Keywords:ferromanganese crust, Scanning SQUID microscope, magnetostratigraphy, environmental magnetism, age model
Ferromanganese crusts are chemical sedimentary rock composed mainly of iron-manganese oxide. Because the ferromanganese crusts grow very slowly on the sea floor at rates of 3-10 mm/Ma, longterm deep-sea environmental changes can be reconstructed from the ferromanganese crusts. Thus, it is important to provide reliable age model for the crusts. A new technology, scanning SQUID (superconducting quantum interference device) microscope (SSM) has been used for paleomagnetism (e.g. Weiss et al., 2000, 2007; Gattacceca et al., 2006; Fu et al., 2014). SSM enable to obtain magnetic image at a scale of ~0.1 mm by measuring vertical component of magnetic field over geological thin sections. Oda et al.(2011) applied SSM on a ferromanganese crust sample from Shotoku Seamount in the northwestern Pacific and successfully developed age model based on magnetostratigraphy. Recently, Geological Survey of Japan (GSJ), AIST has developed an SSM in collaboration with Kanazawa Institute of Technology (Kawai et al., 2016; Oda et al., 2016). Using the SSM, Noguchi et al (2017) successfully applied the same technique on ferromanganese crust from the Takuyo Daigo Seamount and confirmed that the age model based on magnetostratigraphy is consistent with that based on 10Be/9Be. In addition, they are successful in producing a map of environmental magnetic parameters and suggested an increase in higher coercivity minerals after ~3Ma. In the presentation, environmental magnetic mapping will be conducted together with the magnetostratigraphy for ferromanganese crust samples from Hanzawa Seamount, Ryukyu trench and the Shotoku Seamount.