Magnetic and petrographic properties of ODP Site 120-747 (Table 1)

• Main Authors: Heider, Franz, Körner, Ulrike, Bitschene, Peter Rene
• Format: Dataset
• Language: English
• Published: PANGAEA 1993
• Subjects: -; 120-747; COMPCORE; Composite Core; DEPTH; sediment/rock; DSDP/ODP/IODP sample designation; Hysteresis; Bcr/Bc; coercive field; remanent coercive field; saturation magnetization/ saturation remanence; IRM; median destructive field of isothermal remanent magnetization; Joides Resolution; Leg120; Lithology/composition/facies; Magnetic susceptibility; volume; Ocean Drilling Program; ODP; Sample code/label; Sample code/label 2; Sample comment; Saturation isothermal remanent magnetisation; South Indian Ridge; South Indian Ocean; Antarc*; Antarctica
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.715253; https://doi.org/10.1594/PANGAEA.715253

Carbonate sediments from the Kerguelen Plateau (ODP Leg 120) of Eocene to Pliocene age were investigated with rock magnetic, petrographic and geochemical methods to determine the carriers of remanent magnetization. Magnetic methods showed that the major magnetic minerals were titanomagnetites slightly larger than single domain particles. Submicrometre to micrometre-size grains of titanomagnetite were identified as inclusions in volcanic glass particles or as crystals in lithic clasts. Volcanic fallout ash particles formed the major fraction of the magnetic extract from each sediment sample. Three groups of volcanic ashes were identified: trachytic ashes, basaltic ashes with sideromelane and tachylite shards, and palagonitic ashes. These three groups could be equally well defined based on their magnetic hysteresis properties and alternating field demagnetization curves. The highest coercivities of all samples were found for the tachylite, due to the submicrometre-size titanomagnetite inclusions in the matrix. Trachytic ashes had intermediate magnetic properties between the single-domain-type tachylites and the palagonitic (altered) basaltic ashes with low coercivities. Samples which contained mixtures of these different volcanic ashes could be distinguished from the three types of ashes based on their magnetic characteristics. There was neither evidence of biogenic magnetofossils in the transmission electron micrographs nor did we find magnetic particles derived from continental Antarctica. The presence of dispersed volcanic fallout ashes between visible ash layers suggests continuous explosive volcanic activity on the Kerguelen Plateau in the South Indian Ocean since the early Eocene. The continuous fallout of volcanic ash from explosive volcanism on the Kerguelen Archipelago is the source of the magnetic particles and thus responsible for the magnetostratigraphy of the nannofossil oozes drilled during Leg 120.