U-Pb Age Dating and Geochemistry of Soft-Sediment Deformation

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Article U-Pb Age Dating and Geochemistry of Soft-Sediment Deformation Structure-Bearing Late Cretaceous Volcano-Sedimentary Basins in the SW Korean Peninsula and Their Tectonic Implications

Kyoungtae Ko 1, Sungwon Kim 1,* and Yongsik Gihm 2

1 Geology Division, Korea Institute of Geoscience and Mineral Resources, Daejeon, 124, Gwahang-no, Yuseong-gu, Daejeon 34132, Korea; [email protected] 2 School of Earth System Science, Kyungpook National University, Daegu 41566, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-42-868-3501

Abstract: Cretaceous volcano-sedimentary basins and successions in the Korean Peninsula are located along NE-SW- and NNE-SSW-trending sinistral strike–slip fault systems. Soft-sediment deformation structures (SSDS) of lacustrine sedimentary strata occur in the Wido, Buan, and Haenam areas of the southwestern Korean Peninsula. In this study, systematic geological, geochronological, and geochemical investigations of the volcanic-sedimentary successions were conducted to constrain the origin and timing of SSDS-bearing lacustrine strata. The SSDS-bearing strata is conformably underlain and overlain by volcanic rocks, and it contains much volcaniclastic sediment and is interbedded with tuffs. The studied SSDSs were interpreted to have formed by ground shaking during syndepositional earthquakes. U-Pb zircon ages of volcanic and volcaniclastic rocks within the studied volcano- Citation: Ko, K.; Kim, S.; Gihm, Y. U-Pb Age Dating and Geochemistry sedimentary successions were ca. 87–84 Ma, indicating that active volcanism was concurrent with of Soft-Sediment Deformation lacustrine sedimentation. Geochemical characteristics indicate that these mostly rhyolitic rocks are Structure-Bearing Late Cretaceous similar to subduction-related calc-alkaline volcanic rocks from an active continental margin. This Volcano-Sedimentary Basins in the suggests that the SSDSs in the study area were formed by earthquakes related to proximal volcanic SW Korean Peninsula and Their activity due to the oblique subduction of the Paleo-Paciﬁc Plate during the Late Cretaceous. Tectonic Implications. Minerals 2021, 11, 520. https://doi.org/ Keywords: late Cretaceous; soft sediment deformation; Korean Peninsula; basin; volcanic activity 10.3390/min11050520

Academic Editor: Michel Faure 1. Introduction Received: 22 April 2021 In continental arcs and adjacent areas, tectonomagmatic activities produce a variety Accepted: 13 May 2021 Published: 14 May 2021 of sedimentary basins commonly ﬁlled with volcanic and volcaniclastic rocks that form volcano-sedimentary successions [1–4]. Although the successions are unique rock records

Publisher’s Note: MDPI stays neutral that unravel syndepositional tectonism and volcanism and their genetic relationships, the with regard to jurisdictional claims in intrusion of magma along, or covering of volcanic rocks over, basin margins commonly published maps and institutional affil- make reconstruction of the tectonic activities difficult. During sedimentation of the suc- iations. cessions, crustal deformation due to tectonic activity gives rise to moderate to strong earthquakes (Mw; moment magnitude > 5.0) [5]. The passage of seismic waves through near-surface, unconsolidated sediments can result in the development of soft-sediment deformation structures (SSDS) over a wide area (>10 km from the epicenter) as a result of liquefaction and/or fluidization due to elevated pore water pressure [6,7]. As a result Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. of their wide occurrence, SSDSs have a high potential for preservation [8]. Thus, analy- This article is an open access article sis of SSDSs is able to determine syndepositional tectonic activities, which can provide distributed under the terms and clues to unravel the genetic relationships between tectonic and magmatic activities in the conditions of the Creative Commons continental arc and adjacent areas. Attribution (CC BY) license (https:// During the Cretaceous, volcano-sedimentary basins formed along sinistral strike–slip creativecommons.org/licenses/by/ fault systems in the central to southwestern part of the Korean Peninsula (Figure1) due to 4.0/). tectonomagmatic activities caused by oblique subduction of the Paleo-Pacific Plate [9–13].

Minerals 2021, 11, 520. https://doi.org/10.3390/min11050520 https://www.mdpi.com/journal/minerals Minerals 2021, 11, x FOR PEER REVIEW 2 of 16

Minerals 2021, 11, 520 2 of 15 During the Cretaceous, volcano-sedimentary basins formed along sinistral strike– slip fault systems in the central to southwestern part of the Korean Peninsula (Figure 1) due to tectonomagmatic activities caused by oblique subduction of the Paleo-Pacific Plate [9–13]. SedimentarySedimentary successionssuccessions withinwithin thethe basinsbasins werewere depositeddeposited inin alluvialalluvial fan,fan, ﬂuviolacustrine,fluviolacustrine, andand lacustrinelacustrine environments environments [14 [14––16].16]. Vertical Vertical changes changes in inthe the depositional depositional environments environments and andsedimentary sedimentary characteristics characteristics (such as (such grain as size grain and size stacking and stackingpatterns) have patterns) been haveinterpreted been interpretedas the result as of the syndepositional result of syndepositional tectonic subsid tectonicence subsidence of the basins of the[14]. basins However, [14]. However,bounding boundingfaults of the faults basins of the are basins commonly are commonly obscured obscuredby volcanic by volcanicintrusions intrusions or covered or coveredby volcanic by volcanicrocks, preventing rocks, preventing detailed detailed analysis analysis of the timing of the timing of tectonic of tectonic activities. activities. Recently, Recently, SSDSs SSDSswithin withinlacustrine lacustrine strata of strata these basins of these have basins been have interpreted been interpreted to be the result to be of theearthquakes, result of earthquakes,providing clues providing to unravel clues tectonic to unravel activities tectonic during activities sedimentation during sedimentation [12,17–19]. In [this12,17 study,–19]. Inwe this present study, a systematic we present geological, a systematic geochronological, geological, geochronological, and geochemical investigation and geochemical of the investigationorigin and timing of the of origin SSDS- andbearing timing strata of to SSDS-bearing constrain the strata origin to and constrain timing theof tectonomag- origin and timingmatic activities of tectonomagmatic in the Korean activities Peninsula in theand Korean adjacent Peninsula areas. and adjacent areas.

FigureFigure 1.1. MapMap ofof thethe southernsouthern Korean Korean Peninsula Peninsula showing showing the the distribution distribution of of Cretaceous Cretaceous sedimentary sedimen- basins,tary basins, and volcanic and volcanic and igneous and igneous rocks rocks along along sinistral sinistral strike–slip strike fault–slip systems fault systems (modiﬁed (modified from [ 12from]). [12]). 2. Geological Setting During the Cretaceous, the Korean Peninsula was subjected to crustal deformation due to the oblique subduction of the Izanagi Plate beneath the Eurasian Plate [9,20–22]. The crustal deformation caused the formation of NE-SW and NNE-SSW-trending, sinistral strike–slip fault systems, such as the Gongju, Hamyeol, and Gwangju Fault systems, along with the development of back-arc basins in the southeastern part of the Korean Peninsula

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(Figure1). Along the fault systems, particularly in areas of step-over and releasing bends, small-scale, non-marine sedimentary basins formed and ﬁlled with ﬂuviolacustrine sedimentary successions under arid to semi-arid climatic conditions [23]. Contemporaneously, continental arc volcanism produced large amounts of volcaniclastic sediment and volcanic rocks interbedded with sedimentary strata, forming volcano-sedimentary successions. Detailed observations of the volcano-sedimentary successions showed that the stacking patterns and spatial distribution of the volcanic-sedimentary lithofacies were the result of spatiotemporal variations in sediment supply related to explosive volcanism and accommodation space due to syndepositional tectonic activities, which has been interpreted to result from contemporaneous tectonomagmatic activities during the Cretaceous [14,15,24,25].

3. SSDS Bearing Volcano-Sedimentary Successions To unravel the genetic relationships between SSDS-bearing strata and the circum- stances behind SSDS formation and Cretaceous tectonomagmatism in the Korean Penin- sula, this study focused on three SSDS-bearing, lacustrine volcano-sedimentary successions such as Beolgeumri, Gyeokpori, and Uhangri Formations [24,26,27]. These formations are underlain and overlain by or interbedded with volcanic and volcaniclastic rocks.

3.1. Beolgeumri Formation The Beolgeumri Formation is a lithostratigraphic unit of the Wido Volcanics composed of conformably stacked volcanic, volcaniclastic, and sedimentary rocks. Koh et al. [28] Minerals 2021, 11, x FOR PEER REVIEWclassiﬁed the succession into four lithostratigraphic units from bottom to top: the Daeri4 An-of 16

desite, Mangryeongbong Tuff, Beolgeumri Formation, and Ttandallae Tuff (Figure2A,B).

FigureFigure 2. 2.( (AA)) GeologicalGeological mapmap ofof the Wido Volcanics (modiﬁed(modified after [28] [28]),), ( (B)) Schematic Schematic log log of of the the volcano-sedimentary succession in the Wido Volcanics (modified after [12]), (C) Outcrop photo- volcano-sedimentary succession in the Wido Volcanics (modiﬁed after [12]), (C) Outcrop photographs graphs of tuff layer and soft sediment deformation structures (SSDS) in the Beolgeumri Formation. of tuff layer and soft sediment deformation structures (SSDS) in the Beolgeumri Formation.

TheThe DaeriDaeri AndesiteAndesite isis thethe lowermostlowermost lithostratigraphiclithostratigraphic unitunit ofof thethe volcanicsvolcanics andand isis composedcomposed ofof aphyricaphyric toto porphyriticporphyritic andesiteandesite underlainunderlain byby dinosaur-eggdinosaur-egg bearingbearing purple-purple- coloredcolored mudstonesmudstones [[29,30].29,30]. Gihm Gihm et et al. al. [25] [25 interpr] interpretedeted that that the the Daeri Daeri Andesite Andesite was was em- emplacedplaced by subaerial by subaerial lava lavaflows ﬂows in arid in to arid semi to-arid semi-arid floodplain ﬂoodplain environments. environments. The overlying The Mangryeongbong Tuff is about 900 m thick and consists mainly of rhyolitic volcaniclastic sediments formed by pyroclastic density currents. The Beolgeumri Formation between the Mangryeongbong and topmost Ttandallae Tuffs is composed of lacustrine mudstones and sandstones, chert, and a bed of lapilli tuff that were deposited in a lacustrine environment at the terminal part of a regional strike–slip fault system on the southwestern Korean Peninsula [12,25]. Ko et al. [12] reported that the Beolgeumri Formation contains various types of SSDS that are characterized by their wide extent (>4 km), lateral continuity (>200 m), and vertical repetition. The SSDSs are underlain and overlain by undeformed laminated mudstones (Figure 2C). These indicate that the SSDSs were formed mainly by liquefaction and/or fluidization triggered by ground shaking during earthquakes [12]. The topmost Ttandallae Tuff is estimated to be about 40 m thick and is composed of tuff breccias and lapilli tuff deposited by pyroclastic density currents [12]. The weighted mean of 206Pb/238U zircon ages from the Mangryeongbong and the Ttandallae tuffs yielded 86.63 ± 0.83 Ma (n = 14, 2σ, MSWD = 2.0) and 87.25 ± 0.36 Ma (n = 13, 2 σ, MSWD = 1.09), respectively [12].

3.2. Gyeokpori Formation The Gyeokpori Formation belongs to the Buan Volcanics and is classified into numerous stratigraphic units of volcaniclastic and volcanic rocks (Cheonmasan Tuff, Udongje Tuff, Seokpo Tuff, Gyeokpori Formation, Gomso Rhyolite, Yujeongge Tuff, Byeonsan Tuff, and Samyebong Rhyolite in ascending order [28] (Figure 3A,B). The Gyeokpori Formation between the Seokpo Tuff and Gomso rhyolite is composed of conglomerates, gravelly sandstones, mudstones, and beds of volcaniclastic deposits. The Gyeokpori Formation is interpreted to have been deposited in lacustrine environments

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overlying Mangryeongbong Tuff is about 900 m thick and consists mainly of rhyolitic volcaniclastic sediments formed by pyroclastic density currents. The Beolgeumri Formation between the Mangryeongbong and topmost Ttandallae Tuffs is composed of lacustrine mudstones and sandstones, chert, and a bed of lapilli tuff that were deposited in a lacustrine environment at the terminal part of a regional strike–slip fault system on the southwestern Korean Peninsula [12,25]. Ko et al. [12] reported that the Beolgeumri Formation contains various types of SSDS that are characterized by their wide extent (>4 km), lateral continuity (>200 m), and vertical repetition. The SSDSs are underlain and overlain by undeformed laminated mudstones (Figure2C). These indicate that the SSDSs were formed mainly by liquefaction and/or ﬂuidization triggered by ground shaking during earthquakes [12]. The topmost Ttandallae Tuff is estimated to be about 40 m thick and is composed of tuff breccias and lapilli tuff deposited by pyroclastic density currents [12]. The weighted mean of 206Pb/238U zircon ages from the Mangryeongbong and the Ttandallae tuffs yielded 86.63 ± 0.83 Ma (n = 14, 2σ, MSWD = 2.0) and 87.25 ± 0.36 Ma (n = 13, 2 σ, MSWD = 1.09), respectively [12].

3.2. Gyeokpori Formation The Gyeokpori Formation belongs to the Buan Volcanics and is classiﬁed into numerous stratigraphic units of volcaniclastic and volcanic rocks (Cheonmasan Tuff, Udongje Tuff, Seokpo Tuff, Gyeokpori Formation, Gomso Rhyolite, Yujeongge Tuff, Byeonsan Tuff, Minerals 2021, 11, x FOR PEER REVIEW 5 of 16 and Samyebong Rhyolite in ascending order [28] (Figure3A,B). The Gyeokpori Formation between the Seokpo Tuff and Gomso rhyolite is composed of conglomerates, gravelly sandstones, mudstones, and beds of volcaniclastic deposits. The Gyeokpori Formation is withinterpreted a small to-scale, have steeply been deposited sloped delta in lacustrine system at environments the lake margin with [24]. a small-scale,A number of steeply SSDS aresloped observed delta systemin sandstone at the lakeand marginmudstone [24 ].lake A numberfloor deposits of SSDS (not are on observed the steeply in sandstone inclined delta).and mudstone Ko et al. lake[18] ﬂoorreported deposits that (notslump on structures the steeply in inclined the Gyeokpori delta). Ko Formation et al. [18 ]are reported about 2that m thick, slump laterally structures continuous in the Gyeokpori (>200 m), and Formation repeated are vertically. about 2 m These thick, structures laterally are contin- un- derlainuous (>200 and m),overlain and repeatedby undeformed vertically. laminated These structuresblack mudstones are underlain consisting and of overlain folds and by synundeformed-depositional laminated (thrust black and normal) mudstones faults consisting (Figure of3C) folds. In addition, and syn-depositional Byun et al. [31] (thrust re- portedand normal) chaotically faults (Figuredeformed3C). layers In addition, in the ByunGyeokpori et al. [Formation31] reported that chaotically were triggered deformed by seismiclayers in shocks. the Gyeokpori Formation that were triggered by seismic shocks.

Figure 3. (A) Geological map of the Buan Volcanics (modiﬁed(modified after [[28]),28]), ((BB)) SchematicSchematic loglog ofof thethe volcano-sedimentaryvolcano-sedimentary succession in the Buan Volcanics (modiﬁed(modified afterafter [[13]),13]), ((CC)) OutcropOutcrop photographsphotographs ofof softsoft sedimentsediment deformation structures (SSDS) in the Gyeokpori Formation. (SSDS) in the Gyeokpori Formation.

The weighted mean of 206Pb/238U zircon ages from conformably underlying (Seokpo Tuff) and unconformably overlying (Yujeongge Tuff) strata yielded 87.30 ± 0.99 Ma (n = 15, 2σ, MSWD = 2.0) and 86.66 ± 0.93 Ma (n = 20, 2 σ, MSWD = 2.8), respectively [13].

3.3. Haenam Basin The Late Cretaceous Uhangri Formation is a volcano-sedimentary succession deposited in the Haenam Basin in the southwestern part of the Korean Peninsula (Figure 1). The Uhangri Formation is underlain by andesitic tuff and overlain by the Hwangsan Tuff and Jindo Rhyolite (Figure 4A,B). The Uhangri Formation mainly consists of conglomerate, sandstone, laminated shale, and cherty mudstone with interlayered volcaniclastic deposits, deposited in alluvial, lacustrine delta, and lacustrine environments [26,32,33]. A number of fold structures and convolute laminations are found in specific layers of the lacustrine sandstones and mudstones. These intervals are underlain and overlain by undeformed laminated to homogeneous mudstones (Figure 4C). This indicates that these SSDSs were formed by the deformation of unconsolidated sediments via liquefaction and associated fluidization triggered by earthquakes. Chough and Chun [34] also reported intrastratal flows and associated rip-down structures in deltaic sediments. They interpreted these structures to have been formed by syndepositional earthquakes.

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3.3. Haenam Basin The Late Cretaceous Uhangri Formation is a volcano-sedimentary succession deposited in the Haenam Basin in the southwestern part of the Korean Peninsula (Figure1). The Uhangri Formation is underlain by andesitic tuff and overlain by the Hwangsan Tuff and Jindo Rhyolite (Figure4A,B). The Uhangri Formation mainly consists of conglomerate, sandstone, laminated shale, and cherty mudstone with interlayered volcaniclastic deposits, deposited in alluvial, lacustrine delta, and lacustrine environments [26,32,33]. A number of fold structures and convolute laminations are found in specific layers of the lacustrine sandstones and mudstones. These intervals are underlain and overlain by undeformed laminated to homogeneous mudstones (Figure4C). This indicates that these SSDSs were formed by the deformation of unconsolidated sediments via liquefaction and associated fluidization triggered by earthquakes. Chough and Chun [34] also reported intrastratal Minerals 2021, 11, x FOR PEER REVIEW 6 of 16 flows and associated rip-down structures in deltaic sediments. They interpreted these structures to have been formed by syndepositional earthquakes.

Figure 4. (A) Geological map of the Haenam Basin (modiﬁed(modified after [[34]),34]), (B) SchematicSchematic log ofof thethe volcano-sedimentaryvolcano-sedimentary succession in the Haenam Basin (modified (modiﬁed afterafter [[35]),35]), ( C) Outcrop photographs of tuff layer and and soft soft sediment sediment deformation deformation structures (SSDS) in the Uhangri Formation. structures (SSDS) in the Uhangri Formation. 4. Analytical Methods 4. Analytical Methods Representative volcanic and sedimentary samples associated with soft-sediment de- Representative volcanic and sedimentary samples associated with soft-sediment defor- formation structures were collected from the volcanic and volcaniclastic rocks situated mation structures were collected from the volcanic and volcaniclastic rocks situated within, within, underlying, or overlying Cretaceous lacustrine sediments. Zircon grains were ex- underlying, or overlying Cretaceous lacustrine sediments. Zircon grains were extracted tracted from crushed rocks by heavy liquid and magnetic separation, followed by hand- from crushed rocks by heavy liquid and magnetic separation, followed by handpicking picking under a binocular microscope. Observation of the internal structure of the zircon under a binocular microscope. Observation of the internal structure of the zircon grains grains before analysis was carried out using back-scattered electron and cathodolumines- before analysis was carried out using back-scattered electron and cathodoluminescence cence (CL) imaging, which were performed using the JEOL6610LV scanning electron mi- (CL) imaging, which were performed using the JEOL6610LV scanning electron microscope croscopeat the Korea at the Basic Korea Science Basic Institute. Science Institute. For SHRIMP U U-Pb-Pb dating, zircon grains were mounted in epoxy resin disks, along with chips of the FC1 (Duluth gabbro of 1099 Ma [36]) [36]) and SL13 (Sri Lankan gem gem zircon, zircon, U = 238 238 ppm ppm [37]) [37]) reference zircons. U U-Th-Pb-Th-Pb isotopic composition analysis followed the protocols of Williams [38] and Kim et al. [11]. The wavelength and current of the primary ion beam used in the analysis were ≈30 μm and ≈3 nA, respectively. For the calculation of U and Th contents in zircon, SL13 was used as the reference, while the 206Pb/238U ratio was calibrated using the FC1 zircon standard (206Pb/238U = 0.1859 [36]). Common Pb contributions were corrected using the measured 204Pb and the model common Pb composition suggested by Stacey and Kramers [39]. The isotopic ratio of Pb-Th-U in the analyzed zircon and the weighted mean age were calculated using SQUID 2.50 and Isoplot 3.71 [40,41]. Each of the analysis points marked on the Tera–Wasserburg diagram used values that were not corrected for 204Pbc and had an error range of 2σ. The suggested mean zircon ages were 207Pb corrected 206Pb/238U ages, and uncertainties were calculated at a confidence level of 95 %. The zircon U–Pb age data are summarized in Table S1. Fourteen volcanic rocks were analyzed for whole-rock major and trace element abundances, and rare earth element (REE) abundances using inductively coupled plasma atomic emission spectrometry (Thermo Jarrel-Ash ENVIRO II) and ICP mass spectrometry (Perkin–Elmer Optima 3000) at Activation Laboratories, Ltd.(Ancaster, ON, Canada). Analytical uncertainties ranged from 1% to 3%.

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protocols of Williams [38] and Kim et al. [11]. The wavelength and current of the primary ion beam used in the analysis were ≈30 µm and ≈3 nA, respectively. For the calculation of U and Th contents in zircon, SL13 was used as the reference, while the 206Pb/238U ratio was calibrated using the FC1 zircon standard (206Pb/238U = 0.1859 [36]). Common Pb contributions were corrected using the measured 204Pb and the model common Pb composition suggested by Stacey and Kramers [39]. The isotopic ratio of Pb-Th-U in the analyzed zircon and the weighted mean age were calculated using SQUID 2.50 and Isoplot 3.71 [40,41]. Each of the analysis points marked on the Tera–Wasserburg diagram used 204 values that were not corrected for Pbc and had an error range of 2σ. The suggested mean zircon ages were 207Pb corrected 206Pb/238U ages, and uncertainties were calculated at a conﬁdence level of 95 %. The zircon U-Pb age data are summarized in Table S1. Fourteen volcanic rocks were analyzed for whole-rock major and trace element abundances, and rare earth element (REE) abundances using inductively coupled plasma atomic Minerals 2021, 11, x FOR PEER REVIEWemission spectrometry (Thermo Jarrel-Ash ENVIRO II) and ICP mass spectrometry (Perkin–7 of 16 Elmer Optima 3000) at Activation Laboratories, Ltd.(Ancaster, ON, Canada). Analytical uncertainties ranged from 1% to 3%.

5.5. ResultsResults 5.1.5.1. ZirconZircon U-PbU-Pb DatingDating 5.1.1.5.1.1. TuffTuff BedBed inin thethe BeolgeumriBeolgeumriFormation Formation ZirconZircon grainsgrains fromfrom aa tufftuff (BT-1)(BT-1) inin thethe BeolgeumriBeolgeumri FormationFormation werewere ﬁne-fine- toto medium-medium- grainedgrained (20–200(20–200 µμmm diameter)diameter) euhedraleuhedral prismaticprismatic grainsgrains (Figure(Figure5 A).5A). The The aspect aspect ratios ratios rangedranged fromfrom 11 toto 3.3. CLCL imagingimaging showedshowed thatthat thethe grainsgrains hadhad oscillatoryoscillatory zoning,zoning, showingshowing well-developedwell-developed sector sector zoned zoned areas. areas. The 15 analyses analyses by by SHRIMP SHRIMP U-Pb U-Pb dating dating gave gave a a 206 238 weightedweighted meanmean 206Pb/238UU age age of of 87.1 87.1 ± ±1.01.0 Ma Ma (n (=n 1=5, 15, 2σ, 2 σMSW, MSWDD = 1 =.8) 1.8) (Figure (Figure 6A).6A).

FigureFigure 5.5. Cathodoluminescence (CL) (CL) images images of of zircon zircon grains grains from from (A (A) )the the tuff tuff in in the the Beolgeumri Beolgeumri Formation,Formation, ((BB)) the the Gomso Gomso Rhyolite, Rhyolite, ( C(C)) the the tuff tuff in in the the Uhangri Uhangri Formation, Formation, (D (D) the) the andesitic andesitic tuff, tuff, and (andE) the (E Hwangsan) the Hwangsan Tuff. Tuff. Analyzed Analyzed points points and ages and (boldages (bold italics) italics) are shown. are shown.

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FigureFigure 6.6. ConcordiaConcordia plots plots of of the the SHRIMP SHRIMP U U-Pb–Pb isotopic isotopic analyses analyses of ofzircons zircons from from (A) ( Athe) the tuff tuff in the in theBeolgeumri Beolgeumri Formation, Formation, (B) the (B) theGomso Gomso Rhyolite, Rhyolite, (C) the (C) tuff the tuffin the in Uhangri the Uhangri Formation, Formation, (D) the (D) the andesiticandesitic tuff,tuff, and and ( E(E)) the the Hwangsan Hwangsan tuff tuff with with analyzed analyzed points points and and ages. ages. Gray Gray dotted dotted ellipsoids ellipsoids were excludedwere excluded from weightedfrom weighted mean mean calculations. calculations.

5.1.2.5.1.2. GomsoGomso RhyoliteRhyolite inin thethe BuanBuan Volcano-SedimentaryVolcano-Sedimentary SuccessionSuccession ZirconZircon grains from from the the Gomso Gomso Rhyolite Rhyolite (GR (GR-1)-1) in the in the Buan Buan volcano volcano-sedimentary-sedimentary suc- successioncession of the of theBuan Buan area area were were fine- ﬁne- to coarse to coarse-grained-grained (25–250 (25–250 μm diameter)µm diameter) and had and aspect had aspectratios ranging ratios ranging from 1 from to 4. 1The to4. CL The images CL images showed showed that about that about 40% of 40% zircon of zircon grains grains were wereeuhedral euhedral to subhedral to subhedral and have and clear have oscillatory clear oscillatory zoning zoning of the ofwhole the whole grain. grain.Some zircon Some zircongrains grainsare composites, are composites, consisting consisting of inherited of inherited cores cores surrounded surrounded by very by very thin, thin, bright bright CL, CL,and andmagmatic magmatic overgrowths. overgrowths. The cores The coresare characterized are characterized by sector by sectorand oscillatory and oscillatory zoning 206 238 207 206 zoning(Figure(Figure 5B). The5B). combined The combined 206Pb/238U andPb/ 207Pb/U206 andPb apparentPb/ Pb ages apparent of many ages of the of inherited many of thezircons inherited by SHRIMP zircons U by-Pb SHRIMP dating have U-Pb high dating discordance have high due discordance to Pb loss dueor contamination, to Pb loss or contamination,and they range andfrom they Middle range Paleoproterozoic from Middle Paleoproterozoic to early Late Cretaceous, to early Late as Cretaceous, follows: 1912 as follows:Ma, 1875 1912–1860 Ma, Ma 1875–1860 (n = 4), 226 Ma Ma, (n 168= 4),–165 226 Ma, Ma, 110 168–165 Ma, and Ma, 97 110 Ma. Ma, Analyses and 97 Ma.of the Analyses young- 206 238 ofest the euhedrally youngest zoned euhedrally grains zoned show variable grains show 206Pb/ variable238U ages fromPb/ 89.6U Ma ages to from 81.7 89.6Ma ( Man = 14; to 81.7Figure Ma 6B). (n = The 14; FigureSeokpo6B). Tuff The in Seokpo the Buan Tuff Volcanics in the Buan is Volcanicsolder than is the older Gomso than theRhyolite; Gomso it Rhyolite;extruded itat extruded 88.7 ± 2.0 at Ma 88.7 (n ±= 12.00, MSW Ma (nD= = 10, 2.2) MSWD [28]. = 2.2) [28].

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5.1.3 Volcanic Rocks in the Haenam Basin 5.1.3.Zircon Volcanic grains Rocks from in the a tuff Haenam (UH-1) Basin in the Uhangri Formation were fine- to coarse- grainedZircon (20– grains300 μm from diameter) a tuff (UH-1) and had in theeuhedral Uhangri to Formation subhedral were shapes. ﬁne- The to coarse-grained aspect ratios ranged(20–300 fromµm 1 diameter) to 3. CL images and had showed euhedral that to most subhedral zircon shapes.grains contained The aspect prismatic ratios ranged oscil- latoryfrom 1and to3. sector CL images zoning showed of the thatwhole most grain zircon (Figure grains 5C contained). SHRIMP prismatic U-Pb dating oscillatory of euhe- and drallysector-zoned zoning grains of the showed whole grainslightly (Figure variable5C). ages SHRIMP from U-Pb89.0 M datinga to 79.4 of euhedrally-zonedMa (Figure 6C). grainsZircon showed grains slightly from variablean andesitic ages fromtuff (UH 89.0- Ma2) that to 79.4 underlies Ma (Figure the Uhangri6C). Formation were predominantlyZircon grains from small an to andesitic large (20– tuff200 (UH-2)μm diameter) that underlies euhedral the prismatic Uhangri grains Formation with aspectwere predominantlyratios ranging from small 1 toto large5 (Figure (20–200 5D).µ However,m diameter) some euhedral grains prismatichad rounded grains crystal with terminations.aspect ratios CL ranging imaging from showed 1 to 5 (Figurethat the5 D).grains However, had well some-developed grains hadeuhedral rounded oscillatory crystal zoningterminations. with sector CL- imagingzoned areas. showed For SHRIMP that the grainsU-Pb dating, had well-developed the analyzed grains euhedral showed oscil- twolatory age zoning clusters: with Early sector-zoned Jurassic (192 areas.–177 For Ma) SHRIMP and Late U-Pb Creta dating,ceous the (91 analyzed–79 Ma). grains The youngershowed 206 twoPb/ age238U clusters:apparent Earlyages of Jurassic the euhedral (192–177 zoned Ma) grains and Lateshow Cretaceous a relatively (91–79 tight clus- Ma). 206 238 terThe at youngerabout 87.1–Pb/82.2 Ma,U apparentexcluding ages statistical of the outliers euhedral (90.8 zoned Ma grains and 78.8 show Ma). a relativelyThe age resultstight cluster yielded at a about weighted 87.1–82.2 mean Ma,206Pb/ excluding238U age of statistical 85.08 ± 0.79 outliers Ma ( (90.8n = 14 Ma of and16, MSWD 78.8 Ma). = 206 238 2.2;The Figure age results 6D). yielded a weighted mean Pb/ U age of 85.08 ± 0.79 Ma (n = 14 of 16, MSWDZircon = 2.2; grains Figure (156–D).350 μm diameter) from the Hwangsan Tuff (UH-3) were subhedral µ to euhedralZircon and grains preserved (15–350 euhedralm diameter) oscillatory from the zoning Hwangsan (Figure Tuff 5E). (UH-3) SHRIMP were U subhedral-Pb anal- ysesto euhedral (n = 21) yielded and preserved an age range euhedral between oscillatory 86.2 and zoning 81.3 (Figure Ma, with5E). one SHRIMP exception U-Pb (93.3 analyses Ma). (n = 21) yielded an age range between 86.2 and 81.3 Ma, with one exception (93.3 Ma). Although they gave a weighted mean 206Pb/238U age of 83.81 ± 0.82 Ma (n = 20 of 21, MSWD Although they gave a weighted mean 206Pb/238U age of 83.81 ± 0.82 Ma (n = 20 of 21, = 2.7), the age 206Pb/238U apparent ages were slightly variable (Figure 6E). MSWD = 2.7), the age 206Pb/238U apparent ages were slightly variable (Figure6E).

5.2.5.2. Geochemistry Geochemistry VolcanicVolcanic samples fromfrom thethe Wido, Wido, Buan, Buan, and and Haenam Haenam volcano-sedimentary volcano-sedimentary successions succes- sionswere were analyzed analyzed to determine to determine the geochemical the geochemical signatures signatures (Table (Table S2). S2). On the SiO2 versus Na2O + K2O diagram (Figure 7), the Wido, Buan, and Haenam On the SiO2 versus Na2O + K2O diagram (Figure7), the Wido, Buan, and Haenam volcanicvolcanic and and volcanoclastic volcanoclastic rock rock samples samples mostly mostly plot plot in in the the rhyolite rhyolite field. ﬁeld. The The samples samples display the following variations in major element contents: SiO2 (67.25–75.60 wt %), Al2O3 display the following variations in major element contents: SiO2 (67.25–75.60 wt %), Al2O3 (12.90–16.52 wt %), TiO2 (0.10–0.36 wt %), Fe2O3* (1.33–2.91 wt %), MgO (0.17–1.01 wt %), (12.90–16.52 wt %), TiO2 (0.10–0.36 wt %), Fe2O3* (1.33–2.91 wt %), MgO (0.17–1.01 wt %), CaO (0.17–2.12 wt %), Na2O (1.43–5.95 wt %), K2O (2.11–6.08 wt %), and P2O5 (0.01–0.11 CaO (0.17–2.12 wt %), Na2O (1.43–5.95 wt %), K2O (2.11–6.08 wt %), and P2O5 wt(0.01–0.11 %) (Figure wt 8). %) (Figure8).

FigureFigure 7. 7. DiagramsDiagrams of of SiO SiO2 2wtwt % % versus versus Na Na2O2 O+ K +2 KO2 wtO wt% for % forthe the Cretaceous Cretaceous volcanic volcanic rocks rocks from from thethe southwestern southwestern Korean Korean Peninsula. Peninsula.

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FigureFigure 8. 8. PlotsPlots of of major major elements elements vs vs.. SiO SiO22 forfor the the Cretaceous Cretaceous volcanic volcanic rocks rocks from from the the southwestern southwestern KoreanKorean Peninsula. Peninsula.

TheThe Wido, Wido, Buan, Buan, and and Haenam Haenam volcanic volcanic and and volcaniclastic volcaniclastic rock rock samples samples display display LREE LREE depletiondepletion with with strongly strongly to to weakly weakly negative negative Eu Euanomalies anomalies (Eu/Eu* (Eu/Eu* = 0.33 =− 0.330.96−) in0.96) the inchon- the dritechondrite-normalized-normalized REE REEdiagrams diagrams (Figure (Figure 9A,C,E).9A,C,E). On Onthe theprimitive primitive mantle mantle normalized normalized diagramsdiagrams (Figure (Figure 9B,D,F),9B,D,F), the the samples samples display display large large ion ionlithophile lithophile element element enrichment enrichment with Tawith–Nb Ta–Nb troughs troughs and depletion and depletion in P and in P Ti, and indicating Ti, indicating arc-related arc-related volcan volcanism.ism.

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FigureFigure 9. Chondrite-normalized 9. Chondrite-normalized rare earth rare element earth and element primitive and mantle-normalized primitive mantle trace-normalized element for the trace Cretaceous element volcanicfor rocksthe Cretaceous from the southwestern volcanic Koreanrocks from Peninsula. the southwestern Korean Peninsula. 6. Discussion 6. Discussion The SSDS-bearing strata of the Beolgeumri, Gyeokpori, and Uhangri Formations were The SSDS-bearingdeposited strata in lacustrine of the environments Beolgeumri, during Gyeokpori, 87–84 Ma. and These Uhangri formations Formations are underlain and overlain by tuffs formed by explosive volcanic eruptions, suggesting the development were deposited inof lacustrine a lake during environments the interval between during the 87 depositions–84 Ma. ofThese the thick formations volcaniclastic are successions.underlain and overlainVolcaniclastic by tuffs formed sediments by explosive (Gyeokpori volcanic Formation) eruptions, and tuff beds suggesting (Beolgeumri the and devel- Uhangri opment of a lake Formations)during the also interval indicate between syndepositional the deposition volcanic inﬂuencess of the thick on sedimentation volcaniclastic in the successions. Volcaniclasticlacustrine environments. sediments (Gyeokpori Formation) and tuff beds (Beolgeumri and Uhangri Formations) also indicate syndepositional volcanic influences on sedimentation in the lacustrine environments. Modern and Quaternary data show that large amounts of unconsolidated volcaniclastic sediments are dispersed on volcanoes and surrounding areas by pyroclastic density currents and fall out from the eruption column during and immediately after explosive volcanic eruptions [42]. The fine-grained and poorly sorted nature of volcaniclastic sediments prevents infiltration of rainwater into the substrate. This causes an increase in surface runoff, resulting in frequent flooding (e.g., lahar) after explosive volcanic eruptions

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Modern and Quaternary data show that large amounts of unconsolidated volcaniclastic sediments are dispersed on volcanoes and surrounding areas by pyroclastic density currents and fall out from the eruption column during and immediately after explosive volcanic eruptions [42]. The fine-grained and poorly sorted nature of volcaniclastic sediments prevents infiltration of rainwater into the substrate. This causes an increase in surface runoff, resulting in frequent flooding (e.g., lahar) after explosive volcanic eruptions [43]. The flood water erodes and carries large amounts of unconsolidated sediment toward lowlands. Therefore, the rates of sediment supply are increased dramatically—enough to reduce topographic relief by the filling of lowlands via sedimentation [44,45]. Despite high rates of sediment supply after the explosive eruptions, the SSDS-bearing, Beolgeumri, Gyeokpori, and Uhangri Formations accumulated in the lake during and after the eruptions. This indicates that the preservation of lacustrine environments during sedimentation, and rates of accommodation space creation exceeded or at least compensated for the sedimentation rates with the forceful input of sediment. The creation of accommodation space could be attributed to a wet climate that caused an increase in the amount of water flowing into the lake. However, Late Cretaceous sedimentary successions in the Korean Peninsula commonly contain evaporites, calcrete nodules, and raindrop prints, indicating arid to semi-arid climatic conditions [23,46]. Thus, the creation of the accommodation space was interpreted to have resulted from tectonic subsidence, which lowered lake floors. Tectonic subsidence commonly involves moderate and strong earthquakes [5]. Previous studies targeting the SSDS-bearing strata of the Beolgeumri, Gyeokpori, and Uhangri Formations suggest that SSDSs were formed by ground shaking during syndepositional earthquakes [12,18,19,34]. During field observations, we found that all SSDSs are underlain and overlain by undeformed laminated or homogeneous mudstones, suggesting that these SSDSs were not related to depositional events such as slumps. In addition, possible triggering mechanisms for SSDSs, such as rapid sedimentation and passage of large waves (> 10 m in wave height), cannot be applied to lacustrine environments [6,7]. Thus, the development and preservation of the lacustrine environments in which SSDS-bearing strata were deposited were likely due to syndepositional tectonic subsidence, and concomitant earthquakes caused the deformation of the sediments, forming the SSDSs. The geochemical and geochronological data also support this interpretation. The trace element and REE geochemical characteristics of volcanic rocks are similar to those of subduction-related calc-alkaline volcanic rocks from active continental margins. In the classification of Pearce et al. [47], the Wido, Buan, and Haenam rhyolitic volcanic and volcaniclastic samples occur in the volcanic arc granitoid field (Figure 10). During the late Cretaceous, a continental volcanic arc formed as a consequence of the oblique subduction of the Paleo-Pacific Plate. The arc volcanism produced large amounts of volcaniclastic sediment. Contemporaneously, oblique subduction of the Izanagi Plate underneath the Eurasian Plate caused sinistral strike–slip crustal deformation. The sedimentary basins of strike–slip fault systems are characterized by rapid subsidence compared to extensional basins [48]. Geochronological data from numerous SHRIMP and IDTIMS studies [10–13,28,49–51] of the Cretaceous volcanic rocks can be divided into two age groups in the southern Korean Peninsula: (1) Early Cretaceous (115–96 Ma) volcanism related to the major sedimentation in the Gyeongsang Basin, and (2) Late Cretaceous (91–77 Ma) regional volcanism and minor sedimentation in the southern Korean Peninsula, with maximal activity at 87–85 Ma (Figure 11). Thus, from 87 to 84 Ma, the southwestern part of the Korean Peninsula was affected by vigorous tectonomagmatic activities, not only producing large amounts of volcaniclastic sediment but also creating sufficient accommodation space due to tectonic subsidence, as reflected by the SSDSs in lacustrine sediments of the volcano-sedimentary successions. Minerals 2021, 11, 520 12 of 15 Minerals 2021, 11, x FOR PEER REVIEW 13 of 16

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FigureFigure 10.10.Rb/(Y Rb/(Y + Nb) Nb) tectonic tectonic discrimination discrimination diagrams diagrams [47]. [47]. VAG, VAG, volcani volcanicc arc arc granitoids; granitoids; ORG, ORG, oceanoceanFigure ridgeridge 10. Rb/(Y granitoids;granitoids; + Nb) tectonic WPG, within-platewithin discrimination-plate granitoids; diagrams syn syn-COLG[47].-COLG VAG, andvolcani and post post-COLG,c -arcCOLG, granitoids; syn syn-- and andORG, post post- - collisionocean ridge granitoids; granitoids; late WPG, and post within-COLG,-plate late granitoids;- and post syn-collision-COLG and granitoids post-COLG,. syn- and post- collision granitoids; late and post-COLG, late- and post-collision granitoids. collision granitoids; late and post-COLG, late- and post-collision granitoids.

FigureFigureFigure 11. 11. 11.Frequency Frequency Frequency distributiondistribution distribution diagrams diagramsdiagrams of of SHRIMPSHRIMP andandand IDTIMSIDTIMS zircon zircon U U-PbU–Pb–Pb ages ages ages for for for the the the Cretaceous Cretaceous Cretaceous volcanic volcanic volcanic and and and sedimentarysedimentarysedimentary rocks rocks rocks by by by the the the rock rock rock occurrence occurrence occurrence patterns patternspatterns throughout throughout the thethe KoreanKorean Korean Peninsula.Peninsula. Peninsula.

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7. Conclusions (1) Cretaceous volcano-sedimentary successions in the Wido, Buan, and Haenam areas of the central to southwestern part of the Korean Peninsula are distributed along the sinistral strike–slip fault systems. (2) SSDS-bearing lacustrine strata of the Beolgeumri, Gyeokpori, and Uhangri Formations were deposited during a period of syndepositional active volcanism between 87 and 84 Ma. (3) The volcanic and volcaniclastic rocks in this study have the geochemical characteristics of subduction-related calc-alkaline volcanic rocks from active continental margins. (4) The SSDS-bearing strata were interpreted to have been deposited as a result of syndepositional tectonic subsidence and deformed by syndepositional earthquakes in the southwestern Korean Peninsula during the Late Cretaceous.

Supplementary Materials: The following are available online at https://www.mdpi.com/article/ 10.3390/min11050520/s1, Table S1: SHRIMP U-Pb zircon data of the Late Cretaceous volcano- sedimentary successions, South Korea. Table S2: Major and trace element analyses of the Cretaceous volcanic rocks in the Wido, Buan and Haenam areas in the SW Korean Peninsula. Author Contributions: Conceptualization, data acquisition, writing-original draft preparation, visualization, K.K.; writing—original draft, data acquisition, visualization, S.K.; data acquisition, writing—review and editing, Y.G. All authors have read and agreed to the published version of the manuscript. Funding: This work was financially supported by grants from the Korea Institute of Geoscience and Mineral Resources (GP2021-004), funded by the Ministry of Science, Information, Communication and Technology. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Acknowledgments: We thank Keewook Yi at the Korea Basic Science Institute’s Ochang Center for assistance with SHRIMP analysis. Three anonymous reviewers are thanked for their insightful suggestions and comments, which improved the quality of this manuscript. Conflicts of Interest: The authors declare no conflict of interest.

References 1. Busby, C.J. Extensional and Transtensional Continental Arc Basins: Case Studies From the Southwestern United States. In Tectonics of Sedimentary Basins: Recent Adv.; Busby, C.J., Azor, A., Eds.; Blackwell Publishing: Hoboken, NJ, USA, 2012; pp. 382–404. 2. Acocella, V. Structural Control on Magmatism Along Divergent and Convergent Plate Boundaries: Overview, Model, Problems. Earth Sci. Rev. 2014, 136, 226–288. [CrossRef] 3. D’Elia, L.; Martí, J.; Muravchik, M.; Bilmes, A.; Franzese, J.R. Impact of Volcanism on the Sedimentary Record of the Neuquén Rift Basin, Argentina: Towards a Cause and Effect Model. Basin Res. 2018, 30, 311–335. [CrossRef] 4. Espinoza, M.; Montecino, D.; Oliveros, V.; Astudillo, N.; Vásquez, P.; Reyes, R.; Celis, C.; González, R.; Contreras, J.; Creixell, C.; et al. The Synrift Phase of the Early Domeyko Basin (Triassic, Northern Chile): Sedimentary, Volcanic and Tec- tonic Interplay in the Evolution of an Ancient Subduction-Related Rift Basin. Basin Res. 2019, 31, 4–32. [CrossRef] 5. Dorsey, R.J.; Umhoefer, P.J.; Falk, P.D. Earthquake Clustering inferred From Pliocene Gilbert-Type Fan Deltas in the Loreto Basin, Baja California Sur, Mexico. Geology 1997, 25, 679–682. [CrossRef] 6. Owen, G.; Moretti, M. Identifying Triggers for Liquefaction-Induced Soft-Sediment Deformation in Sands. Sediment. Geol. 2011, 235, 141–147. [CrossRef] 7. Owen, G.; Moretti, M.; Alfaro, P. Recognising Triggers for Soft-Sediment Deformation: Current Understanding and Future Directions. Sediment. Geol. 2011, 235, 133–140. [CrossRef] 8. Gihm, Y.S.; Kim, S.W.; Ko, K.; Choi, J.-H.; Bae, H.; Hong, P.S.; Lee, Y.; Lee, H.; Jin, K.; Choi, S.-J.; et al. Paleoseismological implications of liquefaction-induced structures caused by the 2017 Pohang Earthquake. Geosci. J. 2018, 22, 871–880. [CrossRef] 9. Chough, S.K.; Sohn, Y.K. Tectonic and Sedimentary Evolution of a Cretaceous Continental Arc–Backarc System in the Korean Peninsula: New View. Earth Sci. Rev. 2010, 101, 225–249. [CrossRef] Minerals 2021, 11, 520 14 of 15

10. Kim, S.W.; Kwon, S.; Ryu, I.-C.; Jeong, Y.-J.; Choi, S.J.; Kee, W.-S.; Yi, K.; Lee, Y.S.; Kim, B.C.; Park, D.W. Characteristics of the Early Cretaceous Igneous Activity in the Korean Peninsula and Tectonic Implications. J. Geol. 2012, 120, 625–646. [CrossRef] 11. Kim, S.W.; Kwon, S.; Park, S.-I.; Lee, C.; Cho, D.-L.; Lee, H.J.; Ko, K.; Kim, S.J. SHRIMP U-Pb Dating and Geochemistry of the Cretaceous Plutonic Rocks in the Korean Peninsula: A New Tectonic Model of the Cretaceous Korean Peninsula. Lithos 2016, 262, 88–106. [CrossRef] 12. Ko, K.; Kim, S.W.; Lee, H.-J.; Hwang, I.G.; Kim, B.C.; Kee, W.-S.; Kim, Y.-S.; Gihm, Y.S. Soft Sediment Deformation Structures in a Lacustrine Sedimentary Succession Induced by Volcano-Tectonic Activities: An Example From the Cretaceous Beolgeumri Formation, Wido Volcanics, Korea. Sediment. Geol. 2017, 358, 197–209. [CrossRef] 13. Kwon, C.W.; Ko, K.; Gihm, Y.S.; Koh, H.J.; Kim, H. Late Cretaceous Volcanic Arc System in Southwest Korea: Distribution, Lithology, Age, and Tectonic Implications. Cret. Res. 2017, 75, 125–140. [CrossRef] 14. Ryang, W.H.; Chough, S.K. Sequential Development of Alluvial/Lacustrine System; Southeastern Eumsung Basin (Cretaceous), Korea. J. Sediment. Res. 1997, 67, 274–285. 15. Lee, S.H.; Chough, S.K. Progressive Changes in Sedimentary Facies and Stratal Patterns Along the Strike-Slip Margin, North- eastern Jinan Basin (Cretaceous), Southwest Korea: Implications for Differential Subsidence. Sediment. Geol. 1999, 123, 81–102. [CrossRef] 16. Kim, S.B.; Kim, Y.-G.; Jo, H.R.; Jeong, K.S.; Chough, S.K. Depositional Facies, Architecture and Environments of the Sihwa Formation (Lower Cretaceous), Mid-West Korea With Special Reference to Dinosaur Eggs. Cret. Res. 2009, 30, 100–126. [CrossRef] 17. Kang, H.C.; Paik, I.S.; Lee, H.I.; Lee, J.E.; Chun, J.H. Soft-Sediment Deformation Structures in Cretaceous Non-Marine Deposits of Southeastern Gyeongsang Basin, Korea: Occurrences and Origin. Isl. Arc 2010, 19, 628–646. [CrossRef] 18. Ko, K.; Park, S.; Kwon, C.W. Soft-Sediment Deformation Structures in the Cretaceous Gyeokpori Formation of the Buan Area, Korea: Structural Characteristics, Reconstruction of Paleoslope and Triggering Mechanism of Slump. J. Geol. Soc. Korea 2015, 51, 545–560, (In Korean with English abstract). [CrossRef] 19. Byun, U.H.; Van Loon, A.J.T.; Kwon, Y.K.; Ko, K. A New Type of Slumping-Induced Soft-Sediment Deformation Structure: The Envelope Structure. Geologos 2019, 25, 111–124. [CrossRef] 20. Chough, S.K.; Kwon, S.T.; Ree, J.H.; Choi, D.K. Tectonic and Sedimentary Evolution of the Korean Peninsula: A Review and New View. Earth Sci. Rev. 2000, 52, 175–235. [CrossRef] 21. Sagong, H.; Kwon, S.-T.; Ree, J.-H. Mesozoic Episodic Magmatism in South Korea and Its Tectonic Implication. Tectonics 2005, 24, 2004TC001720. [CrossRef] 22. Cho, H.; Son, M.; Cheon, Y.; Sohn, Y.K.; Kim, J.S.; Kang, H.C. Evolution of the Late Cretaceous Dadaepo Basin, SE Korea, in Response to Oblique Subduction of the Proto-Pacific (Izanagi/Kula) or Pacific Plate. Gondwana Res. 2016, 39, 145–164. [CrossRef] 23. Paik, I.S.; Huh, M.; So, Y.H.; Lee, J.E.; Kim, H.J. Traces of Evaporites in Upper Cretaceous Lacustrine Deposits of Korea: Origin and Paleoenvironmental Implications. J. Asian Earth Sci. 2007, 30, 93–107. [CrossRef] 24. Kim, S.B.; Chough, S.K.; Chun, S.S. Tectonic Controls on Spatiotemporal Development of Depositional Systems and Generation of Fining-Upward Basin Fills in a Strike-Slip Setting: Kyokpori Formation (Cretaceous). south-west Korea. Sedimentology 2003, 50, 639–665. [CrossRef] 25. Gihm, Y.S.; Kim, M.; Son, M.; Hwang, I.G. The Influence of Tectonic Subsidence on Volcaniclastic Sedimentation: The Cretaceous Upper Daeri Member, Wido Island, Korea. Isl. Arc 2017, 26, e12183. [CrossRef] 26. Chun, S.S.; Chough, S.K. Depositional Sequences From High-Concentration Turbidity Currents, Cretaceous Uhangri Formation (SW Korea). Sediment. Geol. 1992, 77, 225–233. [CrossRef] 27. Gihm, Y.S.; Hwang, I.G. Syneruptive and Intereruptive Lithofacies in Lacustrine Environments: The Cretaceous Beolkeum Member, Wido Island, Korea. J. Volcanol. Geotherm. Res. 2014, 273, 15–32. [CrossRef] 28. Koh, H.J.; Kwon, C.W.; Park, S.-I.; Park, J.; Kee, W.-S. Geological Report of the Julpo Sheet (1:50,000). Daejon; Korea Institute of Geoscience and Mineral Resources: Daejeon, South Korea, 2013; p. 81, (In Korean with English abstract). 29. Choi, S.; Lee, Y.N. Possible Late Cretaceous Dromaeosaurid Eggshells from South Korea: A New Insight Into Dromaeosaurid Oology. Cret. Res. 2019, 103, 104–167. [CrossRef] 30. Choi, S.; Lee, S.K.; Kim, N.H.; Kim, S.; Lee, Y.N. Raman Spectroscopy Detects Amorphous Carbon in an Enigmatic Egg From the Upper Cretaceous Wido Volcanics of South Korea. Front. Earth Sci. 2020, 7, 349. [CrossRef] 31. Byun, U.H.; Van Loon, A.J.; Kwon, Y.K.; Ko, K. Intrastratal Flow in the Cretaceous Gyeokpori Formation (SW South Korea). Geol. Q. 2020, 64, 611–625. [CrossRef] 32. Lee, D.S. On the Geology and Oily Material-Containing Formation in Haenam Area, Jeollanam-do, Korea. J. Geol. Soc. Korea 1964, 1, 35–49. 33. Lee, D.S.; Lee, H.Y. Geological and Geochemical Study on the Rock Sequences Containing Oily Materials in Southern Coast Area of Korea. J. Korea Inst. Min. Geol. 1976, 9, 45–74, (In Korean with English abstract). 34. Chough, S.K.; Chun, S.S. Intrastratal Rip-Down Clasts, Late Cretaceous Uhangri Formation, Southwest Korea. J. Sediment. Res. 1988, 58, 530–533. 35. Chough, S.K.; Kim, S.B.; Chun, S.S. Sandstone/Chert and Laminated Chert/Black Shale Couplets, Cretaceous Uhangri Formation (Southwest Korea): Depositional Events in Alkaline Lake Environments. Sediment. Geol. 1996, 104, 227–242. [CrossRef] Minerals 2021, 11, 520 15 of 15

36. Paces, J.B.; Miller, J.D. Precise U-Pb Ages of Duluth Complex and Related Maﬁc Intrusions, Northeastern Minnesota: Geochrono- logical Insights to Physical, Petrogenetic, Paleomagnetic, and Tectonomagmatic Processes Associated With the 1.1 Ga Midcontinent Rift System. J. Geophys. Res. 1993, 98, 13997–14013. [CrossRef] 37. Claoué-Long, J.C.; Compston, W.; Roberts, J.; Fanning, C.M. Two Carboniferous Ages: A Comparison of SHRIMP Zircon Dating With Conventional Zircon Ages and 40Ar/39Ar Analysis. In Geochronology Time Scales and Global Stratigraphic Correlation; Berggren, W.A., Kent, D.B., Auberey, M.P., Hardenbol, J., Eds.; S.E.P.M. (Soc. Sediment. Geol.) Spec. Publ: Broken Arrow, OK, USA, 1995; Volume 54, pp. 3–21. 38. Williams, I.S. U-Th-Pb Geochronology by Ion Microprobe. In Applications of Microanalytical Techniques to Understanding Mineralizing Processes; Rev. Econ. Geol. McKibben, M.A., Shanks, W.C., III, Ridley, W.L., Eds.; Society of Economic Geologists: Socorro, NJ, USA, 1998; Volume 7, pp. 1–35. 39. Stacey, J.S.; Kramers, J.D. Approximation of Terrestrial Lead Isotope Evolution by a Two-Stage Model. Earth Planet. Sci. Lett. 1975, 26, 207–221. [CrossRef] 40. Ludwig, K.R. User’s Manual for Isoplot 3.6: A Geochronological Toolkit for Microsoft Excel; [Berkeley Geochronology Center special publication, 2008]; Berkeley Geochronology Center: Berkeley, CA, USA, 2008. 41. Ludwig, K.R. User’s Manual for SQUID 2; [Berkeley Geochronology Center special publication, 2009]; Berkeley Geochronology Center: Berkeley, CA, USA, 2009. 42. Manville, V.; Németh, K.; Kano, K. Source to Sink: A Review of Three Decades of Progress in the Understanding of Volcaniclastic Processes, Deposits, and Hazards. Sediment. Geol. 2009, 220, 136–161. [CrossRef] 43. Major, J.J.; Janda, R.J.; Daag, A.S. Watershed Disturbance and Lahars on the East Side of Mount Pinatubo During the Mid-June 1991 Eruptions. In Fire and Mud: Eruptions and Lahars of Mount Pinatubo; Philippines Newhall, C.G., Punongbayan, R.S., Eds.; University of Washington Press: Seattle, WA, USA, 1996; pp. 895–919. 44. Major, J.J.; Pierson, T.C.; Dinehart, R.L.; Costa, J.E. Sediment Yield Following Severe Volcanic Disturbance?—A Two-Decade Perspective From Mount St. Helens. Geology 2000, 28, 819–822. [CrossRef] 45. Hayes, S.K.; Montgomery, D.R.; Newhall, C.G. Fluvial Sediment Transport and Deposition Following the 1991 Eruption of Mount Pinatubo. Geomorphology 2002, 45, 211–224. [CrossRef] 46. Paik, I.S.; Kim, H.J. Playa Lake and Sheetﬂood Deposits of the Upper Cretaceous Jindong Formation, Korea: Occurrences and Palaeoenvironments. Sediment. Geol. 2006, 187, 83–103. [CrossRef] 47. Pearce, J.A.; Harris, N.B.W.; Tindle, A.G. Trace Element Discrimination Diagrams for the Tectonic Interpretation of Granitic Rocks. J. Petrol. 1984, 25, 956–983. [CrossRef] 48. Nilsen, T.H.; Sylvester, A.G. Strike-Slip Basins. In Tectonics of Sedimentary Basins; Busby, C.J., Ingersoll, R.V., Eds.; Blackwell Publishing Science: Cambridge, MA, USA, 1995; pp. 425–457. 49. Lee, T.-H.; Park, K.-H.; Yi, K.; Geng, J.; Li, H. 2015, SHRIMP U-Pb ages and Hf isotopic composition of the detrital zircons from the Myogok Formation, SE Korea: Development of terrestrial basin and igneous activity during the early Cretaceous. Geosci. J. 2015, 19, 189–203. [CrossRef] 50. Lee, T.-H.; Park, K.-H.; Yi, K. SHRIMP U-Pb ages of detrital zircons from the Early Cretaceous Nakdong Formation, South East Korea: Timing of initiation of the Gyeongsang Basin and its provenance. Isl. Arc 2018, 27, e12258. [CrossRef] 51. Lee, T.-H.; Park, K.-H.; Yi, K. Nature and evolution of the Cretaceous basins in the eastern margin of Eurasia: A case study of the Gyeongsang Basin, SE Korea. J. Asian Earth Sci. 2018, 166, 19–31. [CrossRef]