Pelagic Sections Research Articles

Hypothesis testing on the planktic foraminiferal survival model after the KPB mass extinction: evidence from Tunisia and Algeria

A historical review of the extinction, survival, and evolutionary models of planktic foraminifera proposed for the Cretaceous/Paleogene boundary (KPB) mass extinction event sometimes leaves the impression that there is still no conclusive evidence to support any single one of them. Two main models have been put forward: i) catastrophic mass extinction, almost total for some authors, compatible with the geologically instantaneous paleoenvironmental effects of a large meteorite impact (Chicxulub impact, Mexico); and ii) gradual mass extinction, compatible with the paleoenvironmental effects of massive, long-lasting volcanism (Deccan Traps, India). Over the years, a lot of evidence has been proposed supporting one hypothesis or the other, highlighting isotopic (δ18O, δ13C, 87Sr/86Sr) as well as taphonomic, biostratigraphic, quantitative (relative and/or absolute abundance), phylogenetic, and even teratological. We review previous planktic foraminiferal and stable isotope studies, and provide new quantitative and statistical tests from two pelagic sections: the El Kef section (Tunisia), recognized as the most continuous and expanded lowermost Danian section worldwide, and the Sidi Ziane section (Algeria), affected by relevant hiatus in the lower Danian. The results indicate that all the latest Maastrichtian planktic foraminiferal species except those of Guembelitria went extinct exactly at the KPB, supporting the hypothesis of an almost total extinction. In the light of this new evidence, we maintain that the Maastrichtian planktic foraminiferal specimens found worldwide in lower Danian samples could be the result of similar reworking and vertical mixing processes to those at El Kef and Sidi Ziane.

Sedimentology and sediment geochemistry of the pelagic Paryab section (Zagros Mountains, Iran): implications for sea level fluctuations and paleoenvironments in the late Paleocene to middle Eocene

Sedimentological and geochemical records are presented for an upper Paleocene to middle Eocene deep-water pelagic succession of the Pabdeh Formation in the Paryab section, Zagros Mountains, NW, Iran. In this study, grain-size statistical parameters, cumulative curves, and bivariate analysis on twenty-five sediment samples were used to decipher depositional processes and paleoenvironments. XRD analysis of the fine-grained silt to clay sediments indicates that quartz, calcite, ankerite/dolomite, and clay minerals such as illite, chlorite, and kaolinite constitute the main minerals within these sediments. Elemental and isotopic chemostratigraphies are used to infer depositional conditions and sea level trends through time. TOC-CaCO3 trends of the samples are used to interpret the type of deposition and sediment accumulation rates, rhythmic bedding, and identification of regressional and transgressional phases. In the studied section, the manganese contents exhibit a declining trend along the lowstand systems tract that terminates in a sea level lowstand and the subsequent start of a transgressive trend. Some geochemical parameters such as Mn values and δ13C contents of sediments along a sequence can be used as potential sea level proxies that are tested in this study. The Paleocene-Eocene Thermal Maximum (PETM) interval of the Pabdeh Formation coincides with increasing Mn contents and Mn/Al ratios. Ti/Al and Si/Al ratios show contrasting trends to Mn values and Mn/Al ratios. Generally, elemental and isotopic results of the Pabdeh Formation confirm the presence of a long-term three-stage sea level cycle in the studied interval that is related to the PETM event. Based on elemental analyses such as Co, Mo, Ni, V, and Cr contents, the Pabdeh Formation sediments were deposited in suboxic to slightly anoxic conditions.

The Devonian–Carboniferous boundary in Belgium and surrounding areas

The Devonian–Carboniferous boundary is associated with a major extinction event of the Phanerozoic. It was also a time marked by a rapid but short-lasting change in deposition called Hangenberg Event. In the Namur–Dinant Basin the uppermost Devonian (‘Strunian’) deposits recorded a third-order transgression that produced a progressive switch from coastal siliciclastic to proximal mixed deposits with an increase of the carbonate production on the ramp. Hence, the Comblain-au-Pont and lower Hastiere formations are considered as the transgressive system tract, whereas the middle member of the Hastiere Formation is interpreted as the highstand system tract, capped by an erosion surface corresponding to the third-order sequence boundary. Superimposed on these third-order sequences are well-marked orbitally forced precession cycles (wet–dry climate alternations) of c. 18.6 ka, appearing as irregular c. 30–80-cm-thick couplets of limestone and calcareous shale beds. The Hangenberg Black Shale Event is locally present as dark shales that likely spread over the shelf, marking the maximum flooding surface of the sequence. Before and after this event, carbonate facies rich in benthic macrofauna and microfauna continued to develop. The Hangenberg Sandstone Event, appearing as a sandstone bed in pelagic sections, is variously recorded at the base of the Hastiere Formation, either as a sandy siltstone bed in proximal sections or as a horizon with limestone clasts and reworked fossils in more distal settings. The Hangenberg Sandstone Event beds occur sharply in the stratigraphic record and do not correspond to the long sea level fall of a third-order sequence boundary, but most probably to a short out-of-sequence event. The revision of the stratigraphic distribution of major fossil groups pleads for a continuous biostratigraphic succession with no obvious hiatus. The variable development of some micropalaeontological zones at the end of the Devonian is the result of complex eco-biostratigraphic interactions with the environment rather than the reflection of true hiatuses. It is marked by extinctions of Devonian taxa, concomitantly with the end of the reworking produced by the Hangenberg Sandstone Event, most probably immediately below the entry of the conodont Protognathodus kockeli. It is also coincident with the boundary between the foraminiferal zones DFZ7–MFZ1, rugose coral zones RC0–RC1 and between the palynozones LE–VI. After the short-lasting regressive phase of the Hangenberg Sandstone Event, normal depositional settings returned with the deposition of the Hastiere Formation. Hence, the end of the Hangenberg Sandstone Event is proposed as the most natural proxy to pinpoint the Devonian–Carboniferous boundary.

Late Valanginian extinction and turnover of Tethyan brachiopods: A signal of the Weissert Event (Bakony Mountains, Hungary)

Brachiopods, together with ammonoids, were collected bed-by-bed from several Lower Cretaceous pelagic sections and localities in the Bakony Mountains (Transdanubian Range, Hungary), dated by detailed ammonoid and nannofossil biostratigraphy. These yielded abundant and diverse brachiopod material (1015 specimens, 25 species), and a possibility to determine the stratigraphic ranges of the brachiopod species. Two sections, including the Berriasian to Hauterivian interval, were studied in detail. In the Hárskút HK-12 section the early late Valanginian Weissert Event was documented previously by stable isotope investigations and it was biostratigraphically correlated with the Édesvíz Key section. The Lower Cretaceous brachiopod record in the Bakony was separated into four assemblages. The abundant early Berriasian brachiopod Assemblage 1 diminished and with a stepwise extinction and partial turnover passed to an impoverished Assemblage 2 in the early Valanginian. These species ultimately disappeared at the early/late Valanginian boundary. This extinction is interpreted as the effect of the global Weissert Event. The extinction horizon is marked by an almost monospecific, dwarf brachiopod fauna (Assemblage 3). In the late Valanginian an abundant and diverse brachiopod fauna appeared, with a complete turnover of species (Assemblage 4). The development of this assemblage in the late Valanginian and Hauterivian was probably controlled by environmental changes, (1) by a switch in palaeoclimate, i.e. by the late Valanginian cooling episode and (2) by the change in the sedimentary environment.

Complex and protracted environmental and ecological perturbations during OAE 1a - Evidence from an expanded pelagic section from south Spain (Western Tethys)

Abstract The early Aptian Oceanic Anoxic Event (OAE) 1a represents a major perturbation in the global carbon cycle associated with significant environmental, biotic and sedimentary changes. The signature of this event is a global negative followed by a positive stable carbon isotope excursion (CIE), associated with the input of light-carbon into the climate system and subsequent widespread deposition of organic-rich sediments. This study uses biostratigraphy, C-isotope stratigraphy, biomarkers, and elemental geochemistry to stratigraphically and geochemically characterize OAE 1a at an expanded pelagic marine section from the western Tethys. The high-resolution δ13Corg analysis of the section highlights several successive negative CIEs during the onset of OAE 1a (isotope segment C3), pointing to rapid changes in global carbon cycling. The biomarker data indicate that the organic matter is thermally mature and is mainly of marine origin. The biomarker assemblage together with records of redox-sensitive trace elements suggest that sedimentation took place under generally well oxygenated waters punctuated by three short episodes of sea floor anoxia/dysoxia. The two first episodes of anoxia/dysoxia correlate with enhanced organic productivity during the main negative C-isotope excursion that represents the onset of the OAE 1a. They occurred at the final part of C-isotope negative excursions, likely as a response to C-release, increased temperatures and associated hydrological change and weathering, which resulted in increased fertilization-driven oxygen consumption. This was followed by the positive carbon isotope excursion, due to the burial of OM outpacing carbon input. The third episode of anoxia-dysoxia, which occurred later during the major positive C-isotope excursion, is not associated with fertilization, and perhaps instead reflects a general progressive depletion of oxygen during OAE 1a, linked to stagnation of marine waters. Interestingly, although the environmental parameters return to pre-OAE values at the end of the event, a biotic (especially microbial) perturbation persisted after OAE 1a. Our results suggest that instability in environmental conditions was the main feature during OAE 1a in the western Tethys with notable changes extending from the onset to the post-OAE 1a interval.

Calcareous nannofossils of the Barremian – Aptian interval from the southeastern Tethys (Zagros Basin, West Iran) and their paleoceanographic implications: A record of Oceanic Anoxic Event 1a

Abstract Calcareous nannofossils and stable isotope data (δ13Ccarb) from a pelagic section of the Zagros Basin (west Iran) were used for an integrated oceanographic analysis of the Barremian – Aptian interval. The study aims at analyzing various oceanographic shifts recorded from this period, including the Oceanic Anoxic Event 1a (OAE 1a), in an expanded carbonate rich mudstone sequence of the eastern Tethys. The extreme thickness (510 m) of the succession allows us to study the environmental changes known from the Barremian and Aptian interval in much more detail than previously done. By looking at closely spaced samples it is possible to better understand the onset, the course and the aftermath of the OAE 1a event. Calcareous nannofossils suggest an early Barremian (nannofossil zone CC5/NC5C) to late Aptian age (nannofossil zone CC7b/NC7B) for the studied sequence. The biostratigraphic zonation is based on the last occurrence of Calcicalathina oblongata, the first occurrences of Rucinolithus irregularis and Eprolithus floralis and the last occurrence of Micrantholithus hoschulzii. A total of 98 species has been encountered in the studied interval with good to moderate, in few cases poor preservation. Based on the calcareous nannofossil assemblages, signals for a warming event in the mid-Barremian are characterized by high relative abundances of warm water specie (e.g., Rhagodiscus asper) along with neritic taxa (Micrantholithus spp., Nannoconus spp.) The OAE 1a was identified via calcareous nannofossil biostratigraphy in combination with the δ13Ccarb record. For the OAE 1a (early Aptian), warm and eutroph conditions were likely, as suggested by high relative abundances of R. asper, Diazomatolithus lehmanii, small Zeugrhabdotus spp. and Lithraphidites carniolensis. The late Aptian is characterized by cool surface water conditions.

Cyclostratigraphic and δ13C record of the Lower Cretaceous Adriatic Platform, Croatia: Assessment of Milankovitch-forcing

The 700-m-thick Hauterivian to Albian section from the interior of the large, Adriatic Platform is exposed on Mljet and Korčula islands, Croatia. The cyclic platform consists of meter-scale parasequences, bundled into parasequence sets, superbundles and then into breccia-bounded depositional sequences. Spectral analysis of time series (cycle number vs. cycle thickness) shows peaks in the short-term eccentricity (95 to 130 kyr) bands and 160 to 200 kyr bands.Isotope samples from micrite matrix of mudstone and wackestone have δ13C values generally from −1.5 to +2‰ VPDB, and δ18O from −1 to −3.5‰ VPDB. Adriatic Platform δ13C values are shifted ~2‰ VPDB more negative than marine pelagic values. A δ13C and δ18O meteoric signal is limited to just beneath sequence boundaries, suggesting that the isotopic shift is due mainly to marine phreatic‐ and synorogenic burial diagenesis. Major excursions on the 5-point smoothed δ13C profile of the Adriatic Platform, tied biostratigraphically to δ13C curves from pelagic sections, include the oceanic anoxic events OAE1a, 1b, and 1c.Time series constructed from δ13C values (unsmoothed data) vs. stratigraphic position show peaks in the Milankovitch band, especially short-term eccentricity. Most positive peaks are near parasequence set boundaries (50 to 60%) and regressive parts of parasequences (20%). Although diagenetically shifted, the δ13C record retains a highly clipped memory of astronomically-driven global δ13C fluctuations albeit modified by platform water restriction during cyclic deposition.

Integrated stratigraphy of the Smirra Core (Umbria-Marche Basin, Apennines, Italy): A new early Paleogene reference section and implications for the geologic time scale

Pelagic sections of the Umbria-Marche Basin, in the Northern Apennines (Italy), have provided key geological archives for studying critical intervals of early Paleogene time. In addition to classical sections, the Smirra Coring project provides a new record of relatively undisturbed sediments (~120m from 4 overlapping holes) of the upper Scaglia Formation (Paleocene – middle Eocene). Here we present a new high-resolution integrated magneto-bio-stratigraphy of the ~93-m composite section drilled in Smirra Holes 1 and 2. The correlation of the magnetostratigraphy to published geomagnetic polarity timescales (GPTSs; CK95, GPTS2004, GPTS2012), as constrained by calcareous nannofossil biostratigraphy, reveals that the cores range from Chron C26r to C21n (Thanetian – Lutetian; ~60 to ~46Ma). Sedimentation rates range from ~0.6 to ~1cm/kyr and are comparable with those from coeval sections in the Umbria-Marche Basin. They point to significant discrepancies between existing time scales, which mainly involve the duration of Chron C23 and subchrons within C23n and C24n. Application of the average spectral misfit method on the magnetic susceptibility record reveals a strong signature of orbital forcing and allows an independent estimate of the sedimentation rates. This analysis offers additional insights into solving time scale issues, which mainly concern the duration of Chron C23n. Our results imply a significantly longer duration for C23n.2n, which would accommodate the presence of an extra third 405-kyr eccentricity related cycle in C23n. The Smirra record thus provides new constraints on the early Paleogene time scale, a key record for further cyclostratigraphic and astrochronological research, and a reference framework for paleo-climatic and -oceanographic studies.

Integrated biostratigraphy and carbon isotope stratigraphy of the Upper Jurassic shallow water carbonates of the High-Tatric Unit (Mały Giewont area, Western Tatra Mountains, Poland)

New biostratigraphical and carbon isotope data are presented for the Upper Jurassic limestones of the Raptawicka Turnia Limestone Formation (High Tatric unit, Western Tatra Mountains, Poland) from the Maly Giewont area. The Kimmeridgian, lower Tithonian and lower part of the upper Tithonian have been identified on the basis of calcareous dinocysts and calpionellids. Eight microfossil biozones are distinguished: acme Fibrata, acme Parvula, Moluccana, Borzai, Tithonica acme Pulla(?), Malmica, Chitinoidella and Crassicollaria ( pars ). The Kimmeridgian/Tithonian boundary is indicated at the top of the Borzai Zone 76 m above the base of the Raptawicka Turnia Limestone Formation. The microfossil stratigraphy suggests the late Early Kimmeridgian age ( acme Parvula Zone) of the ammonites described by Passendorfer (1928). The taxon Taramelliceras ex gr. compsum found 14 m above those ammonites is Late Kimmeridgian in age. Seven microfacies types (MF) are identified in the Upper Jurassic limestones of the Maly Giewont area. The Bositra -Saccocomidae MF occurs across the Lower-Upper Kimmeridgian boundary. The planktonic and benthic foraminifera occur in the Upper Jurassic deposits of the Raptawicka Turnia Limestone Formation. The genera Lenticulina Lamarck and Spirillina Ehrenberg are common in the Kimmeridgian and Tithonian limestones. The palaeobathymetric evolution of the Kimmeridgian-Tithonian deposition recorded in the Maly Giewont sections reveals: the transgressive episode at the Lower/Upper Kimmeridgian boundary interval, the transgression peak during the Early Tithonian (Malmica Zone) and gradual shallowing of the High-Tatric swell in the Late Tithonian. Integrated isotope stratigraphy and biostratigraphy enabled correlation with the pelagic section of the Sub-Tatric succession in the Dluga Valley section. The middle part of the Raptawicka Turnia Limestone Formation (Upper Kimmeridgian) might be correlated with the upper part of the Czajakowa Radiolarite Formation (red radiolarites) and Czorsztyn Formation in the Dluga Valley section. The upper part of the Raptawicka Turnia Limestone Formation of Early Tithonian age corresponds mostly to the Jasenina Formation. The overall similarity of the δ 13 C decreasing values recorded in the Kimmeridgian–earliest Tithonian interval of the Maly Giewont (this study) and Dluga Valley sections indicates that the generally shallow-water deposits of the Raptawicka Turnia Limestone Formation accumulated below the zone influenced by changes in the composition of marine water caused, for instance, by intense rainfalls.

Evolutionary trend of Zoophycos morphotypes from the Upper Cretaceous–Lower Miocene in the type pelagic sections of Gubbio, Italy

About 200 Zoophycos specimens, including 90 specimens studied in detail, have been analysed in the continuous Upper Cretaceous–Lower Miocene pelagic sedimentary type sections of the Gubbio area (the Contessa Highway, Contessa Quarry and Bottaccione sections, Northern Apennines). The sediments are reddish to grey limestones and marls of the Scaglia Group and marls with volcaniclastic deposits of the Bisciaro Formation. The aim was to examine the evolutionary trend of what is probably the most debated trace fossil of all time, from the Upper Cretaceous to Lower Miocene. Despite having been found in beds ranging from the Cambrian to the present, no consensus has been reached regarding mode of construction, tracemaker or ethological explanation for Zoophycos. Four Zoophycos morphotypes are recognized at Gubbio showing variations of major and minor lamellae, apex, lobes and whorls: the Cretaceous–Eocene cone-shaped type 1, the Upper Eocene–Middle Oligocene helicoidal type 2, the Oligocene lobate type 3 and the Upper Oligocene–Lower Miocene flat type 4. The very high ichnodensity in some beds (hundreds of specimens in discrete levels of the Bisciaro Formation, now destroyed by quarrying) seems to find explanation in abnormal concentrations of phytodetritus and organic matter on the seafloor in some periods. This very high abundance in discrete levels reflects a change in sedimentation and seafloor conditions at pre-flysch deposition. Due to such high ichnodensity, many adjacent specimens display deformed outer margins. Taphonomic analysis shows a variation of whorls, laminae and U-shaped lobes, reflecting ontogenetic development of the tracemaker(s) (?sipunculid worms).

Devonian/Carboniferous boundary glacioeustatic fluctuations in a platform-to-basin direction: A geochemical approach of sequence stratigraphy in pelagic settings

We investigated high-resolution stratigraphic distribution of selected major and trace elements and gamma-ray spectra of fourteen Devonian/Carboniferous (D/C) boundary sections of Europe located in the late Palaeozoic Laurussia and Gondwana. The aim was to trace the geochemical signature of a marked forced and normal regressive interval which was associated with rapid progradation of siliciclastics into the marine carbonate systems (Rhenish Massif) and a prominent hiatus in shallow-water ramp settings (Namur–Dinant Basin). This interval represents the late Devonian Hangenberg event (HBE) sensu lato (middle praesulcata conodont zone) as defined by previous authors. This regressive interval (FSST to LST) correlates with thin shale layers (HBE shale) sandwiched between monotonous nodular calcilutite/calcisiltite successions at five pelagic sections of Moravia, Carnic Alps, Montagne Noire, and Pyrenees. In all sections with continuous D/C sedimentation (i.e., except those of the Namur–Dinant Basin), the HBE s.l. interval is accompanied by elevated percentages of detrital proxies (Al, K, Rb, Zr) and changes in their ratios (Zr/Rb, K/Al, Rb/K) which are normally interpreted as indicators of increased siliciclastic input, provenance, and grain size. Zr/Rb and other proxies are traceable even without apparent lithological evidence and can, therefore, facilitate stratigraphic correlation. Paleoredox and productivity proxies (U/Th and Ni/Rb enrichment factors) only rarely show elevated values in the Hangenberg black shale interval, indicating that the associated water dysoxia/anoxia was a local rather than global phenomenon. Global correlations based on the HBE black shales should therefore be dropped in favor of the HBE s.l. interval. Moreover, analysis of sedimentation rates in the upper expansa to kockeli zone interval using the published radiometric ages suggests that the HBE s.l. was a time of significant increase in the rate of siliciclastic supply into the ocean, even in the most distal pelagic sections. Consequently, the previous interpretation of the HBE black shale as a condensed succession deposited during rapid sea-level rise seems unlikely. We interpret the HBE s.l. (i.e., including the HBE black shale) as a marine record of glacioeustatic sea-level drop and increased aeolian transport in connection with late Devonian climatic cooling and glaciation. The set of geochemical markers related to the late Devonian sea-level fluctuation can be used for super-regional to global correlations from platform to basin settings. Moreover, they can facilitate current efforts to determine a new D/C boundary definition.

Lithium-isotope evidence for enhanced silicate weathering during OAE 1a (Early Aptian Selli event)

An abrupt rise in temperature, forced by a massive input of CO2 into the atmosphere, is commonly invoked as the main trigger for Oceanic Anoxic Events (OAEs). Global warming initiated a cascade of palaeoenvironmental perturbations starting with increased continental weathering and an accelerated hydrological cycle that delivered higher loads of nutrients to coastal areas, stimulating biological productivity. The end-result was widespread anoxia and deposition of black shales: the hallmarks of OAEs. In order to assess the role of weathering as both an OAE initiator and terminator (via CO2 sequestration) during the Early Aptian OAE 1a (Selli Event, ∼120 Ma) the isotopic ratio of lithium isotopes was analysed in three sections of shallow-marine carbonates from the Pacific and Tethyan realms and one basinal pelagic section from the Tethyan domain. Because the isotopic composition of lithium in seawater is largely controlled by continental silicate weathering and high- and low-temperature alteration of basaltic material, a shift to lighter δ7Li values is expected to characterize OAEs. The studied sections illustrate this phenomenon: δ7Li values decrease to a minimum coincident with the negative carbon-isotope excursion that effectively records the onset of OAE 1a. A second negative δ7Li excursion occurs coeval with the minimum in strontium isotopes after the event. The striking similarity to the strontium-isotope record argues for a common driver. The formation and destruction (weathering) of an oceanic LIP could account for the parallel trend in both isotope systems. The double-spike in lithium isotopes is probably related to a change in weathering congruencies. Such a chemostratigraphy is consistent with the hypothesis that an increase in silicate weathering, in conjunction with organic-carbon burial, led to drawdown of atmospheric CO2 during the early Aptian OAE 1a.

Terrestrial Laser Scanner imaging for the cyclostratigraphy and astronomical tuning of the Ypresian–Lutetian pelagic section of Smirra (Umbria–Marche Basin, Italy)

Terrestrial laser scanner imaging is applied, together with calcimetry and lithofacies logging, for the cyclostratigraphic characterization of the Ypresian–Lutetian pelagites exposed in the Smirra section (Umbria–Marche Basin, Italy). The necessary chronostratigraphic framework is provided by detailed bio- and magnetostratigraphic analyses, which allow locating the Ypresian–Lutetian boundary in this section. Terrestrial laser scanner intensity is compared to carbonate content values obtained through calcimetric analyses carried out on samples taken from the same section, and is found to represent a good proxy for lithology in these pelagic homogenites. Time-series analysis highlights Milankovitch frequencies, particularly evident in the high-resolution terrestrial laser scanner intensity series. The recognition of distinctive low-frequency (>1Myr) features in the amplitude oscillations of short eccentricity as well as its ~400kyr modulation (long eccentricity), promote a tuning of the Smirra series using the most recent astronomic solution (La2010 nominal), which provides insights on the ages of the Y–L boundary and of the main biostratigraphic and magnetostratigraphic events in the Umbria–Marche Basin. Results confirm the value of high-resolution (mm-scale) terrestrial laser scanning for scrutinizing pelagite successions in search of low-frequency cycles that may help in the refinement of the astrochronological time scale.

Black shales – from coolhouse to greenhouse (early Aptian)

Approximately 120 Ma major volcanic outgassing on the Ontong Java Plateau resulted in perturbations of the global carbon cycle, in a change from cool to greenhouse climate conditions and in major changes in oceanography leading to widespread deposition of black shales during the early Aptian Oceanic Anoxic Event 1a (OAE1a). However, onset of black-shale deposition was diachronous and prior to OAE1a occurred under specific paleogeographic and paleoceanographic conditions. The goal of this study is to identify paleoceanographic constraints during coolhouse conditions that resulted in pre-OAE1a black-shale deposition and to investigate if and to what extent the short-term orbitally induced climate changes are also recorded in the sedimentary archive. We compared four lower Aptian pelagic sections from the former southern and northern continental margins of the Alpine Tethys Ocean and traced the evolution of carbon isotopes, carbonate and organic carbon content as well as palynofacies before and at the onset of OAE1a. Throughout the studied interval, the sections record frequent precession-controlled changes in carbonate content, which are reflected by limestone-marlstone alternations in the shallowest and most proximal Cismon core and by limestone-black-shale couplets in the deepest Pusiano section. Depth controlled sub-/anoxia is also suggested by the prominent OAE1a black shales, which occurred first in the deeper Pie del Dosso and Roter Sattel sections and only subsequently in the shallower Cismon core. However, contrary to expectations, the deepest Pusiano section exhibits – instead of an earliest onset of prominent OAE1a black shales – only a minor increase in TOC and a decrease in carbonate content. This suggests that the orbitally driven climate changes most strongly influenced water stratification and hence are most prominently expressed in the deepest sections. Conversely, the volcanically induced long-term climate changes seemed to more strongly affect organic matter production, the extension of the oxygen minimum zone and hence had the strongest impact on sections at intermediate depth.

High resolution δ13C stratigraphy through the Selli Oceanic Anoxic Event (OAE1a) in the Apulia carbonate platform: the Borgo Celano section (western Gargano Promontory, Southern Italy)

We show that the global-scale environmental perturbations leading to the Selli OAE1a were clearly recorded in the middle Bedoulian Apulia carbonate platform at Borgo Celano, in the western Gargano Promontory (Southern Italy). The studied section (Bari Limestones), which is 72.45 m thick and spans the Late Barremian p.p. -latest Early Aptian time interval, has been logged with an average resolution of 3 samples per metre for chemostratigraphic analyses and up to 7 samples per metre for facies analysis in the aim of detailed paleocologic and paleoceanographic investigation. It contains the complete biosedimentary and chemostratigraphic record across the Selli OAE1a, as suggested by a consistent match of the observed isotope excursions with those documented in the Cismon pelagic reference section and the lack of significant non-depositional or erosional hiatuses within the chemostratigraphic Selli level: biostratigraphic and sedimentary-diagenetic analyses document a continuous record of fully subtidal conditions. Furthermore, the Borgo Celano section allows correlation of the shallow- and deep-water records without intervening stratigraphic breaks. Upper Barremian-Lower Bedoulian, chlorozoan-type carbonates showing subtidal-intertidal Milankovitch-type cyclicities characterize the lower part of the Borgo Celano section (C2 pro parte isotopic segment). Starting from the latest C2 segment, a remarkable Crisis Interval (CI) about 4 m thick shows an increasing frequency of bivalves ( Chondrodonta and requieniids), the disappearance of green algae and a reduced diversity of foraminiferal assemblages (foramol-type carbonates). This interval is sharply overlain by an interval, about 3.70 m thick, that is largely dominated by “out-of-balance” microbial limestones almost devoid of metazoans, apart from sparse, small-sized requieniids and Chondrodonta , which accompanies the C3-middle C4 isotope segment. It is interpreted to reflect a sharp hyperthermal and acidification event induced by excess p CO 2 . Starting from the upper C4 segment, less severe but still threatening environmental conditions permitted the deposition throughout the lower C5 segment of peculiar shallow-water tropical-like carbonates, which are dominated by oncoidal floatstones and microbial wackestone/packstone emphasizing the enduring influence of benthic cyanobacteria during the Selli OAE1a. Upsection guilds are dominated by foraminiferal and peloidal wackestones/packstones with sparse bivalves and green algae (upper C5-lowermost C7 isotope segments). Similarly to other carbonate platforms of the central Tethyan Realm (e.g., Apennine and Adriatic), the resilience of the Apulia carbonate platform inner shelf to the environmental perturbations that led to the coeval drowning of its margin, the starvation of its slope and to the deposition of black shales in the bounding Ionian basin is a striking supraregional feature. The inception of the resilience of the Apulia carbonate platform inner shelf is coincident with the lithostratigraphic boundary in between the Borgo Celano and Chondrodonta and requieniids members of the Bari Limestones and physically corresponds in the field with the base of a significant, 1 m thick, Chondrodonta -rich marker bed. These observations confirm the value of routinely applied field and laboratory studies for precise chemostratigraphic and bio-chronostratigraphic correlations on a regional scale. Furthermore, chemostratigraphic data presented here corroborate recent paleoceanographic and stratigraphic models proposed for the Lower Aptian across the transition between the Apulia carbonate platform and the bounding Ionian basin, and provide further elements for regional reconstructions of historical patterns.

Geochemistry of fine-grained sediments of the upper Cretaceous to Paleogene Gosau Group (Austria, Slovakia): Implications for paleoenvironmental and provenance studies

Bulk rock geochemistry of 169 fine-grained sediment samples of the upper Cretaceous to Paleogene Gosau Group (Northern Calcareous Alps, Austria and Slovakia) from borehole and outcrop localities was performed to separate non-marine and marine deposits. Geochemical characteristics of different Gosau depositional systems, basins and sediment provenance using major-, trace-, and rare earth elements were also investigated. Geochemical proxies such as boron concentrations were tested for seeking the possibilities of paleosalinity indicators. Due to the fact that several pelagic sections are represented by extremely low boron contents, B/Al* ratios are recognized as more robust and differentiate reliably between marine (mean: 160 ± 34) and non-marine (mean: 133 ± 33) samples. Using statistical factor analysis, hemipelagic to pelagic samples from the Gießhübl Syncline and Slovakian equivalents can be differentiated from marginal-marine to non-marine samples from the Grünbach and Glinzendorf Syncline related to terrigenous (SiO2, Al2O3, K2O, Th, Rb, Zr and others) and pelagic indicative elements (CaO, Sr, TOT/C and B/Al*). A clear indication for ophiolitic provenance is traced by high amounts of chromium and nickel. Only non-marine successions of the Glinzendorf Syncline show higher Cr and Ni concentrations (up to 250 and 400 ppm, respectively) and enriched Cr/V and Y/Ni ratios trending to an ultramafic source.

Neritic isotope and sedimentary records of the Eocene–Oligocene greenhouse–icehouse transition: The Calcare di Nago Formation (northern Italy) in a global context

From the Middle Eocene to Early Oligocene, the Earth experienced the most significant climatic cooling of the Cenozoic era. The Eocene–Oligocene transition (EOT) represents the culmination of this climatic cooling, leading to the onset of the Antarctic glaciation and, consequently, to the beginning of the present-day icehouse world. Whereas the response of deep-sea systems to this climate transition has been widely studied, its impact on the shallow-water carbonate realm is poorly constrained. Here, the sedimentary expression of the EOT in two shallow-marine carbonate successions (Nago and San Valentino, northern Italy) belonging to the Calcare di Nago Formation is presented. The chronostratigraphic framework was constructed by integrating litho-, bio-, and isotope-stratigraphic data (C and Sr isotopes), allowing to correlate these shallow-marine successions with pelagic sections in central Italy (Massignano), Tanzania (TDP Sites 12 and 17), and the Indian Ocean (ODP Site 744). Within several sections in northern Italy, including Nago and San Valentino, a Priabonian (Late Eocene) transgression is recorded. Oxygen isotopes of ODP Site 744 show a coeval negative shift of 0.4‰, suggesting a glacio-eustatic origin for this transgression. In the Nago and San Valentino sections, no prominent sequence boundary has been detected that would indicate a rapid sea-level drop occurring together with the positive shift in δ18O defining the EOT-1 cooling event. Instead, a gradual shallowing of the depositional environment is observed. At TDP Sites 12 and 17, the EOT-1 is followed by a negative shift in δ18O of around 0.4‰, which correlates with a relative deepening of the environment in the studied sections and suggests a melting pulse between EOT-1 and the Oligocene isotope event 1 (Oi-1). The positive δ18O shift related to the Oi-1 translates in San Valentino into a change in carbonate factory from a photozoan association dominated by larger benthic foraminifera, corals, and red algae to a heterozoan association dominated by bryozoans. The same bryozoan facies occurs in several Italian localities near the Eocene–Oligocene boundary. This facies is interpreted to represent an analogue of modern cool-water carbonates and results from a cooling pulse of at least regional scale, associated to the Oi-1 event.

Sedimentology, biostratigraphy and event stratigraphy of the Early Aptian Oceanic Anoxic Event (OAE1A) in the Apulia Carbonate Platform Margin – Ionian Basin System (Gargano Promontory, southern Italy)

The stratigraphic and biotic signatures of severe environmental changes across the late Early Aptian Oceanic Anoxic Event (OAE1a) in central Tethyan settings have been investigated in the almost undeformed Apulia Carbonate Platform Margin-Ionian Basin system (ACPM-IB) exposed in the Gargano Promontory (southeastern Italy). The nature of the observed Lower Aptian biofacies shifts within the investigated carbonate system are analyzed using an integrated biostratigraphic approach, based on ammonite-calibrated orbitolinids and caprinids coupled with the published δ13C and δ18O record of coeval pelagic sections of the Ionian basin (Coppitella, eastern Gargano, and Paliambela, northwestern Greece). Detailed field analysis of facies and tracing out of key biosedimentary and chemostratigraphic markers of the Lower Aptian have elucidated the evolution of the platform margin and allowed integrated correlations across the Gargano margin to basin transition.It is shown here that the global-scale environmental changes leading to the OAE1a event (i.e., fluctuations of surface-ocean temperature, available trophic resources and, above all, pCO2) are matched consistently by significant shifts of the biotic associations inhabiting the ACPM. The onset of greenhouse, mesotrophic conditions in the surface ocean undergoing an increasing acidification by CO2 excess favored the rapid spread of calcite shelled, filter feeding, eurytopic opportunist organisms (chondrodontids, ostreids, chaetetids sponges, along with minor bryozoans) as well as echinoids and orbitolinids (foramol productivity mode); this change is recorded by the deposition of a 4–6 m Crisis Interval (CI) that sharply overlies the “Urgonian”-type, rudist-rich platform margin complex (Montagna degli Angeli Limestones) formed from predominantly aragonite shelled, stenotopic organisms (mostly caprinid rudists, with minor corals and Dasycladales and Bryopsidales green algae) (chlorozoan productivity mode). The CI heralded the incipient drowning of the ACPM which occurred immediately after the deposition of a hothouse “out of balance” brachiopod (Orbirhynchia nadiae)-cyanobacteria association (microbial productivity mode). The biostratigraphically constrained CI and the related drowning of the ACPM have been physically correlated with specific chemostratigraphic segments of the δ13Ccarb curve that is available for the facing, proximal Ionian Basin. The early (earliest ?) Late Bedoulian, greenhouse CI (early D. deshayesi – early P. cormyi zones) was deposited during the late C2 interval, whereas the early Late Bedoulian, hothouse “out-of-balance” guild and the ACPM drowning (early deshayesi zone) accompanied the subsequent negative excursion and culmination, respectively, at the very base of the Chemostratigraphic Selli Level (CSL) (latest C2 and C3 interval). These correlations permit regional to global interpretations of historical patterns and explanatory paleoeanographic and paleoecologic hypotheses; furthermore, they suggest that the Apulia shallow-water ecosystem reacted to the environmental disruptions linked with the OAE1a sooner than that of the facing open ocean. The onset of the drowning event was synchronous with the hothouse-induced bloom of the “out of balance” brachiopod-cyanobacteria association that occurred simultaneously with the pronounced negative excursion of the δ13Ccarb curve. This suggests a cause-and-effect relationship with the sudden environmental perturbations linked with the injection into the atmosphere-hydrosphere system of 13C-depleted CO2. The numerical age model of the major biotic and stratigraphic events at the Lower Aptian ACPM, along with their inferred genetic processes call for different timings and causal mechanisms associated with platform demise in northern and central Tethyan settings.

A volcanically induced climate warming and floral change preceded the onset of OAE1a (Early Cretaceous)

The Aptian Oceanic Anoxic Event 1a (OAE1a) is preceded by a prominent negative C-isotope excursion (NCIE) attributed to major volcanism on the Ontong Java plateau that is supposed to lead to a pCO 2 increase and a climate change. Lower Aptian sporomorph assemblages in two pelagic sections from the southern Tethys margin (N-Italy) were analysed in order to test if the postulated climate changes affected the terrestrial vegetation. At the base of the NCIE the sporomorph assemblages comprise abundant bisaccate pollen reflecting a warm-temperate climate. Several tens of kiloyears (ka) after the start of the NCIE decreasing bisaccate pollen and increasing Classopollis spp. and Araucariacites spp. suggest the beginning of a long-term temperature rise. Palynomorphs indicate that maximum temperatures were reached several tens of ka after the end of the NCIE and the onset of OAE1a. The highest temperatures coincide with arid conditions, which could reflect a northward shift of the hot-arid Northern Gondwana floral province as a result of an increasing pCO 2. Over 200 ka after the onset of OAE1a reduced volcanic activity and/or increased black shale deposition allowed for a drawdown of most of the excess CO 2 and a southward shift of floral belts.

A biocalcification crisis at the Triassic-Jurassic boundary recorded in the Budva Basin (Dinarides, Montenegro)

Volcanic activity in the Central Atlantic magmatic province, resulting in an increased flux of CO 2 , SO 2 , and CH 4 into the oceans and atmosphere, has been proposed as one of the mechanisms causing the biotic crisis at the Triassic-Jurassic boundary. Oceanic uptake of CO 2 due to extreme greenhouse conditions should have had an impact on ocean chemistry and the position of the calcite compensation depth. In this study, we chose two pelagic sections from the Budva Basin as archives for paleoceanographic change across the Triassic-Jurassic boundary in deep-water settings. Our record represents the first documentation of a sudden termination of carbonate deposition across the Triassic-Jurassic boundary in a pelagic deep-water environment. Based on radiolarian biostratigraphy, the system boundary is placed at the sharp lithological contact between two pelagic formations, the Upper Triassic limestones and Lower Jurassic siliceous limestones alternating with shales. A rapid drop of carbonate content from 90% to less than 10% occurred contemporaneous with a negative anomaly in the stable carbon isotope record measured in both bulk carbonate (1.3‰) and bulk organic matter (1.1‰). The abrupt reduction of carbonate content in the Budva Basin was the result of either increased carbonate dissolution causing shoaling of the calcite compensation depth or reduced carbonate input due to biocalcification crisis. Both nonexclusive scenarios support the hypothesis of decreased ocean saturation with respect to calcium carbonate, which could be a direct consequence of increased CO 2 , SO 2 , and CH 4 fluxes.