OSL dating of marine terrace sediments on the southeastern coast of Korea with implications for Quaternary tectonics

Several flights of marine terraces can be identified along the southeastern coast of Korea. In the Yonghan area, the northern part of this coastline, three sets of marine terraces are usually identifiable; NQt1 (ca. 4 m), NQt2 (ca. 15 m) and NQt3 (ca. 35 m). Aeolian dune sands are well preserved on top of each terrace surface, underlain by palaeo-beach sediments. After various performance tests of the applicability of the single-aliquot regenerative-dose (SAR) protocol (e.g. preheat plateau, dose recovery and thermal transfer tests) we obtained quartz optically stimulated luminescence (OSL) ages ranging between 64±6 and 127±12 ka (NQt3), 51±2 and 80±4 ka (NQt2), and 0.09±0.01 and 0.11±0.01 ka (NQt1) from aeolian dune sands and underlying palaeo-beach sediments on each terrace, all of which appear to be consistent with the established palaeo-sea level record. Of these, the OSL ages of the palaeo-beach sediments from NQt3 (127 ka) and NQt2 (73–80 ka) indicate that these terraces were formed during marine isotopic stage (MIS) 5e and MIS 5a, respectively. We obtained quartz SAR OSL ages of 68±4–92±11 ka from sandy gravel layers collected from the Suryum site (MQt4 terrace, ca. 45 m), where Quaternary faults crosscut the MQt4 terrace. These data, however, do not show an internal consistency in stratigraphic order, and significantly underestimate the expected timing of emergent interglacial high sea stands. Although the reasons for the inconsistency in OSL ages of the samples from the Suryum site (MQt4 terrace) are not well known as yet, the OSL ages of other terrace sediments (the NQt2, NQt3 and MQt2 terraces) imply that, unlike the conventional view, the southeastern part of Korean peninsula has not been tectonically very stable during the Late Pleistocene.