Calcareous nannofossils from the Upper Cretaceous of northern James Ross Island, Antarctica: a pilot study

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Geo log i cal Quar terly, 2012, 56 (4): 765–772 DOI: http://dx.doi.org/10.7306/gq.1053

Cal car e ous nannofossils from the Up per Cre ta ceous of north ern James Ross Is land, Antarctica: a pi lot study

Lilian ŠVÁBENICKÁ, Radek VODRÁŽKA and Dan iel NÝVLT

Švábenická L., Vodrážka R. and Nývlt D. (2012) – Cal car e ous nannofossils from the Up per Cre ta ceous of north ern James Ross Is land, Antarctica: a pi lot study. Geol. Quart., 56 (4): 765–772, doi: 10.7306/gq.1053

The Czech sci en tific ex pe di tion to north ern James Ross Is land, Antarctica has tested the use of cal car e ous nannofossils as a pos si ble tool for strati graphic cor re la tion of Cre ta ceous and Neo gene strata. Only a few sam ples with poor nannofossil con tent gave use ful in for ma - tion for biostratigraphy. The Lower Campanian Chiastozygus garrisonii Zone and Gephyrobiscutum diabolum Subzone, re spec tively, was es tab lished in the lower part of the Santa Marta For ma tion, Lachman Crags Mem ber, from the com mon oc cur rence of Gephyrobiscutum diabolum as so ci ated with Broinsonia parca parca and Acuturris scotus. De pos its of the Late Mio cene Men del For ma - tion yielded ex clu sively re worked nannofossils from the older Up per Cre ta ceous de pos its. Nannofossils in di cate at least two dis tinct strati graphic lev els: Mid dle Coniacian and Santonian–basal Campanian, and these must have been sourced from the im me di ate area. The ma jor ity of the ma rine de posit sam ples stud ied were bar ren of nannofossils, prob a bly due to late diagenetic sec ond ary decalcification.

Lilian Švábenická and Radek Vodrážka, Czech Geo log i cal Sur vey, Klárov 131/3, 118 21 Praha, Czech Re pub lic, e-mails:

lilian.svabenicka@ge ol ogy.cz, radek.vodrazka@ge ol ogy.cz; Dan iel Nývlt, Czech Geo log i cal Sur vey, Brno Branch, Leitnerova 22, 658 69 Brno, Czech Re pub lic, e-mail: dan iel.nyvlt@ge ol ogy.cz (re ceived: April 25, 2012; ac cepted: June 13, 2012; first pub lished on - line: September 27, 2012).

Key words: Antarctica, James Ross Is land, Up per Cre ta ceous, cal car e ous nannofossils, biostratigraphy.

INTRODUCTION

Dur ing geo log i cal re search and map ping by the Czech sci en - tific ex pe di tions to the north ern James Ross Is land that fo cused on the im me di ate area sur round ing the Johann Gregor Men del Czech Ant arc tic Sta tion sit u ated at about 63°48 S (Fig. 1), at - ten tion was paid to the strati graphic in ter pre ta tion of Up per Cre - ta ceous and Up per Mio cene strata. As the biostratigraphy of this re gion has been based on palynomorphs and macrofossils (bi - valves, ammonites), the aim of this study was to in ves ti gate the pres ence of cal car e ous nannofossils in the var i ous lithologies and to val i date their biostratigraphic sig nif i cance.

Al though most of the de pos its stud ied did not con tain any nannofossils, a few sam ples pro vided rel e vant in for ma tion from both the biostratigraphical and palaeo eco logi cal points of view.

Given the scarce pub lished data on cal car e ous nannofossils of the James Ross Ba sin car ried out mainly by Ar gen tine spe cial ists from the Uni ver sity of Bue nos Ai res, the re sults of this study rep - re sent an im por tant con tri bu tion to the knowl edge of this area.

GEOLOGICAL SETTING

Both Lower and Up per Cre ta ceous strata of the Gustav and Marambio groups (James Ross Ba sin) are ex posed in the map - ping area (Fig. 1). In most of the area stud ied they are over lain by Ce no zoic lavas and hyaloclaste brec cias (James Ross Is land Vol ca nic Group), and also by the Ce no zoic Men del, Hobbs Gla cier and Cockburn Is land for ma tions (Nývlt et al., 2011;

Pirrie et al., 2011) and Qua ter nary de pos its.

The stra tig ra phy of the Up per Cre ta ceous strata of north ern James Ross Is land has been stud ied by many au thors (e.g., Ineson et al., 1986; Olivero et al., 1986; Pirrie, 1989; Rinaldi, 1992). The Gustav Group of north ern James Ross Is land com - prises the fol low ing for ma tions: (1) Kotick Point For ma tion, char ac ter ized by interbedded sand stones and silty mudstones or claystones; (2) Whisky Bay For ma tion, dom i nated by coarse-grained de pos its, al though mudstone- and sand - stone-dom i nated in ter vals also oc cur (Ineson et al., 1986). The tran si tion be tween the Whisky Bay For ma tion and the over ly - ing (3) Hid den Lake For ma tion es sen tially rep re sents the start

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of a fin ing-up wards cy cle from the con glom er ate-dom i nated Whisky Bay For ma tion to the sand stone-dom i nated Hid den Lake For ma tion (Whitham et al., 2006). The gen eral fin ing-up - wards trend through the Hid den Lake For ma tion re flects a de - creas ing sup ply of coarse vol ca nic de tri tus to the ba sin, with a pro gres sive de crease in wa ter depth (Pirrie et al., 1992).

The Marambio Group of north ern James Ross Is land com - prises the Santa Marta For ma tion that was orig i nally de fined by Olivero et al. (1986) and sub di vided into three mem bers: Al - pha, Beta and Gamma. Crame et al. (1991) re de fined the Santa Marta For ma tion and com bined the Al pha and Beta mem bers into the Lachman Crags Mem ber. The sam ples stud ied (Figs. 1 and 2) be long to the lower-mid dle part of the Lachman Crags Mem ber (Al pha Mem ber of Olivero et al., 1986). These strata have been in ter preted to have been de pos ited within a mid- to outer-shelf be low storm wave base (Pirrie, 1989).

Com par a tive sam ples (Fig. 1 and Ta ble 1) were gath ered from the basal ter res trial glacigenic de pos its (subglacial melt-out tills and lodge ment tills) of the Men del For ma tion (Nývlt et al., 2011). The Men del For ma tion (max. thick ness of

80 m) was formed be tween 5.9 to 5.4 Ma and is rep re sented by glacigenic, glaciomarine and ma rine sed i ments de pos ited dur - ing two Late Mio cene glacioeustatic cy cles (Nývlt et al., 2011).

The basal strata of the Men del For ma tion over lie vol ca nic rocks of the James Ross Is land Vol ca nic Group and the Up per Cre ta ceous Hid den Lake and Santa Marta for ma tions (Fig. 1).

PREVIOUS BIOSTRATIGRAPHIC STUDIES Early biostratigraphic stud ies fo cused pri mar ily on the well-pre served mol lus can fau nas, es pe cially bi valves and ammonites (e.g., Crame, 1981; Olivero, 1981). Sub se quent stud ies of microfossils from the James Ross Is land re gion have clearly shown the po ten tial for es tab lish ing biostratigraphic frame works us ing foraminifera, di a toms, silicoflagellates and palynomorphs (e.g., Askin, 1988; Har wood, 1988; Huber, 1988). Other pre lim i nary stud ies on James Ross and sur round - ing is lands have also shown the po ten tial of palynomorphs for lo cal and re gional biostratigraphical cor re la tion (e.g., Askin,

766 Lilian Švábenická, Radek Vodrážka and Daniel Nývlt

Fig. 1A – map show ing the lo ca tion of the James Ross Is land re gion; B – geo log i cal sketch map of the Gustav, Marambio and Sey mour Is land groups in the James Ross Is land re gion, based on Crame and Lu ther (1997); C – geo log i cal sketch map show ing Cre ta ceous de pos its of north west - ern James Ross Is land with po si tions of sec tion and sam ples tested for the pres ence of nannofossils. The dashed lines show for ma tion bound aries across sea and ice cover. Based on Ineson et al. (1986). Star in di cates the po si tion of the Johann Gregor Men del Czech Ant arc tic Sta tion; D – strati graphic cor re la tion di a gram for Cre ta ceous de pos its of north west ern James Ross Is land (based on Crame et al., 2006). For geo graph ical lo - ca tion of these sed i ments see Fig ure 1C

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Calcareous nannofossils from the Upper Cretaceous of northern James Ross Island, Antarctica: a pilot study 767

Fig. 2. Slope of Lachman Crags, viewed from the Crame Col (north ern James Ross Is land), formed by Up per Cre ta ceous siltstones (Lachman Crags Mem ber, Santa Marta For ma tion) capped by Neo gene basaltic lavas and hyaloclaste brec cia

All sam ples gath ered from this sec tion are marked on the pho to graph, al though, ex cept for KSM 4 and KSM 5, the sam ples pro vided no cal car e ous nannofossils; for more de tailed lo cal iza tion of sam ples see Ta ble 1

Sam ple no. For ma tion, Mem ber WGS

S WGS W Al ti tude

[m] Nannofossils abun dance KSM 1 Santa Marta, Lachman Crags 63°49’46.5’’ 57°53’11.1’’ 285 – KSM 2 Santa Marta, Lachman Crags 63°49’46.4’’ 57°53’12.3’’ 274 – KSM 3 Santa Marta, Lachman Crags 63°49’46.1’’ 57°53’13.6’’ 264 – KSM 4 Santa Marta, Lachman Crags 63°49’46.0’’ 57°53’14.8’’ 254 +++

KSM 5 Santa Marta, Lachman Crags 63°49’45.7’’ 57°53’16.1’’ 244 + KSM 6 Santa Marta, Lachman Crags 63°49’45.7’’ 57°53’18.4’’ 234 – KSM 7 Santa Marta, Lachman Crags 63°49’45.6’’ 57°53’20.3’’ 224 – KSM 8 Santa Marta, Lachman Crags 63°49’45.2’’ 57°53’22.7’’ 214 – KSM 9 Santa Marta, Lachman Crags 63°49’45.2’’ 57°53’24.5’’ 204 – KSM 9.2 Santa Marta. Lachman Crags 63°49’44.7’’ 57°53’27.6’’ 197 – KSM 10 Santa Marta. Lachman Crags 63°49’44.9’’ 57°53’29.1’’ 194 – KSM 10.2 Santa Marta. Lachman Crags 63°49’43.5’’ 57°53’32.7’’ 189 – KSM 11 Santa Marta. Lachman Crags 63°49’44.5’’ 57°53’34.8’’ 184 – KSM 11.2 Santa Marta. Lachman Crags 63°49’44.2’’ 57°53’35.4’’ 181 –

KHL-1 Hid den Lake 63°48’51.4’’ 57°52’56.1’’ 72 –

KWB-1 Whisky Bay. Lewis Hill 63°48’56.8’’ 57°54’55.0’’ 121 –

KWB-3 Whisky Bay. Brandy Bay 63°48’12.8’’ 57°55’30.8’’ 62 –

KFC-1 Kotick Point 63°51’10.1’’ 58°04’52.9’’ 31 –

PC05-3 Men del 63°47’34.3’’ 57°48’39.7’’ 3 +++

T a b l e 1 Lithostratigraphy, GPS co or di nates and abun dance (oc cur rence)

of cal car e ous nannofossils from the sam ples stud ied

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1983; Olivero and Palamarczuk, 1987; Baldoni and Me dina, 1989; Keating, 1992; Keating et al., 1992; Rid ing et al., 1992;

Rid ing and Crame, 2002).

Cre ta ceous nannofossils from the Ant arc tic area in clud ing the Falkland Pla teau are men tioned by Wind (1979), Huber et al. (1983), Thomas et al. (1990), Wei and Thierstein (1991), Watkins et al. (1996) and Lees (2002). These stud ies fo cused not only on strati graphic in ter pre ta tions but also on lat i tu di nal changes in nannoplankton as sem blages and on the dis tri bu tion of cos mo pol i tan, high-lat i tude and en demic spe cies. Up per Cre ta ceous nannofossils and their biostratigraphic in ter pre ta - tion from the James Ross Ba sin have been stud ied in par tic u lar by Argentinian (Concheyro et al., 1991; Robles Hurtado and Concheyro, 1995) and North Amer i can palaeontologists (Kulhanek, 2007).

MATERIAL AND METHODS

Ma te rial for nannofossil study was col lected from lo cal i ties at walk ing dis tance from the Johann Gregor Men del Czech Ant arc tic Sta tion in the 2004 and 2005 field sea sons. Sam ples were col lected from the Kotick Point (sam ple KFC-1), Whisky Bay (sam ples KWB-1 and KWB-3), Hid den Lake (sam ple KHL-1) and Santa Marta (KSM sec tion sam ples) for ma tions (Figs. 1, 2 and Ta ble 1). Con cern ing pre cise sam ple lo ca tion, sam ple KSM 11 (see Fig. 2) was gath ered from the level of a prom i nent con cre tion ho ri zon, which is 90 m above the base of the Santa Marta For ma tion (Pirrie, 1987). Pos i tive sam ples KSM 5 and KSM 4 cor re spond to lev els of 150 and 160 m above the base of the Santa Marta For ma tion re spec tively. Fur - ther sam ples (PC05 sec tion, see Fig. 1) were ob tained from the re cently de scribed Late Mio cene Men del For ma tion (Nývlt et al., 2011). Nannofossil smear-slides are stored in the col lec - tions of the Czech Geo log i cal Sur vey, Prague. Rock sam ples are de pos ited in the Czech Geo log i cal Sur vey, Prague.

Nannofossils were in ves ti gated in the 2–30 mm frac tion by a decantation method us ing 7% so lu tion of H2O2. The coarse frac tion was al lowed to set tle for 3 min utes in a 45 mm wa ter col umn and re moved; the fine frac tion was saved for slide prep a ra tion af ter 45 min utes. Sim ple smear-slides were mounted us ing Can ada Bal sam and in spected at 1000´ mag ni - fi ca tion, us ing an oil-im mer sion ob jec tive on a Nikon Microphot-FXA trans mit ting light mi cro scope. Biostrati - graphic data were in ter preted us ing the zonation for the Up per Cre ta ceous of the South ern Ocean by Watkins et al. (1996).

RESULTS

SANTA MARTA FORMATION

Cal car e ous nannofossils were pres ent in two of 14 sam ples taken from the KSM sec tion (Fig. 2 and Ta ble 1), in sam ples KSM 4 and KSM 5.

KSM 4

The smear-slide con tained pre dom i nantly in or ganic ma te - rial. Cal car e ous nannofossils (ca. 1–5 spec i mens per one field

of view of the mi cro scope) formed a min i mal pro por tion of the frac tion and the pres er va tion is very poor. Small placoliths (ca. 2–4 mm) of Gephyrobiscutum diabolum (small, placoliths ex tended along the lon ger axis, ca. 1–2 spec i mens per one field of view of the mi cro scope; Fig. 3A1–A4) pre dom i nate; other nannofossils are scarce and pre served mostly as frag ments.

This as sem blage con tains low num bers of stratigraphically sig - nif i cant spe cies such as Acuturris scotus (one spec i men), Broinsonia parca parca, Eiffellithus eximius, Broinsonia cf.

dentata, Lucianorhabdus maleformis-quadrifidus and L. ex gr.

cayeuxii (two spec i mens; Fig. 3). Spec i mens of the ge nus Prediscosphaera are small in pro por tion, in clud ing min ia ture spec i mens (2 mm) re sem bling P. bukryi (Fig. 3J). These spe cies are ac com pa nied by Eiffellithus turriseiffelii (two spec i mens), Ahmuellerella octoradiata, Arkhangelskiella cymbiformis (“large” and broadly el lip ti cal placoliths with a rel a tively nar - row outer rim), Biscutum ellipticum, Biscutum mag num (one frag ment), Broinsonia enormis, Calculites ovalis, Cribro - sphaerella ehrenbergii (one spec i men), Cyclagelosphaera rotaclypeata, Gartnerago obliquum, Kamptnerius magnificus, Prediscosphaera cretacea, P. spinosa, Reinhardtites antho - phorus, Rhagodiscus angustus, Tranolithus orionatus, Thoracosphaera sp., Vekshinella aachena (sensu Watkins et al., 1996), Watznaueria barnesiae (four spec i mens), Zeugrhabdotus scutula, Z. trivectis, and Z. diplogrammus.

The sam ple also pro vided “cubes” of ques tion able or i gin that are com pa ra ble with those found for ex am ple in the Bo he - mian Cre ta ceous Ba sin (Švábenická, 2012).

KSM 5

A smear-slide con tain ing cal car e ous ma te rial of in or ganic or i gin and scarce nannofossils (ca. 1 spec i men per 10 fields of view of the mi cro scope) of ex tremely poor pres er va tion. The fol low ing taxa were iden ti fied: Biscutum sp., Gephyrobiscutum sp., Staurolithites laffitei, Prediscosphaera sp.

Sam ples taken from the Kotick Point For ma tion (KFC-1), Whisky Bay For ma tion (KWB-1, KWB-3) and Hid den Lake For ma tion (KHL-1) pro vided no cal car e ous nannofossils.

MENDEL FORMATION

Cal car e ous nannofossils were pres ent in only one of 13 sam ples taken from the sec tion:

PC05-3

Nannofossils form a min i mal pro por tion of the sed i ment (1–2 spec i mens per 10 fields of view of the mi cro scope). They are badly pre served and mostly frag mented. Strong etch ing is ob vi ous es pe cially on placoliths (the cen tral fields are usu ally miss ing) and holococcoliths (ge nus Lucianorhabdus) show signs of over growth. Prob a ble sec ond ary im pov er ishment of the as sem blage was caused by car bon ate dis so lu tion as in di - cated by the rel a tively high num bers of Watznaueria barnesiae.

The as sem blage is formed of the fol low ing spe cies (Fig. 4):

Arkhangelskiella specillata, Prediscosphaera cretacea, P.

ponticula, P. cf. grandis (sensu Bur nett, 1998), Kamptnerius magnificus, Luciano rhabdus quadrifidus, L. maleformis, L. cf.

inflatus (frag ments), Quadrum gartneri, Q. intermedium

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Fig. 3. Cal car e ous nannofossils of the Santa Marta For ma tion, James Ross Is land, Antarctica, sam ple KSM 4, Lower Campanian A1–A4 – Gephyrobiscutum diabolum, A1 – PPL, A2–A4 – XPL; B1–B5 – Gephyrobiscutum cf. diabolum, B1, B3 – PPL, B2, B4, B5 – XPL; C – Biscutum mag num, frag ment, XPL; D1, D2 – Ahmuelerella octoradiata, spec i men in PPL and XPL; E1, E2 – Eiffellithus eximius, spec i men at 0^o and 15^o, XPL; F1, F2 – Broinsonia dentata, specimenn in PPL and XPL; G – Broinsonia parca parca, XPL; H – Arkhangelskiella ex gr. cymbiformis, XPL; I1, I2 – Prediscosphaera cretacea, XPL; J – Prediscosphaera bukryi, XPL; K – Rhagodiscus angustus, XPL; L – Reinhardtites anthophorus, XPL; M – Vekshinella aachena, XPL; N – Staurolithites laffittei, XPL; O – Tranolithus orionatus, XPL; P – Cyclagelosphaera rotaclypeata, XPL; R – Watznaueria barnesiae, XPL; S1, S2 – Kamptnerius magnificus, XPL; T1–T3 – ?Polycyclolithaceae, “cube” of ques tion able or i gin, spec i men in PPL and XPL; U – Acuturris scotus, XPL; V1, V2 – Lucianorhabdus ex gr. cayeuxii, spec i men in PPL and XPL; PPL – plane po lar ized light, XPL – cross po lar ized light; for mag ni fi ca tion see Fig ure 3A, if not in di cated oth er wise

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(5 and 7 seg ments), Manivitella pemmatoidea, Microrhab - dulus attenuatus, Gartnerago obliquum, Broinsonia enormis, Micula staurophora (three spec i mens), Eiffellithus eximius (spec i men with strongly etched cen tral field with cross), Retacapsa sp. (outer rim).

DISCUSSION

The nannofossil as sem blage of the sam ple KSM 4 (Santa Marta For ma tion) doc u ments the Lower Campanian, Chiastozygus garrisonii Zone (up per part – in ter val of the Gephyrobiscutum diabolum Subzone) sensu Watkins et al.

(1996). This biostratigraphic in ter pre ta tion con curs with the pre vi ously pub lished biostratigraphical frame work based on the mol lus can macrofauna and palynomorphs (see Pirrie et al., 1992). From the palaeo geo graphi cal point of view, the sed i - men tary area of James Ross Is land re gion must have had some re la tion to the Falkland Pla teau dur ing the Early Campanian, be cause both Watkins et al. (1996) and Bur nett (1998) re gard Gephyrobiscutum diabolum as an en demic spe cies of the Falkland Pla teau.

The nearly ubiq ui tous and com mon spe cies Watznaueria barnesiae, in Up per Cre ta ceous as sem blages through out the world, was found here only in very low num bers. Wei and Thierstein (1991) men tioned its spo radic oc cur rence in the Maastrichtian of the Kerguelen Pla teau. Ac cord ing to Watkins et al. (1996), W. barnesiae be came spo radic and rare in high south ern lat i tudes (e.g., the R. parvidentatum Subzone on the Kerguelen and Naturaliste pla teaux in the Up per Campanian) and later also in lower lat i tudes of the South ern Hemi sphere. In ad di tion to scarce W. barnesiae, sam ple KSM 4 pro vided G. diabolum and its short strati graphic range is cor re lated with the Lower Campanian (Watkins et al., 1996).

The spo radic oc cur rence of small spec i mens of the ge nus Prediscosphaera (a cen tral cross sit u ated along the axes of the

el lip tic placolith, see Fig. 3J) here men tioned as P. bukryi needs fur ther ma te rial and study. P. bukryi is known from the Albian–Maastrichtian. Its small spec i mens may be eas ily mis - taken for P. stoveri es pe cially in poorly pre served ma te rial.

P. stoveri is men tioned as a bi po lar spe cies re stricted to high-lat i tudes. In the North Sea, its first oc cur rence is placed at the base the base of UC15d^BP Subzone, lower Up per Cam - panian (Bur nett, 1998); in the South ern Hemi sphere it is first noted in the Biscutum coronum Zone, up per Up per Cam panian and its com mon oc cur rence in the up per most Maastrichtian was used for def i ni tion of the Prediscosphaera stoveri Acme Subzone (Watkins et al., 1996). It is in ter est ing that Watkins et al. (1996) did not men tion any P. bukryi from older Campanian de pos its and vice versa Kulhanek (2007) any P. stoveri from the Maastrichtian of the north ern James Ross Ba sin.

The nannofossil taphocoenose found in sam ple PC05-3 (Men del For ma tion) con tains at least two types of nannofossil as sem blages:

1. An as sem blage with Micula staurophora and Quadrum gartneri, Mid dle to Up per Coniacian, UC10 Zone.

2. An as sem blage with Arkhangelskiella specillata, Prediscosphaera cf. grandis and Lucianorhabdus inflatus may doc u ment the Santonian and ?prob a bly also the low er most Campanian. Sim i larly re worked Campanian–Maastrichtian nannofossil taphocoenoses were re cov ered by Gaździcka and Gaździcki (1994) from the Plio cene Pecten Con glom er ate of Cockburn Is land (about 5 km north-west from Sey mour Is land).

Nannofossils of Campanian, Maastrichtian and/or Ce no - zoic age have not been found. The pres ence of the gen era Lucianorhabdus, Quadrum and Kamptnerius may re flect de - po si tion in a shal low epicontinental sea of nor mal sa lin ity. Ac - cord ing to the sum mary of lithostratigraphy of the James Ross Ba sin (Pirrie et al., 1992), re worked nannofossils of Coniacian age most prob a bly come from the Hid den Lake For ma tion and spe cies of Santonian/?low er most Campanian age from the lower part of the Santa Marta For ma tion.

Fig. 4. Re worked cal car e ous nannofossils from the Up per Cre ta ceous strata into the glacigenic Mio cene de pos its of the Men del For ma tion, sam ple PC05-3

A – Arkhangelskiella sp., XPL; B – Broinsonia enormis, XPL; C – Quadrum gartneri, XPL; D – Micula staurophora, XPL; E – Prediscosphaera sp., cen - tral area of spec i men strongly cor roded, XPL; F – Eiffellithus eximius, XPL; G, H – Kamptnerius magnificus, spec i men in PPL and XPL; I – Microrhabdulus attenuatus, XPL; J – Watznaueria barnesiae, XPL; K, L – Lucianorhabdus quadrifidus, spec i men in PPL and XPL; PPL – plane po lar - ized light, XPL – cross po lar ized light; for mag ni fi ca tion see Fig ure 4A

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The short-dis tance trans port of the Up per Cre ta ceous nannofossils rewashed into the Late Mio cene Men del For ma tion is shown by the fact that both the Santa Marta and Hid den Lake for ma tions crop out in the im me di ate vi cin ity of sec tion PC05.

The ab sence of cal car e ous nannofossils from the Kotick Point, Whisky Bay and Hid den Lake for ma tions and in part from the Santa Marta For ma tion is prob a bly caused by par tial or to tal (?) early diagenetic decalcification of the de pos its. This is also sup ported by spo radic find ings of cal car e ous foraminifers in most of the sam ples stud ied and by the scar city of cal car e ous in ver te brate shells in the area stud ied. In par tic u - lar, con glom er ates, tuffitic sand stones and siltstones of the Kotick Point, Whisky Bay and Hid den Lake for ma tions are al - most bar ren of orig i nal calcitic/aragonitic shells. On the other hand, si li ceous macrofossils are well-pre served (Vodrážka and Crame, 2011), sug gest ing that car bon ate dis so lu tion played an im por tant role dur ing for ma tion of these strata.

CONCLUSIONS

A scarcity of nannofossils in the Up per Cre ta ceous ma rine strata of the James Ross Ba sin en abled only pre lim i nary strati - graphic con clu sions.

The Santa Marta For ma tion (sam ples KSM 4 and KSM 5) is cor re lated with the Lower Campanian. Nannofossils in di cate the Chiastozygus garrisonii Zone (Gephyrobiscutum diabolum Subzone) sensu Watkins et al. (1996) ac cord ing to the com mon oc cur rence (acme) of the spe cies G. diabolum as so ci ated with Broinsonia parca parca and Acuturris scotus. More over, G. diabolum, an en demic spe cies of the Falkand Pla teau, in di -

cates con nec tion of this palaeoregion with this ter ri tory dur ing the de po si tion of the Santa Marta For ma tion.

Strata of the Men del For ma tion, Up per Mio cene, pro vided only re worked nannofossils from older Up per Cre ta ceous de - pos its. Nannofossils in di cate two strati graphic lev els (and prob a bly two source ar eas): Mid dle Coniacian (Micula staurophora and Quadrum gartneri) and Santonian–basal Campanian in ter val (Arkhangelskiella specillata and Lucianorhabdus inflatus). Re worked Up per Cre ta ceous nannofossils most prob a bly come from the Hid den Lake and Santa Marta for ma tions. An autochthonous nannoflora was not de vel oped in the glacigenic to ma rine sed i mentary en vi ron - ment of the Late Mio cene.

Most of the ma rine de pos its stud ied of the Gustav and Marambio groups, James Ross Ba sin, were bar ren of nannofossils prob a bly due to (?late) diagenetic sec ond ary decalcification.

Ac knowl edge ments: The work of D. Nývlt and R. Vodrážka were sup ported by Re search and De vel op ment Pro ject of the Min is try of En vi ron ment of the Czech Re pub lic No. SPII 1a9/23/07 and by the pro ject of the Czech Geo log i cal Sur vey No. 335400. Nannofossil study was sup ported by the Re search Programme of the Czech Geo log i cal Sur vey No. MZP 0002579801. Thanks go also to sci en tific in fra struc - ture of the Johann Gregor Men del Czech Ant arc tic sta tion.

Sug ges tions and com ments of M. Wagreich, Uni ver sity of Vi - enna, T. Peryt, Pol ish Geo log i cal In sti tute – Na tional Re search In sti tute, Warszawa, and an anon y mous ref eree helped to im - prove the manu script.

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APPENDIX

List of cal car e ous nannofossils men tioned in the text, in al - pha bet i cal or der of gen era.

Acuturris scotus (Risatti, 1973) Wind and Wise in Wise and Wind, 1977 Ahmuellerella octoradiata (Górka, 1957) Reinhardt, 1966

Arkkhangelskiella cymbiformis Vekshina, 1959 Arkhangelskiella specillata Vekshina, 1959

Biscutum ellipticum (Górka, 1957) Grün in Grün and Alleman, 1975 Biscutum mag num Wind and Wise in Wise and Wind, 1977 Broinsonia dentata Bukry, 1969

Broinsonia enormis (Shumenko, 1968) Manivit, 1971 Broinsonia parca (Stradner, 1963) Bukry, 1969 ssp. parca

Calculites ovalis (Stradner, 1963) Prins and Sissingh in Sissingh, 1977 Cribrosphaerella ehrenbergii (Arkhangelsky, 1912) Deflandre in Piveteau, 1952 Cyclagelosphaera rotaclypeata Bukry, 1969

Eiffellithus eximius (Stover, 1966) Perch-Niel sen, 1968

Eiffellithus turriseiffelii (Deflandre in Deflandre and Fert, 1954) Reinhardt, 1965 Gartnerago obliquum (Stradner, 1963) Noël, 1970

Gephyrobiscutum diabolum Wise, 1988 Kamptnerius magnificus Deflandre, 1959 Lucianorhabdus cayeuxii Deflandre, 1959

Lucianorhabdus inflatus Perch-Niel sen and Feinberg in Perch-Niel sen, 1986 Lucianorhabdus maleformis Reinhardt, 1966

Lucianorhabdus quadrificus Forchheimer, 1972

Manivitella pemmatoidea (Deflandre in Manivit, 1965) Thierstein, 1971 Micula staurophora (Gardet, 1955) Stradner, 1963

Microrhabdulus attenuatus (Deflandre, 1959) Deflandre, 1963 Prediscosphaera bukryi Perch-Niel sen, 1973

Prediscosphaera cretacea (Arkhangelsky, 1912) Gart ner, 1968 Prediscosphaera grandis Perch-Niel sen, 1979

Prediscosphaera ponticula (Bukry, 1969) Perch-Niel sen, 1984 Prediscosphaera spinosa (Bramlette and Mar tini, 1964) Gart ner, 1968 Prediscosphaera stoveri (Perch-Niel sen, 1968) Shafik and Stradner, 1971 Quadrum gartneri Prins and Perch-Niel sen in Manivit et al., 1977 Quadrum intermedium Varol, 1992

Reinhardtites anthophorus (Deflandre, 1959) Perch-Niel sen, 1968 Rhagodiscus angustus (Stradner, 1963) Reinhardt, 1971 Staurolithites laffittei Caratini, 1963

Tranolithus orionatus (Reinhardt, 1966a) Reinhardt, 1966b Vekshinella aachena (Bukry) Shafik and Stradner, 1971 Watznaueria barnesiae (Black, 1959) Perch-Niel sen, 1968

Zeugrhabdothus diplogrammus (Deflandre in Derflandre and Fert, 1954) Bur nett in Gale et al., 1996

Zeugrhabdotus scutula (Bergen, 1994) Rutledge and Bown, 1996 Zeugrhabdothus trivectis Bergen, 1994