Log Radius ( m m)
Fig. 8 ( a - d ) SEM images of dark bands from sample 6K#893 R-3. ( a ) Based on grain size differ-
ences, we can differentiate DB-1 and SS. DB-1 is less granular than SS. ( b ) Scaly particles (prob-
ably smectite) are observed at the margin between DB-1 and SS. ( c ) A difference in particle
arrangement in DB-2 and MS-1 or −2 is observed around DB-2. ( d ) Deformed clay particles at the
boundary between DB-2 and MS-2. Based on XRD analysis, the clay particles are smectite.
( e ) XRD analysis of clay minerals in MS-1, DB-1, and SS after ethylene-glycol treatment. ( f ) Porosity
and pore size distributions of MS-1, DB-1, and SS (measured by mercury intrusion porosimeter)
The porosities of SS and MS-1 in the sample are all about 22%, whereas the
porosity of DB-1 is about 7% lower (Fig. 8f ). Computer tomography (CT) images
also show that the density of DB-1 is higher than that of the host rocks. A porosity
reduction such as this can be caused by dehydration and/or compression because the
void space collapses as clay flakes assume the preferred orientation (Hirono 2005 ).