Structural development and stratigraphy of the Kyokpo Pull-Apart Basin, South Korea and tectonic implications for inverted extensional basins

Abstract

Abstract Field studies indicate that the Kyokpo Basin initially formed as a pull-apart during the Late Cretaceous Period. Syn-sedimentary normal and strike-slip faults suggest early transtensional movements. Fault-plane analysis indicates an approximately E-W extension direction for this early event. The basin filled with a succession of lacustrine deposits interbedded with abundant pyroclastic rocks and rare volcanic flows. Rapid initial subsidence is demonstrated by deep-water sediments that lie directly on pre-Late Cretaceous rocks. All exposed sedimentary facies were deposited in deep-water environments, indicating continued rapid subsidence during deposition of the entire sequence. Laminated grey siltstones interbedded with thin, distal, sandy turbidites are the most abundant sediments. Channels filled with conglomeratic debris flow deposits (clasts as large as 1 m in diameter) cut into the siltstone beds. Massive and graded pebbly sandstone turbidites are also interbedded with siltstone. A thick accumulation of stacked, conglomeratic, debris flow deposits interbedded with sandstone turbidites forms a subaqueous fan complex at the southern part of the outcrop area. Local compression caused up to 3 km of uplift and erosion following deposition of the Kyokpo strata. Thrust faults and small- and large-scale folds were formed by the W-E directed compression. Timing of the compression cannot be determined but probably correlates with a regional late Miocene transpressional event.