• The Korean Journal of Petroleum Geology
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• v.1 no.1 s.1
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• pp.1-13
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• 1993

The diagenetic history of the carbonate rocks of the Mungok Formation near Machari area, Kangwondo, was investigated based on textural, isotopic, and chemical data. Paragenetic relationship among diagenetic minerals, coupled with their distinct geochemical contents, shows that the Mungok Formation have undergone several stages of diagenetic events: 1) shallow marine, 2) meteoric, 3) shallow to intermediate burial, and 4) deep burial diagenesis. Shallow marine diagenesis includes fibrous calcite cementation, micritization, and framboidal pyritization, and meteoric diagenesis involved dissolution and recrystallization of unstable allochems (both aragonite and HMC), syntaxial overgrowth on echinoderm fragments, and equant calcite cementation. During shallow to intermediate burial, idiotopic dolomite and chert formed, and xenotopic dolomitization took place before stylolitization of the rocks. After the rocks were deeply buried, saddle dolomitization, second stage of silicification, and dedolomitization occurred.

• Journal of the Korean earth science society
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• v.21 no.4
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• pp.449-468
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• 2000

The Ordovician Chongson Limestone deposited in the carbonate ramp to the rimmed shelf shows diverse diagenetic features. The marine diagenetic feature appears as isopachous cements surrounding ooids and peloids. Meteoric diagenetic features are recrystallized finely and coarsely crystalline calcite, evaporite casts filled with calcite, and isopachous sparry calcite surrounding ooid grains. Shallow burial diagenetic features include wispy seam, microstylolite, and dissolution seam whereas deep burial features include stylolite, burial cements. blocky calcite with twin lamellae, and poikilotopic calcite. Dolomites consist of very finely to finely crystalline mosaic dolomite formed as supratidal dolomite, disseminated dolomite of diverse origin, patchy dolomite formed from bioturbated mottles, and saddle dolomite of burial origin. Silicified features include calcite-replacing quartz and fracture-filling megaquartz. Burial cements characterized by poikilotopic texture show ${\delta}^{18}$O value of -10.4 %$_o$ PDB, ${\delta}^{13}$C value of -1.0%$_o$ PDB and 504ppm Sr, 3643ppm Fe, and 152ppm Mn concentrations. Finely and coarsely crystalline limestones show similar ${\delta}^{18}$O and ${\delta}^{13}$C value to those of burial cements; however, they show lower Sr and higher Fe and Mn concentrations than burial cements. This suggests that very finely and coarsely crystalline limestones were recrystallized in freshwater and then they were readjusted geochemically in the burial setting whereas the burial cements were formed in relatively high temperature and low water/rock ratio conditions. Very finely and finely crystalline mosaic dolomites with ${\delta}^{18}$O value of -8.2%$_o$ PDB, ${\delta}^{13}$C value of -1.9 %$_o$ PDB, and 213ppm Sr, 3654ppm Fe, and 114ppm Mn concentrations, respectively are interpreted to have been formed penecontemporaneously in supratidal flat and then recrystallized in the low water/rock ratio burial environment. Geochemical data suggest that the low water/rock ratio burial environment was the dominant diagenetic setting in the Chongson Limestone. The Chongson Limestone has experienced marine and meteoric diagenesis during early diagenesis. With deposition of Haengmae and Hoedongri formations part of the Chongson Limestone was buried beneath these formations and it experienced shallow burial diagenesis. During the Devonian the Chongson Limestone was tectonically deformed and subaerially exposed. During the Carboniferous to the Permian about 3.3km thick Pyongan Supergroup was deposited on the Chongson Limestone and the Chongson Limestone was in deep burial depths and stylolite, burial cements, blocky calcite and saddle dolomite were formed. After this burial event the Chongson Limestone was subaerially exposed during the Mesozoic and Cenozoic by three periods of tectonic disturbance including Songnim, Daebo and Bulguksa disturbance. Since the Bulguksa disturbance during Cretaceous and early Tertiary the Chongson Limestone has been subaerially exposed.

• The Korean Journal of Petroleum Geology
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• v.3 no.1 s.4
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• pp.28-39
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• 1995

The objective of this study is to investigate the origin of the dolomite in the Pungchon Formation of the Choseon Supergroup near Taebaeg City, Kangwondo, Korea. The Pungchon Formation is composed of limestone, dolomitic limestone, and dolomite with thin beds of flat pebble conglomerate (FPC) and mudrock. Texturally, the dolomite in the Pungchon Formation can be divided into four types; 1) coarse-sized, xenotopic dolomite in massive dolomite, 2) medium-siEed, idiotopic dolomite in flat pebble conglomerate, 3) xenotopic dolomite replacing ooids, algalnodules, and echinoderms, and 4) the dolomite in mottled fabric. The dolomite in mottled fabric can be subdivided into three types; a) coarse-sized, xenotopic saddle dolomite cement, b) medium-sized, idiotopic, cloudy-centered, clear-rimmed (CCCR) dolomite, and c) coarse-sized, idiotopic dolomite. The carbon isotopic composition of the Pungchon dolomite is in the range of $-2.8-1.4\%_{\circ}(PBD)$, suggesting that the carbon isotopic composition was buffered by the preexisting marine carbonates. Lighter oxygen isotopic values ($\delta^{18}O-15.7-8.7\%_{\circ}, PBD$) indicate that the Pungchon dolomite may have formed under high temperature in a burial diagenetic environment. The higher initial $^{87}Sr/^{86}Sr$ ratio of the Pungchon dolomite (0.7010-0.7161) than that of the coeval Cambrian seawater (0.7088-0.7092) indicates that dolomitizing fluids had been modified from the isotopic exchange with continental crust. Low Sr and Na contents(<200 ppm) of dolomite agree well with previously reported data for burial dolomite. Hifh Fe and Mn contents of the dolomite support the idea that the Pungchon dolomite may have formed in a deep burial diagenetic environment.