
Lingula Edmondia
1.24 4.56 0.27 1.59 3.29
Q11 958.0 Lingula 1.53 4.15 0.37 1.19 0.35
Q3 959.4 No fauna 1.08 0.23 4.45 0.05 1.14 0.21
Q01 959.8 Few fau nal spec i mens – Lingula <1 0.78 2.97 0.26 1.09 0.49
nyzcyS 7
S40 883.8 Re mains of fresh wa ter fauna <1 0.64 3.92 0.16 0.60 1.47 0.28
<2 <5 0.59-0.73
S03 884.4 Lingula 1.12 0.78 4.17 0.19 0.10 1.51 0.53
S26 884.8 No fauna <1 1.34 4.16 0.32 0.67 1.57 0.56
S02 886.8 Dunbarella
Posidonia Edmondia
Sanguinolites 2.23 0.10 3.09 0.03 1.20 2.33 0.35
S17 887.2 Dunbarella
Posidonia Anthracoceras
<1
1.85 4.09 0.45 0.00 1.59 1.31
S14 887.6 Edmondia
Sanguinolites
Dunbarella Anthracoceras
Lingula
1.68 4.34 0.39 0.07 1.54 1.04
S9 888.0 1.35 3.81 0.35 0.00 1.30 0.36
S7 888.6 Posidonia Phestia
Dunbarella 1.40 4.03 0.35 1.42 0.51
S3 889.4 Posidonia
Phestia
Dunbarella Anthracoceras
Lingula 0.91 3.79 0.24 0.03 1.50 0.49
S01 889.8 Posidonia
Phestia Dunbarella
Anthracoceras
Gastrioceras 1.10 0.90 3.97 0.23 0.00 1.51 0.70
EF El Al El Al
s s av av
=
where: Els – el e ment con cen tra tion in the sam ple, Als – Al con cen - tra tion in the sam ple, Elav – el e ment con cen tra tion in av er age crustal rocks or av er age shale, and Alav – Al con cen tra tion in av er age crustal rocks or av er age shale.
U is the most im por tant re dox-sen si tive trace el e ment for re con struc tion of the sed i men tary en vi ron ment (e.g., Leeder, 1988; Fisher and Wignall, 2001; Rimmer, 2004; Kombrink, 2008; Algeo and Tribovillard, 2009; Pearce et al., 2010;
Wójcik -Tabol, 2015). The U con tent of sed i ments is a com bi - na tion of authigenic and de tri tal com po nents, and authigenic U is a suit able in di ca tor of re dox con di tions (Jones and Man - ning, 1994). Authigenic ura nium can be cal cu lated as Uaut = Utot - Th/3, with Th/3 as an es ti mate of the de tri tal ura nium frac tion in mud stones (Wignall and Myers, 1988). Re duc ing con di tions may pre cip i tate ura nium to en rich the sed i ment in authigenic (non -de tri tal) ura nium. Its val ues <5 in di cate oxic con di tions, while val ues 5–12 and >12 in di cate dysoxic and suboxic to anoxic con di tions, re spec tively (Jones and Man - ning, 1994). Algeo and Tribovillard (2009) pro posed to use en - rich ment fac tors (EF) for rapid as sess ment of the authigenic frac tion of U (sim i larly for Mo), in di cat ing that the de tect able authigenic en rich ment cor re sponds to EF>3, and the sub stan - tial en rich ment to EF>10.
The U con tents of the sam ples from the Dunbarella ma rine ho ri zon range from 3.5 to 11.6 ppm (Fig. 8 and Ap pen dix 1).
Only three sam ples showed val ues >6 ppm, which sug gest ma - rine de po si tion un der re duc ing con di tions (Leeder et al., 1990;
sam ples from the lower part of the ho ri zon in the Kopina 1 bore - hole and from the mid dle part of the ho ri zon in the Syczyn 7 bore hole). Most of the sam ples have low EFU val ues, cal cu lated rel a tive to av er age shale (Wedepohl, 1991) (1.09–2.76), and the lack of authigenic U. This in di cates oxic sed i men tary en vi - ron ment (Fig. 8, Ta ble 1 and Ap pen dix 2).
Mo con cen tra tion, which (next to U) has been re ported as the most im por tant in di ca tor in dis tin guish ing oxic, suboxic and anoxic fa cies (Algeo and Ly ons, 2006; Algeo and Rowe, 2012;
Marynowski et al., 2017), shows sig nif i cant vari abil ity in the sam ples from the Dunbarella ho ri zon. The EFMo val ues range from 0.17 to 20.93 (Ta ble 1), but high Mo con cen tra tions were ob served only in the sam ples from the lower part of the ho ri zon in the Kopina 1 bore hole (sam ples K2, K3 and K4) and from the mid dle part of the ho ri zon in the Kulik bore hole (sam ple Q15), sug gest ing ox y gen-de pleted sed i men tary fa cies.
Algeo and Tribovillard (2009) ana lysed pat terns of covaria - tion be tween Mo and U in mod ern and an cient anoxic ma rine sys tems. To com pare en rich ments of these el e ments, they pro - posed us ing en rich ment fac tors (EFMo, EFU) that are use ful for rapid as sess ment of the authigenic frac tion of Mo and U. Algeo and Tribovillard (2009) stated that EFMo ver sus EFU crossplots (Fig. 9), in which the Mo/U mo lar ra tio (~7.5–7.9) of sea wa ter is a guide to in ter pret ing rel a tive en rich ments of Moauth ver sus Uauth, can be ap plied for palaeoenvironmental anal y ses. Oxic fa cies show lit tle or no Mo and U en rich ments, suboxic fa cies ex hibit mod est en rich ment with Moaut./Uaut. (clearly lower than the sea wa ter ra tio), while anoxic fa cies ex hibit strong en rich - ment ac com pa nied by pro gres sively higher Moaut./Uaut. ra tios (Algeo and Tribovillard, 2009).
Most of the sam ples from the Dunbarella ho ri zon show low Uaut. en rich ment and lack of Moaut. en rich ment, cor re spond ing to the sea wa ter Mo/U mo lar ra tio of <0.2, in di cat ing oxic con di - tions (Fig. 9 and Ap pen dix 2). Sam ples show ing low Uaut. and Moaut. en rich ments (EFU and EFMo be tween 1–3) yield ing sea - wa ter Mo/U mo lar ra tio of ~0.2–0.7, sug gest vari able re dox con - di tions, prob a bly rang ing from oxic or suboxic. Only one sam ple (from the lower part of the ho ri zon in the Kopina 1) has dis tinctly higher Moaut. en rich ment and mod er ate Uaut. en rich ment, rep re - sent ing the Mo/U mo lar ra tio greater than that of sea wa ter, which strongly sug gests anoxic fa cies.
In ad di tion to U and Mo, other re dox-sen si tive trace met als can be use ful as palaeoredox prox ies. V, Cr and Co tend to be more sol u ble un der ox i diz ing con di tions and less sol u ble un der re duc ing con di tions, re sult ing in authigenic en rich ments in ox y -
Fig. 8. Ver ti cal dis tri bu tion of ura nium in the Dunbarella ma rine ho ri zon
gen-de pleted sed i men tary fa cies (Tribovillard et al., 2006). All the re dox-sen si tive trace el e ments ex am ined in this study (ex - cept for Mo) ex hib ited low EFs (cal cu lated rel a tive to av er age shale – Wedepohl, 1991) vary ing from 0.38 to 3.01, with the mean val ues for the el e ments rang ing from 0.87 to 1.77 (Fig. 10 and Ap pen dix 1).
TRACE ELEMENT INDICES
V/Cr, Ni/Co and V/(V + Ni) trace el e ment in di ces have been sug gested to eval u ate palaeoredox con di tions in many stud ies (e.g., Dill et al., 1988; Hatch and Leventhal, 1992; Jones and Man ning, 1994; Rimmer, 2004; Algeo and Maynard, 2008;
Fig. 9. Crossplot of en rich ment fac tors EFMo vs EFU for sam ples from the Dunbarella ho ri zon (LCB)
The lines show Mo/U mo lar ra tios equal to the sea wa ter value (1×SW) and to frac tions thereof 0.3×SW and 0.1×SW by Algeo and Tribovillard (2009)
Fig. 10. En rich ment fac tors (EF) for sam ples from the Dunbarella ho ri zon of the LCB
Racka et al., 2010; Marynowski et al., 2012; Racki et al., 2012; Wójcik-Tabol, 2015). Jones and Man - ning (1994) pro posed to use V/Cr ra tios to es ti - mate the palaeoredox depositional con di tions, with V/Cr <2 in di cat ing ox i diz ing con di tion, 2<
V/Cr <4.25 in di cat ing a dysoxic sed i men tary en vi - ron ment, and V/Cr >4.25 in di cat ing a re duc ing en - vi ron ment. The Ni/Co ra tios <5 in di cate oxic en vi - ron ments, Ni/Co ra tios be tween 5 and 7 sug gest dysoxic en vi ron ments, while higher ra tios (Ni/Co
>7) sug gest anoxic con di tions (Jones and Man - ning, 1994; Rimmer, 2004). Hatch and Leventhal (1992) used V/(V + Ni) ra tios as a pa ram e ter dis - tin guish ing oxic and anoxic bot tom wa ters by sug - gest ing that a high V/(V + Ni) ra tio (>0.84) in di - cates the pres ence of H2S in the wa ter col umn (euxinic con di tions), a ra tio be tween 0.46 to 0.84 rep re sents anoxic to dysoxic con di tions, and a ra - tio <0.46 rep re sents oxic con di tions.
The V/Cr ra tios in sam ples from the Dunbarella ho ri zon are gen er ally uni form and rel - a tively low (0.9–1.4), sug gest ing oxic en vi ron - ments, while Ni/Co ra tios vary ing from 2.6 to 6.7 for a sam ple from the lower part of the ho ri zon in the Kopina 1 bore hole (sam ple K4) in di cate dysoxic en vi ron ments (Fig. 11). V/(V + Ni) ra tios for all stud ied sam ples range be tween 0.57 and 0.73, which sug gests dysoxic to anoxic con di - tions that do not cor re spond with the other trace el e ment in di ca tors ana lysed above (Fig. 12).
Sim i lar re sults were re ported, inter alia, for the De vo nian–Mis sis sip pian black shales (Rimmer, 2004; Rimmer et al., 2004), Mid dle Ju ras sic mudstones (Szczepanik et al., 2007; Zatoñ et al., 2009), and Up per Famennian of the Holy Cross Moun tains (Racka et al., 2010), since the V/(V + Ni) ra tios pre dicted lower ox y gen con di tions than ei ther Ni/ Co or V/Cr.
GEOCHEMICAL PROXIES VS.
PALAEONTOLOGICAL RECORD
De tailed palaeontological study of the Dun - barella fau nal ho ri zon in the Lublin Coal Ba sin (Po land) has shown the pres ence of abun dant macrofauna – mostly mollu scs, brachi o pods, and
some rep re sen ta tives of cri noids, ar thro pods and fish (Krzeszowska, 2015). The dis tri bu tion of fauna in the ana lysed ho ri zon within the in ves ti gated bore holes fluc tu ates in terms of both abun dance and tax on omy, and cy clic sed i men ta tion typ i - cal of ma rine Westphalian ho ri zons was ob served.
Palaeontological study of the Dunbarella sho wed the pres - ence of in ter vals with a dif fer ent palaeontological re cord. The sam ples stud ied rep re sent de pos its con tain ing:
– typ i cal ma rine fauna (e.g., Dunbarella, Posidonia, Anthra co ceras, Gastrio ceras), oc ca sion ally ac com pa - nied by bi valve taxa of high sa lin ity tol er ance (Edmondia, Sanguinolites),
– brack ish or high sa lin ity-tol er ant fau nas (Lingula, Edmo - ndia, Sanguino lites),
– fresh wa ter fauna (e.g., Carbonicola, Naia dites) or in de - ter mi nate re mains,
– no fauna (Ta ble 1).
All the ana lysed sam ples rep re sent sim i lar lithologies (claystones and sandy claystones).
Ver ti cal vari a tions in the palaeontological re cord re fer to sea level and sa lin ity changes. Cy clic sed i men ta tion and con se - quent vari abil ity of the fau nal spec trum in ma rine ho ri zons are re lated to changes in en vi ron men tal con di tions, ma rine in gres - sions, and pe ri odic sea fresh en ing. Sev eral pro cesses have been pro posed to con trol the cy clic sed i men ta tion: autogenic changes in fa cies and allogenic changes that are mainly re lated to pe ri od i cal sea level fluc tu a tions (>100 m) gen er ated by gla - cial ep i sodes of the Gond wana tec tonic sub si dence and cli mate (Calver, 1968; Lud wig, 1994; Hampson et al., 1999; Joachimski et al., 2006; Suess et al., 2007; Rygel et al., 2008; Waksmun - dzka, 2013).
The geo chem i cal in ves ti ga tions, pre sented for the first time for the Dunbarella ho ri zon, fo cus mainly on geo chem i cal prox ies to de ter mine the palaeoredox con di tions. Pre vi ous stud ies of the ho ri zons con tain ing re mains of fresh wa ter fauna in the as pect of Fig.12. Crossplots of Ni/Co vs V/(V+Ni) re dox in di ces
Fig. 11. Crossplots of Ni/Co vs V/Cr re dox in di ces
the wa ter sa lin ity (e.g., Th/K2O, P2O5/Al2O3 and Rb/K) pro vided pre dom i nantly am big u ous re sults (Krzeszowska and Koko wska - - Paw³owska, 2017).
Most of the Dunbarella ma rine ho ri zon in the ana lysed bore - holes is rep re sented by in ter vals con tain ing ma rine bi valves ac - com pa nied by goniatites. The most im por tant spe cies for stra - tig ra phy are Dunbarella papyracea and Anthra coceras vanderbeckei – the marker spe cies for the Dunbarella fau nal ho ri zon.
Goniatite-bear ing in ter vals with ma rine bi valves can in di - cate a rel a tively deep-wa ter en vi ron ment (Kombrink, 2008). If in ter vals with goniatites form in ox y gen-re stricted con di tions, it can re sult in en rich ment in U, Mo and other re dox-sen si tive trace el e ments, and high TOC and S con tents (Fisher and Wignall, 2001; Kombrink, 2008). There fore, they can be rec og - nized us ing geo chem i cal meth ods. Geo chem i cal stud ies on Up per Car bon if er ous ma rine bands have shown that marked en rich ments in re dox-sen si tive trace el e ments, and high TOC and S con tents were ob served in same goniatite lev els, for ex - am ple, in the Gastrioceras listeri Ma rine Band (Westpha lian A, Middlecliff Quarry, Eng land), the Vanderbeckei Ma rine Band (Westphalian A and B bound ary, Rowe bore hole, West Mid - lands, Eng land), the Namurian Goniatites Ma rine Band of the Geverik well (Neth er lands) (Fisher and Wignall, 2001;
Kombrink, 2008; Kombrink et al., 2008; Pearce et al., 2010).
The ma jor en vi ron men tal prox ies (DOPt, V/Cr, Ni/Co, TOC, TOC, U and Mo) in most of the sam ples rep re sent ing in ter vals with goniatite in the Dunbarella ho ri zon in di cate oxic con di tions dur ing de po si tion. Sim i lar re sults were pre sented for the Westphalian ma rine bands (Do mina, Veldhof and Aegir) of the Neth er lands. Those ma rine bands rep re sent pre dom i nantly a Lingula fa cies char ac ter ized by low or ganic car bon con tents (1–2 wt.%), and mostly lack ing sig nif i cant trace el e ment en rich - ments (Kombrink, 2008; Kombrink et al., 2008).
Anoxic con di tions are sug gested only by geo chem i cal in di - ca tors cal cu lated for sam ples from the low est part of the Kopina 1 bore hole. Sam ples K3 and K4 show gen er ally higher TOC, DOPt and Ni/Co val ues than those from other parts of the Dunbarella ho ri zon. In ad di tion, the U and Mo en rich ment, the pres ence of authigenic U, and the Mo/U mo lar ra tios (es pe cially in sam ple K4) also sug gest ox y gen-re stricted con di tions. It is also worth not ing that the de pos its (sam ple K2) di rectly un der ly - ing the above-men tioned sam ples (K3, K4) con tain fresh wa ter fauna and show sim i lar geo chem is try, sug gest ing ox y gen-re - stricted con di tions.
The sam ples with brack ish and high sa lin ity-tol er ant fau nas gen er ally show ma jor en vi ron men tal in di ces val ues in di cat ing oxic con di tions dur ing de po si tion, as well as the sam ple with fresh wa ter fauna or non-as sign able re mains, and those the lack of fauna.
Palaeontological data al low iden ti fi ca tion of in ter vals with sim i lar geo chem i cal char ac ter is tics, rep re sent ing ma rine, off - shore or brack ish, and fresh wa ter sed i men ta tion. Thus, the palaeontological study seems to be the only method to dentify the Dunbarella ho ri zon.
CONCLUSIONS
Palaeontological study of the Dunbarella ma rine marker ho - ri zon showed the pres ence of macrofauna rep re sent ing dif fer - ent palaeoenvironments, from ma rine and brack ish (non-ma - rine) to fresh wa ter con di tions (cf. Krzeszowska, 2015). Ver ti cal vari a tions of fau nal as sem blages are re lated to rapid and prob - a bly short-term sea level and sa lin ity changes con trolled by ma - rine in gres sions and pe ri odic ba sin fresh en ing.
Geo chem i cal pa ram e ters are rel a tively sim i lar through out the Dunbarella ho ri zon. They do not show as large fluc tu a tions as the palaeontological re cord does. The prox ies (TOC, Dopt, re dox-sen si tive trace el e ment con cen tra tions, Moaut./Uaut., V/Cr, Ni/Co) sug gest mostly per ma nently ox y gen ated con di tions.
Ox y gen-re stricted con di tions are sug gested only by the val - ues of geo chem i cal in di ca tors cal cu lated for sam ples from the low est part of the Kopina 1 bore hole section.
Two com ple men tary, palaeo eco logi cal (based on the fau nal spec trum) and geo chem i cal stud ies were ap plied to de ter mine palaeoenvironmental con di tions of the Dunbarella ho ri zon.
They have al lowed con firm ing sig nif i cant changes in palaeo-sa - lin ity and rel a tively con stant re dox con di tions dur ing de po si tion of the ana lysed ho ri zon. To make a com plete re con struc tion of sed i men tary en vi ron ments, an in te grated ap proach, in clud ing palaeo ec ol ogy, geo chem is try and sedimentology, should be used.
Ac knowl edge ments. I would like to thank Prof. Z. Saw³o - wicz, Prof. N. Tribovillard and anon y mous Re viewer for their help ful and con struc tive com ments that helped me to im prove the pa per.
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