Cretaceous Palaeomagnetic Results From Murge (Apulia, Southern Italy): Tectonic Implications

Abstract

The Adriatic area is of key importance in the reconstruction of the kinematic history of the Mediterranean region. Concerning its relative position with respect to the African plate, palaeomagnetic studies (Márton & Veljovic 1983; VandenBerg 1983) have found evidence that ‘autochthonous’ Istria and Gargano rotated counter‐clockwise with respect to Africa, after the Cretaceous. However, the geodynamic role of the southern part of Apulia has remained unclear. In order to decide whether the boundary between the Adriatic microplate and Africa may be drawn between Gargano and Murge and whether the different parts of Apulia could have undergone differential rotations after the Cretaceous, we carried out palaeomagnetic investigations in Murge and the Salentina Peninsula. In the field, several carefully selected facies were collected and oriented with a magnetic compass at eight geographically distributed localities (46 sites, 224 cores and 13 hand samples). Because of extremely weak NRM, several sites failed to yield a meaningful palaeomagnetic signal. This category comprises all sites younger than the Turonian bauxite horizon and also six sites of Cenomanian‐early Turonian age. Samples from the remaining sites were subjected to detailed thermal and AF demagnetization. Kirschvink (1980) and subtracted vector analysis, and IRM experiments, including the thermal demagnetization of three‐component IRM. As a result, we were able to demonstrate that some of the sites are devoid of overprint. On the other hand, there were sites with unremovable overprint. the latter were rejected from tectonic evaluation, despite the sometimes high degree of clustering of the individual NRMs within a site: so were those with unstable remanence. Eventually, a Cenomanian‐Turonian palaeomagnetic mean direction was calculated for Murge on a locality (before tectonic correction D= 327°, I= 44°, k= 55. α95= 17°, N= 3, after tectonic correction Dc= 327°, Ic= 38°, K= 76, α95= 15°) and a site (before tectonic correction D= 324°, I= 41°, k= 44, α95= 6.5°, after tectonic correction Dc= 327°, Ic= 40°, k= 42, α95= 6.7°) basis and a palaeomagnetic pole (latitude 56°, longitude 261°) was computed from the tectonically corrected locality mean direction. Since coeval palaeomagnetic poles for Murge, Gargano and Istria cluster, we conclude that the stable part of the Adriatic region moved in a highly integrated manner. Their displacement with respect to Africa has manifested itself in a moderate CCW rotation since the Turonian. Copyright © 1994, Wiley Blackwell. All rights reserved