Diagenetic effect on magnetic properties of marine core sediments from the southern Okhotsk Sea

Abstract

It is well known that magnetic records of marine sediments are affected to a certain degree by early diagenesis, the extent and mode of which are controlled by depositional environments. In order to investigate variations in the effects of early diagenesis, we have analyzed 11 gravity cores estimated to be Holocene in age that constitute a depth transect off the southern coast of the Okhotsk Sea. The rock magnetic parameters have peaks produced by the presence of volcanic ashes, basaltic granules and/or relatively coarser-grained layers. The concentrationdependent parameters display characteristic trends of a rapid decrease within the homogeneous silty clay zone in the middle parts of the cores, assuming that the total amount of magnetic minerals decreases through early diagenesis at this interval. This decrease is found in all of the cores from the transect (from both near-shore and offshore sites). In near-shore sites where larger volumes of organic materials are supplied compared to offshore sites, the depth of the decrease in magnetic minerals is relatively shallow. These results imply that the presence of organic materials accelerates the pyritization through the bacterial reduction of ferric ion, thereby causing the decreases in magnetic minerals to become shallower.

Sea-ice distribution and atmospheric pressure patterns in southwestern Okhotsk Sea since the Last Glacial Maximum

“…No 14 C age measurements using foraminiferal tests were performed on core GH00-1002 because of poor carbonate preservation. Age model for core GH00-1002 was constructed mainly on the basis of tephrostratigraphy (Kawamura et al, 2007) and bulk organic carbon (BOC)-based 14 C ages. Linear sedimentation rate between the upper 2 points of the BOC-based 14 C ages intersects at 3800 yrBP of the volcanic ash Ta-a (1739 AD).…”

Influence of seawater exchanges across the Bab-el-Mandeb Strait on sedimentation in the Southern Red Sea during the last 60 ka

“…The most striking feature is that the TOC/CaCO 3 profile is negatively correlated with the magnetic susceptibility normalized with respect to Fe (i.e., dilution‐corrected, Figure ). This relationship suggests that preservation of magnetite is inversely related to the TOC, an observation that has been frequently reported [ Abrajevitch and Kodama , ; Froelich et al ., ; Karlin and Levi , ; Kawamura et al ., ; Leslie et al ., ; Liu et al ., ; Richter et al ., ; Roberts and Turner , ; Robinson et al ., ; Rowan et al ., ]. High TOC values associated with low K levels reflect, therefore, diagenetic dissolution of magnetite while low TOC and high susceptibilities indicate very low iron reduction [ Snowball , ].…”

Relevance of magnetic properties of soil in the magnetic observatories to geomagnetic observation

“…This idea is also applicable to non-volcanic areas in Japan, because surface soil in Japan often contains materials of a volcanic origin. For example, many volcanic tephra layers are widespread within sediments in Hokkaido (Machida and Arai, 2003) and some of them show strong magnetic susceptibility (Kawamura et al, 2007). The change in soil magnetization produced by a change in the ground temperature has also been suggested as a possible cause of the change in geomagnetic observational data at observatories in Japan (e.g., Ogawa and Koyama, 2009;Yamazaki et al, 2012).…”