Magnetic polarity sequences from downhole measurements in ODP holes 998B and 1001A,leg 165, Caribbean Sea |
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| Authors: | Louvel Véronique Galbrun Bruno |
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| Institution: | (1) Laboratoire de Mesures en Forage, ODP-NEB, BP 72, 13545 Aix-en-Provence Cedex 4, France;(2) Département de Géologie Sédimentaire, Université Paris VI, ESA CNRS 7073, case 117, 4 place Jussieu, 75252 Paris Cedex 5, France |
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| Abstract: | The magnetostratigraphy of sediments drilled at two sites (998 and 1001) in the Caribbean Sea during the Ocean Drilling Program (ODP) Leg 165 is established directly from downhole measurements. For the first time in the ODP, the magnetostratigraphy of sediments is determined from both logging magnetic data and paleomagnetic analysis of core material for an age interval of about 16 m.y. across the Cretaceous/Tertiary boundary. The total magnetic induction and the susceptibility of the surrounding sediment were recorded in situ and continuously by the GHMT (Geological High-sensitivity Magnetic Tool). The aim of processing these data is to determine the magnetic polarity. At Site 998 (Cayman Rise), no paleomagnetic results are available from the recovered cores given a hard secondary overprint. Nonetheless, a magnetostratigraphic sequence from early Miocene to late Oligocene is proposed from the analysis of the GHMT data. The comparison with biostratigraphic results shows the accuracy of the resulting magnetic polarity. At Site 1001 (Hess escarpment), cores were recovered in two holes thus allowing the comparison of the magnetostratigraphic results obtained from the GHMT data and from paleomagnetic analysis of core samples over a length of 200 m representing about 16 m.y. from early Eocene to late Cretaceous times. The sedimentation rates computed from the determined magnetochrons are very similar and correspond to the ones obtained from shipboard biostratigraphic results. One of the most striking result obtained from the magnetostratigraphic results, especially the GHMT data, at Site 1001, is the abrupt decrease in the sedimentation rate across the K/T boundary. This suppressed sedimentation lasted at least 4 Ma after the K/T event. |
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| Keywords: | Caribbean Sea core-log integration magnetic logging tool magnetostratigraphy Ocean Drilling Program Cretaceous/Tertiary Boundary |
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