2010 年 50 巻 5 号 p. 623-632
Progressive change of microfabrics of deep-sea sediments during early diagenesis was analyzed using two drill cores collected from the Sites U1305 and U1306 of the Integrated Ocean Drilling Program Expedition 303 in the Labrador Sea in the northwest Atlantic Ocean. Microfabrics were analyzed by scanning electron microscope and deduced from anisotropy of magnetic susceptibility. Different microfabrics in three layers were distinguished in both cores: Surface layer with general void ratio >2.5, subjacent layer with void ratio 2.5-1.5, and deep layer with void ratio <1.5. Microfabrics of the sediments change downward (toward deeper part), as well as magnetic susceptibility anisotropy. Microfabrics in the surface layer are non-directional and characterized by the presence of many macropores larger than 10 μm in diameter. Clay platelets in this layer are linked to each other with edge-to-edge or high-angle edge-to-face (EF) contact. In the underlying layer, contact relations of clay platelets change to low angle EF type. Coarse siliciclastic fractions of this layer show horizontal preferred orientation, most probably due to overloading of the surface layer. Sizes of macropores decrease to several μm in diameter. In the lowest layer, clay platelets take horizontal preferred orientation according to further burial consolidation. Thus, the microfabrics of the sediments are developed from non-directional to preferred horizontal orientation with burial consolidation by following processes; 1) rotation of coarse grains in the layer with the void ratio >2.5 and 2) change of clay microfabrics in the layer with the void ratio <2.5.
