HR: 0800h
AN: GP21A-10    [Abstracts]
TI: Palaeomagnetic and AMS Study of the Tarfaya Coastal Basin (Morocco): a new Cenomanian/Turonian (~94 Ma) Paleopole for the African Plate
AU: Palencia-Ortas, A
EM: ali@fis.ucm.es
AF: Dpto Geisica, Fac CC Fisicas, Universidad complutense de Madrid, Avda Complutense s/n, Madrid, 28040, Spain
AU: * Ruiz-Martinez, V C
EM: vcarlos@fis.ucm.es
AF: Dpto Geisica, Fac CC Fisicas, Universidad complutense de Madrid, Avda Complutense s/n, Madrid, 28040, Spain
AU: Villalain, J J
EM: villa@ubu.es
AF: Dpto Fisica, Universidad de Burgos, Burgos, 09006, Spain
AU: Martin-Hernandez, F
EM: fatima@geo.uu.nl
AF: Paleomagnetic Laboratory Fort Hoofddijk, Utrecht University, Utrecht, Netherlands
AU: McIntosh, G
EM: gregc@fis.ucm.es
AF: Dpto Geisica, Fac CC Fisicas, Universidad complutense de Madrid, Avda Complutense s/n, Madrid, 28040, Spain
AB: The Cenomanian/Turonian oceanic anoxic event (OAE2) is a transgressive phase that is registered as a cyclic marine sedimentation in the outcrops from the Tarfaya coastal basin. Very high sedimentation rates (av. 5-10 cm/ka) enables the investigation of past geomagnetic field record at high temporal resolution. With the aim of studying the magnetic signature of these key sediments, 114 samples have been sampled along a 15m vertical profile (approximately 150-300 ka) of orbital-scale forced sedimentation. Rock magnetic investigations reveal mineralogy principally controlled by the diamagnetic and paramagnetic matrix, along with very low concentrations of low coercivity, ferromagnetic material which is probably an iron sulphide. Anisotropy of magnetic susceptibility is dominated by the dia-/para-magnetic matrix. A well-defined fabric can be seen with the minimum susceptibility axis perpendicular to the foliation plane, and the magnetic lineation oriented NNW-SSE. The magnetic lineation, rotated to the position of Africa in the late Cretaceous, is compatible with extension associated with the opening of the proto-North Atlantic Ocean and/or the paleocurrent associated with the upwelling system deposition that occurred during the late Cenomanian/early Turonian marine transgression. Thermal and Alternating Field demagnetizations of the marine samples from Tarfaya Basin show a single, stable, low coercivity and low unblocking temperature directional component. Some intervals of reversal polarity have been found (apparently without a lithological control), suggesting the record of very short reversal polarities events (even assuming an "early" diagenetic remanence blocking in the entire section), though contradictory magnetic interactions related to iron-sulphide ferromagnetic minerals can't be excluded. The new paleopole obtained in this African craton platform, 94 Ma ago, confirm the Late Cretaceous segment of the synthetic Apparent Polar Wander path proposed for Africa (BC02).
DE: 1518 Magnetic fabrics and anisotropy
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 1540 Rock and mineral magnetism
DE: 8157 Plate motions: past (3040)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly