New biostratigraphic evidence (texanitid ammonites, inoceramids and calcareous nannofossils) for the...

*Addresses of the authors: 1Institute of Geology and Palaeontology, Faculty of Science, Charles University in Prague, Albertov 6, Prague 2, 128 43; 2Institute of Geology, The Czech Academy of Sciences, v.v.i., Rozvojová 269, Prague 6, Lysolaje, 165 00; 3Czech Geological Survey, Klárov 3, Prague 1, 118 21 / [email protected]; [email protected]; [email protected]; [email protected].

New biostratigraphic evidence (texanitid ammonites, inoceramids and calcareous nannofossils) for the Upper and the uppermost Coniacian in the Bohemian Cretaceous Basin

Andrea Svobodová1,2, Martin Košťák1, Stanislav Čech3 & Lilian Švábenická3,*

Svobodová, A., Košťák, M., Čech, S. & Švábenická, L. (2014): New biostratigraphic evidence (texanitid ammonites, inoce-ramids and calcareous nannofossils) for the Upper and the uppermost Coniacian in the Bohemian Cretaceous Basin. [Neue biostratigrafische Hinweise (texanitide Ammoniten, Inoceramen und kalkige Nannofossilien) für oberes und oberstes Conia-cium im Böhmischen Kreidebecken.] – Z. Dt. Ges. Geowiss., 165: 577–589, Stuttgart.

Abstract: The re-discovered original specimen of the texanitid ammonite Texanites pseudotexanus, described as Mortoni-ceras texanus by Hibsch (1929) and illustrated as Mortoniceras pseudotexanus by Storm (1931), as well as three fragments of Paratexanites serratomarginatus documented (and one illustrated) by Fritsch (in Fritsch & Schlönbach 1872) as Ammo-nites Texanus, all from the Bohemian Cretaceous Basin (BCB), were systematically re-evaluated. The occurrence of these two zonal markers confirms the presence of Upper and uppermost Coniacian strata in the BCB. Sediment samples from the specimen of T. pseudotexanus provided calcareous nannofossils, including Lucianorhabdus cayeuxii and Lithastrinus grillii, documenting the uppermost Coniacian, lower part of the UC11c Subzone. These data are in accordance with the occurrence of the inoceramid bivalves Magadiceramus subquadratus, M. crenelatus and M. complicatus. Sediment samples from the specimen of P. serratomarginatus provided calcareous nannofossils, including Lithastrinus grillii and Lithastrinus septe-narius, documenting the Upper Coniacian (UC11 nannofossil Zone).

Kurzfassung: Das wiederentdeckte Original von Texanites pseudotexanus (Mortoniceras texanus in Hibsch 1929, Morto-niceras pseudotexanus in Storm 1931) sowie drei Fragmenten von Paratexanites serratomarginatus (Ammonites Texanus in Fritsch & Schlönbach 1872) werden aus dem Böhmischen Kreidebecken systematisch beschrieben. Die Funde dieser Index-Arten des Oberconiaciums belegen das Vorkommen von oberem und oberstem Coniacium im Böhmischen Kreidebecken. Von den Exemplaren wurden auch Proben für die Analyse der kalkigen Nannofossilien genommen. Die Anwesenheit der Nannoplanktonarten Lucianorhabdus cayeuxii und Lithastrinus grillii (Nannoplankton-Subzone UC11c) bestätigt das stra-tigrafische Alter und belegt oberstes Coniacium. Diese Daten harmonieren auch mit dem Vorkommen der Inoceramen Ma-gadiceramus subquadratus, M. crenelatus und M. complicatus. Auch Sedimentproben aus dem Gehäuse von P. serratomar-ginatus enthalten kalkige Nannofossilien wie zum Beispiel Lithastrinus grillii und Lithastrinus septenarius, die oberes Coniacium (Nanoplankton-Zone UC 11) nachweisen.

Keywords: Bohemian Cretaceous Basin, Upper Coniacian, biostratigraphy, ammonites, inoceramids, calcareous nannofossils

Schlüsselwörter: Böhmisches Kreidebecken, Oberconiacium, Biostratigrafie, Ammoniten, Inoceramen, kalkige Nannofossilien

© 2014 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany DOI: 10.1127/zdgg/2014/0023

www.schweizerbart.de1860-1804/0023 $ 6.30

Z. Dt. Ges. Geowiss. (German J. Geosci.), 165 (4), p. 577–589, 6 figs., 1 table ArticlePublished online October 2014

1. Introduction

Ammonites of the subfamily Texanitinae Collignon, 1948 include genera such as Texanites, Protexanites, Plesiotexa-nites, and Paratexanites (according to Cobban & Kennedy 1991 it is a group of at least fifteen genera and subgenera) and are biostratigraphically important for the interval from the Middle Coniacian to the Upper Campanian (Lamolda & Hancock 1996). The worldwide distributed genus Texanites

is biostratigraphically important in the Coniacian/Santonian boundary interval (Kennedy et al. 1981, Kennedy 1984, Kennedy & Kaplan 2000). The occurrence of texanitid am-monites in the Bohemian Cretaceous Basin (BCB) is excep-tional and was first reported by Schlönbach, who recorded (Schlönbach 1869: 294) Ammonites Texanus F. Roem. The same specimen was later figured by Fritsch (in Fritsch & Schlönbach 1872: Pl. 6, Fig. 5) as Ammonites Texanus Roem. This specimen comes from the Chloumek Ridge, specifically

578 Andrea Svobodová et al.

from the locality Vinařice near Mladá Boleslav, and it is re-described and re-interpreted herein as Paratexanites ser-ratomarginatus (Redtenbacher 1873), an index ammonite taxon for the Upper but not uppermost Coniacian (Lamolda & Hancock 1996, Kaplan & Kennedy 2000, Remin 2010). Another texanitid ammonite mentioned by Hibsch (1917a) and described by Hibsch (1929) as Mortoniceras texanus de Grossouvre, 1894, was recorded from silty marl sediments of the locality Prackovice nad Labem in the railway cutting between Malý and Velký Debus Hills nad Prackovicemi (Fig. 1). Storm (1931) re-determined and figured this speci-men as Mortoniceras pseudotexanus de Grossouvre. How-

ever, this ammonite figured in Storm’s poorly known fo-raminiferal paper (Storm 1931) has been disregarded by subsequent authors, with the exception of Soukup (1956), who mentioned this ammonite record. This specimen has been considered lost ever since the 1940s but was re-discov-ered in 2013 in the collections of the Institute of Geology and Palaeontology, Faculty of Science, Charles University in Prague. It is re-determined herein as Texanites pseudotexa-nus (de Grossouvre 1894), an index ammonite taxon for the uppermost Upper Coniacian. The sediment matrix surround-ing the external mould of this ammonite provided enough material for detailed micropalaeontological analysis based

Fig. 1: (A) Palaeogeographic position of the Bohemian Cretaceous Basin (Turonian–Coniacian). (B) Schematic map of the Bohemian Cretaceous Basin with localities of Upper Coniacian ammonite records (maps after Košťák et al. 2004).

579New biostratigraphic evidence for the Upper and the uppermost Coniacian in the Bohemian Cretaceous Basin

ginatus on the Chloumek Ridge. Since then, there is no new information concerning the lithology and biostratigraphy of the locality.

Hibsch (1917a, 1929), Storm (1931) and Soukup (1956) reported a single record of Texanites pseudotexanus from the topmost parts of the silty marl complex of the Březno For-mation (“Tonmergel des Oberturon und Emscher” sensu Hibsch (1917a, 1917b) – i.e. 380 m above sea level near Ústí nad Labem. The silty marl sediments are covered by the Ter-tiary volcanic pyroclastic material. The thickness of the silty marl sequence was estimated by Hibsch (1917a) to be about 100 m. Borehole data, however, show a greater thickness of about 240 m, and only ca 105 m for the Upper Coniacian strata (Macák 1967) in the vicinity of Ústí nad Labem. In the Upper Coniacian silty marl complex, inoceramid bivalves of the Magadiceramus subquadratus group predominate (Macák 1967). Soukup (1956: Pl. 1, Figs. 1–3 ) reported Ino-ceramus ex gr. subcardissoides (= M. subquadratus compli-catus Heine and M. subquadratus obesus Seitz, according to Seitz 1970), and Macák & Müller (1963: Pl. 1, Figs. 1, 2, Pl. 2, Figs. 1, 2) recorded Inoceramus subquadratus Schlüter (= M. subquadratus subquadratus and M. s. crenelatus Seitz, revised by Seitz 1970) and Inoceramus pachti Arkhanguel-sky (= M. subquadratus subquadratus in Macák 1967 and Seitz 1970). The highest part of the Upper Coniacian silty marl complex of the Březno Formation in the boreholes is characterised by M. s. subquadratus and M. s. crenelatus (Fig. 3: 7). The calcareous nannofossils in a sample from the T. pseudotexanus specimen show that the level with this am-monite find represents the youngest Coniacian sediments in the BCB. Inoceramids of the uppermost Coniacian spheno-ceramid Teilzone (sensu Kennedy & Kaplan 2000) have not yet been found in the silty marl complex of the Březno For-mation near the town of Ústí nad Labem.

3. Ammonite systematics

Order: Ammonoidea Zittel 1884Suborder: Ammonitina Hyatt 1889Superfamily: Acanthoceratoidea de Grossouvre, 1894Family: Collignoniceratidae Wright & Wright 1951Subfamily: Texanitinae Collignon 1948

Genus: Paratexanites Collignon 1948Type species: Mortoniceras zeilleri de Grossouvre 1894: 67, Pl. 14, Fig. 1.

Paratexanites serratomarginatus (Redtenbacher 1873)Fig. 3: 1‒3.

Synonymy:1869 Ammonites Texanus F. Roem.; Schlönbach, p. 294.1872 Ammonites Texanus Roem.: Fritsch & Schlönbach, p. 28, Pl. 6, Fig. 5.1873 Ammonites serrato-marginatus Redtenbacher, p. 110, Figs. 2a–d.

on nannofossils (see below). The calcareous nannofossils obtained from this specimen and from the specimen of P. serratomarginatus figured by Fritsch (in Fritsch & Schlön-bach 1872) allowed additional chronostratigraphic evalua-tion and biostratigraphic correlation.

2. Geological setting and stratigraphy

The calcareous mudstones on the Chloumek (formerly Chlomek) Ridge that yielded the specimen of Paratexa-nites serratomarginatus illustrated by Fritsch & Schoenbach (1872: Pl. 6, Fig. 5) were referred to the highest parts of the Březno Beds sensu Fritsch (1893; today Březno Formation; see Fig. 2). These mudstones are intercalated by thick sand-stone layers, assigned to the “Chlomek Beds” sensu Fritsch (1897). The specimen in question almost certainly came from either Bed 5 or Bed 7 (cf. Fritsch 1897: 17, Fig. 11; see Fig. 2). From the overlying calcareous sandstones (i.e., the “Chlomek Beds”), Fritsch (1897) additionally reported (but did not figure) Scaphites binodosus Roemer, which definitely represents a different scaphitid taxon as S. bino-dosus is a Lower Campanian species. Soukup (1955) re-cognised beds with “Inoceramus inconstans” Woods and “Barroisiceras haberfellneri” (Hauer) several tens of me-tres below the occurrence of the ammonite P. serratomar-

Fig. 2: The section of the former locality Vinařice (Chloumek Ridge), schematised and improved after Fritsch (1897: 17, Fig. 11). According to Fritsch 1897, the section was drawn in 1865 but was no longer exposed in the last decade of the 19th century. Dark grey: marls of the Březno Formation. Yellow: sandstone banks referred to the Chlomek Beds (Fritsch 1897). Red dashed line: horizon yield-ing Paratexanites serratomarginatus according to the data of Fritsch (1897). Blue dashed line: P. serratomarginatus, original record of Fritsch (1897) re-interpreted by Soukup (1955). The up-permost parts of the section = Chlomek Beds* sensu stricto by Fritsch (1897).


Fig. 3 : (1)‒(3) Paratexanites serratomarginatus (Redtenbacher 1873). (1) Specimen No. O3146 (National Museum of Prague). (2) Figure reprinted from Fritsch & Schlönbach (1872: Pl. 6, Fig. 5; specimen No. O3146 originally figured as a mirror image in the monograph). (3) Specimen No. O3147 (National Museum of Prague).Upper Coniacian, Vinařice (Chloumek Ridge) near Mladá Boleslav. Scale bar 1cm. (Photo of Fig. 2: J. Sklenář). (4)‒(6) Texanites pseudotexanus (Grossouvre 1894). (4) Specimen No. IGP 22496 (plaster cast/positive). (5) Specimen No. IGP 22496 (plaster cast/positive) – detail of the inner whorl (umbilical part) in oblique illumination to enhance tuberculation. (6) Specimen No. IGP 22496 (original – external mould). Chlupáč’s Museum of Earth History (Institute of Geology and Palaeontology, Faculty of Science, Charles University in Prague). Uppermost Coniacian, Prackovice nad Labem (railway cutting between Malý and Velký Debus Hills nad Prackovicemi). Scale bar 1cm. (7) Magadiceramus crenelatus (Heine). Lateral view of the right valve. Borehole TH-29 Strážky, depth 74.50 m. Upper part of the Březno Formation. Unregistered specimen. Coll. F. Macák (Czech Geological Survey). Scale bar 1cm.


Fritsch & Schlönbach (1872) additionally described, but did not figure, a fragment of a granulated belemnite rostrum from Chlomek (Vinařice) as Belemnites Merceyi, Mayer? It was reported from the horizon of the“Baculiten-Mergel” in-tercalated by a sandstone bank, referred to “oberen Quader” or “Micraster cor anguinum” Zone (Fritsch 1897). Strati-graphically, this record approximately corresponds to the find horizon of the figured specimen of P. serratomargina-tus. The relationship of this fragment to other belemnite taxa was discussed by Košťák et al. (2004). The fragment most probably belongs to Gonioteuthis praewestfalica Ernst & Schulz, a species known from the Middle Coniacian to the lower Lower Santonian. This belemnite fragment seems to be lost.

Stratigraphic distribution: P. serratomarginatus is the index taxon of the Upper but not uppermost Upper Coniacian. The P. serratomarginatus interval Zone is defined by the first oc-currence (FO) of this taxon and its upper boundary is defined by the FO of Texanites pseudotexanus (de Grossouvre 1894).

Geographic occurrence: Austria (Gosau Group), France, Germany, Poland, Czech Republic (central part of the BCB), Tunisia, Zululand (South Africa), Japan.

Genus: Texanites Spath 1932Type species: Ammonites Texanus Roemer 1852 (p. 31; Pl. 3; Fig. 1A–E)

Texanites pseudotexanus (de Grossouvre 1894)Fig. 3: 4‒6.

Synonymy:non 1869 Ammonites Texanus F. Roem.; Schlönbach, p. 294.non 1872 Ammonites Texanus Roem.; Fritsch & Schlönbach, p. 28, Pl. 6, Fig. 5.1876 Ammonites Texanus Roemer; Schlüter, p. 41 and 151, Pl. 41; Fig. 1–2.1894 Mortoniceras pseudotexanus de Grossouvre, p. 84.1917a Mortoniceras texanus de Grossouvre; Hibsch, p. 12.1929 Mortoniceras texanus de Grossouvre; Hibsch, p. 115–116.1931 Mortoniceras pseudotexanus de Grossouvre; Storm, p. 8‒9, 22, Pl. 1.1956 Mortoniceras pseudotexanus de Grossouvre; Soukup, p. 3, 7.For the complete synonymy list see Kennedy & Kaplan (2000: 86).

Material: Specimen No. IGP 22496. The single specimen (external mould + plaster cast taken from the mould) from the locality Prackovice nad Labem (railway cutting between Malý and Velký Debus Hills nad Prackovicemi) is deposited under No. IGP 22496 in the Chlupáč’s Museum of Earth His-tory (Institute of Geology and Palaeontology, Faculty of Sci-ence, Charles University in Prague).

1893 Ammonites (Schlönbachia) Texanus Römer; Fritsch 1893, p. 74, Fig. 49.1948 Behavites (Parabehavites) serratomarginatus (Redten-bacher); Collignon, p. 83.1981 Paratexanites serratomarginatus (Redtenbacher 1873); Kennedy, Klinger & Summesberger, p. 117–127, Figs. 1–7.1984 Paratexanites serratomarginatus (Redtenbacher 1873); Kennedy, p. 117, Figs. 35F, G, Pl. 23, Figs. 5–6, Pl. 26, Figs. 1–3, Pl. 27, Figs. 1–7.For the complete synonymy list see Kennedy et al. (1981: 117) and Kennedy (1984: 117).

Material: Specimens No. O3146 and O3147. The specimen from Vinařice figured by Fritsch (in Fritsch & Schlönbach 1872: Pl. 6, Fig. 5) as Ammonites texanus and refigured by Fritsch (1893: Fig. 49) (No. O3146; Fig. 3: 1, 2) and two whorl fragments from Vinařice mentioned by Fritsch (in Fritsch & Schlönbach 1872; No. O3147; Fig. 3: 3), stored in the National Museum in Prague.

Description: The incomplete specimen (No. O3146) of the whorl (length 52 mm) comprises six ribs. Height of the whorl is 38mm. Prorsiradiate ribs (7 mm wide at the submarginal tubercles) are strongly developed, almost straight to slightly curved. Bullae at the umbilical shoulder are only weakly de-veloped, better visible in specimen No. O3147 (Fig. 3: 2), which preserves three ribs (fragment length 12 mm) and re-presents either a younger specimen or an inner whorl. The marginal and submarginal tubercles are clavate and they are regularly arranged close together in pairs. External clavate tubercles are slightly larger than lateral ones. Their shape and orientation are similar and they are terminating the ribs. The ventral “keel” part is not preserved (except for relicts of one? row of the external clavate tubercles). The sutures are not preserved.

Discussion and remarks: The genus Paratexanites differs from Texanites in having four tubercles (the tubercle rows are indicated by numbers 1–4 from umbilcal [1] to marginal [4]), lacking the second (2), lateral tubercle row (Texanites has five tubercle rows). About 12 species are discussed within the genus (Klinger & Kennedy 1980 – see also the comparison between Paratexanites taxa and the discussion in this paper as well as in Kennedy 1984). P. emscheris (Schlüter) and P. sellardsi Young are similar to P. ser-ratomarginatus but differ from P. serratomarginatus in hav-ing coarser ribs and robust tubercles (some other differences are observable in the umbilical bullae and ribs; Kennedy et al. 1981: 126). From the type species of P. zeilleri, P. ser-ratomarginatus differs in having closely spaced marginal and submarginal tubercles (Kennedy 1984: 117).

The size of the preserved fragment from the BCB as well as the character of the marginal and submarginal tubercles (see above) suggest a later ontogenetic stage of a larger spec-imen (Kennedy et al. 1981: 118). The morphological charac-ters of P. serratomarginatus from Vinařice correspond to common specimens from Austria and France.


Description: The specimen is flattened or laterally com-pressed and it is preserved as an external mould. The plaster cast shows all the important morphological features. Very evolute shell (D = 230 mm in preserved part, U = 105 mm, comprising ca. 46 % of the shell diameter) with shallower umbilicus. Height of the whorl Wh = 68 mm. Umbilical walls high, steep to slightly rounded. Simple, strong, radiate, prorsiradiate primary ribs well developed with four marked ventrolateral tubercles (including submarginal and mar-ginal). Ribs arising from weakly developed bullae at the um-bilical shoulder. Number of ribs per whorl 24–25. Tubercles regularly arranged rounded, conical (1–3), strongly clavate (4), ribs ending in prolonged clavate external (5) tubercles, forming an undulose keel. The ventral “keel” part is not pre-served, except for a single and incomplete row of the exter-nal clavate tubercles. Sutures are not preserved.

Discussion and remarks: The genus Texanites is charac-terised by pentatuberculate ornamentation. T. pseudotexanus differs from similar species of the genus (T. texanus, T. gal-licus, T. quinquenodosus) in the character of the ribs, the number of ribs per whorl, their separation and (in part) their orientation (for detailed differential characteristics see Kennedy et al. 1981, Kennedy 1984, Kennedy et al. 1995, Kaplan & Kennedy 2000). In T. pseudotexanus, there is a constant number of ribs per whorl (24–26), while a higher

number is typical for T. gallicus (32–34), T. texanus (26–28) and T. quinquenodosus (27–32). T. gallicus has a less invo-lute shell compared to T. pseudotexanus and T. texanus has weaker ribs than T. pseudotexanus (Kennedy et al. 1981, Ka-plan & Kennedy 2000).

The mass occurrence of T. pseudotexanus approximately in the middle part of the T. pseudotexanus Zone is termed the pseudotexanus Event (Kennedy & Kaplan 2000, Kaplan & Kennedy 2000). It is connected with the initial transgressive pulse in the Münsterland Cretaceous Basin (Kaplan & Kennedy 1996, Kennedy & Kaplan 2000). An increase in endemism of ammonite fauna beginning in the late Middle to Late Coniacian and abundant records of T. pseudotexanus were considered to be restricted to the this basin. However, new records from Poland (Lipnik-Kije Basin; Remin 2010) and previous records from Bornholm (Denmark; Kennedy & Christensen 1991) show a wider geographic distribution and greater abundance of this taxon. Above the pseudotexanus Event, a change from acanthoceratid to desmoceratid am-monite assemblages is reported by Kaplan & Kennedy (2000). Due to the extreme rarity of the late Coniacian am-monite faunas in the BCB and the virtual absence of out-crops, we are not able to confirm if the horizon yielding T. pseudotexanus also represents the pseudotexanus Event (and the associated level of change in ammonite assemblages). According to the calcareous-nannofossil data (see below),

Fig. 4: Biostratigraphic scheme for the Upper Coniacian in the BCB. Blue rectangle with pE = pseudotexanus-Event (sensu Kaplan & Kennedy 2000). Red lines = suggested levels of ammonite records from the BCB.*Sensu Burnett (1998).


the horizon yielding T. pseudotexanus represents the higher part of the Texanites pseudotexanus ammonite Zone (Fig. 4). This should correspond to the top of the pseudotexanus Event reported from NW Germany (Kaplan & Kennedy 2000). Kennedy & Christensen (1991: 214) mentioned a record of Texanites psudotexanus from Czechoslovakia; however, it is not clear if they were referring to the specimen of Fritsch & Schlönbach (1872 = P. serratomarginatus) and/or the specimen of Hibsch (1929 = T. pseudotexanus) as no reference is associated with this remark.

Stratigraphic distribution: T. pseudotexanus is the index taxon of the uppermost Upper Coniacian., The T. pseudo-texanus interval Zone is defined by the FO of this taxon and its upper boundary (the Coniacian/Santonian boundary) is defined by FO of Kitchinites emscheris (Germany), Kitch-inites emscheris ‒ Nowakites savini (Poland), or Texanites gallicus (northern Spain).

Geographic occurrence: Europe (Germany – Münsterland Cretaceous Basin, Poland – Lipnik-Kije Basin, England, Denmark ‒ Bornholm, Czech Republic – NW part of the BCB), Madagascar, North America (USA – Texas).

4. Calcareous nannofossils

4.1 Material and methods

Two sediment samples for nannofossil study were taken from the specimen of Texanites pseudotexanus (spec. No. IGP 22496; Fig. 3: 4‒6) from Prackovice nad Labem and from the specimen of Paratexanites serratomarginatus (spec. No. 03147; Fig. 3: 3) from Vinařice respectively. The laboratory processing followed the technique mentioned by Švábenická (2001). In order to obtain the relative sample abundances and semiquantitative information about nanno-fossil species, 300 specimens were counted in each slide. Each slide was then scanned for an additional two hours for the possible identification of scarce but biostratigraphically important species. The slides were examined under an Olympus BX51 light microscope using an immersion objec-tive with a magnification 100x. Digital images of nannofos-sil specimens were made using an Olympus DP70 digital camera and a Nikon Microphot-FXA. Biostratigraphic data were interpreted with reference to the UC zones of Burnett (1998).

4.2 Results

In sample 1 taken from Texanites pseudotexanus, the nan-nofossil preservation is rather poor. Some specimens show evidence of etching and overgrowth, and in the majority of the coccoliths the central area structure is destroyed. More-over, the nannofossils commonly occur as fragments and their identification is nearly impossible. Nannofossil abun-dance varies from 1 to 10 specimens per field of view.

In total, 49 calcareous nannofossil taxa were identified (Table 1). The most significant component of the assemblage is the genus Watznaueria forming 36 % (the species W. bar-nesiae representing 34 % of all identified nannofossils in the sample), followed by the the genera Zeugrhabdotus (15 %), Micula (14 %), Lucianorhabdus (7 %) and Eiffellithus (6 %).

The preservation of nannofossils in sample 2 taken from Paratexanites serratomarginatus is even worse than in sam-ple 1. Strong etching and dissolution is evident. Only 39 nan-nofossil taxa were identified (Table 1). Watznaueria bar-nesiae represents 56 % of assamblage (Watznaueria spp. 58 %). The percentages of the other genera are as follows: Micula 10 %, Zeugrhabdotus 6 %, Lucianorhabdus 3 % and Eiffellithus 2 %. The nannofossil abundance is very low, be-tween 1 and 5 specimens per field of view.

4.3 Taphonomic and palecologic discussion

The presence of Lucianorhabdus spp., Braarudosphaera bigelowii and Thoracosphaera operculata indicates shallow-water conditions and the potential input of terrigenous mate-rial. Moreover, one specimen of Kamptnerius magnificus in each sample was recorded, a species with cool surface-water affinities (Thierstein 1976, 1981, Wind 1979, Pospichal & Wise 1990, Lees 2002).

To a lesser degree, also holococcoliths of the genus Cal-culites (C. ovalis and C. obscurus) are present as well as a transitional form of Quadrum–Uniplanarius (U. cf. gothi-cus; see Fig. 5: 8, 9). In the case of the species U. gothicus, they may be recrystallised specimens of Quadrum gartneri. Under the light microscope, such modified specimens of the genus Quadrum may seem like members of genus Uni-planarius (Švábenická 2010). Burnett (1998) reported the first occurrence of the species U. gothicus at the boundary between the Lower and Upper Santonian. However, in the Bohemian Cretaceous Basin, such specimens appear already in the uppermost Turonian (Švábenická 2010).

The rare occurrence of representatives of the family Stephanolithiaceae (genera Corollithion, Cylindralithus) in sample 2 can be explained by the poor state of preservation, because these individuals are sensitive to the character of the sedimentary environment and are less resistant to dissolu-tion. During recrystallisation or dissolution, they are there-fore preferentially destroyed (Melinte & Lamolda 2007, Švábenická 2010). It should be noted that also the low abun-dance of Lucianorhabdus spp. can be explained by the gen-erally poor nannofossil preservation, because it is also disso-lution-sensitive. However, less frequent occurence of this shallow-water taxon can equally be caused by a deeper envi-ronment.

4.4 Nannofossil biostratigraphy

The following biostratigraphically important species (Bur-nett 1998) have been recorded: Lucianorhabdus cayeuxii (rare occurrence in sample 1), Lucianorhabdus arcuatus,


CALCAREOUS NANNOFOSSIL TAXA

Sample No. 1

Sample No. 2

Texanites pseudote-xanus

Paratexanites serrato-marginatus

Ahmuellerella octoradiata – RBiscutum melaniae R –Braarudosphaera bigelowii bigelowii

R R

Braarudosphaera bigelowii parvula

R –

Broinsonia signata – RCalculites obscurus R RCalculites ovalis F FCorollithion exiquum R –Cribrosphaerella ehrenbergii C CCyclagelosphaera margerelii R FCylindralithus biarcus R REiffellithus eximius F REiffellithus gorkae – REiffellithus turriseiffelii C FEprolithus floralis – RGartnerago obliquum F RHelicolithus trabeculatus F RChiastozygus litterarius F –Kamptnerius magnificus R RLithastrinus grillii R RLithastrinus septenarius – RLithraphidites carniolensis R FLucianorhabdus arcuatus R RLucianorhabdus cayeuxii F –Lucianorhabdus maleformis F FLucianorhabdus quadrifidus R RManivitella pemmatoidea R RMarthasterites furcatus R FMicrorhabdulus belcigus R –Micula concava R –Micula cubiformis R –Micula staurophora C CMicula swastica R –Nannoconus sp. R RPlacozygus fibuliformis R –

CALCAREOUS NANNOFOSSIL TAXA

Sample No. 1

Sample No. 2

Texanites pseudote-xanus

Paratexanites serrato-marginatus

Prediscosphaera sp. R FPrediscosphaera cretacea R RPrediscosphaera grandis* R –Quadrum gartneri R RRetacapsa crenulata R FRhagodiscus angustus R FThoracosphaera operculata F RTranolithus orionatus R R?Uniplanarius gothicus R FWatznaueria barnesae A AWatznaueria britannica R –Watznaueria fossacincta R RWatznaueria manivitae R FZeugrhabdotus bicrescenticus R –Zeugrhabdotus biperforatus F RZeugrhabdotus diplogrammus C FZeugrhabdotus embergeri R –Zeugrhabdotus erectus R –Zeugrhabdotus scutula R F

Table 1: Distribution of calcareous nannofossils in both studied samples. Sample 1 – taken from the specimen of Texanites pseudo-texanus. Sample 2 – taken from Paratexanites serratomarginatus. Abbreviations used for abundance: R = rare (1–2 specimens), F = few (3–10 specimens), C = common (11–100 specimens), A = abundant (greater than 100 specimens). *Sensu Burnett (1998).

Fig. 5: Calcareous nannofossils from the Upper Coniacian in Bohe-mian Cretaceous Basin. Polarised light. Scale bar represents 5 μm. (1) Cyclagelosphaera margerelii; sample 1. (2) Watznaueria bar-nesae; sample 1. (3) Watznaueria fossacincta; sample 1. (4) Watznaueria britannica; sample 1. (5) Watznaueria manivitae; sample 1. (6), (7) Quadrum gartneri; samples 1, 2. (8), (9) Quad-rum-Uniplanarius, ?Uniplanarius gothicus; samples 1, 2. (10), (11) Micula staurophora; samples 1, 2. (12) Micula concava; sample 1. (13) Micula cubiformis; sample 1. (14) Micula concava (object above) and Micula staurophora (object below); sample 1. (15) Mi-cula swastica; sample 1. (16), (17) Zeugrhabdotus biperforatus; sample 1. (18) Zeugrhabdotus embergeri; sample 1. (19) Zeugrhab-dotus erectus; sample 1. (20), (21) Zeugrhabdotus scutula; samples 1, 2. (22) Marthasterites furcatus; sample 1. (23) Chiastozygus lit-terarius; sample 1. (24) Eprolithus floralis (side view); sample 2. (25), (26) Rhagodiscus angustus; samples 1, 2. (27) Retacapsa crenulata; sample 2. (28) Broinsonia signata; sample 2. (29) Ahmu-ellerella octoradiata; sample 2. (30) Manivitella pemmatoidea; sample 2. (31)‒(33) Lithastrinus grillii; samples 1, 1, 2. (34), (35) Lithastrinus septenarius; sample 2. (36) Cylindralithus biarcus; sample 2.


Fig. 6: Calcareous nannofossils from the Upper Coniacian in Bohemian Cretaceous Basin. Polarised light. Scale bar represents 5 μm. (1), (2) Braarudosphaera bigelowii bigelowii; samples 1, 2. (3) Braarudosphaera bigelowii parvula; sample 1. (4)‒(6) Calculites ovalis; sam-ples 1, 1, 2. (7) Calculites obscurus; sample 1. (8) Eiffellithus turriseiffelii; sample 1. (9) Eiffellithus eximius; sample 1. (10) Eiffellithus gorkae; sample 2. (11) Gartnerago obliquum; sample 1. (12), (13) Kamptnerius magnificus; samples 1, 2. (14), (15) Lucianorhabdus ca-yeuxii; sample 1. (16)‒(18) Lucianorhabdus arcuatus; samples 2, 1, 1. (19), (20) Lucianorhabdus maleformis; samples 1, 2. (21) Luciano-rhabdus quadrifidus; sample 1. (22) Lithraphidites carniolensis; sample 1. (23) Microrhabdulus belgicus; sample 1. (24) Placozygus fibuliformis; sample 1. (25), (26) Nannoconus sp. (cross-sections); samples 1, 2. (27) Helicolithus trabeculatus; sample 1. (28) Predis-cosphaera grandis sensu Burnett (1998); sample 1. (29) Prediscosphaera sp. (side view); sample 1. (30) Cribrosphaerella ehrenbergii; sample 2.


Lithastrinus grillii, Lithastrinus septenarius (present only in sample 2), Zeugrhabdotus biperforatus, Quadrum gartneri, Prediscosphaera grandis (sensu Burnett 1998, present only in sample 1), Marthasterites furcatus, Micula concava, Mi-cula staurophora and Micula swastica (rare occurrence in sample 1).

Sample 1 can be asssigned to the UC11c nannofossil Subzone (sensu Burnett 1998), an equivalent of the CC16 Lucianorhabdus cayeuxii Zone proposed by Sissingh (1977) and modified by Perch-Nielsen (1985). The UC11c Subzone is defined as the interval from the first occurrence of Luciano-rhabdus cayeuxii to the last occurrence of Lithastrinus septe-narius and its stratigraphic range extends from the upper-most Coniacian to the Lower Santonian. The presence of L. cayeuxii (Fig. 6: 14, 15) confirms the existence of uppermost Coniacian strata (beginning of the UC11c Subzone). L. sep-tenarius, the last occurrence of which marks the upper boundary of the UC11 Zone, was not found. Moreover, the relative common occurrence of Helicolithus trabeculatus in sample 1 may indicate the Upper Coniacian and the Conia-cian/Santonian boundary interval (Hampton et al. 2007).

Within the Coniacian/Santonian boundary interval, a sig-nificant increase in the numbers of Lucianorhabdus spp., Micula concava and Calculites spp., which can also be re-garded as an “acme” zone, is described, e.g. by Burnett (1998) and Melinte & Lamolda (2002, 2007). With regard to the calcareous nannofossil assemblage content, Melinte & Lamolda (2002, 2007) determined more then 20 % of Lu-cianorhabdus spp., more then 10 % of M. concava and about 10 % of Calculites spp. in that interval. In contrast, in sample 1, Lucianorhabdus spp. represents 7 %, Calculites spp. 1.7 % and M. concava only 0.7 % of the assamblage. The presence of the biostratigraphic marker L. cayeuxii shows that the studied sample belongs to the UC11c Subzone but probably to its lower part, i.e. the uppermost Coniacian, due to the absence of the “acme” zones of Lucianorhabdus spp., M. concava and Calculites spp. Other taxa discussed in the context of the Coniacian/Santonian boundary interval, such as Orastrum campanensis (Blair & Watkins 2009, Egger et al. 2013) and Amphizygus minimus (Howe et al. 2007) were not found.

The overlap into the UC12 Zone may be inferred from sample 1 based on the absence of L. septenarius. However, Wagreich (1992) reports from the Northern Calcareous Alps, Lower Gosau Group, the LO of L. septenarius in the Middle Coniacian, approximately in the same level as the FO of L. grillii. However, the two separate samples have been ac-quired from macrofossil specimens and not a complete pro-file, thus the UC12 Zone can here not be accurately identi-fied.

The nannofossil assemblage of sample 2 contained the marker species Lithastrinus grillii and L. septenarius, evi-dencing the UC11 Zone, probably within the subzone range UC11a–b. The “acme” zone of Lucianorhabdus spp., Micula concava and Calculites spp. was not observed.

5. Conclusions

The two index ammonites clearly document the existence of the Paratexanites serratomarginatus and Texanites pseudo-texanus zones in the Bohemian Cretaceous Basin (BCB). The record of T. pseudotexanus comes from the middle to upper part of the Texanites pseudotexanus Zone. The precise stratigraphic position of the P. serratomarginatus record is not exactly known at present; however, the presence of this index ammonite taxon clearly documents the Upper Conia-cian.

The occurrence of P. serratomarginatus and T. pseudo-texnus in the BCB corresponds to other records in Europe. Ammonites, as well as calcareous nannofossil records and inoceramid bivalve data enabled more precise stratigraphic dating of the sedimentary units in the central and northwest-ern parts of the BCB, which are considered herein to belong to the Upper and uppermost Coniacian.

The record of the inoceramid Magadiceramus crenelatus (Heine) from the borehole TH-29 Strážky documents the up-permost part of the Upper Coniacian silty marl complex of the Březno Formation in the northwestern part of the BCB in the he vicinity of Ústí nad Labem.

Nannofossils from the specimen of T. pseudotexanus produced evidence for the uppermost Coniacian, UC11c nannofossil Subzone with Lucianorhabdus cayeuxii. Nanno-fossils from the specimen of P. serratomarginatus confirmed the Upper Coniacian age, UC11 nannofossil Zone, based on the co-occurrence of Lithastrinus grillii, L. septenarius and common Micula staurophora, probably representing the middle to upper part of the P. serratomarginatus Zone.

6. Acknowledgements

We thank Jan Sklenář (National Museum of Prague) for pre-paring the Paratexanites serratomarginatus specimen (the original of Fritsch & Schlönbach 1872) and for providing the calcareous nannofossil sample from its matrix. Frank Wiese (University Göttingen) kindly helped us with translation of some parts into German language. We are grateful to C. J. Wood (Minehead) and an anonymous reviewer for insightful comments on earlier draft of the manuscript. The research is supported by: PRVOUK P44.

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Appendix

Taxonomic index in alphabetical order of genera (see also Table 1)

Ahmuellerella octoradiata (Górka 1957) Reinhardt 1966Biscutum melaniae (Górka 1957) Burnett 1977Braarudosphaera bigelowii bigelowii (Gran & Braarud 1935) Deflandre 1947Braarudosphaera bigelowii parvula Stradner 1960Broinsonia signata (Noël 1969) Noël 1970Calculites obscurus (Deflandre 1959) Prins & Sissingh in Sissingh 1977Calculites ovalis (Stradner 1963) Prins & Sissingh in Sissingh 1977Corollithion exiquum Stradner 1961Cribrosphaerella ehrenbergii (Arkhangelsky 1912) Deflan-dre in Piveteau 1952Cyclagelosphaera margerelii Noël 1965Cylindralithus biarcus Bukry 1969Eiffellithus gorkae Reinhardt 1965Eiffellithus eximius (Stover 1966) Perch-Nielsen 1968Eiffellithus turriseiffelii (Deflandre in Deflandre a Fert 1954) Reinhardt 1965Eprolithus floralis (Stradner 1962) Stover 1966Gartnerago obliquum (Stradner 1963) Noël 1970Helicolithus trabeculatus (Górka 1957) Verbeek 1977Chiastozygus litterarius (Górka 1957) Manivit 1971Kamptnerius magnificus Deflandre 1959Lithastrinus grillii Stradner 1962Lithastrinus septenarius Forchheimer 1972Lithraphidites carniolensis Deflandre 1963Lucianorhabdus arcuatus Forchhemer 1972Lucianorhabdus cayeuxii Deflandre 1959Lucianorhabdus maleformis Reinhardt 1966Lucianorhabdus quadrifidus Forchheimer 1972Manivitella pemmatoidea (Deflandre in Manivit 1965) Thierstein 1971

Marthasterites furcatus Deflandre 1959Microrhabdulus belgicus Hay & Towe 1963Micula concava (Stradner in Martini & Stradner 1960) Verbeek 1976Micula cubiformis Forchheimer 1972Micula staurophora Gardet 1955 (Synonyms: Micula decussata Vekshina 1959)Micula swastica Stradner & Steinmetz 1984Nannoconus sp. Kamptner 1931Placozygus fibuliformis (Reinhardt 1964) Hoffmann 1970Prediscosphaera sp. Vekshina 1959Prediscosphaera cretacea (Arkhangelsky 1912) Gartner 1968Prediscosphaera grandis (sensu Burnett 1998) Perch-Niel-sen 1979Quadrum gartneri Prins & Perch-Nielsen in Manivit et al. 1977Retacapsa crenulata (Bramlette & Martini 1964) Grün in Grün & Allemann 1975Rhagodiscus angustus (Stradner 1963) Reinhardt 1971Thoracosphaera operculata Bramlette & Martini 1964Tranolithus orionatus (Reinhardt 1966a) Reinhardt 1966b?Uniplanarius gothicus (Deflandre 1959) Hattner & Wise 1980Watznaueria barnesae (Black 1959) Perch-Nielsen 1968Watznaueria britannica (Stradner 1963) Reinhardt 1964Watznaueria fossacincta (Black 1971) Bown in Bown & Cooper 1989Watznaueria manivitae Bukry 1973Zeugrhabdotus bicrescenticus (Stover 1966) Burnett in Gale et al. 1996Zeugrhabdotus biperforatus (Gartner 1968) Burnett 1997Zeugrhabdotus diplogrammus (Deflandre in Deflandre & Fert 1954) Burnett in Gale et al. 1996Zeugrhabdotus embergeri (Noël 1958) Perch-Nielsen 1984Zeugrhabdotus erectus (Deflandre in Deflandre & Fert 1954) Reinhardt 1965Zeugrhabdotus scutula (Bergen 1994) Rutledge & Bown 1996

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Manuscript received: 13.03.2014Accepted for publication: 18.08.2014

New biostratigraphic evidence (texanitid ammonites, inoceramids and calcareous nannofossils) for the...

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