Search

The massive concentration of black, laminated, organic carbon-rich shales at certain time periods during the Cretaceous period (∼140–65 Ma) led to the concept of Oceanic Anoxic Events (OAEs). These events are characterized by unusually enhanced preservation of organic matteracross environments ranging from the deep oceans to shelf seas. Enhanced productivity of siliceous and organic-walled primary producers and/or strongly dysaerobic or anoxic conditions in all major oceans were both suggested as likely causes (Meyer and Kump, 2008). Fundamental chemical and biological changes in the world ocean must have been associated with these events.

The global carbon cycle during the mid‐Cretaceous (∼125–88 million years ago, Ma) experienced numerous major perturbations linked to increased organic carbon burial under widespread, possibly basin‐scale oxygen deficiency and episodes of euxinia (anoxic and H2S‐containing). The largest of these episodes, the Cenomanian‐Turonian boundary event (ca. 93.5 Ma), or oceanic anoxic event (OAE) 2, was marked by pervasive deposition of organic‐rich, laminated black shales in deep waters and in some cases across continental shelves. This deposition is recorded in a pronounced positive carbon isotope excursion seen ubiquitously in carbonates and organic matter. Enrichments of redox‐sensitive, often bioessential trace metals, including Fe and Mo, indicate major shifts in their biogeochemical cycles under reducing conditions that may be linked to changes in primary production. Iron enrichments and bulk Fe isotope compositions track the sources and sinks of Fe in the proto‐North Atlantic at seven localities marked by diverse depositional conditions. Included are an ancestral mid‐ocean ridge and euxinic, intermittently euxinic, and oxic settings across varying paleodepths throughout the basin. These data yield evidence for a reactive Fe shuttle that likely delivered Fe from the shallow shelf to the deep ocean basin, as well as (1) hydrothermal sources enhanced by accelerated seafloor spreading or emplacement of large igneous province(s) and (2) local‐scale Fe remobilization within the sediment column. This study, the first to explore Fe cycling and enrichment patterns on an ocean scale using iron isotope data, demonstrates the complex processes operating on this scale that can mask simple source‐sink relationships. The data imply that the proto‐North Atlantic received elevated Fe inputs from several sources (e.g., hydrothermal, shuttle and detrital inputs) and that the redox state of the basin was not exclusively euxinic, suggesting previously unknown heterogeneity in depositional conditions and biogeochemical cycling within those settings during OAE‐2.

High-resolution geochemical records from a depth transect through the Cenomanian/Turonian (C/T) Tarfaya Basin (northwest African Shelf) reveal high-amplitude fluctuations in accumulation rates of organic carbon (OC), redox-sensitive and sulphide-forming trace metals, and biomarkers indicative of photic zone euxinia. These fluctuations are in general coeval and thus imply a strong relationship of OC burial and water column redox conditions. The pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher-frequency forcing. Determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event (OAE2) and its duration. We propose that eccentricity is the main forcing factor at Tarfaya and controlled fluctuations in wind-driven upwelling of nutrient-rich, oxygen-depleted intermediate waters from the adjacent Atlantic and the periodic development of photic zone and bottom water euxinia on the mid- Cretaceous northwest African shelf. Accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six-fold increase in OC burial from ∼2 g/m² · yr prior to the OAE2 to ∼12 g/m² · yr during the OAE2. Photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing. Mass balance calculations imply that ∼2% of the overall global excess OC burial associated with the OAE2 was deposited in the Tarfaya Basin, an area that represented only ∼0.05% of the total global C/T ocean floor. In fact, the lateral extent of similar black shales along the African continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the OAE2.

We present a review of the current taxonomical status of the genus Paratrochamminoides Soliman, 1972. We recognise five main subgroups of this genus based upon the following modes of coiling: trochospiral, streptospiral, glomospiral, triloculine or milioline, and thalmannamminiform. Species that display streptospiral coiling and an interiomarginal aperture are placed in the genus Conglophragmium Bermúdez & Rivero, 1963, whereas the genus Paratrochamminoides is here understood to encompass all other coiling modes. The morphological characters of 23 named and unnamed species that we recognise as belonging to Paratrochamminoides and Conglophragmium are presented in tabular form. Of these, 22 are considered here to be valid species. Emended descriptions are provided for both genera, and diagnoses are given for each of the species.

Vor 94 Millionen Jahre glich die Erde einem Dampfbad. Grosse Teile der Meere verwandelten sich in stinkenden Kloaken, an deren Boden sich totes biomaterial anhäufte. Zu Schwarzschiefer geworden, enthüllt es, dass auch in dieser extremen Treibhauswelt Schwankungen der Erdbahn das Klima beeinflussten.

Berichte - Reports, Institut f��r Geowissenschaften

Cretaceous sediments from Ocean Drilling Program Leg 159 on the Côte d’Ivoire-Ghana Marginal Ridge (CIGMR), eastern equatorial Atlantic, are characterized by distinct stratigraphic changes in sedimentary facies associated with changes in the composition of the clayey and organic fractions, as well as of the calcareous nannofossil, radiolarian, foraminiferal, and palynomorph assemblages. In the absence of reliable magnetostratigraphic information, an integrated biostratigraphy provides the only means used to calibrate the geologic history of the Leg 159 area. The existence of marine depositional environments as early as the late Aptian to early Albian close to the Leg 159 drill sites puts constraints on the timing of the opening of the equatorial Atlantic gateway. Marine sedimentation on the ridge suggests that the West African and South American cratons were largely detached at this segment of the margin by the middle to late Albian. During the Cenomanian to Coniacian the ridge appears to have remained in an elevated position with concurrent low deposition or condensation (Site 959), high carbonate debris accumulation (Site 960), and even erosion (Site 962). Total organic Carbon measurements and microfaunal data lead us to suggest that, following the early opening of the seaway during the Albian, circulation remained restricted in the fragmented sub-basins of the CIGMR. It probably was not until the Santonian that a deep-water connection and circulation system became established between the Central and the South Atlantic. The sedimentary and faunal record at Site 959 show that a rapid subsidence occurred during the Santonian, with sub-calcite compensation depth conditions maintained until and beyond the Cretaceous/Tertiary boundary.

An analysis of 71 samples from the Zumaya Section of northern Spain ranging in age from Cenomanian to lower Eocene enabled us to calibrate the biostratigraphic ranges of Deep-Water Agglutinated Foraminifera (DWAF) to the standard planktonic foraminiferal zonal schemes. Comparison with the standard Geroch and Nowak zonation of DWAF provides further evidence for the supraregional validity of this zonation, as well as new information on the palaeobiogeography of many of the species first described from the Flysch Carpathians. The nominate taxa of six of the seven Turonian-Palaeocene DWAF zones defined by Geroch and Nowak (1984) were observed in their proper stratigraphic succession at Zumaya (the Ammobaculites problematicus, Uvigerinammina jankoi, Goesella rugosa, Hormosina ovulum gigantea, and Spiroplectammina spectabilis zones of Geroch & Nowak). Only the index taxon of the lower Paleocene Rzehakina fissistomata Zone was not observed, however this zone may be recognised based on alternate criteria (the last occurrence of Goesella rugosa). The benthic foraminiferal extinction at the Palaeocene/Eocene boundary is proposed as an alternate criterion to delimit the top of the Spiroplectammina spectabilis Zone / Analiza 71 próbek z profilu Zumaya w północnej Hiszpanii, obejmującego utwory od cenomanu do dolnego eocenu, pozwoliła na wyznaczenie zasięgów stratygraficznych głębokowodnych otwornic aglutynujących oraz na korelacje tych zasięgów ze standardową biozonacją opartą na otwornicach planktonicznych. Analizując zasięgi otwornic aglutynujących z tego profilu profilu potwierdzono uniwersalny charakter biozonacji zaproponowanej przez Gerocha i Nowaka (1984) oraz stwierdzono jej przydatność również dla obszarów pozakar-packich. Praca dostarcza także nowych danych z zakresu paleobiogeografii gatunków otwornic aglutynujących, opisanych z fliszu karpackiego. Badania potwierdziły następstwo stratygraficzne pięciu poziomów (Ammobaculites problematicus, Uvigerinammina jankoi, Goesella rugosa, Hormosina ovulum gigantea oraz Spiroplectammina spectabilis sensu Geroch & Nowak) opartych na gatunkach wyznaczonych jako przewodnie przez Gerocha i Nowaka (1984). Jedynie gatunek indeksowy dla dolnopaleoceńskiego poziomu Rzehakina fissistomata nie został znaleziony w badanym profilu. W pracy zaproponowano zastępcze kryterium do wyznaczenia poziomu Rzehakina fissistomata zanik gatunku Goesella rugosa. Zanik licznych gatunków otwornic bentonicznych na granicy paleocenu i eocenu może być dodatkowym kryterium do wyznaczenia górnej granicy poziomu Spiroplectammina spectabilis.

Berichte - Reports, Geologisch-Pal��ontologisches Institut und Museum, Christian-Albrechts-Universit��t, Kiel

Im Rahmen der vorliegenden Arbeit wurden quartäre Sedimente untersucht, die während der SONNE-147-Fahrt vor der Küste Perus beprobt wurden. Die Untersuchungen umfassten eine Bestimmung der TC-, TOC-, N-, Karbonat-, Opal- und Chlorin-Konzentrationen im Sediment sowie deren Korngrößenzusammensetzung. Über die Analyse von Oberflächenproben konnten typische Sedimentationsmuster für das peruanische Auftriebsgebiet definiert werden. Eine statistische Analyse der Messwerte brachte genauere Erkenntnisse zur Beziehung zwischen den einzelnen Proxy-Daten und deren Bedeutung für Paläo-Rekonstruktionen. Die Rekonstruktion der Auftriebsproduktivität basiert auf drei Sedimentkernen, in denen unterschiedliche Zeitabschnitte überliefert sind: 20,8 bis 17,2 kyr BP (SO147-41SL); 16,2 bis 1,5 kyr BP (SO147-106KL) und 10,4 bis 0,8 kyr BP (SO147-4SL). Die zeitlichen Variationen in den gemessenen Proxy-Daten geben Auskunft über Veränderungen der Auftriebsintensität seit dem Letzten Glazialen Maximum. Über Spektralanalysen konnten zyklische Variationen in den Produktivitätswerten sichtbar gemacht werden. Markante Perioden liegen bei 1500, 1000, 590, 570, 380, 333, 314, 280, 242, 218, 157, 32, 23, 20, 17 und 11 Jahren. Diese sind nachweißlich an solar gesteuerte Klimaschwankungen gekoppelt. Kleinerskalige Zyklen zwischen 7 und 14 Jahren markieren in den Auftriebssedimenten die Überlieferung von El Niño.