Palaeomagnetic time and space constraints of the Early Cretaceous Rhenodanubian Flysch zone (Eastern Alps)

© The Authors 2017. The Rhenodanubian Flysch zone (RDF) is a Lower Cretaceous-lower Palaeocene turbidite succession extending for ~500 km from the Danube at Vienna to the Rhine Valley (Eastern Alps). It consists of calcareous and siliciclastic turbidite systems deposited in a trench abyssal plain. The age of deposition has been estimated through micropalaeontologic dating. However, palaeomagnetic studies constraining the age and the palaeolatitude of deposition of the RDF are still missing. Here, we present palaeomagnetic data from the Early Cretaceous Tristel and Rehbreingraben Formations of the RDF from two localities in the Bavarian Alps (Rehbrein Creek and Lainbach Valley, southern Germany), and from the stratigraphic equivalent of the Falknis Nappe (Liechtenstein). The quality of the palaeomagnetic signal has been assessed by either fold test (FT) or reversal test (RT). Sediments from the Falknis Nappe are characterized by a pervasive syntectonic magnetic overprint as tested by negative FT, and are thus excluded from the study. The sediments of the Rehbreingraben Formation at Rehbrein Creek, with positive RT, straddle magnetic polarity Chron M0r and the younger M'-1r' reverse event, with an age of ~127-123 Ma (late Barremian-early Aptian). At Lainbach Valley, no polarity reversals have been observed, but a positive FT gives confidence on the reliability of the data. The primary palaeomagnetic directions, after correction for inclination shallowing, allow to precisely constrain the depositional palaeolatitude of the Tristel and Rehbreingraben Formations around ~28°N. In a palaeogeographic reconstruction of the Alpine Tethys at the Barremian/Aptian boundary, the RDF is located on the western margin of the Briançonnais terrain, which was separated from the European continent by the narrow Valais Ocean

Paleoenvironmental Changes at ODP Site 702 (South Atlantic): Anatomy of the Middle Eocene Climatic Optimum

The Middle Eocene Climatic Optimum (MECO) was an unusual global warming event that interrupted the long-term Eocene cooling trend ca. 40 Ma. Here we present new high-resolution bulk and benthic isotope records from South Atlantic ODP Site 702 to characterize the MECO at a high latitude setting. The MECO event, including early and peak warming as well as recovery to background levels, had an estimated ~300 Kyr duration (~40.51 to ~40.21 Ma). Cross-plots (delta O-18 vs. delta C-13) suggest that the mechanisms driving coupled changes in O and C isotope values across the MECO were weaker or absent before the event. The paleoecological response has been evaluated by quantitative analysis of calcareous nannofossils and benthic foraminifera assemblages. We document a shift in the biogeographical distribution of warm and temperate calcareous nannoplankton taxa, which migrated toward higher latitudes due to increased temperatures during the MECO. Conversely, changes in the organic matter flux to the seafloor appear to have controlled benthic foraminifera dynamics at Site 702. Benthic phytodetritus exploiting taxa increased in abundance coinciding with a positive delta C-13 excursion, ~150 Kyr before the start of the delta O-18 negative excursion that marks the start of MECO warming. Our data suggest that paleoecological disturbance in the deep sea predates MECO delta O-18 excursion and that it was driven by changes in the type and/or amount of organic matter reaching the seafloor rather than by increased temperature

Late Paleocene to Early Eocene Magneto-Biostratigraphy from the Cicogna section (Belluno Basin, NE Italy): A record of continental weathering

During the Late Paleocene-Early Eocene (\u30360 Ma to 50 Ma), Earth's climate experienced a warming trend that culminated at the Early Eocene Climatic Optimum (EECO). The EECO was characterized by warm conditions at even extreme high latitudes, subdued latitudinal temperature gradients, and virtually nonexistent polar ice sheets. The early Paleogene long-term climate was punctuated by several short-lived hyperthermal events, the most prominent of which is the Paleocene Eocene Thermal Maximum (PETM). Here we present paleomagnetic and calcareous nannofossil data from the Tethyan marine Cicogna section (Belluno Basin, NE Italy). The paleomagnetic results, integrated with calcareous nannofossil biostratigraphy, indicate that the Cicogna section extends from Chron C25r to Chron C23r spanning the NP7/NP8-NP12 nannofossil Zones with a relatively constant sediment accumulation rate of \u30318 m/My. Rock-magnetic data show sediment enrichment in hematite-maghemite respect to magnetite generally across the PETM and from \u30354 Ma up to the section top. We observed a correlation between rock-magnetic properties and global climate as revealed by a standard benthic oxygen isotope record from the literature. Our interpretation is that the warm and humid conditions typical of the PETM and the EECO enhanced continental weathering with the consequent production, transport, and sedimentation of more oxidized iron oxide phases (e.g. hematite-maghemite) relative to less oxidized phases (e.g., magnetite). Our temporal coupling between oxidation state of sedimentary magnetic phases and global climate therefore demonstrates the existence in the Paleocene-Eocene of the silicate weathering negative feedback mechanism for the long-term stabilization of the Earth's surfaces temperature as proposed by various authors

The Late Miocene-Early Pliocene Biogenic Bloom: An Integrated Study in the Tasman Sea

The Late Miocene-Early Pliocene Biogenic Bloom (∼9–3.5 Ma) was a paleoceanographic phenomenon defined by anomalously high accumulations of biological components at multiple open ocean sites, especially in certain regions of the Indian, and Pacific oceans. Its temporal and spatial extent with available information leaves fundamental questions about driving forces and responses unanswered. In this work, we focus on the middle part of the Biogenic Bloom (7.4–4.5 Ma) at International Ocean Discovery Program Site U1506 in the Tasman Sea, where we provide an integrated age model based on orbital tuning of the Natural Gamma Radiation, benthic foraminiferal oxygen isotopes, and calcareous nannofossil biostratigraphy. Benthic foraminiferal assemblages suggest changes in deep water oxygen concentration and seafloor nutrient supply during generally high export productivity conditions. From 7.4 to 6.7 Ma, seafloor conditions were characterized by episodic nutrient supply, perhaps related to seasonal phytoplankton blooms. From 6.7 to 4.5 Ma, the regime shifted to a more stable interval characterized by eutrophic and dysoxic conditions. Combined with seismic data, a regional change in paleoceanography is inferred at around 6.7 Ma, from stronger and well-oxygenated bottom currents to weaker, oxygen-depleted bottom currents. Our results support the hypothesis that the Biogenic Bloom was a complex, multiphase phenomenon driven by changes in ocean currents, rather than a single uniform period of sustained sea surface water productivity. Highly resolved studies are thus fundamental to its understanding and the disentanglement of local, regional, and global imprints

The late Miocene-early Pliocene biogenic bloom: an integrated study in the Tasman sea

The Late Miocene-Early Pliocene Biogenic Bloom (∼9–3.5 Ma) was a paleoceanographic phenomenon defined by anomalously high accumulations of biological components at multiple open ocean sites, especially in certain regions of the Indian, and Pacific oceans. Its temporal and spatial extent with available information leaves fundamental questions about driving forces and responses unanswered. In this work, we focus on the middle part of the Biogenic Bloom (7.4–4.5 Ma) at International Ocean Discovery Program Site U1506 in the Tasman Sea, where we provide an integrated age model based on orbital tuning of the Natural Gamma Radiation, benthic foraminiferal oxygen isotopes, and calcareous nannofossil biostratigraphy. Benthic foraminiferal assemblages suggest changes in deep water oxygen concentration and seafloor nutrient supply during generally high export productivity conditions. From 7.4 to 6.7 Ma, seafloor conditions were characterized by episodic nutrient supply, perhaps related to seasonal phytoplankton blooms. From 6.7 to 4.5 Ma, the regime shifted to a more stable interval characterized by eutrophic and dysoxic conditions. Combined with seismic data, a regional change in paleoceanography is inferred at around 6.7 Ma, from stronger and well-oxygenated bottom currents to weaker, oxygen-depleted bottom currents. Our results support the hypothesis that the Biogenic Bloom was a complex, multiphase phenomenon driven by changes in ocean currents, rather than a single uniform period of sustained sea surface water productivity. Highly resolved studies are thus fundamental to its understanding and the disentanglement of local, regional, and global imprints

Modifications in calcareous nannofossil assemblages during the Early Eocene: a tethyan perspective

The available oxygen isotope records indicate a long-term warming trend from the late Paleocene through the early Eocene (ca. 59-52 Ma) that peaked at the Early Eocene Climatic Optimum (EECO) (Zachos et al., 2001). This trend was interrupted by at least two or more prominent carbon cycle perturbations, the PETM at ca. 55.5 Ma and the Eocene thermal maximum 2 (ETM2; also referred to as Elmo, H-1) at ca. 53,6 Ma (Kennett and Stott, 1991; Lourens et al., 2005). Here we present calcareous nannofossil data from the hemipelagic Cicogna section located in the Piave River Valley in north eastern Italy (Dallanave et al., 2009). This continuous sedimentary record was studied to reconstruct the main features in the calcareous nannoplankton communities during this critical interval. As is clearly shown by the results, some of the observed prominent modifications are related to short-lived phases of climate perturbation, as for instance the transient and abrupt appearance of odd species during the PETM or the prominent variations in the relative abundance within the assemblages during these events. These short-term changes are usually transitory and calcareous nannoplankton seem to be able to return back to pre-event state. Nonetheless, the overall shape of calcareous nannofossil assemblages showed long lasting or gradual changes, for example the extinction of genera Fasciculithus and Prinsius, the explosion of Zyghrablithus bijugatus and the gradual decrease of heterococcoliths/nannoliths ratio. Either transient or permanent modifications in calcareous nannofossils are associated to dramatic perturbation of paleoenviromental conditions or long trend climate evolution, respectively. References: Dallanave et al., 2009. Earth and Planetary Science Letters, 285, 39-51. Kennett and Stott, 1991. Nature, 353, 225-229. Lourens et al., 2005. Nature, 235, 1083-1087. Zachos et al., 2001. Science, 292, 686-693

Stable isotope and calcareous nannofossil assemblage records for the Cicogna section : toward a detailed template of late Paleocene and early Eocene global carbon cycle and nannoplankton evolution

We present records of stable carbon and oxygen isotopes, CaCO3 content, and changes in calcareous nannofossil assemblages across an 81m thick section of upper Paleocene-lower Eocene marine sedimentary rocks now exposed along Cicogna 5 Stream in northeast Italy. The studied stratigraphic section represents sediment accumulation in a bathyal hemipelagic setting from approximately 57.5 to 52.2 Ma, a multimillion- year time interval characterized by perturbations in the global carbon cycle and changes in calcareous nannofossil assemblages. The bulk carbonate 13C profile for the Cicogna section, once placed on a common time scale, resembles that at sev10 eral other locations across the world, and includes both a long-term drop in 13C, and multiple short-term carbon isotope excursions (CIEs). This precise correlation of widely separated 13C records in marine sequences results from temporal changes in the carbon composition of the exogenic carbon cycle. However, diagenesis has likely modified the 13C record at Cicogna, an interpretation supported by variations in bulk carbonate 15 18O, which do not conform to expectations for a primary signal. The record of CaCO3 content reflects a combination of carbonate dilution and dissolution, as also inferred at other sites. Our detailed documentation and statistical analysis of calcareous nannofossil assemblages show major dierences before, during and after the Paleocene Eocene Thermal Maximum. Other CIEs in our lower Paleogene section do not exhibit 20 such a distinctive change; instead, these events are sometimes characterized by variations restricted to a limited number of taxa and transient shifts in the relative abundance of primary assemblage components. Both long-lasting and short-lived modifications to calcareous nannofossil assemblages preferentially aected nannoliths or holococcoliths such as Discoaster, Fasciculithus, Rhomboaster/Tribrachiatus, Spenolithus and 25 Zygrhablithus, which underwent distinct variations in abundance as well as permanent evolutionary changes in terms of appearances and disappearances. By contrast, placoliths such as Coccolithus and Toweius, which represent the main component of the assemblages, were characterized by a gradual decline in abundance over time. Comparisons of detailed nannofossil assemblage records at the Cicogna section and at ODP Site 1262 support the idea that variations in relative and absolute abundance, even some minor ones, were globally synchronous. An obvious link is through climate forcing and carbon cycling, although precise linkages to changes in \u3b413C records and 5 oceanographic change will need additional work

Age constraints for the Trachilos footprints from Crete.

We present an updated time frame for the 30 m thick late Miocene sedimentary Trachilos section from the island of Crete that contains the potentially oldest hominin footprints. The section is characterized by normal magnetic polarity. New and published foraminifera biostratigraphy results suggest an age of the section within the Mediterranean biozone MMi13d, younger than ~ 6.4 Ma. Calcareous nannoplankton data from sediments exposed near Trachilos and belonging to the same sub-basin indicate deposition during calcareous nannofossil biozone CN9bB, between 6.023 and 6.727 Ma. By integrating the magneto- and biostratigraphic data we correlate the Trachilos section with normal polarity Chron C3An.1n, between 6.272 and 6.023 Ma. Using cyclostratigraphic data based on magnetic susceptibility, we constrain the Trachilos footprints age at ~ 6.05 Ma, roughly 0.35 Ma older than previously thought. Some uncertainty remains related to an inaccessible interval of ~ 8 m section and the possibility that the normal polarity might represent the slightly older Chron C3An.2n. Sediment accumulation rate and biostratigraphic arguments, however, stand against these points and favor a deposition during Chron C3An.1n