심해퇴적물의 자성광물 특성을 이용한 연령결정: 중앙태평양 사례연구

Abstract

Stable oxygen isotope (δ18O) is an easy and accurate age determination tool for well-preserved carbonate-rich Quaternary deep-sea sediments. However, this tool is not applicable in the area where calcareous fossils are absent or diagenetically altered. In such cases, magnetic mineral-based chronology, irrelevant to the carbonate component, can be used as an alternative stratigraphic tool. Under the conditions of the negligible amount of authigenic magnetic minerals, deep-sea sediments are expected to record similar magnetic properties when they are deposited in the areas governed by the same detrital sources and zonal wind system. We tested this hypothesis using two deep-sea sediment cores, PC090301 and PC090302, retrieved from adjacent sites of the Central Pacific (6°40N, 177°28W 5°53N, 177°26W) at water depths of 3409 m and 4136 m, respectively. Foraminiferal δ18O and magnetic properties were analyzed for both cores. The age of PC090301 is well established by correlating between foraminiferal δ18O and the composite global marine δ18O record, whereas PC090302 failed to yield reliable chronology due to the dissolution of foraminifera. Nonetheless, both cores show the remarkable similarity in vertical profiles of magnetic parameters such as ARM, NRM/ARM, and SIRM, implying that the magnetic characteristics of the two cores can be used for stratigraphic correlation. This similarity is likely due to theally altered. In such cases, magnetic mineral-based chronology, irrelevant to the carbonate component, can be used as an alternative stratigraphic tool. Under the conditions of the negligible amount of authigenic magnetic minerals, deep-sea sediments are expected to record similar magnetic properties when they are deposited in the areas governed by the same detrital sources and zonal wind system. We tested this hypothesis using two deep-sea sediment cores, PC090301 and PC090302, retrieved from adjacent sites of the Central Pacific (6°40N, 177°28W 5°53N, 177°26W) at water depths of 3409 m and 4136 m, respectively. Foraminiferal δ18O and magnetic properties were analyzed for both cores. The age of PC090301 is well established by correlating between foraminiferal δ18O and the composite global marine δ18O record, whereas PC090302 failed to yield reliable chronology due to the dissolution of foraminifera. Nonetheless, both cores show the remarkable similarity in vertical profiles of magnetic parameters such as ARM, NRM/ARM, and SIRM, implying that the magnetic characteristics of the two cores can be used for stratigraphic correlation. This similarity is likely due to the