• Economic and Environmental Geology
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• v.36 no.6
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• pp.491-499
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• 2003

The Okinawa Trough is a rift basin formed by extension. Analysis of multichannel seismic reflection profiles from the northwestern margin of the northern Okinawa Trough reveal that the trough is characterized by a series of tilted fault blocks bounded by listric normal faults and half-grabens developed between blocks, showing typical rifted structures. The trough display three kinds of sedimentary sequences with different seismic reflection characteristics: prerift, synrift and postrift sediments. The prerift sequence develops parallel to the dip direction of tilted fault blocks. The synrift sediments, mostly deposited in the half-grabens between tilted fault blocks, are generally well characterized by divergence of the reflectors towards the blocks indicating contemporaneous deposition during tilting. The postrift sediments are featured by continuous and parallel reflectors. The width of the half-graben and the throw-displacement rate of the basin bounding fault are closely connected. The throw-displacement rate is the maximum when the rifting event is the most active and the width of the half-graben is proportional to the rate.

• Journal of the Korean Geophysical Society
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• v.7 no.3
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• pp.225-232
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• 2004

To investigate the depositional environment and the geological structure of the Jeju Basin in the South Sea of Korea, we acquired 54-channel seismic data of about 1,980 line-km. The study area lies at the northeastern part of the East China Sea Trough, a Tertiary back-arc basin. The sedimentary basin formed by rifted activities resulted in the formation of graben and/or half-graben structures. The basin is composed of pre-rift, syn-rift and post-rift sediments bounded by regional unconformity. The pre-rift and syn-rift sediments consist of Oligocene, Early and Middle Miocene sequence, whereas the post-rift sediments consist of Late Miocene and Plio-Pleistocene sequences. Seismic and well data from the Jeju Basin indicate that Oligocene-Miocene sediments were deposited under fluvial and lacustrine depositional conditions. Following compressional tectonic movements in the Late Miocene time and a subsequent period of erosion, regional subsidence during the Pliocene time brought the Jeju Basin under marine conditions, resulting in the deposition of dominantly marine sediments.

• The Korean Journal of Petroleum Geology
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• v.14 no.1
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• pp.53-62
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• 2008

Seismic interpretation was carried out based on biostratigraphy of Fukue-1 well in Japan side of the Domi Basin and compared with the Cheju Basin and Tertiary basins in north-west Kyushu. East China Sea Basin including Domi Basin began to develope in the latest Cretaceous$\sim$Paleocene related to rifting. The basin was filled with a thick package of syn-rift sediments during Paleocene to Oligocene and was under post-rift stage effected by transtenssion during Miocene. Previous studies suggest that the basin had been mostly filled with Miocene formation (>3 km), but the Miocene formation is interpreted to be comparatively thin in this study. The thickness of the Miocene formation varies from tens of meters to hundreds of meters and become thicker to the south-west of Cheju Basin. The index taxa of the Oligocene$\sim$Eocene nannofossils and dinoflagellates found in the Cheju Basin and Tertiary basins in north-west Kyushu also corroborate the result of this study.

• Proceedings of the KSEEG Conference
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• 2005.04a
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• pp.317-319
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• 2005

• The Korean Journal of Petroleum Geology
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• v.9 no.1_2 s.10
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• pp.16-23
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• 2001

The study area in the East Sea is located on the northeastern margins of the Ulleung Basin near the Kita-Yamato Bank. The research area provides the important clue to the development of Miocene basins which are characterized by the normal faults and volcanic activities related to rifting in the continental crust. Kita-Yamato Bank is a small sediment-filled graben which was formed by failed rifting in the Early Miocene. The basins rapidly vary the bathymetry, depth of acoustic basement and thickness of sedimentary layer. The tension in the study area caused the extensional lithospheric deformation before/during the Early Miocene. In consequence, tectonic forces resulted in the depression or subsidence of basement from continental rifting in the Kita-Yamato Bank followed by the opening of the Ulleung Basin, and caused the onset of graben or half-graben structure bounded by large blocked syn-rift faults. Afterward no significant tectonic deformation exists, with the consequence that post-rift normal faults with small heave were formed and reactivated by the resultant forces such as tectonic subsidence, sediment loading and volcanic activity. The Cenozoic sediment layer has a maximum thickness of 1.0 s along the center of the graben or half-graben, which overlies the consolidated acoustic basement. Seismic units V and IV supposed to be syn-rift sedimentary rocks are deformed by both the volcanic activities and numerous basement-involved normal faults induced from extension. In the uppermost layer, slump scars resulted from the slope failure are recognized.

• Economic and Environmental Geology
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• v.40 no.4
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• pp.473-490
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• 2007

Strata of the Kachi-1 well, Kunsan Basin, offshore western Korea, were analyzed by using integrated stratigraphy approach. As a result, five distinct unconformity-bounded units are recognized in the well: Triassic, Late Jurassic-Early Cretaceous, Early Cretaceous, Late Cretaceous, and Middle Miocene units. Each unit represents a tectono-stratigraphic unit that provides time-sliced information on basin-forming tectonics, sedimentation, and basin-modifying tectonics of the Kunsan Basin. In the late Late Jurassic, development of second- or third-order wrench faults along the Tan-Lu fault system probably initiated a series of small-scale strike-slip extensional basins. Continued sinistral movement of these wrench faults until the Late Cretaceous caused a mega-shear in the basin, forming a large-scale pull-apart basin. However, in the Early Tertiary, the Indian Plate began to collide with the Eurasian Plate, forming a mega-suture zone. This orogenic event, namely the Himalayan Orogeny, continued by late Eocene and was probably responsible for initiation of right-lateral motion of the Tan-Lu fault system. The right-lateral strike-slip movement of the Tan-Lu fault caused the tectonic inversion of the Kunsan Basin. Thus, the late Eocene to Oligocene was the main period of severe tectonic modification of the basin. After the Oligocene, the Kunsan Basin has maintained thermal subsidence up to the present with short periods of marine transgressions extending into the land part of the present basin.

• Economic and Environmental Geology
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• v.51 no.3
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• pp.233-248
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• 2018

Strata of the Central sub-basin in the Gunsan Basin, offshore, western Korea were analyzed by using integrated stratigraphy approach. As a result, five distinct unconformity-bounded units are recognized in the basin: Sequence I (Cretaceous or older(?)), Sequence II (Late Cretaceous), Sequence III (late Late Cretaceous or younger(?)), Sequence IV (Early Miocene or older(?)), Sequence V (Middle Miocene). Since the late Late Jurassic, along the Tan-Lu fault system wrench faults were developed and caused a series of small-scale strike-slip extensional basins. The sinistral movement of wrench faults continued until the Late Cretaceous forming a large-scale pull-apart basin. However, in the Early Tertiary, the orogenic event, called the Himalayan Orogeny, caused basin to be modified. From Late Eocene to Early Miocene, tectonic inversion accompanied by NW strike folds occurred in the East China. Therefore, the late Eocene to Oligocene was the main period of severe tectonic modification of the basin and Oligocene formation is hiatus. The rate of tectonic movements in Gunsan Basin slowed considerably. In that case, thermal subsidence up to the present has maintained with marine transgressions, which enable this area to change into the land part of the present basin.

• Journal of the Korean Geophysical Society
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• v.9 no.4
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• pp.409-416
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• 2006

Reflection seismic survey has been conducted using R/V Yuzmogeologia of Russia on the area of between northern part of Powell basin and South Scotia Ridge. 48-channel seismic data have been processed using Promax system. Hesperides and Eastern Deep located in the central part of the South Scotia Ridge show similar geological structure comprising two distinct sedimentary layers. The lower layer filled with fault breccia is considered to be formed with the expansion of the deeps. The upper layer is filled with pelagic sediments which implies this layer is formed after the spreading of the deeps has stopped. The south branch of the South Scotia Ridge is characterized by bigger width than the north branch. Topographical depression shown in the south branch is formed by many faults accompanied with the seafloor expansion of Powell basin.

• The Korean Journal of Petroleum Geology
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• v.7 no.1_2 s.8
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• pp.7-12
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• 1999

A new high-resolution rnagnetotelluric (MT) survey was conducted for pull-apart basin analysis (Cretaceous Eumsung Basin), combined with surface sedimentological results. Two cross-basinal MT profiles represent an asymmetric form with a subbasin in the southeastern part. These basinal architectures are well compatible with paleoflow directions and facies transitions of surface sedimentology. The results also suggest that the basin fills reflect pull-apart opening with rapid subsidence of the central blocks. Combined with the surface sedimentological data on asymmetric lithofacies distribution, facies transitions, and paleoflow directions of the alluvio-lacustrine systems, the MT data help explain basin-fill processes during the basin formation. For petroleum exploration and basin analysis, the high-frequency MT technique can be a useful substitute for the costly burden of a seismic-reflection survey on land.

• Economic and Environmental Geology
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• v.39 no.2 s.177
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• pp.129-149
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• 2006

Previously published stratigraphic, sedimentologic, paleontologic, paleomagnetic and geophysical data are reviewed to make an understanding on the tectonic evolution of the Cretaceous Gyeongsang (Kyongsang) basin, southeast Korea. A stratigraphic framework and a tectonic model on the formation and deformation of the Gyeongsang Basin are newly proposed on the basis of integration these data with magmatism and mineralization ages in the basin. A newly proposed stratigraphic framework indicates that strata in the basin can be subdivided into five distinct stratigraphic units that represent pre-rifting, syn-rifting, inversion I, II, and III stages. The Gyeongsang Basin was formed initially as a pre-rifting stage due to north-south extension in the Late Jurassic prior to a syn-riftins stage that resulted from east-west extension during the Early Cretaceous. In the Late Cretaceous, the basin was deformed by three-staged sequential deformation of north-south, northwest-southeast, and east-west compressions. The tectonic history of the basin has been largely controlled by the change of motion of the Izanagi Plate from north to northwest during the Cretaceous. In the early Cretaceous, the Izanagi Plate began to subduct northward beneath the Eurasian Plate and caused the left-lateral strike-slip fault systems in the southern part of the peninsula. The left-lateral wrenching of these fault systems was causally linked to development of pull-apart basins, such as the Gyeongsang Basin in the southeastern part of the peninsula. However, northwestward movement of the Izanagi Plate during the Late Cretaceous probably led to the extensive volcanism as well as sequential deformations in the basin. The stratigraphic and tectonic model, which is newly proposed as a result of this study, may be expected to enhancing the efficiency for exploration and exploitation of useful mineral resources in the basin as well as establishing geologic history in the Cretaceous Gyeongsang Basin. Together with the spatial and temporal correlation of the Cretaceous basins in adjacent areas, this stratigraphic and tectonic model provides a new geologic paradigm to delineate the sophisticated tectonic history of East Asia turing the Cretaceous.