Early Cretaceous Tectonism and Diatoms in Korea

Abstract

Abstract: The Early Cretaceous Sindong Group, a non‐marine molasse, unconformably overlies the folded earliest Cretaceous Myogok Formation. The tectonism that folded the Jaseong Synthem including the Myogok and other formations is here called the Nakdong‐Jaeryeonggang (N‐J) tectonism. The Oknyeobong and Dabokni Formations are discussed to show that they belong to the Jaseong Synthem. The Dabokni Formation yielded fossil diatoms whose age has been referred as the “earliest Cretaceous” based on the geologically constrained age of the fossil‐bearing deposit. The age of the N‐J tectonism appears Barremian as it is between the Hauterivian Myogok Formation and the Aptian Sindong Group with the TPN (Trigonioides‐Plicatounio‐Nippononaia) fauna. The N‐J tectonism, an orogeny, quite deformed pre‐Aptian strata in Korea, but can hardly find its reported equivalent in NE China. A revised correlation table shows that the Jaseong‐Sindong sequence corresponds to the Jehol Group of China. The Sindong‐Hayang transition was characterized by basin migration and dextral rotation probably caused by the Tan‐Lu fault system in a broad sense.