A. Kopf et Jh. Behrmann, FABRIC EVOLUTION AND MECHANISMS OF DIAGENESIS IN FINE-GRAINED SEDIMENTS FROM THE KITA-YAMATO TROUGH, JAPAN-SEA, Journal of sedimentary research, 67(3), 1997, pp. 590-600
In a study of fabrics in clay-rich sediments from Site 799 of the Ocea
n Drilling Program (ODP), located in the Kita-Yamato trough (Japan Sea
), we have investigated the relationships between diagenetic processes
and evolution of petrofabric, magnetic fabric, and related pore-space
reduction. Position fabrics, shape preferred orientations (SPO), and
crystallographic preferred orientations (CPO) in the sediments were qu
antified using optical microscopy and X-ray texture analysis. Commonly
, uniaxial vertical shortening resulting from progressive loading of t
he sediment pile by burial and loss of pore space by dewatering is wel
l imaged in the building of preferred orientation fabrics, SPO of illi
te flakes and CPO of smectite (001) poles are axially symmetric around
the core axis (the vertical), with fabric intensities increasing with
depth. These fabrics are proposed to have evolved from initially rand
om orientation distributions of flocculated clay fallout from an oxic
bottom water column. Distortion of arrays of marker particles, such as
organic detritus, biogenic microclasts, and framboidal pyrite, corrob
orate these results. Magnitudes of uniaxial vertical shortening calcul
ated from loss of porosity and petrofabric parameters are roughly simi
lar, Intergranular slip and distortion of grains facilitating pore-spa
ce collapse are the dominant deformation mechanism. Solution and preci
pitation of SiO2 is an important additional fabric-building mechanism
below the opal-A/opal-CT transition at 450 m depth, Below this depth,
smectite fabrics are also randomized by recrystallization.