HR: 0800h
AN: GP41F-02    [Abstracts]
TI: Magnetostratigraphy of Lutetian marine sediments in the External Sierras (Southern Pyrenees)
AU: * Rodriguez-Pinto, A
EM: adrianar@unizar.es
AF: Geodinamica Interna. Ciencias de la Tierra, Universidad de Zaragoza, Pedro Cerbuna s/n, Zaragoza, 50009, Spain
AU: Pueyo, E L
EM: unaim@igme.es
AF: Area de Estudios Geologicos. Instituto Geologico y Minero de España, Manuel Lasala 44 9B, Zaragoza, 50006, Spain
AU: Barnolas, A
EM: a.barnolas@igme.es
AF: Area de Estudios Geologicos. Instituto Geologico y Minero de España, Manuel Lasala 44 9B, Zaragoza, 50006, Spain
AU: Pocovi, A
EM: pocovi@unizar.es
AF: Geodinamica Interna. Ciencias de la Tierra, Universidad de Zaragoza, Pedro Cerbuna s/n, Zaragoza, 50009, Spain
AU: Gil-Pena, I
EM: i.gil@igme.es
AF: Area de Estudios Geologicos. Instituto Geologico y Minero de España, Manuel Lasala 44 9B, Zaragoza, 50006, Spain
AU: Villain, J J
EM: villa@ubu.es
AF: Lab. de Paleomagnetismo. Dep. de Física. Universidad de Burgos, Avenida de las flautas 4, Burgos, 06009, Spain
AU: Mochales, T
EM: tania@unizar.es
AF: Geodinamica Interna. Ciencias de la Tierra, Universidad de Zaragoza, Pedro Cerbuna s/n, Zaragoza, 50009, Spain
AU: Mochales, T
EM: tania@unizar.es
AF: Area de Estudios Geologicos. Instituto Geologico y Minero de España, Manuel Lasala 44 9B, Zaragoza, 50006, Spain
AU: Samso, J M
EM: jmsamso@telefonica.net
AF: Area de Estudios Geologicos. Instituto Geologico y Minero de España, Manuel Lasala 44 9B, Zaragoza, 50006, Spain
AB: Magnetostratigraphy has been extensively applied in the southern Pyrenees (Spain). At the moment there are more than 50 km of series most of them in continental and transitional facies and only a few in marine sediments. Seeing that Lutetian age has received very little attention and Ypresian - Lutetian transit in marine series has been rarely studied, in this work we present a composite Lutetian magnetostratigraphic study made of three sections of carbonate platform facies. The composite section has been calibrated with the available biostratigraphic studies (mostly benthonic faunas). The three sections are located in hanging wall of the Southwestern Pyrenean sole thrust (External Sierras). The SIV section (260 m and 105 samples), is located in the southeastern limb of the Balzez anticline, and comprises lower Guara Formation. The BZ profile (600 m and 285 samples) is located in the northwestern flank and cuts a progressive unconformity within the Guara formation. The ISU section (550 m and 237 samples) is located along the Isuela valley immediately south of the well-known Pico del Aguila anticline. In total more than 600 standard cores were sampled every 2 - 3 meters of section. Paleomagnetic analyses were conducted in the University of Burgos paleomagnetic laboratory. Detailed stepwise thermal demagnetization (every 25-50°C) and some AF demagnetizations were able to unravel the NRM components. IRM essays and the thermal demagnetization of three components IRM allowed controlling the magnetic mineralogy. A 2G magnetometer, an ASC TD-SC oven and a M2T-1 pulse magnetizer were utilized. Only one paleomagnetic component has been characterized between 200° - 250° and 450°C - 575°. This component represents a primary record of the Eocene magnetic field because it presents two antipodal directions and passes the fold test (Balzez data). Comparison with the global polarity time scale (GPTS) displays the following correlation; chrons C21 and C20 were unambiguously identified in the SIV section. Chrons C21 to C19 Chrons were identified in Isuela samples as well as in the long BZ section. This data perfectly fits with the expected Lutetian polarity sequence (GPTS). A remarkable result from this study is the lack of coincidence between the base of the Guara Fm. and the base of the Lutetian as it was previously assumed. This study demonstrates that the onset of the Guara platform sedimentation started within the normal polarity of chron 22 during Cuisian (Upper Ypresian) times. These sections, together with future biostratigraphic research, may become in a reference chronologic frame both for the Pyrenean basin and for global studies.
DE: 1520 Magnetostratigraphy
DE: 1535 Reversals: process, timescale, magnetostratigraphy
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly