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The Toarcian oceanic anoxic event (T-OAE; ∼183 million y ago) is possibly the most extreme episode of widespread ocean oxygen deficiency in the Phanerozoic, coinciding with rapid atmospheric pCO2 increase and significant loss of biodiversity in marine faunas. The event is a unique past tipping point in the Earth system, where rapid and massive release of isotopically light carbon led to a major perturbation in the global carbon cycle as recorded in organic and inorganic C isotope records. Modern marine ecosystems are projected to experience major loss in biodiversity in response to enhanced ocean anoxia driven by anthropogenic release of greenhouse gases. Potential consequences of this anthropogenic forcing can be approximated by studying analog environmental perturbations in the past such as the T-OAE. Here we present to our knowledge the first organic carbon isotope record derived from the organic matrix in the calcite rostra of early Toarcian belemnites. We combine both organic and calcite carbon isotope analyses of individual specimens of these marine predators to obtain a refined reconstruction of the early Toarcian global exogenic carbon cycle perturbation and belemnite paieoecology. The organic carbon isotope data combined with measurements of oxygen isotope values from the same specimens allow for a more robust interpretation of the interplay between the global carbon cycle perturbation, environmental change, and biotic response during the T-OAE. We infer that belemnites adapted to environmental change by shifting their habitat from cold bottom waters to warm surface waters in response to expanded seafloor anoxia. [ABSTRACT FROM AUTHOR]

Cyclostratigraphic analysis of the Maastrichtian limestone–marl alternations of Bidart (SW France) allows the hypothesis of orbital control on lithological cycles to be evaluated. Magnetic susceptibility (MS), oxygen and carbon isotope measurements, sampled at a high resolution, are analyzed using various cyclostratigraphic tools. A statistically significant orbital signal is detected, with a remarkable record of the precession corresponding to the limestone–marl couplets. This well expressed orbital forcing allows the building of a relative cyclostratigraphic time scale for the MS and δ13C records based on the 100kyr eccentricity cycle. The total duration of the section is estimated at 1.44±0.22Myr. Correlation based on calcareous nannofossil biostratigraphy and comparison of the scaled Bidart δ13C record to the astronomically calibrated δ13C signal of ODP Hole 762C shows that the studied section extends from −71.5 to −70Ma, covering the upper part of Chron C32n.1n and 2/3 of Chron C31r. Oxygen isotope data suggest a 2°C cooling of sea-surface temperatures during the studied interval. When placed on the long-term δ18O trend of the Bidart section, this interval is here recognized as the onset of the early Maastrichtian cooling event. With its excellent record of the precessional forcing, the Bidart section, along with other sections of the Basque Country, is a useful tool for the refinement of the Maastrichtian timescale. [ABSTRACT FROM AUTHOR]

Abstract: One of the most expanded upper Campanian–Maastrichtian successions worldwide has been cored in a series of boreholes in eastern Denmark. A high-resolution holostratigraphic analysis of this part of the Chalk Group has been undertaken on these cores, notably Stevns-1, in order to provide a record of changes in chalk facies, water depths and sea-water temperatures. Combined lithological data, a suite of petrophysical logs including gamma ray (GR) logs, nannofossil and dinoflagellate palaeontology, stable carbon isotopes, seismic reflection and refraction sections form the basis for the definition of two new formations and six members, three of which are new, and for recognition of Boreal nannofossil subzones UC15eBP to UC20dBP. The upper Campanian–lowermost Maastrichtian Mandehoved Formation is subdivided into the Flagbanke and Boesdal Members and the Maastrichtian Møns Klint Formation is subdivided into the Hvidskud, Rørdal, Sigerslev, Kjølby Gaard Marl and Højerup Members. The Boesdal and Rørdal Members show high GR values and a pronounced chalk-marl cyclicity. The Rørdal and the thin Kjølby Gaard Marl Members have a regional distribution and can be traced over most of the Danish Basin, whereas the Højerup Member is restricted to the easternmost part of Sjælland. The other members consist of rather featureless white chalk. [Copyright &y& Elsevier]

Abstract: An integrated framework of magnetostratigraphy, calcareous microfossil bio-events, cyclostratigraphy and δ 13C stratigraphy is established for the upper Campanian–Maastrichtian of ODP Hole 762C (Exmouth Plateau, Northwestern Australian margin). Bulk-carbonate δ 13C events and nannofossil bio-events have been recorded and plotted against magnetostratigraphy, and provided absolute ages using the results of the cyclostratigraphic study and the recent astronomical calibration of the Maastrichtian. Thirteen carbon-isotope events and 40 nannofossil bio-events are recognized and calibrated with cyclostratigraphy, as well as 14 previously published foraminifer events, thus constituting a solid basis for large-scale correlations. Results show that this site is characterized by a nearly continuous sedimentation from the upper Campanian to the K-Pg boundary, except for a 500kyr gap in magnetochron C31n. Correlation of the age-calibrated δ 13C profile of ODP Hole 762C to the δ 13C profile of the Tercis les Bains section, Global Stratotype Section and Point of the Campanian–Maastrichtian boundary (CMB), allowed a precise recognition and dating of this stage boundary at 72.15±0.05Ma. This accounts for a total duration of 6.15±0.05Ma for the Maastrichtian stage. Correlation of the boundary level with northwest Germany shows that the CMB as defined at the GSSP is ~800kyr younger than the CMB as defined by Belemnite zonation in the Boreal realm. ODP Hole 762C is the first section to bear at the same time an excellent recovery of sediments throughout the upper Campanian–Maastrichtian, a precise and well-defined magnetostratigraphy, a high-resolution record of carbon isotope events and calcareous plankton biostratigraphy, and a cyclostratigraphic study tied to the La2010a astronomical solution. This section is thus proposed as an excellent reference for the upper Campanian–Maastrichtian in the Indian Ocean. [Copyright &y& Elsevier]

The duration of polarity Chron C31r is estimated with a cyclostratigraphic approach. Two sites are investigated: ODP Site 762 (Indian Ocean) and the Contessa Highway section (Gubbio, Italy). Cyclostratigraphic analysis is performed on greyscale variations (Site 762) and magnetic susceptibility variations (Contessa section). Both sites reveal an astronomical control of the sedimentation, highlighted by the identification of all the orbital periodicities. Cyclostratigraphic signals are tuned on 405 ka eccentricity cycles extracted from the La04 astronomical solution. In both sites, cycle counting gives an estimate of the duration of polarity Chron C31r of about 2.09 ± 0.03 Ma. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution carbon isotope stratigraphy of the upper Campanian–Maastrichtian is recorded in the Boreal Realm from a total of 1968 bulk chalk samples of the Stevns-1 core, eastern Denmark. Isotopic trends are calibrated by calcareous nannofossil bio-events and are correlated with a lower-resolution δ13C profile from Rørdal, northwestern Denmark. A quantitative approach is used to test the reliability of Upper Cretaceous nannofossil bio-events and provides accurate biohorizons for the correlation of δ13C profiles. The Campanian–Maastrichtian boundary (CMB) is identified through the correlation of dinoflagellate biostratigraphy and δ13C stratigraphy between Stevns-1 and the Global boundary Standard Stratotype-section and Point at Tercis les Bains (SW France), allowing the identification of new chemical and biostratigraphic markers that provide a precise placement of the stage boundary on a regional scale. The boundary interval corresponds to the third phase of a stepwise 0.8‰ negative δ13C excursion, lies in calcareous nannofossil subzone UC16dBP, and encompasses the last occurrence of nannofossil Tranolithus stemmerikii and first occurrence of nannofossil Prediscosphaera mgayae. Fifteen δ13C events are defined and correlated to sixteen reliable nannofossil biohorizons, thus providing a well-calibrated standard high-resolution δ13C curve for the Boreal Realm. [Copyright &y& Elsevier]

Abstract: The taxonomy of the calcareous nannofossil Arkhangelskiella is revised using the results of a biometric analysis performed on 599 specimens from various stratigraphic levels throughout the upper Campanian-Maastrichtian of the Stevns-1 borehole, Denmark. Combined qualitative labelling and biometric measurements suggest that this genus comprises at least three distinct morphogroups in this stratigraphic interval, with possibly one additional morphotype. The results show that the descriptions formerly used for the erection of these groups as distinct species do not fit to their observed range in the coccolith length and in the rim width, and that the central opening is an important additional parameter allowing distinction between the different morphogroups. Biometric analysis shows, however, that the morphogroups are strongly overlapping on all measured parameters. Therefore, the three distinct variants of Arkhangelskiella cymbiformis (var. NT, var. N and var. W) formerly described by Varol are reintroduced and emended rather than using distinct species. In addition, a fourth variant is described, A. cymbiformis var. SW. Using observed relationships between the parameters as well as stratigraphic ranges of these groups throughout the latest Cretaceous, evolutionary trends are outlined. [ABSTRACT FROM AUTHOR]

This paper is dedicated to the connection, by a provider, of multiple groups of nodes spread over a network. The role of the provider is to interconnect the members of every group. For this purpose, it must distribute the available links of the network between the groups. The general aim then is to allocate these links in such a way that the communications latencies in the allocated structure are equivalent to the ones in the original (full) network for each group. We study two approaches constructing structures preserving the maximum latency (called the diameter). Unfortunately we show that the associated optimization graph problems are difficult (one cannot be approximated by a constant and the other is NP-complete). Due to these difficulties we relax the constraint on the diameter and propose to construct a unique tree connecting all the groups together. We give a heuristic to treat this problem and we propose several analytical results on its maximum and average latencies performance. [ABSTRACT FROM PUBLISHER]

Abstract: The response of calcareous nannofossils to the end-Cretaceous warming is investigated in the Tropical Pacific DSDP Site 577A (Shatsky Rise) through the record of species richness, Shannon diversity, distribution patterns and statistical treatments. This event is marked by a strong acme of the tropical species Micula murus and is accompanied by a decrease of Placozygus spiralis, the disappearance of Biscutum constans and a decrease in bulk δ 13C, indicative of a decrease in primary productivity. An increase in abundance of other Micula species at Site 577A and a drop in species richness recorded in all sites of Shatsky Rise, suggest stressed environmental conditions coincident with the end-Cretaceous warming. The acme of M. murus at Shatsky Rise and in the Atlantic Ocean is recorded within magnetochron C29r and correlates (1) with the intense warming as expressed in intermediate waters through the δ 18O of benthic foraminifera, and in surface waters through poleward migration, reduced diversity and dwarfism in planktonic foraminifer assemblages, (2) with a sharp decline in marine 187Os/188Os, chemical marker of Deccan volcanic activity, and (3) with a rise in the atmospheric pCO2 record of terrestrial plants in Texas, USA, probably triggered by Deccan volcanic degassing. However, a drop of calcareous nannofossil cool-water taxa in the Equatorial and South Atlantic, as well as a first rise in abundance of M. murus in the South Atlantic and Tropical Pacific occur in the topmost part of chron C30n, and correlates with the rise in palaeotemperature record of terrestrial plants in North Dakota, USA. This suggests that initiation of the warming in the atmosphere and surface waters may predate the striking warming of intermediate water masses by 150/200kyr. The coincidence and the links between climate change, volcanism, geochemical and biotic events at the end of the Maastrichtian thus remain to be fully elucidated. [Copyright &y& Elsevier]

Calcareous nannofossil biostratigraphy and carbon-isotope stratigraphy on bulk organics of the middle-upper Eocene Souar Formation (Tunisia) allow for a refined stratigraphy of this interval in the southwestern Neo-Tethys margin. The Souar Formation represents the deepest sedimentary deposits of the central northern Tunisian Basin and was only dated previously by coarse data on planktonic foraminifera. Together with our new data, a correlation is proposed to previous Tunisian records of the Halk El Menzal carbonate platform to the NE and shallow-water deposits of central Tunisia to the SW, which leads us to the erection of a synthetic stratigraphic chart of the middle-upper Eocene in central and northeastern Tunisia. Our results allow for a review of the accurate position of the Lutetian / Bartonian and the Bartonian / Priabonian stage boundaries in Tunisia relative to calcareous nannofossil biohorizons. We apply Bayesian statistics to build our age-depth model which points to a hiatus in the Lutetian (CNE12 Zone) that we relate to the middle Lutetian regressive sequence leading to the Lu-4 M-cycle. Radiolarian-rich sediments and cherts of the late Lutetian and early Bartonian are interpreted as a response to an increase in productivity, tied to the seasonal upwelling of nutrient-rich waters. Correlation to other sections in Tunisia highlights the strong contrast in facies between the carbonate-rich sequences of the edges of the dorsal and the silica-rich deposition in the Souar Formation. This contrast is particularly pronounced in the interval before and across the Middle Eocene Climatic Optimum (MECO) characterized by a maximum of nummulitic carbonate production on the platform and a minimum of carbonate production in the deep basinal parts of the Tunisian dorsal, rather dominated by silica-rich sediments. • Middle-Late Eocene calcareous nannofossil biostratigraphy in the SW Neo-Tethys. • The MECO corresponds to the Reneiche member in the Tunisian stratigraphic chart. • The MECO is characterized by a δ 13Corg excursion and biosiliceous productivity. • Increase in terrigenous flux to the Tunisian dorsale during the MECO. • Major sedimentation rate variations due to changes in the on-land weathering. [ABSTRACT FROM AUTHOR]

The Early Jurassic nannofossil Schizosphaerella has displayed major changes in its mean valve size through time. These variations are investigated in detail in the Sinemurian to lowermost Toarcian of the Sancerre-Couy core (Paris Basin), based on previously published measurements of 7050 specimens. Through multivariate morphon analysis and mixture analysis, we decipher three distinct overlapping varieties of Schizosphaerella (small, medium, large) and show that mean size changes of this taxon can be mostly related to variations in the relative abundance of these three varieties. Comparison to facies changes and to newly and previously acquired geochemical data (bulk carbonate C and O isotopes and organic C isotopes, %CaCO 3 and TOC) suggest that, whilst sea-surface temperature was indeed an important driver of size changes in Schizosphaerella , it is insufficient on its own to explain the full variability of our dataset. Likewise, sea-level controlled proximal-distal variations and levels of nutrient supply were additional drivers of Schizosphaerella size changes. The small population of Schizosphaerella remains, however, a good indicator for warmer episodes. [Display omitted] • Schizosphaerella is composed of three pseudo-cryptic variants • The 3 variants strongly overlap and are only distinguishable by biometric studies • Sea-level and temperature are main drivers of Schizosphaerella size changes • Bulk δ18O matching global trends limited to late Pliensbachian [ABSTRACT FROM AUTHOR]

The Lower Cretaceous Tuxen (lower Hauterivian - upper Barremian) and Sola (upper Barremian - Albian) Formations in the Danish Central Graben (North Sea) constitute one of the oldest chalk successions recorded globally, but have received little attention with regards to sedimentary facies and depositional processes. This study presents the first comprehensive carbonate facies analysis of the succession, retrieved from seven drill cores from the Valdemar and Adda Fields. A total of 50 facies are identified, based on a continuum of six lithologies ranging from chalk to marlstone and tuffaceous siltstone to sandstone that display eight different sedimentary structures or fabrics, and two redox-associated lithological color variations (green and red) in the Adda Field. The eight sedimentary structures record: (i) comprehensive bioturbation of homogeneous sediment during fully oxygenated benthic conditions and low sedimentation rates; (ii) a similar bioturbation process but in heterogeneous sediment with lithological contrasts permitting visible burrows to form, perhaps due to rhythmic alternation between pelagic (clay-poor) and hemipelagic (clay-rich) sedimentation; (iii) pelagic to hemipelagic suspension settling in dysoxic to anoxic bottom-water conditions; (iv) patchy cementation of the shallow sea bed during incipient hardground formation; (v) reworking of bioclasts and chalk intraclasts by bottom or wave-induced currents and cohesive debris flows; (vi) pressure solution during late burial diagenesis; (vii) shear deformation by intense plastic deformation of unlithified sediment from limited lateral displacement; and (viii) silicification during burial diagenesis. The facies distribution indicates that active tectonism took place prior to the onset of anoxia that resulted in deposition of the Munk Marl Bed, which in the Valdemar Field was followed by tectonic waning and repeated anoxia. The Valdemar Field constituted a basinal depocenter and was flanked to the east by an early inversion high in the Adda Field characterized by condensation and bypass. The Fischschiefer Member represents a return to prevailing anoxia, consistent with global records of the early Aptian Oceanic Anoxic Event 1a (OAE-1a). [ABSTRACT FROM AUTHOR]

The early Eocene (c. 56 - 48 million years ago) experienced some of the highest global temperatures in Earth's history since the Mesozoic, with no polar ice. Reports of contradictory ice-rafted erratics and cold water glendonites in the higher latitudes have been largely dismissed due to ambiguity of the significance of these purported cold-climate indicators. Here we apply clumped isotope paleothermometry to a traditionally qualitative abiotic proxy, glendonite calcite, to generate quantitative temperature estimates for northern mid-latitude bottom waters. Our data show that the glendonites of the Danish Basin formed in waters below 5 °C, at water depths of <300 m. Such near-freezing temperatures have not previously been reconstructed from proxy data for anywhere on the early Eocene Earth, and these data therefore suggest that regionalised cool episodes punctuated the background warmth of the early Eocene, likely linked to eruptive phases of the North Atlantic Igneous Province. The early Eocene was characterized by exceptionally high global temperatures and no polar ice. Here, clumped isotope paleothermometry of glendonite calcite from the Danish Basin shows that these were formed in waters below 5 °C, indicating that regionalised cool episodes punctuated the background warmth of the early Eocene. [ABSTRACT FROM AUTHOR]

The Rhaetian (~201–209 Ma, the latest stage of the Triassic) is an important time-interval for the study of environmental changes preceding the End-Triassic Mass extinction. A detailed sedimentological and chemostratigraphic study was conducted in the lower Kössen Formation at Hochalm (Austria), the type-section of the Hochalm Member (Mb). This section exposes mid-Rhaetian sediments deposited in an intraplatform shallow marine basin on the north-western margin of the Tethys. The study highlights eight apparent shallowing-upward sequences from the middle of Unit 2 to Unit 4 of the Hochalm Mb stacked within the long-term transgression that characterizes the Kössen Formation. Both the bulk carbonate and the bulk organic matter δ13C records indicate the presence of a distinct increase in carbon isotope values in the lower part of the lower Hochalm Mb. This excursion might represent a new chemostratigraphic marker that could be used for refining the Rhaetian stratigraphy and represents another important Late Triassic carbon-cycle perturbation prior to the major disturbance associated with the End Triassic biotic crisis. • Detailed paleoenvironmental model of the Hochalm Mb. • Shallowing-deepening sequences related to sea-level changes. • Carbon isotope stratigraphy in mid-Rhaetian Hochalm Mb. • Distinct increase in carbon isotopes in the lower Hochalm Mb. [ABSTRACT FROM AUTHOR]

Coniacian to Maastrichtian changes in calcareous nannofossil assemblages have been investigated in the eastern Tethyan Shahneshin section (central Zagros Basin, Iran). The nannofossil assemblages are mainly composed of Watznaueria spp. (avg. 54%), Retecapsa spp (avg. 7.9%), Cribrosphaerella ehrenbergii (avg. 7.7%) and Micula spp. (avg. 5.7%). Throughout the late Campanian, there is a trend to lower abundances in Watznaueria spp. together with increasing abundances of C. ehrenbergii and Arkhangelskiella cymbiformis , which are considered in this basin as the main cool-water taxa. Our results reveal that, despite a diagenetic impact on calcareous nannoflora, a number of primary paleoecological trends are preserved which depict well features of the progressive Late Cretaceous cooling. The first pronounced cooling episode occurs across the late Campanian to early Maastrichtian. The onset of pronounced cooling in the eastern Tethys appears to occur prior to the Campanian/Maastrichtian Boundary event (CMBE) δ13C negative excursion, in contrast with the Boreal realm where pronounced cooling only occurs in the early Maastrichtian, postdating the onset of the CMBE. The coincidence of this earlier cooling in the Zagros Basin with an interval characterized by a significant increase in benthic foraminifera suggests an amplified response of the assemblage due to a change to shallower environments. Hence, the late Campanian calcareous nannofossil assemblage turnover in central Zagros is either a response to an early cooling trend in the eastern Tethys or to sea-level fall or both. The mid-Maastrichtian warming and late Maastrichtian cooling episodes are also delineated in the nannofossil assemblage of Shahneshin and likely correlate with similar episodes in the Boreal Realm. • The first quantitative study on the Late Cretaceous calcareous nannofossil assemblages from the Eastern Tethys (Zagros). • The first palaeoecological record of the Late Cretaceous cooling in the eastern Tethyan Realm (Zagros). • Cribrosphaerella ehrenbergii and Arkhangelskiella spp. are considered as the best cool-water indicators in the Zagros Basin in this study. • The late Campanian–early Maastrichtian cooling appears to occur earlier in eastern Tethys compared to the Boreal Realm. [ABSTRACT FROM AUTHOR]

A high-resolution study of carbon isotope stratigraphy and calcareous nannofossil biostratigraphy has been undertaken on the Upper Cretaceous sediments of the Gurpi Formation (Fm.) in the Bowan section (Zagros Basin, Iran). The integrated stratigraphy of the section allows for large-scale correlation with Upper Cretaceous reference sections (Gubbio, Italy; German Chalk; Shahneshin, Iran) and suggests the age of the Gurpi Fm. at Bowan to be latest Santonian to early Selandian. Correlation of the isotopic data from Bowan to the Shahneshin section in the central Zagros mountains shows remarkable similarity that may be related to effects specific to the peculiar stratigraphy of the area and, possibly, to the long-term evolution of seawater δ13C in the Zagros Basin. A sequence stratigraphic framework is proposed for both sections. Correlation of the two sections to data from the Boreal realm, Indian Ocean, equatorial Pacific Ocean, and other Tethyan sections suggests that it is possible to identify some of the previously defined major carbon isotope events in the Iranian sections. Significant differences, however, are observed in absolute values and overall amplitude of carbon isotope trends. In particular, our results show that the Santonian/Campanian boundary event (SCBE) which is a well-defined, double-peaked, positive excursion at Gubbio and in the Boreal realm is absent in the Zagros Basin, eroded by a major sequence boundary. Moreover, the most pronounced feature in Upper Cretaceous carbon isotope ratios of the Zagros Basin carbonates is an overarching maximum culminating in the early Campanian which correlates with a discrete, low-amplitude (0.25‰) positive excursion defined as the papillosa Zone event at Gubbio and in the Boreal realm. Our results thus reveal a contrasting evolution of carbonate δ13C during the early Campanian between different oceanic basins but also within the Tethys. • The Upper Cretaceous bio- and isotopic data of central Zagros reveals the long-term evolution of seawater δ13C. • The most prominent feature in δ13C trend of Zagros appears to be the significant increase in the papillosa Zone event. • Two significant hiatuses at the uppermost Campanian–early Maastrichtian and latest Maastrichtian–early Danian are identified. • The two identified significant hiatuses in the Zagros Basin are linked here to tectonic uplifts. • The Santonian/Campanian boundary event (SCBE) is poorly expressed in the Zagros Basin. [ABSTRACT FROM AUTHOR]

The late Campanian – Maastrichtian (~74–66 Ma) was characterized by a long-term cooling trend that marks a transition from extreme greenhouse conditions associated with the mid-Cretaceous to cooler conditions that precede the Cenozoic climate. Sparse availability of stable isotope data and the low temporal resolution of biozonations hinder our understanding of this interval, especially for open ocean records. Provincialism of calcareous planktonic taxa also occurred during this time, making it difficult to develop a global biostratigraphic scheme. Calcareous nannofossils are sensitive indicators of surface water, making this fossil group a useful proxy for understanding Late Cretaceous climatic events and correlating these events across different ocean basins. This study expands on the work of Thibault and Gardin (2007), that explored the paleoclimatic evolution of late Maastrichtian calcareous nannofossils from Deep Sea Drilling Project (DSDP) Hole 525A in the South Atlantic. The completeness of its late Campanian – Maastrichtian record makes Hole 525A an ideal site for this study. Furthermore, high-resolution stable isotope datasets have been published, making this section useful for correlation to other ocean basins. A total of 72 smear slides from DSDP Hole 525A, spanning approximately 74–66 Ma, were analyzed. Absolute abundances were determined by counting approximately 300 specimens and two additional traverses were scanned for rare species. Given that this is a low middle latitude site, the calcareous nannofossil assemblage is predominantly comprised of cosmopolitan species, with little evidence of provincialism. This means that sea surface temperature changes are not as well expressed at this site. Despite the dominance of cosmopolitan species, abundance increases of "Cool-water indicators" (Ahmuellerella octoradiata, Kamptnerius magnificus and Nephrolithus frequens) are still observed in this section.In addition to the evidence presented for cool surface water conditions prevailing during the late Maastrichtian (Chron C30N) (Thibault and Gardin, 2007), increases in "Cool-water indicators" are also observed at the base of the early Maastrichtian (Chron C32n1r through the middle of Chron C31r) and two peaks during the late early Maastrichtian (uppermost Chron C31r). These fluxes of "Cool-water indicators" further support onset of global cooling during the late Campanian – early Maastrichtian, evidenced by a rapid, positive oxygen benthic foraminiferal isotope excursion recorded at numerous deep ocean sites. Traditionally viewed as a low-fertility indicator, the gradual decrease in abundance of Watznaueria barnesiae is observed throughout the section, seemingly following the gradual global cooling trend. Fluctuations in abundance are superimposed on this general decrease. The highest abundances precede the Campanian/Maastrichtian boundary. Increases in abundance also occur throughout the middle Maastrichtian (Chron 31n through Chron 30r), possibly coinciding with the collapse of rudist bivalve-dominated reef systems and the extinction of inoceramid bivalves during the Mid-Maastrichtian event. ReferencesThibault, N., & Gardin, S. (2007). The late Maastrichtian nannofossil record of climate change in the South Atlantic DSDP Hole 525A. Marine Micropaleontology, 65(3), 163-184. [ABSTRACT FROM AUTHOR]

The Middle Ordovician outer shelf section of Steinsodden (Norway) shows exquisite marl-limestone alternations with subtle variations in thickness. The section is very well-dated by conodonts allowing correlation to the Baltoscandian conodont and graptolite zonations, and spans the Dapingian to Darriwilian stages. Here, we demonstrate an unambiguous orbital origin of the alternations, allowing for an astronomical calibration of this important time interval that spans the main radiation phase of the Great Ordovician Biodiversification Event (GOBE). A shift in carbonate sedimentation from precession-dominated in the Dapingian and lower Darriwilian to 405 kyr eccentricity-dominated in the middle Darriwilian is in direct coincidence with an increase in the diversity of Baltoscandian conodonts. The conodont diversification correlates with a similar increase in the diversity of Baltoscandian brachiopods, which in turn, have been shown to coincide with a +1‰ increase in benthic oxygen isotopes. The amplitude of isotopic change and its coincidence to the major switch in the dominance of orbital components reflect a scenario that bears similarities to that of the Eocene/Oligocene boundary transition, suggesting that glaciation could have triggered the main radiation phase of the GOBE. [ABSTRACT FROM AUTHOR]

Drilled in 1983, DSDP Site 534A is a prime location to investigate marl-limestone alterations from the middle Tithonian to the earliest Barremian. In 336 metres, the studied interval encompasses a nearly complete succession, allowing a high-resolution long-term study for this critical interval of Earth's history. To strengthen the Stratigraphy of the Jurassic-Cretaceous system boundary, we integrate the already published magnetostratigraphic, chemostratigraphic (bulk carbonate carbon isotopes) and biostratigraphic framework of the core (based on nannofossils, radiolarians, dinoflagellates and calpionellids) with cyclostratigraphy based on high-resolution (4cm) XRF data. Astronomical tuning of the core suggests a total duration of ~19 million years for the studied interval. Interestingly, long-term trends in the Ca/Fe ratio compare well with that of carbon isotopes. These trends are forced by the 9.1 Myr grand eccentricity cycle, placing the Weissert event close to a maximum of this grand cycle. Astronomical configuration appears to have played a major role in the development of this oceanic anoxic event. [ABSTRACT FROM AUTHOR]

In the Northern Calcareous Alps of Austria, Tethyan marls, clays and limestones of the upper Zlambach facies outcrop in excellent conditions in the Roßmoosgraben section (east of Bad Goisern, Oberösterreich). These sediments were deposited in a toe-of-slope to basinal paleoenvironment and thus constitute a rare example of Rhaetian open ocean conditions of the northern Tethys. Calcareous nannofossils are abundant in these sediments and their preservation is generally moderate, allowing for assessing potential changes in assemblages. Absolute and relative abundances of nannofossils and changes in the size of Prinsiosphaera triassica have been established for 65 samples across the V. stuerzenbaumi to C. marshi ammonite zones and compared to high-resolution bulk carbonate carbon isotopes. Two large 1.5 per mil negative excursions in carbon isotopes are recorded in the C. marshi zone and are accompanied by significantly lower total abundance in calcareous nannofossils but no significant change in the composition of the assemblage. Organic-rich black shales prevail in the uppermost 3 m of the Roßmoosgraben section and contain an unusually high abundance of the nannolith Tetralithus and significantly smaller specimens of Prinsiosphaera triassica. In addition, the total number of coccoliths, which represent the earliest representatives of coccolithophorids, is higher in this interval. These results suggest that a possible change in fertility conditions of surface waters favoured the thriving of the primitive coccolithophorids and accompanied bottom water anoxia. Our study shows that even though Rhaetian calcareous nannofossil assemblages have a low diversity, changes in their composition and in their size can be used to depict significant environmental changes. Also, the Rhaetian was characterized by unstable environmental conditions as attested by rapid shifts in the carbon cycle and episodes of ocean anoxia. [ABSTRACT FROM AUTHOR]

The organic matter content of marine sediments is often used to infer past changes in ocean conditions. However, the organic carbon pool preserved in coastal sediments is a complex mixture derived from different sources and may not reflect in situ processes. In this study, we combine taxonomic identification of reworked palynomorphs with pyrolysis organic geochemistry and reflected‐light organic petrographic microscopy to investigate the provenance, composition and preservation of organic matter in a marine sediment core retrieved from the NE Greenland shelf. Our study reveals continuous yet variable input of land‐derived organic carbon to the marine environment throughout the late Younger Dryas–Holocene, with the highest input of inert carbon in the late Younger Dryas. Although the sediments contain some recent marine palynomorphs, there is no other evidence of fresh marine organic carbon. In contrast, our results indicate that these shelf sediments represent a significant sink of recycled organic carbon. The results of pyrolysis geochemistry revealed that ~90% of the total organic carbon in the sediments is inert. The organic petrography analyses revealed that >70–84% of the organic carbon in the sediment core is terrigenous. Reworked dinoflagellate cysts showed a continuous provenance of Cretaceous land‐derived material, most likely from the nearby Clavering Island. Our study points to the importance of constraining the organic matter origin, composition and preservation in marine sediments to achieve more accurate palaeoenvironmental reconstructions based on organic proxies. [ABSTRACT FROM AUTHOR]

Abstract Middle to late Rhaetian toe–of–slope to basin deposits (Zlambach Formation) of the Northern Calcareous Alps in the Tethyan realm have been studied with respect to depositional palaeoenvironments and chemo- and sequence stratigraphy, using high-resolution stable isotope and X-ray fluorescence measurements, microfacies and microfossil analysis. Our results show that the Zlambach Formation represents a regressive-transgressive succession which includes one 3rd order and two 4th order depositional sequences as well as several subordinate sedimentary cycles reflecting variations of calciturbidite input from the Dachstein platform due to minor sea-level fluctuations. We present the first high-resolution δ13C carb record for the Middle and Upper Rhaetian interval of the west Tethyan open marine realm. The data show, in contrast to earlier suggestions, that growth and progradation of the Dachstein carbonate platform margin was continuous until the early Choristoceras marshi ammonoid zone (upper Rhaetian). In the late C. marshi zone the Hallstatt basin was affected by significant environmental perturbations as recorded by a 1.0‰ C carb negative excursion followed by a 1.3‰ positive excursion and contemporaneous fluctuations in benthic microfossil abundance and diversity. The occurrence of comparable carbon isotope excursions in the late C. marshi zone of intraplatform basinal deposits of the Northern Calcareous Alps suggests that these perturbations were of a higher significance than previously thought. These isotope excursions could be related to regional ecologic changes such as the late Rhaetian termination of the Dachstein platform margin growth. [ABSTRACT FROM AUTHOR]

A high-precision global time scale for the Early Jurassic is important for understanding the relationship between biotic, climatic and sea-level changes that occurred during this time interval. In this study, we present a cyclostratigraphic analysis of iron (Fe) and titanium (Ti) elemental data from the Pliensbachian marine mudstone succession of the Sancerre-Couy drill core (Paris Basin, France). Time-series analysis of the data, coupled with existing broad chronological constraints, reveals 405 kyr long-eccentricity, 133–100 kyr short-eccentricity, and 34 kyr obliquity cycles in Ti and Fe abundance. Based on astronomical tuning of the 405 kyr long eccentricity cycles, we construct an astrochronology for the Pliensbachian Stage in the Sancerre-Couy record spanning ∼7.9 Myr. Anchored in numerical time, our new Pliensbachian timescale can be correlated with the thicker, likely more complete, astronomically calibrated Pliensbachian record in the Mochras Farm (Llanbedr) borehole. This exercise suggests the presence of significant hiatuses near the base and top of the Sancerre-Couy record. The recently developed sedimentary noise model for inferring sea-level change has also been applied and compared to previous estimates of Pliensbachian sea-level change derived from the Sancerre-Couy record and elsewhere. Analysis of the sedimentary noise modeling results, previously published nannofossil abundance data and our elemental data suggests the presence of million-year scale cycles linked to long-period astronomical forcing. This work provides new constraints on the chronology of the Pliensbachian and its constituent faunal zones, and the role of long-period astronomical forcing in mediating Early Jurassic paleoclimate and sea-level. • The Pliensbachian Stage spanned ∼7.9 Myr. • The timing and duration of Pliensbachian ammonite zones and subzones are constrained. • Sedimentary noise modeling provides new details on relative sea-level changes. • Long astronomical forcing had an impact on paleoclimate and sea-level variations. [ABSTRACT FROM AUTHOR]