Author(s)

Antonio Fernando Menezes Freire, Marcelo Costa Monteiro

Department of Geochemistry, Petrobras Research Center, Rio de Janeiro, Brazil.
Department of Sedimentology and Stratigraphy, Petrobras Research Center, Rio de Janeiro, Brazil.

The ratio of total organic carbon to total nitrogen (TOC:TN) and the stable carbon isotope ratio of organic matter (δ¹³C_org) are widely applied for inferring the origin of organic matter (OM) in Quaternary marine sediments. A plot of TOC:TN vs. δ¹³C_org is useful for such studies but is strongly based on qualitative constraints. This study is based on the qualitative characterization of the source of Quaternary OM via analysis of TOC:TN and δ¹³C_org signatures, but also proposes a probability parameter, which combines both signatures, to infer the amount of Terrestrial OM Input (TOMI). This index provides a method for quantifying the proportion of terrestrial OM vs. marine OMin a more comprehensive manner. The TOMI index concept was applied to a study area in theJoetsuBasin, eastern margin of theJapanSea, where previous studies have characterized theOMfrom the Last Glacial Maximum (LGM) to the present. The upwards increase in TOC indicates thatOMproduction during the Holocene was higher than during the LGM. The enriched δ¹³C_org signature upwards and decrease in TOC:TN suggest predominantly marine phytoplankton OM during the Holocene. Throughout the LGM, low OM production with depleted δ¹³C_org values and high TOC:TN values in the sediments suggest a predominantly C₃ terrestrial plant source for the OM. Using these data, it was possible to calculate a proxy for a sea level variation curve during that period and to investigate the influence of the proximity of the coastal line to the continental slope on the input of terrestrial material to the basin. The proposal provides information for the application of sequence stratigraphic concepts. The TOMI index could confirm that the proximity to the shoreline and shelf break has a strong influence on the input of terrestrial material during lowstand periods.

δ¹³C_org; Joetsu Basin; Japan Sea; Terrestrial Organic Matter Input; TOMI Index; TOC:TN

A. Freire and M. Monteiro, "A Novel Approach for Inferring the Proportion of Terrestrial Organic Matter Input to Marine Sediments on the Basis of TOC:TN and δ¹³C_org Signatures," Open Journal of Marine Science, Vol. 3 No. 2, 2013, pp. 74-92. doi: 10.4236/ojms.2013.32009.