Magnetostratigraphy and Rock Magnetic Characterization of Baltic Sea IODP Expedition 347 Sites M0059 and M0060.

Abstract:

We have studied the rock magnetic and paleomagnetic properties of a ~205 meter-long composite core from Site M0059 (Little Belt, BSB3) and ~210 meter-long core from Site M0060 (Anholt Loch, BSB1) recovering for the most part clays, (silty) sands, sandy clays and gravel. We deployed 454 (Site M0059) and 297 (site M0060) 8-cc discrete samples at approximately every 50 cm down-core from inside the respective site splices. The magnetic susceptibility (X) of the total of 751 samples was normalized to wet sample mass. We also performed stepwise alternating field demagnetization (AF) of the NRM up to a maximum field of 80 mT and the results show that the characteristic remanent magnetization (ChRM) was isolated by a series of weak AF’s, typically between 0–25 mT, and that a low field of 5 mT removed weak VRM. After the removal of the VRM overprint the NRM intensity of the two sites is characterized by a general positive relationship with (X). The inclination data from both sites show positive and negative inclination values with a certain degree of scattering around 0°. At Site M0059 the upper lithologic units show inclinations that vary within 10 degrees either side of the geoaxial dipole prediction (GAD) for this location. In contrast the inclinations of Site M0060 show greater variability: only a few of the samples from the lower units approach this site’s GAD prediction, although the inclination values in the upper lithologic units are closer to the GAD prediction. Measurements of the temperature dependence of bulk susceptibility (k-T) indicate the presence of at three magnetic mineral phases, which display characteristic Curie point temperatures of 360-400°C, 520 and 575°C for both sites and an additional Curie temperature of 610°C for Site M0060. We have obtained four 14C radiometric age determinations from 4 different stratigraphic levels at site 59A. These dates range in age from 4100+/-100 to 810+/-60 years and allow us to correlate the directional data to the FENNOSTACK regional master curve (Snowball et al. 2007). An interval of relatively steep inclinations between approximately 18 m and 16 m depth in Site M0060 probably corresponds to the period of steep inclination experienced in Fennsocandia between 3090 and 2590 Cal. a BP, which is delimited by inclination features e and e1, respectively, in FENNOSTACK.