Traces of evaporites in Upper Cretaceous lacustrine deposits of Korea: Origin and paleoenvironmental implications

Abstract

Diverse types of halite and sulfate evaporite traces occur in the Upper Cretaceous lacustrine deposits of the Jindong Formation and the Jangdong Tuff in Korea, in which dinosaur tracks are common. The halite traces usually occur as casts or moulds, and they include traces of primary halite hoppers, primary and intrasedimentary skeletal halite, and intrasedimentary tiny halite. The sulfate traces occur as intrasedimentary and displacive casts filled with sediments and sparry calcite, and the casts occur as diverse modes from single crystal casts through nodular aggregates to massive aggregates. Some aggregates of the sulfate casts are aligned in crack pattern, and selective occurrence of the laths in ripple troughs are observed. Soluble sulfate evaporite minerals such as gypsum, glauberite, or mirabilite are probable for the precursors of these traces. These halite and sulfate traces are interpreted to have been formed in a saline lake and mudflats. It is interpreted that meteoric water was responsible for the evaporite precipitation in the Jindong Lake and Jangdong Lake. Recycled brine produced by the repeated dissolution of evaporites might contribute to the evaporite precipitation in the paleo-Jindong Lake and the paleo-Jangdong Lake. The development of saline lake deposits in the Jindong Formation and the Jangdong Tuff suggests that the southern part of the Korean Peninsula remained an inland continental area during the Cretaceous resulting in semi-arid paleoclimatic condition due to an orographic effect by the location of the Korean Peninsula on continental margin in mid-latitude with topographic barriers during the Cretaceous. The occurrence of dinosaur tracks in the lake margin deposits of saline lake with frequent inflow of dilute meteoric water suggests that Upper Cretaceous dinosaurs inhabiting lakes on the Korean Peninsula might have drunken brackish water.