Mariusz Kędzierski & Agata Ochabska

CAL CAR E OUS NANNOFOSSIL BIOSTRATIGRAPHY AND

SED I MEN TARY EN VI RON MENT OF VALANGINIAN–HAUTERIVIAN

RHYTHMITES (SILESIAN NAPPE, POL ISH CARPATHIANS)

Mariusz KÊDZIERSKI & Agata OCHABSKA

In sti tute of Geo log i cal Sci ences, Jagiellonian Uni ver sity, Oleandry Str. 2A, 30-063 Kraków, Po land; e-mail: mariusz.kedzierski@uj.edu.pl; agata.ochabska@gmail.com

Kêdzierski, M. & Ochabska, A., 2012. Cal car e ous nannofossil biostratigraphy and sed i men tary en vi ron ment of Valanginian–Hauterivian rhythmites (Silesian Nappe, Pol ish Carpathians). Annales Societatis Geologorum Polo-niae, 82: 225–237.

Ab stract: The re sults of semi-quan ti ta tive and qual i ta tive stud ies of nannofossil as sem blages in dark to light grey,

rhyth mi cally bed ded, cal car e ous mudstones of the Up per Cieszyn Beds, Silesian Nappe of the Outer Carpathians are pre sented. The ver ti cal vari a tion in the car bon ate con tent of these mudstones and changes in the com po si tion of nannofossil as sem blages, as well as the Shan non di ver sity in dex (SI), re sult from hu mid-arid cli mate changes, driv ing the trophic con di tions of sur face wa ters and nannoplankton biocalcification. These changes were con trol-led by the vari able in flu ences of both the Tethyan and Bo real prov inces. The light grey mudstones were de pos ited dur ing the dom i nance of warm wa ters from the Tethyan realm and some nannoconids, typ i cal of the warm, strat i fied wa ter of lower palaeolatitudes, oc cur here. The dark grey mudstones rep re sent in flu ences of the Bo real prov ince, in di cated by the ap pear ance of Crucibiscutum sp. and a gen er ally higher biodiversity dem on strated by SI. Cli ma tic changes af fected the strat i fi ca tion of sur face wa ter, ex pressed also by dif fer ent lin ear fits for pairs of SI, Watznaueria barnesiae and Rhagodiscus asper. On the ba sis of the pres ence of Eiffellithus striatus, E. windii and sig nals of both Tethyan and Bo real in flu ences. the sec tion stud ied rep re sents the up per most Valanginian– low er most Hauterivian bound ary in ter val, i.e., the up per part of the BC5/BC6 nannofossil zones, re lated to the furcillata-radiatus ammonite zones.

Key words: cal car e ous nannofossils, biostratigraphy, Lower Cre ta ceous, Silesian Nappe, Pol ish Carpathians,

Tethyan-Bo real in flu ences.

Manu script received 1 October 2012, ac cepted 21 December 2012

IN TRO DUC TION

ma jor, cli mate-in duced, en vi ron men tal per tur ba tions and the cold est in ter val dur ing the Early Cre ta ceous, sup pos edly con nected with the for ma tion of the po lar ice cap. Di rect ev -i dence for Early Cre ta ceous glac-iat-ions, such as clasts from sea sonal ice raft ing and glendonides or tillite, have been re -ported (e.g., Frakes et al., 1995; Price, 1999; Al ley and Frakes, 2003). McArthur et al. (2007) drew at ten tion to the Late Valanginian and Early Hauterivian as the time of for -ma tion of the po lar ice cap, which waned in the Late Hau-terivian. The con se quence of for ma tion of the ice cap was a drop in sea level, pos tu lated on a chart by Hardenbol et al. (1998) to have been as much as 90 m, or 50 m as claimed by Stoll and Schrag (1996), on the ba sis of sud den in puts of strontium, re sult ing from the emer gence of the con ti nen tal shelves.

The sup posed for ma tion of the po lar ice cap was trig -gered by a global drop in palaeotemperature. On the ba sis of d18

O data, taken from bel em nite ros tra, it was es ti mated as

about 10°C, drop ping from 20°C in the Berriasian down to 10°C in the Early Hauterivian (Podlaha et al., 1998). The early Late Valanginian verrucosum and peregrinus ammo-nite zones are con sid ered to be a time of a cold sea sur face, with a de cline of about 4° (McArthur et al., 2007). Iso to pic data from Si be rian sub-Arc tic bel em nites show the low est tem per a tures in the Late Valanginian, co in cid ing with a fall in sea level and pulses of nu tri ent in puts, due to melt ing of the ice (Price and Mutterlose, 2004). Also ox y gen and car -bon iso tope data, taken from bel em nites and glendonites in Arc tic Svalbard, point out cool palaeotemperatures (4–7°C), in dic a tive of gla cial, po lar con di tions in the Valanginian (Price and Nunn, 2010). Data from car bon-iso tope stud ies of ter res trial plants also ev i dence a cool pe riod or ice house in the Late Valanginian (Gröcke et al., 2005). How ever, the cool ing trend of ocean bot tom wa ter, drop ping from 15°C in late Early Valanginian to 11°C in the Late Valanginian– Early Hauterivan, was con nected with a sec ond-or der rise in sea level, al low ing for the dis place ment of cold, Bo real wa

-ters by warm Tethys ones (Van de Schootbrugge et al., 2000). Vašíèek and Michalík (1997) also noted a Bo real ammonite mi gra tion dur ing the high stands of the

verru-cosum ammonite Zone (early Late Valanginian). They also

re ferred to the Lower Valanginian petransiens and Lower Hauterivian radiatus ammonite zones as times of Bo real ammonite in flu ences in the Silesian Ba sin in the West ern Carpathians. The verrucosum ammonite Zone was also a time of Tethyan ammonite mi gra tion into both north ern and south ern, high lat i tudes (Kutek et al., 1989; Kutek and Mar- cinowski, 1996; Aguirre-Urreta, 1998; Alsen, 2006).

Lit tler et al. (2011) pre sented ev i dence to the con trary, for warm sea-sur face wa ter that ex ceeded tem per a tures of 32°C in the palaeolatitudes 15°–20°N and reached about 26°C in the vi cin ity of palaeolatitude 53°S. Also Borne-mann and Mutterlose (2008) con cluded that an in crease in

nu tri ent avail abil ity in di cates en hanced upwelling, rather than cool ing in the west ern At lan tic dur ing the Valanginian. Re cently, Barbarin et al. (2012), on the ba sis of ox y gen iso topes from fish teeth, pos tu lated that the Valanginian bot -tom wa ter tem per a ture ranged from 18.4 to 21.6°C at about 500–800 m in depth, in the sub trop i cal zone of the Vocon-tian Ba sin (SE France). Fur ther more, Jenkyns et al. (2012) dem on strated the el e vated sea-sur face tem per a tures at high lat i tudes dur ing the Ju ras sic–Cre ta ceous “cold snaps”, which dropped down to the 25–26°C level dur ing the cold est part of the Callovian–Oxfordian bound ary. This may in di cate the pres ence, if any, of con ti nen tal icecaps only in con sid -er able ar eas of high al ti tude on Antarctica.

The Early/Late Valanginian was a time of a ma jor shift of d13C called the Weissert Ep i sode (Weissert and Erba, 2004; Föllmi et al., 2006; McArthur et al., 2007; Föllmi,

Fig. 1. Lo ca tion maps of the area and sec tion stud ied. A. Lo ca tion of the area stud ied on the back ground of the geo log i cal sketch map

(af ter Burtan, 1984). B. De tailed, top o graphic map with lo ca tions of the sec tion stud ied and ammonite finds, de scribed by Vašíèek et al. (2010)

2012). It was ac com pa nied or fol lowed by en rich ment in phos pho rus and trace met als (Föllmi, 1995; Van de Schoo-tbrugge et al., 2003; Kuhn et al., 2005). De spite the car bon iso tope anom aly, the Weissert Ep i sode was not en tirely re -lated to en hanced, ma rine, pri mary pro duc tion and bot tom an oxia in some re gions (McArthur et al., 2007; Westermann

et al., 2010). The Valanginian sed i ments of the Vocontian

Ba sin were de pos ited on a well ox y gen ated bot tom, un der rel a tively sta ble, ma rine, palaeoenvironmental con di tions (Kujau et al., 2012). It can not be ex cluded that, in con trast to other Me so zoic oce anic anoxic events, the Weissert Ep i -sode re sulted in in creased de po si tion of or ganic mat ter in mar ginal seas and on con ti nents, com bined with the de mise of shal low-wa ter car bon ate plat forms (Westermann et al., 2010).

This was in ter preted to be the re sult of the break-up of Pangaea and cre ation of new, con ti nen tal rift bas ins (see Föllmi, 2012), in clud ing the Proto-Silesian rift ba sin, at the mar gin of the North Eu ro pean Plat form. The break-up and rift ing of Pangaea led to the sub mer gence of the wide spread car bon ate plat form, with the main phase re fer able to the Va- langinian verrucosum to radiatus ammonite zones (Föllmi

et al., 1994; Weissert et al., 1998; Föllmi et al., 2006;

Föllmi, 2012). This gen eral sce nario also is re corded in the Silesian Unit. The sub mer gence of the car bon ate shelf of the Proto-Silesian Ba sin also was pos tu lated by Szyd³o and Ju-gowiec (1997, 1999). In con clu sion, fol low ing the Proto-Silesian rift ing, the Tithonian–Berriasian car bon ate-rich Cieszyn Lime stone For ma tion gave way to the dark Up per Cieszyn Shales in the Valanginian. The sec tion stud ied rep -re sents this ini tial stage of this change.

The main goal of this study was to rec og nize the stra tig -ra phy and palaeoenvironmental changes of the Up per Cie-szyn Beds in the vi cin ity of Poznachowice (Silesian Unit) on the ba sis of cal car e ous nannofossil as sem blages.

GEO LOG I CAL SET TING

Palaeo ge ogra phy and geo log i cal back ground

The sec tion is lo cated be tween the Raciechowice Anti-cline and the Wiœniowa Tec tonic Win dow and rep re sents the Silesian Unit suc ces sion (Fig. 1A) (KuŸniar 1923, 1924; Burtan, 1984). The Silesian Unit, the larg est com plex nappe of the Outer Carpathians, was folded and thrusted north -ward dur ing the Mio cene and now a days stretches out from Czech Re pub lic through Po land to the Ukrai nian Flysch Carpathians. It com prises a thick se ries of mainly flysch de -pos its, rang ing from the Kimmeridgian up to the Lower Miocene. They ac cu mu lated in an oce anic rift or back-arc ba sin, lo cated on thinned, con ti nen tal crust of the North Eu -ro pean Plat form. The Late Ju ras sic–Early Cre ta ceous ba sin, named the Proto-Silesian or Severin-Moldavidic Ba sin, was sub di vided into sev eral smaller bas ins dur ing the Late Cre -ta ceous, with the Silesian Ba sin (Silesian Unit) the larg est one among them (e.g., Œl¹czka et al., 2006; Golonka et al., 2008a).

In ad di tion to the his tor i cal trea tises by Staszic (1815), Push (1836), Hohenegger (1861) and Uhlig (1902), the stra -tig ra phy and tec tonic his tory of the Silesian Unit are known

from more re cent pa pers by Kokoszyñska (1949), G¹sio-rowski (1962), Vašièek (1972, 1975, 2008), Burtan (1974, 1978, 1984) and Szymakowska (1981). Micropalaeontolo-gical stud ies of the Lower Cre ta ceous of the Silesian Unit by Geroch (1966), Olszewska (1997), Gedl (2001), Olszewska and Malata (2006), OlOlszewska et al. (2008), in -clud ing nannofossil in ves ti ga tions by Szyd³o and Jugowiec (1997, 1999), Švábenická (2008), Svobodova et al. (2011) and Halásová et al. (2012), nar rowed the age of the Up per Cieszyn Beds to the Valanginian–Hauterivian (Fig. 2). Nev er the less, ac cord ing to Olszewska et al. (2008), sed i men ta -tion of the un der ly ing Cieszyn Lime stone al ready may have been com pleted at the end of the Valanginian, and there fore, sed i men ta tion of the Up per Cieszyn Beds be gan at least in the Early Hauterivian. Re cently, the dis cov ery of two am-monites, Criosarasinella mandovi Thieuloy and

Tesche-nites subflucticulus Reboulet, a few hun dred me ters from

the sec tion (Fig. 1B), in di cated the up per most Valanginian, i.e., peregrinus and furcillata ammonite zones, ac cord ing to Reboulet et al. (2009) (vide Vašièek et al., 2010).

The Up per Cieszyn Beds rep re sent the lower part of the Hradište For ma tion, dis tin guished as the for mal, lithostrati-graph i cal unit, named as the Cisownica Shale Mem ber, which is as signed to the Valanginian–Hauterivian (Golonka

et al., 2008b) and con sid ered to be the old est sed i men tary

rocks in the study area (Fig. 2) .

Fig. 2. Lithostratigraphic scheme of Silesian Nappe. Stud ied

in ter val col oured in dark grey (af ter Vašíèek et al., 2010 and au -thors, cited therein)

Characteristics of the sec tion stud ied

The sec tion of the Up per Cieszyn Beds is lo cated in the west ern bank of the Krzyworzeka stream (co or di nates: N49°49'56'', E20°07'13''), in Poznachowice Dolne vil lage, south from Dobczyce in the di rec tion of Wiœniowa, along Road No. 964 (Fig. 1B). The sec tion con sists of al ter nat ing dark and light grey, thinbed ded (2–20 mm), lam i nated, car -bon ate mudstones, in places interbedded with thin (up to 5 mm) beds of fine-grained, cal car e ous sand stones. They dip al most ver ti cally and fre quently are cut by faults. The dark and light grey mudstones com prise reg u larly re cur ring groups of car bon ate-rich beds (Fig. 3).

MA TE RIAL AND METH ODS

Ev ery 2 cm of the sec tion, em brac ing 147 beds with three groups of light grey and two groups of dark grey mud-stones re spec tively, were sam pled for the pres ent study (Fig. 3). This con sti tutes a re cord of 60 cm of the sec tion with 30 rock sam ples, des ig nated P1 through P30. Mi cro scope slides were made, us ing the sim plesmear slide tech -nique (Bown and Young, 1998), and then ex am ined un der the light Nikon Eclipse E600 Pol mi cro scope at a mag ni fi -ca tion of ×1000.

The rel a tive abun dance (per cent age) of cal car e ous nannofossils was de ter mined on the ba sis of about 300 spec -i mens, counted on a smear-sl-ide (v-ide Bown and Young, 1998). In sam ples, where the to tal nannofossil abun dance was at least less than 300 spec i mens, the per cent age was cal cu lated, with re spect to all spec i mens avail able for anal y -sis (Tab. 1). The het er o ge ne ity or re la tion ship of di ver sity and abun dance of each of the taxa counted is given by the Shan non In dex (SI) (Shan non and Weaver, 1949). As sem -blages, dom i nated by one or a few taxa, tend to show low val ues of SI. In con trast, high SI value, char ac ter ize highly di ver si fied as sem blages. More over, re gres sion anal y sis was per formed for se lected vari ables with con tin u ous (or al most con tin u ous) oc cur rence.

RE SULTS

Cal car e ous nannofossils have been found in all of the slides ex am ined and some of them are ex em pli fied on Fig. 4. In gen eral, they are poorly or mod er ately pre served and rep re sent 29 taxa, be long ing to 17 gen era (Tab. 1). The cal -car e ous nannofossil as sem blages are dom i nated by Watzna-

ueria barnesiae spe cies, the per cent age of which var ies from 74% in sam ple P20 to 92% in sam ple P10.

Stauroli-thites mutterlosei, StauroliStauroli-thites spp., Rhagodiscus asper, Retecapsa spp. in clud ing R. angustiforata, W. fossacincta

or Zeugrhabdotus spp. are also com mon (Tab. 1). How ever, rare but very dis tinc tive oc cur rences of Cruciellipsis

cuvi-llieri and Crucibiscutum sp. were also noted (Fig. 4). The

pres ence of C. cuvillieri is al most con tin u ous, whereas

Cru-cibiscutum sp. was found in sam ples P4 and P20, taken

from the dark grey mudstone groups of strata (Fig. 3).

Crucibisctum sp., which was noted in the sam ples, dif fers

Fig. 3. Sec tion stud ied, with lo ca tion of rock sam ples in di cated

by sam ple num bers. Dis tin guished groups of light and darkcol -oured mudstones are sep a rated by white, dot ted lines. Shades of grey de pend on as sumed car bon ate con tent

from known spe cies by hav ing a wide, cen tral area with an ax ial cross and nar row rim (Fig. 4B). More over, some rare ap pear ances of nannoconids were noted in three sam ples P3, P25 and P27, taken from the groups of light grey mud-stone strata.

The num ber of spe cies in a sam ple (NOS) changes from 3 in sam ple P24 up to 20 in sam ples P3 and P27. The Shan -non di ver sity in dex (SI) var ies from 1.56 in sam ple P10 to 3.02 in sam ple P20.

The vari ables of the re gres sion anal y sis, apart from SI and NOS, in clude W. barnesiae, R. asper, Zeugrhabdotus spp., S. mutterlosei and Staurolithites spp. (Tab. 2; Fig. 5).

The re gres sion anal y sis shows a sig nif i cant, strong cor -re la tion, i.e., |r| above 0.5, only for th-ree pairs of vari ables: SI vs. W. barnesiae, SI vs. R. asper and W. barnesiae vs. R.

asper. Other pairs have zero to me dium, lin ear fit.

Ta ble 1 Num ber of spe cies, Shan non In dex and abun dances of cal car e ous nannofossils stud ied

se l p ma s f o o N S O N xe d ni n o n na h S m ut uc si B . ps at a g n ol b o a ni ht al ac ic l a C s uc i n oc s u d b a hr at er C m ut uc si bi c ur C . ps ir eil li v uc s is pil ei c ur C ar e a h ps ol e g al cy C . ps ii n a m he l s u hti l ot a m oz ai D s ut ai rt s s u hti ll eff i E ii d ni w s u hti ll eff i E s u hti ll eff i E . p ps ii ztl u hc s o h s u hti l o ht n ar ci M s us ut b o s u hti l o ht n ar ci M s u n oc o n n a N . p ps at ar ofi ts u g n a as p ac et e R all er ir us as p ac et e R as p ac et e R . p ps re ps a s uc si d o g a h R s uc si d o g a h R . ps at a gil l oc ai n ot ee p S x ur c se ti hti l or u at S ie s ol re tt u m se ti hti l or u at S se ti hti l or u at S . p ps s uc si d o b u T . p ps e ai se nr a b ai re u a nz t a W ac i n n ati r b ai re u a nz t a W at c ni c as s of ai re u a nz t a W s u m m ar g ol pi d s ut o d b a hr g ue Z ir e gr e b me s ut o d b h ar g ue Z s ut o d b a hr g ue Z . p ps P30 15 2.414 0.5 0.5 0.5 0.5 0.5 0.9 0.9 0.9 3.7 4.1 0.5 82.1 1.8 0.9 1.8 P29 16 1.962 0.3 0.3 0.3 0.6 0.3 0.6 2.5 0.3 0.3 0.3 1.5 0.3 86.5 5.2 0.3 0.3 P28 17 1.92 0.3 0.3 0.3 0.3 0.3 0.9 0.9 1.2 0.3 1.2 1.7 0.3 88.4 0.9 1.7 0.3 0.9 P27 20 2.256 0.3 0.3 0.8 0.5 0.3 0.3 0.5 0.3 0.3 0.3 1.3 1.5 0.3 2.6 2.8 0.5 84.8 1.3 0.3 1.0 P26 15 2.129 0.9 0.9 0.4 0.9 0.9 2.2 1.3 0.4 0.9 2.2 85.8 0.4 2.2 0.4 0.4 P25 14 2.026 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1.5 1.0 1.0 1.0 85.7 5.9 0.5 P24 3 1.822 9.1 81.8 9.1 0.0 P23 16 1.7 0.3 0.3 0.3 0.3 0.3 0.6 0.3 1.2 1.2 0.3 0.3 0.6 90.5 3.0 0.3 0.3 P22 15 2.101 0.3 1.2 0.6 0.9 0.9 2.4 0.6 0.3 2.7 0.3 85.5 2.9 0.3 0.3 0.9 P21 15 2.414 0.3 0.9 0.3 1.7 0.3 1.5 0.9 2.9 0.6 0.3 0.6 2.3 81.4 0.3 5.8 P20 14 3.021 1.4 0.5 0.5 0.5 0.5 0.5 0.5 8.7 3.2 0.5 3.2 2.7 74.0 3.7 P19 13 2.029 0.3 0.9 0.6 0.0 0.3 1.8 0.9 0.3 1.5 0.3 85.5 0.3 5.1 2.1 P18 7 2.552 1.6 3.2 4.8 1.6 3.2 75.8 9.7 P17 14 2.204 0.3 0.6 0.3 1.5 2.5 1.5 0.3 0.9 2.2 1.2 84.6 1.8 1.8 0.3 P16 13 1.964 0.3 1.5 0.9 2.2 2.5 0.3 0.6 1.8 1.2 87.1 0.9 0.3 0.3 P15 11 2.016 0.7 0.7 0.7 1.3 0.7 0.7 1.3 2.0 85.2 6.0 0.7 P14 11 2.072 0.3 0.6 1.5 4.0 3.4 0.3 0.3 84.6 2.8 0.6 1.5 P13 11 2.182 0.9 0.3 2.1 2.1 0.9 1.5 0.9 83.9 4.2 1.5 1.5 P12 17 2.589 0.9 0.5 0.5 1.4 0.5 0.5 1.9 0.5 4.2 1.9 2.3 0.9 81.2 0.9 0.5 0.5 0.9 P11 8 2.713 4.8 4.8 2.4 2.4 4.8 76.2 2.4 2.4 P10 9 1.555 1.5 1.5 0.7 0.7 0.7 0.7 92.0 0.7 1.5 P9 17 2.066 0.3 0.3 0.3 1.8 0.3 0.6 0.9 0.9 0.3 0.6 1.8 0.6 86.8 2.2 0.3 0.6 1.2 P8 9 2.16 0.0 1.1 1.1 3.2 1.1 1.1 2.2 6.5 82.8 1.1 P7 19 2.24 0.3 0.3 0.5 2.7 0.3 0.5 1.9 2.9 0.5 0.3 0.8 0.8 0.3 84.9 0.3 0.5 0.3 0.8 1.3 P6 15 2.392 1.5 0.3 0.3 1.2 0.3 2.7 5.5 0.3 0.6 0.9 1.5 82.0 0.6 0.6 1.5 P5 11 2.518 1.0 2.0 1.0 1.0 2.0 4.9 5.9 1.0 79.4 1.0 1.0 P4 16 2.37 0.6 0.3 0.3 0.3 2.7 0.9 1.8 4.6 1.5 0.3 1.5 0.3 82.6 0.6 0.3 1.2 P3 20 2.511 0.3 0.3 0.3 0.9 0.3 0.6 0.6 0.3 0.3 0.9 5.5 0.3 0.3 1.8 1.2 81.9 0.9 0.3 1.2 1.5 P2 17 2.672 0.3 0.3 0.3 0.9 0.3 1.2 2.4 6.8 0.3 0.3 1.5 3.6 1.2 78.9 0.9 0.3 0.6 P1 17 2.312 0.3 0.3 0.3 0.3 0.3 2.2 0.6 1.8 2.2 3.4 0.6 0.3 0.3 1.8 0.9 83.7 0.6 Ta ble 2 Cor re la tion co ef fi cient r for se lected vari ables.

NOS SI W. barnesiaeR. asper Zeugr-habdotus spp. Stauro-lithites spp. Shannon index 0.1656 W. barnesiae 0.2209 -0.9043 R. asper 0.2068 0.6770 -0.5695 Zeugrhabdotus spp. 0.0944 0.0547 0.0593 -0.0387 Staurolithites spp. -0.4241 0.1911 -0.439 0.0016 -0.2338 S. mutterlosei 0.3128 0.3426 -0.1761 0.1553 0.01356 0.0517 |r| val ues above 0.5 are in bold type

DIS CUS SION

Pres er va tion of nannofossil as sem blages

The sus cep ti bil ity of cal car e ous nannofossils to dis so lu -tion dur ing de po si -tion and diagenesis de pends on nanno-fossil struc ture (Steinmetz, 1994) and the pres ence of clays and or ganic mat ter in the de posit (Turchyn and DePaolo, 2011).

The taxon, most re sis tant to dis so lu tion among those studied, is Watznaueria barnesiae. Frag ile muroliths and placoliths, such as Staurolithites crux or Biscutum constans, are prone to dis so lu tion (Hill, 1975; Thierstein, 1980; Roth and Bowdler, 1981; Bown and Young, 1998).

Roth and Bowdler (1981) con cluded that as sem blages with per cent ages of Watznaueria spp., ex ceed ing 40%, may have been sig nif i cantly changed by diagenesis. Alternati-vely, nannofossil as sem blages dom i nated by Watznaueria may also be re cords of a pris tine sig nal (e.g., Thom sen, 1989; Pittet and Mattioli, 2002). Such ev i dence is ex plained by the r-se lected life strat egy of that ge nus, which can be found in great abun dance in the sed i ments of en vi ron ments that were hos tile for other taxa (e.g., Lees et al., 2004). Moreover, the clays and/or or ganic mat ter in the sed i ment con trol the com po si tion of the biogenic car bon ates and,

con se quently, the nannofossil as sem blages (Pearson et al., 2001; Turchyn and DePaolo, 2011).

Tak ing the above state ment into ac count, one might ex -pect a better preservational sig nal, i.e., higher di ver sity of as sem blages, from the more clayey mudstone strata than from the car bon atebear ing, light grey mudstones. In gen -eral, such trend would be ob served in the dark grey mud-stone strata of the sec tion, where the per cent age of W.

barnesiae, the most re sis tant spe cies, is the low est. Hence,

the as sem blages, strongly dom i nated by this spe cies, re -flect ing diagenetic change, should oc cur in the light grey mudstone strata. In fact, the re la tion ship be tween the per -cent age of W. barnesiae and the dark to light grey mudstone strata is not clear. The rea son may be the amounts of clay and or ganic mat ter that are above the thresh olds for sig nif i -cant dis so lu tion of nannofossil cal cite (vide Turchyn and DePaolo, 2011). There fore, the per cent age of W. barnesiae and as sem blage diveristy do not de pend on car bon ate con -tent.

This can be ev i denced by the |r| value, counted for the

W. barnesiae vs. NOS pair, which is 0.22, show ing very lit

-tle lin ear fit. More over, W. barnesiae is not as so ci ated with any other taxa, ex cept for R. asper, a ro bust murolith, which also seems to be dis so lu tion re sis tant. A few sam ples, with

Fig. 4. Cal car e ous nannofossils in cross-polar ised light. A. Biscutum sp., sam ple P25. B. Crucibiscutum sp., sam ple P20; C.

Watzna-ueria bri tan nica, sam ple P17; D. Retecapsa surirella, sam ple P14; E. R. angustiforata, sam ple P29; F. Crucielipsis cuvillieri, sam ple P18;

G. Eiffellithus striatus, sam ple P25; H. E. windii, sam ple P20; I. Speetonia colligata, sam ple P3; J. Rhagodiscus asper, sam ple P21; K.

Rhagodiscus sp., sam ple P30; L. Staurolithites sp., sam ple P24; M. S. crux, sam ple P6; N. S. mutterlosei, sam ple P30; O. S. mutterlosei, sam ple P8; P. Zeugrhabdotus embergeri, sam ple P3; Q. Nannoconus sp., sam ple P25; R. Micrantholithus hoschultzii, sam ple P8. The scale-bar is the same for the all pho to graphs

an NOS be low 10 taxa (P8, P10, P11, P18, P24), might be sus pected of hav ing un der gone some diagenetic change, but the per cent age of W. barnesiae ex ceeds 90% only in one of the above sam ples, P10. The next sam ple with a per cent age of above 90%, P23, has 16 taxa. Fur ther more, sam ple P18, with 7 taxa only, is the one with the low est W. barnesiae per cent age (75.8%).

With re gard to the above con sid er ations, we sup pose that as sem blages stud ied are not at all or only very lit tle (e.g., sam ple P10) af fected by diagenetic pro cesses and may rep re sent the pri mary com po si tion.

Valanginian to Hauterivian cal car e ous nannoplankton ecol ogy

The Early Cre ta ceous is known as a time of a glob ally wide spread de po si tion of black shale, rich in or ganic mat ter. They used to be at trib uted to anoxic events, which in the Cre ta ceous are known as Oce anic Anoxic Events (OAE). Re cently, it be came ap par ent that OAEs are only one pos si -ble re sult of en vi ron men tal changes. There fore, the gen eral

term, ep i sodes of en vi ron men tal changes (EECs), is more ap pro pri ate (Föllmi, 2012). Early Cre ta ceous EECs are de -fined by a spe cific car bon-iso tope re cord and black, or -ganic-rich de pos its in de pend ently. These fea tures may both in di cate the oc cur rence of EECs, but only one of them may be di ag nos tic (Föllmi, 2012). The Valanginian EECs il lus -trate the above ex pla na tion.

Valanginian EECs had a ma jor im pact on the plank -tonic micro fauna, es pe cially the calpionellid group, which nearly be came ex tinct. This was con nected to the platetec -tonic re-or ga ni za tion, but in the strati graphic re cord, it is rec og nized as a biocalcification crisis.

The Valanginian biocalcification cri sis may be char ac ter ized by a 65% re duc tion in nannofossil palaeofluxes. De -spite the sub mer gence of car bon ate plat forms, it may be trig gered by a two- to three-fold in crease in pCO2, caused

by ma jor vol ca nic ac tiv ity. The cri sis was ex pressed in the pe lagic realm by a de cline in the abun dance of nannoconids (nannoconid cri sis) in cal car e ous nannofossil as sem blages (Erba, 2004; Erba and Tremolada, 2004; Weissert and Erba, 2004). Lately, it was sug gested that nannoconid abun dance

Fig. 5. Shan non In dex, num ber of spe cies, per cent age of cal car e ous nannofossils and lin ear fits for se lected vari ables. Stars: oc cur

shows a polyphase de cline, with two stages of de crease in -ter rupted by an in crease in the abun dance of Nannoconus. It seems to be re lated to tem per a ture de crease and vari abil ity in nu tri ent sup ply. The nannoconid re cov ery oc curred dur -ing the cold est pe riod of the Valanginian cool -ing phase and was in ferred to be con nected to the in put of more oligotro-phic sur face wa ters (Barbu and Melinte-Dobrinescu, 2008; Barbarin et al., 2012). More over, palaeoclimatic changes probably were the cause of longterm trends (1–4 my), re flected in shifts from Watznaueria spp.dom i nated as sem -blages in the Up per Barremian–Lower Valanginian to

Na-nnoconus spp.-dom i nated assemblages in the Upper

Valan-ginian (Melinte and Mutterlose, 2001).

The cor re la tion co ef fi cient in di cates a strong de pend -ence of SI and the per cent age of W. barnesiae, as well as that of R. asper. These nannofossil spe cies also have a strong neg a tive cor re la tion for their fit. The al most per fect lin ear fit of SI and W. barnesiae in di cates that the oc cur rence of this spe cies had a great in flu ence on as sem blage di -ver sity (Tab. 2; Fig. 5). Ob vi ously, this is caused by the high per cent age of W. barnesiae and its dom i nance in the all sam ples. Nev er the less, the high, pos i tive cor re la tion of R.

asper and SI in di cates that R. asper is the spe cies that is in

-dic a tive of en hanced nannofossil di ver sity. Con se quently, the cor re la tion co ef fi cient for the fit of W. barnesiae and R.

asper has a strong, neg a tive value. Both spe cies are

regar-ded as warm-wa ter spe cies (e.g., Perch-Niel sen, 1985; Mut- terlose 1991, 1992). More over, W. barnesiae rep re sents an

r-se lected life strat egy, sim i lar to that of the pres ently ex tant Emiliania huxleyi. Ac cord ingly, it was dom i nant in

palaeo-en vi ron mpalaeo-ents hos tile for other taxa (e.g., Street and Bown, 2000; Lees et al., 2004; Lees et al., 2005). Mutterlose and Kessels (2000) con sid ered the W. barnesiae-Nannoconus sp.-R. asper as sem blage to be typ i cal for low-lat i tude, warm, and nu tri ent-poor sur face wa ters, which may have cor re sponded to the mod ern, sub trop i cal and trop i cal

Emi-liania huxleyi-Gephyrocapsa oceanica communities.

Nev er the less, the strong, neg a tive cor re la tion co ef fi -cient r for the R. asper vs. W. barnesiae pair in di cates their dif fer ent en vi ron men tal pref er ences, in ad di tion to their re la tion ship to wa ter tem per a ture. Such ob ser va tions were al -ready re ported by Thom sen (1989), for ex am ple, who found sea sonal vari a tions in W. barnesiae and R. asper abun -dance. Peaks in the abun dance of these spe cies oc curred in dif fer ent laminae, in di cat ing dif fer ent en vi ron men tal con -nec tions. Hardas et al. (2012) found that in creased wa -ter-col umn strat i fi ca tion dur ing the Mid dle Cenomanian Event caused a dis tinc tive de crease in the abun dance of R.

asper. This may be ap pli ca ble in the pres ent study, be cause

of the peak in the oc cur rence of R. asper in sam ple P20 that co in cides with the ap pear ance of Crucibiscutum sp., high-lat i tude taxa, indicating the influence of cold water which mixed the surface-water column.

On the other hand, W. barnesiae has a very strong, neg -a tive cor re l-a tion with SI, in con tr-ast to R. -asper, which h-as -a strong, pos i tive cor re la tion with SI. This sim ply shows that

R. asper is more abun dant in sam ples with biodiversity that

is higher, by com par i son with those con tain ing W.

barne-siae. If SI is taken as a mea sure of trophic con di tions, then

higher biodiversity may in di cate en vi ron ments more hos pi

-ta ble to nannoplankton de vel op ment than the en vi ron ments of the poorly di ver si fied as sem blages, dom i nated by W.

barnesiae.

In the ma te rial stud ied, the dom i nance of W. barnesiae prob a bly re flects strong, oligotrophic con di tions of a fully ma rine en vi ron ment, with a strat i fied wa ter-col umn, and the ap pear ance of R. asper in di cates slight changes, lead ing to less oligotrophic (mesotrophic?) con di tions. In ter est ingly, the oc cur rence of the Tethyan nannoconids is con nected with the dom i nance of W. barnesiae, which ad di tion ally sup ports the in ter pre ta tion of a pre dom i nance of warm, strat i fied, oligotrophic wa ters (see Erba, 2004; Erba and Tremolada, 2004).

Nev er the less, finds of nannoconids were rare in the pre- sent study and, in gen eral, re flect a Valanginian biocalcificat ion cri sis. Nannoconids were found only in those sam -ples with sup pos edly higher car bon ate con tents i.e., the light grey mudstones of sam ples P4, P25 and P27. Some Tethyan taxa, such as C. cuvillieri and C. oblongata oc cur con stantly through out the sec tion, but their abun dances in -crease slightly within those in ter vals, where nannoconids oc cur (Tab. 1; Fig. 5). The al ter na tion of the dark-and lightcol oured mudstones, to gether with changes in the com po si -tion of nannofossils as sem blages, may have been caused by hu mid-arid cli mate changes, driv ing the trophic con di tions of sur face wa ters and nannoplankton biocalcification, as pos tu lated by Gréselle et al. (2011) and Föllmi (2012). The sce nario in ferred is as fol lows: a hu mid and con tem po ra ne -ously cool cli mate, con nected to sea-level fall caused the ero sion of the in ner shelf and re stricted car bon ate pro duc tion (e.g., Brachert et al., 2003). This in ten si fied the weath er ing pro cesses and the re lated in put of nu tri ents into sur face wa ters. As a re sult, oligotrophic, strat i fied sur face wa -ters of the arid pe riod were mixed and trans formed into less oligotrophic or mesotrophic en vi ron ments. This is re corded by the dark-col oured mudstones, and an in crease in SI and oc cur rences of R. asper. Ac cord ingly, light-col ored mud-stone rep re sents an arid and rel a tively warmer cli mate, with a strat i fied wa ter col umn, ev i denced by a de crease in SI, the pre dom i nance of W. barnesiae and occurrences of nanno-conids.

Cal car e ous nannofossil biostratigraphy

A few nannofossil zonations are widely used for the Lower Cre ta ceous. Bown et al. (1998) pro posed a new zonation for bo real as sem blages and cor re lated it with the Tethyan NK zones of Bralower et al. (1989) and with the NC zones of Roth (1978, 1983), Bralower (1987) and Bra-lower et al. (1993), as well as with the CC zones of Sissingh (1977) (Fig. 6).

In ad di tion to the above schemes, other nannofossil zonations have been pro posed in the Carpathians. Melinte (1997) dis tin guished two main nannofossil groups, char ac -ter ized by an in flu ence of the Bo real or Tethyan realm. The lower part of the Lower Valanginian is de fined by the oc cur rence of Tethyan and cos mo pol i tan nannofossils. The in -ter val with the Lower/Up per Valanginian bound ary shows a mix ture of Tethyan and Bo real taxa. The up per part of the Up per Valanginian is char ac ter ized by Tethyan taxa.

Me-linte (1997) pro posed a sub di vi sion off the Valanginian into the fol low ing three in ter val nannofossil zones: Retecapsa (= Cretarhabdus) angustiforata; Speetonia colligata and

Calcicalathina oblongata. The S. colligata Zone also is

sub di vided into three subzones: Reinhardtites fenestratus;

Micrantholithus speetonensis and Diadorhombus rectus,

where the M. speetonensis nannofossil Zone is the total range taxon biozone.

GaŸdzicka in Dziadzio et al. (2004) pro posed a zonation scheme for the Lower Cre ta ceous in cen tral and SE Po -land. The rea son for the pro posal of the new zonation was the spe cific na ture of the nannofossil as sem blages of the Pol -ish Low land, which ex cluded it from the use of the Tethys or Bo real zonations. This zonation in tro duced the PN 2 to PN 5 in ter val zones for the Valanginian and the low er most Hauterivian, where the PN 4 and PN 5 had been de fined pre vi ously by Mutterlose (1991). The PN 2 Zeugrhabdotus

diplogrammus Zone rep re sents the low er most part of Valanginian and its lower bound ary is de fined by the FO of the in dex spe cies. The def i ni tion of the lower bound ary of the next PN 3 Watznaueria barnesae Zone seems to be ques tion able. This is de fined by the ap pear ance of a poorly di ver si fied as sem blage, dom i nated by the in dex spe cies. A zone that is de fined in this way is use less, be cause it might be con nected to no time-re lated, en vi ron men tal or preser-vational sig nal. In stead, the poorly di ver si fied in ter val, dom i nated by W. barnesiae, may only char ac ter ize the up -per part of the PN 2 Zeugrhabdotus diplogrammus Zone. The PN 3 Watznaueria barnesae Zone rep re sents the up per part of the Lower Valanginian. The PN 4 Eiffellithus

stria-tus Zone is de fined by the FO of the in dex spe cies, as well

as the PN 5 Conusphaera rothii. The up per bound ary of the PN 5 Zone is de fined by the FO of the next in dex spe cies,

Eprolithus antiquus. The PN 4 Zone rep re sents the lower

part of the Up per Valanginian, em brac ing the verrucosum ammonite Zone, and the PN 5 Zone rep re sents the up per part of the Up per Valanginian and the low er most part of the Hauterivian (GaŸdzicka in Dziadzio et al., 2004).

In the pres ent study, sam ples yielded stratigraphically im por tant spe cies, such as E. windii or E. striatus. The first oc cur rence of E. striatus de fines the base of the CC4 Zone and is in the up per part of both the NK3B and BC5 zones. The next nannofossil spe cies Nannoconus bucheri and

Lithraphidites bollii, which first oc cur above this zone, were not found in the ma te rial. Thus, the up per limit of the age was taken from the last oc cur rence of E. windii, which was noted in the lower part of the NC4 Zone. The in ter val be tween the FO of E. striatus and the LO of E. windii is equiv a lent of the up per part of the Up per Valanginian and lower part of the Lower Hauterivian.

How ever, the Valanginian EECs, de spite their trig ger -ing mech a nism, also in duced Bo real and Tethyan ex -changes of fauna. The spread of Tethyan nannoplankton species into the Bo real realm of NW Eu rope was re corded in the ear li est Late Valanginian, the Valanginian–Haute-rivian bound ary in ter val and Late HauteValanginian–Haute-rivian (Mutterlose, 1992, 1993). These mi gra tions may have some strati graphic po ten tial. The Early Cre ta ceous spe cies C. salebrosum al most ex clu sively is known in highlat i tudes of both hemi -spheres, par tic u larly dur ing the Valanginian to Hauterivian. This prob a bly re flects a high-lat i tu di nal ther mal gra di ent, which may be am pli fied by a lowstand of the sea-level (Mu- tterlose and Kessels, 2000). Nev er the less, that spe cies is of -ten re corded in low lat i tudes in the early Late Valanginian

verrucosum ammonite Zone to gether with other bo real taxa

(Mutterlose, 1993; Melinte, 1997; Melinte and Mutterlose,

Fig. 6. Strati graphic po si tion of in ter val stud ied – marked in dark grey col our. Bold, ver ti cal lines in di cate Bo real in flu ences, re corded

in West ern Carpathians by Vašíèek and Michalík (1997) in radiatus ammonite Zone and by Švábenická (2008) and Svobodova et al. (2011) in campylotoxus-verrucosum and ligatus-balearis ammonite zones

2001; Kessels et al., 2006; Melinte-Dobrinescu and Jipa, 2007; Barbu and Melinte-Dobrinescu, 2008; Švábenická, 2008; Svobodova et al., 2011). The verrucosum ammonite Zone seems to have been the time of the most con spic u ous in va sion of the Bo real taxa into the Tethys ocean realm. The next time of the Bo real nannofossil in flu ences in the low lat -i tudes was -in the Early Hauter-iv-ian. Con clud -ing, Bo real spe cies, in clud ing C. salebrosum, can be found at low lat i -tudes in the BC3-4 and BC6-8 nannofossil zones (Kessels et

al., 2006; Švábenická, 2008; Svobodova et al., 2011). It is

note wor thy that this nannofossil, re ported ear lier from the W¹wa³ sec tion by Mutterlose (1993), was missed by Dzia-dzio et al. (2004) and probably as a result, they emphasized mainly Tethyan influences.

The en vi ron men tal con nec tions of C. salebrosum most prob a bly can be ex tended to the en tire ge nus

Crucibiscu-tum. Ac cord ingly, the ap pear ance of Crucibiscutum sp. in

sam ples of the pres ent study is in dic a tive of a high-lat i tude in flu ence (Mutterlose and Kessels, 2000; Bown and Con-cheyro, 2004; Kessels et al., 2006; Pauly et al., 2012a, b).

In ad di tion to the in dex nannofossil spe cies used for def i ni tion of the BC zones, Švábenická (2008) and Svobodova et al. (2011) de ter mined di ag nos tic nannofossil as -sem blages for each BC Zone, in terms of the in flu ences of the Tethyan or Bo real prov inces (Fig. 6). These spe cific as -sem blages could be used for strati graphic pur poses. Accor-dingly, the Bo real in flu ences, in di cated by oc cur rences of

M. speetonensis and Sollasites horticus, char ac ter ize the up

-per part of the Lower Valanginian and BC4b nannofossil sub-Zone. This cor re sponds well to the verrucosum ammonite Zone, com monly re ferred to the time of in va sion by dis -tinct Bo real taxa into the Tethys ocean realm (e.g., Melinte, 1997; Vašíèek and Michalík, 1997; Melinte and Mutterlose, 2001; Kessels et al., 2006; Barbu and Melinte-Dobrinescu, 2008). The Up per Valanginian, i.e., the BC4-BC5 nanno-fos sil zones, is char ac ter ized by the pre dom i nance of Te-thyan nannofossil taxa, such as: E. windii, R. asper, S.

col-ligata or Cruciellipsis cuvillieri, with mi nor ad di tions of

nannoconids. On the other hand, the rare oc cur rences of

Crucibiscutum sp. in sam ples of the pres ent study sug gest

some Bo real in flu ences. These in flu ences with in va sion by high-lat i tude nannofossils, were re corded in the BC4b Zone, cor re spond ing to the verrucosum ammonite Zone and the BC9 Zone of the Up per Hauterivian by Švábenická (2008) and Svobodova et al. (2011). How ever, the BC4b Zone is char ac ter ized by the pres ence of Micrantholithus

speetonensis and Conusphaera rothii, which were not

found in the sam ples of the au thors. More over, the BC4b Zone oc curs be low the FO of E. striatus, found in sam ples of the pres ent study and the BC9 Zone is above the LO of both E. striatus and E. windii and is characterized by taxa that are absent in section studied.

Nev er the less, Vašíèek and Michalík (1997) noted some Bo real in flu ences in the Outer Carpathians, also in the low -er most Haut-erivian radiatus ammonite Zone. This fits well to the nannofossils re cord of the pres ent ac count. Tak ing into ac count also the ammonite data, pro vided by Vašíèek et

al. (2010), it may be con cluded that the sec tion rep re sents

the BC5-BC6 zones bound ary in ter val, i.e., the Valangi-nian/Hauterivian boundary (Fig. 6).

CON CLU SIONS

1. The as sem blages of cal car e ous nannofossils stud ied are dom i nated by the fol low ing taxa: W. barnesiae. Com -mon are Retecapsa spp., R. asper, Staurolithites mut

terlo-sei, Staurolithites spp. and Zeugrhabdotus spp.

2. Tethyan nannofossil taxa pre dom i nate in the ma te rial stud ied, but some un com mon Bo real spe cies, i.e.,

Crucibis-cutum sp., also were found.

3. Rhagodiscus asper and W. barnesiae rep re sent dif fer ent eco log i cal strat e gies, de spite their sup posed as so ci a -tion with warm sur face wa ter. The per cent age of R. asper in creases with in creas ing SI (cor re la tion co ef fi cient r = 0.677) and de creases with in creas ing per cent ages of W. bar-

nesiae (cor re la tion coefficient r = –0.5695).

4. The oc cur rence of some Tethyan nannoconids, in -creas ing per cent ages of W. barnesiae in light grey mud-stones, to gether with the ap pear ance of Crucibiscutum sp. and in creas ing per cent ages of R. asper in dark grey mud-stone, in di cate dif fer ent sur face-wa ter con di tions dur ing se-dimentation. These re sulted from hu mid-arid cli mate chan-ges, driv ing the trophic con di tions of sur face wa ters and na-nnoplankton biocalcification.

5. Dark grey mudstones were de pos ited un der the in flu -ences of the Bo real realm. In con trast, light grey mudstones re flect pre dom i nance of the in flu ences of the Tethyan prov -ince.

6. On the ba sis of the pres ence of Eiffellithus striatus, E.

windii and both Tethyan and Bo real in flu ences, the sec tion

stud ied rep re sents the Valangian/Hauterivian bound ary in -ter val, i.e., the bound ary of the BC5-BC6 zones, re lated to the furcillata-radiatus ammonite zones.

Ac knowl edge ments

Au thors are grate ful to Al fred Uchman for in tro duc ing them in the sub ject area and Lower Cre ta ceous of the Silesian Unit. Authors are also thank ful for the re marks, com ments and sug ges -tions from re view ers Grzegorz Haczewski and Mi chael Wagreich and from Ed i tor Micha³ Zatoñ. Lin guis tic cor rec tions made by Frank Simpson greatly im proved the manu script. The study was sup ported by Jagiellonian Uni ver sity Grant DS No. 001673.

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