Paleoenvironmental changes across the Cenomanian/Turonian Boundary Event (Oceanic Anoxic Event 2) as indicated by benthic foraminifera from the Demerara Rise (ODP Leg 207)

This study is based on Cenomanian to lower Turonian sediments of Ocean Drilling Program (ODP) Sites 1258, 1259, 1260, and 1261 from the Demerara Rise (Leg 207, western tropical Atlantic, off Suriname) that are oriented along a paleodepth transect. Studied sediments include the Cenomanian/Turonian Boundary Event (CTBE) or Oceanic Anoxic Event 2 (OAE 2) and consist of laminated black shales with TOC values between 5% and 10% below and above OAE 2 and up to 29% within the OAE 2 interval. Benthic foraminiferal assemblages in this eutrophic environment are generally characterized by low diversities and strong fluctuations of abundances, indicating oxygen depletion and high organic matter fluxes. Dominant taxa at all sites are Bolivina anambra, Gavelinella dakotensis, Tappanina sp., Praebulimina prolixa, and Neobulimina albertensis. Based on the positive stable carbon isotope excursion characteristics of OAE 2 we subdivided the studied successions into three intervals: (1) the interval below OAE 2; (2) the carbon isotope excursion reflecting OAE 2; and (3) the interval above OAE 2. In the bathymetrically shallower Sites 1260 and 1261 benthic foraminiferal assemblages indicate anoxic to sometimes slightly dysoxic bottom-water conditions below the OAE 2 interval. The bathymetrically deepest Site 1258, in contrast, reflects more oxygenated bottom waters with an almost continuous occurrence of benthic foraminifera. It is therefore suggested that the shallower sites were located within the oxygen minimum zone (OMZ), whereas Site 1258 was below the OMZ. During OAE 2 anoxic conditions prevailed at the shallower sites. At Site 1258 benthic foraminifera indicate severe dysoxic but not anoxic conditions. This pattern is proposed to reflect a strengthening of the OMZ possibly related to increased primary production during OAE 2. A short-term repopulation event of benthic foraminifera in the lower third of the OAE 2 interval was observed at all sites, reflecting a brief bottom-water oxygenation event. This short-lived event parallels a surface-water cooling and is probably equivalent to the “Plenus Cool Event” in Europe and the “benthonic zone” in the U.S. Western Interior. The benthic foraminifera of a ~0.5 Ma interval following OAE 2 still indicate oxygen depletion of bottom waters. Subsequently, however, a strong increase in benthic foraminiferal abundance and diversity reflects better oxygenation of the bottom-water masses, probably related to a weakening of the OMZ due to decreasing organic matter flux.     

Calcareous nannofossil biostratigraphy of the Cenomanian/Turonian boundary interval of ODP Leg 207 at the Demerara Rise

During Ocean Drilling Program Leg 207 at Demerara Rise (western tropical Atlantic) expanded sections of organic-rich laminated shales of late Cretaceous age, including the Cenomanian/Turonian boundary interval (CTBI) were recovered. These sediments yield rich assemblages of calcareous nannofossils, offering a unique possibility to calibrate the stable carbon isotope curve (δ¹³C_org). The calcareous nannofossils of Sites 1258, 1259, 1260 and 1261 have been investigated in order to gain a detailed biostratigraphic framework for the CTBI in the tropical latitudes. The bioevents observed have been correlated with the characteristic δ¹³C_org excursion of the CTBI. The events occurring during the excursion, and slightly below and above it, include the first occurrences of the calcareous nannofossil species Cylindralithus biarcus, Quadrum gartneri, Quadrum intermedium, Eprolithus octopetalus, Eprolithus eptapetalus, Eiffellithus eximius and the last occurrences of Corollithion kennedyi and Axopodorhabdus albianus. These bioevents have been correlated with those of other biostratigraphically and chemostratigraphically studied CTBI sections.     

Albian calcareous nannofossils from ODP Site 1258, Demerara Rise

Site 1258, drilled during Ocean Drilling Program (ODP) Leg 207 on Demerara Rise off the northern coast of South America, recovered organic-rich Albian sediments that yield abundant, moderately to well preserved calcareous nannofossils. Biostratigraphic analysis shows the section primarily spans Roth’s (Initial Reports DSDP 44. US Government Printing Office, Washington (1978) 731) middle to late Albian Zone NC9. A disconformity separates these sediments from overlying uppermost Albian laminated shales from Zone NC10. The presence of Seribiscutum primitivum within the Albian section represents the first known occurrences of this species at such low latitudes, as Demerara Rise was located within 15° of the equator during the mid-Cretaceous. This species exhibits a bipolar distribution and is considered a cool-water, high-latitude species. Its presence on Demerara Rise indicates cooler water incursions either through changes in surface circulation or upwelling conditions during the opening of the Equatorial Atlantic.     

Surface-water chemistry and fertility variations in the tropical Atlantic across the Paleocene/Eocene Thermal Maximum as evidenced by calcareous nannoplankton from ODP Leg 207, Hole 1259B

Calcareous nannoplankton assemblages at Ocean Drilling Program (ODP) Site 1259 on Demerara Rise (western equatorial Atlantic) underwent an abrupt and fundamental turnover across the Paleocene/Eocene Thermal Maximum (PETM) ~55.5 m.y. ago. The PETM is marked by a dissolution interval barren or nearly-barren of nannofossils due to the rapid acidification of the world oceans. Toweius, Fasciculithus, and Chiasmolithus sharply decrease at the onset, whereas Chiasmolithus, Markalius cf. M. apertus, and Neochiasmolithus thrive immediately after the event, which also signals the successive first appearances of Discoaster araneus, Rhomboaster, and Tribrachiatus. The environmental indications of these changes were further investigated by correspondence analysis on quantitative nannofossil counts. The PETM event has been attributed to CO₂-forced greenhouse effects. At Site 1259, the elevated pCO₂ and subsequent lowered surface-water pH values at the onset of the PETM caused intensive carbonate dissolution, producing the nannofossil-barren interval. The chemically stressed habitats may well have also induced the evolution of ephemeral nannofossil “excursion taxa”, such as Rhomboaster and malformed discoasters (D. araneus and Discoaster anartios). Based on its sudden increase, Markalius cf. M. apertus is considered to have been a local opportunistic species that took advantage of the surface-water changes. At the same time, a presumably higher runoff from continental areas fertilized the western equatorial Atlantic as indicated by an increase in the abundance of r-mode specialists preferring high-nutrient conditions, such as Chiasmolithus, Coccolithus pelagicus, and Hornibrookina arca. Contrasts between the results of this study and previous work at ODP Site 690 in the Southern Ocean, the New Jersey continental margin, and the central paleoequatorial Pacific further demonstrate that the response to the PETM can be influenced by local differences in geologic setting and oceanographic conditions.     

Phaeodarian Radiolaria from the Upper Cretaceous beds of central Japan

Upper Cretaceous Phaeodarea (Radiolaria) were recovered from the Shoya Formation, which crops out 100 km northwest of Tokyo, central Japan. The Shoya Formation consists of about 600 m-thick marine sedimentary rocks, represented by alternating beds of sandstone and mudstone, which are overlain by about 10 m of Phaeodarian-bearing siliceous mudstone. The latter is assigned to the Upper Cretaceous (late Campanian to early Maastrichtian) based on the associated Polycystine Radiolarian fossils. In spite of the poor general preservation of nearly all Phaeodarian specimens as recrystallized quartz infillings, three new Phaeodarian species, Challengeranium cretaceum, Challengeron paleotriangulum, and Medusetta fossilis, were identified on the basis of their shape and ornamentation. Our finding, together with two other very recent reports of fossil Phaeodarians clearly document that the origin of Phaeodarian Radiolarians can be extended back to at least the Upper Cretaceous.     

Maastrichtian Challengeriidae (phaeodarian radiolaria) from deep sea sediments of SW Pacific

The paper reports three species of fossil phaeodarian Radiolaria of the family Challengeriidae, of which two (Protocystis pacifica and Challengeron takahashii) are new and one is determined at generic level. They have been found in a Maastrichtian sample from Site 275 of the Deep Sea Drilling Project located on Campbell Plateau, near New Zealand. Together with the two species of the same family recently described by Bragina [Paleontol. J. 37 (2003) 8] from the upper Cenomanian of Sakhalin Island, and three other species found by Takahashi [Tenth Meeting of the International Association of Radiolarian Palaeontologists, Abstracts and Programme, Lausanne (2003) 107] from the upper Campanian to lower Maastrichtian of central Japan, they represent the only Cretaceous phaeodarian species so far known. The family Challengeriidae, to which most of these species belong, seems to contain the most resistant phaeodarians to fossilization. These species prove that the skeleton structure of Cretaceous Challengeriidae is similar to Recent ones and that the difference between them is only at species level.     

Albian Palynostratigraphy of ODP Leg 207 (Holes 1257A, 1258C and 1260B), Demerara Rise,Equatorial Atlantic

Palynological analyses were carried out in 96 core samples with the objective of determining the relative age of calcareous clays, in holes 1257A, 1258C and 1260B of ODP Leg 207, drilled on the Demerara Rise, northern coast of Suriname, Equatorial Atlantic. The palynological assemblages recovered consisted of spores, pollen grains, dinoflagellate cysts, palynoforaminifers and prasinophytes and appeared reasonably well preserved. The miospores showed little diversification, where the most significant genera were Crybelosporites and Elaterosporites. The dinocysts showed greater diversity and abundance, predominating over the miospores in the three holes. In the three holes analyzed, eight genera and three species of spores, eight genera and eleven species of pollen grains, and 24 genera and 44 species of dinoflagellates were identified. The middle to late Albian age was determined on the basis of bioevents of recognized species with chronostratigraphic value. The species diagnosed mostly included the miospores Elaterosporites protensus, Elaterosporites verrucatus, Inaperturopollenites simplex and the dinocysts Cribroperidinium muderongense, Dinopterygium cladoides, Litosphaeridium arundum, Litosphaeridium conispinum, Oligosphaeridium complex and Stiphrosphaeridium anthophorum.     

Tocopherols and associated derivatives track the phytoplanktonic response to evolving pelagic redox conditions spanning Oceanic Anoxic Event 2

Tocopherols serve a critical role as antioxidants inhibiting lipid peroxidation in photosynthetic organisms, yet are seldom used in geobiological investigations. The ubiquity of tocopherols in all photosynthetic lifeforms is often cited as an impediment to any diagnostic paleoenvironmental potential, while the inability to readily analyze these compounds via conventional methods, such as gas chromatography–mass spectrometry, further diminishes the capacity to serve as useful ‘biomarkers’. Here, we analyzed an exceptionally preserved black shale sequence from the Demerara Rise that spans Oceanic Anoxic Event 2 (OAE-2) to reexamine the significance of tocopherols and associated derivatives (i.e. tocol derivatives) in ancient sediments. Tocol derivatives were analyzed via liquid chromatography–quadrupole time-of-flight–mass spectrometry and included tocopherols, a methyltrimethyltridecylchroman, and the first reported detection of tocopherol quinones and methylphytylbenzoquinones in the geologic record. Strong correlations between tocol derivatives were observed over the studied interval. Tocol derivative concentrations and ratios, which normalized tocopherols to potential derivatives, revealed absolute and relative increases in tocopherols as exclusive features of OAE-2 that can be explained by two possible mechanisms related to tocopherol production and preservation. The development of photic zone euxinia during OAE-2 likely forced an upward migration of oxygenic photoautotrophs, increasing oxidative stress that elicited heightened tocopherol biosynthesis. However, shoaling euxinic conditions may have simultaneously acted to enhance tocopherol preservation given the relatively high lability of tocopherols in the water column. Both scenarios could produce the observed stratigraphic distribution of tocol derivatives in this study, although the elevated tocopherol concentrations that define OAE-2 at the Demerara Rise are primarily attributed to enhanced tocopherol production by shoaling phytoplanktonic communities. Thus, the occurrence of tocopherols and associated derivatives in sediments and rocks of marine origin is likely indicative of shallow-water anoxia, tracking the phytoplanktonic response to the abiotic stresses associated with vertical fluctuations in pelagic redox.     

Calcareous nannofossil biostratigraphic framework for middle Eocene sediments from ODP Hole 1260A, Demerara Rise

Ocean Drilling Program (ODP) Site 1260 recovered a near-continuous and expanded (187-m thick) middle Eocene carbonate sequence at mid-bathyal depths on Demerara Rise off Suriname, South America. A calcareous nannofossil biostratigraphic framework has been established for the sequence to aid multi-proxy cyclostratigraphic analyses. The diversity of calcareous nannofossils is reasonably high and preservation moderate throughout most of the section, and the proximity to the continent is indicated by the occurrence of braarudosphaerids in the lower three quarters of the section. The species richness of sphenoliths is particularly high, and our data confirm the occurrence of new sphenoliths during the middle Eocene as shown recently by Bown and Dunkley Jones (2006). In particular we corroborate the occurrences of Sphenolithus strigosus and S. runus that these authors found in their Zone NP16 Tanzania sediments, however we extend the ranges of these taxa down into Zone NP15 (CP13). Moreover we document the occurrence of Bramletteius serraculoides in Zone NP15 (CP13b) and the occurrence of Sphenolithus predistentus in NP16 (CP14a), extending their known ranges down column.     

Ostracodes bathyaux du Crétacé terminal - Éocène moyen en Atlantique tropical (Plateau de Demerara, Leg 207)

Ostracode faunal assemblages which lived in bathyal environments are analysed from uppermost Maastrichtian - middle Eocene sediments of sites 1260 and 1261, drilled on the distal margin of Demerara, off Surinam (Leg 207, western tropical Atlantic). As for numerous other groups, the Cretaceous/Tertiary mass extinction event led to the disappearance of numerous bathyal ostracode species and it was followed by a very slow recovery during the Palaeocene. It appears that this extinction event was more devastating for detritus-feeder ostracode species than for filter or silt-eater groups, which crossed the K/T boundary without any or little morphological change. This extinction selectivity may be explained by the drop in productivity of surface waters which took place at the K/T boundary. Finally, psychrospheric ostracode species were encountered in Middle Eocene sediments, confirming thus the general cooling of deep oceanic realm recognised in general for this time interval.     

On the status of the Permian radiolarian genus Multisphaera Nazarov and Afanasieva, 2000

Based on the detailed morphological study of the type species of the genus Multisphaera Nazarov and Afanasieva, the author emends the status and diagnosis of this genus and of the subfamily Multisphaerinae Nazarov and Afanasieva. He found that the initial spicule of the type species is not multi-rayed, as initially thought, but a tetrahedral spicule. Accordingly, the genus is assigned to the former tribe Tetrentactiniini Kozur and Mostler that is herein raised to the family rank and comprises all Upper Devonian to lower Permian genera with a tetrahedral initial spicule. Consequently, the subfamily Multisphaerinae is considered a junior synonym of the family Tetrentactiniidae. To better solve the taxonomic problems of this family the author compares the morphological diversity of its members with the morphological diversity of the lower Tithonian (uppermost Jurassic) tetrahedral spicule-bearing entactinarian Radiolaria occurring in the Solnhofen area, southern Germany. Although these genera have the same type of spicule as the Paleozoic ones, they seem to belong to a new family because between the lower Tithonian and the lower Permian genera there is a long time interval of about 120 Ma in which no radiolarians with a tetrahedral initial spicule have been recorded so far. This comparison shows once more the conservative character of the initial spicule and the wide morphological diversity of the extraspicular shell.     

Oceanic Anoxic Event at the Cenomanian–Turonian boundary interval (OAE-2): ichnological approach from the Betic Cordillera, southern Spain

Ichnological analysis of dark sediments of the Oceanic Anoxic Event at the Cenomanian–Turonian boundary interval (OAE-2) from the Betic Cordillera, southern Spain, reveals the presence of ichnofabrics containing trace fossils Chondrites isp., Palaeophycus heberti , Planolites isp., Thalassinoides isp., Trichichnus linearis , Zoophycos isp., and other bioturbational structures. Analysis of the ichnofabrics and trace fossil diversity allowed the reconstruction of relative oxygenation. Before the OAE-2, oxygenation of sediments was generally good, but it was punctuated by short anoxic events. During the OAE-2i, several longer anoxic intervals were interrupted by shorter dysaerobic and oxic periods. After the OAE-2, oxygenation improved and almost all trace fossils known before OAE-2 reappeared, although oxygenation dropped a few times to anoxia. Generally, the short oxygenation changes reveal a periodicity, which may suggest a Milankovitch control.     

Tithonian-Berriasian foraminiferal faunas from the Torinosu-type calcareous blocks of the southern Kanto Mountains, Japan: their implications for post-accretionary tectonics of Jurassic to Cretaceous terranes

The Torinosu-type limestones, having many lithologic characters showing their original deposition on shallow shelves, are widely distributed in the Jurassic to Cretaceous terranes of Japan. The foraminiferal faunas from the Jurassic to the lowermost Cretaceous of Japan were first revealed in the calcareous blocks of the southern Kanto Mountains. Distinguished microfaunas consist of 39 species including many marker species of the Upper Jurassic to Lower Cretaceous in Europe, West Asia, and North Africa such as Melathrokerion spirialis, Charentia evoluta, Freixialina planispiralis, Nautiloculina oolithica, Everticyclammina cf. virguliana, Haplophragmium lutzei and Pseudocyclammina lituus. These faunas suggest a Tithonian to Berriasian age of Torinosu-type limestones. They are contained in four tectonostratigraphic units (Kamiyozawa, Hikawa and Gozenyama Formations; Ogouchi Group) continuously accreted from Middle Jurassic to Late Cretaceous. The younger deposition age of Torinosu-type limestones than the accretion age (Bajocian to Bathonian) in the Kamiyozawa Formation and their older age than the accretion age of the Ogouchi Group (late Albian to middle Maastrichtian) are important to date the post-accretionary tectonics of Jurassic to Cretaceous terranes of Japan and to explain the emplacement process of Torinosu-type limestones.     

Discovery of Middle Jurassic (Bajocian) Radiolaria from the sedimentary cover of the Vedi ophiolite (Lesser Caucasus,Armenia)

The Vedi ophiolite, situated southeast of Yerevan (Armenia), represents part of the Neotethyan oceanic lithosphere preserved in the Lesser Caucasus. This ophiolite unit constitutes a large tectonic klippe, a result of obduction during the Upper Cretaceous (Coniacian–Santonian). Relatively well-preserved Radiolaria extracted from radiolarites overlying ophiolitic lavas along the Vedi River consist of Middle Jurassic (Bajocian, U.A.Z. 3–4) species, typical of the Tethyan tropical bioprovince. Assemblages are dominated by Nassellaria and characterised by the presence of species Cyrtocapsa mastoidea, Hexasaturnalis hexagonus, Laxtorum (?) hichioense, Stichocapsa japonica and Striatojaponocapsa plicarum s.l. This microfauna provides evidence for the oldest age available so far for the sedimentary cover of the Vedi ophiolite.     

Upper Moscovian-middle Kasimovian conodonts (Pennsylvanian, Carboniferous) from the Las LLacerias Section (Cantabrian Zone, north Spain)

Las LLacerias Section in the western part of the Picos de Europa Unit (Cantabrian Zone) in northern Spain offers the best (essentially continuous) Upper Moscovian-Kasimovian succession in the Pennsylvanian of the Cantabrian Zone. The section consists almost entirely of limestones, and conodonts are scarce in general, but some Myachkovian levels are significantly more productive. Most specimens recovered are Pa pectiniform elements, and are generally well preserved. Idiognathodus, Streptognathodus, Gondolella, and Neognathodus are the most significant genera and Ubinates and Hindeodus are present. Idiognathodus is the dominant genus. Most of the idiognathodids differ morphologically from those elsewhere, and one, Idiognathodus covadongae, is formally recognized a new species. The presence of Idiognathodus eccentricus in the upper part of the Kreviakinian levels suggests a correlation with the lower Missourian of the United States. Neognathodus disappears in the upper part of the Myachkovian beds. Gondolella pohli was recovered from a short interval in the upper portion of the Myachkovian beds. Paleoecological conditions representing shallow, open, normal marine offshore deposits of the Idiognathodus-biofacies are interpreted for the lower portion of the Myachkovian interval.     

<Emphasis Type="Italic">Scalaspira</Emphasis> (Gastropoda) from the Paleogene of the Transcaspian Region

The composition and distribution of the species of the genus Scalaspira Conrad, 1862 in the Eocene-Oligocene of western Kazakhstan are revised. Following Tembrock we assign this genus to Buccinidae and synonymize Aquilofusus Kautsky, 1925 with it. The stratigraphic interval studied contains at least eight species. Three species are new: S. alexeevi (Middle? and Upper Eocene, Chegan Formation), S. korobkovi, and S. kumsuatensis (Upper Oligocene, Karatomak Beds).     

Radiolarian evidence of late cenozoic oceanic paleotemperatures,Ross sea,Antarctica

Radiolarian and paleomagnetic studies of 59 Antarctic piston cores reveal that since the middle Gauss ($\text{t ? 3}\text{m.y.}$) radiolarian faunas from the southern Ross Sea consistently have lacked certain species commonly found just to the north in the Southern Ocean. Common Antarctic species generally absent from southern Ross Sea sediments include: Spongopyle osculosus, Cenosphaera nagatai, Chromyechinus antarctica, Stylatractus neptumus, Diploplegma banzare, Prunopyle titan, and Desmospyris spongiosa. These species appear to have consistently preferred water slightly warmer than that of the southern Ross Sea. Their occurrence at intervals in cores from the northern Ross Sea and from north of the Ross Sea has been used as a quantitative paleoclimatic indicator. The resulting paleoclimatic curves reveal that the early Gauss was warmer than the late Gauss, the Matuyama and the Brunhes. Warm and cold periods during the Matuyama and the Brunhes appear to be of equal amplitude. Temperatures in the region since the early Gauss were never warmer by more than about 3°C than they are today. Radiolarian abundance and diversity appear to have been controlled primarily by changes in factors affecting their production.     

Ostracodes et stratigraphie du néogène et du quaternaire méditerranéens

A stratigraphical chart of marine ostracoda from Lower Miocene to Recent is established. Selected species (approximatively 220) are those morphologicaly well characterized and known from different parts of the Mediterranean area. It appears that: • lower Miocene ostracodes are still poorly known; • specific diversity is high during the Tortonian and the Lower Messinian before the complete disappearance of marine Mediterranean species during the Upper Messinian évaporitic episodes; • during the early Pliocene, about half of the Upper Miocene marine species are reintroduced with the Atlantic waters; other species migrate for the first time in the Mediterranean Sea by the same way; • at the end of the Pliocene or at the beginning of the Pleistocene several species known in Mediterranean since the Middle Miocene or before, such as Cytherella sp. gr. transversa and Ruggieria tetraptera, as well some “nordic guests” such as Hemicythere villosa and Cythere lutea, appear. This work is an opportunity to confirme a Late Miocene age for the Neogene of Skyros (Aegean Sea), to assign the “Upper Pliocene” of Terquem to the Lower Pleistocene and to refute the existence of a pliocene psychrosphere.     

Cyclic changes in Turonian to Coniacian planktic foraminiferal assemblages from the tropical Atlantic Ocean

Abundance patterns of planktic and benthic foraminifera from a tropical Atlantic drill site (Ocean Drilling Program Site 1259, Demerara Rise, Suriname margin) display a pronounced 400 kyr cyclicity, uninterrupted throughout our  87.8–92 Ma record, between two clearly distinguishable assemblages: (1) a pelagic foraminifer fauna, which represents a deep oxygen minimum zone, and (2) another assemblage representing a shallow oxygen minimum zone where the foraminifer fauna is dominated by a higher diversity population of mostly small clavate and biserial species common in epicontinental seas. The cyclic changes in the long eccentricity band (400 kyr) between these two assemblages are proposed to reflect changes in the mean latitudinal position of the Intertropical Convergence Zone (ITCZ). Associated fluctuations in precipitation and trade wind strength may have influenced the upwelling regime at Demerara Rise leading to the observed cyclicity of planktic foraminiferal assemblages. The severe Turonian to Coniacian paleoclimatic and paleoceanographic changes in the Atlantic Ocean (e.g., gateway opening, cooling, and glaciation), however, seem to have no influence on the composition of tropical planktic foraminiferal faunas. There is no apparent relationship between foraminifer abundances and a major deflection in the stable isotope record interpreted elsewhere as a sign of the growth and decay of a large polar ice sheet.