Age and synchronicity of planktonic foraminiferal bioevents across the Cenomanian–Turonian boundary interval (Late Cretaceous)

The upper Cenomanian \u2013 lower Turonian is a key-stratigraphic interval, as it encompasses the Late Cretaceous supergreenhouse and a major perturbation of the global carbon cycle (i. e., Oceanic Anoxic Event 2) as evidenced by a global positive carbon isotope excursion and by the nearly world-wide deposition of organic-rich marine facies. A turnover in planktonic foraminiferal assemblages and in other marine organisms is documented across this stratigraphic interval, but reconstruction of the timing and identification of the cause and effect relationships between environmental perturbations and organism response require a highly- resolved stratigraphic framework. The appearance and extinction levels of planktonic foraminiferal species generally allow accurate intra- and supra-basinal correlations. However, bioevents cannot be assumed to be globally synchronous, because the stratigraphic and geographic distribution of species is modulated by ecological preferences exhibited by each taxon and controlled by oceanic circulation, often resulting in earlier or delayed events in certain geographic areas (i. e., diachronous datums). The aim of this study is to test the synchronicity of the planktonic foraminiferal bioevents recognized across the C/T boundary and to provide the most reliable sequence of events for correlation of low to mid-latitude localities. For this purpose, we have compiled a highly-resolved biostratigraphic analysis of the European reference section for the C/T boundary at Eastbourne, Gun Gardens (UK), and core S57 (Tarfaya, Morocco), and correlated the sequence of bioevents identified with those recorded in other coeval sections available in the literature, including the GSSP section for the base of the Turonian Stage at Rock Canyon, Pueblo (Colorado), where we calculated reliable estimates of planktonic foraminiferal events that are well-constrained by radioisotopically and astrochronologically dated bentonite layers. Results indicate that the extinctions of Thalmanninella deeckei, Thalmanninella greenhornensis, Rotalipora cushmani and \u201cGlobigerinelloides\u201d bentonensis in the latest Cenomanian are reliable bioevents for correlation. In addition, our analysis highlights other promising lowest occurrences (LOs) that need to be better constrained by bio- and chemostratigraphy, including the LO of Marginotruncana schneegansi falling close to the C/T boundary. By contrast, the appearance of Helvetoglobotruncana helvetica and of some Dicarinella species, the extinction of anaticinellids and the onset of the \u201cHeterohelix\u201d shift are likely diachronous across low to mid-latitude localities. Finally, our study suggests that different species concepts among authors, different sample size and sampling resolution, as well as species paleoecology are important factors that control the stratigraphic position at which bioevents are identified

History-sensitive accumulation rules for life-time prediction under variable loading

This is the post-print version of the article. The official published version can be obtained from the link below - Copyright @ 2011 SpringerA general form of temporal strength conditions under variable creep loading is employed to formulate several new phenomenological accumulation rules based on the constant-loading durability diagram. Unlike the well-known Robinson rule of linear accumulation of partial life-times, the new rules allow to describe the life-time sensibility to the load sequence, observed in experiments. Comparison of the new rules with experimental data shows that they fit the data much more accurately than the Robinson rule

Geological controls on the geometry of incised-valley fills: Insights from a global dataset of late-Quaternary examples

Incised valleys that develop due to relative sea-level change are common features of continental shelves and coastal plains. Assessment of the factors that control the geometry of incised-valley fills has hitherto largely relied on conceptual, experimental or numerical models, else has been grounded on case studies of individual depositional systems. Here, a database-driven statistical analysis of 151 late-Quaternary incised-valley fills has been performed, the aim being to investigate the geological controls on their geometry. Results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised-valley fills through their effect on the degree and rate of river incision, and on river size and mobility. The studied incised-valley fills developed along active margins are thicker and wider, on average, than those along passive margins, suggesting that tectonic setting exerts a control on the geometry of incised-valley fills, likely through effects on relative sea-level change and river behaviour, and in relation to distinct characteristics of basin physiography, water discharge and modes of sediment delivery. Valley-fill geometry is positively correlated with the associated drainage-basin size, confirming the dominant role of water discharge. Climate is also inferred to exert a potential control on valley-fill dimensions, possibly through modulations of temperature, peak precipitation, vegetation and permafrost, which would in turn affect water discharge, rates of sediment supply and valley-margin stability. Shelves with slope breaks that are currently deeper than 120 m contain incised-valley fills that are thicker and wider, on average, than those hosted on shelves with breaks shallower than 120 m. No correlation exists between valley-fill thickness and present-day coastal-prism convexity, which is measured as the difference in gradient between lower coastal plains and inner shelves. These findings challenge some concepts embedded in sequence stratigraphic thinking, and have significant implications for analysis and improved understanding of source-to-sink sediment route-ways, and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs

Multi-layered Ruthenium-modified Bond Coats for Thermal Barrier Coatings

Diffusional approaches for fabrication of multi-layered Ru-modified bond coats for thermal barrier coatings have been developed via low activity chemical vapor deposition and high activity pack aluminization. Both processes yield bond coats comprising two distinct B2 layers, based on NiAl and RuAl, however, the position of these layers relative to the bond coat surface is reversed when switching processes. The structural evolution of each coating at various stages of the fabrication process has been and subsequent cyclic oxidation is presented, and the relevant interdiffusion and phase equilibria issues in are discussed. Evaluation of the oxidation behavior of these Ru-modified bond coat structures reveals that each B2 interlayer arrangement leads to the formation of α-Al 2 O 3 TGO at 1100°C, but the durability of the TGO is somewhat different and in need of further improvement in both cases

Status of the planktonic foraminiferal species Ticinella bejaouaensis Sigal, 1966 (Aptian-Albian)

Observations of the holotype and paratype of Ticinella bejaouaensis Sigal 1966, deposited at at the Natural History Museum in Paris, allowed to support the previous indication by Randrianasolo and Anglada (1998), further confirmed by Moullade et al. (2002), that the holotype and paratype of T. bejaouaensis are not conspecific and their distributions do not overlap as they occur in the upper Albian and around the Aptian/Albian boundary, respectively. In agreement with Randrianasolo and Anglada (1998) and Moullade et al. (2002), the species corresponding to Sigal\u2019s paratype from Tunisia must be named eubejaouaensis, whereas the name of T. bejaouaensis is confined to the late Albian holotype. Moreover, based on new descriptions and SEM analysis, the former latest Aptian T. bejaouaensis, now eubejaouaensis, possesses a text ultrastructure features different from the true ticinellids suggesting that this taxon is even not congeneric with Ticinell

Reassessing planktonic foraminiferal biostratigraphy across the Cenomanian–Turonian boundary interval (middle Cretaceous)

The upper Cenomanian\u2013lower Turonian is a key-stratigraphic interval of the mid-Cretaceous, as it encompasses a hot greenhouse phase and a major perturbation of the global carbon cycle (i.e, the Oceanic Anoxic Event 2) testified by a globally registered positive carbon isotope excursion and by the nearly world-wide deposition of dark organic-rich facies, pinched in between the normal whitish biogenic carbonates in open marine environments. A turnover in planktonic foraminiferal assemblages (extinction of single-keeled rotaliporids replaced by double-keeled dicarinellids and marginotruncanids) and in other marine organisms has been related to these environmental perturbations. However, the reconstruction of the timing of environmental changes and of the cause and effect relationships between ecological forcing and organism response requires a highly-resolved stratigraphic framework. The appearance and extinction levels of planktonic foraminiferal species represent a powerful tool to biostratigraphically constrain Cretaceous pelagic and hemipelagic sequences allowing accurate intra- and supra-basinal correlations. However, bioevents cannot be assumed to be globally synchronous, because the stratigraphic and geographic distribution of species is modulated by the ecological preferences exhibited by each taxon. The aim of this study is to assess the reproducibility and reliability of planktonic foraminiferal bioevents across the C\u2013T boundary interval by correlating each bioevent to the carbon isotope profile, in order to test their synchronicity across mid-low latitude localities. To perform this study, we have completed a highly-resolved biostratigraphic analysis of the European reference section for the C/T boundary at Eastbourne, Gun Gardens (UK), and of core S57, drilled in the Tarfaya Basin (Morocco). The sequence of bioevents identified has been compared to those recorded in other coeval sections previously studied (the GSSP section for the base of the Turonian Stage at Rock Canyon, Pueblo, Colorado; wadi Bahloul in Tunisia; Clot Chevalier and Pont d\u2019Issole in SE France; and Gongzha in Tibet) that satisfy the condition of lacking major unconformities and of yielding a highly-resolved planktonic foraminiferal biostratigraphy and \u3b413C record. Results indicate that the extinctions of Thalmanninella deeckei, Thalmanninella greenhornensis, Rotalipora cushmani and \u201cGlobigerinelloides\u201d bentonensis in the latest Cenomanian are extremely reliable bioevents for correlation. In addition, our analysis highlights other promising lowest occurrences (LOs) within the uppermost Cenomanian and lowermost Turonian that, however, need to be better constrained by bio- and chemostratigraphy, including the LOs of Praeglobotruncana oraviensis, and of Marginotruncana schneegansi, the latter event falling close to the C/T boundary. Other bioevents, including the appearances of Helvetoglobotruncana helvetica, the secondary marker for the base of the Turonian, and of most Dicarinella species, appear to be diachronous. The \u2018Heterohelix shift\u2019 is a regional diachronous ecologic response not recorded in all sections. Although the stenotopic ecological behavior of these species might explain these results, we believe that evolutionary transition between species, different species concepts among authors, and rarity of the species might partially account for the discrepancies observed in the identification of extinction and appearance levels in the sections compared in this study

Revised ages of blueschist metamorphism and the youngest pre-thrusting rocks in the San Juan Islands, Washington

New ages of rocks in the San Juan Islands (SJI), northwest Washington, significantly change our understanding of the evolution of the SJI thrust system. Re-examination of foram-bearing mudstones at Richardson on Lopez Island indicates a late Aptian (112-115 Ma), not late Albian (100 Ma) age as currently in the literature. The age brackets of thrusting, marked by these pre-thrusting mudstones and 84 Ma post-thrusting sedimentary rocks, span a much longer period than previously thought, diminishing controls on rates of displacement in the thrust system and timing of regional deformation in western Washington. New 40Ar/39Ar plateau ages of phengite in blueschist facies meta-volcanic rock, also at Richardson, are 124 \ub1 0.7 Ma (2_, late Barremian). These blueschist facies volcanic rocks are in fault contact with the fossiliferous mudstones. Therefore, at Richardson the blueschist facies metamorphism, previously inferred to be associated with the thrusting, now appears to have occurred prior to thrusting. Further, the Ar ages demonstrate that blueschist-facies fabric formed earlier than the thrust event and is therefore not directly useful in analyzing the thrusting kinematics. The Richardson 40Ar/39Ar age is similar to isotopic ages found in the eastern San Juan Islands and in the Shuksan blueschist terrane in the northwest Cascades, and thus fits into an emerging regional age-pattern of blueschist facies metamorphism during Late Jurassic - Early Cretaceous (up to Barremian) but not late Albian - Cenomanian. If this pattern is more broadly confirmed for the San Juan Islands, all the blueschist facies metamorphism can be regarded as having formed in subduction zones elsewhere along the continental margin rather than in the anomalous setting of an on-land thrust system as in the San Juan Islands