Diagenetic Evolution of Neogene Volcanic Ashes (Celebes and Sulu Seas)

Abstract

Mineralogical and geochemical analyses were performed on 40 ash layers of Pleistocene to late Miocene age, recovered during Leg 124 in the Celebes and Sulu Seas (Sites 767, 768, and 769). They provide information on alteration processes related to burial diagenesis. The zonal distribution of secondary volcanic products emphasizes a major diagenetic change, characterized by the complete replacement of volcanic glass by an authigenic smectite-phillipsite assemblage, in tephra layers dated at 3.5-4 Ma. This diagenetic "event" occurs simultaneously in the two basins, and, on the basis of isotopic data, under low-temperature conditions. It is independent of distinct sedimentation rates and related to a relative quiescence of on-land volcanic activity. This period suggests a more uniform paleooceanographic situation having tectonic significance, and probably reflects a kinetic and environmental control of diagenetic reactions.

Timing, magnitude and geochemistry of major Southeast Asian volcanic eruptions: identifying tephrochronologic markers

“…(, ), Desprairies et al . () and Pouclet et al . () abbreviated in the legend as “Ku09a”, “Ku09b”, “Des91” and “Pou91” respectively.…”

“…() and another 44 tephra layers were studied by Desprairies et al . () and their sources are believed to be in Mindanao and Visayas (Negros) mainly. Around Luzon, 22 tephra layers younger than 870 ka (19 younger than 478 ka) were found in core MD97‐2142 and 10 tephra layers younger than 2.14 Ma were found in core MD97‐2143 (Ku et al ., ).…”

Occurrence of Zeolites in Sedimentary Rocks: An Overview

“…Biogenic silica can be a significant factor in forming both phillipsite and clinoptilolite and has contributed to the formation of clinoptilolite from mafic vitroclastic material (Kastner and Stonecipher 1978) and probably has contributed somewhat to the formation of marine phillipsite from mafic materials (Czynscinski 1973). Desprairies et al 1991). Desprairies et al 1991).…”

“…The general occurrence of phillipsite rather than clinoptilolite in deposits of younger age and shallower depths has been attributed to the dissolution of phillipsite and the precipitation of clinoptilolite, a more stable phase, with the addition of biogenic silica (Couture 1977), i.e. One example of closed-system alteration is provided by drill core of Site 767 in the Celebes Sea (Desprairies et al 1991). This results in zeolitic alteration of silicic glass at sub-bottom depths of as little as 150 m and temperatures of 20°C or less, compared with depths of hundreds of meters and temperatures of 40°-50°C for zeolites in many marine silicic tephra deposits on land (Iijima 1978(Iijima 1988a.…”

Ash layers in deep‐sea sediments as tracers of arc volcanic activity: Japan and Central America as case studies

“…Specific examples show the alteration is due to corrosive bottom water in high latitudes(Gardner et al 1985) and to the seeking of hydrothermal fluids near the sediment surface(Desprairie et al 1991).…”