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Richter, C.
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Richter, C.
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- PublicationRestrictedMagnetobiostratigraphic chronology and palaeoenvironmental history of Cenozoic sequences from ODP sites 1165 and 1166, Prydz Bay, Antarctica(2003-09-15)
; ; ; ; ; ; ; ;Florindo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Bohaty, S. M.; Department of Earth Sciences, University of California, Santa Cruz, CA 95064, USA ;Erwin, P. S.; Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK ;Richter, C.; Ocean Drilling Program, 1000 Discovery Drive, Texas A&M Research Park, College Station, TX 77845-9547, USA ;Roberts, A. P.; School of Ocean and Earth Science, Southampton Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK ;Whalen, P. A.; Department of Geosciences, University of Arkansas, Fayetteville, AR 72701, USA ;Whitehead, J. M.; Department of Geology, University of Nebraska, Lincoln, NE 68588-0340, USA; ; ; ; ; ; A transect of three sites was drilled during Leg 188 of the Ocean Drilling Program (ODP), proximal to the East Antarctic Ice Sheet (EAIS) across the Prydz Bay continental shelf (Site 1166), slope (Site 1167), and rise (Site 1165). We present results of a palaeomagnetic and rock magnetic study of sediments recovered at sites 1165 and 1166. Magnetostratigraphic interpretations are presented for both holes and are mainly constrained by diatom and radiolarian biostratigraphies, interpreted in the light of recent refinements to Southern Ocean zonal schemes and datum calibrations for these microfossil groups. Site 1165 records a history of sedimentation on the continental rise extending back to earliest Miocene times (about 22 Ma). Several long-term changes characterise this record, including an overall trend of decreasing sedimentation rates from the bottom to the top of the hole. There is a progressive decrease in the sedimentation rate above about 308 mbsf (meters below sea floor), which is marked by a transition from dark-grey fissile claystones to greenish-grey diatom-bearing clays. At this transition, ice-rafted debris, sand grains, and total clay content also increase. The chronology presented here indicates a middle Miocene age (~14.3 Ma) for the lithological transition. Correlation to ODP Hole 747A from the Kerguelen Plateau suggests that this lithological transition coincides with the base of the Mi-3/3a δ18O event, which suggests palaeoclimatic control on middle Miocene sedimentation changes at Site 1165. Core recovery was poor at Site 1166. Consequently, the magnetostratigraphic data are of limited value. The deepest cores recovered at Site 1166 record brief intervals in the early history of the EAIS for the Prydz Bay region, extending back through the early stage of glaciation to pre-glacial times. An Early Cretaceous fluvio-lacustrine unit, lagoonal deposits and sandy fluvio-deltaic units of mid-late Eocene age contain a sporadic record of the transition from humid and mild conditions to cool temperate conditions.184 26 - PublicationOpen AccessVariations of the geomagnetic field during the Holocene: Relative paleointensity and inclination record from the West Pacific (ODP Hole 1202B)(2006)
; ; ; ; ;Richter, C.; Department of Geology, University of Louisiana at Lafayette, P.O. Box 44530, Lafayette, LA 70504, USA ;Venuti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Verosub, K.; Department of Geology, University of California at Davis, One Shields Avenue, Davis, CA 95616, USA ;Wei, K. Y.; Department of Geosciences, National Taiwan University, P.O. Box 13-318, Taipei, Taiwan, ROC, 106; ; ; We conducted detailed rock magnetic investigations on 36m of drill core collected during Ocean Drilling Program Leg 195 at Hole 1202B (24◦48.24 N, 122◦30.00 E), in the Southern Okinawa Trough, with the goal of extracting a reliable paleointensity signal with centennial resolution. An age-depth model was established from a chronology obtained by accelerator mass spectromety 14C dating. The sedimentary section spans almost the entire Holocene (0–9.4 kyr) and exhibits sedimentation rates close to 400 cm/kyr. The magnetic properties are dominated by stable, pseudo-single domain magnetite. High-field hysteresis data and the grain-size sensitive ratio of anhysteretic remanent magnetization (ARM) to low field magnetic susceptibility indicate a narrow range of grain sizes and concentrations. Magnetic parameters vary by a factor of 4 thereby fulfilling the usual criteria for a relative paleointensity study. The relative geomagnetic paleointensity was obtained by normalizing the intensity of natural remanent magnetization (NRM) by the ARM and the low field magnetic susceptibility. Both normalizations yield nearly identical results (r = 0.89). Spectral analysis indicates that the record is not significantly affected by local environmental conditions. Comparison of thisWest Pacific paleointensity curve with other curves suggests a geomagnetic origin for the signal. Millennial-scale features of our record correlate to variations of the archeomagnetic dipole moment. This suggest that the sediments at Hole1202B recorded changes of the geomagnetic field over the studied time interval.462 562 - PublicationOpen AccessData report: paleomagnetic and environmental magnetic properties of sediments from site 1202 (kuroshio current)(2005-06-04)
; ; ; ;Venuti, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Richter, C.; University of Lousiana at Lafayette ;Verosub, K. L.; University of California at Davis; ; We present paleomagnetic and mineral magnetic results from ocean sediments from the southern Okinawa Trough (west Pacific). We obtained samples from two holes from Ocean Drilling Program Site 1202 and determined the natural remanent magnetization, magnetic susceptibility, anhysteretic remanent magnetization (ARM), hysteresis properties, and thermomagnetic behavior. Hole 1202A was studied between 100 and 120 meters below seafloor (mbsf) and Hole 1202B between 0 and 140 mbsf, both at 1-cm resolution. Hysteresis properties and thermomagnetic behavior were measured on selected samples. The measurements show a stable magnetization carried by pseudo-singledomain- sized low-titanium magnetite. Magnetic inclinations are predominantly positive and record the Brunhes (C1n) normal polarity chron. Susceptibility and ARM, as well as the environmentally significant rock magnetic ratios (ARM/k and ARM30 mT/ARM0 mT), reflect changes in sediment input from Taiwan and the East China Sea continental shelf changes in the path of the Kuroshio Current and changes in climatic conditions.427 259