A stratum, which is called the lower Cretaceous Sinuiju Formation, is distributed in the areas of Sonsang-dong, Paektho-dong and Ryonsang-dong of Sinuiju City, North Phyongan Province.
The Sinuiju Formation, 2 320 to 3 280 metres thick, consists of dark gray, light gray and greenish gray and purplish red sandstone, conglomerate, siltstone, mudstone and terrigenous clastic rocks.
According to the characteristics of constituent rocks and arrangement order of strata, the formation is divided into eight members.
The first, third and fourth members are terrigenous clastic rocks, the second member is eruptive or eruptive sediments, and the members from fifth to eighth are eruptive sediments.
The animal and plant fossils are mainly involved in the third and fourth members. Various species of plant fossils and animal fossils, including insects, fishes, conchostracans, ostracods, bivalves, gastropods, archaeopteryx, pterosaur, protomammalia and dinosaur teeth, have been unearthed up to now. They form a biota group. The Korean paleontologists named the biota in the areas as the Sinuiju Biota.
The composition of rocks, sedimentary characteristics and fossils of the Sinuiju Formation are well compared with the Yixian Formation and the Jiufotang Formation in Liaoning Province of China and, in particular, genera and species of most invertebrates (for example, insects, conchostracans, bivalves, gastropods, ostracods, etc.) and plant fossils are almost coincident with them.
Invertebrates are dominant in the whole biota group in the Sinuiju Formation, and other fossils typically known in the Yixian Formation and the Jiufotang Formation (for example dinosaurs, ichthyosauria, shrimps, turtles, choristoderes, squamates, angiosperms, etc.) have not been discovered up to now.
If we discover more diversified and well-preserved fossils in the future by intensifying the studies of the Sinuiju Formation, they will further enrich the Sinuiju Biota.
Prof. and Dr. Won Chol Guk, head of a department
of Kim Il Sung University