Darriwilian carbon isotope stratigraphy in the Taebaeksan Basin, Korea and its implications for Middle Ordovician paleoceanography

Abstract

The middle Darriwilian carbon isotope excursion (MDICE) event is first documented from central eastern Korea (Taebaeksan Basin), the eastern part of the Sino-Korean Block, and is well correlated with global carbon isotope chemostratigraphy. The Korean MDICE record shows three broad positive peaks and complements records from the Middle Ordovician peri-Gondwanan epeiric seas showing incomplete records due to disconformity. This study reconstructed paleoceanographic conditions with nitrogen isotopic compositions and clay mineral compositions to understand the causes of carbon isotope excursions. The heavier excursion in nitrogen isotopic curve and abrupt increase of kaolinite in the early MDICE interval are interpreted as a result of epeiric sea denitrification associated with strong seawater stratification, and the main cause of those conditions was likely increased precipitation in the adjacent land. Subsequent sea-level rise caused an anti-estuarine circulation in the Taebaeksan sea and increased the organic carbon burial in the adjacent basin setting, which might have sustained the MDICE. The documentation of the MDICE event in this study supports the view that the MDICE occurred globally. This study provides not only information on the regional paleoceanographic conditions that occurred in the Middle Ordovician epeiric seas during the course of MDICE, but also reports that the MDICE event occurred as a response to seawater circulation associated with global sea-level rising in the Middle Ordovician.