연구논문 : 제주도에 분포하는 서귀포층의 퇴적 구조와 생흔 화석의 고환경적 의의

On the basis of sedimentary structures and trace fossils, the Seowipo Formation of Jeju Island is divided into six sedimentary fades; cross-stratified pebbly sandstone facies, shell bed facies, ripple drift cross-laminated sandstone facies, parallel-laminated sandstone facies, massive sandstone facies and mudstone facies. Cross-stratified pebbly sandstone fades which consists of high angle cross stratified sandstones with layers of shell fragments and basalt pebbles seems to be deposited in foreshore environment. Shell bed fades is mainly composed of bioclastic sandstones dominantly with reworked molluscan shells. Its basal part is characterized by Gastrochaenolites and Thalassinoides and contacts erosionally with lower mudstone fades. The upper part of shell bed facies is densely bioturbated and trace fossils Chondrites, Helminthopsis and Thalassinoides are recognized in its upper region. This facies is thought to have been deposited in offshore environment during storm events. Ripple drift cross-laminated sandstone facies consists of laminated sandstones with flaser bedding, lenticular bedding, convolute bedding, ripple drift cross stratification, and low angle cross stratifications resemble hummocky cross stratifications. This fades is considered to have been deposited in shoreface environment which was occasionally storm-influenced. Parallel-laminated sandstone facies dominantly comprises parallel to low angle laminated sandstones which alternates occasionally with mudstones. Relatively diverse trace fossils such as Ophiomorpha, Phycodes, Planolites, Skolithos, Taphrhelminthopsis and Thalassinoides with bivalves are recognized in this facies. This facies seems to have been deposited in foreshore environment. Massive sandstone fades which consists mainly of semiconsolidated massive sandstones with sporadical occurring Ophiomorpha is known to have been deposited in foreshore environment. Mudstone facies representing massive mudstones with occasionally occurred Thalassinoides was probably deposited in the offshore environment. Most of the lithofacies and facies successions reflect that the Seowipo Formation was deposited in the foreshore to offshore environments which was occasionally storm influenced. Trace fossils of 10 ichnogenera and 12 ichnospecies were described from the Seogwipo Formation.