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a General map of the study area’s plate tectonics boundaries. b The structural map of SE Korea and the Korea–Tsushima Strait region. The Tsushima fault is the principal strike-slip displacement zone dividing the Korea Strait and the Tsushima Strait basins. Land geologic map of SE Korea is simplified from the Korea Institute of Geology, Mining and Materials (KIGAM) (1995), and Quaternary faults are marked by red lines on the map taken from Choi et al. (2007). c Geological structure map of the study area based on an interpretation of the seismic profiles used. Contour lines are in meters
Source publication
We examined the architecture of Pleistocene sequences of the Korea Strait (KS) margin controlled by ocean currents and compressional tectonic regimes, using a dense grid of high-resolution single-channel seismic profiles and sediment cores. Along with uplifted strata featuring an erosional and/or non-depositional flat seabed in the northern shelf o...
Citations
... Furthermore, the study area is sediment-starved due to the absence of a river system. Previous studies reported that the Plio-Quaternary depositional sequences in the continental margin were influenced by sea-level fluctuation, closely related to the regional hydrodynamic conditions, fluvial system, and glacier-influenced sedimentation (Lofi De Schepper et al. 2014;Yoo et al. 2017;Choi et al. 2018Choi et al. , 2019Rovere et al. 2019;Gauchery et al. 2021;Kim et al. 2021;Lee et al. 2022). ...
... Choi et al. (2018) suggested that the late Pleistocene deposits around the Ulsan Sea Channel comprised only the falling stage system tract (FSST) and lowstand system tract (LST) because of the Nakdong River system located away from the shelf margin and unique hydro-condition environment (i.e., dominant unidirectional ocean current). Yoo et al. (2017) and Choi et al. (2019) reported that the Quaternary shelf sequences of the Korea Strait consist of the Pleistocene (FSST and LST on the shelf margin, and highstand system tract (HST) on the shelf) and Holocene (HST, TST and LST) depositional sequences. Hernández-Molina et al. (2000a,b) reported that middle to late Pleistocene-Holocene succession in the Cadiz Margin comprised compound clinoforms correlated to the fifth-order sea-level change. ...
Sequence analysis of 2D seismic profiles and sediment data from the southwestern margin of Ulleung Basin reveals that the latest Neogene-Quaternary deposits comprise five depositional sequences (DS1–DS5), separated by erosional unconformities (H1–H5). The lower two sequences (DS1 and DS2), correlated with the Miocene strata, are acoustically characterized by hummocky and chaotic seismic facies, and were significantly deformed with several faults and folds. During the late Miocene, distinct geologic structures, including the Ulsan Structure (US), Dolgorae Thrust Belt (DTB), and Gorae Structure (GS) were also developed sequentially, which were closely related to formation of lower two sequences. However, the upper three sequences (DS3–DS5), belonging to the Plio-Quaternary strata, is acoustically characterized by well-stratified and prograding reflection configurations, and remained relatively undeformed. The tectonic movement related to the regional structures (US, DTB, and GS) was almost stopped since the Pliocene, whereas the part of the GS has been uplifted until the present. These results indicated that sedimentation for the upper three sequence since the Pliocene was mainly influenced by periodically repeated sea-level changes rather than tectonic activity.
... Sediment samples were collected at 23 sites with depths of 10-20 m in June 2016 using a hand core sampler (Fig. 1). Surface sediment of the survey area was composed of mud and originated from Nakdong River (Choi et al., 2019). Processing of sediment samples and enumeration of the cysts were conducted by the same method as below for cyst observation. ...
Alexandrium catenella was tracked from seed-bed to bloom at a hot spot of cyst deposition on the southern coast of Korea from June 2016 to Feb. 2020. Changes in cyst abundance and germinability from sediment, as well as the vegetative cell abundance and encystment in the water column were intensively monitored. Cyst germination of ca. 73% occurred synchronously in November of 2016 to 2019, when bottom water temperature was around 15 °C. After mass germination, vegetative cells formed a seed populations at low density (<10 cells L⁻¹) during winter. Overwintering populations initiated growth in March and then proliferated into high density (ca. 4 × 10⁴ cells L⁻¹) spring blooms in mid-April 2017 when moderate temperature (15 °C) was recorded. There was no bloom in spring of 2018 and 2019, but small vegetative populations developed. Decline of the spring bloom was followed by massive encystment and an increase in Noctiluca abundance. An average spring encystment ratio of 0.002 was estimated for the study years. Newly formed cysts lay dormant during the warm season lasting about six months and then seeded the next population of vegetative cells. An average contribution ratio of cells recruited from the sediment was ca. 0.09 for seeding winter populations. The range in shift ratios for spring production of a daughter cyst population to prior cyst abundance of the mother population in fall was 0.1 to 0.6 for consecutive years, depending on annual variation of local environments. Tracking mass transformation of A. catenella cysts will contribute to more effective science based management of paralytic shellfish poisoning on the southern Korean coast.
