The age of the Paludi Formation: a major constraint to the beginning of the Apulia-verging orogenic transport in the northern sector of the Calabria–Peloritani Arc

A stratigraphic revision of the Paludi Formation, cropping out in Northern Calabria on the north-eastern side of Sila Massif, has confirmed that it has been deposited between two main tectonic phases. Actually the formation is involved only by top to the north-east thrusts, different from those separating the crystalline and ophiolitic nappes of Northern Calabria, and rests unconformably on the Sila Unit, the uppermost nappe of the tectonic stack. In the frame of the interpretation of Northern Calabria as a fragment of the Alps, the Paludi Formation play the role of a deposit post-dating the eo-alpine tectonic phases and pre-dating the Apenninic orogenic transport. Therefore the Aquitanian age of the formation, obtained by nannofloras analyses, can be considered the minimum age to the Apulia-verging orogenic transport, witnessed by top to north-east thrusts. It fairly corresponds to the age referred to the Lucanian ocean closure.     

Astronomical tuning of the Tortonian 87Sr/86Sr curve in the Mediterranean basin

ABSTRACT This work presents a detailed ⁸⁷Sr/⁸⁶Sr isotope curve for the interval 7.5–9.7 Ma obtained by a high-resolution analysis (sampling spacing of about 40 kyr) of an astronomically calibrated land-based sedimentary sequence exposed in the central Mediterranean area (Gibliscemi section, southern Sicily). The main aim is to verify a synchronous response of the Mediterranean seawater Sr isotope record to the oceanic forcing on the basis of multiple comparisons of the Gibliscemi record with published coeval ⁸⁷Sr/⁸⁶Sr curves. A good correlation with the ⁸⁷Sr/⁸⁶Sr data from the ODP site 926 (equatorial Atlantic ocean), considered to be the Sr chemostratigraphic reference section for the Late Miocene, and from the Pacific DSDP site 590B was registered. Conversely, the comparison of the Gibliscemi Sr isotope data with ⁸⁷Sr/⁸⁶Sr ratios from the coeval segment of the land-based Sardella section (eastern Mediterranean) shows important differences highlighting a local control on the seawater Sr isotope changes in semi-isolated subbasins within the Late Miocene Mediterranean.     

Magnetostratigraphy of the impact breccias and post‐impact carbonates from borehole Yaxcopoil‐1, Chicxulub impact crater,Yucatán,Mexico

Abstract— We report the magnetostratigraphy of the sedimentary sequence between the impact breccias and the post‐impact carbonate sequence conducted on samples recovered by Yaxcopoil‐1 (Yax‐1). Samples of impact breccias show reverse polarities that span up to ～56 cm into the post‐impact carbonate lithologies. We correlate these breccias to those of PEMEX boreholes Yucatán‐6 and Chicxulub‐1, from which we tied our magnetostratigraphy to the radiometric age from a melt sample from the Yucatán‐6 borehole. Thin section analyses of the carbonate samples showed a significant amount of dark minerals and glass shards that we identified as the magnetic carriers; therefore, we propose that the mechanism of magnetic acquisition within the carbonate rocks for the interval studied is detrital remanent magnetism (DRM). With these samples, we constructed the scale of geomagnetic polarities where we find two polarities within the sequence, a reverse polarity event within the impact breccias and the base of the post‐impact carbonate sequence (up to 794.07 m), and a normal polarity event in the last ～20 cm of the interval studied. The polarities recorded in the sequence analyzed are interpreted to span from chron 29r to 29n, and we propose that the reverse polarity event lies within the 29r chron. The magnetostratigraphy of the sequence studied shows that the horizon at 794.11 m deep, interpreted as the K/T boundary, lies within the geomagnetic chron 29r, which contains the K/T boundary.     

Geometric Brownian motion as a model for river flows

Let X(t) be the flow of a certain river at time t. A geometric Brownian motion process is used as a model for X(t) and is found to give very good forecasts of future flows. The forecasted values generated by this one‐dimensional model are compared with those provided by a deterministic model that requires the evaluation of 18 entries. Based on two important criteria, the stochastic model is superior, on average, to the deterministic model for forecasts up to 4 days ahead. Copyright © 2002 John Wiley & Sons, Ltd.     

Sediment mobility and bedload transport conditions in an alpine stream

The mobility conditions of bedload transport in an alpine high‐gradient step–pool stream (Rio Cordon) are analysed. Since 1986, a device system at the downstream end section of the stream has been operating in order to monitor the water discharge, suspended sediment and bedload transport. Sediment distribution of bedload transported by various floods has been analysed, and equal‐mobility evidence is recognized only for the high‐magnitude flows ever recorded (RI > 50 years). The thresholds for size‐selective and equal‐mobility transport conditions are identified and quantified by using both data provided by the fractional transport rate and by length displacements of marked particles. Size‐selective bedload transport seems to dominate when the critical shear stress of the size fractions τ_ci considered is exceeded, whereas the equal‐mobility condition is approached as levels of excess shear stress become higher (τ_eqi = 1·45τ_ci). Copyright © 2006 John Wiley & Sons, Ltd.