In Sung Paik

Desiccation cracks in vertic palaeosols of the Cretaceous Hasandong Formation, Korea: genesis and palaeoenvironmental implications

Abstract The Hasandong Formation (Upper Cretaceous), Korea contains diagnostic vertic features such as pedogenic slickensides, pseudoanticlines, and large desiccation cracks. The Hasandong vertic palaeosols developed on floodplain deposits and display a diverse range of desiccation cracks, including calcite-filled, vertically stratified, and thin varieties. The calcite-filled cracks are 5–10 cm wide on the surface and up to 60 cm deep, and may have been formed by selective calcite precipitation in the cracks due to preferential vegetation. The vertically stratified cracks are those with crack-fillings having alternating sandstone and mudstone subparallel to crack walls. They are interpreted to have been formed by repeated crack opening and filling at crack margins due to seasonal drying and wetting. The thin cracks are less than 1 mm to a few mm wide and a few cm long, and are recognized by light colour mottling around them. Thin crack development may have resulted from intermittent incomplete cracking during sedimentation. The Hasandong vertic palaeosols have stratigraphic and lateral variations in vertic features, which are attributed to the changes in palaeoenvironments. Deep and large desiccation cracks with unbridged sediment-infilling formed in flood basins. The low topographic position of the distal floodbasin area resulted in weakly developed vertic palaeosols with calcite-filled desiccation cracks and some rhizocretions, and proximal location to a main channel may be responsible for rare development of deep and wide cracks and intercalation with calcrete-intraclast conglomerates. Differences in these vertic features along with interbedded calcic palaeosols may provide useful criteria for the palaeoenvironmental changes in and correlation of the floodplain deposits.

Multiple Tracksites with Parallel Trackways from the Cretaceous of the Yeosu City Area Korea: Implications for Gregarious Behavior in Ornithopod and Sauropod Dinosaurs

At least six sites with multiple parallel ornithopod trackways and one site with three parallel sauropod trackways have been mapped in the track-rich Cretaceous sequence on Sado and Chudo islands, Yeosu City area, South Korea. A preliminary study of the stratigraphic context of these tracks indicates that they were made by gregarious subadult or adult dinosaurs that frequented lake basin settings subject to a cyclic depositional regime and periodic ash fall. Bird and theropod dinosaur tracks also occur in the sequence. Mapped sites reveal between 4 and 14 regularly spaced, ornithopod trackways suggestive of herding behavior. One site reveals an 84 m-long trackway, the longest on record for an ornithopod. Only one site reveals parallel sauropod trackways indicating three animals of equal size traveling eastwards with an inter-trackway spacing of about 2.25–2.5 m. The footprints show well preserved pes claw impressions, slightly wide gauge and large manus/pes ratios (low heteropody). The sedimentological and ichnofaunal sequences share some similarities with the famous Jindong successions 50 km to the east, but they also differ significantly in age and ichnofaunal composition.

Some confierous fossil woods from the Cretaceous of Korea

Thirteen silicified fossil woods were collected from the Cretaceous deposits of Haenam Basin and islands of Gwanmae and Byeongpung, Jeollanam-do as well as from the Cretaceous Dadaepo Formation, Busan, Korea. Anatomical features of all of these specimens showed that they were coniferous woods. On the basis of the detailed anatomical features they were identified asDadoxylon byeongpungense sp. nov.,Cupressinoxylon uhangriense sp. nov.,Taxodioxylon cf.nihongii Nishida et H. Nishida,Taxodioxylon albertense (Penhallow) Shimakura, andMesembrioxylon sp. All of them, exceptMesembrioxylon, are described for the first time from the Korean Peninsula. It should be noted that no dicotyledonous wood has been found from this study. Generally the sampled horizons are considered as Upper Cretaceous with dinosaur footprint fossils. In Japan, the Upper Cretaceous sediments bear abundant dicotyledonous fossils. Therefore further studies should be needed to clarify the age of these horizons and the vegetation in the ancient world with dinosaur.

First record of a complete giant theropod egg clutch from Upper Cretaceous deposits, South Korea

Here, we report the first occurrence of a complete Macroelongatoolithus clutch from outside of China. Excavated from Upper Cretaceous strata of Aphae-do in Shinan-gun, Jeollanam-do Province, South Korea, the clutch of 19 eggs is characterised by large, elongate, symmetrical eggs arranged in a single-layered ring-shaped clutch. Eggs are inclined towards the centre of the 2.3-m diameter clutch, and average 41.17 cm long and 15.58 cm wide. Of the 19 eggs, 8 clearly retain a paired configuration. This specimen represents only the second report of large theropod eggs from South Korea and is the most complete Macroelongatoolithus clutch known from the region to date. Eggshell microstructural features are consistent with Macroelongatoolithus xixiaensis (oofamily Elongatoolithidae), previously known only from Cenomanian strata of southeastern China. This first record of a giant theropod egg clutch, here assigned to M. xixiaensis, extends the stratigraphic and paleogeographic range of Macroelongatoolithus eggs and parent animals to include the Campanian of South Korea.

Time, Space and Structure on the Korea Cretaceous Dinosaur Coast: Cretaceous Stratigraphy, Geochronology, and Paleoenvironments

The stratigraphy, geological ages, and paleoenvironments of the Korea Cretaceous Dinosaur Coast (KCDC) are reviewed and synthesized in order to understand the occurrence and diversity of the vertebrate fossils and track remains in time and space. Various absolute age measurements obtained during the last decade yield new age data to correlate with the dinosaur fossil-bearing Cretaceous deposits in Korea. The radiometric age of the lower (Sindong Group) and middle (Hayang Group) parts of the Gyeongsang Basin (the largest basin of the KCDC) located in the eastern part of the KCDC gives dates ranging from Aptian to Campanian, which is younger than the previous biostratigraphic age estimates, but the results may be influenced by metamorphism. Likewise, radiometric dates from the Cretaceous sequence in the western part of the KCDC give numerical values suggesting a correlation with the Upper Cretaceous Yucheon Group of the Gyeongsang Basin. Dinosaur evidence (e.g., tracks, eggs, bones) along the KCDC is variable in relation to stratigraphy and paleoenvironment. Dinosaur tracks are preserved mostly in stratigraphically higher Cretaceous lake margin deposits, whereas dinosaur bones occur mostly in older Cretaceous floodplain deposits. Most dinosaur eggs are found in Upper Cretaceous deposits, and they occur in floodplain deposits of alluvial fan and meandering river settings. Thus, we conclude that dinosaurs inhabited volcanically influenced, alluvial fan, fluvial plain, and lake margins on the Korean Peninsula throughout the Cretaceous under a semi-arid climate with strong seasonality. The rarer occurrence of dinosaur tracks in older Cretaceous deposits in some basins might be attributed to the limited exposures of lake-margin deposits. It is inferred that the presence of large lakes as water sources, rich vegetation of gymnosperm trees as food, and semi-arid paleoclimatic conditions formed a general landscape and environmental setting favorable for dinosaurs and their preservation in the Cretaceous deposits of South Korea.

High alumina glaucony from the Early Ordovician Mungok Formation, Korea

The Lower Ordovician Mungok Formation in Yeongweol area contains several thin glaucony-bearing horizons. These horizons are located in the peloidal grainstone interval, about 5–10 m above the base of the Mungok Formation. The glauconies are characterized by a granular habit, inherited from the precursor peloids. The glaucony rims were altered to iron oxides. The grains also have shrinkage inner margin girdles and cracks, which are filled with microquartz and quartz and occasionally with illite. The chemical composition indicates that the Mungok glaucony is a highly evolved, high-alumina type. The glauconies show high silica (>50%), high alumina (>12%), and low iron (<10%) contents. The occurrence of glauconies in the lower Mungok Formation indicates that the host sediment was deposited in a shallow, open marine setting during the high stand of sea level.

Miocene Tilia (Malvaceae) woods in Korea: including a new taxon

The Miocene fossil woods with Tilia affinity have been described for the first time in Korea. Two specimens of them were discovered from the fluvial deposits of the Sinjeongri (Lower Coal-bearing) Formation of the Janggi Basin at Donghae-myeon, Pohang City, and one specimen was identified from an exhibited collection in a local company of Ulsan City. These specimens were identified as a new taxon of Tilia wood from the Neogene; that is Tilia koreana sp. nov. Jeong, E.K. et Kim, K. One of the two specimens from the Sinjeongri Formation was identified up to genus level due to poor preservation.

Occurrences and origins of soft-sediment deformation structures in the late Pleistocene marine terrace deposits of the southeastern coast of Korea

Soft-sediment deformation structures (SSDS) are examined in the late Pleistocene marine terrace deposits of the southeastern coast of the Korean Peninsula. The marine terrace deposits are exposed in thicknesses of more than 10 m, and consist of lagoon, foreshore to backshore, coastal dune, and foreshore to backshore deposits in ascending order. The SSDS are restricted to the coastal dune deposits and the upper part of the underlying foreshore to backshore deposits, and are grouped into ductile and brittle deformation structures. The ductile deformation structures include irregular laminations, compacted laminations in the hinge zone of folds, asymmetric folds of foreset laminae, and water escape structures. The brittle deformation structures include syndepositional faults or deformation bands. The most probable triggering mechanism for the SSDS is liquefaction by moderate-magnitude earthquakes (M = 5–5.5). Likely, the SSDS were generated over time in various stress fields, including those of main shocks, aftershocks, and later seismic events. The evolution of the SSDS-bearing deposits in the study area can be summarised as follows: 1) rising of the groundwater table in the coastal dune deposits as a result of seismic shock, 2) formation of SSDS by liquefaction in the lower part of the dune deposits and upper part of the underlying foreshore to backshore deposits, 3) descending of the groundwater table, and 4) deposition of foreshore to backshore deposits on the SSDS-bearing dune deposits with erosion of the top of the dune deposits.

A large and distinct skin impression on the cast of a sauropod dinosaur footprint from Early Cretaceous floodplain deposits, Korea

The occurrence and features of skin impressions in a sauropod footprint, the largest (>50 cm in diameter) reported to date for this taxon, from the Lower Cretaceous Haman Formation (Albian) in Korea are described, and its preservation and paleoenvironmental implications are interpreted. The skin impression-bearing deposits are floodplain sediments formed by sheetflood processes. The large impression is preserved in silty mudstone with microbial lenses and wisps overlying a planar- to cross-laminated and fine-grained sandstone to siltstone bed. The paleoenvironment of the skin impression-bearing deposits is interpreted as a saline sandflat to mudflat where microbial mats can form around lakes or ponds under semi-arid paleoclimatic conditions with alternating wetting and drying intervals. These paleoenvironmental conditions would have permitted the distinct preservation of skin impressions in a dinosaur footprint. The observations here suggest that some sauropod dinosaurs in the Cretaceous had a well-developed polygonal skin texture covering nearly the whole of their foot pads, as seen in modern elephants, which would increase stability when walking on muddy and wet ground.

Miocene fossil plants from the Eoil Basin (Gampo area), Gyeongju, Korea

The Eoil Flora, from two sites of the Gampo Conglomerate and one site of the Eoil Formation in the Eoil Basin, consists of 17 species belonging to 11 families and two angiosperms of uncertain systematic position. The following 14 genera are represented: Equisetum, Sorbus, Ulmus, Fagus, Pterocarya, Alnus, Populus, Salix, Decodon, Acer, “Alangium”, Fraxinus, Dicotylophyllum and Monocotylophyllum. The flora consists mainly of deciduous broad-leaved tree species, dominated by Alnus arasensis followed by “Alangium” aequalifolium. The Eoil Flora represents riparian and surrounding vegetation, as indicated by the mode of fossil occurrence, lithology and sedimentary facies of the plant-bearing beds. The Eoil Flora is comparable to the Janggi Flora of the Pohang area and the Aniaitype floras of Japan. Aniai-type floras, including the Eoil Flora, share features common to broad-leaved deciduous vegetation under mesic to humid temperate climates. This flora also characterizes the paleoenvironment of this region just before the tectonic event associated with the opening of the East Sea (Sea of Japan).