Table of Contents
Journal of Geological Research
Volume 2012, Article ID 839840, 14 pages
http://dx.doi.org/10.1155/2012/839840
Research Article

Geochemical Analysis as a Complementary Tool to Estimate the Uplift of Sediments Caused by Shallow Gas Hydrates in Mounds at the Seafloor of Joetsu Basin, Eastern Margin of the Japan Sea

1Petrobras Research Center (CENPES), Department of Geochemistry, Avenida Horácio Macedo 950, Cidade Universitária, Ilha do. Fundão, 21941-915 Rio de Janeiro, RJ, Brazil
2Meiji University, 1-1-1 Higashi-Mita, Tama-ku Kawasaki, Kanagawa 214-8571, Japan
3Diatom Minilab Akiba Ltd., 632-12 Iwasawa, Hanno, Saitama 357-0023, Japan

Received 29 June 2012; Revised 12 August 2012; Accepted 12 August 2012

Academic Editor: Atle Nesje

Copyright © 2012 Antonio Fernando Menezes Freire et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The Holocene sediments of the eastern margin of the Japan Sea are characterized by high total organic carbon (TOC) and total nitrogen (TN) contents, low TOC/TN and TS/TOC values with enriched signatures, as a result of high marine productivity during present oxic highstand. On the other hand, the LGM sediments are characterized by low TOC and TN contents, high TOC/TN and TS/TOC values with depleted signatures, characteristic of C3-derived terrestrial organic matter input during that anoxic lowstand. However, at the top of mounds at the seafloor, where gas hydrate and authigenic carbonate nodules occur, the host sediments have a mixture of both Holocene and LGM geochemical signatures. Both gas hydrate and authigenic carbonate, formed by the anaerobic oxidation of methane, increased the sedimentary volume and caused an uplift of older sediments, inducing mound formation. The thickness of the Holocene sediments over mounds is very small or absent exposing the last glacial maximum (LGM) sediments to the seafloor. The uplift of the LGM sediments within mounds is estimated to be >2 m. We conducted geochemical analysis to detect such sediment movement, using samples collected by shallow cores in the Joetsu Basin, eastern margin of the Japan Sea.