• Economic and Environmental Geology
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• v.25 no.3
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• pp.337-349
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• 1992

The Tertiary basins in Korea have widely been studied by numerous researchers producing individual results in sedimentology, paleontology, stratigraphy, volcanic petrology and structural geology, but interdisciplinary studies, inter-basin analysis and basin-forming process have not been carried out yet. Major work of this study is to elucidate evidences obtained from different parts of a basin as well as different Tertiary basins (Pohang, Changgi, Eoil, Haseo and Ulsan basins) in order to build up the correlation between the basins, and an overall picture of the basin architecture and evolution in Korea. According to the paleontologic evidences the geologic age of the Pohang marine basin is dated to be late Lower Miocence to Middle Miocene, whereas other non-marine basins are older as being either Early Miocene or Oligocene(Lee, 1975, 1978: Bong, 1984: Chun, 1982: Choi et al., 1984: Yun et al., 1990: Yoon, 1982). However, detailed ages of the Tertiary sediments, and their correlations in a basin and between basins are still controversial, since the basins are separated from each other, sedimentary sequence is disturbed and intruded by voncanic rocks, and non-marine sediments are not fossiliferous to be correlated. Therefore, in this work radiometric, magnetostratigraphic, and biostratigraphic data was integrated for the refinement of chronostratigraphy and synopsis of stratigraphy of Tertiary basins of Korea. A total of 21 samples including 10 basaltic, 2 porphyritic, and 9 andesitic rocks from 4 basins were collected for the K-Ar dating of whole rock method. The obtained age can be grouped as follows: $14.8{\pm}0.4{\sim}15.2{\pm}0.4Ma$, $19.9{\pm}0.5{\sim}22.1{\pm}0.7Ma$, $18.0{\pm}1.1{\sim}20.4+0.5Ma$, and $14.6{\pm}0.7{\sim}21.1{\pm}0.5Ma$. Stratigraphically they mostly fall into the range of Lower Miocene to Mid Miocene. The oldest volcanic rock recorded is a basalt (911213-6) with the age of $22.05{\pm}0.67Ma$ near Sangjeong-ri in the Changgi (or Janggi) basin and presumed to be formed in the Early Miocene, when Changgi Conglomerate began to deposit. The youngest one (911214-9) is a basalt of $14.64{\pm}0.66Ma$ in the Haseo basin. This means the intrusive and extrusive rocks are not a product of sudden voncanic activity of short duration as previously accepted but of successive processes lasting relatively long period of 8 or 9 Ma. The radiometric age of the volcanic rocks is not randomly distributed but varies systematically with basins and localities. It becomes generlly younger to the south, namely from the Changgi basin to the Haseo basin. The rocks in the Changgi basin are dated to be from $19.92{\pm}0.47$ to $22.05{\pm}0.67Ma$. With exception of only one locality in the Geumgwangdong they all formed before 20 Ma B.P. The Eoil basalt by Tateiwa in the Eoil basin are dated to be from $20.44{\pm}0.47$ to $18.35{\pm}0.62Ma$ and they are younger than those in the Changgi basin by 2~4 Ma. Specifically, basaltic rocks in the sedimentary and voncanic sequences of the Eoil basin can be well compared to the sequence of associated sedimentary rocks. Generally they become younger to the stratigraphically upper part. Among the basin, the Haseo basin is characterized by the youngest volcanic rocks. The basalt (911214-7) which crops out in Jeongja-ri, Gangdong-myon, Ulsan-gun is $16.22{\pm}0.75Ma$ and the other one (911214-9) in coastal area, Jujon-dong, Ulsan is $14.64{\pm}0.66Ma$ old. The radiometric data are positively collaborated with the results of paleomagnetic study, pull-apart basin model and East Sea spreading theory. Especially, the successively changing age of Eoil basalts are in accordance with successively changing degree of rotation. In detail, following results are discussed. Firstly, the porphyritic rocks previously known as Cretaceous basement (911213-2, 911214-1) show the age of $43.73{\pm}1.05$ 및 $49.58{\pm}1.13Ma$(Eocene) confirms the results of Jin et al. (1988). This means sequential volcanic activity from Cretaceous up to Lower Tertiary. Secondly, intrusive andesitic rocks in the Pohang basin, which are dated to be $21.8{\pm}2.8Ma$ (Jin et al., 1988) are found out to be 15 Ma old in coincindence with the age of host strata of 16.5 Ma. Thirdly, The Quaternary basalt (911213-5 and 911213-6) of Tateiwa(1924) is not homogeneous regarding formation age and petrological characteristics. The basalt in the Changgi basin show the age of $19.92{\pm}0.47$ and $22.05{\pm}0.67$ (Miocene). The basalt (911213-8) in Sangjond-ri, which intruded Nultaeri Trachytic Tuff is dated to be $20.55{\pm}0.50Ma$, which means Changgi Group is older than this age. The Yeonil Basalt, which Tateiwa described as Quaternary one shows different age ranging from Lower Miocene to Upper Miocene(cf. Jin et al., 1988: sample no. 93-33: $10.20{\pm}0.30Ma$). Therefore, the Yeonil Quarterary basalt should be revised and divided into different geologic epochs. Fourthly, Yeonil basalt of Tateiwa (1926) in the Eoil basin is correlated to the Yeonil basalt in the Changgi basin. Yoon (1989) intergrated both basalts as Eoil basaltic andesitic volcanic rocks or Eoil basalt (Yoon et al., 1991), and placed uppermost unit of the Changgi Group. As mentioned above the so-called Quarternary basalt in the Eoil basin are not extruded or intruaed simultaneously, but differentiatedly (14 Ma~25 Ma) so that they can not be classified as one unit. Fifthly, the Yongdong-ri formation of the Pomgogri Group is intruded by the Eoil basalt (911214-3) of 18.35~0.62 Ma age. Therefore, the deposition of the Pomgogri Group is completed before this age. Referring petrological characteristics, occurences, paleomagnetic data, and relationship to other Eoil basalts, it is most provable that this basalt is younger than two others. That means the Pomgogri Group is underlain by the Changgi Group. Sixthly, mineral composition of the basalts and andesitic rocks from the 4 basins show different ground mass and phenocryst. In volcanic rocks in the Pohang basin, phenocrysts are pyroxene and a small amount of biotite. Those of the Changgi basin is predominant by Labradorite, in the Eoil by bytownite-anorthite and a small amount pyroxene.

• The Journal of the Petrological Society of Korea
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• v.25 no.4
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• pp.373-388
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• 2016

To understand human activity in the past, the information about past environmental change including geomorphological and climatic conditions is essential and this can be traced by using age dating and geochemical analysis of sediments from the prehistoric sites. The sedimentary sequence of Seokgwan-dong Paleolithic Site located in Seoul was 5m long unconsolidated sediments and consists of lower part bedrock weathering sediments, slope deposits and upper-part fluvial deposits. In this study, upper part sediments were used to reconstruct past environmental change through age dating and various physical and chemical analyses including grain size, magnetic susceptibility and mineral and elements. The fluvial sediments can be divided into 4 units including three organic layers. Grain size analysis results showed that the sediments were very poorly sorted with fining upward features. Magnetic susceptibility was relatively high in the organic layers, indicating environmental changes causing mineral composition change at that times. The mineral and major element composition are similar to Jurassic biotite granite which mainly consists of quartz, K-feldspar, biotite and muscovite. The radiocarbon age of $14,240{\pm}80yr$ BP was obtained from the lower most organic layer of Unit III(O), suggesting that the fluvial sediments formed at least from the early stage of deglacial period after the end of Last Glacial Maximum. Subsequent wet and warm climates and resultant fluvial process including slope sedimentation during the Holocene may have been responsible for the sedimentary sequence in Seokgwan-dong paleolithic site and surrounding area. The observed organic layers suggests frequent wetland occurrence combined with natural levee changes in this area.

• The Journal of Engineering Geology
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• v.26 no.1
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• pp.63-70
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• 2016

The aim of this study is the safety and an accident prevention in limestone terrain by the underground tunneling. The geology of the study area consists of a Paleozoic sedimentary sequence dominated by limestone, sandstone, shale, and carbonaceous shale. The sequence gently dips to the northeast but the joint contains steep with variable trend. A significant fracture zone is developed in the limestone and shale beds, sub-parallel to bedding, and follows in part the limestone-sandstone contact. Monitoring of groundwater levels in the area shows marked fluctuations in the water table, which repeatedly rose to a level of -4 m before sinking to -15 m. These cycles occurred in mid-May, 2007 and in early and middle June. The data indicate that these fluctuations were unrelated to rainfall that occurred during the study period. We infer that the fluctuations were associated with the development of underground karstic networks along the deep fracture zone, and overlying ground subsidence is likely related to the rapid sinking of groundwater and the associated strong downward suction force.

• The Korean Journal of Petroleum Geology
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• v.4 no.1_2 s.5
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• pp.1-11
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• 1996

Multichannel deep seismic reflection data in the Main Pass area of the northern Gulf of Mexico are interpreted in this study for the stratigraphy and the depositional history. Structural analysis of deep seismic reflection data provides new information on the locations of paleo-shelf margins and the basement. The basement occurs at about $7.5{\cal}km$ depth at the northern end of seismic line LSU-1 in the Mississippi shelf. The Jurassic and early Cretaceous shelf margins occupy approximately the same position, whereas the Oligocene shelf margin occurs about 28 km farther landward. Ten major seismic stratigraphic sequences are identified for the Mesozoic and Cenozoic sed-imentary section. Correlation of sequence boundaries defined in this study with those in other areas of the circum-Gulf region indicates that majo. regional unconformities formed at the mid-Miocene (10.5 Ma), mid-Oligocene (30 Ma), mid-Cretaceous (97 Ma), and top-Jurassic (131 Ma). Three distinct periods a.e recognized in the depositional history of the Main Pass area of the northern Gulf of Mexico: (1) shallow ma.me deposition du.ins the period from the opening of the Gulf to the mid-Cretaceous, (2) deep marine deposition in the Cretaceous to the mid-Oligocene, and (3) shallow marine deposition prevailed since the mid-Oligocene to present. A comparison of depositional rates between the Main Pass area and the Destin Dome area indicates that the northern Gulf of Mexico continental margin was initiated as a terrigenous sediment wedge province in the late Cretaceous.

• The Journal of the Petrological Society of Korea
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• v.18 no.4
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• pp.293-305
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• 2009

The Gilan-Cheongsong area, which is in contact with Yeongyang and Uiseong Blocks of Gyeongsang Basin, Korea, consists of Precambrian metamorphic rocks, Triassic Cheongsong granite, Cretaceous sedimentary rocks(Iljik, Hupyeongdong, Jeomgok Formations), and Cretaceous igneous rocks(andesite, quartz porphyry, felsite). In this area are developed faults trending in (W)NW, NNW, ENE, NS, (N)NE directions which are representative in the Gyeongsang Basin. We analyzed the geometric and kinematic characteristics of fracture systems to inquire into movement history and sense of these faults in this area. This study suggests that these faults were mainly strike-slip movement. The orientations of fracture sets show ENE, NNW, (W)NW, (N)NE, NS in descending order of frequency. Their prolongation presents (W)NW, NNW, ENE, (N)NE, NS in descending order of predominance, and also agrees with that of faults in this area. The development sequence and movement sense of fracture sets are summarized as follows; (1) (W)NW: dextral shearing $\rightarrow$ (2) (W)NW and NNW: conjugate shearing(the former: dextral, the latter: sinistral) $\rightarrow$ (3) NNW: dextral shearing $\rightarrow$ (4) (W)NW: sinistral shearing $\rightarrow$ (5) ENE: dextral shearing $\rightarrow$ (6) ENE and NS: conjugate shearing(the former: sinistral, the latter: dextral) $\rightarrow$ (7) (N)NE: sinistral shearing, and this result is closely associated with the development sequence and movement sense of faults developed in this area.

• The Korean Journal of Petroleum Geology
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• v.8 no.1_2 s.9
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• pp.1-43
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• 2000

A comparison study for understanding a stratigraphic response to tectonic evolution of sedimentary basins in the Yellow Sea and adjacent areas was carried out by using an integrated stratigraphic technology. As an interim result, we propose a stratigraphic framework that allows temporal and spatial correlation of the sedimentary successions in the basins. This stratigraphic framework will use as a new stratigraphic paradigm for hydrocarbon exploration in the Yellow Sea and adjacent areas. Integrated stratigraphic analysis in conjunction with sequence-keyed biostratigraphy allows us to define nine stratigraphic units in the basins: Cambro-Ordovician, Carboniferous-Triassic, early to middle Jurassic, late Jurassic-early Cretaceous, late Cretaceous, Paleocene-Eocene, Oligocene, early Miocene, and middle Miocene-Pliocene. They are tectono-stratigraphic units that provide time-sliced information on basin-forming tectonics, sedimentation, and basin-modifying tectonics of sedimentary basins in the Yellow Sea and adjacent area. In the Paleozoic, the South Yellow Sea basin was initiated as a marginal sag basin in the northern margin of the South China Block. Siliciclastic and carbonate sediments were deposited in the basin, showing cyclic fashions due to relative sea-level fluctuations. During the Devonian, however, the basin was once uplifted and deformed due to the Caledonian Orogeny, which resulted in an unconformity between the Cambro-Ordovician and the Carboniferous-Triassic units. The second orogenic event, Indosinian Orogeny, occurred in the late Permian-late Triassic, when the North China block began to collide with the South China block. Collision of the North and South China blocks produced the Qinling-Dabie-Sulu-Imjin foldbelts and led to the uplift and deformation of the Paleozoic strata. Subsequent rapid subsidence of the foreland parallel to the foldbelts formed the Bohai and the West Korean Bay basins where infilled with the early to middle Jurassic molasse sediments. Also Piggyback basins locally developed along the thrust. The later intensive Yanshanian (first) Orogeny modified these foreland and Piggyback basins in the late Jurassic. The South Yellow Sea basin, however, was likely to be a continental interior sag basin during the early to middle Jurassic. The early to middle Jurassic unit in the South Yellow Sea basin is characterized by fluvial to lacustrine sandstone and shale with a thick basal quartz conglomerate that contains well-sorted and well-rounded gravels. Meanwhile, the Tan-Lu fault system underwent a sinistrai strike-slip wrench movement in the late Triassic and continued into the Jurassic and Cretaceous until the early Tertiary. In the 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 the Tan-Lu fault until the late Eocene caused a megashear in the South Yellow Sea basin, forming a large-scale pull-apart basin. However, the Bohai basin was uplifted and severely modified during this period. h pronounced Yanshanian Orogeny (second and third) was marked by the unconformity between the early Cretaceous and late Eocene in the Bohai basin. In the late Eocene, the Indian Plate began to collide with the Eurasian Plate, forming a megasuture zone. This orogenic event, namely the Himalayan Orogeny, was probably responsible for the change of motion of the Tan-Lu fault system from left-lateral to right-lateral. The right-lateral strike-slip movement of the Tan-Lu fault caused the tectonic inversion of the South Yellow Sea basin and the pull-apart opening of the Bohai basin. Thus, the Oligocene was the main period of sedimentation in the Bohai basin as well as severe tectonic modification of the South Yellow Sea basin. After the Oligocene, the Yellow Sea and Bohai basins have maintained thermal subsidence up to the present with short periods of marine transgressions extending into the land part of the present basins.

• Korean Journal of Heritage: History & Science
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• v.44 no.1
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• pp.4-29
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• 2011

Paleoenvironments of the shell deposit-bearing sequence in the Hasandong Formation at Daesong-ri area, Hadong-gun, Korea, are interpreted on the basis of sedimentary facies and taphonomy of the shell deposits, with a discussion of their stratigraphic implications. A shell deposit-bearing sequence without reddish beds is mostly grayish, and the bedding is laterally extensive. These deposits are interpreted to have been formed in sandflats, mudflats, and shallow lakes generated by flooding on an alluvial plain. The shell deposits are classified into three types according to the occurrence, and the concentration of a single species of Brotiopsis wakinoensis in the shell deposits is deemed to have been attributed to the exclusive inhabitation of the genus Brotiopsis. Type 1 and 2 shell deposits are interpreted to have been fossilized in sandflats and mudflats after death in their habitat of shallow lakes and subsequent transformation by sheetflooding and lake flooding. Type 3 shell deposits are interpreted to have been fossilized in their habitat of shallow lakes during a stabilized period of lake development. The development of the shell deposit-bearing lacustrine sequence in a few tens of meters in thickness in the Hasandong Formation of fluvial deposits is compared to the shift of depositional environments from the Hasandong Formation (fluvial deposits) through the Jinju Formation (lacustrine deposits) to the Chilgok Formation (alluvial plain deposits), which suggests that additional lithostratigraphic classification is needed in the Hasandong Formation. The shell deposits at the study area can provide valuable data to understanding the paleoenvironments during the Early Cretaceous Period of Korea, and should give basic data to evaluate the value of the Cretaceous mollusc deposits in Korea as a geological heritage.

• Journal of the Korean earth science society
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• v.21 no.5
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• pp.635-646
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• 2000

Geological achievements of the 20th century revolutionized our views about geological understanding and concept. A good example is the concept of continental drift suggested early in the 20th century and later explained in terms of seafloor spreading and plate tectonics. Our understanding of the compositions of materials forming earth has also improved during the20th century. Radio and stable isotopes together with biostratigraphy and sequence stratigraphy allow us to interpret the evolution of sedimentary basins in terms of plate movement and sedimentation processes. The Deep Sea Drilling Project initiated in 1960s and continued as the Ocean Drilling Project in 1980s is one of the most successful international research observations, and new developments in computational techniques have provided a wholly new view about the interior of the earth. Most of the geological features and phenomena observed in deep sea and around continental margins are now explained in terms of global tectonic processes such as superplumes flowing up from the interior of our planet and interacting with such as Rodinia Pannotia and Nena back in the Precambrian time. The space explorations which began in the late 1950s opened up a new path to astrogeology, astrobiology, and astropaleontology. The impact theory rooted in the discovery of iridium and associated phenomena in 1980s revived Cuvier's catastrophism as a possible explanation for the extinctions of biotas found in the geological record of this planet. Due to the geological achievements made in the 20th century, we now have a better understanding of geologic times and processes that were too long to be grasped by human records.

• Journal of the Korean earth science society
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• v.28 no.1
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• pp.54-63
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• 2007

The sedimentary sequence of the non-marine Cretaceous Jinju Formation from Sacheon, Korea, contains a number of rod-shaped stromatolites (RSS) characterized by concentric lamination with curd-shaped, stratiform, and small columnar stromatolites. Unlike the world trend, a massive distribution of rod-shaped stomatolite was discovered in the region. The mineral composition, diagenetic alteration, and weathering process of the kind were analyzed by EPMA. The gross morphology of RSS is almost identical to broken plant twigs or stems formed by microbial activity onto which it grew. RSSs are interpreted as stromatolitic algae over plant twigs, which formed through concentric carbonate precipitation by epiphytic algal photosynthesis. The distribution of localities and horizons of the stromatolite imply that RSS is allochthonous and autochthonous. Two types of cyanobacterial filaments and one type of peen algal filament were discovered. The size frequency distribution of calcified filamentous microfossils found in stromatolite was $2.2{\mu}m\;and\;7.8{\mu}m$ in mean diameter of the former, $32.3{\mu}m$ in mean diameter of the latter. The cyanobacterial fossils played a key role in the formation of stromatolite, while the green algal filament was auxiliary stromatolite-builder stromatolites. The filamentous microfossils including trichome were found within the stromatolitic laminae.

• The Korean Journal of Quaternary Research
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• v.23 no.2
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• pp.34-47
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• 2009

AMS radiocarbon dates indicated that Eurimji reservoir, located at Jecheon City, Chungbuk Province, has been formed during the late Holocene Epoch. The sedimentary sequence at bottom reveals histories in hydrology, climate conditions and past vegetation dynamics. Ages controlled sedimentological and palynological analyses on ER 3-1 Core contribute to reconstruct paleoclimate and past hydrological conditions. These analyses suggest that lower interval (307.5m~309.5m elevations) of the ER 3-1 Core was deposited in stable from 1,920 yrBP to 1,420 yrBP, but upper layer sediment above these elevations was composed of reworked sediments during the pre and post 2,000 yrBP. Pollen assemblage indicates that watershed vegetation of the Eurimji reservoir, during the period of 1,920 yrBP~1,420 yrBP, was closely comparable to modern vegetation dominated Pinus and Quercus mixed vegetation. Also, riparian including Alnus, Fraxinus and Salix were inhabited along the banks of stream, and aquatics such as Typha, Nymphaea and Persicaria flourished at shore of the reservoir. According to cultural chronicle, it infers that the Eurimji reservoir was formed from the Bronze Age to the Iron Age or the beginning of ancient society. An integrated data suggested that Quercus-Pinus-Abies mixed forest flourished under cool and dry climate conditions during 3,200 yrBP~200 yrBP.