A palaeomagnetic study of the Upper Mesozoic succession in Northern Tunisia

Abstract

Summary. The Upper Mesozoic section from Northern Tunisia provided an Upper Jurassic palaeomagnetic pole of 65.2°S 20.3°E α95= 6.1 calculated from the means of normal and reversely magnetized samples from the uppermost Callovian, Oxfordian, Kimmeridgian and Portlandian rocks. In general the only Cretaceous rocks to yield acceptable results were the few samples collected from fresh outcrops. A polarity sequence can be established for the Upper Jurassic which can be correlated with the oceanic Keathley anomaly sequence. One consequence of the proposed correlation of the oceanic anomaly with the terrestrial palaeomagnetic sequence is to suggest a slightly different age for the Oxfordian‐Kimmeridgian boundary. One interpretation of the frequent intermediate directions of magnetization in the Cretaceous sequence is that there may be a number of unrecognized short period reversals within the Cretaceous and, more particularly, during the so‐called Cretaceous normal period.

Palaeomagnetic study of an allochthonous terraine: the Scisti Silicei Formation, Lagonegro Basin, southern Italy

“…Channell's (1975) results from an E-W anticline at Vietri di Potenza show only two sites with acceptable within-site scatter, of which only one (directed 40°, -25') can be considered to relate to an expectable palaeolatitude. For the Lucania region (Table 2), the results from three allochthonous areas can be considered to possess inclinations, relative to bedding, which correspond in magnitude and sign with contemporaneous palaeolatitudes of both allochthonous areas in Sicily (Catalano et al 198 1 ;Nardi 1982) and an autochthonous block in Tunisia (Nairn, Schmitt & Smethwick 1981). The consistency of the palaeolatitudes, but differences in declinations, observed within nappe structures in Lucania, can be simply explained in terms of the observed differences in orientation of the monoclinical axes in different areas.…”

Mesozoic volcanics of western sicily

“…1 c). The directions of remanence of the rocks may be compared with directions found from sediments in the same units (CHANNELL et al, 1980;NARDI, 1982) and with contemporaneous autochthonous rocks in Sicily (GREoOR et al, 1975;BARBERI et al, 1974;SCHULT, 1973) and Tunisia (NAIRN et al, 1981). In an early study SCHULT (1975) interpreted his measurements in terms of rotation of Sicily, but taking into account the tectonic environment a different interpretation is presented here.…”

“…The directions of magnetization found in sites 11 and 12 (Table 3) are similar to those recorded from the ammonitico rosso within the same tectonic unit (CATALANO et al, in prep). These directions are rotated some 30 ~ clockwise from the directions found in an autochthonous section of upper Jurassic rocks described from northern Tunisia (NAIRN et al, 1981). The dykes at Torrente Forgia, Custonaci have been somewhat less altered and some structure is still recognizable.…”

“…NAIRN (1960) demonstrated differences in direction of allochthonous Stephanian rocks from coeval autochthonous rocks in the St. Etienne coal basin, and KOTASEK and Kp, s (1968) showed a dispersion of remanence directions in Werfenian rocks along a thrust front in Slovakia. One of the key features in the present investigation was the knowledge of remanence directions of the Upper Cretaceous and Cenozoic volcanic rocks of the stable Iblean platform (SCHULX, 1973;BARBERI et al, 1974;GR~GOR et al, 1975).…”

Palaeomagnetic database: the effect of quality filtering for geodynamic studies

“…The palaeopoles from the Caucasus show an elongated, arcuate distribution indicative of rotations among small-scale blocks of different widths (MacDonald 1980). The Tunisian pole (Nairn et al 1981) has a clockwise rotation relative to the African pole and is on the edge of the European palaeopoles. This fact could be a clue to understanding its evolution as being linked to the European plate.…”