The age of the Nodular Limestone Formation (Late Cretaceous), Narmada Basin,central India

The age of the marine Nodular Limestone Formation of the Bagh Group is refined at Substage level through ammonoid and inoceramid index taxa. The study is based on the fresh collections from three well-defined successive intervals (Lower Karondia, Upper Karondia and Chirakhan members) of this formation having excellent exposures in different localities of the Narmada Basin, central India. The first record of the widely distributed Turonian ammonoid genera Spathites Kummel and Decker and Collignoniceras Breistroffer from the Nodular Limestone Formation constrained its age exclusively to Turonian. The Early Turonian species Spathites (Jeanrogericeras) aff. revelieranus (Courtiller) and Mytiloides labiatus (Sclotheim) occur in the lower part, while the Middle Turonian marker Collignoniceras cf. carolinum (d’Obrbigny) and Inoceramus hobetsensis (Nagao and Matsumoto) occurs in the upper part of the Karondia Member. The record of the index species Inoceramus teshioensis (Nagao and Matsumoto) in association with Placenticeras mintoi Vredenburg from Chirakhan Member allows a definite Late Turonian age. The present contribution is an attempt to resolve the controversies in the age of the Nodular Limestone Formation and also demarcation of the three divisions (Early, Middle and Late) of the Turonian Stage in the Narmada Basin, central India.     

Facies related phylostratigraphy of the benthic neoselachian Ptychodus from the Late Cretaceous (Cenomanian/Turonian) of the Pre-North Sea Basin of Europe

The phylostratigraphy, taphonomy and palaeoecology of the Late Cretaceous neoselachian Ptychodus of northern Germany appears to be facies related. Ptychodus is not present in lower Cenomanian shark-tooth-rich rocks. First P. oweni records seem to relate to middle Cenomanian strata. P. decurrens appears in the middle to upper Cenomanian mainly in non-coastal environments of the shallow marine carbonate ramp and swell facies which isolated teeth were found partly in giant ammonite scour troughs on the Northwestphalian-Lippe High submarine swell in the southern Pre-North Sea Basin. They are recorded rare in deeper basin black shales facies (upwelling influenced, OAE Event II). P. polygyrus seems to be restricted to upwelling influenced basin and deeper ramp facies mainly of the uppermost Cenomanian and basal lower Turonian (OAE II Event). P. mammillaris is mostly represented during the lower to middle Turonian in the inoceramid-rich ramp and the near shore greensand facies along the Münsterland Cretaceous Basin coast north of the Rhenish Massif mainland. Finally, P. latissimus is recorded by two new tooth sets and appears in the upper Turonian basin swell facies and the coastal greensands. Autochthonous post-Turonian Ptychodus remains are unrecorded in the Santonian–Campanian of Germany yet. Reworked material from Cenomanian/Turonian strata was found in early Santonian and middle Eocene shark-tooth-rich condensation beds. With the regression starting in the Coniacian, Ptychodus disappeared in at least the Münster Cretaceous Basin (NW-Germany), but remained present at least in North America in the Western Interior Seaway. The Cenomanian/Turonian Ptychodus species indicate a rapid neoselachian evolution within the marine transgression and global high stand. A correlation between inoceramid shell sizes, thicknesses and their increasing size during the Cenomanian and Turonian might explain the more robust and coarser ridged enamel surfaces in Ptychodus teeth, if Ptychodus is believed to have preyed on epifaunistic inoceramid bivalves.     

Cenomanian oysters from the Sergipe Basin, Brazil

Cenomanian (mid Cretaceous) oysters from the Sergipe Basin in northeastern Brazil are described, with revisions of previously described forms. Nine genera and subgenera, including eleven species, are distinguished: Rastellum diluvianum (Linné, 1767), Amphidonte (Ceratostreon) reticulata (Reuss, 1846), A. (Ceratostreon) flabellata (Goldfuss, 1833), Exogyra (Costagyra) olisiponensis Sharpe, 1850, Ilymatogyra (Afrogyra) africana (Lamarck, 1801), Rhynchostreon (Rhynchostreon)mermeti (Coquand, 1862), R. (Laevigyra) obliquatum (Pulteney, 1813), R. (Laevigyra) sp., Pycnodonte (Phygraea) vesiculosa (J. Sowerby, 1823), Curvostrea rouvillei (Coquand, 1862) and Ambigostrea sp. No undoubted Turonian oysters are known from Sergipe, althoughR. (R.) mermeti possibly straddles the Cenomanian–Turonian boundary. This is in sharp contrast with the situation in the more northerly Brazilian basins, from where several Turonian but no Cenomanian forms have been described. Well-preserved material from Sergipe confirms the close relationship between Exogyra (Costagyra) Vialov andVultogryphaea Vialov. The palaeobiogeographical affinity of the oyster fauna is typically Tethyan with many taxa that are known particularly from the southern Tethys. The inferred palaeoenvironment as implied by the oysters is that of a shallow shelf.     

Ammonite and inoceramid bivalve faunas from the Davutlar Formation of the Devrekani–Kastamonu area, northern Turkey, and their biostratigraphical significance

The ammonite and inoceramid bivalve faunas of the Davutlar Formation of the Devrekani–Kastamonu area in central-north Turkey, are described. The formation yields an ammonite assemblage of Pseudophyllites indra (Forbes, 1846), Pachydiscus (Pachydiscus) haldemsis (Schlüter, 1867), Pachydiscus (Pachydiscus) oldhami (Sharpe, 1855), Didymoceras binodosum (Kennedy and Cobban, 1993), Bostrychoceras polyplocum (Roemer, 1841) and Baculites alavensis Santamaria Zabala, 1996. The inoceramid assemblage is Cataceramus subcompressus (Meek and Hayden, 1862), Cataceramus goldfussianus (d'Orbigny, 1846), Platyceramus vanuxemi (Meek and Hayden, 1860), Cataceramus cf. mortoni (Meek, 1876), Cataceramus pteroides (Giers, 1964), Cataceramus aff. barabini (Morton, 1834), Platyceramus pierrensis (Walaszczyk et al., 2001), “Inoceramus” convexus Hall and Meek, 1856, Cordiceramus heberti (Fallot, 1885), “Inoceramus” tenuilineatus Hall and Meek, 1856, “Inoceramus” borilensis Jolkicev, 1962, as well as some forms with no or equivocal specific affiliation. Both ammonite and inoceramid faunas suggest an early Late Campanian age for the formation, most probably Bostrychoceras polyplocum and Didymoceras donezianum ammonite Zones / Cataceramus subcompressus and “Inoceramus” tenuilineatus inoceramid Zones. Both ammonite and inoceramid assemblages are well represented throughout the Euramerican biogeographical region.     

Biostratigraphical correlations of the calcareous nannofossil Marthasterites furcatus in the Bohemian Cretaceous Basin and Outer Flysch Carpathians,Czech Republic

The first occurrence (FO) of Marthasterites furcatus was correlated with the FOs of other nannofossils, inoceramid bivalves and foraminifers in the Bohemian Cretaceous Basin and Outer Flysch Carpathians. The correlation showed that the FO of M. furcatus was diachronous, becoming younger from east to west. In the Silesian Unit it appears in the lower Turonian in association with Eprolithus moratus (UC6b nannofossil Zone). In the Pavlovské vrchy klippes it appears in the upper middle Turonian together with Lithastrinus septenarius (UC9 Zone). In the Bohemian Cretaceous Basin, the FO of M. furcatus was observed in the lower upper Turonian just above the FO of Liliasterites angularis. The presence of M. furcatus in Turonian strata is scarce and discontinuous up to its sudden quantitative increase (represented by 5–27% in assemblages) below the FO of the inoceramid bivalve species Cremnoceramus waltersdorfensis and C. deformis erectus in the Turonian–Coniacian boundary interval. The top of the M. furcatus acme was recorded below the FO of Micula staurophora. The second quantitative rise of M. furcatus (12% in assemblage) was found in the lower lower Campanian of the Pavlovské vrchy klippes above the FO of Broinsonia parca parca in the UC14a Zone and the last occurrence of the planktonic foraminifer Whiteinella baltica. Above this second acme M. furcatus disappears. The significantly earlier appearance of M. furcatus in the Silesian Basin may be connected with a southeast-heading surface current from the North European epicontinental sea where the species appeared in the early Turonian too.     

Thoracican cirripedes (Crustacea) from the Hauterivian (Lower Cretaceous) of Hannover,northern Germany

Diverse thoracican cirripedes from the Hauterivian of the Hannover district of northern Germany are described, including seven species, belonging to five genera. Of these, a new genus belonging to the Scalpellidae, Jaegerscalpellum, includes one Hauterivian species, J. elegans sp. nov., an Aptian species, J. comptum (Withers, 1910) and an Albian species, J. politum (Darwin, 1851) are also referred to it. A new Cretiscalpellum, C. mutterlosei sp. nov. is described from the Hauterivian, and C. matrioni sp. nov. is described from the Middle Albian of France. The oldest record of the Unilatera Gale, 2018, Pedupycnolepas pulcher sp. nov. is described from the Hauterivian; this displays typical shell structure of the group, retained by living Verrucidae. Finally, four species of Zeugmatolepadidae, subfamily Martillepadinae, are recorded from the Hauterivian, including Martillepas hausmanni (Koch and Dunker, 1836), M. decoratus sp. nov., M. auriculum sp. nov. and Etcheslaepas borealis (Collins, 1990). The Hauterivian fauna from Hannover shows affinities both with Late Jurassic and later Cretaceous (Aptian-Cenomanian) forms, and includes the earliest scalpellids, unilateran (Pedupycnolepas) and Cretiscalpellum species known. It constrains the age of the Cretaceous cirripede evolutionary radiation to the earliest Cretaceous.     

Carbon isotope stratigraphy and depositional oxia through Cenomanian/Turonian boundary sequences (Upper Cretaceous) in New Zealand

Stratigraphic sections across the Cenomanian/Turonian boundary (C/T boundary) are identified in New Zealand and were deposited in southern high latitudes of the palaeo-Pacific. Lithological evidence for Cretaceous Oceanic Anoxic Event 2 (OAE2), which preceded and spanned the C/T boundary, is lacking in these sections. The correlative interval is identified, however, from a positive 2‰ carbon isotope excursion (CIE) and from clustered highest occurrences of Cenomanian-restricted dinoflagellate taxa together with the lowest occurrence of Turonian Heterosphaeridium difficile. A zone lacking benthic macrofossils encompasses the CIE. In some sections, this interval is also characterized by distinctive red mudstone beds; the thickest such red bed (6–18 m thick) may overlap or just overlie the main part of the CIE interval. Shelly macrobenthos, notably inoceramid bivalves, disappeared >500 kyr prior to the CIE. This suggests that environmental deterioration associated with OAE2 may have preceded the inferred volcanic trigger that has been identified from other regions. Strong intermediate water depth oxia during OAE2, which contrasts with oceanic anoxic conditions that occurred elsewhere on the globe, apparently prevailed during the later phase of OAE2 in the southernmost Pacific. New data from New Zealand indicate that causal mechanism(s) of OAE2 may be complex.     

Foraminifers and radiolarians across the Albian-Cenomanian and Cenomanian-Turonian Boundaries (Northern Peri-Tethys)

Changes in morphological diversity and taxonomic composition of late Albian-early Turonian foraminiferal and radiolarian assemblages from the northern Peri-Tethys are considered. Several stages are defined in evolution of planktonic foraminifers: polytaxic (Albian-Cenomanian), oligotaxic (Cenomanian-Turonian boundary period), and polytaxic (Turonian). The Albian-Cenomanian stage was characterized by intense development of rotaliporids representing an intricate group of planktonic foraminifers, which became extinct in the terminal Cenomanian. An intense speciation of the radiolarian genus Crolanium and last occurrences of its most species, the index species C. cuneatum included, was characteristic of the terminal Albian. Spheroid and discoid radiolarians were dominant in the Cenomanian, while the Turonian was marked by intense development of all the radiolarian morphotypes.     

Turonian-Santonian echinoids from Wadi Qena,Eastern Desert,Egypt; a new arrangement of apical disc plating in spatangoids

Eighteen echinoid species (seven regular and eleven irregular) belonging to twelve genera have been described from the Turonian-Santonian succession of two sections located in the northern part of Wadi Qena, Eastern Desert. The diversity of the recorded species is low in the Turonian (six species), but comparatively high in the Coniacian-Santonian (twelve species). Of the recorded species, Most of these species (72%) are recorded for the first time from Wadi Qena area, one left in open nomenclature, Mecaster sp., represents a new species, and two, Phymosoma microtuberculatum and Thylechinus (T.) said, represent new records for Egypt. The taxonomic rank of Parapygus sudrensis has been changed. Phymosoma microtuberculatum which is known from the ‘Senonian’ of southwest Europe is recorded herein in the lower Turonian. Two echinoid assemblage zones are recognizable in each of the studied two sections. They are correlated with other fossil assemblage zones in Egypt. Faunal affinity and paleobiogeography of the species are discussed. A new arrangement of apical disc plating in spatangoids is described and discussed.     

Turonian cephalopods (ammonoids and a nautiloid) from the Wadi Daya Formation of the Talerzha Basin (South Riffian Ridges Domain,northern Morocco)

The Wadi Daya Formation, or the Calcaires crayeux of the older literature, attains a thickness of 10–40 m in the Talerhza Basin of the South Riffian Ridges. Previously, this unit was first dated as “Vraconian” (i.e., late upper Albian), but then reinterpreted as Cenomanian-Turonian and Cenomanian-Coniacian on the basis of foraminiferal and ostracod assemblages, respectively. Here, we record for the first time in the South Riffian Ridges, some typically Turonian ammonoids and a nautiloid species, namely Romaniceras (Yubariceras) cf. ornatissimum (Stoliczka), Spathites (Jeanrogericeras) cf. reveliereanus (Courtiller), Neoptychites cephalotus (Courtiller), Pachydesmoceras linderi (de Grossouvre), Lewesiceras peramplum (Mantell) and Angulithes galea (Fritsch, in Fritsch & Schlönbach). These species are herein described and illustrated. In view of these data, the underlying Marnes et marno-calcaires jaunes Formation, formerly dated as “Vraconian”, could in fact be of a middle to late Cenomanian date, in accordance with the age assignment based on planktonic foraminifera. Deposition of the overlying Marnes jaunes Formation, previously dated as Cenomanian-“Senonian”, probably started during the latest Turonian or earliest Coniacian.     

Biostratigraphic and isotopic record of the Cenomanian–Turonian deposits in the Ohaba-Ponor section (SW Haţeg, Romania)

The middle Cenomanian–lower Turonian deposits of Ohaba-Ponor section (Southern Carpathians) were studied from biostratigraphic and isotopic points of view. Both the qualitative and semiquantitative nannofloral analyses, as well as the stable isotope (δ¹³C and δ¹⁸O) data support significant palaeoenvironmental changes in the investigated interval. Two δ¹³C positive excursions were recognized: (1) an excursion up to 1.8‰ (PDB) within the middle/late Cenomanian boundary; (2) an excursion up to 2.2‰ (PDB) in the Cenomanian/Turonian boundary interval. The oldest δ¹³C positive excursion recorded (placed within the Acanthoceras jukes-brownei/Eucalycoceras pentagonum Ammonite Zone boundary interval, and in the NC11 Calcareous Nannofossil Zone respectively) could be assigned to the middle Cenomanian Event II (MCEII). During the above-mentioned event, significant increase in abundance of Watznaueria barnesae, followed by successive blooms of Biscutum constans and Eprolithus floralis, were observed. The youngest δ¹³C positive excursion was identified in the Cenomanian/Turonian boundary interval (in the NC12 and lower part of the NC13 Calcareous Nannofossil Zones). Even the amplitude of this δ¹³C positive excursion is lower in the Ohaba-Ponor section, as generally reported, this may represent the regional record of the OAE2. The successive peaks of the nannofossils Biscutum constans, Zeugrhabdotus erectus and Eprolithus floralis indicate episodes of cooler surface water and high fertility, which preceded and lasted the Cenomanian/Turonian boundary event. Additionally, fluctuations of δ¹⁸O values between −2 and −6‰ suggest also cooler conditions within the Cenomanian/Turonian boundary interval.     

A new fossil species of snakeflies (Raphidioptera: Mesoraphidiidae) from the Late Cretaceous of Kazakhstan,with notes on Turonian Neuropterida

Alloraphidia kyzylzharica sp. nov. is described from the Late Cretaceous (early Turonian) locality at Kyzylzhar, southern Kazakhstan. It is very similar to A. dorfi, but easily distinguished from it by wing shape and venation. We restrict the genus Alloraphidia to these two species. Ascalapharia raphidiformis is considered a member of Baissopteridae, sit. nov. Turonian Neuropterida are mainly characterized by a mixture of specialized genera of extinct families, and genera (sometimes modern) of highly advanced taxa, reflecting a sequence of global mid-Cretaceous crisis of non-marine biocoenoses.     

The Albian to Turonian carbon isotope record from the Shilaif Basin (United Arab Emirates) and its regional and intercontinental correlation

The sedimentary record of the Arabian Shelf offers a unique opportunity to study the Cretaceous (Albian–Turonian) greenhouse climate from a palaeoequatorial perspective. In particular, hemipelagic to pelagic carbonate successions from the extensive Shilaif intra‐shelf basin have the potential to produce an excellent record of carbon cycle perturbations during this interval. This study presents a 269 m thick chemostratigraphic (carbonate δ¹³C and δ¹⁸O) record from the Middle Albian to Early Turonian of central Abu Dhabi (United Arab Emirates), representing over 14 Myr of uninterrupted carbonate sedimentation. The Mauddud to Shilaif formations represent outer ramp to basinal intra‐shelf carbonates with variations from laminated organic‐rich to clean bioturbated intervals. Isotopic evidence of the latest Albian Anoxic Event (Oceanic Anoxic Event 1d), Middle Cenomanian Event I and the Cenomanian–Turonian Anoxic Event (Oceanic Anoxic Event 2) are confirmed and biostratigraphically calibrated by means of calcareous nannofossils. The carbon isotope record allows correlation with other regional records and well‐calibrated records across the Tethyan Ocean and represents a significant improvement of the chronostratigraphic framework of the United Arab Emirates (Shilaif) and Oman (Natih) intra‐shelf basins. The study further confirms that low carbon isotope values corresponding to the two source rock intervals in the Shilaif Formation clearly precede the isotopic expressions of Oceanic Anoxic Event 1d and Oceanic Anoxic Event 2.     

Caprinula and Sauvagesia rudist faunas (Bivalvia) from the Cenomanian of NW Jordan. Stratigraphy and taxonomy

Three species of a canaliculated rudist Caprinula d'Orbigny, 1847, C. sharpei (Choffat, 1885), C. cedrorum (Blanckenhorn, 1890) and C. cf. boissyi d'Orbigny, 1840 and a radiolitid Sauvagesia sharpei (Bayle, 1857) are described from the Hummar Formation (upper Cenomanian) in NW Jordan, in the vicinity of Ajlun. Caprinula sharpei, C. cedrorum and S. sharpei are described for the first time from Jordan. Many specimens of S. sharpei are characterized by the presence of cavities flanking the lamellar myophores in the left valve and the apparence of the dorsal cavity and teeth/socket system moulds in the inner part of the outer shell layer of the right valve. A hiatus (or erosional unconformity) between Hummar Formation and upper Turonian Wadi As Sir Limestone Formation is suggested by the presence of karstic structures, reworked limestone clasts, and rudist fragments and a sharp boundary. Early diagenetic processes such as dissolution and silicification present in the loose rudist material is described.     

Late Cretaceous planktonic foraminifera from Kerguelen Plateau (ODP Leg 183): new data to improve the Southern Ocean biozonation

An almost complete Upper Cretaceous sedimentary sequence recently recovered on the Kerguelen Plateau (southern Indian Ocean) during ODP Leg 183 was analysed for planktonic foraminifera in order to refine and integrate the zonal schemes previously proposed for the Southern Ocean area. Detailed biostratigraphic analysis carried out on holes 1135A, 1136A and 1138A (poleward of 50°S palaeolatitude during Late Cretaceous time) has allowed recognition of low and mid–high latitude bioevents, useful for correlation across latitudes, in addition to known Austral bioevents. The low latitude biozonation can be applied to Turonian sediments, because of the occurrence of Helvetoglobotruncana helvetica, which marks the boundary between Whiteinella archaeocretacea and Helvetoglobotruncana helvetica zones. The base of the Whiteinella archeocretacea Zone falls within the uppermost Cenomanian–Turonian black shale level in Hole 1138A. The stratigraphic interval from upper Turonian to uppermost Santonian can be resolved using bioevents recognized in the mid–high latitude sections. They are, in stratigraphic order: the last occurrence of Falsotruncana maslakovae in the Coniacian, the first occurrence of Heterohelix papula at the Coniacian/Santonian boundary, the extinction of the marginotruncanids in the late Santonian, and the first occurrence of Globigerinelloides impensus in the latest (?) Santonian. The remainder of the Late Cretaceous fits rather well in the Austral zonal scheme, except that Globigerinelloides impensus exhibits a stratigraphic range in agreement with its record at the mid–high latitude sections and extends further downwards than previously recorded at southern sites. Therefore, despite the poor recovery in certain intervals and the presence of several hiatuses of local and regional importance as revealed by correlation among holes, a more detailed zonal scheme has been obtained (mainly for the less resolved Turonian–Santonian interval). Remarks on some species often overlooked in literature are also provided.     

Calcareous nannofossil biostratigraphy and paleoecology of the Cenomanian – Turonian transition in the Tarfaya Basin, southern Morocco

An abundant and diverse nannoflora occurs across the Cenomanian/Turonian (C/T) boundary at Tazra in the Tarfaya Basin of southern Morocco. The nannoflora of this sequence permits recognition of three biozones (CC10-CC12), three subzones (CC10a, CC10b and CC10c), and thirteen important nannolith bioevents previously reported from this interval elsewhere. The floral record shows erratic species abundance fluctuations that clearly vary with lithology and reflect at least in part preservational bias and diagenetic processes. In general, four dissolution resistant taxa are dominant: Watznaueria barnesae, Eiffellithus turriseiffelii, Eprolithus floralis, and Zeugrhabdotus spp. The late Cenomanian Zone CC10 marks a rapid excursion in ∂¹³C and is characterized by the successive extinction of four taxa, which are widely recognized as reliable biomarkers: Corollithion kennedyi, Axopodorhabdus albianus, Lithraphidites acutus, and Helenea chiastia. This interval is also marked by high species richness and high abundance of the tropical species Watznaueria barnesae, suggesting warm tropical waters. The subsequent ∂¹³C plateau and organic carbon-rich black shale deposition of the oceanic anoxic event (OAE2) is characterized by low species richness, but high nannofossil abundance, and peak abundance of the cool water and high productivity indicator Zeugrhabdotus spp., followed by the first peak abundance of cool water Eprolithus floralis. This interval correlates with the planktic foraminiferal diversity minimum and the Heterohelix shift, which marks the expansion of the oxygen minimum zone (OMZ). The C/T boundary is identified based on the FO of Quadrum gartneri, which is <1 m below the FO of the planktic foraminifer C/T marker Helvetoglobotruncana helvetica. In the early and middle Turonian, the two dominant species, tropical W. barnesae and cool water E. floralis, alternate in abundance and suggest fluctuating climatic conditions.     

Turonian ammonites from northwestern Aquitaine,France

The position of the Cenomanian-Turonian boundary is established for the first time in Charente-Maritime, northwestern Aquitaine (France), on the basis of ammonite occurrences and the δ¹³C isotope curve, corresponding to Oceanic Anoxic Event 2, that straddles the boundary. The earliest Turonian ammonites recognised are a monospecific occurrence of the early early Turonian pseudotissotiine Bageites bakui Zaborski, 1998, previously known only from northern Nigeria. Newly collected material and well-preserved specimens from existing collections supplement previous records, and include species of Placenticeras, Morrowites, Kamerunoceras, Romaniceras (Romaniceras), Spathites (Jeanrogericeras), Mammites, Fagesia, Neoptychites, Choffaticeras (Leoniceras), Collignoniceras and Lecointriceras. These confirm the presence of the upper lower Turonian nodosoides Zone and the lower middle Turonian turoniense and kallesi zones/subzones of authors.     

Chuaria circularis from the early Mesoproterozoic Suket Shale, Vindhyan Supergroup, India: Insights from light and electron microscopy and pyrolysis-gas chromatography

Chuaria circularis (Walcott 1899) from the Suket Shale of the Vindhyan Supergroup (central India) has been reinvestigated for its morphology and chemical composition using biostatistics, electron microscopy and pyrolysis-gas chromatography. Morphology and microscopic investigations provide little clues on the specific biological affinity ofChuaria as numerous preservational artifacts seem to be incorporated. On the contrary, the predominance of η aliphatic pyrolysates of presently studiedChuaria from India rather supports an algal affinity. Moreover, the reflectance ofC circularis can be used to obtain a comparative maturity parameter of the Precambrian sediments. The review of the age and geographical distribution ofC circularis constrains that this species cannot be considered as an index fossil for the Proterozoic time.     

Epibionts, their hard-rock substrates, and phosphogenesis during the Cenomanian–Turonian boundary interval (Bohemian Cretaceous Basin, Czech Republic)

Hard inorganic substrates (rock clasts and rocky bottom) belonging to the Ka k Member of the Korycany Formation (upper Cenomanian–?lower Turonian) and to the Bílá Hora Formation (lower Turonian) have offered a good opportunity for the study of encrusting faunas of the Cenomanian–Turonian boundary interval. Distributional features of cemented epibionts and the recorded period of phosphogenesis enabled the differentiation of two-phases in the Ka k Member conglomerate formation. During the first phase, the rock substrates were occupied by a so-called A-association of encrusters (29 species, with dominance of oysters and bryozoans). This fauna partly changed during the subsequent phosphogenic period and not only survived the following period of reworking and the second phase of conglomerate formation, but also persisted until the onset of calmer sedimentation in the early Turonian. This changed community is named theAtreta-Bdelloidinacommunity (23 species). The opportunistic agglutinated foraminifersBdelloidina cribrosaand/orAcruliammina longalocally dominated the respective communities during several physico-chemically stressed episodes. On sloping substrates, the bivalvesAtretaandSpondylusattached themselves in a preferred orientation (so-called slope orientation). This feature indicates the original position in which some mobile substrates were colonized. Other questions, such as the taphonomy of encrusters and the character of their substrates are also briefly discussed.