EXPLANATORY TEXT FOR GEOLOGICAL MAP OF KOREA 1:1,000,000 scale
Edited by Merited Geologist Ryu Jong Rak and Dr.Assistant Prof. Ri Juk Nam Cartographic Design and Production by Choe Nam and Ri Sil Hun
Central Geological Survey of Mineral Resources Ministry of Natural Resources Development Pyongyang Democratic People's Republic of Korea
1994
Ail rights of this text and atached Geological Map of Korea remain with the Central Geological Survey of Mineral Re sources, Ministry of Natural Resources Development, DPR Korea. No parts of the geological map and the text may be reproduced, stored in a retrie val system, or transmitted, in any form or by any means without the prior written consent of the Central Geological Survey of Mineral Resources. Violators will be prosecuted.
CONTENTS Page Pref ace l Description
I. Archean Erathem 1. Archean stratigraphy ...... 3 2. Archean intrusives ...... 3 II. Lower Proterozoic Erathem 1. Lower Proterozoic stratigraphy ...... 4 1) Songj in Series ...... 4 2) Pukdaechon Series ...... 6 3) Namdaechon Series ...... 6 2. Lower Proterozoic Intrusives ...... 7 III. Middle-Upper Proterozoic Erathem 1. Middle-Upper Proterozoic stratigraphy ...... 8 2. Middle to Upper Proterozoic intrusives ...... 13 IV. Lower Paleozoi c Erathem (Hwangju Group) 1. Cambrian system ...... 13 1) Lower Cambrian Junghwa Series ...... 13 2) Middle Cambrian Hukgyo and Mujin Series ...... 15 3) Upper Cambrian Kophung Series ...... 15 2. Ordovician system ...... 15 1) Lower Ordovician Singok Series ...... 15 2) Middle Ordovician Mandal Series ...... 16 3) Upper Ordovician Sangsori Series ...... 16 3. Silurian system ...... 16 1) Lower Silurian Koksan Series ...... 16 2) Upper Silurian Wolyangri Series ...... 16 V. Middle Paleozoic stratigraphy and intrusives 1. Devonian-Carboniferous Rimjin Group ...... 18 2. Middle Paleozoic lntrusives (Namgang Complex) ...... 20 VI. Upper Paleozoic stratigraphy and intrusives 1. Upper Paleozoic .stratigraphy ...... 20 l) Phyongan Group ...... 20 2 ) Tuman Group ...... 22 2. Upper Paleozoic intrusives ...... 22 VII. Mesozoic stratigraphy and intrusives 1 . Mesozoic s tratigraphy ...... 24 1) Triassic-Jurassic ...... 24 2) Cretaceous ...... 30 2. Mesozoic intrus ives ...... 32 1) Triassic intrusives (Hyesan and Phyonggang Complexes) ...... 32 2) Middle Jurassic intrusives (Tanchon Complex) .. .. . 33 3) _C retaceous intrusives (Amnokgang Complex) ...... 33 VIII. Tertiary stratigraphy and intrus ives 1. Tertiary stratigraphy ...... 34 1) Eocene ...... 34 2) Oligocene ...... 34 3) Miocene ...... 36 4) Pliocene ...... 37 2. Tertiary intrusives ...... : ...... 37 IX. Quaternary stratigraphy and intrusives 1. Quaternary stratigraphy ...... 39 2. Quaternary intrusives (Hoeryong Complex) ...... 39
Figures 1. Stratigraphic units and intrusives of Korea 2. Columnar section of the Machonryong Group ...... 5 3. Distribution of the Pre-Cambrian strata ...... 9 4. Columnar section of the North type Sangwon Group ...... 10 5 . Columnar section of the South type Sangwon Group .: ...... 12 6. Columnar section of the Hwangju Group ...... 14 7. Columnar section of the Rimjin Group in the Cholwon- Kumchon regions ...... 19 8 . Columnar section of the Phyongan Group ...... 21 9. Columnar section of the Tuman Group ...... 23 10. Distribution of the Mesozoic strata and intrusives ...... 27 11. Columnar section of the Taedong and Jasong groups ...... 29 12. Columnar section of the Taebo Group ...... 31 13. Columnar section of the Anju Group in the Anju-Pakchon regions ...... 36 14. Columnar section of the Hamgyong Group in the Kilju Myongchon regions ...... 38
Tables 1. Stratigraphic units of Mesozoic Erathem ...... 25 2 . Stratigraphic units of local regions of Taedong Group .... 26 3. Stratigraphic units of Tertiary Erathem ...... 35 PREFACE
Korean Peninsula is located at 33°06' 43" - 43° 00' 36" N latitude and at 124°10' 47" - 131° 52' 40" E longitude, covering an area of 222 , 209.231 square kilometers including the main land and some 4 , 198 islands. Korea is situated in the eastern part of the Asian Continent and is surrounded by the Korea East Sea, Korea West Sea and Korea South Sea. She is rugged with mountains occupying 79.87 % of the whole territory. Mt. Paektu (2750 m) in the northernmost Korea is the highest peak in the East Asian Continent.
From ancient times, Korea has been known as an embroidered land blessed with abundant mineral resources represented by gold and silve r. The beautiful landscape and the wealth of natural resources are derived from unique and diversified geological and tectonic processes s ince Archean.
However , the natural resources had not been fully utilized for Koreans when Korea was unde r the reign of the Japanese imperialists. When libe rated from Japanese colonization in 1945, Korea had been left with only a few geologists and without any reliable ge ological map available . The 1 : 50,000 scale geological survey cove red only 12 % of the whole country wi th much less coverage in its northe rn part, being only 6 %. A map in the scale of 1:1,000,000 publishe d by the Japanese in 1938 was no more than a sketch map.
Therefore . geol ogical survey in Korea started from s cratch. Under the wis e leade rshi p and warm care of the great l e a der Presi dent Kim Il sung and the Worke r s ' Party of Korea, numerous qualified geologists had been brought up, which e nable d 1:200,000 scale geological map throughout the northern half of the Korean Penins ula to be completed in 1962. Subsequently, the geological mapping in the scale of 1:50,000 had been v igorously conducte d all over the country, r e sulting in a final stage.
As state d earlie r, the primary results of the above surveys res ulted in t h e publicatiion of the 1:1,000,000 Geological and Tectonic Maps of Korea in 1964 . Further detailed geological surveys continue d, and on this bas is 1:500,000 Tectonic and Geological Maps were published in 1970 and 1971 respectively.
During the c ours e of these laborious field works , numerous new formations and intrusives h ave bee n established which have rec tifi ed previously-held erroneous geological and t e ctonic conce pts. Some o f the major discove ries and new systematization are : Archean and Proterozoic stratigraphy, subdivision of the lowe r Paleoz oic, discove ry of Ordovician, Si lurian and Devonian fossils, refined stratigraphy of the Pe rmian Tuman Formation in ').,~tJl'1 oortheastern corner of Korea, classification of the Mesozoic ,. Mid tntrusives throughout the country and clarification of the )1~Mo .. Cenozoic tectonic movements. Thus the novel understanding of ,aoology of Korea have based itself on the new dimension of sound ~eologlcal, paleontological and petrographic evidence, which have become the basis of a higher stage of development. In 1970s much attention was paid on clarifying the law of distribution of useful minerals. The efforts together with the application of newly established concepts have led to discovery of nume rous new mineral deposits, many of which had been in the past thought absent in Korea. The geological survey in Korea entered a new era in 1980s under the meticulous care of the dear leader Comrade Kim Jong 11. Geological surveys have been carried out in more details. The results were fruited in the form of fifteen-vol umed "Mineral Deposits in Korea" in 1984, and six-volumed "Geological Cons tructi on of Korea".
The present "Geologic~! Map of Korea" in the scale of 1 :1,000,000 is based on the results of all cumulative efforts until today and totally up-dated the previous Geological Map of Korea with the same scale published in 1971 in Korean l anguage. The s t ratigraphic units in the attached map are marked witlt series as the smallest ones. Formations in the series with minor thickness were included in the system or are marked in the merged s eries. Int rusive rocks are marked by age, complex or intrusive phas e. This Geol ogical Map of Kore a pre pared in English by the autho rity of the DPR Korea is aimed at accommodating the need of and request from world- wide academic circles, i nstitutions, bus iness groups and individual scientists. We hope this publi cation will help readers understand relatively little known geology o f Korea.
2 DESCRIPTION
I. ARCHEAN ERATHEM
1. Archean stratigraphy
The Archean Erathem in Korea, called Rangrim Group, is widely developed in the Rangrim and Kyonggi Anticlinoria, and even in uplifts in the Phyongnam Synclinorium in small scale. They consist mainly of migmatized greenstone. biotite gneiss. quartzite, granulitic gneiss and a small amount of amphibolite, marble and crystalline schist. In addition. there are evenly high alumosilicate, flaky graphite, including cordierite and almandine in meta-sediments. · The lower section is composed of alternating bed with ancient greenstone and elastic sedimenta ry-metamorphic rocks.
The middle section is mainly made of terrigenous argillaceous carbonates, and in part metamorphic rock of intermediate-basic effusive sediments. The upper section consists chiefly of terrigenous elastic rocks and in part metamorphic rocks of intermediate-acidic effusive origin.
The Rangrim Group had undergone the injection metasomatic migmatization by granitoids of the Ryonhwasan Complex. The granitoids belonging to the Ryonhwasan Complex (2040 Ma/Ar) intruded into the sedimentary-metamorphic rocks of the Rangrim Group.
The Rb/Sr ages of biotite gneiss in the Kyonggi Anticlinorium showed about 2025 Ma or 2765-2640 Ma.
2. Archean intrusives
The Archeozoic intrusives consist of the Andol Complex consisting of mafic-ultramafic rocks, and Ryonhwasan Complex consisting of metasomatic granites.
The Ando! Complex exists in migmatized gneiss as small sills or dikes. The Complex is composed of peridotite, hornblendite . gabbro, serpentinite and metagabbro. The Ando! Complex was formed by . intrusive action that took place simultaneously with Ryonhwasan Tectonic Movement.
3 T~e Ryonhwasan Complex is divided into the first, second and lbitd classes based on occurrence and petrological features. The first class consists of biotite granite, almandian cord!erite-biotite granite, semi-alaskite, gneissose granodiorite. At the contact with gneisses of the Rangrim Group occur shade migmatites and bedded shade migmatite. The second class consists of porphyroblastic biotite granites which are distributed within the area of the first class granite, but as augen gneiss rarely in Rangrim Group gneiss They, replaced by sedimento-metamorphic rocks, contain almandine, cordierite and flaky graphite. The pinkish porphyro blastic granite metasomated the ancient green rocks, but do not contain garnet, cordierite and flaky granite. The third class includes almandine leucogranite. At the contact between the third class granites and Rangrim Group gneisses, layered migmatite of injection metasomatic type and branched migmatites develop. Veins associated with the Ryonhwa san Complex are grey pegmatites.
II. LOWER PROTEROZOIC ERATHEM
1. Lower Proterozoic stratigraphy
The Lower Proteroz oic in northern half of the Republic is called Machonryong Group. It is divided into Songjin, Pukdaechon and Namdaechon Series in ascending order (Fig.2). ·
rhe Lower Proterozoic in other areas of Korea are called differently; Musan and Uiju Groups.
1) Songjin Series
The lower part of the Songjin Series is composed of plagioclase amphibolite and pyroxene amphibolite intercalate d with biotite gneiss and ferrugenous quartz ite. The upper part of the Series is composed of alternations of various crystalline schist, graphitic schist, garnet- plagioclase · gneiss, biotite gneiss, quartzite, marble and amphibolite. Rocks of the Songjin Series are migmatized by layered injection of the Riwon Complex.
The Songjin Series is 1500 to 2000 m thick as a whole.
4 _,.,,·-·- ··~ ·~,..... _ -· ._....., __.,_ ,...... ~.... = ...... "._..____ ,.._._ ..__ Gro Ser- Thie Section L.LthoJu~y up ies (m) ...... __,., ft...... ~-...... "".. Siliceous schist quartz .It<• , '-" .-...... - '-"- serici tic bioti tic sch i st ...... - . ~. ----- c: . ,,_ ...... Aug en sillimani te, bioti te 0 ~ ..c: -·...... schist, stauvolite biotite schJ sl , () ...... _...... -..._ . 1700 serici tic chlorite sch ist, d) ~ ~- ...... - cl;! . ..,,_ . -.... . quartzite, limestone interbed 'O s s ------.,,,,...... ,,,,_,,,- 2800 tl! ----...... - Alternating mica schis t and z crystalline limestone, au gen - ..-, sillimani te biotite schist,
0 - D -- • ~ a bite schist on amphibole - - ~. - .- " " " . II • ~ --;.._ ..... -Lt ... -- 11-:. -:_u --- Tremoli te dolomite and marble, \lO c::: h-1'-' ':f ~ Magnesite str omatoli te fossil 0 » c: I... 0 c: ..c:: 0 () -3000 v v ..c: ~ - - Alternating crystalline schist () tl! """" " ~ cl;! 'O - amphiboli te, limestone l:: ..ld - - - :I ...... ~ H -I -K ~;z= Massif dolomite, schist, amphiboli te, marble interbed, ,, v v - K I s tromatoli te fossils -H - u ,, . Jr - ...... -u """'n II v v v ··············· Alternating crystalline schist, -...... - 1500 amphibolite, quartzite, bioti t e II -II u c: ...... ~ gneiss ·~ - - 5 ' "'") "" ...... - tlO v ' -v ~ v 2000 .:: --. 0 - - ...... Alternation V'J v -~ ~ of bioti te v v II u II ...... II • gneiss and amphibolite ...... v v -v
Fig. 2 Columnar Section of Machonryong Group
5 2) Ptlkdaechon Series
It consists of massive dolomitic marble in the lower part, alternation of amphibole schist and calcareous schist in the middle part, and alternation of tremolitic dolomite and calcitic marble in the upper part.
The well-known magnesite ore bodies occur in the upper part of the Pukdaechon Series in South Hamgyong Province.
The total thickness of the Pukdaechon Series reaches about 3000 m.
3) Namdaechon Series The lower part of the Namdaechon Series is composed of an alternation of mica schist and crystalline limestone, with albite schist and tourmaline albite schist in its top part.
The middle part is made of augen silimanite biotite schist. staurolite biotite schist, biotite muscovite schist, sericite chlorite schist, and alusite garnet schist, intercalated with quartzite and crystalline limestone.
The upper part comprises siliceous schist, micaceous quartzite and quartzite.
The thickness of the Namdaechon Series ranges from 1700 to 2800 m in Komdok-Hochon region.
The K/Ar ages of biotite schist of the Namdaechon Series in the Machonryong Group showed 1700-1740 Ma. The age of lead ore of the Pukdaechon Series indicated 1790 Ma (u-pb ' method) and 1920 Ma (Th method). Whereas, the K-Ar ages of phlogopite of the Songjin Series fell in the range of 1820 ~nd 1910 Ma.
Musan Group: The Musan Group is composed mainly of biotite gneiss, paramica gneiss, amphibole biotite gneiss, amphibolite, silimanite biotite schist, biotite epidote schist, ferrugenous quartzite, and micaceous quartzite, etc.
The rocks of the Musan Group were migmatized by layered injection of the granite of the Riwon Complex.
Uiju Group: The Uiju Group is divided into three formations. The lower formation is composed of mainly biotite gneiss, biotite schist, siliceous schist, quartzitic gneiss and migmatite. It also
6 ~~ -~~-~~:~~~,~-~·~· :~§f~~ .~~~~; includes (in less amount) ferrugenous quartz! lo, mttir:Q
Three groups of intrusives are discerned in the Lower Proterozoic: Pyoksong, Riwon and Sakju Complexes.
The Pyoksong Complex consists of mafic-ultramafic rocks formed during the earliest geosynclinal stage, constituting country rocks and conformable bedded bodies or veins. It is composed of fine hornblende, porphyroblastic hornblendite, tremolite actinolitic rock, amphibole gabbro, plagioclase amphibolite, medium-coarse grained amphibolite and pegmatic amphibolite.
The Riwon Complex distributes mainly in Machonryong, Tuman Rjver and Amnok River regions. It intruded into the Archean and Lower Proterozoic and are overlain angular unconformably by the Sangwon System. The representative intrusives of the Riwon Complex are distributed in Chaho, Huchiryong, Sangnong, Huisabong, Ryongyangri, Kapsan and Musan. The complex is made of medium to fine grained biotite granite, granodiorite, medium to fine grained tourmaline leucocratic granite. The boundary of the complex is often ambiguous caused by formation of migmatite zone due to severe injection into country rock.
7 III. MIDDLE-UPPER PROTEROZOIC ERATHEM
1 . Middle-Upper Proterozoic stratigraphy In Korea the Middle and Upper Prolerozoics have not yet been distinguished for lack of solid geological and paleontological evidence. We tentatively included the following formations in the Middle Proterozoic: Sangwon (north type) and Hwanghae Groups, Huchang , Chunchon and Ryulr1 complexes. The Upper Proterozoics are : Sangwon Group (south type), and Kuhyon Group in northern half of the Republic, and Okchon Group in south Korea.
The Sangwon Group ls underlain unconformably by the Lower Proterozic Erathem and Js overlain unconformably by the Upper Proterozoic strata or Lower Paleozoic Hwangju Group.
Based on the stratigraphic succession, thickness, lithological and metamorphic phases, folding structure and absolute ages, it is divided into the "south type" and the "nortb type" . The former (south type) is typically developed in the Haeju Subsidence Zone within the Phyongnam Synclinorium, whereas the latter (north type) in the Pyongyang Uplift Zone within the Pyongyang Synclinorium (Fig. 3).
The northern type Sangwon Group in the Pyongyang Uplift Zone is divided into J ikhyon. Sadangu and upper schist Series in ascending order. The Jikhyon series is composed of basal quartzite (5-20 m), quartz-Chlorite schist, marble, and intercalated quartzite. Its age was determined as 1245-1400 Ma by Pb/Pb method, corresponding to Middle Proterozoic.
The Sadangu Series is composed of lower Naedong limestone formation, Upper Obongsan dolomite, limestone formation, Majonri marble and phyllite formation. The Pb/Pb age of the Naedong Formation showed 1160 Ma.
The upper schist series is composed of green schist, quartz mica schist, limestone and intercalated quartzite (Fig. 4).
The Hwanghae Group is exposed in the Ongjin and Yulla Anticlines, both in the Phyongnam Synclinorium. It was intruded by Pyoksong and Ongjin Complexes, and is overlain with an angular unconformity by the Upper Proterozolc (south type Sangwon Group).
The lower unit of the Group, 800 to 1000 m thick, is composed of limestone, green schist and siliceous schist.
The middle part comprises actinolite epidote rock, amphibolite, amphibole schist, green rock, etc., with biotite schist and limestone at its top. The thickness of the middle unit is
8 60k m O 120km l::HOH3::J:d:;i:===::::t:==:::11
• AR lllllllll P Rz" North Sangwon"
• AR2-PR, ~ P Rs "so uth Sang won " ~PR,
Fig. 3 Distribution of the Pre-Cambrian Strata
9 Li thoJ ogy (m)
I +" r... Ill ~..... ;:;:~,-:<-7 150 green sc:h1st, serici te- chlori te ~:d :.-:-:. ... :-:--:-.: S schist, quartzite, limy schist, g ,CJ, •. --:-•. :-:-...... 200 banded siliceous schist i.:.._~¥:..:+'~-+~T....,.~--.r'---+-~~t----~~~~~- ~ -....; 1-T-'-,...... 'T""-i l ime stone, magnetite bearing =L...... -,...... --. 250 0 - --~- ...... sericite-chlorite schist, quartzite, ...... ~ s -.i .. sericite-chlorite schist, t'd 350 ~ stromntolite fossil dolomite, interlayered limestone, stromatolite fossil
U.my schist
quartzite, siliceous phyllite,
.,... ·~ '""""'· sericite-chlorite schist, limy schist limestone, quartzite, ~~ ~ ~:: siliceous schist r:JJ ~ ••·••· •·••••· ~ i:: ...... r:JJ t'd ...... · .·:;: 5 .... 25 quartzite, interlayered limestone Fig. 4 Columnar Section of the North Type Sangwon Group
between 500 and 1000 m.
The upper unit is composed of alternating quartz porphyry, quartzite porphyry, tuffaceous breccia and sericite-siliceous schist. Its thickness varies from 400 and 1000 m.
The Chunchon Group in the type Chunchon region, Kangwon Pro vince (South), is underlain by folded basement. The Group is compos~d of sericite schist, biotite schist, biotite chlorite schist, marble, striped gneiss, augen gneiss and quartzite, the lower part of which is called Jangrak Series and the upper part Chunsong Series.
The Jangrak Series was intruded by a granite with the age of
10 1420 Ma. The age of Ryulri Group was determined as 1430 Ma and 1525 Ma by Rb/Sr method. whereas that of Jirisan Group as 1234 Ma. These ages from Ryongnam region, south Korea, well correlate to those of the Chunchon Group, middle Korea. Thus the Ryulri. Jirisan and Chunchon Groups are all assigned to the Middle Proterozoic in age. The "South type Sangwon Group" in the Haeju Subsidence Zone is divided into Jangbong quartzite series (250-300 m), Obongri phyllite series (850 ~ 950 m), Jangsusan quartzite series (1100- 1150 m), Ansimryong calcar~ous phyllite series (400-450 m), Unjoksan limestone series (456- 500 m), Tokjaesan dolomite series (450-750 m), Chongsokduri limestone series (800-900 m), Mukchon siliceous phyllite series (1700-1900 m), and Myoraksan series (alternating limestone and dolomite, 1000-1100 m) in ascending order. The absolute ages (Pb/Pb) of the above Unjoksan and Chongsokduri series range from 800 to 905 Ma. indi cating Late Proterozoic (Fig. 5). The "South type Sangwon Group" in Junggang-Hyesan-Riwon region, northeast Korea, has the same stratigraphic succession and the degree of metamorphism as that in the above Haeju Subsidence Zone. In Riwon-Kimhyonggwon-Kapsan region, Jangbong, Obongri and Jangsusan Series, the basal part of the Sangwon Group, develop. but the upper part . consisting of the limestone series is missing there. In Hyesan region, Kuhyon Group (Uppermost Proterozoic) is absent. In Junggang region, · near the Korea-China border, a whole succession of Myoraksan Series (Uppermost Proterozoic) is developed . There its stratigraphy is closely associated with the Upper Proterozoic Erathem in Hunjang and Tunghw~ in China. The Jangbong quartzite series (K/Ar glauconite age, 853 Ma) in Junggang region is underlain unconformably by the Ongjin Complex granite with 1370 Ma of age (Fig. 3).
Some outcrops of the Upper Proterozoic Erathem (thin and weakly metamorphosed) are known to develop in the Rangrim Anticlinorium: Hwaphyong, Manpho, Kanggye, Chosan-Kophung, Pyoktong, Yomju and Kwaksan regions. ·
The Kuhyon Group is mainly distributed within the Haeju Subsidence Zone . The group is underlain unconformably by various horizons of the Sangwon Group and the Yonsan Intrusive Comp lex, and is overlain unconformably by the Cambrian rocks. It is divided into the Pirangdong and Rungguri Series.
The Pirangdong Series is composed of calcareous conglomerate, e I Cfl I Q) ·;::: Q) Thie. Cll .µ e Section Li thol ogy >.. Q) C/J C/l ~ ( m) c: - - ro alter nating clayey tll I 1000 limestone , .:.:: I I I ro I dolomite and limest one, • inter layered coaly sla t ~ . 0 I I "">.. llOO l: ~-v-,-L- stromatoli thic fossil c: 0 ...... 950 alt e r nating phylli t e qua r tzi te I .C:: ...... !le: () I a nd s iliceous phyllite. ::;. c: l: ...... 1100 i n t er layered coaly phy lli te ..r::0 () 70 c l ayey limestone, red l imestone, ..:.: ~ ·~ --,---l-'V'.J.,- \ 0 0 280 stroma toli thi c foss il i::: =' 0 l'.: c:td ...... )'. 100 bande d s iliceous s c hi s t , I tiO ...... ia s quartz ite, phy lli te. c: 0 ~ 400 ro C/l inte r layer e d coal y phylli te C/J ..r:: •.-1 f-L-r-\Y('- I L. lime s tone, i nter layered 'bO ;:) ....., , 800 Q) c:: "O I v J I dol omite, stromatoli t hic 0. o~ I >.. ..r:: 0 I I 900 C) rl'I fossil E-< ::I I I I I I J tlO 450 ..r:: c: .....,,~ i::: ~v-_.:;z:: dolomite . .µ ro .x I'd j ::l "O rl'I I . , s t roma to li t hic fossil I'd 0 , v 750 0 E-< I C/J C/l ~ i::: ta 450 "den0 - s limestone , c l ayey l imestone ;;:i - 500 -1- 1 - s 'tlO - •.-j c: 400 Ul 0 calcar e ou s s c hist c:: >.. s
12 gravel-bearing limestone and calcare ous phyllite .
The Rungguri Series is composed of phyllite and siliceous phyllite, calcareous conglomerate, limestone, dolomite, gravel bearing phyllite , and its thickness is in the range of 1000 to 1250 rn. The Upper Proterozoic in the Kyonggi Anticlinorium, south Korea, is the Okchon Group. Its lower section is made of quartzite, but its base has yet been unknown. The middle section consists of chlorite schist, phyllite, quartzite, dark schist, siliceous limestone, graphitic phyllite and striped limestone. The upper section consists of siliceous elastic rocks with intercalated limestone.
2. Middle to Upper Proterozoic intrusives
The Ongjin Complex is exposed in Ongjin, Sinwon, Pongchon regions in South Hwanghae Province , as well as Ichon, Phanmun and River Amnok regions. It consists o f granodiorite, medium to coarse-grained porphyro leucocratic granite and alkaline granite . The K/ Ar age o f the Ongjin Complex was determined to be 1371 Ma, Middle Proterozoic. The Yonsan Complex is composed mainly of gabbro-diabase which intruded into the Sangwon Group as sills.
IV. LOWER PALEOZOIC ERATHEM (HWANGJU GROUP)
The Hwangju Group is shallow sea d e posits that covered the sedimentary cover of paraplatform during Cambrian through Silurian (Fig. 6).
1. Cambrian system
1) Lower Cambrian Junghwa Series
The Junghwa Series is composed of an alte rnation of sandstone and aleurolite , with intercalated bla ck slate. Fossil zones are recognized in the series, which indicate that the Series belongs to Early Cambrian in age .
13 ...._. t."'O ..c:: I VI '-10 C.J •r-1 a; Thie. 0 s.. Section Lithology ""(!J 0. Q) 0.. l'.Il lfl (m) i •r-1 . - c: I S.. »r... 180 -- ro 0. •.-4 310 . limestone , c r inoids, coral s, f ossil I filJ I 140 s.. ""0 , Fig. 6 Columnar Section of th.e Hwangju Gr oup 14 Redlichia chinensis Zone Redlichia nobilis Zone Rediichia coreanica Zone Redlichia songsinens is Zone Redlich ia Saitoi Zone -'C""o::.crc.;;ec.oo.;;.s4p'--ir...;;;a_"'-ru""'g'""'o~s~a~ _Zone Kootenia longiformia Zone The thickness of the Junghwa Series ranges from 330 to 450 m in the Phyongnam Synclinorium, and 150-170 m in Rangrim Anticlinorium. 2) Middle Cambrian Hukgyo and Mujin Series The Hukgyo Series consists mainly of aleurolite (siltstone) and its intercalated limestone. A yellow-green fine sericitic sandstone formation (20-25 m thick) appears at the top of this series. The total th.ickness of the .series is 120 to 170 m. The Mujin Series is made of two formations in ascending order; Rimchon Formation, consisting mainly of alternated thin dark slate and limestone (15- 80 m), and Myongwolri Formation (110- 150 m) consisting of dark-grey manganese limestone. 3) Upper Cambrian Kophung Series The Kophung Series is made of grey dolomite, dark- grey limestone, white or greyish dolomite, and dark grey c layey limestone in ascending order with the thickness of 310- 400 m. 2. Ordovician System 1) Lower Ordovician Singok Series It is composed of yellow- grey marly slate, clayey limestone, conglomeratic limestone, grey dolomite, siliceous dolomite, white-yellow marly limestone, grey dolomite, yellowish light grey breccicated calcareous dolomite and marl (Sinchang marl). The thickness of the series ranges from 230 to 320 m. 15 2) Middle Ordovician Mandal Series The Mandal Series is composed of dark-grey limestone in the lower section and grey dolomite in the upper section. The thickness is between 350 and 400 m. 3) Upper Ordovician Sangsori Serles Until recently it had been generally believed that the Upper Ordovician and Silurian sediments were absent in Korea. However, their presence was confirmed in Hwangju and Poptong regions during the 1969-1976 field campaign. At Sangsori in Poptong County, a complete succession of the Upper Ordovician lying on t he Middle Ordovician is exposed. The type Sangsori Series is divided into the upper and the lower formations. The lower formation consists of alternated dark dolomite and slate, with intercalated limestone and marl. Near its base exist grey-yellow pelite, marl and dolomitic limestone. The thickness of the lower Sangsori Series at the type locality is 130 m. The upper Sangsori Series (300-350 m) comprises grey - light grey limestone, and dolomite in its lower part and clayey limestone in the uppe r horizon. Coral remains are abundant in the Sangsori Series. They have been generically identified a s Agetolites and Fo.vistella of Late Ordovician. 3. Silurian System 1) Lowe r Silurian Koksan Series It is typically exposed in Singye-Koksan region in North Hwanghae Province. The Koksan Series is composed of grey green slate and yellow green aleurolite in which grey limestone is intercalated. Its thickness is 50-70 m. 2) Upper Silurian Wolyangri Series The series is 180-200 m thick. and consists of dark grey clayey limestone, dark grey limestone, with dark slate interbed. 16 The series is fossiliferous. Th~y j~Pi Corals Paleofavosites aspera ~sofavosites sp. Kogsanensis sp. Favosites forvesi Crinoids CyclocycLicus sp. Pen tagonocycl icus mono cos tat us Bystrowicrinus amgusti/batus Brachiopods Nalivkinia elongata Nildforovaena cf. Flabellum There are many limestone gravels in the Songrimsan Series conglomerate bed in Songrim region, which contain coral remains. These facts provide evidence that the Upper Ordovician Si lurian sediments had once been deposited in the Hwangju-Songrim region in the Phyongnam Synclinorium. The Cambrian-Ordovician deposits in the Okchon Subsidence, south Korea. show different stratigraphic succession from that of Phyongnam Synclinorium. The Cambrian system in Tuwibong region in the Okchon Subsidence Zone is divided into Jangsan. Myobong, Taegi, Sesong and Hwajol Formations in ascending order. The Jangsan Formation is composed of basal conglomerate, white quarlz ile, aud t he Myubong, of an alternation of green violet slate, micaceous slate and silty slate. The Myobong Formation is chronologically equivalent with the Junghwa and Hukgyo series, and Rimchon Formation of the Mujin Series. The Taegi Formation is made of green-grey to light grey limestone. It is correlatable to the Myongwolri Formation of the Mujin Series. The Sesong Formation is composed of dark- grey to dark sandstone. arenaceous slate and yellow pelitic limestone, and is comparable to the lower part of the Kophung Series. The Hwajol Formation contains dark sandstone, limestone and marly limestone. It is correlated to the upper part of the Kophung Series . Ordovician system in the Okchon Subsidence is divided into Tongjom, Tumugol, Mak.kol, Jigunsan and Tuwibong Formations. The Tongjom Formation is equivalent to the lower Singok Series and 17 the Makkbl Formation to the upper Singok Series and lower Mandal Series. The Tuwibong Formation is composed of light grey dark limestone, interbedded with marl. It is 200 m thick. The Formation is correlated to the upper Mandal and Sangsori Series. The Hoedongri Formation, recently assigned to Silurian in age, is composed of blue-grey to white limestone with the ~hickness of some 200 m. V. MIDDLE PALEOZOIC STRATIGRAPHY AND INTRUSIVES 1. Devonian-Carboniferous Rimjin Group The Rimjin System is distributed in a band type from Kangnyong-Ongjin region, South Hwanghae Province to Cholwon of Kangwon Province. It is divided into Anhyop, Puapsan and Sangnyong series in ascending order (Fig. 7). The Anhyop Series consists of sandy conglomerate at the base, calcareous conglomerate, calcareous sandstone, slate, limestone and phyllite. Its thickness varies from 200 to 900 m. The Puapsan series is composed of alternating limestone and phyllite in the lower part, alternating aleurolite, slate and psephitic (conglomeratic) sandstone in the middle, and alte rnating sandy quartzite, aleurolite and slate in the upper. It is 950 to 1100 m thick. Mafic-intermediate effusives and their tuffs and spilite, keratophyre, etc. are widely distribute d in the Rimjin Group. Numerous fossil and floral remains occur in this series including corals ( Atry~ sp.), echinoderms, crinoids, conodonts and others ( Charophita sp.). They denote that the Rimjin Group is included in Devonian- Lower Carboniferous (see another pair text, Tectonic Map of Korea). 18 I "O ..c::: I tll ..... 0 I Q) Thie. 0 u ·~ Section Lithology Q)"" 0. Q)"" ( m) '1.. ~ U'l 200< phylli te. calcareous phylli te tll ...... :::l 100- phylli te 0 ...... 120 quartzited sandstone. ~ ""Q) c: ·- .. -· c.... ""Q) 0 alternating bi oti te spotte d ·~ ~ >.. 7 50 c:: 0 c:: . : • : &) . : :~: 0 ..J ~ ...... ~ siltstone and calcareous phylli te . .Cl ~ s... ~~ U'l . w -. 1000 ~ ...... fauna calcareous schist C,) . . .. • 20- . ~ 0 rudaceous limestone, fauna ~"T-;-TO 40 ...... 110- a l ternating phylli te and sandstone ~&:..=i:...:. 120 370 alte rnating phylli te, ~-.-:- ~ . = ··: .:.:.~ · .:..: ·: s siltstone and quartzited sandstone, 0. ~ '~. - ~ 410 brachi opoda , c rinoi dea, flora :::l 0.. ···· ·········· . , ...... 440 alternating phylli te , ~~i;;;J_;;; ~ s iltstone and quartzited sandstone, ··-·· ·· ··· 510 brachiopoda, cri noidea, fossils c:: .·-...... -· n ...- ... ~ s... - - - -.-! Q) 150 limestone, slate, calcare ous c:: 0. ..-4 ·- ..-.... 0 0. ~ sandstone coral, charophy ta, > 0 Q) ...... " .... 280 ostracod . flor a Cl «>"- o- o 50 - ~ . ~ - ~ pe bble bearing schist • ...,._ 0 ---. o 0. >----/I BO 0 - ~ slate, lime stone , >.. ---.-- --' 500 ..c::: -"' ~ biotite-chloritic schist, s iltstone, c:: ...... -.. .. . Fig. 7 Columnar Sec tion of the Rimjin Group in the Cholwon-Kumchon Re gions 19 i_,;° 1t;i\ Mtddle Paleozoic Intrusives (Namgang Complex) The Namgang Comp l ex in the Phyongnam Synclinorium occur as sills or dikes intruded into the Hwangju and Rimjin Groups, consisting of diabase and gabbro. The intrusives are accompanied with pyrite and chalcopyrite. The Namgang Complex in the Rangrim Anticlinorium is made of gabbro, diabase and hornblendite which penetrated the Archean group . Pyrite and chalcopyrite commonly occur in the intrusives. Alkaline ihtrusives are widely distributed in the Rimjingang Foldbelt that includes the Rimjin Group as main component. A granite body in Kangnyong is considered to be the same age as that of the Namgang Complex, but details are unknown . VI. UPPER PALEOZOIC STRATIGRAPHY AND INTRUSIVES 1. Upper Paleozoic stratigraphy In Korea the Upper Paleozoic Erathem develop mainly in two regions: Middle Carboniferous to Lower Triassic paraplatform sediments in Phyongnam Synclinorium (Phyongan Group), and Upper Carboniferous to Permian geosynclinal sediments (Tuman .Group) in the Tuman River region, northeastern corner of Korea. 1) Phyongan Group The group is divided into Hongjom (C2 ), Ripsok (C 3 ), Sadong (~ ). Kobangsan (Pa) and Thaejawon (P2 -T1 ) Series in ascending order (Fig . 8). The Hongjom Series contains two cyclic sediment packages ; the lower section being elastic-sediment dominated, and the upper limestone dominated. A distinctive basal conglomeratic bed develops in Nyongwol region. The thickness of the series ranges from 80 to 300 m. The Ripsok Series is composed of alternating dark grey green slate. aleuroli t e, sandstone and dark grey limesto'ne. Its upper part bears anthracite seams. It is 45 to 200 m thick. The Sadong Series is c omposed of various lithologies; grey 20 I "O I ,a r rJl Thie ·~ 0 0 (.) ·s:: Q) Section Lithology Q.) 0. Q.) (m) Cl.. µJ If) -· . . (.) ·-·-·-·-··- •.-( ~-·-·--·..-.··-·-·--· grey-green silty slate, ell s... ~~7_:_7...:_-:-...:.....-: ell ilJ alternation of purple slate and silty «'- ~ - ·-· ·- ..... 0 c: ·---·-·-- 800 slate, conglomeratic sandstone, s...... l 0 ~_:...... ,:_.-=-. -=--: f- ~ green slate, marly slate. ro I ·~ Q.) calcar eous concretion included, (tl_ silicified wood .c:: ~~---~: 1200 :- ..- .. : ..~. : ·.· .· .: ..· : f- blue-green slate, silty slate, ;• .. .· :·: ·,. ·.. ..·. ~ : . -· ·- sandstone, rudaceous sandstone -· ·- ::-.:d: ~-~-:~·-; ': •.-:-;_~ -· ·- -· ~- ·- alternation of grey-green black slate l- §';:§ -·-·- Q.) :·. . : .... :: .·.. ... ·. ·. . 500 and siltstone. plant 0. :o:·. •;.: ;,-:-.o:::o :-. 0. c:: remains, pebbly sandstone ::> <\I ·:.o:: ·.:.·.O:•··t ·-•: .·.- c: rJl -· .{)' ·- ro b.() -. -· ·- I alternation of grey-green slate, .... c:: -·-·-·-·- E <\I ··············· siltstone and light-grey ... .t:J sandstone, plant remains, 0 600 0.. ::.:: ::·:· :;_::: :-:· :'.:'· : medium to coarse sandstone --·--- grey- green slate, siltstone, coal seam , pebbly sandstone all i te slate. coarse grained 120 s... ~ c·;···1 sandstone, plant remains 0 -- - ~ "O I middle coal seam: alternation of 0 ro - siltstone, sandstone and slate plants ..J If) ::: ·:·-::-:::_.:. ::·:: 240 - main coal seam? alternating ..x: sandstone and siltstone fJl $.... Q) 0 -· ;:I tll 60 0 0. a. j coal seam: slate, siltstone. $.... 0. •.-( Q) 200 ::> Cl:: limestone, flora, fauna ~ --· ···· ···· ·-· •.-( Q.) E silver grey slate, arandisite i:: 0 .-; ····· · ...... 80 0 ·~ limestone, yellow-brown fauna .0 'C ,_. ~ ! s... "O .._ . ·- ..... c:: -~· ·- multi-coloured slate, siltstone. ro 0 .. 300 u ~ ·- limestone, fauna, flora ::c .._.- · ·- Fig. 8 Columnar Se~tion of the Phyongan Group 21 1andstone, aleurolite, dark slate, coaly slate, coal and alumina oJeurolite. This series is the major source of coal deposit in Korea. The thickness of the series varie s from 120 to 240 m. Three cyclic sediments form the Kobangsan Series. Each cycle consists of light grey sandstone in the lower part and aleurolite/dark coaly slate in the upper. Anthracite is usually hosted in the lower part of the cycle. The thickness of the series varies from 500 to 600 m. The Thaejawon Series is composed of grey to grey-green quartz sandstone, varicoloured slate and aleurolite, and reddish brown calcareous aleurolite. The series in the Tuwibong area contains rhyolite , quartzitic trachyte and tuff in its middle section . The series is 800 to 1200 m thick in Phyongnam Synclinorium, and about 2500 m at maximum in the Okchon Subsidence Zone. 2) Tuman Group The geosynclinal Tuman Group is distributed in the Hambuk Foldbel t. It is divided into three units; Amgi (C3 -P1 ) , Kyeryongs an (P1 ) and Songsang (P2 ) Series (Fig. 9) . The basal unit, the Amgi Serie s, consists of alternating dark grey to black aleurolite , pelite and sandstone . Intercalated in them are limestone and tufface ous rocks. The series is 500 to 700 m thick. The middle unit, Kyeryongsan Serie s, is composed of sandstone, aleurolite, pelite and limestone, as well as metamorphos ed basic to intermediate effusives . The unit is 1500 to 2000 m thick in total. The series carries numerous fossils, denoting its age being Early Permian. The Songsang Se ries has sandstone, aleurolite, coaly aleurolite and slate with a total thickne ss o f 1800 to 2500 m. 2. Upper Paleoz oic Intrusives The Upper Paleozoic intrusi ves are develope d i n the Hambuk Foldbel t and are represente d by two groups; 1) Chongjin Complex composed of ultramafic rocks (a special ophiolite series), and 2) Tuma ngang Complex ~ade of granitoids and granit e porphyry. 22 I "O I ..c:: I (/) Thi c 0 ·;::: o tJ ·t:; QJ Section Lithology il> c.. d! (m) 0.. J:.t:I (/J ...... ·.·.· ·. ·.·.·.·.· .. ·.· 300 poly-component sandstone, ...... ·.. · ! pebbly sandstone, siltstone, ... . ·.·. ·.· .. 500 interlayered slate + r + r + r+ r + r granitoporphyry , felsite, porphyrite + r+ r+ alternation of siltstone and slate, 1:lOa - -- - 500 «I -·-·-·- and acid effusive rock, tl) -_:-...:.-...:..- l 1:lO diabase porphyrite, interlayered c:: 0 .::=-:-=-~=:-:-:= 1 5 0 0 coaly siltstone, plant (/J r emains including coral , fossils ...... ·.·.·: ·.· ... ., -, -, fine-coarse grained sandstone of -, ., ., - - - - 500 poly-components, tuffaceous sandstone, felsite, v v v siltstone, interlayered slate v v v v v v v andesite- porphyrite, tuff, 800 conglomerate tuffaceous conglomerate, v --e:." v v '- tuffaceous sandstonei v v calcareous sandstone and siltstone, limestone, radiolarian, brachiopoda. ... :-.% ... ·. : ..'-{. ·..... b ryozoa, crinoidea and v. v • v other fossil 0 v 0 " 0 v v v r..V v 700 andesite- porphyrite, tuff, tuffite, ~ v •yo~ s tuffaceous conglomerate, bryozoa, v 0 v • 900 IV~oV brachiopoda, crinoidea fossil i--o-v 0 v • .· ..· . .·. : ·.··. .-...:...... _.. - biotite-siliceous schist. quartzite, I (/J I -.-1 ;:::l r.. limestone, interlayered c:: 0 Q) 0 r.. c.. tuffaceous rock, sponges, crinoidea, .0 Q) c. :.:.. "" ... <±:: corals, fragments of r.. c... :::i ...... ··-...... ,,,.. 700 «I ·~· brachiopoda fossils C,) ~ . -" . -·- .._;..... Fig. 9 Columnar Section of the Tuman Group 23 The Chongjin Complex has such ultramafic to mafic rocks as serpentinite, peridotite, pyroxenite, gabbro, gabbro-diabase and gabbro-diorite. The serpentinite is considered to have association with peridotite and pyroxenite in its origin. The Tumangang Complex is composed of various intrusives, represented by gabbro-diorite, quartz- diorite, biotite granite, plagioclase granite, granodiorite and alaskite. The K/Ar ages of the Complex showed 193 and 208 Ma. VII. MESOZOIC STRATIGRAPHY AND INTRUSIVES 1. Mesozoic stratigraphy The Mesozoic Erathern in Korea is strat i graphically divided into 1) Lower Jurassic (Taedong Group), 2) Middle-Upper Jurassic (Jasong Group), 3) Lower-Upper Cretaceous (Taebo Group) , and 4) Upper Cretaceous - Paleocene units. All boundaries between stratigraphic units are unconformable. The distribution of Mesozoic sediments is confined within fault block basins (Figs. 11 & 12, Table 1). Because of diffe rent stratigraphic sections and thicknesses in each fault block. they have been labelled differently with each other (Tab. 1). 1) Triassic- Jurassic (1) Upper Tr iassic-Lower Jurassic (Taedong Group) The Taedong Group is distributed in t he River Taedong Basin, Junggang Basin, Jangphari Basin, Susongchon Basin, and Pujon- Sinhung Basin (Tab.2). The Taedong Group in the River Taedong Basin contains three cycle sediment packages: the lower section consists of conglomerate (200 - 250 m thick), alternating aleurolite, slate and sandstone (100 - 150 m thick), the middle section consists of slate, aleurolite, sandstone, gravel-bearing sandstone (250 - 400 m thick), and the upper part of section contains tuffaceous 24 Tab. 1 Stratigraphic Units of Mesozoic Erathem River River River . Ri ver River River River Taedong Chonri . Jangphari KimPho Ramphc Pansong Rak tong Age A mnok and J aeryong Chongchon Basin J angJ a B . Tu rnan · . Fore_ Basin Jaer~ong Basin Basin Basin as in Basin Basin Basin Basin deep Basins r . ..-- ~ Jaedok Yuchon Ponghwa- Series ~ Series san ::i i-""",,.,..,~....,...------~""'1 Kz c'.; S . e Nungju Hayang eries ! c.:i Series Series I t-- 0 ~ ~ . c llJ ""' , • Pakchon "" . . "" cw c ~ Han bong- Pongchon- S . Vl J inan S1ndong t-o U'l _g U'l san Series Sanson·gri bong eson ~ . . Kc u . . Series Series Series. ~ -~ 'oD 'oD series Kunur1 Series Series 0~ . CJ1 ._, i::: c . ~ ::l o o Series (/) 11< .0 ~ cw t Taebosan Phyong- 1 i..: ~ ::l ·: Series Pongsu hwari Ryongsong Ryonmuri Ryongnam 1 3 J e,, I ;( 1 h Series Series Series Series 'oD ::i ~0 U'l~ s·imc on S~eles § ~· ~ . Series (,/) ~~~-i->-~~....,...,."""~~~ ,____ "" Jungam _, Series Jz ~ I ... tii:l e,, c: Ul 'oD :i .~ Songrim- Chonri Jangphari CbongjinThongjin Rampho Pansong T3 -·J , c::o 'oD ""' S S . i S . . S . i::: Q) san e r. er1es Ser es er1es Series Series er1es 'O ::l (/) Q) '"':> Basins Series Thick- Distribution ness (m) River Taedong Songrimsan 1000 Pyongyang, Songrim City Junggang Junggang 880 Junggang County, Hyesan City, Unhung County J angphari Jangphari 950 Kapsan County, Rochon Susongchon Chongjin, 700 Chongjin City, Hoeryong Obongsan City Pujon - Jangphari Pujon County, S inhung Sinhung Chonri County Chonri 480 Changdo County, Kimhwa County Kimpho Tonggi 800 Kimpho County Ramp ho Ramp ho 2650 Puryong County, Puyo County Pansong Pansong 1700 Chongson County, Nyongwon County, Tanyang County, Mungyong County 26 60krn o lZOkm R H H I [::;:::} Gr.anite !:_:_:_-_. , Mesozoic Str·ata Fig. 10 Distribution of the Mesozoic Strata and Intrusives sandstone, dark aleurolite, feldspathic sandstqne (150 - 200 m thick). (2) Middle-Upper Jurassic (Jasong Group) It is distributed in the Jangjagang Basin. In other basins, only Upper Jurassics are developed (Tab. 2). The Middle Jurassic formation is called Jungam Series (Fig. 11). The series overlies unconformably an intrusive body of Tanchon Complex. and is overlain unconformably by the Upper Jurassic formation. It is made of alternating conglomerate, conglomeratic sandstone, sandstone, siltstone, slate and anthracite seams. The anthracite directly covers the basal conglomerate. The series is 260 - 360 m thick. The Upper Jurassic formations ove rlie various lithologies (including Middle Jurassic sediments and Tanchon intrusive complex) with an unconformity, and in turn disconcordantly covered by Lower Cretaceous sediments. Igneous rocks of the Cretaceous Amnokgang Complex penetrated the Upper Jurassic formations. Clastic sediments were predominant in Sinuiju and Jaeryonggang basins, but volcanic activities predominated in other basins. The representative Jurassic section in the Sinuiju Basin shows, 1) reddish silt, light grey-yellow brown fine- grained sandstone, silt and conglomerate (70 - 110 m thick), 2) andesite, porphyrite, tuff and agglomerate (200 - 500 m), 3) light greyish green sandy silt with coal seams, sandstone, shale and sandy conglomerate (1650 - 1800 m). and 4) sandstone and conglomerate (over 150 m), in ascending order. The total thickness of the Sinuiju Series reaches over 2000 m. Numerous fossils have been recorded from the Sinuiju Series; fishes, insects, frogs and Pterosauria. Whereas , Ryonmuri Series in the Chosan Basin where thick volcanogenics accumulated shows the section as follows in ascending order: 1) Jangthori? conglomerate formation, sandstone, s iltstone, carbonaceous shale, tuffaceous sandstone (20-150 m thick), 2) Jubongsan andesite porphyrite formation and tuff with tuffaceous sandstone and siltstone (600-1000 m), 3) conglomerate (with coal measures), sandstone, siltstone and s hale (250-320 m), and 4) Kuchonbong andesite porphyry, and agglomerate (700-800 m). The Ryonmuri Series is 1600 m or more thick. 28 Thie Series Lithology ( m) v v v v y v v v v v v 450 andesite-porphyrite brecciated v v v ~ v v v v v v v 800 andesite - porphyrite, agglomerate v v v v v v v I.---+------t v v v v v v v 30 conglomerate, sandy conglomerate, tuffaceous molass . ttiffaceous ) ~i~~¥~~ sandstone, siltstone, coaly 300 mudstone, coal, plant remains v v v v v v () 1 andesite-porphyrite, t uff, vvv~ 600 v v v v agglomerate, tuffaceous- rudaceous " v ~fo'~ V sandstone, tuffaceous sandstone, v v v v v v v tuffaceous siltstone, v v v v v~ 1000 sandstone, interlayered siltstone, V(JV V plant remains ~vvv v v v v - 2-0--1--r-u._d_a_c_e_o_u_s_s_a_n_d_s_t_o_n_e_,_s_i_l_t_s _t_o_n_e_.__ _ I tuffaceous sandstone, coaly 1 50 siltstone, coal, flora 260 conglomerate, rudaceous sandstone, ! siltstone, coal, s late, 360 plant remains +{:j+~+;. sandstone, siltstone, plant remains, ;_.;:...:_~:...:..:..::..:.:.::.: siltstone coaly slate, sandstone, interlayered marl, slate. interlayered sandstone, fossils, siltstone, plant remains, fossils. sandstone, siltstone, interlayered coal , conglomerate, rudaceous sandstone, :.- · . · . · : ~ coaly slate, interlayered coal ~-;.?~~ Fig. 11 Columnar Section of the Taedong and Jasong Groups 29 2) Cretaceous Three stratigraphic units are separated in the Cretaceous section; Lower Cretaceous, Upper Cretaceous and Uppermost Cretaceous-Paleocene. The Raktong Foredeep, south Korea, has the wide distribution of Cretaceous formations called Kyongsang Group. Other Cretaceous deposits on land are named Taebo Group. The Kyongsang Group is separated into Sindong Series (K1 ), Hayang Series (Kz ) and Yuchon Series (K2 -P1 ). The Sindong Series (or Raktong Series) is exposed along the western margin of the Raktonggang Foredeep unconformably overlying Archean and Jurassic granitic rocks. The series has alluvial elastic sediments - boulder conglomerate, conglomeratic sandstone, siltstone, shale and marl with lenses of limestone and carbonaceous shale. The lower section is grey and the upper reddish. It attains up to 3500 m in thickness. The Hayang Series (or Silla Series) unconformably rests on the Sindong Series. It is penetrated by Pulguksa and Masan granites. Stratigraphically it is separated into, in ascending order, 1) Silla conglomerate (240 m), 2) Haman red sandstone, shale and porphyry (1200 m), 3) Panya dark grey shale and sandstone (1100 m), 4) Songnaedong red shale and sandstone (800 m), and 5) Chaeyaksan porphyrite formation (500 m), and 6) Konchonri dark grey shal e and sandstone (BOO m). The series is 4640 m thick. The Yuchon Series, Cretaceous-Paleogene in age, overlies disconcordantly Hayang Series and older rocks, and is penetrated by Masan intrusives. The series is made of andesite, rhyolite and their tuff, in which black shale, sandstone and agglomerate are intercalated. In the lower section, intermediate volcanic rocks are abundant and in the upper rhyolite . The Yuchon Series is 1000 m thick. The Taebo Group in terrestrial basins shows various facies and stratigraphic sections in each basin. The Lower Cretaceous Hanbongsan Series in Taedonggang Jaeryonggang basins is divided into Choltori, Oeampho and Anri formations in ascending order. The Choltori Formation consists of red conglomerate and sandy conglomerate in the lower section, dark grey silty shale and marl w~th gypsum and glauberite in the middle. and red sandstone, siltstone, dark grey sandstone and siltstone in the upper. The formation is 1200 to 1950 m thick. The Oeampho Formation consists of tuffaceous conglomerate in 30 I 0. I ..c:: I Cl.I Thi o :;j o c.> ·~a> Section c Lithology s.. o.. a> (m) C-' ~ C/l \I' \I' \I /\ }(,, ,,, ,, quartzophyre, felsophyre, felsite, .!id '\ 0 ~· ·-:::;..., 700 quartz-trachyte, porphyritic "C !,~ ll.>-,...,,..., ~ ~gglomerate, siltstone, interlayered. ~ v-v-11 - ....., -v- v-v 1000 tuff, plant remains, tuff, ~ ~ .,. conglomerate, agglomerate 'O/o'!/o'- sandstone, rudaceous sandstone, siltstone mudstone, plant remains. fossils ==== 860 Anri Formation: limestone, mudstone, limy mudstone, siltstone, I ;;:_--:-:; .:::..;.-:; ,:;;.-:.L sandstone interlayered gypsum, ;;~-~;; 1930 tuffaceous sandstone, siltstone, Cl.I ;::s limy mudstone 0 t.f!iii~t Q) () ctl Oeampho Formation: siltstone, +.I 900 Q) silty mudstone, mudstone , f.. (.) ~ sandstone, interlayered gypsum, plant remains, tuffaceous conglomerate, sandstone, interlayered siltstone Choltori Formation: sandstone, siltstone, silty mudstone, mudstone, interl ayered gypsum, plant remains, conglomerate, rudaceous sandstone Fig. 12 Columnar Section of the Taebo Group 31 the lower- section, and siltstone, silty shale, black shale (with gypsum) and sandstone are intercalated in the upper. It is 900 to 1740 m thick. The Anri Formation starts from basal conglomerate and consists of siltstone, silty shale, dark s hale and sandstone. Gypsum is contained in_ the shale. The Anri Formation is 900 to 1740 m t hick. Hanbongsan Series has a plenty of floral r e mai ns. The Upper Cretaceous Formation, Ponghwasan S~ries, is developed only in Ryesonggang Basin (Fig. 9). The se-ries. covers unconformably the Lower Cretaceous Sansongri Series. I t is made of lacustrine and r iverine sediments. Its l ower part is made of dark grey sandst one, siltstone and calcareouos shale (80 m thick), and upper part, of alternating red conglomerate, ·siltstone, tuffaceos siltstone, tuffa ceous sandstone, conglomeratic silty s hale (350 m thick). Rocks of t he Ponghwasan Series have l arge contents of carbonates and contain salt mine rals s uch as gypsum. The Upper Cretaceous-Paleocene formation (Jaedok Series) develops patchly in Kilju, Chongjin and Uam regions. The series rests on the Lower Proterozoic Machonryong Group and Jurassic Tanchon granites. It i s disturbed by Cretaceous-Paleocene intrusives - Hangmusan Complex. The Jaedok Series consists of white, grey, greyish green, brown quartz-trachyte, rhyolite a nd syenite with the thickness of about 700 m. The K/Ar age o f the acidic volcanic rocks of the Jaedok Series is 61 Ma. The series continues through Chongjin , Uam r egion to the southern part o f the Sikhote-Alin. - 2 . Me sozoic intrusives Based on their ages, Mesozoic intrusive rocks are grouped into 1) Triassic (Hyesan and Phyonggang Complexes). 2) Jurassic (Tanchon Complex), 3) Cretareous (Amnokgang and Pulguksa Complexes ) , and 4) Upper Cretaceous-Paleocene (Hangmusan Complex) int rusives (Fig. 1). 1) Triassic intrusives (Hyesan and Phyonggang Complexes ) Hyesan and Phyonggang Complexes are included in the Triassic group. Intrusive bodies of the Hyesan Complex were formed by i ntrus ion of acidic magmas that had taken p lace a l ong fault structur es during the Songri m Move ment. 32 The Hyesan Complex intrusives are exposed concentrically along Jangphari and Pujongang fault zones, Changsong-Unsan and Chonma major faults, Unryul-Haeju fault, Jaeryonggang, Pansong and Kongju Fracture Zones. They are diorite, porphyritic biotite granite, biotite amphibole granite, granodioritc and leucogranite. The K/Ar age is 270 Ma (Fig. 10). The Phyonggang Complex intrusives distribute out of the Middle Paleozoic Rimjingang Foldbelt and Upper Paleozoic Hambuk Foldbelt. The Phyonggang Complex is largely divided into two intrusive phases. The first phase is represented by pyroxenite and alkaline gabbro. The second phase comprises nepheline syenite, alkaline amphibole syenite, alkaline pyroxene syenite, alkaline amphibole biotite syenite, alkaline syenite, gneissose biotite syenite, porphyritic biotite grano-syenite, quartz syeni te, alkaline granite, etc. The measurement of K/Ar age of the Phyonggang Complex resulted in 180 Ma for Sochon intrusive, and 250 Ma and 217 Ma for Ryangchon intrusive. These ages fall within the Triassic. 2) Middle Jurassic intrusives (Tanchon Complex) The Tanchon Complex is granitoids formed along a deep-seated fault zone during the Taebo Moveme nt. The Tanchon Complex is distributed most extensively in Korea, almost occupying 10 % of the country. The Complex is made of gabbrodiorite, granodiorite, biotite granite, two mica granite and fine two mica granite which are penetrated by pegmatite and aplite dykes. The K/Ar ages of the complex fell within the range of 130 - 190 Ma. 3) Cre tace ous intrusives (Amnokgang Complex) Three groups are discerned in the Cretaceous intrusives; Lower Cretaceous intrusives (Amnokgang Complex), Upper Cretaceous intrusives (Pulguksa granite), and Upper Cretaceous-Paleocene intrusives (Hangmusan Complex and Masan rocks}. The tectonic event that accompanied above igneous activities has been called Jaeryonggang Movement. The movement is characterized by felsic to intermediate magmatic activities. The Amnokgang Complex is composed of diorite, quartz-diorite , granodiorite, granite porphyry and quartz porphyry, toget her with such dykes as aplite, quartz porphy ry, felsite. diorite and ·r.1() rph;yrile. The K/Ar ages of the Complex fell within the range of ·1·rn to 150 Ma. The Pulguksa Complex intrusives are exposed concentrically within the Raktonggang Foredeep. They are composed of granodiorite, amphibole granite and granite porphyry with granitoids being most dominant. The absolute age of the complex by K/Ar method showed 120 - 85 Ma. The Hangmusan Complex (K/Ar age 55 Ma) is characterized by alkaline granite, granosyenite, quartz syenite and syenite. It is accompanied with various dykes and veins such as syenopegmatite, orthophyre and aplite. Plagioclase granite, micrographic granite, biotite quartz monzonite and granoporphyry are major components of the Masan rocks intrusive complex (K/Ar age 73-68 Ma). The Masan rocks granitoids contain less biotite but more quartz and kalifeldspar than Pulguksa granitoids. VIII. TERTIARY STRATIGRAPHY AND INTRUSIVES 1. Tertiary stratigraphy The Tertiary system is distributed ma inl y in the coastal areas on both sides of the Korean Peninsula. Minor development of the Tertiary formations are also seen in inland regions like Hyesan and Paegam (Fig. 1 & Tab. 3). 1) Eocene The Eocene deposits, called Sinri Series, is composed of alternating black shale, medium to coarse-grained sandstone, psephitic sandstone, fine-grained sandstone, and psammitic aleurolite, black shale and coals in the lower and basalt and tuff in the upper part. The lower elastic dominant part is 50 to 150 m and the upper basalt-bearing part 30 to 200 m thick (Fig. 13). 2) Oligocene The Oligocene is distributed widely in the Anju Basin and West Korea Bay Basin. Minor distribution is found in various parts of Korea; Kilju-Myongchon, Sinuiju and Sariwon regions. 34 Tab. 3 Stratigraphic Units of Tertiary Erathem Lower Kilju- Reaches Hyesan- Hamhung- Bay Anju Sariwon Sinuiju e Myongchon of River Paegam Wonsan Yongil Is. Jeju ~ Tuman Pliocene Chilbosan Chilbosan Paegam Chilbosan Sogwipho Series Series Seri~s Series Formation Kidong Jungsan Sinhung 0. ;:! Series Series Series 0 0. t.:l"" =' Koc h am 0 Saeppyol Series Cll .-I (.!) Q) ·r-4 Q) "" Cll ~ Kum so Series •.-! bi) CJ\ ~ b.O Cl) (!) c:: c:: Series •r-i Q) 0 tlO Miocene 0 i.. (/')"" >- 0 » Q) Q) tlD Hamjin (/') c:: z El . 0 ell Series bll ..c ::c c:: (.) Phyongryuk Hamyon ..c::=' 'Q(I El c:: Series Series ell 0 ::i:: ..c:: f""' Namsok ~- Series Janggi Ryongdong Changdong Group Sangdan Series Oligocene 0. Series Pongsan - 0=' Ryongrim Series i.. (.:1 Series Series .....,;:I c:: Sinri Eocene Fig. 13 Columnar Section of the Anju Group in the Anju-Pakchon Regions The formation in . the Anju Basin where major coal measures are develope d. is divided into the Ryongrim and Changdong Series. The total thickness of the Oligocene formation ranges from 1800 to 2900 m. 3) Miocene The Miocene is wel l devel oped in the foredeeps in Kilju Myongchon and Yongil regions. Limited distribution of the Miocene is also seen in inland basins along Tuman River, Sinhung, Hamhung, Anbyon, Thongchon and Pukphyong regions . The Miocene formations cover various deposits of pre- Miocene ages wi th an 36 unconformity, and are overlain unconformably by Pliocene deposits (Fig. 14) . The Miocene sedime nts are partly marine and partly non-marine. Marine sediments are Phyongryuk, Hamjin and Kumso Series, and non marine are Kocham and Kidbng Series. In the upper Hamjin Series develop trachytic tuff, brecciated trachyte and trachyte. Miocene and Pliocene systems in the Pukphyong and Yongil foredeeps in the southern Korean Peninsula are composed of an alternation of marine and non-marine deposits and volcanic effusives. The age of the Yongil Group is early Miocene to Plio cene. 4) Pliocene Plioce ne sediments in Korea are grouped into Chilbosan and Pae gam Series, and Pukphyong, Yonam and Sogwipho formations in south Korea. The Chilbosan Series in the Kilju-Myongchon Foredeep is composed of Jaedoksan alkaline basalt (80-400 m in thickness), Musudan alkaline trachyte (170-350 m), Hamaebong felsite (140- 200 m), Kkachibong rhyolite (50 - 600 m). The isotope ages of t he Chilbosan Series indicated 5 Ma for trachyte , and 10 Ma for rhyo lite. The Sogwipho Formation in the Jeju Island consi sts of trachyte and intercalated shallow marine sediments. 2 . Tertiary intrusives Tertiary intrusives are represented by Pongsan Complex, and are exposed in various parts of the country; Pongsan, Kangdong, Sangwon and Pakchon in northern Korea, and Phohang in south Korea. The intrusives are all small in scale and belong to pipe type or vein type. The Pongsan Complex is composed of vitreous pyroxene peridotitic breccia and brecciated vitreous pyroxene peridotite. 37 I "C .c: I en Thie ·~ 0 0 (.) ~ Q) Section Lithology Q) 0. Q) ( m) 0.. ~ rJ'J c:: Q) Cd " " c:: .en \/ "\/ \/ \/ rhyolite. alkaline rhyoli te . Q) " " " 1000 felsite, u 0 /\ /\ /' /\ .c ., ., ., ., ~ 0 ..-t ., ., ., •.-4 \I trachyte, tuff, basalt •.-i "I\ " )\ 2000 ..-t " \I " 0.. ..c:: " "\ C,) r " ,.. " r r:: bi) -·~ ··--~·.··~o·· c:: ... -. 1\50 sandstone, conglomerate, siltstone, 0 . "C .;.·.·4 ...... · s •.-4 -=-:-:-~ - ~.:..7· 300 mammals, plant remains. spore pollen ::.:: 0 ... -=-~.. - ~_:...- :f sandstone, arenaceous siltstone, e -. $) -.. Cd 300 ..c:: • . . •• . - r- coaly siltstone, coal, basalt, (.) . .- $ 0 . diatom earth . ostracods, ::.:: .:_-:--·-.:_11 ·-· :::.·- .- 400 plant remains, spore pollen >, --. . . b) ... Q) 0 r... . ~ -. : .. .: . - ~ sandstone , Cd c:: ff.I 100 siltstone. conglomerate, . Q) -·-·-·- ~ e ·- ·-·-- s .... . u ;::i • • 0 • . 200 ostracod fossils r... 0 ::.:: .• 0 •• .. .. Q) ~ E-< l: c:: ~cf=,-·-·-~~{ tuffac eous siltstone, mudstone, -i....., . .:... •.:_-:- S>:: k 120 . •-•- •-I s iltstone, interlayered sandstone e s trachyte ,· bones Cd -·-·-·:~ 400 of whale, ::c -·-·-··-·-·- animal fossils. plant remains :.:: .:..~.:..'7+:-....: 150 sandstone, siltstone, some ~ ·- ·-·- · >, ...... s conglomerate, Lamellibranchia ta s... -- - 400 bi) :~ :~·&>-~ fossils, plant remains c:: • • • • 0 • 0 .. -~,: - ·_:_.:.....:.. mainly conglomerate, sandstone. ~ ·----.:.... -- 200 ..c:: .. j inter layered coal oysters, plant 0.. ; ·o · £>" · •. . . 500 remains, spore pollen °__~. o ._o ----.. Q) ~ ·· - -· ...... 0 ... ,.. ,.. r 600 basalt, andesite, agglomerate, tuff, c:: Q) en ..r .....- ...... - Q) c:: e ,... s CJ~ .-,... r r graywacke, interlayered bentonite cC ...... - -r ... 1000 0 (,) z ,... .- .- tiOo ...... ~ ... r.-4-.-i bi) .-!~ I C:: 100 sandstone, siltstone, mudstone, 0 'OOo -·-+-·-·-· ·-· c:: 't:l -·-·-·-·.·. : .. - .. f conglomerate, tuffaceous muds tone 0 .. .. ~~ 150 coal. plant remains £ -...... Fig. 14 Columnar Section of the Hamgyong Group in the Kilju-Myongchon Regions 38 IX. QUATERNARY STRATIGRAPHY AND INTRUSIVES 1. Quaternary stratigraphy The Quaternary deposits are separated into lower, middle and upper units. The lower unit consists of an alternation of volcanic effusives (mainly basalt) and elastic sediments which contain basal conglomerates together with diatom earth. The middle unit harbours various rock types. Rhyolite, trachyte, tuff, obsidian, and pumice from Mt. Paektu Volcanic Belt, in which alkaline trachyte and its tuff make up the lower section, and rhyolite, volcanic glass and pumice the upper section. The total thickness of the middle unit is about 450 m. Alkaline trachyte in the Mt. Paektu Volcanic Belt showed the age from. 87 to 550 thousand years. The upper unit is alluvial, fluvial or marine deposits forming low flat plains along the coast and major rivers. In some areas (for example, Songchon and Su songchon Rivers) the alluvial deposits are extremely thick, being over 50 m, but in most of other areas (Taedong and Amnok Rivers) 15 to 20 m thick. Marine deposits belonging to the upper unit is 14 m thick in Kumya, 20 m in Pompho, and 30 m in Hamhung. At least two series of eruptions of Mt. Paektu have been documented and confirmed; 1050- 1410 and 1597-1702 A.D. Quaternary volcanic islands in the Korea East Sea are Island Jeju (recent eruption in 1002, 1442 and 1570 A.D.), Ullung and Tok. In the Ul·lung Island, volcanic activities shifted from basalt at the beginning, subsequently trachyte effusion, followed by phonolite during a dormant time when they are subaerially exposed. 2. Quaternary intrusives (Hoeryong Complex) The Hoeryong Complex intrusives are mo stly developed in the drainage area of the River Tuman, and rarely along the large fractures particularly in the vicinity of the River Nam. The intrusives are mushroom, pipe or vein shaped. 39 General Stratigraphy Hambuk Foldbe l t Rang rim Phyongnam Synecli Kyonggi Raktonggang Ki lju-Myongchon Fo r e deep, Yongi l Intrusive Tectonic Era Period Code G~~- Series Fot~":i~- Ant iclinorium· se, Rimj in gang Ant i clinorium Rocks Move ments Foredeep Foldbelt Foredeep Quaternary Hoeryong Comp . Kidong Jung- Sinhung Kocham san Chilbosan .u.., 0 Kumso Sae- Yoni l Gr. N 0 Hamj in ppyol Hamhung ~ Phyongryuk Hamyon C) Namsok Pongsan Comp. Hangmusan Comp-: Hangmusan Pulguksa Granites Amnokgang Jaeryonggang Comp. .,.,u 0 N 0 VY Tanchon Taebo ~ Comp. .,.,u (f) (f) Phyonggang ·~ Comp . Song rim E-< Hyesan Comp. Tumangang Tumangang Comp. Chongj in Comp. Namgang Comp. Rimj ingang Kophung Muj!n Hukgyo Myobong Junghwa Jangsan "0 ' ~ Gi------10 Myoraksan ~ Okchon Gr. Yonsan Comp. tlO • Majonri §I. ~~ i----- PR a ~ ~ 1-Vl....__,____ _ Ong.Jin Comp, I"' Pyoksong 5 . i.----- Comp. ~ t ----1 t ~ (,{) 0 ~ ,.....___ __. ;z Sak,ju Comp. OngJ in Riwon Comp. Mafic Rocks Mus an Songj in Ryonhwasan Ryonhwasan Comp. AR Rang rim Gr. Andol Comp. Fig. 1 Stratigraphic Units and Intrusives of Korea