Proc. IODP, 308, Data report: natural remanent magnetization of IODP Holes U1319A, U1320A, U1322B, and U1324B and magnetic carrier identification by scanning electron microscopy

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Chapter contents Abstract Introduction Material and methods Magnetic techniques Scanning electron microscopy techniques Results Paleomagnetic analysis of Brazos-Trinity Basin IV (Holes U1319A and U1320A) Paleomagnetic analysis of the Ursa Basin (Holes U1322B and U1324B) SEM analyses of the magnetic mineral assemblage (Hole U1319A) Summary and outlook Acknowledgments References Figures F1. Map of Gulf of Mexico. F2. AF demagnetization, Sites U1319 and U1320. F3. AF demagnetization, Sites U1322 and U1324. F4. Hole U1319A NRM results. F5. Hole U1320A NRM results. F6. Hole U1322B NRM results. F7. Hole U1324B NRM results. F8. SEM micrographs. Tables T1. Inclination and declination per site. T2. Inclination and declination per core. T3. Semiquantitative EDS analyses. PDF file			Previous \| Next doi:10.2204/iodp.proc.308.209.2009 Introduction During Integrated Ocean Drilling Program (IODP) Expedition 308 in the northern Gulf of Mexico, samples were recovered and subsequently investigated from four drill sites in Brazos-Trinity Basin IV (Holes U1319A and U1320A) and at the continental slope of the Mississippi Fan (Ursa region; Holes U1322B and U1324B) (Fig. F1). Shipboard magnetic measurements on the archive core halves comprised volume-dependent magnetic susceptibility and natural remanent magnetization (NRM), including stepwise alternating-field (AF) demagnetization up to a 30 mT peak field. These two magnetic parameters were correlated to global δ¹⁸O and magnetic susceptibility stacks and combined with ages derived from micropaleontological analyses to establish a preliminary integrated age model that is described in more detail by the Expedition 308 Scientists (2005). Based on this stratigraphy, the entire drilled sediment successions of the Brazos-Trinity Basin IV appear to be younger than 150 ka. Sediments from Ursa Basin are younger and were deposited within the last 60 k.y., during marine isotope Stages (MIS) 1–4. Therefore all four sites have ages that correspond to the normal polarity of the Brunhes Chron (C1n). The NRM signal additionally includes rock magnetic information. Fu et al. (2008) describe the formation of a gyroremanent magnetization (GRM) during AF demagnetization of the sample NRM from Hole U1319A and relate this phenomenon to the presence of diagenetic greigite (Fe₃S₄) layers. This information was subsequently employed in the reconstruction of the geochemical and sedimentological environment in Hole U1319A. We present here the results of our detailed cryogenic magnetometer analyses including NRM intensity, inclination, and declination records for all four recovered drill sites of Expedition 308. Several directional and rock magnetic corrections explained in the following text were applied to enhance the use of this data set. NRM declination additionally served to reorient the drill cores for further tectonic studies. Top of page \| Previous \| Next

Introduction