Chemical sedimentology of the Cambrian-Ordovician boundary section at Dayangcha, NE China

Abstract

The Dayangcha section is being considered as potential international stratotype for the Cambrian-Ordovician boundary. It consists of grey bedded limestone with mudstone interbeds. Deposition is believed to have been below normally occurring storm wave base. Strong positive correlation between Al₂O₃ and MgO, K₂O, TiO₂, Fe₂O₃, Be, Cr, Co, Ni, Zn and Ba was found for the section as a whole, indicating that these components are bound to the siliciclastic fraction. The overall composition of the siliciclastic fraction approximates to that of average platform shale. However, minor consistent differences occur between siliciclastic fractions of limestone and mudstone. These differences indicate continental sources of siliciclastics for the mudstones, whereas the limestones were mostly fed by global atmospheric dust. The highly similar results for the Cambrian and Ordovician indicate generally stable conditions across the boundary.

Key Words:

• Cambrian-Ordovician boundary
• hemipelagic limestone
• geochemistry
• main elements
• trace elements
• China