The significance of Messinian occurrences of Globorotalia margaritae and Globorotalia puncticulata in Sicily

Globorotalia puncticulata and Globorotalia margaritae are critical species that define internationally recognized planktonic foraminiferal biozones in the Pliocene. These biozones are defined from stratotype sections on Sicily and their fauna are commonly considered to have been introduced to the Mediterranean after an influx of Atlantic water that terminated the late Miocene desiccation of the basin. Herein new discoveries of these species in rocks that predate the late Miocene desiccation are described. These data are supported by magneto- and lithostratigraphy that have been integrated at a single continuous section. Not only do these discoveries question the existing foraminiferal biozone stratigraphy, they also suggest new models for the dispersal of planktonic species. It is proposed that Globorotalia puncticulata and perhaps even Globorotalia margaritae evolved in the Mediterranean during earliest Messinian times (during or before chron C3Bn1n) and dispersed into the Atlantic. This suggests that a marine connection remained between the two sea areas until at least chron C3An.1n. Using the existing geomagnetic polarity time scale, these occurrences are some 2 Myr earlier than previously recorded in the Mediterranean. The distribution of G. margaritae and G. puncticulata in Mediterranean sections is likely to reflect palaeoenvironment or the preservation of deposits rather than the absolute age of the sediments.     

FORWARD MODELING IN THE FREQUENCY-SPACE DOMAIN*

Forward modeling of zero-offset data is performed in the frequency-space domain using a one-way extrapolation equation. The use of the frequency domain offers several advantages over conventional time domain methods. The greatest advantage of the frequency domain is that all time derivatives are evaluated exactly by a simple multiplication. Synthetic zero-offset sections are computed with a high degree of accuracy for arbitrary velocity and reflectivity structures. Examples are shown for realistic complicated models and compared with results from physical modeling.     

Remarks on the magnetic support of quiescent prominences

The development of magnetic field structures which can lead to prominence configurations of the Kuperus-Raadu type is discussed. Starting from streamer type configurations and preserving the total current in the system we find that simple two-dimensional static configurations lead to prominences which in general lie systematically much lower than the heights found from observations. We therefore conclude that either more complex field configurations are needed to explain the recent observations by Leroy et al. (1983) or the initial configurations must be very special.