Depositional facies, architecture and environments of the Sihwa Formation

Abstract

This paper presents detailed facies and architectural analyses and palaeoenvironmental reconstruction of the Sihwa Formation (Lower Cretaceous), mid-west Korea, which comprises an about 3-km-thick non-marine succession containing abundant dinosaur eggshells. Based on constituent facies, bedset geometry, stacking pattern, and bounding surface characteristics, the entire succession can be classified into three architectural elements. Element I occurs along the basin margin and shows a monotonous stacking of tabular or crudely stratified conglomeratic units. It represents alluvial-fan deposits of debrisflow- dominated fan and sheetflood-dominated fan. Element II is characterized by multi-storey, sheet or upward-widening, conglomeratic channel-fills whose maximum thickness exceeds 1.5 m. Each channelfill unit is encased within red？brown silty sandstones of Element III with sharp erosional bases but diffuse gradational upper boundaries. It consists generally of (1) cut-and-fill deposit (trough crossstratified or openwork conglomerate) in the lower part and (2) composite low-relief bar deposit (lenticular conglomerate and stratified gravelly sandstone) in the upper part. Shallowness of each cutand- fill unit, absence of fining-upward lateral accretion package and the predominance of simple-bar deposit collectively suggest deposition from ephemeral braided streams. Element III typically shows a fining-upward stacking of (1) single- or multi-storey small-scale (