Foraminifers and sta ble iso tope re cord of the Dubivtsi chalk (up per Turonian, West ern Ukraine): palaeoenvironmental im pli ca tions
Zofia DUBICKA and Danuta PERYT
Dubicka Z. and Peryt D. (2012) – Foraminifers and sta ble iso tope re cord of the Dubivtsi chalk (up per Turonian, West ern Ukraine):
palaeoenvironmental im pli ca tions. Geol. Quart., 56 (1): 199–214. Warszawa.
A com bined micropalaeontological and sta ble iso tope study of the Dubivtsi chalk in the West ern Ukraine in di cates its mid dle late Turonian age. One long-term and clearly dis tin guish able pos i tive ex cur sion of the iso tope curve (d13C) in the Dubivtsi chalk is prob a bly equiv a lent to a wide spread up per Turonian pos i tive peak re corded in West ern and South ern Eu rope and named Peak +1, Hyphantoceras Event or Hitch Wood Event. Such cor re la tion is also sup ported by inoceramid fauna and in creas ing d18O val ues. Sed i men ta tion of the pure Dubivtsi chalk oc curred un der highly oligotrophic con di tions, re flected by the low di ver sity and very low abun dance of plank tonic and ben thic foraminifera and a flood abun dance of pithonellid calcispheres. These con di tions prob a bly were trig gered by re gres sion, a low level of re gional tec tonic ac tiv ity, and near ab sence of up lifted ar eas in ad ja cent ar eas and hence the sup ply of nu tri ents to the ba sin was lim ited.
Zofia Dubicka and Danuta Peryt, In sti tute of Paleobiology, Pol ish Acad emy of Sci ences, Twarda 51/55, 00-818 Warszawa, Po land, e-mails: zdubicka@twarda.pan.pl, d.peryt@twarda.pan.pl (re ceived: Jan u ary 11, 2012; ac cepted: March 12, 2012).
Key words: Turonian, foraminifers, car bon iso topes, ox y gen iso topes, biostratigraphy, palaeoenvironments.
INTRODUCTION
The Turonian is be lieved by many au thors to be one of the warm est pe ri ods of the Phanerozoic eon (e.g., Wil son et al., 2002; Bice et al., 2006; Bornemann et al., 2008). How ever, oth ers (e.g., Stoll and Schrag, 2000; Voigt et al., 2004) doc u - mented some sig nif i cant cli mate cool ing events in its up per part. More over, sev eral pos si ble stages of con ti nen tal ice growth dur ing the pe riod were dis cussed (e.g., Miller et al., 2005; Bornemann et al., 2008). Al though the prob lem of gla ci - ation dur ing the Cre ta ceous supergreenhouse is sub ject to de - bate (e.g., Wiese and Voigt, 2002; Bornemann et al., 2008), there is no doubt that isochronous vari a tions of d18O curves within sev eral West and Cen tral Eu ro pean bas ins in di cate a pe - riod of late Turonian cli mate cool ing, which is characterized by two dis tinct cool ing phases, in ter preted by Wiese and Voigt (2002) as a re sult of high vol ca nic ac tiv ity, and sep a rated by a pe riod of cli mate sta bil ity. The cool ing phases dur ing the Turonian de duced from isochronous vari a tions of d18O curves match per fectly the pos i tive ex cur sions on d13C iso tope pro files (Wiese and Voigt, 2002, fig. 8), which show con sis tent strati - graphic trends, and com monly iden ti cal d13C val ues, and thus pro vide a ba sis for high-res o lu tion strati graphic cor re la tion
(Jarvis et al., 2006). One of four key car bon-iso tope ex cur sions re cog nized by Scholle and Ar thur (1980) in the Cenomanian to lower Campanian spans the Cenomanian/Turonian bound ary (e.g., Schlanger et al., 1987; Ar thur et al., 1990; Pratt et al., 1993; Peryt et al., 1994). Sub se quently much more cor re la tive events have been iden ti fied be tween the Albian/Cenomanian and Santonian/Campanian bound aries (39 events de fined, and fur ther 33 da tum lev els pro vi sion ally iden ti fied by Jarvis et al., 2006). The Cenomanian–Santonian car bon-iso tope ref er ence curve pre sented by Jarvis et al. (2006) is, as noted by them, re - mark ably sim i lar in shape to sup pos edly eustatic sea level curves, in creas ing d13C val ues ac com pa ny ing sea level rise.
Chemostratigraphy com bined with biostratigraphy (usu ally based on ammonites and inoceramids) of fers po ten tial for im - prov ing global cor re la tion and may pro vide a proxy for eustatic sea level vari a tion (Jarvis et al., 2006). How ever, plank tonic foraminifera have proved to be vi tal in high res o lu tion biostratigraphy of mid-Cre ta ceous (e.g., Moullade, 1966;
Caron, 1985; Leckie, 1987) and youn ger ma rine se quences (e.g., Bolli, 1966; Premoli Silva and Sliter, 1994; Robaszynski and Caron, 1995) and use ful palaeoecologic in for ma tion can be ob tained from an cient as sem blages as sim ple morphotypes in - hab ited the near-sur face wa ters while keeled, com plex forms prob a bly oc cu pied deeper hab i tats dur ing the mid-Cre ta ceous,
as to day (e.g., Hart and Bailey, 1979; Leckie, 1987; Premoli Silva and Sliter, 1994). The aim of this pa per is to es tab lish an in te grated de tailed stra tig ra phy of the up per Turonian part of the Dubivtsi sec tion (West ern Ukraine) based on plank tonic foraminifers and sta ble iso topes and to cor re late it with the sec - tions with con tem po ra ne ous strata lo cated in NW Eu rope. We also pres ent quan ti ta tive and qual i ta tive stud ies of plank tonic and ben thic foraminifers, which com pared with bulk in or ganic car bon and ox y gen sta ble iso tope data make it pos si ble to in ter - pret the sed i men tary en vi ron ment in this part of the Cre ta ceous Bo real Sea.
GEOLOGICAL SETTING
The Dubivtsi 1 sec tion is lo cated in the SW mar gin of the East Eu ro pean Plat form, within a tec tonic unit called Bor der Synclinorium oc cur ring to the NE of the Mid-Pol ish Anticlinorium (the in verted part of the Mid-Pol ish Trough;
Po¿aryski et al., 1979), and spe cif i cally in its south east ern part – L’viv–Stryi Syncline (Pasternak et al., 1987; Œwidrowska et al., 2008; Figs. 1 and 2). Start ing from the Turonian (and end - ing in the late Maastrichtian) the Pol ish Low land was al most en tirely char ac ter ized by var i ous chalk fa cies (Walaszczyk in Voigt et al., 2008), and the same sit u a tion is true for the pro lon - ga tion of the Mid-Pol ish Trough to the south-east, into the Ukraine (Œwidrowska et al., 2008).
In the West ern Ukraine the Turonian and Coniacian strata are in cluded into the Dubivtsi Suite with a to tal thick ness ex - ceed ing 158 m (Ivannikov et al., 1987; Gavrilishin et al., 1991). The suite is over ly ing the Cenomanian lime stones and con sists of two parts. The lower subsuite of Turonian age are white and grey lime stones, with flood abun dances of Pithonella (Fig. 3) as rec og nized by Rozumeyko (1978); and
with flint con cre tions that ap pear 15–20 m above the base of the suite and in crease in num ber up ward in the sec tion (Gavrilishin et al., 1991; Vashchenko et al., 2007). The up per subsuite (lime stones, of ten ar gil la ceous, and marls with com - mon inoceramid frag ments) is of Coniacian age (Gavrilishin et al., 1991).
In the huge aban doned quarry Dubivtsi (N 49°05.547’, E 24°48.433’) lo cated 1 km to the east of Dubivtsi vil lage and to the south of Halych, and which here is re ferred to as Dubivtsi 1 (Fig. 2), there oc curs a 31 m thick sec tion sub di vided into four
Fig. 1. Sketch tec tonic map of Cen tral Eu rope show ing the lo ca tion of the Dubivtsi sec tion (after Œwidrowska et al., 2008)
Fig. 2. Lo ca tion map
A – sketch map of the West ern Ukraine show ing the lo ca tion of the study area north of Ivanofrankivs’k; B – geo log i cal map of area be tween Halych and Ivanofrankivs’k with the lo ca tion of the Dubivtsi sec tion (af ter Vashchenko et al., 2007)
lithological units: chalk (strongly lithified, with CaCO3 con tent rang ing from 97.8 to 99.9%); hardgrounds; inoceramid lime - stones (4.4 m thick) and marls (1.5 m; Fig. 4). The two lower units be long to the lower Dubivtsi Suite, and two up per units to the up per Dubivtsi Suite. The thick ness of the Turonian in the re gion is 50–100 m (Gavrilishin et al., 1991). There are ten flint lay ers (marked as F1–F10) rel a tively reg u larly scat tered in the chalk pro file (Fig. 4); how ever, flints do not oc cur in the last few metres of the chalk sec tion. In the mid dle part of the Dubivtsi chalk (5.4, 6 and 14.6 m above the base of the sec tion;
Fig. 4) three clay-rich beds oc cur. These are des ig nated as beds
A1 (10 cm thick), A2 (1 cm thick) and Z (3–5 cm thick; Fig. 4).
There are four hardgrounds above the chalk de pos its (Fig. 4).
Pre lim i nary data on the li thol ogy and inoceramid bio - stratigraphy in the Dubivtsi 1 quarry suc ces sion have been pre - sented by Pabian (2004); pre vi ous pub lished char ac ter is tics and fau nal lists of the Dubivtsi Suite (Gavrilishin et al., 1991) re fer to the en tire suite and al though most of the listed fauna can be found in the stratotype sec tion of the suite (i.e., Dubivtsi vil - lage), de tailed in for ma tion sup port ing such an as sump tion (pre - vi ous stud ies do not men tion the ver ti cal dis tri bu tion of the fauna) is not avail able.
Fig. 3. Pithonellid-rich car bon ates show ing packstone tex ture from the Dubivtsi 1 sec tion (A–D), with plank tonic foraminifers (B–D) and bi valve frag ments (C–D) and pho to mi cro graphs of Pithonella ovalis Kaufmann (E–H)
A, C – sam ple 8; B – sam ple 4; D – sam ple 28
F1 F2 F3 F5
F4 F6 F7 ZF8 F9 F10 (I)
A1 A2
1 11 12 13 17 16
15 20 21 22 23 24 26
29 28 31 32 42 43 44 45 46 47 48 49
27 25
18 19
14
2 3 4 5 6 7 8 9 10
(IV) (III) (II)
Q
(IV) (III)
(II) Hg 1 Hg 2 Hg 3 Hg 4
1m
chalk
flint layer with flints densely distributed flint layer
sparsely distributed with flints marls
sample hardground
Zoophycos inoceramid
limestones
2
10
F1 A F5
F3 F2
A1
F3
3
33 34
41 38 40
37 39
36
35 26 cm
33 cm 25 cm
Hg2 Hg3 Hg4
Hg1
30cm
F9 F10
(I)
(I) (II) (III) (IV) stylolitic seams
30
5 10 15 20 25 30 [m]
Fig. 4. The com pos ite Dubivtsi 1 sec tion show ing char ac ter is tic strata and the sam pling sites F1–F10 – flint lay ers; A1, A2 and Z – clay-rich lay ers; I–IV – lo cal mark ers – stylolitic seams; Q – Qua ter nary;
the white el lip soid in the lower left photo shows the se nior au thor for scale
MATERIAL AND METHODS
Twenty seven sam ples from the com pos ite sec tion were ana - lysed for plank tonic and ben thic foraminifera as well as for car - bon and iso tope sta ble iso topes; in ad di tion, five more sam ples were sub ject to foraminiferal study. Sam ples were col lected ev - ery 1 m. Washed res i dues were ob tained by disaggregating the rocks by two dif fer ent meth ods (Glau ber’s Salt method and liq - uid ni tro gen method; Remin et al., 2011). The res i dues were cleaned in an ul tra sonic bath. The ³63 mm frac tion, con tain ing 300 or more spec i mens per sam ple, was used for foraminiferal counts. The rel a tive abun dance of plank tonic and ben thic foraminifera within foraminiferal as sem blages (P/B ra tio), cal - car e ous-hyaline and ag glu ti nated forms within ben thic foraminiferal as sem blages, and ben thic foraminiferal spe cies within ben thic foraminiferal as sem blages as well as the pro por - tion of infaunal and epifaunal morphogroups within ben thic foraminiferal as sem blages were cal cu lated.
Ben thic foraminifers were iden ti fied at a ge neric level in this study, ac cord ing to Loeblich and Tappan’s (1987) sys tem - at ics. Al lo ca tion of foraminiferal taxa into morphogroups was
largely per formed fol low ing Corliss and Chen (1988) and Nagy et al. (1995). The fig ured spec i mens (Figs. 5–7) are de - pos ited in the In sti tute of Paleobiology, Pol ish Acad emy of Sci - ences, Warszawa (ZPAL F. 63).
Car bon and ox y gen sta ble iso topes have been ana lysed in bulk sam ples. The car bon ate pow der was re acted with 100%
orthophosphoric acid at 70°C us ing a KIEL IV on line au to matic car bon ate prep a ra tion line con nected to the Finnigan Mat delta plus mass-spec trom e ter at the Light Sta ble Iso topes Lab o ra tory of the In sti tute of Geo log i cal Sci ences and In sti tute of Paleobiology, Pol ish Acad emy of Sci ences, Warszawa. All iso - tope data were re ported in per mil rel a tive to VPDB re lated to NBS19. The pre ci sion (reproducibility of rep li cate anal y ses) of both car bon and ox y gen iso tope anal y ses was usu ally better than ±0.2‰.
Abun dances of to tal car bon were de ter mined by us ing an Eltra CS-500 IR an a lyzer with a to tal in or ganic car bon mod ule, at the Uni ver sity of Silesia (Sosnowiec, Po land). Cal cium car bon ate con tent was cal cu lated as CaCO3 = 8.333 × to tal in or ganic car bon, as sum ing that all car bon ate is pres ent as cal cite or ar agon ite.
Fig. 5. Plank tonic foraminifers of the Dubivtsi chalk
A – Marginotruncana coronata (Bolli); B – Heterohelix reussi (Cushman); C – Dicarinella imbricata (Mornod); D – Falsotruncana sp.;
E – Whiteinella brittonensis (Loeblich and Tappan); F – Whiteinella baltica Douglas and Rankin; A, C, D – sam ple 1; B – sam ple 32, E – sam ple 5, F– sam ple 20; scale bar – 100 mm; a – edge view, b – dor sal view, c – ven tral view, d – side view, e – lat eral view
RESULTS
FORAMINIFERS
The Dubivtsi chalk yielded well-pre served ben thic and plank - tonic foraminiferal as sem blages that show low di ver sity and very low abun dance and very abun dant pithonellids (Figs. 3, 5, 6, 8 and 9). Thir teen spe cies of plank tonic foraminifera were re corded:
Helvetoglobotruncana helvetica (Bolli), Marginotruncana coronata (Bolli), M. marginata (Reuss), M. pseudolinneiana Pessagno, Dicarinella imbricata (Mornod), D. hagni (Scheibnerova), D. canaliculata (Reuss), Whiteinella baltica Douglas and Rankin, W. brittonensis (Loeblich and Tappan),
Falsotruncana sp., Globigerinelloides caseyi (Bolli, Loeblich and Tappan), Heterohelix reussi (Cushman), Hedbergella delrioensis (Carsey) (most of them are shown in Figs. 5 and 6). The small-sized, sim ple heterohelicids, planispiral Globigerinelloides and trochospiral Whiteinella oc cur in the en tire sec tion (Fig. 8), al - though they are very rare. Keeled forms of plank tonic foraminifers are com mon only in the low est and higher part of the chalk suc ces - sion (Figs. 8 and 9). In most sam ples the P/B ra tio in the 0.06–0.75 mm size frac tion is about 20%, ex cept for the low est sam ple, where it is al most 50% (Fig. 9).
Ben thic foraminiferal num bers per gram dried sed i ment in the Dubivtsi chalk are very low and do not ex ceed 4 in di vid u - als/g. Eleven spe cies of ben thic foraminifers have been re -
Fig. 6. Plank tonic foraminifers of the Dubivtsi chalk
A – Helvetoglobotruncana helvetica (Bolli); B – Dicarinella imbricata (Mornod); C – Falsotruncana sp.; D – Marginotruncana marginata (Reuss); E – Dicarinella hagni (Scheibnerova); F – Marginotruncana pseudolinneiana Pessagno; G – Dicarinella
canaliculata (Reuss); A, B, D–G – sam ple 1, C – sam ple 4; other ex pla na tions as in Fig ure 5
Fig. 7. Ben thic foraminifers of the Dubivtsi chalk
A – Valvulineria lenticula (Reuss); B – Gyroidinoides nitidus (Reuss); C – Cibicides polyrraphes var. polyrraphes (Reuss); D – Gavelinella vesca (Bykova); E – Globorotalites hangensis Vassilenko; F – Gavelinella vesca (Bykova); G – Eponides karsteni (Reuss); H – Cibicides polyrraphes var. polyrraphes (Reuss); I – Praebulimina reussi (Mor row); J – Gavelinella ammonoides (Reuss); K – Gavelinella ammonoides (Reuss); A –sam ple 5, B – sam ple 19, C, H – sam ple 1, D – sam ple 20, E – sam ple 30, F – sam ple 10, G – sam ple 27, I – sam ple 28, J – sam ple 20, K – sam ple 14; other ex pla na tions as in Fig ure 5
corded in stud ied ma te rial. Nine spe cies rep re sent cal car e ous forms and only two ag glu ti nated spe cies have been found (Fig. 9). Cal car e ous foraminifers form 90% of the as sem blages and three spe cies, i.e., Gavelinella ammonoides (Reuss), G.
vesca (Bykova) and Gyroidinoides nitidus (Reuss), dom i nate the as sem blages. Their con tri bu tion to the to tal var ies be tween 60 and 80% (Fig. 9D). The ag glu ti nated com po nent of the ben - thic foraminiferal as sem blages is very low; only two spe cies are re corded: Arenobulimina sp. and Marssonella oxycona (Reuss). Their con tri bu tion var ies be tween 1 and 10% of the as sem blages (Fig. 9D).
STABLE ISOTOPES
The re sults of sta ble iso tope study are shown in Fig ure 10 and. The d13C val ues for the Dubivtsi chalk vary be tween +1.94 and +2.78‰; the av er age is 2.34 ±0.26‰ (Fig. 10). The curve shows a steady and con tin u ous rise through the sam pled in ter - val from the bot tom of the pro file (the d13C value of the low est stud ied sam ple was 1.96‰) to the pos i tive ex cur sion with val - ues of +2.78‰ in the mid dle part of Dubivtsi chalk, fol lowed by a grad ual and con tin u ous de cline down to +1.94‰ near the top of the Dubivtsi chalk, al though the high est sam ple in the Dubivtsi chalk sec tion shows slight in crease to +2.0‰
(Fig. 10). The d18O val ues range from –2.67 to –1.56‰
through out the stud ied sec tion (Fig. 11); the av er age is –2.09
±0.31‰.
INTERPRETATION AND DISCUSSION
STRATIGRAPHY
The inoceramid fauna oc cur ring in the Dubivtsi pro file con - tains Mytiloides striatoconcentricus (Gümbel), which is glob - ally known from the up per Turonian to the low er most Coniacian (Walaszczyk, 1992). In ad di tion, the up per Turonian sed i ments of the area of Po land, Ger many, France and Eng land are sim i larly de vel oped to the mid dle part of the up per Turonian, which can in di cate (Pabian, 2004; Walaszczyk, pers.
comm.) a mid dle late Turonian age for the Dubivtsi sec tion.
This age is also sup ported by the herein de scribed planktic foraminiferal cor re la tion with the Mid dle Vistula River Val ley sec tion, Cen tral Po land. Tax o nom i cally, the foraminiferal as - sem blages re corded in the Dubivtsi 1 sec tion are char ac ter is tic for global Turonian strata (Fig. 12). The last ap pear ance of Helvetoglobotruncana helvetica is re corded in the low est part of the pro file (in sam ple 3), de fin ing the up per bound ary of the
Fig. 8. Dis tri bu tion of plank tonic foraminifers in the Dubivtsi 1 sec tion Ex pla na tions as in Fig ure 4
stan dard foraminiferal To tal Range Zone Helveto globo - truncana helvetica. The last ap pear ance of H. helvetica and the ab sence of rep re sen ta tives of the ge nus Praeglobotruncana in the ana lysed pro file in di cate that it cor re sponds to the bound ary in ter val be tween lo cal Helvetoglobotruncana helvetica and Marginotruncana coronata zones dis tin guished in the Mid dle Vistula River Val ley (Peryt, 1980; Walaszczyk and Peryt, 1998). The bound ary of the above-men tioned zones is lo cated in the Mid dle Vistula River Val ley sec tion in the mid dle part of the up per Turonian within the inoceramid zone Inoceramus costellatus (Fig. 11). Thus based on the oc cur rence of Mytilo - ides striatoconcentrinus and the planktic foraminiferal cor re la -
tion with the Mid dle Vistula River Val ley pro file, the Dubivtsi chalk can be placed in the mid dle part of up per Turonian within the Inoceramus costellatus Zone (Fig. 12).
The long-term and clearly dis tin guish able pos i tive ex cur sion of the d13C val ues re corded in the mid dle part of Dubivtsi chalk, rep re sent ing the mid dle part of the up per Turonian, can be cor re - lated with a wide spread pos i tive peak re corded in the mid dle part of up per Turonian, in the up per Subprionocyclus neptuni Zone, in south-east Eng land (Do ver – Gale, 1996; Culver and Trunch – Jarvis et al., 2006) called the Hitch Wood Event (Gale, 1996;
Fig. 10). This ex cur sion (Peak +1; Jarvis et al., 2006) de fin ing the Hitch Wood Event in Eng land is also very well-de vel oped in
Fig. 9. Changes in as sem blages of plank tonic and ben thic foraminifers of the Dubivtsi chalk
A – P/B ra tio; B – dis tri bu tion of par tic u lar morphotypes of plank tonic foraminifera; C – pro por tion of cal car e ous and ag glu ti nated foraminifera in ben thic foraminiferal as sem blages; D – abun dance fluc tu a tion of spe cies and group of spe cies of ben thic foraminifera in foraminiferal as sem blages; E – pro por - tion of epifaunal and infaunal morphotypes in ben thic foraminiferal as sem blages; other ex pla na tions as in Fig ure 4
NW Ger many in Salzgitter-Salder (Voigt and Hilbrecht, 1997;
Wiese, 1999; Wiese and Kaplan, 2001; Walaszczyk et al., 2010), where it is called the Hyphantoceras Event, as well as in North ern Spain (Wiese, 1999), the Czech Re pub lic (Wiese et al., 2004) and, in ad di tion, it can be clearly seen in Turonian car - bon-iso topes pro files from It aly (Jenkyns et al., 1994; Stoll and Schrag, 2000) and Ti bet (Wendler et al., 2011).
The in crease in the d18O val ues in the Dubivtsi 1 pro file co - in cides with pos i tive d13C val ues re flect ing the Hyphantoceras Event or Hitch Wood Event (Fig. 8). In many lo ca tions in West ern Eu rope the pos i tive car bon-iso tope ex cur sion re lated to the Hyphantoceras/Hitch Wood Event is ac com pa nied by in - creas ing d18O val ues (see Wiese and Voigt, 2002, fig. 3) that are in ter preted as due to cli ma tic cool ing.
PALAEOENVIRONMENTS
The mid dle and up per Turonian bulk rock d18O curves for West ern and Cen tral Eu rope (Voigt and Wiese, 2000; Wiese and Voigt, 2002) show two dis tinct cool ing phases. The first cool ing phase (termed Phase I) is lo cated in the higher mid dle Turonian whereas the sec ond-one (Phase III) is in the higher S.
neptuni Zone. Phase III is clearly iden ti fied in Salzgitter-Salder (NW Ger many; Voigt and Hilbrecht, 1997; Walaszczyk et al., 2010), Liencres (North ern Spain; Wiese, 1999) and Kent (SE Eng land; Jenkyns et al., 1994; Fig. 11). It can be also re cog - nised in the Dubivtsi 1 sec tion tak ing into ac count that the d18O val ues in the lower and mid dle part of the Dubivtsi chalk sec - tion are the high est in com par i son to the Up per Cre ta ceous
strata ex posed near Halych that rep re sent a long strati graphi cal in ter val, from the lower Cenomanian to the low est Campanian (Fig. 11). Sub se quently, they drop by about 0.7‰ (Figs. 10 and 11). It is re mark able that this in crease co in cides with changes in plank tonic foraminiferal as sem blages in the Dubivtsi 1 sec tion (Fig. 11). All keeled taxa, which are be lieved to have been the deep est-dwell ing plank tonic foraminifers (e.g., Bé, 1977; Hart and Bailey, 1979; Leckie, 1987; Premoli Silva and Sliter, 1999), dis ap pear in the low est part of the Dubivtsi chalk and ap pear again in its higher part. We re late the ab sence of keeled forms (marginotruncanids, dicarinellids) with a sea level drop.
The Dubivtsi 1 sec tion orig i nated in a sta ble cratonic en vi ron - ment (East Eu ro pean Plat form) and thus changes in the palaeobathymetry of the ba sin were mainly driven by global eustasy. Con se quently, the sea level fall iden ti fied in the Dubivtsi 1 sec tion sup ports the idea of a large drop in global sea level which is co in ci dent with a cli mate cool ing. The pro gres - sive shallowing as so ci ated with cool ing Phase III is also ob - served in other Eu ro pean sec tions (Voigt and Wiese, 2000).
More over, in tense sea level changes in the up per Turonian, with two sec ond-or der re gres sive peaks were doc u mented from the up per part of the Ea gle Ford Shale and the lower part of the Aus tin Chalk in the West ern In te rior Ba sin, Dal las area, Texas (Han cock and Walaszczyk, 2004).
This cool ing phase (re flected in pos i tive d18O fluc tu a tions) co-oc cur ring with sea level fall was in ter preted as be ing due to global changes in ocean cir cu la tion (Voigt and Wiese, 2000) and also as an ev i dence for gla ci ation, with ice sheets about half the size of the mod ern Ant arc tic ice cap (Stoll and Schrag,
Fig. 10. Cor re la tion of d13C curve for Dubivtsi chalk with the curves char ac ter is tic for Salzgitter-Salder, NW Ger many (af ter Voigt and Hilbrecht, 1997; Walaszczyk et al., 2010), Trunch, SE Eng land (af ter Jarvis et al., 2006) and Do ver, SE Eng land (af ter Jenkyns et al., 1994) C. woollgari – Collignoceras woollgari; S. neptuni (S. n.) – Subprionocyclus neptuni; F. petrocoriensis – Forresteria petrocoriensis; S. plana – Sternotaxis plana; M. cortestudinarium – Micraster cortestudinarium; I. lam.-api.-cuv. – Inoceramus lamarcki-apicalis-cuvieri; I. cost.-cuv.-stu.-inae. – Inoceramus costellatus-cuvieri-stuemckei-inaequivalvis; I. str.-M. lab. – Inoceramus striatoconcentricus-Mytiloides labiatoidiformis; P. germari – Prionocyclus germari; H. helv. – Helvetoglobotruncana helvetica; lim its of Peak +1 = Hyphantoceras Event = Hitch Wood Event as drawn by Jarvis et al. (2006)
Fig. 11. d18O curve mea sured for the Cenomanian–lower Campanian sec tion of the L’viv–Stryi Ba sin (af ter unpubl. data of Z. Dubicka) and dis tri bu tion of par tic u lar morphotypes of plank tonic foraminifera show ing the heavi est val ues of d18O
and the lack of keeled morphotypes of plank tonic foraminifera in the mid dle part of the up per Turonian Ex pla na tions as in Fig ure 4
2000; Bornemann et al., 2008). How ever the lack of gla cial de - pos its does not sup port the idea of Cre ta ceous ice sheets.
In con trast to West ern Eu ro pean sec tions, the Up per Cre ta - ceous strata of the Dubivtsi 1 sec tion were de pos ited in a sta ble cratonic en vi ron ment (East Eu ro pean Plat form) and thus the changes in palaeobathymetry of the ba sin were mainly driven by global eustasy. Con se quently the sea level fall as sumed for Dubivtsi co in cides with the large drop in global sea level and cli - mate cool ing. On the one hand we can in ter pret the cli mate cool - ing as due to changes in ocean cir cu la tion as op posed to vol ca nic the ory (Wiese and Voigt, 2002) but on the other hand that sea level low was trig gered by the growth of ice sheets. We con cur with Stoll and Schrag (2000) and Bornemann et al. (2008) that the late Turonian was one of the most prob a ble in ter vals of the oc cur rence of glaciations dur ing the Late Cre ta ceous.
The dis tri bu tion of plank tonic foraminifers in mod ern and past ma rine wa ters de pends mainly on tem per a ture, sa lin ity, wa ter depth, and pri mary pro duc tiv ity in sur face wa ters (Bé, 1977; Hemleben et al., 1989; Ar nold and Parker, 1999). The di ver sity of mod ern plank tonic foraminifer as sem blages is highly con nected with lat i tude and de creases from the trop ics to wards the poles. It is be lieved that ver ti cal mi gra tion in the wa ter col umn of plank tonic foraminifers is re lated to shell mor - phol ogy (Bé, 1977; Caron and Home wood, 1983; Leckie, 1987; Premoli Silva and Sliter, 1994; Price and Hart, 2002).
Keeled plank tonic foraminifera are as sumed to be deep-dwell - ers whereas se rial, planispiral and trochospiral forms with glob u lar cham bers are con sid ered to be more shal low-dwell ing spe cies, in hab it ing the up per 100 m of the ocean wa ter col umn.
The tax o nomic com po si tion of Cre ta ceous plank tonic foraminiferal as sem blages cor re lated with sedimentological data rep re sent ing transgressive-re gres sive cy cles have of ten been de scribed (e.g., Hart and Bailey, 1979; Hart, 1980;
Minard, 1980; Owens and Gohn, 1985; Walaszczyk, 1987;
Georgescu, 2006). Gen er ally keeled morphotypes are not found in shal low shelf en vi ron ments and their in crease in num -
ber is ob served with in creas ing wa ter depth and dis tance from the shore line (Leckie, 1987).
Their di ver sity and dis tri bu tion are also highly con nected with the sup ply of nu tri ents into the ba sin. Thus a change in the plank tonic foraminiferal as sem blage can also in di cate a change in palaeotrophic con di tions in the sur face wa ters. Biserial heterohelicids and thin-walled hedbergellids are r-strat e gists (e.g., Boersma and Premili Silva, 1989; Petrizzo, 2002). They are char ac ter ized by small-sized, sim ple tests, short life span, and by re pro duc ing quickly enough to closely track their nu tri tional re sources and in habit more nu tri ent-rich wa ter. They thrive best un der meso- and eutrophic con di tions (Leckie, 1987;
Nederbragt, 1991; Leckie et al., 1998; West et al., 1998; Premoli Silva and Sliter, 1999; Petrizzo, 2002). The as sem blages of plank tonic foraminifers from the Dubivtsi chalk are char ac ter - ized by very low-di ver sity and low abun dance, es pe cially of r-strat e gists. While the ab sence of plank tonic keeled forms is prob a bly re lated to the sea level drop, the low-oc cur rence of r-strat e gists (heterohelicids, hedbergellids, globigerinelloidids) which are shal low-dwell ing spe cies can in di cate low pri mary pro duc tion and a highly oligotrophic en vi ron ment.
Ben thic di ver sity is cou pled to pe lagic di ver sity and abun - dance in the mod ern oceans, al beit in a com plex way (e.g., Graf, 1992; Rosenberg, 1995). Ox y gen and food avalaibility are the most im por tant fac tors con trol ling mod ern ben thic foraminiferal dis tri bu tion on the sea floor (e.g., Jorissen et al., 1995; Moodley et al., 1998; van der Zwaan et al., 1999;
Brüchert et al., 2000). Ox y gen de fi ciency alone al most never acts as a lim it ing agent ham per ing the me tab o lism. The great est con trol co mes from the changes in the amount of food avail able as well as from pos si ble changes in the qual ity of food. The ul ti - mate down ward or ganic flux rate con trols both the food avail - abil ity and the ox y gen con cen tra tions at the sea floor (Barmavidjaja et al., 1992). A high flux of or ganic mat ter causes low ox y gen con cen tra tions within the sed i ment pore wa ters be cause ox y gen is used in ox i da tion of the or ganic ma te -
Fig. 12. Ranges of plank tonic foraminifers in the Mid dle Vistula River Val ley sec tion (af ter Peryt, 1980;
Walaszczyk and Peryt, 1998) and the in ferred strati graphic range of the Dubivtsi chalk (grey field) The inoceramid and plank tonic foraminifer zonations af ter Walaszczyk and Peryt (1998)
rial. It sug gests that a key fac tor con trol ling ben thic biodiversity and abun dance in the geo log i cal past must have been palaeoproductivity in the over ly ing wa ter col umn (Herguera and Berger, 1991; Loubere, 1991; Gale et al., 2000).
Ben thic foraminifers with an infaunal life po si tion liv ing within the sed i ment are thought to be more tol er ant of ox y gen de fi ciency (Kaiho, 1991; Kaminski et al., 1995). Infaunal spe - cies dom i nate in as sem blages as so ci ated with rel a tively high or ganic-car bon flux, and epifaunal ones in more oligotrophic en vi ron ments (e.g., Thomas, 1990; Jorissen et al., 1995). In highly oligotrophic re gions all food par ti cles will be con sumed or oxi dised at the sed i ment sur face and the un der ly ing sed i ment will con tain only small quan ti ties of or ganic mat ter, which can - not sus tain an abun dant infaunal pop u la tion. Con se quently the pop u la tion of ben thic foraminifera is dom i nated by epifaunal morphotypes. Rounded trochospiral, plano-con vex trocho - spiral, biconvex trochospiral/planispiral, milioline and tu bu lar morphotypes mainly live epifaunally. Rounded planispiral, flat tened ovoid, ta pered and cy lin dri cal, flat tened ta pered morphotypes live dom i nantly infaunally, al though ex cep tions do oc cur (Corliss and Chen, 1988; Nagy et al., 1995).
We in ter pret Gavelinella ammonoides (Reuss), G. vesca (Bykova), Gyroidinoides nitidus (Reuss), Globorotalites hangensis Vassilenko, Eponides karsteni (Reuss), Cibicides polyrraphes (Reuss) and Valvulineria lenticula (Reuss) re - corded in Dubivtsi chalk as spe cies that have an epifaunal mode of life, while Praebulimina reussi (Mor row), Marssonella oxycona (Reuss) and Arenobulimina sp. are spe - cies with an in ferred infaunal life po si tion. Lenticulina is re - garded as a highly adapt able and tol er ant spe cies that may change hab i tats from epifaunal to infaunal in re sponse to chang ing en vi ron men tal con di tions and food sup ply. We in ter - pret it here as an epifaunal form. Foraminifers with an in ferred epifaunal mode of life com prise more than 90% of ben thic foraminiferal as sem blages in the Dubivtsi chalk (Fig. 10).
Low abun dance and di ver sity, dom i nated by cal car e ous epifaunal morphotypes, ben thic foraminiferal as sem blages in the Dubivtsi chalk in di cate a well-ox y gen ated oligotrophic en - vi ron ment on the sea floor (e.g., Jorissen et al., 1995; van der Zwaan et al., 1999). The very low con tri bu tion of infaunal and ag glu ti nated foraminifers, which thrive best in en vi ron ments as so ci ated with rel a tively high or ganic mat ter flux (e.g., Bernhard, 1986), sup ports this in ter pre ta tion.
The plank tonic microfossil as sem blages of the Dubivtsi chalk are dom i nated by pithonellids con sid ered by Keupp (1987) as cal car e ous dinoflagellate cysts. Gale et al. (2000) rec og nized that the in creased abun dance of calcispheres in Up - per Cre ta ceous sed i ments rep re sents a re duc tion in wa ter pro - duc tiv ity, which co-oc curs with de crease in the abun dance of foraminifera. Thus, the pithonellid-rich car bon ates from the Dubivtsi chalk can in di cate oligotrophic sur face wa ters and sup port our palaeoenvironmental in ter pre ta tion based on plank tonic and ben thic foraminiferal as sem blages. More over, our data agree with the idea that a pre dom i nance of pithonellid calcispheres co in ci dent with a low abun dance of foraminifera is a good in di ca tor for re duced sur face wa ter pro duc tiv ity (Gale et al., 2000). In the up per Turonian of the West ern Ukraine, dinoflagellates oc cu pied an eco log i cal niche where other mi - cro or gan isms (foraminifera) could not thrive prob a bly be cause
of an in suf fi cient amount of food. Dinoflagellates as op por tun - ists can live in vari able en vi ron men tal con di tions be cause of their cyst-pro duc ing strat egy (calcispheres), which helps them sur vive in un fa vour able en vi ron men tal con di tions. Ac cord ing to Hemleben et al. (1989) di a toms are a ma jor part of the diet of many mod ern spe cies of plank tonic foraminifers, and we sup - pose that plank tonic foraminifera and mi cro or gan isms pro duc - ing pithonellids do not be long to the same food chain (cf. Peryt et al., 2002).
The cal cium car bon ate con tent in the ana lysed rock sam ples amounts to al most 100%. This in di cates that very lit tle siliciclastic sed i ments have been sup plied from the land into the ba sin even dur ing the sig nif i cant sea level drop. This, in turn con firms the idea of tec tonic qui es cence in the stud ied and ad - ja cent ar eas un til the mid dle Conianian when the Subhercynian phase of Al pine oro gen esis trig gered an up lift of the south east - ern part of the Dan ish–Pol ish Trough and sup plied a large amount of terrigenous ma te rial to the ba sin (Pasternak, 1959;
Pasternak et al., 1987; Walaszczyk, 1992). The very low level of re gional tec tonic ac tiv ity and near ab sence of emerged ar eas dur ing the late Turonian would mean that few nu tri ents were sup plied from the land. More over, the re gres sion and the re - lated changes in oce anic cir cu la tion could be ad di tion ally re - spon si ble for the trans port of a small amount of nu tri ents from the open ocean into the epicontinental ba sin. Con se quently, the late Turonian ba sin in which the Dubivtsi chalk orig i nated was highly oligotrophic, and this was prob a bly a rea son that the plank tonic and ben thic foraminiferal as sem blages show un usu - ally very low di ver sity and low abun dance.
CONCLUSIONS
A com bined micropalaeontological and sta ble iso tope study of the Dubivtsi chalk in the West ern Ukraine al lowed us to de ter mine its mid dle late Turonian age and to pre cisely cor - re late the Ukrai nian strata with co eval rocks in West ern Eu - rope. In par tic u lar, one long-term and clearly dis tin guish able pos i tive ex cur sion of the iso tope curve (d13C) in the Dubivtsi chalk is equiv a lent to a wide spread up per Turonian pos i tive peak re corded the up per S. neptuni Zone in West ern and South - ern Eu rope named the Hyphantoceras Event or Hitch Wood Event. The d18O curve for the Dubivtsi chalk shows an in creas - ing trend sim i lar to other lo cal i ties where the Hyphantoceras/Hitch Wood Event has been re corded.
Sed i men ta tion of pure Dubivtsi chalk oc curred un der highly oligotrophic con di tions, which is re flected in plank tonic and ben thic foraminiferal as sem blages. Those con di tions prob - a bly were trig gered by re gres sion and re lated changes in oce - anic cir cu la tion and a low level of re gional tec tonic ac tiv ity, which in con se quence re sulted in a very low sup ply of nu tri ents to the ba sin. The rise in abun dance of pithonellid calcispheres co in cid ing with drop in the abun dance of foraminifera can be a good in di ca tor for re duc tion in sur face wa ter pro duc tiv ity.
Ac knowl edge ments. The study was sup ported by the Na - tional Sci ence Cen tre grant N N307 657340. Con struc tive com ments by jour nal re view ers M. A. Kaminski and an anon y - mous re viewer helped to im prove the manu script and are grate -
fully ac knowl edged. We thank K. Dembicz who helped dur ing field stud ies, and L. Marynowski and M. Rakociñski who did the chem i cal anal y ses. The field work was sup ported by the re -
search pro ject No. UKRAINA/193/2006 funded by the Min is - try of Sci ence and Higher Ed u ca tion.
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