Sedimentary Processes of Volcaniclastic Sediments, Leg 136

Abstract

Sediment cores recovered from three holes drilled during Ocean Drilling Program Leg 136 include volcaniclastics probably derived from the Hawaiian islands. The volcaniclastics shallower than 10 meters below seafloor are fresh and are composed of basaltic glass (sideromelane), basaltic fragments (mainly tachylite), Plagioclase, olivine, pyroxene, and opaque minerals. Most of these glasses are probably products of hydrovolcanism. Visibly, some of these volcaniclastics are recognized as bedded ash layers having thicknesses that range from 5 to 10 cm. However, many volcaniclastics are disrupted by bioturbation to some degree, and are sometimes totally mixed with ambient brown clays. No visible correlative ash layer among these holes was found. It seems that many ash layers thinner than the bedded layers were disrupted by bioturbation because of the low sedimentation rate of volcaniclastics.The volcaniclastics were probably transported one of two ways: through air fall and pelagic settling or through turbidity-current transport. Other archipelagic apron volcaniclastic sediments of volcanic seamounts suggest that turbidite transport is the favored explanation of origin.

Submarine Mass Movements and Their Consequences

“…Similar submarine landslides have been described in the modern Pacific, Indian and Atlantic oceans. Naka et al (1993Naka et al ( , 2002 described several volcaniclastic sand and silt layers embedded within the pelagic sediments around the Hawaiian Islands. The clast types include altered volcanic glass, volcanic lithic and crystalline fragments, celadonite, and zeolites.…”

“…For example, Whitman et al (1986) Albian to upper Aptian in age and composed of volcaniclastic turbidites. Naka et al (1993Naka et al ( , 2002 interpreted these volcaniclastic turbidites as the products of submarine landslides along the southeastern flank of Hawaii Island. Some of the turbidites contain large amounts of shallow-marine carbonate debris, including ooids, benthic foraminifera, algae, bryozoans, and rudist fragments.…”