The Tephra Discharged by Catastrophic Caldera-Generating Eruptions in the Central Kurils, and the Turbidite of a Large Holocene Submarine Earthquake As Identified in the Core of Glomar Challenger Site 193, Northwest Pacific

摘要

Abstract This paper presents results of a specialized analysis applied to deposits reached at site 193 which was drilled during the 19th cruise of the drillship Glomar Challenger in the Pacific Ocean east of the Central Kuril Islands. These data can serve as a basis for the initial phase of future submarine tephrochronologic surveys in the area. Special attention was paid to layers, lenses, and spots of tephra of varying composition and thickness, as well as to sediments having a higher admixture of volcanic glass particles. It was found that at least 8 ashfalls have occurred in the area of site 193, of which 7 took place during the last 115 ka. It is shown that these were more likely related to large and caldera-generating explosive eruptions at volcanic centers in the Kuril Islands. Preliminary dating of these has been carried out. For the first time, a core sample was identified to contain turbidite due to a hypothetical submarine earthquake that occurred in the Early Holocene. We suggest a hypothesis to explain why the sea sediment core samples are disrupted, hypothesizing that thick interbeds of water-rich pyroclastic material of aleuropelite dimension were converted to hydrosols by thixotropy.