Formation age of Holocene carbonate concretions collected around the Port of Nagoya

Abstract

A large number of carbonate concretion samples were collected during the dredging around Nagoya Port. Most of the concretion samples had biological remains such as crab, sea urchin, and bivalve as their nuclei. In this study, radiocarbon (14C) ages of the shells of the biological remains inside the concretions, as well as of the concretions, were determined. Based on the metabolic carbon ratios in the bivalvia and sea urchin shells calculated from the δ13C values, the 14C age of the shells was estimated to be 7,350−7,050 cal BP. The 14C dates of the carbonate concretions were older than those of the shells due to the metabolic carbon with older ages into the concretion carbon. The corrected age after removal of the old carbon was estimated to be 7,530−7,270 cal BP. The almost the same corrected ages between the shells and the concretions indicate that the carbonate concretions in the Nagoya Port area were formed by rapid concretion after the death of the organisms, which is consistent with the morphological findings of rapid concretion in the sediment.