Cyclic sedimentation across a Middle Ordovician carbonate ramp (Duwibong Formation), Korea |
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Authors: | Yong Il Lee Kiseong Hyeong Chan Min Yoo |
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Institution: | (1) School of Earth and Environmental Sciences, Seoul National University, 151-747 Seoul, Korea;(2) Marine Resources Laboratory, Korea Ocean Research and Development Institute, 425-744 Ansan, Korea |
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Abstract: | Summary The Middle Ordovician Duwibong Formation (about 100 m thick), Korea, comprises various lithotypes deposited across a carbonate
ramp. Their stacking patterns constitute several kinds of meter-scale, shallowing-upward carbonate cycles. Lithofacies associations
are grouped into four depositional facies: deep- to mid-ramp, shoal-complex, lagoonal, and tidal-flat facies. These facies
are composed of distinctive depositional cycles: deep subtidal, shallow subtidal, restricted marine, and peritidal cycles,
respectively. The subtidal cycles are capped by subtidal lithofacies and indicate incomplete shallowing to the peritidal zone.
The restricted marine and peritidal cycles are capped by tidal flat lithofacies and show evidence of subaerial exposure. These
cycles were formed by higher frequency sea-level fluctuations with durations of 120 ky (fifth order), which were superimposed
on the longer term sea-level events, and by sediment redistribution by storm-induced currents and waves. The stratigraphic
succession of the Duwibong Formation represents a general regressive trend. The vertical facies change records the transition
from a deep- to mid-ramp to shoal, to lagoon, into a peritidal zone. The depositional system of the Duwibong Formation was
influenced by frequent storms, especially on the deep ramp to mid-ramp seaward of ooid shoals. The storm deposits comprise
about 20% of the Duwibong sequence. |
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Keywords: | Cyclic sedimentation Carbonate ramp Storm deposits Korea Ordovician |
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