REE and Sr–Nd Isotope Characteristics of Cambrian–Ordovician Carbonate in Taebaek and Jeongseon Area, Korea

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Article REE and Sr–Nd Isotope Characteristics of Cambrian–Ordovician Carbonate in Taebaek and Jeongseon Area, Korea

Tae-Hyeon Kim 1,2,* , Seung-Gu Lee 1 and Jae-Young Yu 2

1 Geology Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Korea; [email protected] 2 Division of Geology and Geophysics, Kangwon National University, Chuncheon 24341, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-042-868-3969

Abstract: Carbonate formations of the Cambro-Ordovician Period occur in the Taebaek and Jeongseon areas, located in the central–eastern part of the Korean Peninsula. This study analyzed the rare earth element (REE) contents and Sr–Nd isotope ratios in these carbonates to elucidate their depositional environment and diagenetic history. The CI chondrite-normalized REE patterns of the carbonates 1/2 showed negative Eu anomalies (EuN/(SmN × GdN) = 0.50 to 0.81), but no Ce anomaly (Ce/Ce* = 2 1/3 CeN/(LaN × NdN) = 1.01 ± 0.06). The plot of log (Ce/Ce*) against sea water depth indicates that the carbonates were deposited in a shallow-marine environment such as a platform margin. The 87Sr/86Sr ratios in both Taebaek and Jeongseon carbonates were higher than those in the seawater at 87 86 the corresponding geological time. The Sr/ Sr ratios and the values of (La/Yb)N and (La/Sm)N suggest that the carbonates in the areas experienced diagenetic processes several times. Their 143 144 87 86 Nd/ Nd ratios varied from 0.511841 to 0.511980. The low εNd values and high Sr/ Sr ratios Citation: Kim, T.-H.; Lee, S.-G.; in the carbonates may have resulted from the interaction with the hydrothermal ﬂuid derived from Yu, J.-Y. REE and Sr–Nd the intrusive granite during the Cretaceous Period. Isotope Characteristics of Cambrian–Ordovician Carbonate in Keywords: carbonate; REE; Ce anomaly; Sr isotope; Nd isotope; carbonate depositional environment Taebaek and Jeongseon Area, Korea. Minerals 2021, 11, 326. https:// doi.org/10.3390/min11030326

Academic Editor: Giovanni Mongelli 1. Introduction The rare earth element (REE) patterns of carbonates can help understand their deposi- Received: 15 March 2021 tional environment and diagenetic processes [1–3]. Tanaka et al. [1] inferred the seawater Accepted: 19 March 2021 depth of carbonate deposition according to the variation of Ce anomalies with the sea water Published: 21 March 2021 depth. Madhavaraju et al. [2] deduced the paleo-redox condition changes from the Ce anomalies of the REE patterns of carbonates. In particular, the values of (La/Yb)N and Ce Publisher’s Note: MDPI stays neutral anomalies can be good indicators of the carbonate depositional environment [2,3]. Recently, with regard to jurisdictional claims in Zhang et al. [3] reported that the REE pattern of a carbonate varies according to its tectonic published maps and institutional affil- setting. In addition, the 87Sr/86Sr ratios of carbonates are known to be insignificantly iations. affected by the pore water during early diagenesis, but they can be raised by the interaction with hydrothermal fluid during a later diagenetic process [4–6]. The residence time of Nd in sea water is between 200 and 1000 years, while inter-ocean mixing requires about 1500 years [7]. For this reason, 143Nd/144Nd ratios in the Pacific, North Atlantic, and Indian Copyright: © 2021 by the authors. oceans were all different despite the same geological time [8]. The 143Nd/144Nd ratio of Licensee MDPI, Basel, Switzerland. carbonate has not yet been studied extensively, but recent studies showed a decrease in This article is an open access article the 143Nd/144Nd ratio in carbonate during diagenesis. This is due to the diagentic reaction distributed under the terms and with a fluid having lower 143Nd/144Nd than the carbonate [9,10]. conditions of the Creative Commons Cambrian and Ordovician carbonate formations occur in the Taebaek and Jeongseon Attribution (CC BY) license (https:// areas located in the central–eastern part of the Korean peninsula (Figure1). These for- creativecommons.org/licenses/by/ mations have been steadily investigated in various fields such as carbonate depostional 4.0/).

Minerals 2021, 11, 326. https://doi.org/10.3390/min11030326 https://www.mdpi.com/journal/minerals Minerals 2021, 11, x FOR PEER REVIEW 2 of 15

sedimentology [11–22], but their REE and Sr–Nd isotope geochemistry has not been investigated. Examining and interpreting the geochemical data from the carbonate rocks in the East Asian region may be the key to understanding the regional sedimentary environment and its evolution in the past. Fortunately, a considerable amount of geochemical work on the carbonate formations of the same geological time has been done in Japan and China; thus, it is necessary to examine the characteristics of the REE patterns and Sr–Nd isotope ratios of carbonate in the Korean peninsula. The aim of this study was to carry out a geochemical analysis of the carbonates in the study area and interpret their REE patterns and Sr–Nd isotope ratios to elucidate the depositional environments and diagenetic processes. The REE patterns and the isotopic ratios of the carbonates were also compared and discussed with those in Japan and China.

2. Geological Background Minerals 2021, 11, 326 2 of 15 2.1. Taebaek Area The Cambrian carbonates in Taebaek area include the Myobong, Daegi, and Hwajeol Formationssedimentology of the [11 Taebaek–22], but group their REE (Figure and Sr–Nd1). Among isotope these, geochemistry the Daegi has Formation not been in-mostly consistsvestigated. of carbonates, Examining and and it interpretingis widely distri the geochemicalbuted throughout data from the the central–eastern carbonate rocks part of thein Korean the East Peninsula, Asian region including may be thethe key Jeongseon, to understanding Samcheok, the regionaland Taebaek sedimentary areas (Figure envi- 1). Theronment Daegi Formation and its evolution is known in the to past. have Fortunately, been deposited a considerable in a shallow amount marine of geochemical environment suchwork as ona platform the carbonate margin formations [13,16,17]. of theKim same and geological Park [13] time suggested has been that done the in Daegi Japan For- and China; thus, it is necessary to examine the characteristics of the REE patterns and mation was deposited at a depth shallower than 10 m below sea level. Sim and Lee [16] Sr–Nd isotope ratios of carbonate in the Korean peninsula. The aim of this study was to studiedcarry the out asequence geochemical stratigraphy analysis of of the the carbonates Daegi Formation in the study and area concluded and interpret that the their Daegi FormationREE patterns experienced and Sr–Nd several isotope sea-level ratios to fluctu elucidateations the within depositional the shallow environments depth andrange. A biostratigraphydiagenetic processes. and fossil The study REE patterns [17] also and suggested the isotopic that ratios the ofDaegi the carbonates Formation were was also formed in acompared shallow andmarine discussed environment. with those in Japan and China.

FigureFigure 1. Geological 1. Geological map map of Taebaek of Taebaek and and Jeongseon Jeongseon areas, areas, southeas southeasterntern (SE) (SE) Korean Korean Peninsula Peninsula (modiﬁed (modified from from Kang Kang and and Choi [17].Choi [Locations17]. Locations of samples of samples are are marked marked with with a ared red star star.. Ordo, Cam,Cam, and and Precam Precam refer refer to Ordovician,to Ordovician, Cambrian, Cambrian, and and Precambrian,Precambrian, respectively. respectively.

2. Geological Background 2.2. Jeongseon Area 2.1. Taebaek Area The Jeongseon area, located northwest of Taebaek, consists of the Ordovician Yong- The Cambrian carbonates in Taebaek area include the Myobong, Daegi, and Hwajeol tanFormations and Cambrian of the Taebaek Taebaek groupgroups (Figure (Figure1). Among1). The these,stratigraphy the Daegi differs Formation little mostlyfrom that of theconsists Taebaek of area, carbonates, except and for it the is widely presence distributed of the “Hoedongri” throughout the Formation. central–eastern The part “Hoedon- of the Korean Peninsula, including the Jeongseon, Samcheok, and Taebaek areas (Figure1) . The Daegi Formation is known to have been deposited in a shallow marine environment such as a platform margin [13,16,17]. Kim and Park [13] suggested that the Daegi For- mation was deposited at a depth shallower than 10 m below sea level. Sim and Lee [16] studied the sequence stratigraphy of the Daegi Formation and concluded that the Daegi Formation experienced several sea-level ﬂuctuations within the shallow depth range. A biostratigraphy and fossil study [17] also suggested that the Daegi Formation was formed in a shallow marine environment.

2.2. Jeongseon Area The Jeongseon area, located northwest of Taebaek, consists of the Ordovician Yongtan and Cambrian Taebaek groups (Figure1). The stratigraphy differs little from that of the Minerals 2021, 11, x FOR PEER REVIEW 3 of 15 Minerals 2021, 11, 326 3 of 15

Taebaekgri” Formation area, except was fornamed the presenceafter the ofplace the “Hoedongri”where the conodont Formation. fossil The thought “Hoedongri” to be of Si- Formationlurian was was first named discovered after the [11]. place Since where then, the many conodont investigations fossil thought have to focused be of Silurian on the co- wasnodont first fossil discovered in the [11 area]. Since to find then, out many the investigationsgeological age have of these focused fossils on the and conodont their strati- fossilgraphic in thesignificance area to find [12,14,15]. out the Recently, geological Lee age [18,19] of these insisted fossils that and the their conodont stratigraphic fossils are significancenot Silurian [ 12but,14 ,Ordovician.15]. Recently, Kwon Lee [18et, 19al.] insisted[20] discussed that the the conodont evolution fossils history are not of the SilurianTaebaek but basin Ordovician. regarding Kwon the Hoedongri et al. [20] discussed Formation the as evolution an Ordovician history stratum. of the Taebaek This study basinalso regards regarding the the Hoedongri Hoedongri Formation Formation as asOrdovician. an Ordovician Won stratum.et al. [21] This and studyWoo et also al. [22] regardssuggested the that Hoedongri the carbonates Formation in the as Ordovician. area were deposited Won et al. in [ 21a ]shallow and Woo marine et al. environ- [22] suggestedment. Most that of the the carbonates carbonates in in the the area Jeongseon were deposited area have in a shallowsuffered marine recrystallization environment. due to Mostlater ofmetamorphism the carbonates [12,14,15]. in the Jeongseon area have suffered recrystallization due to later metamorphism [12,14,15].

2.3.2.3. PetrographyPetrography TheThe carbonates carbonates in in the the study study areas areas consist consist of dark-grayof dark-gray to black to black fine-grained fine-grained limestone limestone andand whitewhite crystalline limestonelimestone (Figure(Figure2 2).). They can be petrographically petrographically classifiedclassified as well- well-sortedsorted micrite micrite to fine-grained to fine-grained calcite. calcite. The Thecarbonates carbonates also alsoinclude include minor minor amounts amounts of dolo- ofmite dolomite and illite. and Figure illite. 3 Figure shows3 showstheir microsco their microscopepe images. images. The carbonates The carbonates in the study in the areas studyare mostly areas aremicrites mostly that micrites have been that haverecrystall beenized recrystallized (Figure 3A); (Figure however,3A); however, some calcite some crys- calcitetals can crystals be observed can be observed(Figure 3B). (Figure Therefore,3B). Therefore, identification identification of their of origin their origin using using petrogra- petrographyphy is difficult. is difficult. Although Although a little a quartz little quartz was wasobserved, observed, this this was was ne negligiblegligible because because there therewas almost was almost no residue no residue after after acid acid digestion. digestion.

FigureFigure 2. 2.Carbonate Carbonate samples samples in studyin study area: area: (A) white(A) white crystalline crystalline limestone; limestone; (B) dark-gray (B) dark-gray ﬁne-grained fine- limestone.grained limestone.

Minerals 2021, 11, x FOR PEER REVIEW 3 of 15

gri” Formation was named after the place where the conodont fossil thought to be of Si- lurian was first discovered [11]. Since then, many investigations have focused on the conodont fossil in the area to find out the geological age of these fossils and their stratigraphic significance [12,14,15]. Recently, Lee [18,19] insisted that the conodont fossils are not Silurian but Ordovician. Kwon et al. [20] discussed the evolution history of the Taebaek basin regarding the Hoedongri Formation as an Ordovician stratum. This study also regards the Hoedongri Formation as Ordovician. Won et al. [21] and Woo et al. [22] suggested that the carbonates in the area were deposited in a shallow marine environment. Most of the carbonates in the Jeongseon area have suffered recrystallization due to later metamorphism [12,14,15].

2.3. Petrography The carbonates in the study areas consist of dark-gray to black fine-grained limestone and white crystalline limestone (Figure 2). They can be petrographically classified as well- sorted micrite to fine-grained calcite. The carbonates also include minor amounts of dolomite and illite. Figure 3 shows their microscope images. The carbonates in the study areas are mostly micrites that have been recrystallized (Figure 3A); however, some calcite crystals can be observed (Figure 3B). Therefore, identification of their origin using petrography is difficult. Although a little quartz was observed, this was negligible because there was almost no residue after acid digestion.

Minerals 2021, 11, 326 4 of 15 Figure 2. Carbonate samples in study area: (A) white crystalline limestone; (B) dark-gray fine- grained limestone.

Figure 3. Microscope images of carbonate samples in study area: (A) recrystallized micrites; (B) micrites and calcites.

3. Methods Thirteen carbonate samples were collected from ﬁve outcrops (samples JS-1 to JS-5) and eight drilling cores (samples TB-1 to TB-8). All the samples used were fresh and not very weathered. The samples were crushed using a jaw crusher and then pulverized in an agate mortar until their grain sizes were less than 150 µm. Ultra-pure HCl and HNO3 reagents (Merck, Darmstadt, Germany) were used throughout sample preparation to minimize possible contamination from the reagents.

3.1. REE Analyses For REE analyses, 0.5 to 1.0 g of the powdered samples were digested using 20 mL of 2 M HCl according to the method of Kim et al. [23], and then the digested sample solutions were filtered to remove the possible residue through the filter membrane having a 0.4 µm pore size. The silicate residues are known to have little effect on the solution chemistry [1,22]. Subsequently, the solutions were filtered using a 0.4 µm membrane filter and loaded into the cation-exchange resin (Bio-Rad, AG 50W-X8) column. The Ca matrix and Ba were removed by passing 2 M HCl and 2.4 M HNO3 through the column, respectively. The REE fractions were recovered using 50 mL of 6 M HCl. The separated solutions were dried on a hot plate and diluted with 2% HNO3 solution containing internal standards of In, Bi, and Re. The diluted REE solutions were analyzed using ICP-MS (Perkin Elmer, NexION350) at the Korea Institute of Geoscience and Mineral Resources (KIGAM). The sensitivity fluctuation of ICP-MS during the measurement was corrected from the internal standardization using In, Bi, and Re [24]. The levels of REE in the blank solutions were less than 10 ppt (10 µg/l). The accuracy and the precision of the analytical results were assessed with JDo-1 and JLs-1 carbonate reference materials curated by the Geological Survey of Japan (GSJ). The analysis results are reported with 95% confidence interval from the mean. The isobaric interferences were corrected by subtracting the signals of the corresponding oxides from each measurement. The oxides included 151Eu–135Ba16O, 159Tb–143Nd16O, 160Gd–144Nd16O, 165Ho–149Sm16O, and others.

3.2. Sr and Nd Isotope Ratios The sample digestion process for 87Sr/86Sr analysis was the same as that for REE analysis. The digested solutions were completely evaporated and then the residual cakes were dissolved again with 8 M HNO3. The dissolved solutions were then loaded into the Sr-specific resin (SR-R50-S 50-100 mesh, Eichrom) and eluted with 8 M HNO3 to collect elements other than Sr such as Rb, REE, and others. Lastly, Sr was separated from the resin with 0.05 M HNO3 solution. The other element fractions were dried up and loaded onto the cation-exchange resin (Bio-Rad, AG 50W-X8) column for REE separation. Nd was eluted from the separated REEs with 0.2 M 2-hydroxyisobutric acid (HIBA) washed through a quartz column filled with the cation-exchange resin (Bio-Rad, AG 50W-X8, 200-400mesh). The isotope composition of Sr and Nd was measured using a Neptune Plus MC-ICP- MS (Thermo Fisher Scientific Ltd.) with nine Faraday cups Neptune Plus, at KIGAM. The Minerals 2021, 11, 326 5 of 15

87 86 Minerals 2021, 11, x FOR PEER REVIEWanalytical method of this study gave the Sr/ Sr of the NBS987 Sr standard as 0.7102765 of 15 143 144 ± 0.000022 (N = 20, 2σm) and the Nd/ Nd of the JNdi-1 Nd standard as 0.512090 ± 0.000060 (N = 20, 2σm).

4. Results 4.1. REE Patterns All thethe samplessamples except except JS-3 JS-3 in in the the Taebaek Taebae andk and Jeongseon Jeongseon areas areas had had relatively relatively low REElow concentrationsREE concentrations ranging ranging from 2.47from to 2.47 15.64 toµ 15.64g/g (Table μg/g1 (Table). The CI1). chondrite-normalizedThe CI chondrite-normal- [ 25] REEized patterns[25] REEindicated patterns indicated that the carbonates that the carb wereonates LREE were enriched LREE (Figure enriched4). The(Figure (La/Yb) 4). TheN values(La/Yb) ofN values the Taebaek of the andTaebaek Jeongseon and Jeongseon carbonates carb variedonates from varied 6.33 from to 9.73 6.33 and to 8.749.73 and to 15.94, 8.74 respectively.to 15.94, respectively. All REE patterns All REE except patterns that except of JS-5, that dolomite, of JS-5, showeddolomite, negative showed Eu negative anomalies, Eu but no Ce anomalies. The values of Eu /(Sm × Gd )1/2 in the carbonates ranged from anomalies, but no Ce anomalies. TheN valuesN of EuNN/(SmN × GdN)1/2 in the carbonates 0.50 to 0.81. The average value of Ce /(La 2 × Nd )1/3 was 1.01 ± 0.06. The REE pattern ranged from 0.50 to 0.81. The averageN valueN of CeNN/(LaN2 × NdN)1/3 was 1.01 ± 0.06. The ofREE JS-5 pattern showed of neitherJS-5 showed Ce nor ne Euither anomalies. Ce nor Eu anomalies.

Table 1. Rare earth element (REE) contents of Taebaek and Jeongseon carbonates. Table 1. Rare earth element (REE) contents of Taebaek and Jeongseon carbonates.

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu (La/Yb) b Ce/Ce* Eu/Eu* La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu (La/Yb)NN Ce/Ce* Eu/Eu* TB-1TB-1 984984a a 18351835 226 226 884 884 191 191 46 46 191 191 29 29 185 185 40 40 118 118 17 106 106 16 16 6.33 6.33 0.96 0.96 0.74 0.74 TB-2TB-2 1821 1821 3712 3712 430 430 1694 1694 353 353 70 70 336 336 57 57 339 339 68 68 184 184 25 159 159 24 24 7.78 7.78 1.00 1.00 0.62 0.62 TB-3TB-3 2417 2417 4076 4076 472 472 1771 1771 378 378 72 72 360 360 57 57 342 342 69 69 195 195 27 174 174 27 27 9.43 9.43 0.90 0.90 0.60 0.60 TB-4TB-4 2708 2708 5507 5507 589 589 2294 2294 463 463 107107 420420 64 64 389 389 76 76 214 214 30 194 194 27 27 9.4 9.477 1.03 1.03 0.74 0.74 TB-5TB-5 2744 2744 5717 5717 665 665 2567 2567 542 542 108108 508508 79 79 488 488 102102 274274 42 256 36 36 7. 7.2727 1.03 1.03 0.63 0.63 TB-6TB-6 2732 2732 5571 5571 628 628 2442 2442 478 478 80 80 422 422 71 71 441 441 87 87 240 240 35 208 208 31 31 8.91 8.91 1.02 1.02 0.54 0.54 TB-7TB-7 3003 3003 6329 6329 782 782 3204 3204 668 668 178178 666666 96 96 547 547 99 99 263 263 38 230 230 34 34 8.8 8.888 0.99 0.99 0.81 0.81 TB-8TB-8 2607 2607 4993 4993 569 569 2210 2210 424 424 93 93 399 399 59 59 333 333 67 67 191 191 29 182 182 28 28 9.73 9.73 0.97 0.97 0.69 0.69 JS-1 JS-1 524 524 1053 1053 122 122 441 441 78 78 16 16 71 71 11 11 62 62 12 12 32 32 5 28 28 4 4 12.30 12.30 1.02 1.02 0. 0.6565 JS-2 JS-2 2801 2801 6637 6637 844 844 2927 2927 553 553 90 90 550 550 83 83 499 499 91 91 251 251 36 222 222 32 32 8.74 8.74 1.12 1.12 0.51 0.51 JS-3 JS-3 4434 4434 9066 9066 1117 1117 4003 4003 718 718 147147 674674 100100 614614 114114 336336 48 306 306 45 45 10.41 10.41 1.02 1.02 0.65 0.65 JS-4 JS-4 1042 1042 2138 2138 244 244 1009 1009 156 156 38 38 156 156 20 20 105 105 19 19 53 53 7 46 46 6 6 15.94 15.94 0. 0.9797 0.75 0.75 JS-5 JS-5 1904 1904 4544 4544 593 593 2334 2334 427 427 136136 409409 56 56 315 315 49 49 135 135 17 102 102 11 11 13. 13.1111 1.12 1.12 0.97 0.97 a b 2 1/3 All units in ppb (µg/kg); “N” denotes the CI chondrite-normalized value. Ce/Ce* values are given according to CeN/(LaN × NdN) ; 1/2 Eu/Eu* values are given according to EuN/(SmN × GdN) . a All units in ppb (μg/kg); b “N” denotes the CI chondrite-normalized value. Ce/Ce* values are given according to CeN/(LaN2 × NdN)1/3; Eu/Eu* values are given according to EuN/(SmN × GdN)1/2.

FigureFigure 4.4. CICI chondrite-normalizedchondrite-normalized REE REE patterns patterns of of carbonates carbonates in Taebaekin Taebaek and and Jeongseon. Jeongseon. (A) CI(A chondrite-normalized) CI chondrite-normalized REE patternsREE patterns of Taebaek of Taebaek carbonates carbonates (core samples(core samples TB-1 to TB-1 TB-8 to collected TB-8 collected at 173 m,at 173 215 m, 226215 m, 257226 m,m, 287257 m,m, 302287 m,m, 331302 m,m,and 331 353m, and m, respectively),353 m, respectively), (B). CI chondrite-normalized(B). CI chondrite-normalized REE patterns REE patterns of Jeongseon of Jeongseon carbonates carbonates (outcrop (outcrop samples samples JS-1 to JS-1 JS-5). to Cam.JS-5). denotesCam. denotes Cambrian. Cambrian. Ls and Ls Do and denote Do limestonedenote limestone and dolomite, and dolomite, respectively. respectively. To improve To visibility, improve the visibility, REE patterns the REE of TB-3,patterns 4, 5, of 6, TB-3, 7, and 4, 85, were 6, 7, multipliedand 8 were by multiplied 1.5, 2, 2.5, by 3.5, 1.5, 3.5, 2, and2.5, 3.5, 7, respectively. 3.5, and 7, respectively .

4.2. 87Sr/86Sr and 143Nd/144Nd Ratios The 87Sr/86Sr ratios of the Taebaek and Jeongseon carbonates varied from 0.70968 to 0.71116 and 0.70884 to 0.71114, respectively (Table 2, Figure 5). The average 87Sr/86Sr ratio of the Taebaek carbonates was 0.71013, which is a little higher than the average value Minerals 2021, 11, 326 6 of 15

4.2. 87Sr/86Sr and 143Nd/144Nd Ratios 87 86 Minerals 2021, 11, x FOR PEER REVIEW The Sr/ Sr ratios of the Taebaek and Jeongseon carbonates varied from 0.709686 of 15 to 0.71116 and 0.70884 to 0.71114, respectively (Table2, Figure5). The average 87Sr/86Sr ratio of the Taebaek carbonates was 0.71013, which is a little higher than the average value 0.70975, of the Jeongseon carbonates. Sr concentrations of these samples ranged 0.70975, of the Jeongseon carbonates. Sr concentrations of these samples ranged from 232 from 232 to 652 ppm, and there was no signiﬁcant difference between the two areas. The to 652 ppm, and there was no significant difference between the two areas. The 143Nd/144Nd 143Nd/144Nd ratios of the carbonates ranged from 0.511448 to 0.511980. Dolomite, TB-4, ratios of the carbonates ranged from 0.511448 to 0.511980. Dolomite, TB-4, had the mini- had the minimum value. Excluding dolomite, the range of 143Nd/144Nd ratio started from mum value. Excluding dolomite, the range of 143Nd/144Nd ratio started from 0.511841. The 0.511841. The εNd values of the samples ranged from −23.2 to 12.8. The εNd value was calculatedεNd values usingof the the samples following ranged equation: from −23.2 to 12.8. The εNd value was calculated using the following equation: (143Nd/144Nd//)sample − (143Nd/144Nd)CHUR ×× 10,000,10, 000, (143Nd/144Nd/)CHUR where the (143Nd/144Nd)CHUR is given by 0.512638 [7]. 143 144 where the ( Nd/ Nd)CHUR is given by 0.512638 [7]. Table 2. Sr and Nd isotope ratios of Taebaek and Jeongseon carbonates. Table 2. Sample Name Sr (ppm) Sr and Nd isotope87Sr ratios/86Sr of Taebaek and Jeongseon143Nd/ carbonates.144Nd εNd(0) a TB-1 278 0.709892 87 86 0.511970143 144 −13.0 a Sample Name Sr (ppm) Sr/ Sr Nd/ Nd εNd(0) TB-2 258 0.709791 0.511870 −15.0 TB-1 278 0.709892 0.511970 −13.0 TB-3 234 TB-2 0.709681 258 0.709791 0.511886 0.511870 −−14.715.0 TB-4 270 TB-3 0.710028 234 0.709681 0.511448 0.511886 −−23.214.7 TB-5 304 TB-4 0.710442 270 0.710028 0.511900 0.511448 −−14.423.2 TB-6 246 TB-5 0.711157 304 0.710442 0.511960 0.511900 −−13.214.4 TB-6 246 0.711157 0.511960 −13.2 TB-7 299 TB-7 0.709789 299 0.709789 0.511851 0.511851 −−15.315.3 TB-8 321 TB-8 0.710263 321 0.710263 0.511841 0.511841 −−15.615.6 JS-1 306 JS-1 0.708841 306 0.708841 0.511895 0.511895 −−14.514.5 JS-2 266 JS-2 0.709559 266 0.709559 0.511980 0.511980 −−12.812.8 JS-3 652 0.710083 0.511856 −15.3 JS-3 652 0.710083 0.511856 −15.3 JS-4 358 0.709116 0.511881 −14.8 JS-4 358 JS-5 0.709116 232 0.711142 0.511881 0.511940 −−14.813.6 JS-5 232a 0.711142 143 144 0.511940143 144 143 −14413.6 εNd values are given according to εNd = {(( Nd/ Nd)sample − ( Nd/ Nd)CHUR)/( Nd/ Nd)CHUR} × a εNd values are given according4 143 to εNd 144= {((143Nd/144Nd)sample − (143Nd/144Nd)CHUR)/(143Nd/144Nd)CHUR} × 104; (143Nd/144Nd)CHUR 10 ;( Nd/ Nd)CHUR = 0.512638. = 0.512638.

FigureFigure 5. TheThe 8787Sr/Sr/86Sr86 ratiosSr ratios of the of Taebaek the Taebaek and Jeongseon and Jeongseon carbonates carbonates plotted plotted as a 87Sr/ as86 aSr87 varia-Sr/86Sr variationtion diagram diagram in Lower in Lower Paleozoic Paleozoic sea water sea water (modified (modiﬁed from from Son Sonand andKim Kim[4]). [4]).

5. Discussion 5.1. Carbonate Depositional Environment Carbonate is mostly deposited in shallow marine environments and, thus, its REE pattern reflects the characteristics of sea water at the time of its deposition [1–3]. Sea water Minerals 2021, 11, 326 7 of 15

5. Discussion 5.1. Carbonate Depositional Environment Minerals 2021, 11, x FOR PEER REVIEW 7 of 15 Carbonate is mostly deposited in shallow marine environments and, thus, its REE pattern reflects the characteristics of sea water at the time of its deposition [1–3]. Sea water usually shows REE patterns having negative Eu and Ce anomalies [26–30]. REEs generallyusually shows have REE trivalent patterns oxidation having negative states in Eu natural and Ce environments, anomalies [26–30]. but CeREEs can generally have a tetravalenthave trivalent state oxidation in oxidizing states environments in natural envi whileronments, Eu can but have Ce a can divalent have a state tetravalent in reducing state environmentsin oxidizing environments[1–3]. Shallow while marine Eu can environments have a divalent can have state fairly in reducing oxidizing environments conditions [1–3]. Shallow marine environments can have fairly oxidizing conditions and precipitate and precipitate CeO2, resulting in Ce deficiency and, consequently, negative Ce anomalies inCeO the2, patternsresulting in in seaCe waterdeficiency [1–3 ].and, Due consequently, to this redox negative behavior Ce of anomalies Ce, the Ce in anomalies the patterns in carbonatein sea water rocks [1–3]. are Due often to used this redox as an indicatorbehavior ofof paleo-redoxCe, the Ce anomalies condition in and carbonate the influence rocks ofare terrigenous often used sedimentsas an indicator [1–3]. of Tanaka paleo-redox et al. [condition1] plotted and the the log influence (Ce/Ce*) of values terrigenous of sea watersediments against [1–3]. depth Tanaka and et showed al. [1] plotted that projecting the log (Ce/Ce*) the log values (Ce/Ce*) of sea value water of Japaneseagainst depth Per- mianand showed carbonate that using projecting this plot the can log help (Ce/Ce*) understand value of the Japanese depositional Permian environment carbonate ofusing the carbonate.this plot can help understand the depositional environment of the carbonate. FigureFigure6 6 shows shows the the log(Ce/Ce*) log(Ce/Ce*) valuesvalues ofof TaebaekTaebaek andand JeongseonJeongseon carbonates, carbonates, ranging ranging fromfrom −−0.0450.045 to −0.049,0.049, displayed displayed on on a a plot plot of log(Ce/Ce*) of of sea sea water water vs. sea sea water depth. TheThe plotplot suggestssuggests thatthat thethe carbonatescarbonates werewere depositeddeposited inin shallowshallow marinemarine environments,environments, whichwhich isis consistentconsistent withwith thethe interpretationinterpretation byby previousprevious sedimentarysedimentary studies [[13,16,17].13,16,17]. LimestoneLimestone inin thethe studystudy areasareas showsshows aa shallowshallow marinemarine environmentenvironment faciesfacies includingincluding oliticolitic andand bioclasticbioclastic limestonelimestone [[13,16],13,16], withwith aa sedimentarysedimentary structurestructure indicatingindicating aa shallowshallow marinemarine environmentenvironment includingincluding aa shallowshallow upwardupward structurestructure [[21,22].21,22]. ItIt alsoalso containscontains manymany fossilsfossils indicatingindicating a a shallow shallow marine marine environment, environment, such such as astrilobite trilobite and and feeding feeding traces traces [17,21]. [17 ,Fig-21]. Figureure 6 matches6 matches well well with with the the results results of these of these sedimentary sedimentary and and biological biological studies. studies. The TheREE REEpatterns patterns of marine of marine carbonates carbonates generally generally have havenegative negative Ce anomalies; Ce anomalies; however, however, they theymay mayhave havelittle littleto no to Ce no anomalies Ce anomalies because because of carbonates of carbonates mixing mixing with the with terrigenous the terrigenous clasts clasts[2,3]. Carbonates [2,3]. Carbonates in the instudy the studyarea showed area showed no Ce no anomalies, Ce anomalies, suggesting suggesting that they that were they weredeposited deposited in a carbonate in a carbonate depositional depositional environment, environment, such such as a asplatform a platform margin, margin, which which can canbe easily be easily affected affected by the by theterrigenous terrigenous clasts. clasts.

FigureFigure 6.6. PlotPlot of log(Ce/Ce*) against against the the depth depth of of sea sea water. water. The The values values of of Taebaek Taebaek and and Jeongseon Jeongseon carbonatescarbonates (marked(marked redred diamond) diamond) are are plotted plotted for for comparison comparison with with seawater seawater Ce Ce anomalies. anomalies. Here, Here, log log (Ce/Ce*) = log{CeN/(La2 N2 × NdN1/3)1/3}, where “N” denotes the CI chondrite-normalized value. (Ce/Ce*) = log{CeN/(LaN × NdN) }, where “N” denotes the CI chondrite-normalized value. REE REE values of seawater are quoted from German and Elderfield [26], Piepgras and Jacobsen [27], values of seawater are quoted from German and Elderﬁeld [26], Piepgras and Jacobsen [27], Bertram Bertram and Elderfield [28], Sholkovitz et al. [29], and German et al. [30]. and Elderﬁeld [28], Sholkovitz et al. [29], and German et al. [30]. 5.2. Geochemical Significance of Sr and Nd Isotope Ratios in the Taebaek and Jeongseon Carbonates Minerals 2021, 11, 326 8 of 15 Minerals 2021, 11, x FOR PEER REVIEW 8 of 15

5.2. Geochemical Significance of Sr and Nd Isotope Ratios in the Taebaek and Jeongseon Carbonates Figure 5 shows the 87Sr/86Sr ratios of the Taebaek and Jeongseon carbonates plotted Figure5 shows the 87Sr/86Sr ratios of the Taebaek and Jeongseon carbonates plotted on on the 87Sr/86Sr variation diagram of lower Paleozoic sea water, indicating that the car- the 87Sr/86Sr variation diagram of lower Paleozoic sea water, indicating that the carbonates 87 86 frombonates the from study the area study had higherarea had87Sr/ higher86Sr thanSr/ thoseSr than of Paleozoicthose of Paleozoic seawater ofseawater the same of age.the sameThe age. higher 87Sr/86Sr ratios might be due to diagenesis [4–6,31–33]. The carbon- 87 86 ate formationsThe higher inSr/ theSr Korean ratios peninsulamight be due experienced to diagenes manyis [4–6,31–33]. diagenetic The processes carbonate in for- the pastmations[4,31 in–33 the], Korean and the peninsula carbonates experienced in the study many area diagenetic were recrystallized processes by in hydrothermalthe past [4,31– water33], and during the carbonates the diagenesis in the[4 study,31–34 area]. Son we andre recrystallized Kim [4] applied by Banner’shydrothermal later diagenesiswater dur- modeling the (bulk diagenesis recrystallization [4,31–34]. Son model) and [ 5Kim] to explain[4] applied the higherBanner’s87Sr/ later86Sr diagenesis ratio. They model suggested(bulk recrystallization that the higher model)87Sr/86 Sr[5] ratio to explain was caused the higher by the 87Sr/ Sr86 exchangeSr ratio. They between suggested carbonate that mineralsthe higher and 87Sr/ the86Sr hydrothermal ratio was caused fluid by during the Sr theexchange diagenetic between recrystallization carbonate minerals or refusion and precipitationthe hydrothermal of the fluid minerals during [4 ,the5]. Thediagenetic hydrothermal recrystallization fluid which or refusion interacted precipitation with the host of rockthe minerals causing later[4,5]. diageneticThe hydrothermal recrystallization fluid which generally interacted had awith high the87Sr/ host86 Srrock ratio causing [4–6]. Figurelater diagenetic7 shows therecrystallization Sr concentration generally and 87hadSr/ a86 highSr change 87Sr/86Sr paths ratio according[4–6]. Figure to the7 shows two modelsthe Sr concentration of carbonate and rock 87 diageneticSr/86Sr change processes paths byaccording Banner to [5 ].the The two corresponding models of carbonate data of Taebaekrock diagenetic and Jeongseon processes carbonates by Banner plotted [5]. Th one corresponding Figure7 support data the of bulk Taebaek recrystallization and Jeongs- model.eon carbonates plotted on Figure 7 support the bulk recrystallization model.

Figure 7. Banner’s [5] [5] later model of diagenesis processe processess in Paleozoic carbonate. Covariation Covariation in in Sr isotopic composition andand SrSr concentrationconcentration inin TaebaekTaebaek andand JeongseonJeongseon carbonate.carbonate.

Figure 88 showsshows the (La/Sm)N Nandand (La/Yb) (La/Yb)N valuesN values of the of carbonates the carbonates in the in study the study area, area,normalized normalized with Post with Archean Post Archean Australian Australian Shale Shale(PAAS (PAAS [35]), [on35]), a onscatter a scatter diagram diagram with withpossible possible diagenetic diagenetic pathwa pathways.ys. Castorina Castorina et al. et [10] al. [10reported] reported that that the the(La/Yb) (La/Yb)N PAASN PAASand and(La/Sm) (La/Sm)N PAASN ratios PAAS ratioscan help can distinguish help distinguish various various diagenetic diagenetic processes processes on carbonates on carbonates (Fig- (Figureure 8). 8The). The (La/Sm) (La/Sm)N PAASN values PAAS values of the of carbonate the carbonate rocks rocks fell within fell within the specified the speciﬁed range, range, but but(La/Yb) (La/Yb)N PAASN values PAAS values were relatively were relatively higher higher than the than range the range of modern of modern seawater. seawater. This indi- This indicatescates that thatthe thecarbonates carbonates experienced experienced early early diagenesis. diagenesis. However, However, the the87Sr/8786Sr/Sr ratio86Sr ratiodoes doesnot increase not increase during during the early the earlydiagenesis diagenesis process, process, because because the 87 theSr/8687SrSr/ isotope86Sr isotope ratio of ratio the ofsource the source that causes that causes early diagen early diagenesisesis has a hassimilar a similar value valueto the to 87Sr/ the8687SrSr/ isotope86Sr isotope ratio of ratio car- ofbonate carbonate [5,6]. [Thus,5,6]. Thus,the carbonate the carbonate rocks rocksmight might have haveexperienced experienced a combination a combination of early of earlydiagenesis diagenesis processes processes to increase to increase the (La/Sm) the (La/Sm)N valueN value and anda later a later diagenesis diagenesis process process to in- to increasecrease the the 87Sr/87Sr/86Sr86 ratio.Sr ratio. MineralsMinerals 20212021,, 1111,, 326x FOR PEER REVIEW 99 ofof 1515

Figure 8. Covariation in (La/Sm)NN andand (La/Yb) (La/Yb)N Nofof Taebaek Taebaek and and Jeongseon Jeongseon carbonate. carbonate. “n” “n” denotes denotes thethe PAASPAAS (Post(Post Archean Archean Australian Australian Shale, Shale, Taylor Taylor and and McLennan McLennan [35 [35])-normalized])-normalized value. value. Modern Modern sea watersea water values values are quotedare quoted from from Garnit Garnit et al. et [36 al]. [36] (modiﬁed (modified from from Castorina Castorina et al. et [10 al.]). [10]).

8787 86 Figure9 9 shows shows the the covariation covariation of ofε NdεNd(0)(0) valuesvalues andand Sr/Sr/ SrSr ratios ratios of Taebaek andand 87 87 86 86 JeongseonJeongseon carbonates. The The εεNdNd valuesvalues used used with with Sr/Sr/Sr canSr canbe very be veryhelpful helpful to character- to char- acterizeize the diagenetic the diagenetic processes. processes. In Figure In Figure 9, th9e, carbonates the carbonates from from the study the study area areashow show rela- relativelytively low lowεNd(0)εNd values(0) values compared compared to those to those of the of common the common carbonates, carbonates, ranging ranging from from23.21 23.21to −12.89 to − with12.89 an with average an average value valueof −15.03. of − Jakubowicz15.03. Jakubowicz et al. [9] et al.observed [9] observed that the that εNd the(0) 87 86 87 86 εandNd(0) Sr/ andSr valuesSr/ Sr in values diagenetic in diagenetic seep carbonates seep carbonates tend to decrease tend to decrease and increase, and increase, respec- respectively,tively, as diagenesis as diagenesis progresses. progresses. As previously As previously described, described, the 87Sr/ the8687SrSr/ ratio86Sr may ratio be may in- becreased increased by interaction by interaction with withthe diagenetic the diagenetic source source that causes that causes the diagenetic the diagenetic process, process, such suchas hydrothermal as hydrothermal fluid fluid interacting interacting with with the ho thest host rock rock [4–6,31–33]. [4–6,31–33 Although]. Although not notmuch much re- researchsearch has has been been done done on on the the εεNdNd(0)(0) with with diagenesis diagenesis of of carbonat carbonate,e, this this is also expected toto result inin lowerlower εεNdNd(0)(0) values of carbonate due to itsits interactioninteraction withwith aa diageneticdiagenetic sourcesource withwith lowerlower εεNdNd(0)(0) values values than than carbonate carbonate [9]. [9]. 87 86 Figure9 9 showsshows that the the carbonates carbonates from from the the study study area area had had higher higher 87Sr/86SrSr/ andSr lower and lowerεNd(0) εvaluesNd(0) valuesthan those than of those Jakubowicz of Jakubowicz et al. et[9]. al. εNd [9].(0)ε Ndgenerally(0) generally ranges ranges from from−3 to− +23 toin +2the in Pacific the Pacific Ocean Ocean [8], but [8 ],these but thesevalues values were weremuch muchlower lowerin the incarbonates the carbonates from the from study the ε studyarea. This area. decrease This decrease in εNd(0) in valueNd(0) is value assumed is assumed to be due to beto duethe change to the change during during the diage- the diageneticnetic processes. processes. The sources of the hydrothermal fluid mediating the diagenesis of the carbonates in the study area have been disputed among the researchers [4,31–34]. Noh and Oh [31] determined K–Ar age and examined the chemistries of the carbonates in their study areas, and they concluded that the hydrothermal water originated from Mesozoic intrusive activities. Large Mesozoic granite bodies occur around the outskirts of the study area (Figure1). Cheng and Chang [ 37] found that the εNd and Sr isotopic compositions of the Mesozoic “Daebo” granite on the Korean Peninsula have the characteristics of a lower 87 86 continental crust. Figure8 shows that the εNd(0) and Sr/ Sr values in the carbonates from the study area plotted fairly close to the range of Daebo granite. All these findings possibly support that the 143Nd/144Nd and 87Sr/86Sr ratios of the carbonates from the study area were modified by diagenetic processes mediated by the interactions with the hydrothermal fluids derived from Mesozoic intrusive bodies. Minerals 2021, 11, 326 10 of 15 Minerals 2021, 11, x FOR PEER REVIEW 10 of 15

Nd 87 8786 86 Figure 9. CovariationCovariation in in ε εNd(0)(0) and and Sr/ Sr/Sr ofSr Taebaek of Taebaek (red rectangle) (red rectangle) and Jeongseon and Jeongseon (green (greendia- diamond)mond) carbonate carbonate.. Mesozoic Mesozoic granite granite pluton pluton of of Korea Korea (yellow (yellow star star and and black black triangle) triangle) and diagenesis seep carbonate (orange circle) data data quoted quoted from from Cheng Cheng and and Chang Chang [37], [37], Jwa Jwa [38], [38], and and Jakubowicz Jakubowicz et al. [9], respectively. et al. [9], respectively.

5.3. ComparisonThe sources with of the the Carbonateshydrothermal in Japan fluid and mediat Chinaing the diagenesis of the carbonates in the studyREE dataarea ofhave the been carbonates disputed in Japanamong and the Chinaresearchers have been[4,31–34]. extensively Noh and accumulated Oh [31] de- bytermined many K–Ar investigators age and [examined39–52]. Figures the chemistrie 10 and s11 of show the carbonates the CI chondrite-normalized in their study areas, and they concluded that the hydrothermal water originated from Mesozoic intrusive ac- REE patterns and Ce/Ce* against (La/Yb)N plots of the carbonates in Japan and China, respectively.tivities. Large Mesozoic granite bodies occur around the outskirts of the study area (Figure 1). ChengZhang and et al.Chang [3] recently [37] found reported that the REEεNd and characteristics Sr isotopic ofcompositions the carbonates of the from Mesozoic various “Daebo” granite on the Korean Peninsula have the characteristics of a lower continental places around the world. The authors observed that the Ce anomalies and (La/Yb)N values ofcrust. the Figure carbonates 8 shows varied that depending the εNd(0) onand their 87Sr/ depositional86Sr values in environments. the carbonates Thefrom carbonates the study depositedarea plotted under fairly open close sea to environmentsthe range of Daeb haveo relativelygranite. All low these Ce/Ce* findings and (La/Yb)possiblyN supportvalues, butthatthose the 143 depositedNd/144Nd underand 87Sr/ shallow86Sr ratios marine of the environments carbonates havefrom relativelythe study high area Ce/Ce*were modi- and (La/Yb)fied by Ndiageneticvalues [3 ].processes This is because mediated shallow by the marine interactions environments with the have hydrothermal more terrigenous fluids materialderived from input Mesozoic [3,53]. According intrusive bodies. to the observation of Zhang et al. [3], the Chinese carbonates were deposited in various environments (Figures9 and 10). Their REE patterns, Ce anomalies, and (La/Yb)N values vary widely depending on the environments at the time of deposition [41,43–48,50–52]. The local redox condition should speciﬁcally affect Ce anomalies. Ling et al. [48] explained that the oxidizing condition due to oxygen supply to the shallow sea produced negative Ce anomalies in Chinese Ediacaran carbonate. Extensive REE studies have been conducted on the Permian carbonates in Japan [2,39,40,42,49]. The Permian carbonates were mostly deposited in open sea environments such as an atoll. Figure 10 shows that the Permian carbonates have REE patterns with negative Ce anomalies and relatively low (La/Yb)N values. The average Ce anomalies and (La/Yb)N values of these carbonates are 0.38 and 7.21, respectively. Minerals 2021, 11, 326 11 of 15

Figure 10. CI chondrite-normalized REE patterns of the carbonates in Japan and China. (a) Permian Japan carbonates, (b) Ediacaran (Type of disappear Ce anomaly), (c) Ediacaran China Carbonates (with Ce anomaly), (d) Lower Ordovician China Carbonates, (e) Middle Ordovician, (f) Permian China Carbonates (with Ce anomaly), (g) Permian China Carbonates (with no Ce anomaly), (h) Cretaceous China Carbonates, and (i) Paleogene China Carbonates. REE values are quoted from Kawabe et al. [39], Kunimaru et al. [40], Tanaka et al. [2], Bao et al. [41], Tanaka et al. [42], Zhang et al. [43], Zhao et al. [44], Jin et al. [45], Fu et al. [46], Qiu et al. [47], Ling et al. [48], Hori et al. [49], Zhang et al. [50], Yang et al. [51], and Su et al. [52].

The Cambrian–Ordovician carbonates of this study showed REE patterns with no Ce anomalies and high (La/Yb)N values. The average Ce anomalies and (La/Yb)N values in the Cambrian–Ordovician carbonates were 1.01 and 9.87, respectively. Figure 11 shows that the Korean carbonates plotted in the shallow marine area, while Japanese carbonates plotted in the open sea setting. This suggests that the Korean carbonates were deposited at places such as platform margins or inland, which are relatively more influenced by the influx of terrigenous material. At present, it may be difficult to understand the details of the past tectonic setting using carbonate geochemistry, but our results show the differences in the carbonate depositional environment among Korea, China, and Japan. Furthermore, a detailed study on platform margin carbonates, open sea carbonates, and various carbonate

Minerals 2021, 11, x FOR PEER REVIEW 12 of 15 Minerals 2021, 11, 326 12 of 15

affect Ce anomalies. Ling et al. [48] explained that the oxidizing condition due to oxygen supplydepositional to the environments shallow sea inproduced Korea, Japan, negative and China Ce anomalies is expected in to Chinese clarify the Ediacaran depositional carbonate.environment of the carbonates in East Asia.

Figure 11. TheThe plot plot of of Ce/Ce* Ce/Ce* against against (La/Yb) (La/Yb)N ofN theofthe carbonates carbonates in Korea in Korea (red (red diamond), diamond), Japan Japan (blue circle), and China China (black (black cross). cross). REE REE values values of of Japan Japan and and China China carbonates carbonates are are quoted quoted from from Kawabe et al. al. [39], [39], Kunimaru Kunimaru et et al. al. [40], [40], Tanaka Tanaka et et al. al. [2], [2], Bao Bao et et al. al. [41], [41 ],Tanaka Tanaka et etal. al. [42], [42 Zhang], Zhang et al.et al.[43], [43 Zhao], Zhao et al. et al.[44], [44 Jin], Jinet al. et al.[45], [45 Fu], Fuet al. et al.[46], [46 Qiu], Qiu et al. et [47], al. [47 Ling], Ling et al. et [48], al. [48 Hori], Hori et al. et [49], al. [49 ], Zhang et al. [50], [50], Yang Yang et al. al. [51], [51], and and Su Su et et al. al. [52]. [52]. The The blue blue and and yellow yellow rectangles rectangles denote denote setting setting carbonates in an open sea depositional environment and a shallow marine depositional environ- carbonates in an open sea depositional environment and a shallow marine depositional environment ment such as a platform margin, inland. such as a platform margin, inland.

6. ConclusionsExtensive REE studies have been conducted on the Permian carbonates in Japan [2,39,40,42,49].Cambrian The and Permian Ordovician carbonates carbonate were formations mostly deposited occur in the in Taebaekopen sea and environments Jeongseon suchareas as located an atoll. in theFigure central–eastern 10 shows that part the of Permian the Korean carbonates peninsula. have The REE REE patterns patterns with of negativethe carbonates Ce anomalies in the study and relatively area show low negative (La/Yb) EuN values. anomalies, The butaverage no Ce Ce anomalies. anomalies This and (La/Yb)suggestsN thatvalues the of carbonates these carbonates in the Taebaek are 0.38 and and Jeongseon 7.21, respectively. areas were deposited in a shallow marineThe environment Cambrian–Ordovician such as a platform carbonates margin, of this which study can showed be significantly REE patterns influenced with no Ce by anomaliesthe terrigenous and high material (La/Yb) input.N values.87Sr/86 TheSr ratios average of the Ce carbonates anomaliesin and the (La/Yb) study areaN values are higher in the Cambrian–Ordovicianthan that of seawater, suggesting carbonates an were interaction 1.01 and between 9.87, respectively. the carbonates Figure and 11 hydrothermal shows that thefluid Korean during carbonates the late diagenetic plotted in process. the shallow Subsequently, marine area, the while (La/Sm) JapaneseN and carbonates (La/Yb)N ratios plot- tedof carbonates in the open in studysea setting. area suggest This suggests that the carbonatesthat the Korean had experienced carbonates anwere early deposited diagenetic at processplaces such (possibly as platform mediated margins by pore or inland, water). which Therefore, are relatively carbonates more in theinfluenced study area by arethe influxestimated of terrigenous to have experienced material. At a combination present, it may of early be difficult and late to diagenesis. understand High the 87detailsSr/86 Srof theand past low 143tectonicNd/144 settingNd values using suggest carbonate that ge theochemistry, main source but of theour fluidresults resulting show the in the differ- late encesdiagenesis in the of carbonate Taebaek and depositional Jeongseon carbonatesenvironment was among hydrothermal Korea, China, fluid from and theJapan. “Daebo” Fur- thermore,intrusive granite a detailed around study the on outskirts platform of marg the studyin carbonates, area. Carbonates open sea in carbonates, the study area and show var- ioushigh carbonate (La/Yb)N valuesdepositional and no environments Ce anomalies. in This Korea, indicates Japan, that and the China carbonates is expected in the to study clar- ifyarea the were depositional deposited environment in an environment of the carbonates different from in East those Asia. of Japan and China, nearby East Asian countries. These geochemical characteristics are expected to help identify the 6.carbonate Conclusions depositional environments in East Asian countries and provide an in-depth understandingCambrian and of their Ordovician depositional carbonate processes. formations occur in the Taebaek and Jeongseon areas located in the central–eastern part of the Korean peninsula. The REE patterns of the Minerals 2021, 11, 326 13 of 15

Author Contributions: Conceptualization and methodology, S.-G.L. and T.-H.K.; investigation, T.-H.K.; writing—original draft preparation, T.-H.K.; writing—review and editing, J.-Y.Y. and S.-G.L.; funding acquisition, KIGAM. All authors read and agreed to the published version of the manuscript. Funding: This research was supported by the Basic Research Project of the Korea Institute of Geo- science and Mineral Resources (KIGAM), funded by the Ministry of Science and ICT (GP2020-003). Acknowledgments: The authors thank the two anonymous reviewers for their helpful and construc- tive reviews of the manuscript. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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