High‐resolution chronology of sediment below CCD based on Holocene paleomagnetic secular variations in the Tohoku‐oki earthquake rupture zone. (13th August 2017)

• Record Type: Journal Article
• Authors: Kanamatsu, Toshiya; Usami, Kazuko; McHugh, Cecilia M. G.; Ikehara, Ken
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 18:Number 8(2017)
• Page Start: 2990
• Page End: 3002
• Publication Date: 2017-08-13
• Subjects: paleomagnetic secular variation -- lock‐in depth -- tephra -- deep‐sea sediment; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1002/2017GC006878
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: Using high‐resolution paleomagnetic data, we examined the potential for obtaining precise ages from sediment core samples recovered from deep‐sea basins close to rupture zones of the 2011 and earlier earthquakes off Tohoku, Japan. Obtaining detailed stratigraphic ages from deep‐sea sediments below the calcium compensation depth (CCD) is difficult, but we found that the samples contain excellent paleomagnetic secular variation records to constrain age models. Variations in paleomagnetic directions obtained from the sediments reveal systematic changes in the cores. A stacked paleomagnetic profile closely matches the Lake Biwa data sets in southwest Japan for the past 7000 years, one can establish age models based on secular variations of the geomagnetic field on sediments recovered uniquely below the CCD. Comparison of paleomagnetic directions near a tephra and a paleomagnetic direction of contemporaneous pyroclastic flow deposits acquired by different magnetization processes shows precise depositional ages reflecting the magnetization delay of the marine sediment record. Plain Language Summary: Generally obtaining detailed ages from deep‐sea sediments is difficult, because available dating method is very limited. We found that the deep‐see sediment off North Japan recorded past sequential geomagnetic directions. If those records correlate well with the reference record in past 7000 years, then we could estimate age of sediment by pattern matching. Additionally a volcanic ash emitted in 915 A.D., which was intercalated in our samples, indicates a time lag in our age model. This observation makes our age model more precise. Key Points: Construction of paleomagnetic secular variation stacks in Japan Trench, north Japan for the last 7000 years Declination variation for the last 3000 years is robust record for the chronology Estimation of lock‐in depth by a well‐dated tephra horizon