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ABSTRACT: Paleokarst of the Ordovician Maggol Limestone, Taebacksan Basin, South Korea: Implications for Regional Tectonism

Ryu, In-Chang , Korea University, Seoul, South Korea

Carbonate breccias sporadically occur in the Ordovician Maggol Limestone in the Taebacksan basin, South Korea. They typically comprise three-part breccia facies: lower chaotic, middle mosaic, and upper fracture. A three-part breccia facies sequence represents a spectrum of cave-forming, cave-filling, and cave-collapsing processes, which is causally linked to paleokarstification.

The occurrence of karst-related carbonate breccias in the Maggol Limestone neatly coincides with a pronounced drop in second-order sea level at the end of Early Ordovician. Although this sea level drop was recorded as a global paleokarst unconformity elsewhere, conspicuous development of paleokarst unconformity has not been recognized in the Maggol Limestone. This study, however, allows recognition of a diffuse paleokarst zone which is characterized by a thinning-upward stack of peritidal cycles associated with karst-related carbonate breccias near the cycle tops. The paleokarst zone is interpreted to be a consequence of repeated pulses of high-frequency sea level fluctuations of fourth- and fifth-order. This suggests that a substantial tectonic subsidence may have nullified the effect of significant drop in second-order sea level at the end of Early Ordovician. As a result, high-frequency sea level fluctuations may have attributed to the development of multiple stack of karst-related carbonate breccias in the Maggol Limestone. This implication notably contrasts with a slowly subsiding carbonate platform model for the Taebacksan basin as has been previously suggested. The tectonic subsidence at the end of Early Ordovician in the basin may be supported by the coeval off-platform lowstand quartzite lenses as well as tectonic, fault-related carbonate breccias. Here we newly propose that the basin has been changed from a slowly subsiding carbonate platform basin to a rapidly subsiding intracratonic rift basin during the late Early Ordovician.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia