Young Jae Shinn

Taebaek Group (Cambrian-Ordovician) in the Seokgaejae section, Taebaeksan Basin: a refined lower Paleozoic stratigraphy in Korea

The Taebaek Group (Cambrian-Ordovician) in the Taebaeksan Basin comprises mixed carbonate-siliciclastic sequence and is exposed well in the Seokgaejae section located in the central-eastern part of the Korean Peninsula. The group in the Seokgaejae section consists of in ascending order the Myeonsan, Myobong, Daegi, Sesong, Hwajeol, Dongjeom, Dumugol, Makgol, Jigunsan and Duwibong formations. This study describes in detail the well-exposed outcrop sections of the Taebaek Group in the Seokgaejae Pass in order to refine the lithostratigraphy of the lower Paleozoic strata in the Taebaeksan Basin, Korea. The refined lithostratigraphy delineates clearly the lithologic boundary between the Myobong and Daegi formations, the Hwajeol and Dongjeom formations, the Dumugol and Makgol formations, and the Makgol and Jigunsan formations. The preliminary information on trilobite faunal assemblages suggests that the Cambrian-Ordovician boundary can be placed within the lowermost part of the Dongjeom Formation.

High-resolution acoustic characteristics of epicontinental sea deposits, central-eastern Yellow Sea

Abstract Large amounts (45390 line km) of closely spaced (2.2–4.4 km) high-resolution subbottom profiles (Chirp, 2–7 kHz) made it possible to identify detailed echo types and their distribution in an epicontinental shelf environment. On the basis of seafloor morphology, surface bedforms and subbottom acoustic characters, 10 echo types were identified in the uppermost sedimentary sequence of the central-eastern Yellow Sea. Flat seafloor with sharp bottom echoes (echo types 1-1, 1-2 and 1-3a; transgressive sediment sheets or relict sands) is widespread in the offshore area and underlain to the west by an acoustically transparent wedge (echo type 1-3b; highstand muds). Mounded seafloor with either smooth surface or superposed bedforms (echo types 2-1, 2-2 and 2-3; tidal ridges) and flat seafloor with regularly spaced, wavy bedforms (echo type 1-4; large-scale dunes) are dominant in the eastern nearshore area. Large-scale mounds with continuous, inclined internal reflectors (echo type 2-4; giant mud bank) occur in the southeastern nearshore area. Various-scale eroded seafloor (echo types 3-1 and 3-2; channels) and flat seafloor with regularly spaced, wavy bedforms (echo type 1-4; large-scale dunes) are present in the northern part of the sea. The distribution pattern of echo types in the central–eastern Yellow Sea reflects depositional processes and sediment dispersal systems during the Holocene transgression and highstand period: (1) development of tidal ridges and large-scale dunes in response to strong tidal currents and waves in the eastern nearshore area; (2) construction of transgressive to highstand mud bank (Huksan mud belt) by deposition of muds derived from the Keum river in the southeastern nearshore area; (3) active erosion due to intensified currents in the northern part; and (4) highstand mud deposition derived from the Huanghe river on the transgressive sediment sheets in the offshore area.

Depositional processes of late Quaternary sediments in the Yellow Sea: a review

This review focuses on the depositional processes of late Quaternary sediments in the eastern Yellow Sea, an epicontinental sea with a flat and broad seafloor (less than 100 m in water depth) and extensive tidal flats along the southeastern coast. The Yellow Sea was subaerially exposed during the last glacial period when sea level was about 120 m below the present level. During erosional retreat of shorefaces and river mouths, sedimentation was largely controlled by high-amplitude rise in sea level, forming transgressive sheets (echo type 1–3a) and sediment ridges (echo types 2-1 and 2–2) with extensive development of ravinement surfaces. The distribution of surface sediments reflects an interplay of sediment input from the surrounding landmass and the hydrodynamic regime in response to sea-level rise. Muddy sediments in the central part represent the Huanghe-River source and form a highstand sheet (echo type 1–3b). Large birdfoot-like sand bodies off the Jiangsu coast also represent highstand deposits when sea level reached the present position at about 6 ka. In the southeastern part of the Yellow Sea, sediments are dominated by sand ridges (echo types 2-1, 2–2 and 2–3), largely shaped by tidal currents. The southwestern corner of the Korean Peninsula is dominated by a thick deposit of mud, the Heuksan mud belt. The muds largely originate from the Geum River, whose distribution is controlled by strong southward coastal currents. In the coastal regions of the southeastern Yellow Sea, sedimentation is controlled by a combined effect of waves and tides with distinctive season-alities in sedimentary facies owing to the monsoonal climate: tidedominated mud deposition in summer and wave-dominated sand deposition/erosion in winter: Winter storms play a role in sedimentation on intertidal flats. Quantitative monitoring of sediment transport suggests that the textural variation results from the overwhelming role of winter waves superimposed on tidal currents in pulling sands and resuspending muds. Due to low sedimentation rate, the tidal flats formed retrogradational, coarsening-upward pattern during the Holocene sea-level rise.

The Jangsan and Myeonsan formations (Early Cambrian) of the Taebaek Group, mideast Korea: depositional processes and environments

The present study focuses on the depositional processes and environments of the lower part of the Taebaek Group (Cambrian-Ordovician) during the initial basin-forming inundation of the Taebaeksan Basin, an eastern margin of the North China platform. The lowermost part of the Taebaek Group is represented by two contrasting lithologic units, the Jangsan and Myeonsan formations. The Jangsan Formation consists of cross-bedded, massive, and foreset-bedded quartzose sandstone (quartzite) interpreted as shallow marine deposits ranging from inner shelf to nearshore environments. Deposition occurred in a stable cratonic basin where continuous subsidence and the accompanied sea-level rise accommodated large supply of sediments. The Myeonsan Formation comprises basal disorganized conglomerate, cross-bedded and laminated sandstone, and homogeneous or laminated mudstone, which largely formed in a tidally influenced restricted embayment. The formation is localized in the margin of the basin, as represented by the basal mass-flow conglomerate and the rapid transition to the tide-influenced marine succession. In the Early Cambrian, initial sedimentation in the Taebaeksan Basin was largely controlled by abundant sediment supply, accompanied with sea-level rise.

Lithofacies distribution and depositional environment in the Lower Cretaceous McMurray Formation, BlackGold Lease, northern Alberta: implications for geometry and distribution of oil sand reservoirs

Within BlackGold Lease located in northern Alberta, the Lower Cretaceous McMurray Formation contains the most prolific bitumen reservoirs deposited in fluvial to tidally-influenced estuarine environments. Based on core descriptions and wire-line log evaluation, this study reveals six lithofacies: cross-stratified sandstone and mudstone-clast breccia (Lf1), sandstone-dominated IHS (Lf2), mudstone-dominated IHS (Lf3), thinly interbedded sandstone and mudstone (Lf4), laminated mudstone (Lf5), and clean sandstone with interbedded mudstone (Lf6). To understand the evolution of depositional environments vertical and lateral associations of lithofacies are examined using well cross-sections and lithofacies slice maps. During overall rise in relative sea level, the McMurray Formation evolved through three stages of deposition: early stage represents fluvial channels with minor tidal influence, middle stage represents tidally-influenced estuary with well-developed meandering channels, and late stage represents a drowning of tidally-influenced estuary. The potential bitumen reservoirs are fluvial channel sandstones in the early stage and lower point-bar deposits in the middle stage. The fluvial channel sandstones are well stacked and correlatable between wells, forming sheet-like sandstone bodies that align in a SW-NE direction parallel to the inferred orientation of major channel systems. The lower point-bar deposits consist mainly of base-of-channel and sandstone-dominated IHS deposits. The direction of point-bar migration, which is crucial in horizontal well design for bitumen production, is inferred from lithofacies slice maps. The lateral changes in lithofacies from base-of-channel to abandoned channel-fills through IHS deposits, shown in lithofacies slice maps, probably indicate that the point bar once migrated toward abandoned channel-fills. Based on this lateral lithofacies trend, the dip direction of some point-bar deposits are approximately estimated to be southwestward or northwestward, which is oblique or perpendicular to the major channel orientation.

Hydraulic properties measurement of tight sandstone for CO2 geological storage

Permeability is one of the important rock properties in oil and gas exploration as essential input data of reservoir characterization and production simulation. As production of unconventional resources such as tight gas/oil, shale gas and coal bed methane increases, there is a growing need to measure the permeability of tight formation rocks. Direct measurement by conventional steady-state flow methods, however, is limited due the length of time needed for pressure equilibration. In this study the pressure pulse-decay method is applied to measure low permeability (lower than 9.87E-18m2) rocks. This method is based on the analysis of unsteady-state gas flow. The dissipation rates of dimensionless differential pressure (ΔPD) with time indicates permeability of various core samples. The low permeability measured by using the pressure pulse-decay method, is compared with the permeability recovered from the steady-state method for validation. These low permeability measurements are conducted to six tight sandstones from the Gyeongsang and Janggi basins, South Korea and Tsushima Island, Japan. The apparent permeability measured by the pressure pulse-decay method was approximately twice higher than permeability measured by steady-state method. By comparing the relationship between permeability and mean pressure, this may result from gas slippage effects.

High‐Resolution Seismic Reflection Studies of Late Quaternary Sediments in the Eastern Yellow Sea

The post-glacial sedimentation in the eastern Yellow Sea is addressed through echo type analysis of high-resolution subbottom profiles (Chirp, 2-7 kHz) aided by sediment cores. A total of eleven echo types are identified based on the seafloor morphology and acoustic characteristics. Distribution and development of echo types suggest that post-glacial sedimentation was controlled by the rate of sea-level rise, variations in sediment supply, and hydrodynamic conditions. During the transgressive period (about 11.5-8 ka), rapid retreat of shoreface and tidal processes formed transgressive lag deposits (echo type 1-1) and tidal ridges (echo types 2-1, 2-2, and 2-3) in the inner-shelf area. A transgressive sediment sheet (echo type 1-3a), largely composed of bioturbated silty mud (unit 2), extensively covers the transgressive surface of erosion in the central Yellow Sea. The seafloor in the northern Yellow Sea was sculptured by strong tidal currents, resulting in channels and valley-like depressions (echo types 3-1 and 3-2). As the inner-shelf area offshore the Jiangsu coast was flooded, a seaward prograding wedge (echo type 2-5) formed in the distal part of the paleo-Huanghe delta. During the late transgressive to highstand period (since 8 ka), two distinctive mud deposits, i.e., Huanghe-derived mud belt (echo type 1-3b; unit 1) and elongated mud bank (echo type 2-4) formed in the central part and the southeastern nearshore area, respectively. Transgressive ridges and large-scale dunes (echo types 1-4, 2-2, and 2-3) have been modified by strong tidal currents and waves in the eastern nearshore area.

Regional strike-slip and initial subsidence of Korea Plateau, East Sea: tectonic implications for the opening of back-arc basins

This study focuses on the initial subsidence mechanism of Korea Plateau in the East Sea. New interpretation of digitized multichannel seismic profiles (vertically unexaggerated) in the southern part of the South Korea Plateau delineates that acoustic basement comprises a number of normal-fault blocks, forming intra-plateau basins and troughs. In the western part of the plateau, the normal faults are oblique to the continental margin, whereas in the eastern part, they are bounded by an orthogonal transfer fault. The entire faults are suggestive of a large-scale dextral strike-slip fault system. The dextral fault system in the plateau was accompanied by a regional strike-slip fault along the North Korean continental margin, which offsets the prominent NE-SW granite belts on land and under the sea. The regional dextral strike-slip fault system activated during the late Oligocene/early Miocene to middle Miocene. The regional dextral strike-slip along the western continental margin of the sea was coupled with the complex dextral fault on the eastern margin from Sakhalin to Honshu. The regional strike-slip deformation was due to the changes in plate motion, i.e., southward drift (late Oligocene/early Miocene) and clockwise rotation (middle Miocene) of the Japanese Arc away from the Eurasian Plate.

Estimation of original kerogen type and hydrogen index using inorganic geochemical proxies: Implications for assessing shale gas potential in the Devonian Horn River Formation of western Canada

Considerable attention has been directed to the Devonian Horn River Formation in western Canada with respect to geochemical evaluation of gas-generation and storage potential. Because organic geochemical analyses are not always useful for characterizing the type and amount of original organic matter, we surmise the original kerogen type and original hydrogen index (HIo) and subsequently estimate a reliable original total organic carbon (TOCo) based on a combination of inorganic and organic geochemical data. Productivity (SiO2 and Ba) and terrestrial input (Al2O3, Hf, Nb, and Zr) proxies are used to estimate original kerogen types, which suggest that the Evie and Muskwa Members formed under conditions of high productivity and minor terrestrial input. These members also formed under reducing conditions, as indicated by the redox proxies (Mo, U, and Th/U). Under such conditions, primarily type II kerogen was preserved. By considering the fraction of biogenic silica, the estimated HIo values (400–500 mg hydrocarbon/g total organic carbon [TOC]) for the middle Otter Park Member are lower than that for Evie and Muskwa Members and higher than the upper and lower Otter Park Member. The stronger correlation between TOCo and trace elements suggests that HIo is useful for reconstructing the coherent variation in TOCo. Based on the original kerogen type and TOCo, the gas-generation and storage potentials of the Evie, middle Otter Park, and Muskwa Members are higher than those of other members. The source-rock potential is excellent for the Evie Member with an approximately 75% difference between TOCo and measured present-day TOC.