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Yong Seok Choi1, Yong Il Lee1
(1) Seoul National University, Seoul, South Korea

Abstract: Sequence stratigraphic interpretation of the Lower Ordovicican Mungok Formation, Korea

Hierachically-controlled sequence stratigraphic analysis shows that the Lower Ordovician mixed carbonate-siliciclastic Mungok Formation consists of three depositional sequences: T1, T2, and T3. Sequence boundaries are marked by abrupt facies shifts and may show indication of exposure and low angle truncation.

Sequence T1 overlies the Wagok Formation and comprises the basal portion of the Mungok Formation. Sequence T2 comprises most of the lower half of the Mungok Formation and locally truncates the uppermost bed of sequence T1 showing an angular discordance. Sequence T3 comprise the upper half of the Mungok Formation and is bounded below by a subaerial exposure surface but shows gradational boundary with the overlying Yeongheung Formation.

Within this sequence stratigraphic framework, facies characteristics indicate that the mixed carbonate-siliciclastic sediments of the Mungok Formation were mostly deposited in subtidal environments on low gradient ramps. High-frequency cycles also consist of subtidally-deposited upward-shallowing facies successions. Cycles of shallow-water and basinal deposits are not represented well, probably due to cycle amalgamation. Cycle stacking patterns do not show a consistent thickness change that reflects a large-scale sea-level change. This irregular thickness variation is common in subtidal deposits and is interpreted to have resulted from unfilled accommodation space. In the Mungok Formation frequent storms may have played significant role in controlling the upward limit of sediment accumulation.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana