Extinctions within major pelagic groups (e.g., radiolarians and conodonts) occurred in a stepwise fashion during the last 15 Myr of the Triassic. Although a marked decline in the diversity of pelagic faunas began at the end of the middle Norian, the cause of the middle Norian extinction is uncertain. Here we show a possible link between the end-middle Norian radiolarian extinction and a bolide ...

During the Middle-to-Late Miocene, diatomaceous sediments were deposited in North Pacific margin and marginal basins. The Onnagawa Formation is one of such deposits, which shows cyclic sedimentary rhythms reflecting oscillations marine environment Japan Sea. However, age still poorly constrained due to poor preservation siliceous microfossils. To better constrain its age, we performed U-Pb dati...

Introduction: Cosmic spherules are subspherical to spherical particles of <1 mm diameter which are produced by melting of interplanetary dust and large objects during atmospheric entry. Although cosmic spherules are known principally from the ice sheets of polar regions and Cenozoic deep-sea sediments [1-3], a few spherules older than Mesozoic were recovered from the sedimentary rocks of pelagi...

Silicon isotope ratios (expressed as δSi) in marine microfossils can provide insights into silica cycling over geologic time. Here we used δSi of sponge spicules and radiolarian tests from the Paleogene Equatorial Transect (Ocean Drilling Program Leg 199) spanning the Eocene and Oligocene (~50–23 Ma) to reconstruct dissolved silica (DSi) concentrations in deep waters and to examine upper ocean ...

[1] The reworking of older radiolarian microfossils into near-surface sediments of the tropical Pacific has long been the source of confusion for the development of radiolarian stratigraphy and of puzzlement over the mechanism(s) that could effect such pervasive reworking. Widespread dissolution “pits” in the sediments of the tropical Pacific are believed to be associated with hydrothermal circ...

Major and minor elements of successively collected 70 Middle Triassic radiolarian bedded cherts from the Mino Belt in central Japan were studied. In order to reveal pre-diagenetic, primary geochemical signatures related to marine biogeochemical cycles, composite data of chert-shale couplets in addition to raw data were examined. The results show that Mn, Cu, Sr, Ba and P were supplied significa...

rents; (4) specific water masses; (5) conditions of preservation; (6) presence and strength of upwelling onto shelves and under boundary currents; (7) eutrophic conditions; and (8) tectonic events (isolating radiolarian populations). These biologic indicators and their related forms are useful in determining similar parameters in the fossil record. Studies of radiolarians from Neogene Deep Sea ...

Abstract Siliceous sedimentary rocks are major constituents of the rock succession in Central European part Kulm Basin (Mississippian) and crop out eastern Rhenish Massif western Harz Mountains. These occur five lithostratigraphical units: Oberrödinghausen Formation, subdivided into Kahlenberg Subformation (“Untere Alaunschiefer”) Hardt (“Schwarze Kulm-Kieselschiefer/-Lydite”), Laisa Formation ...