On the palaeomagnetic and rock magnetic constraints regarding the age of IODP 325 Hole M0058A
Emilio Herrero-Bervera, Luigi Jovane, 2013. "On the palaeomagnetic and rock magnetic constraints regarding the age of IODP 325 Hole M0058A", Magnetic Methods and the Timing of Geological Processes, L. Jovane, E. Herrero-Bervera, L.A. Hinnov, B. Housen
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We have studied the rock magnetic and palaeomagnetic properties of a 41 m long core (Hole M0058A) recovering calcareous sediments located seaward of Noggin Reef, offshore Queensland, Australia to decipher the magnetostratigrapy of the site. We deployed 1 cm3 samples at every 10 cm down-core and subsampled the core by means of U-channels in order to obtain a continuous record. Stepwise alternating field demagnetization from natural remanent magnetization to 80 mT showed that the characteristic remanent magnetization was isolated at low demagnetization fields between 0 and 15 mT. We conducted magnetic granulometry analyses and Curie point determinations. The low-field v. temperature analyses indicate the presence of Ti-poor magnetite with Curie points from 560 to 563 °C. Hysteresis loop experiments were performed. The results show Mrs/Ms and Hcr/Hc ratios corresponding to single domain to multi-domain and super-paramagnetic to single domain ranges. Both discrete and continuous inclination results indicate a remarkable correlation of three excursional inclinations occurring during intervals of low intensity of magnetization closely corresponding to the Laschamp (c. 41 ka), Skálamælifell (c. 94 ka) and Blake (c. 115–120 ka) ‘aborted reversals,’ and indicate that the base of the core is much older than the Blake excursion.
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Magnetostratigraphy is best known as a technique that employs correlation among different stratigraphic sections using the magnetic directions defining geomagnetic polarity reversals as marker horizons. The ages of the polarity reversals provide common tie points among the sections, allowing accurate time correlation. Recently, studies of magnetic methods and the timing of geological processes have acquired a broader meaning, now referring to many types of magnetic measurements within a stratigraphic sequence. Many of these measurements provide correlation and age control not only for the older and younger boundaries of a polarity interval, but also within intervals. Thus, magnetostratigraphy no longer represents a dating tool based only on geomagnetic polarity reversals, but comprises a set of techniques that includes measurements of geomagnetic field parameters, environmental magnetism, rock-magnetic properties, radiometric dating and astronomically forced palaeoclimatic change recorded in sedimentary rocks, and key corrections to magnetic directions related to geodynamics, palaeocurrents, tectonics and diagenetic processes.