초록 ▼

1. 서 언
1:50,000 축척의 군산ㆍ부안ㆍ방축도ㆍ장자도도폭 지질조사는 2012년에서 2013년까지 2년간에 걸쳐 지식경제부 출연과제로 이루어졌다. 도폭 지역은 새만금을 비롯하여 서해안 개발을 위해 이미 조사되었어야 하는 지역에 해당된다. 도폭 지역은 인접한 서천ㆍ이리ㆍ김제ㆍ줄포ㆍ하왕등도 등 지질도폭 지역과 함께 고원생대, 신원생대 기반암과 중생대 지층이 발달한 곳으로 경기육괴 서남부의 지체구조 발달의 역사를 이해하는데 있어 학술적으로도 매우 중요한 지역이다. 군산ㆍ부안ㆍ방축도ㆍ장자도도폭 지질조사의 목적은 지질도와 지질보고

1. 서 언
1:50,000 축척의 군산ㆍ부안ㆍ방축도ㆍ장자도도폭 지질조사는 2012년에서 2013년까지 2년간에 걸쳐 지식경제부 출연과제로 이루어졌다. 도폭 지역은 새만금을 비롯하여 서해안 개발을 위해 이미 조사되었어야 하는 지역에 해당된다. 도폭 지역은 인접한 서천ㆍ이리ㆍ김제ㆍ줄포ㆍ하왕등도 등 지질도폭 지역과 함께 고원생대, 신원생대 기반암과 중생대 지층이 발달한 곳으로 경기육괴 서남부의 지체구조 발달의 역사를 이해하는데 있어 학술적으로도 매우 중요한 지역이다. 군산ㆍ부안ㆍ방축도ㆍ장자도도폭 지질조사의 목적은 지질도와 지질보고서를 발간하여 국토의 개발·이용·보존, 한국 지질계통의 수립과 도폭 지역에 부존된 자원탐사개발 등 다양한 이용분야에 활용될 수 있는 기초 지질자료를 제공하는 것이다.
군산ㆍ부안ㆍ방축도ㆍ장자도도폭 지역은 국립지리원이 발간한 축척 1:50,000의 군산ㆍ부안ㆍ신시도ㆍ위도 지형도의 각 일부에 해당하는 지역으로 동경 126°15′00″에서 126°45′00″, 북위 35°40′00″에서 36°00′00″사이의 지역이다. 행정구역으로는 전북 군산시, 옥구읍, 옥산면, 김제군 진봉면, 광활면, 부안군 부안읍, 동진면, 계화면, 상서면, 하서면 등의 육상지역과 유부도, 비응도, 말도, 명도, 방축도, 관리도, 대장도, 장자도, 장구섬, 선유도, 무녀도, 신시도, 야미도, 비안도, 두리도, 덕산도, 치두도, 사당도 등의 섬이 포함된다. 도폭지역의 주요 교통편은 서해안 고속도로를 이용하거나 대전-논산-강경-전주를 잇는 국도, 전주에서 군산으로 연결되는 국도 등을 이용할 수 있으며 농업용 도로를 비롯 하여 다수의 국가지원 지방도를 포함한다.

Abstract ▼

1. INTRODUCTION
The Gunsan, Buan, Bangchukdo and Jangjado sheets was mapped using 1:25,000 scaled base maps during the years of 2012 and 2013, as one of the fundamental projects of the Korea Institute of Geoscience and Mineral Resources (KIGAM), funded by the Ministry of Industry and Commerce. Th

1. INTRODUCTION
The Gunsan, Buan, Bangchukdo and Jangjado sheets was mapped using 1:25,000 scaled base maps during the years of 2012 and 2013, as one of the fundamental projects of the Korea Institute of Geoscience and Mineral Resources (KIGAM), funded by the Ministry of Industry and Commerce. These quadrangles, located in mid-west Korean Peninsula, is bounded by the coordinates of longitude 126°15′00″ to 126°45′00″ East and latitude 35°40′00″ to 36°00′00″ North. These sheet areas are important to provide the fundamental geologic information for national developments of Social Overhead Capital (SOC) as well as to understand the tectonic evolution history of the Korean Peninsula. The area encompasses several local districts of the Gunsan-si, Buan-gun and Gimje-si, and includes . The geographic features are mainly characterized by several mountains formed on lowlands of granites and numerous islands. Local plains or open fields are developed largely on lowland granitic regions. Wave-cut platform or marine terraces and sea caves are developed along the Gugunsan islands and sea shores.
2. GENERAL GEOLOGY
The Gunsan, Buan, Bangchukdo and Jangjado sheets, located in the southwestern part of the Gyeonggi massif and Ogcheon belt, consists of Paleoproterozoic Biotite Gneiss, and Granite Gneiss, Neoproterozoic sedimentary formations and amphibolite, Paleozoic Oksan Formation, Jurassic Nampo Group (?) and igneous rocks, Cetaceous sedimentary formations, volcanics and intrusives, and Quaternary alluvium and beach deposits. The stratigraphy of these sheets is presented in Table 1. The lowermost units of the Gunsan, Buan, Bangchukdo and Jangjado areas correspond to the Biotite Gneiss and Granite Gneiss, and the Neoproterozoic Geumseongni, Impi and Bangchukdo formations were deposited on this basement, and then, the Amphibolite was emplaced. In the Iri Sheet, the 'Mica Schist', including the zircons as young as about 850 Ma, was described as presumably belonging to the Ogcheon Group.
However, this dark gray fine-grained rock in the Geumseong-ri area corresponds to phyllite or slightly metamorphosed dark gray mudstone, and also is found between quartz mica schist masses at Susong-dong and Songchang-dong, Gunsan.
That is why we establish the Neoproterozoic Geumseongni Formation that includes the phyllite masses as well as quartz mica schist in this report.
Paleozoic Oksan Formation was defined in the Iri Sheet, and is distributed on a small scale near Oksan in the Gunsan Sheet.
Low metamorphosed dark-colored sediments are developed in the Gunsan Sheet area. The 1:250,000 Gwangju Sheet described them as presumably Permian units (Lee et al., 1997). On the basis of plant fossils that survived since the Triassic, the 'Mudstone and Sandstone' and 'Conglomerate and Mudstone' seem to correspond to the Amisan and Jogyeri formations of the Jurassic Nampo Group, respectively.
Because of some problems in stratigraphic correlation, the usage of formation names is reserved for future correct correlation. Jurassic Biotite Granite, Two Mica Granite and Porphyritic Granite prevail in the Gunsan and Buan areas, and the ages of latter two have been dated to be 170~175Ma (Kim et al., 2012) and 168.8±5.4Ma in this report, respectively.
Cretaceous sedimentary rocks are divided into the Nansan, Sanbukdong, Jangsinni and Biando formations in ascending order. Because the Yamido Rhyolite, dated to be 93.6±2.1Ma, erupted over the Nansan Formation in the Sinsido Island, the Nasan Formation seems to be Early Cretaceous in age. Plant fossils belonging to the Family Cheirolepidaceae and Family Cupressaceae are produced in the Sanbukdong Formation, indicating the age of Early Cretaceous. The Jangsinni and Biando formations seem to be related to the Late Cretaceous volcanic activities, and their ages are presumed to be early Late Cretaceous.
Three Cretaceous volcanic terrains are developed in the Bangchukdo, Jangjado and Buan area: the Gugunsan, Gyehwado and Buan volcanic terrains. The Gugunsan area is occupied by the Munyeodo Trachyte, Yamido Rhyolite and Seonyudo Rhyolite Breccia. The rhyolite breccia is thought to be related to the caldera collapse of the area. The Gyehwado Tuff includes boulders of granite, sedimentary rocks and volcanic materials, and intertongues with sediments along the western margin of the volcanic mass.
As for the Cretaceous volcanic rocks in the Buan area, the Byeonsan Tuff is prevailing in the area, and is intruded by the Baengnyeonni Rhyolite. The Gisangbong Tuff was deposited over the two and then, the Samyebong Rhyolite erupted in this volcanic terrain. Late Cretaceous Quartz Porphyry and Vein Quartz intruded the older rocks including the upper four units in the Buan area.
The Quaternary units consist of alluvium and beach sand occupying the lowland along the drainage and coastal areas.
2-1. Paleoproterozoic Sequences
The Biotite Gneiss and Granite Gneiss are the lowermost units of the area, and mainly occur in the northeastern margin of the Gunsan Quadrangle, and in the western part of the Buan Sheet. The Biotite Gneiss has typical mineral assemblage of quartz, biotite, muscovite and feldspar. Zircon occurs as accessary mineral (Figs. 4-1, 4-2).
The Granite Gneiss intruded the Biotite Gneiss and was intruded by Mesozoic intrusives and volcanics. The Granite Gneiss has typical mineral assemblage of quartz, feldspar, and biotite (Fig. 4-3).
2-2. Neoproterozoic Sequences
The Neoproterozoic sequence of the area consists of the Geumseongni, Impi and Bangchukdo formations, and the Amphibolite. The Geumseongni Formation occurs in the central-eastern part of the Gunsan Sheet including Gunsan-si and Oksan-myeon, and consists of quartz mica schist and phyllite (or mica schist) with minor quartzite. Dark gray phyllite is distributed at Susong-dong and Songchangdong, Gunsan as well as at Geumseong-ri, Oksan-myeon (Fig. 4-4). The ages of detrital zircons contained in the phyllite were dated, and the young ages display around 850Ma (Kim et al., 2012). In microscopic observation, no conspicuous metamorphism is recognized (Fig. 4-5). The phyllite of the Susong-dong consists of well-round quartz on clayey matrix without any deformed minerals (Fig. 4-5d), and that of Geumseong-ri shows ductile deformation (Kim et al., 2012).
The Impi Formation is distributed at Oksan-myeon and Jinbong-myeon on a small scale, and composed of quartzofeldspatic schists and mica schists with intercalation of calcareous layers (see also Kim et al., 2012).
The Bangchukdo Formation shows four facies combinations (Fig. 4-6); 1) sandstone and dark gray mudstone (or biotite gneiss); 2) alternating ssandstone and light gray mudstone; 3) sandstone and granule conglomerate; and 4) solely of cross-bedded sandstones. The rocks of this Neoproterozoic formation are rarely metamorphosed and deformed (Fig. 4-7). Song (2010) presented that the ages of youngest zircons contained in the Bangchukdo Formation dated to be the Neoproterozoic age. The Amphibolite is distributed in Gogunsan islands, intruded the Bangchukdo Formation (Fig. 4-8).
2-3. Paleozoic Sequence
The Oksan Formation is distributed mainly in the Iri Sheet, and extends to the Gunsan Sheet, especially at Oksan on a small scale, and composed of sandstone, dark gray mudstone and conglomerate (Fig. 4-9; see also Kim et al., 2012).
2-4. Jurassic Sequences
The low metamorphosed sediments including the quartzite pebble-bearing conglomerate and dark gray mudstone prevail in the central part of the Gunsan Sheet between two major N-S trending faults. Lee et al. (1997) described these sediment as being Permian, but our study of plant fossils reveals that these prevailed since the Triassic and, indicates that the sediments belong to the Nampo Group (Fig. 4-10). It seems that the sediments including quartzite pebble-bearing conglomerate correspond to the Jogyeri Formation, and the dark gray mudstone dominant unit would belong to the Amisan Formation of the Nampo Group in the Chungnam Coalfield. Because of some problems in correlation, the usage of the formations is reserved, and 'Mudstone and Sandstone' and 'Conglomerate and Mudstone' are adopted in this report. The unit 'Mudstone and Sandstone' consists mainly of dark gray mudstone, and partly of alternating mudstone and sandstone (Fig. 4-11). Sandstones are composed mainly of quartz and muscovite. The unit 'Conglomerate and Mudstone' is distributed around the Wolmyeong reservoir, Gunsan and at Ogok-ri and Susan-ri, Okgu, and is composed of conglomerate, mudstone and sandstone (Fig. 4-12). The existence of well-round quartzite pebble as clasts displays the affinity to the Jogyeri Formation.
2-5. Jurassic Granites
The Biotite Granite mainly occurs at Okgu, Hoehyeon and Jinbong in the Gunsan Sheet and at Dongjin-myeon and Buan-eup in the Buan Sheet, and contacts with the Two Mica Granite with NE-SW trending fault around Buan. The Biotite Granite and Two Mica Granite display generally granular texture but partly mylonitic foliation. At Simpo-ri, Jinbong, the Biotite Granite is composed of recrystallized quartz grains forming mylonitic foliation as well as primary minerals such as quartz, K-feldspar and biotite (Fig. 4-13).
The Two Mica Granite is distributed in the western part of Gunsan Sheet, and presumably overlain by the Cretaceous Sanbukdong and Nansan formations, The granite contains pink feldspar as the Biotite Granite does. In contrast, that of the Buan Sheet is bright colored, and extends to the Gimje and Iri sheet area. Under the microscope, both of these two mica granites consist of quartz, K-feldspar, plagioclase, biotite and muscovite (Fig. 4-14). The amount of biotite in Two Mica Granite varies from place to place in the western part of Gunsan Sheet.
The Porphyritic Granite, distributed at Haseo-myeon and Dongjin-myeon in Buan Sheet, intruded the Biotite Gneiss, and was covered by the Cretaceous Jangsinni Formation, and then was intruded by Late Cretaceous Baengnyeonni Rhyolite. The granite consists mainly of quartz, plagioclase and biotite (Fig. 4-15).
The phenocrysts are usually as large as 1~2cm. The U-Pb age of zircons in this granite was dated to be 168.8±5.4Ma by SHRIMP analysis.
2-6. Cretaceous Sequences
The Nansan Formation is distributed at Nansan, Okseo (Gunsan Sheet) and at Sinsido and Gonnido islands (Jangjado Sheet), and consists of reddish conglomerate and pebbly sandstone with minor reddish mudstone. Around Nansan, boulders of granite, sandstone, tuffs are included in the conglomerate, which shows channels in lower part, and pebbly sandstones prevail in the upper part (Fig. 4-16). In the Sinsido area, channel and lateral propagation of conglomerate beds are recognized (Fig. 4-17). The Yamido Rhyolite, dated to be 93.6±2.1Ma, erupted over the Nansan Formation, implying the Early Cretaceous age of this formation. The Nansan Formation is also developed in the southeastern margin of the Gonnido island, where alternating sandstone and mudstone were deposited (Fig. 4-18).
The Sanbukdong Formation is distributed in the mid-northern part of the Gunsan Sheet, and assumed to overlie the Jurassic Two Mica Granite. The formation consists mainly of dark gray mudstone and sandstone with minor reddish mudstone and sandstone (Fig. 4-19). Sedimentary structures such as ripple marks and sun cracks are often found. Plant fossils of Family Cheirolepidaceae and Family Cupressaceae recognized in the formation indicates the age of Early Cretaceous (Fig. 4-20). Note that dinosaur tracks and Esterites fossils are also found and indicate the environment of shallow lake in the warm temperate region (Fig. 4-21). Dinosaur tracks are well preserved on this formation (Fig. 4-22), and is expected to be one of natural monuments.
The Jangsinni Formation is distributed at Jangsin-ri, and Daehang-ri in Buan Sheet, and is deposited on the Jurassic Porphyritic Granite or on Paleoproterozoic Granite Gneiss (Fig. 4-23). The formation is composed of alternating sandstone and reddish mudstone with minor conglomerate and dark gray mudstone. Note that the reddish mudstone contains angular quartz grains, indicating the possible volcanic origin (Fig. 4-24), and that the attitudes of beds become steep near the basin boundary fault. The Biando Formation is distributed around the Biando and Sadangdo islands in Jangjado Sheet, and is intruded by the Deoksando Granite at the Biando island. The Biando Formation consists of alternating reddish or gray mudstone and sandstone, and calcrete layers develop in the mudstone bedaround Biando (Fig. 4-25), and of lapilli tuff, lapillistone and tuffaceous sediments at the Sadangdo island (Fig. 4-26).
2-7. Cretaceous Volcanic Rocks
The Gyehwado Tuff mass is isolated from the Gogunsan and Buan volcanic terrains. The Tuff consists of tuff breccia, lapilli tuff and tuffaceous conglomerate in the main terrain, and tuffaceous conglomerate with intercalating reddish mudstone and pebbly sandstone or tuff blocks mingled with reddish mudstone on the western margin (Fig. 4-27).
The Cretaceous geology of the Gugunsan area is composed of the Munyeodo Trachyte, Yamido Rhyolite and Seonyudo Rhyolite Breccia. The Munyeodo Trachyte and Yamido Rhyolite are so similar in field as not to be distinguished in field, but under the microscope. The former displays pilotaxitic texture and the latter shows the trachytic texture (Fig. 4-29). The Munyeodo Trachyte is distributed at the Munyeodo and Sinsido islands, and the Yamido Rhyolite and Seonyudo Rhyolite Breccia in the other areas in the Gogunsan islands. The Seonyudo Rhyolite Breccia displays moderately circular form, and is presumed to be associated with the caldera collapse in the Gogunsan volcanic terrain (Fig. 4-31). Because the U-Pb age of the Yamido Rhyolite is dated to be 93.6±2.1Ma by SHRIMP analysis (Fig. 4-30), the Gogunsan volcanic mass is thought to be formed in in the period prior to the Buan volcanics.
The Buan volcanic mass of the Buan Sheet is composed of Byeonsan Tuff, Baengnyeonni Rhyolite, Gisangbong Tuff and Samyebong Rhyolite, and extends to the Julpo Sheet area. The Byeonsan Tuff was intruded by the Baengnyeonni Rhyolite and then, the Gisangbong Tuff was deposited over the two. Finally, the Samyebong Rhyolite erupted in the Buan volcanic terrain as the last volcanic activity. The Byeonsan Tuff is widely distributed in the area, and consists mainly of lapilli tuffs, and of block tuffs, ash tuff, tuffaceous sediments around the Songpo harbor or on the base of this unit (Fig. 4-32).
The Gisangbong Tuff is easily discriminated from the Byeonsan Tuff in that the former consists of dark-colored crystal rich lapilli tuffs (Fig. 4-35). The tuff does not extend to the Julpo Sheet area. Under the microscope, the tuff displays the welding of the ash matrix (Fig. 4-35).
2-8. Cretaceous Intrusive Rocks
The Deoksando Granite is distributed at Deoksando and Biando. At Biando, the granite intrudes the Biando Formation. This biotite granite consists of quartz, feldspar and large amount of mafics, and displays an equigranular texture. The U-Pb age of zircons was dated to be 86.3±0.69Ma by SHRIMP analysis (Fig. 4-37).
The Feldspar Porphyry mainly occurs as dykes or small stocks at the Bideukchi village, and at small islands near the Sadangdo island. Under the icroscope, the rock consists of quartz phenocrysts on the microcrystalline matrix (Fig. 4-38). As small amount of biotite is detected, the rock may comprise the granite porphyry. The Vein Quartz, the last Cretaceous igneous rock, is found at aengnyeon-ri, Seoksang-ri and Sinheung-ri in the Buan Sheet, and intrudes the Paleoproterzoic Biotite Gneiss, Jurassic Two Mica Granite, and Cretaceous Baengnyeonni Rhyolite and Gisangbong Tuff.
2-9. Quaternary Sequences
Quaternary unconsolidated clastic sediments consist of Alluvium along the rivers and streams in the lowland and valleys, and Beach Sand including the beach sand, dune sand and beach gravels.
3. GEOLOGIC STRUCTURES
The Gunsan Sheet area is divided into three structural domains by two major N-S trending faults (Fig. 5-1). Domains Ⅰand Ⅱ are mainly occupied by the Neoproterozoic Geumseongni Formation and Jurassic Nampo Group, respectively. Bedding or foliation traces of the two units show similar trends, and display two different synclines around Ogok-ri and Geumseong-ri, divided by the fault between Domains Ⅰand Ⅱ (Fig. 5-1). Bedding traces in Domain Ⅲ show the dimension of the Cretaceous basins of Nansan and Sanbukdong formations, and seems to be affected by the N-S trending fault between Domains Ⅱ and Ⅲ.
Three faults develop in the Buan area; one is the southern tip of the Hamyeol Fault related to the Cretaceous Puyeo Basin. The basin of Jangsinni Formation is controlled by the NE-SW basin boundary fault. Conspicuous folds are developed in the Neoproterozoic Bangchukdo Formation, and the axes of anticlines display E-W or WNW-ESE directions, indicating N-S or NNE-SSW compression without knowing the timing (Fig. 5-2).
In the Gogunsan volcanic terrain, several sets of joints are developed: NW-SE or WNW-ESE, N-S, NE-SW-trending closely spaced joint sets (Fig. 5-3). These are thought to be tension joints, and relative relation exists between joint sets.
4. GEOLOGIC HERITAGES
The fold structures at Maldo was designated as a natural monument in 2009, and displays two folding episodes, thrust faults and sedimentary structures such as ripple marks and cross bedding (Fig. 6-1). Several geological features such as chevron folds at the Gwangdaedo island afford sightseeing points(Fig. 6-2).
Dinosaur tracks were discovered during the geological mapping of the Gunsan Sheet in 2013, and is expected to be designated as another natural monument in near future.
5. ENGINEERING GEOLOGY
Several quarries for granites were established to presumably construct the Saemangeum dikes, but now nearly closed and environmental restoration was made.

목차 Contents

• 표 지 ... 1
• 목 차 ... 7
• 1. 서 언 ... 9
• 2. 지형 ... 11
• 3. 지질배경 및 층서 ... 13
• 4. 지질각론 ... 18
• 가. 고원생대 ... 18
• (1) 흑운모편마암 ... 18
• (2) 화강편마암 ... 21
• 나. 신원생대 ... 22
• (1) 금성리층 ... 22
• (2) 임피층 ... 24
• (3) 방축도층 ... 25
• (4) 각섬암 ... 27
• 다. 고생대 옥산층 ... 28
• 라. 쥬라기 남포층군 ... 29
• (1) ‘이암 및 사암’ ... 30
• (2) ‘역암 및 이암’ ... 32
• 마. 쥬라기 화강암류 ... 33
• (1) 흑운모화강암 ... 33
• (2) 복운모화강암 ... 34
• (3) 반상화강암 ... 36
• 바. 백악기 퇴적층 ... 37
• (1) 난산층 ... 37
• (2) 산북동층 ... 39
• (3) 장신리층 ... 43
• (4) 비안도층 ... 44
• 사. 백악기 화산암류 ... 47
• (1) 계화도응회암 ... 47
• (2) 고군산군도 지역의 화산암 ... 49
• (가) 무녀도조면암 ... 49
• (나) 야미도유문암 ... 50
• (다) 선유도유문각력암 ... 51
• (3) 부안화산체 화산암류 ... 52
• (가) 변산응회암 ... 53
• (나) 백련리유문암 ... 54
• (다) 기상봉응회암 ... 55
• (라) 삼예봉유문암 ... 56
• 아. 백악기 관입암류 ... 57
• (1) 덕산도화강암 ... 58
• (2) 석영반암 ... 59
• (3) 맥석영 ... 60
• 자. 제4기 층 ... 60
• 5. 지질구조 ... 62
• 가. 군산도폭 지역 ... 62
• 나. 부안도폭 지역 ... 63
• 다. 방축도ㆍ장자도도폭 지역 ... 65
• 6. 지질문화재 ... 66
• 가. 말도 습곡구조 ... 66
• 나. 고군산군도와 부안의 문화재적 지질노두 ... 67
• 다. 군산 공룡발자국 ... 68
• 7. 응용지질 ... 68
• 참 고 문 헌 ... 69
• SUMMARY ... 71
• 끝페이지 ... 86