Abstract:

Methods of rock-mineral identification, scanning electron microscopy and energy spectrum are used to analyze 115 sediment samples from 10 drilling holes at four sites of ODP Leg 204 in order to make clear the relation between lithology and gas hydrate distribution. We find that the samples are nearly similar to each other in mineral compositions, mainly consisting of clay with minor terrestrial clasts dominated by quartz. The samples are rich in diatom and microfossils (such as foraminifers) and take the forms of diatomaceous clay, foraminiferal diatomaceous clay or tuffaceous and siliceous organic clay. Quartz clasts are mostly angular, and small both in grain size and quantity. The samples show lenticular, crumb and whirl-lamination structures, and mottled texture typical of chaotic accumulation, suggesting deep-sea or semi-pelagic turbidite or interbeds. Since drilling-proved gas hydrate samples are distributed in the turbidite, such sediments are considered as a favorable reservoir for gas hydrate of ODP Leg 204.

Key words: rock-mineral identification, scanning electron microscopy, turbidite, gas hydrate, ODP Leg 204