Neocardioceras Research Articles

Biotic response to the latest Cenomanian drowning and OAE2: A case study from the Eastern Desert of Egypt

The changes in macrofauna and microfauna, before, during and after the latest Cenomanian global Oceanic Anoxic Event (OAE2), from the Eastern Desert of Egypt are documented, along with an inferred paleoenvironment. The age of the studied OAE2 interval is constrained by the last occurrence of the marker calcareous nannofossils species Axopodorhabdus albianus along with the previously identified positive δ13C excursion from the coeval ammonite Vascoceras cauvini Zone (= Neocardioceras juddii Zone), enabling correlation with the peak ‘b’ of the OAE2. Based on the studied microfaunal assemblages, a warm shallow restricted lagoonal environment with mesotrophic conditions and strong seasonality is inferred. The presence of a rare ammonite (and ostracods) attest to the intermittent introduction of marine waters within this inner ramp setting. In terms of sequence stratigraphy, two 3rd order depositional sequences are recorded. The top surface of the first depositional sequence, at the sequence boundary, SB Ce 5 (the start of the OAE2), is marked by an abrupt faunal change with reduced abundances of the macrofaunal elements. This is in tune with other Egyptian records of relatively smaller loss (10 %) at the Cenomanian-Turonian boundary, as compared to much higher numbers (53–79% of species), globally. This faunal (biotic bottleneck) and lithological change (from siliciclastic-dominated deposits to a largely carbonate-dominated one) at the SB Ce 5 is attributed as a response to the latest Cenomanian drowning (the highest sea-level during the Phanerozoic), that also resulted in the formation of carbonate platform.

On the co-occurrence of Rubroceras and Vascoceras (Ammonoidea, Vascoceratidae) in the upper Cenomanian of the West Portuguese Carbonate Platform

The upper Cenomanian and basal Turonian ammonite assemblages of the West Portuguese Carbonate Platform (WPCP) are characterised by the occurrence of many Tethyan species, with emphasis on Vascoceratidae. They include Vascoceras gamai, type-species of the genus, and several other taxa created in 1898, by Choffat, based on abundant materials collected from exposures of the Baixo Mondego region (West Central Portugal), in the northern range of the carbonate platform. As noted by Berthou et al., in 1975 and subsequent works, many of these Vascoceras are upper Cenomanian and form two distinct assemblages, respectively with Euomphaloceras septemseriatum and Pseudaspidoceras pseudonodosoides. The occurrence of this latter species can be correlated with the uppermost Cenomanian Neocardioceras juddii standard zone, since both species co-occur in assemblages with vascoceratid ammonites described by Cobban et al. (1989) in New Mexico (United States). It is precisely from the same assemblages that the genus Rubroceras was originally described, as an interesting example of the late Cenomanian evolutionary diversification of the Vascoceratidae, when highly ornamented forms with transverse ribs persisting in the body chamber appeared in Tethyan assemblages with Vascoceras, characterised by much more smooth morphologies.As in New Mexico, the occurrence of Rubroceras in the WPCP is restricted to a stratigraphic unit with Pseudaspidoceras pseudonodosoides, Vascoceras gamai, V. barcoicense and V. silvanense. Besides Rubroceras alatum and R. burroense, other additional taxa are Spathites (Jeanrogericeras) subconciliatus, Vascoceras adonense, Vascoceras sp. A and Parapuzosia (Austiniceras) sp. This assemblage mostly occurs in the outcrops of Nossa Senhora dos Olivais, near Tentúgal, in the northern range of the carbonate platform. It is found above beds with Euomphaloceras septemseriatum and Vascoceras gamai, and below the highest upper Cenomanian unit of the area, with P. pseudonodosoides, Spathites (Jeanrogericeras) subconciliatus, Fagesia catinus, and depressed Vascoceras, such as V. durandi, V. douvillei and V. kossmati.In addition to New Mexico and West Portugal, representatives of Rubroceras are presently known from other carbonate platforms of North Africa, Arabian Peninsula and Nigeria, where they have been found in ammonite assemblages correlative to the Neocardioceras juddii standard zone. They are apparently absent from the remaining basins of the Iberian microplate with abundance of Vascoceratidae representatives, namely the Iberian Through (Spain), whose late Cenomanian oceanic communication was more processed from the North. Further studies will provide a better understanding of this important biotic dispersal event across the Tethyan Realm, as an additional marker of uppermost Cenomanian ammonite assemblages.

The Cenomanian–Turonian boundary in Jordan: Ammonite biostratigraphy and faunal turnover

Well-exposed fossiliferous Upper Cenomanian–Lower Turonian marine sedimentary rocks are present in west-central Jordan. Ammonites serve as an important faunal marker for this interval and can be used to subdivide the Cenomanian–Turonian transition into two upper Cenomanian biozones (Neolobites vibrayeanus and Vascoceras cauvini) and two lower Turonian biozones (Vascoceras proprium and Choffaticeras segne). A revised stratigraphic range of the Vascoceras cauvini Zone in the study area is proposed, consisting of the Metoicoceras geslinianum and Neocardioceras juddii zones of the standard zonation. Based on intercontinental biostratigraphic correlation, a minor unconformity appears to be present around the Cenomanian–Turonian boundary, and a part of the lower Turonian is probably missing. In addition, a faunal turnover is recorded in the uppermost Cenomanian, marked by the disappearance of most of the Cenomanian taxa, including Costagyra olisiponensis (Sharpe), Ceratostreon flabellatum (Goldfuss), Ilymatogyra africana (Lamarck), Rhynchostreon suborbiculatum (Lamarck), Harpagodes nodosus (Sowerby), and Heterodiadema libycum (Desor). This bioevent is thought to be an effect of the Oceanic Anoxic Event OAE 2; the dramatic shifts in species richness and diversity spanning the Cenomanian–Turonian boundary in the study area occurred in response to the major paleoclimatic and paleoenvironmental perturbations prevailing at that time. The stratigraphic and paleontological patterns studied in Jordan are very similar to those recorded in Egypt in terms of litho- and biostratigraphy, event stratigraphy, and macroinvertebrate content, suggesting the presence of uniform triggering mechanisms and bio-sedimentary responses in the Upper Cretaceous basins of the Middle East and providing clues for a high-resolution correlation between the two areas.

Cenomanian–Turonian carbon isotope stratigraphy of the Western Canadian Sedimentary Basin

The Cenomanian–Turonian boundary was characterized by distinctive positive carbon isotope excursions that were related to the formation of widespread oceanic anoxia. High-resolution geochemical proxies (TOC, CaCO3, δ13Corg, and δ13Ccarb) obtained from bulk rock, planktic foraminifers, and inoceramids from four marine marlstone-dominated stratigraphic sections in the Western Canada Sedimentary Basin (WCSB) were used to establish a regional carbon isotope stratigraphic framework and to investigate paleoenvironmental variability in four different depositional settings. Compared to background δ13Corg, (<−27‰) and δ13Ccarb (<2‰) values which were correlative to stable isotope excursions during Oceanic Anoxic Event (OAE) II worldwide, the δ13Corg (>24‰), and δ13Ccarb (>4‰) derived from inoceramid prisms in the studied sections within WCSB, were elevated during the Late Cenomanian–Early Turonian. During this interval, TOC and CaCO3 values which increased sporadically to >40% and 7%, respectively, were not consistent enough to be used for stratigraphic correlations. Based on the δ13Corg excursions, two bentonite beds were regionally correlated across this portion of the Western Interior Seaway (WIS). The eruption associated with the “Red” bentonite occurred approximately coeval with the maximum δ13Corg-excursion during OAE II in the Neocardioceras juddii Zone, whereas the “Blue” bentonite coincides with the termination of OAE II in the latest Watinoceras devonense zone. During the Late Cenomanian–Early Turonian in the WCSB, benthic foraminifers were sparse or totally absent, indicating the existence of fully anoxic bottom-water conditions. Planktic foraminifera were common in the well-oxygenated surface waters. A benthic oxic zone characterized by several agglutinated species occurs in the eastern part of the WSCB at the beginning of OAE II in the Sciponoceras gracile zone. The termination of the OAE II in the WCSB coincides with the first occurrence of small ammonites (Subprionocyclus sp.) in the western part of the basin.

High-resolution stratigraphy of the Cenomanian–Turonian boundary interval at Pueblo (USA) and wadi Bahloul (Tunisia): stable isotope and bio-events correlation

A high-resolution stratigraphy has been developed for the interval encompassing the Cenomanian–Turonian boundary (CTBI), by means of several lithological, biological and geochemical events. This work entails the study of two sections selected on the base of the completeness of their sedimentary record and their contrasting paleogeographical setting: (1) The Rock Canyon Anticline section west of Pueblo, Colorado, (US Western Interior Basin), which is the Global Boundary Stratotype Section and Point (GSSP) candidate for the base of the Turonian stage, as well as the reference section for the ammonite biostratigraphy of the CTBI; and (2) The wadi Bahloul section in Central Tunisia which is the best and complete section spanning this time interval in the southern Tethyan Margin. These sections record similar biogeochemical events that can be correlated over a great distance. Several important biological and geochemical events determined in these sections relative to the ammonite zonation of the CTBI are listed below in chronological order from old to young: 1. FO (first occurrence) of Sciponoceras gracile- Metoicoceras geslinianum ammonite Assemblage-Zone, 2. δ 13C peak I, 3. LO (last occurrence) of Rotalipora cushmani, 4. “ Heterohelix shift”, 5. FO of the ammonites Pseudaspidoceras pseudonodosoides and Neocardioceras juddii, 6. δ 13C peak II, 7. δ 13C peak III, 8. LO of Cenomanian ammonites ( Ps. pseudonodosoides and N. juddii), 9. LO of Anaticinella, 10. FO of Turonian ammonites ( Watinoceras devonense, base of the Turonian stage), 11. “filament event”, 12. FO of Pseudaspidoceras flexuosum, 13. FO of the Tethyan Helvetoglobotruncana helvetica, 14. FO of Mammites nodosoides, 15. FO of the Western Interior H. helvetica. In the two sections, the Cenomanian–Turonian (C/T) boundary, as defined by the ammonite biostratigraphy, is placed within an interval about 50 cm thick. This interval is termed here as the C/T boundary “precision interval”. The δ 13C peak III slightly precedes the precision interval. The genus Anaticinella planktic foraminifer disappears in the middle part of this interval. The “filament event” occurs just above it and is coeval with the first occurrence of Turonian ammonites. These events are useful for placing the C/T boundary precision interval in absence of ammonite markers. Comparing ammonite and planktic foraminiferal biostratigraphy we have dated and correlated changes occurring in planktic foraminiferal assemblages. On this base, as an important result, we have demonstrated the diachroneity of the FO of Helvetoglobotruncana helvetica and the variable duration of the Whiteinella archaeocretacea PRZ.

Ammonites at the Cenomanian–Turonian boundary in the Sergipe Basin, Brazil

Two distinctive ammonite faunas are described from the Cenomanian–Turonian boundary interval in the Sergipe Basin, Brazil. The Jardim 1 section assemblage comprises Euomphaloceras costatum Cobban, Hook &amp; Kennedy, 1989, Burroceras transitorium Cobban, Hook &amp; Kennedy, 1989, Pseudaspidoceras pseudonodosoides Choffat, 1898, and Vascoceras cf. gamai Choffat, 1898. This same association is found in New Mexico, where it occurs with the upper Cenomanian index fossil Neocardioceras juddii (Barrois &amp; Guerne, 1898). On this basis the Sergipe assemblage is referred to the N. juddii Zone, and correlated with beds 79–84 of the Pueblo, Colorado section. These lie 1.14–0.63 m below the Global boundary Stratotype Section and Point (GSSP) for the base of the Turonian Stage, the base of bed 86, which corresponds to the first occurrence of the ammonite Watinoceras devonense Wright &amp; Kennedy, 1981. The Japaratuba 16 locality in Sergipe yielded an assemblage of Pachydesmoceras kossmati Matsumoto, 1987, Watinoceras coloradoense (Henderson, 1908), Pseudaspidoceras flexuosum Powell, 1963, Pseudovascoceras nigeriense (Woods, 1911), Vascoceras globosum globosum (Reyment, 1954), V. simplex (Barber, 1957), and Pseudotissotia nigeriensis (Woods, 1911). The co-occurrence of W. coloradoense and P. flexuosum is also found in the Pueblo section, in bed 97, 1.65 m above the base of the Turonian. These ammonite records thus allow the placement of the Cenomanian–Turonian boundary in the Sergipe-Alagoas Basin, and correlation with the Global Boundary Stratotype Section and Point at Pueblo.

Stratigraphy, microfossils and depositional environments of the lowermost part of the Welton Chalk Formation (late Cenomanian to early Turonian, Cretaceous) in eastern England

SUMMARY The lowermost part of the Welton Chalk Formation in eastern England conforms to a succession of eight beds, lettered here A to H in ascending order. Beds A and B are equated with the Plenus Marls ( Metoicoceras geslinianum Zone) of southern England. The Black Band (beds C to E) has yielded palynological assemblages containing the dinoflagellate cysts Adnatosphaeridium tutulosum and Carpodinium obliquicostatum. Their presence, along with the absence of Litosphaeridium siphonophorum, indicates a late Cenomanian age ( Neocardioceras juddii Zone) for the Black Band. Bed H contains the planktonic foraminiferan Praeglobotruncana praehelvetica, an early morphotype of a Turonian marker fossil. The dark, organic-rich marls of beds C to G are probably contiguous with those of the lowermost part of the Herring Formation in the North Sea Basin and together comprise the regional sedimentary record of a much more widespread ‘black shale’ depositional episode. Alternative hypotheses concerning the origin and timing of this episode are reviewed with reference to new microfossil evidence from eastern England. The late Cenomanian to early Turonian dinoflagellate cyst stratigraphy discussed here appears to be compatible with stratigraphies based on planktonic foraminifera, ammonites and geochemistry (δ 13 C) in north-west Europe and the western interior of the USA, possibly indicating connected basin water masses over much of the area during the Cenomanian–Turonian transition.

Age of the Cenomanian-Turonian boundary in the Western Interior of the United States

High precision 40Ar/ 39Ar laser-microprobe ages of individual sanidines, 40Ar/ 39Ar plateau age spectra on bulk sanidine concentrates, U-Pb zircon ages, and zircon and apatite fission-track ages from three bentonites bracketing the Cenomanian-Turonian boundary in the Western Interior of the United States suggest an age for the boundary of 93.1 ± 0.3 (2σ. The lowermost bentonite comes from the Upper Cenomanian Sciponoceras gracile biozone, and gives a weighted mean laser-fusion single-crystal 40Ar/ 39Ar age of 93.50 ± 0.52 Ma (2σ, standard error of the mean, n = 14) for sanidine. The middle bentonite comes from the Upper Cenomanian Neocardioceras juddii biozone, accepted in both North America and Europe as the uppermost Cenomanian ammonite zone; it gives an average single-crystal 40 / 39Ar age of 93.33 ± 0.50 Ma ( n = 29), a bulk-sample 40Ar/ 39Ar plateau age of 93.09 ± 0.34 Ma (2σ) for sanidine, and concordant 206Pb/ 238U and 207 Pb/ 235U ages of 93.48 ± 0.32 Ma on zircon. The upper bentonite comes from near the base of the Turonian, immediately above the first occurrence of the basal Turonian bivalve Mytiloides and sanidines from it give an average single-crystal 40Ar/ 39Ar age of 93.46 ± 0.60 Ma ( n = 12) and a bulk-sample 40 Ar/ 39Ar plateau age of 92.87 ± 0.34 Ma. The composition of these Cenomanian-Turonian bentonites from Colorado and Utah, the types of phenocrysts present, and the morphology of included zircons all indicate that the pre-alteration ash was rhyolitic and probably generated in a subduction setting involving a significant crustal component.

Elemental abundance anomalies in the late Cenomanian extinction interval: a search for the source(s)

Elemental abundances have been measured by neutron activation methods across the Cenomanian-Turonian (late Cretaceous) extinction interval in samples collected from sixteen sites in the Western Interior Basin of North America and from twelve widely separated locations around the globe, including six ODP/DSDP sites. In most Western Interior Basin sites, in Colombia, and in western Europe (weaker), two closely spaced elemental abundance peaks occur in the upper Cenomanian (∼ 92 m.y.), spanning the ammonite zones of Sciponoceras gracile through Neocardioceras juddii. Elements with anomalously high concentrations include Sc, Ti, V, Cr, Mn, Co, Ni, Ir, Pt and Au. The lower peak coincides with the disappearance (extinction) of the foraminifer Rotalipora cushmani. In North American sections R. greenhornensis also disappears at or just below this horizon, but in Europe it disappears considerably earlier than R. cushmani. A series of molluscan extinction and speciation or migration events also begins near the stratigraphic level of the lower elemental abundance peak. The well-documented positive δ 13C excursion begins just before the extinctions and the elemental anomalies, and continues into the lower Turonian, well above the upper anomaly. This carbon isotope excursion has been observed in East European sections where we find little or no evidence of the elemental anomalies, suggesting that the two phenomena may not be tightly coupled. Elemental abundance ratios in the anomalies closely resemble those of Mid-Atlantic Ridge basalt or Hawaiian lava (tholeiitic), but not those of C1 chondrite, black shale, average crustal rocks, or lamproite and kimberlite of roughly similar age in southeastern Kansas. The excess Ir and other siderophiles hint at possible large-body impact(s) for the source. However, we have not located microspherules (other than biogenic calcispheres) or shocked mineral grains in any of our samples. Furthermore, Sc, Ti, V and Mn are not enriched in differentiated Solar-System bodies. Although the weak geochemical signal from comet impact(s) could be masked by the strong terrestrial-like overprint, these anomalies more likely resulted either from intense seafloor spreading activity or merely from increased circulation of deep, metal-rich water associated with the large late Cenomanian through early Turonian eustatic rise and deep-water opening of the South Atlantic. The flooding of continental seaways and margins also could have contributed to the anomalies by preventing much continental detritus from diluting the normal background marine geochemical component.

Record of sea-level changes, oxygen depletion and the δ 13C anomaly across the Cenomanian-Turonian boundary, Bohemian Cretaceous Basin

The sedimentary record across the Cenomanian-Turonian boundary in Bohemia confirms the crucial role of eustasy as the driving force of the Cenomanian-Turonian anoxic event. The late Cenomanian siltstone facies of the Peruc-Korycany Formation was deposited after major sea-level rise at the beginning of the Metoicoceras geslinianum Zone (above the UZA 2.4/2.5 3rd-order sequence boundary of Haq et al., 1988). Increasing depletion in oxygen during the late Cenomanian is reflected in dark, pyrite-rich siltstones characterized by low C/S ratios and progressive deterioration of benthic foraminiferal assemblages. Small-scale steps in sea-level rise followed by oxygen depletion during the M. geslinianum Zone can be correlated between the Bohemian Cretaceous and the Plenus Marls of SE England. This indicates that the impingement of oxygen-poor waters on the European shelf, which reached inland as far as the Bohemian Massif, was driven by eustasy even at the level of 4th-order cyclicity. The late Cenomanian part of the global δ 13C anomaly is in part overprinted by diagenesis, and in part falls within a stratigraphic hiatus between the upper M. geslinianum and the Neocardioceras juddii Zones. A record of a waning δ 13C anomaly helped to assign the basal Bı́lá Hora Formation to the early Turonian W. coloradoense Zone. The basal Bı́lá Hora carbonates reflect a major early Turonian sea level rise and waning of dysaerobic conditions.

The Cenomanian-Turonian boundary problem in NW-Germany with comments on the north-south correlation to the Regensburg Area

The lithostratigraphical successions across the Cenomanian-Turonian boundary are described. Two dif­ferent facies can be distinguished: A shallow water red marly limestone facies ('Rotpliiner') characterised by evidence of condensation and stratigraphical hiati; and a more complete deeper water facies with alternating marly limestones and black shales ('Black Shales' or 'SchwarzweiBe Wechselfolge'). A se­quence of litho- and ecoevents permits subdivision and correlation of the two facies. The base of both facies is apparently isochronous and rests on white coccolith limestones, the so-called 'Arme rhotoma­gense Schichten' of the Upper Cenomanian Calycoceras naviculare Zone. The stage boundary was traditionally drawn at the facies change, but biostratigraphical evidence places the boundary within the Rotpliiner/Black Shale formations. In Lower Saxony the extinction datum of Rotalipora cushmani agrees with records from other areas, i.e. within the Upper Cenomanian Metoicoceras ges/inianum Zone below the entry of Actinocamax plenus. From the Teutoburger Wald (Miinsterland) and Regensburg area (Bavaria) an apparent di­achroneity of this datum is indicated. The uppermost Cenomanian Neocardioceras juddii Zone of the international scheme has been identified only in the Black Shale facies. The diagnostic ammonites and inocaramid (Mytiloides aff. duplicostatus) of the basal Turonian Pseudaspidoceras f/exuosum Zone have not been recorded in either facies. For practical purposes the base of the Turonian is taken at the entry of Myti/oides, as is usual in Central Erope. Below this level there is a 'zone of uncertainty' with poorly preserved inoceramids of questionable generic identity. Above the entry of recognizable Mytiloides, an interregional fades-independent Myti/oides mytiloides ecoevent is traceable across W.-Germany to east­ern England. Critical species concepts within Mytiloides are reviewed in the context of possible facies dependence. Of importance for the North-South correlation is the recognition of Mytiloides sp. at the base of the Praeglobotruncana helvetica Zone in the Regensburg area.

Albian-Turonian stage boundaries and subdivisions in the western Portuguese Basin, with special emphasis on the Cenomanian-Turonian boundary in the ammonite facies and rudist facies

The precise chronostratigraphy from the Aptian-Albian boundary to the upper Cenomanian has been established mainly on the distribution of large benthic Foraminifera and dinocysts. Ammonites are rare, and nannofossils and planktonic Foraminifera are absent. In this study species with well-known stratigrap- hic ranges were used and, where possible, reference is made to sequences dated with ammonites. The upper Cenomanian, the Cenomanian-Turonian boundary and the lower Turonian were studied first in the ammonite facies, where Choffat at the turn of the century described different species of Vascoceras. The type sections contain Cenomanian ammonites (Euomphaloceras, Calycoceras and Pseudocalycoceras. Vascoceras ex gr. gamai appears in the Cenomanian Metoicoceras geslinianum Zone. Above this zone, Spathites (Jeanrogericeras) subconciliatus marks the Neocardioceras juddii Zone, here placed in the uppermost Cenomanian. Thus, the lower Turonian is marked by the appearance of Fagesia superstes and F. thevestensis. The different sections in the rudist facies and ammonite facies are correlated. Only Radiolites peroni seems to appear in the lower Turonian. The presence of Durania arnaudi in the Turonian depends on the assignment of the Neocardioceras juddii Zone to the uppermost Cenomanian. Only the lower part of the Turonian has been identified in Portugal. The stratigraphy of the coarse sandstones which separate the lower Turonian from the Coniacian horizon with Hemitissotia ceadourensis, is poorly known.

The Ammonoidea of the Plenus Marls and the Middle Chalk

he ammonite fauna of the Plenus Marls and Middle Chalk (Upper Cenomanian and Turonian) is described; it comprises 49 species and subspecies (8 new), referred to 27 genera. These provide a basis for revision of the ammonite zonation of the Upper Cenomanian and Turonian of Great Britain and correlation with the sequences in the Paris Basin and the stratotype areas in Sarthe and Touraine. It is demonstrated that the Cenomanian—Turonian boundary is best taken between the Neocardioceras juddii Zone below and the Watinoccras coloradoense Zone above.