• Economic and Environmental Geology
• /
• v.46 no.2
• /
• pp.141-151
• /
• 2013

This study examines the mineralogy of sepiolites occurred within the carbonaceous rocks of Songak schist and Pyeongtaek migmatitic gneiss of Precambrian Seosan group, in the western part of Chungnam. Host rocks of the sepiolite were dolomitic rocks and have experienced hydrothermal alteration and metamorphism. Mesozoic granite is assumed as a main source of hydrothermal alteration for the dolomitic rocks. Some of the tremolite asbestos coexist with the sepiolites. Representative sepiolite and tremolite samples were collected from the layers cracks or fractures of the dolomitic rocks and/or examined with microscope with microscope, XRD, SEM and TEM. Sepiolites are mainly recognized along the cracks assumed as pathways of hydrothermal solution. Tremolites are mainly found at layers or cracks of the dolomitic rocks and occur as asbestos as well as non-asbestos forms. It was confirmed that some of the tremolite asbestos were coexisted with the sepiolites. Overall results suggest that the occurrences of sepiolites within the dolomitic rocks mainly result in the hydrothermal alteration and the fluid from the acidic rocks, possibly granites. It also suggests that coexisting tremolite asbestos were formed by similar geological environment.

• The Korean Journal of Petroleum Geology
• /
• v.14 no.1
• /
• pp.12-20
• /
• 2008

Oil sands in Canada are representative example of unconventional resources whose reserve estimates are as large as those in Saudi Arabia. Typical reservoir rocks of oil sands consist of channel-related deposits formed in a tide-dominated depositional setting. The tidal deposits are commonly characterized by spatially complicated and heterogeneous properties. Successful engineering methods to develop oil sands require in-depth understanding in the spatial distribution of reservoir properties. Geological model for oil sand reservoir characterization can be built on the basis of comparative studies of ancient and modem analogues. In particular, modern analogue studies become increasingly indispensable, since they provide better understanding in the reservoir-rock forming process and more importantly in the external mechanism responsible for the reservoir heterogeneity. Tide-dominated environment along the west coast of Korea is considered as one of the most excellent modem analogues of oil-sand forming depositional environment. Korean tidal environment provides insights on the origin of mud breccia, facies and stratigraphic architecture which are key issues to the characterization of oil sand reservoirs.

• Korean Journal of Heritage: History & Science
• /
• v.44 no.1
• /
• pp.4-29
• /
• 2011

Paleoenvironments of the shell deposit-bearing sequence in the Hasandong Formation at Daesong-ri area, Hadong-gun, Korea, are interpreted on the basis of sedimentary facies and taphonomy of the shell deposits, with a discussion of their stratigraphic implications. A shell deposit-bearing sequence without reddish beds is mostly grayish, and the bedding is laterally extensive. These deposits are interpreted to have been formed in sandflats, mudflats, and shallow lakes generated by flooding on an alluvial plain. The shell deposits are classified into three types according to the occurrence, and the concentration of a single species of Brotiopsis wakinoensis in the shell deposits is deemed to have been attributed to the exclusive inhabitation of the genus Brotiopsis. Type 1 and 2 shell deposits are interpreted to have been fossilized in sandflats and mudflats after death in their habitat of shallow lakes and subsequent transformation by sheetflooding and lake flooding. Type 3 shell deposits are interpreted to have been fossilized in their habitat of shallow lakes during a stabilized period of lake development. The development of the shell deposit-bearing lacustrine sequence in a few tens of meters in thickness in the Hasandong Formation of fluvial deposits is compared to the shift of depositional environments from the Hasandong Formation (fluvial deposits) through the Jinju Formation (lacustrine deposits) to the Chilgok Formation (alluvial plain deposits), which suggests that additional lithostratigraphic classification is needed in the Hasandong Formation. The shell deposits at the study area can provide valuable data to understanding the paleoenvironments during the Early Cretaceous Period of Korea, and should give basic data to evaluate the value of the Cretaceous mollusc deposits in Korea as a geological heritage.

• Economic and Environmental Geology
• /
• v.48 no.6
• /
• pp.431-449
• /
• 2015

The study area is located in the western part of the Precambrian stock type of Sancheong anorthosite complex, the Jirisan province of the Yeongnam massif, in the southern part of the Korean Peninsula. We perform a detailed field geological investigation on the Sancheong anorthosite complex, and report the characteristics of lithofacies, occurrences, foliations, and research formation process and its mechanism of the Sancheong anorthosite complex. The Sancheong anorthosite complex is classified into massive and foliation types of Sancheong anorthosite (SA), Fe-Ti ore body (FTO), and mafic granulite (MG). Foliations are developed in the Sancheong anorthosite complex except the massif type of SA. The foliation type of SA, FTO, MG foliations are magmatic foliations which were formed in a not fully congealed state of SA from a result of the flow of FTO and MG melts and the kinematic interaction of SA blocks, and were continuously produced in the comagmatic differentiation. The Sancheong anorthosite complex is formed as the following sequence: the massive type of SA (a primary fractional crystallization of parental magmas under high pressure)${\rightarrow}$ the foliation type of SA [a secondary fractional crystallization of the plagioclase-rich crystal mushes (anorthositic magmas) primarily differentiated from parental magmas under low pressure]${\rightarrow}$the FTO (an injection by filter pressing of the residual mafic magmas in the last differentiation stage of anorthositic magmas into the not fully congealed SA)${\rightarrow}$the MG (a solidification of the finally residual mafic magmas). It indicates that the massive and foliation types of SA, the FTO, and the MG were not formed from the intrusion and differentiation of magmas which were different from each other in genesis and age but from the multiple fractionation and polybaric crystallization of the coeval and cogenetic magma.

• Economic and Environmental Geology
• /
• v.52 no.5
• /
• pp.381-393
• /
• 2019

Carbonate breccias occur sporadically in the Middle Cambrian Daegi Formation on the southern limb of the Baegunsan Syncline, Taebaeksan Basin. These carbonate breccias have been largely interpreted either as sedimentary breccias or as tectonic, fault-related breccias. Recent study, however, indicates that the majority of these breccias are a solution-collapse breccia which is causally linked to the paleokarstification. Extensive karstification is attributed to prolonged subaerial exposure of the carbonate platform. The exposed surface is a record of interruption in sedimentation on the carbonate platform. In the stratigraphic record, such karst-related post-depositional features are recognized as meteoric diagenetic features, paleosols, and solution-collapse breccias. Solution-collapse breccias are particularly well preserved and most profound in the carbonate rocks below the major unconformities, which also are evidence of prolonged subaerial exposure. The Middle Cambrian Daegi Formation provides an example of solution-collapse breccias. The formation and preservation of the solution-collapse breccias imply that a stratigraphic discontinuity surface (unconformity) can be designated within the Daegi Formation.

• Economic and Environmental Geology
• /
• v.31 no.6
• /
• pp.463-472
• /
• 1998

The survey was carried out in order to delineate the occurrence of ore deposits and the mineralized characteristics in the Estancia de la Virgen area through the 1:2,000 scaled geological mapping and topographic measuring surveys. Gold-silver mineralization is in the fault block developed between the San Agustin Fault and Cabanas Fault. It is associated with ore bearing quartz veins controlled by the fault structure. The contents of Au and Ag range from traces up to 72 g/t and 180 g/t respectively. According to traversing the outcrops, the quartz veins are traced by 0.5 Km trended to north and south. In those extended part, they continue for 1,000 m intermittently. Gold-silver mineralization could be divided into three stages. In the first stage, pyrite, galena, sphalerite, and chalcopyrite were formed with the primary silver and gold associated with galena and copper sulfides respectively. In the second stage, Cu-Bi-Au-Ag bearing sulfides such as chalcocite, covellite, and linarite are formed and usually deposited on the cataclastic fractures of galena and/or chalcopyrite. In the third stage, both the carbonation of galena and sphalerite and the sulphatization of galena, took place in the surface environment. And then primary silver was carried away off and was deposited on galena and/or copper sulfides during oxidation near the water table. Low partitionings of Fe in sphalerite assist that the minerals were formed at the relatively low temperature, which is coincided with previously reported homogenization temperature of fluid inclusions.

• Economic and Environmental Geology
• /
• v.52 no.6
• /
• pp.519-528
• /
• 2019

In 2017, Korea Institute of Geoscience and Mineral Resources (KIGAM) has excavated a trench at Yongjang-li in the city of Gyeongju to examine the evidence of fault movement related with the 2016 earthquake in unconsolidated sediments. In the trench profile, the author has observed the features of ongoing soil-forming processes and groundwater movement overlapped on the sedimentary layers. The soil formation was in its initial stage, and most of the original sedimentary layers could be observed. The color changes depending on the redox conditions and by the Mn/Fe oxide precipitation, however, were the most significant features obscuring sedimentary records. The dark Mn oxide precipitates formed at the groundwater levels often concealed the sedimentary unit boundaries. The groundwater levels varied depending on the particle sizes of the sedimentary layers contacting the groundwater, and the Mn oxide precipitates have formed at varying depths. The groundwater could move upward along the narrow pores in the fine-textured sedimentary layer more than a few meters showing the gray color indicating a reducing condition for iron.

• Economic and Environmental Geology
• /
• v.47 no.5
• /
• pp.489-496
• /
• 2014

The occurrence and mineralogical characteristics of asbestos in dolostone at Ungdo, Seosan were investigated by analyses of PLM, XRD, and SEM/EDS. Representative outcrops of dolostone at Ungdo were examined and four dolostone samples were collected according the occurrence type to identify the shape of asbestos in dolostone samples. The host rock of dolostone had been produced from the hydrothermal alteration and/or thermal metamorphism of which main source was assumed as the acidic granite. Tremolites were observed near the cracks or fractures of the dolostone as tamping or gob types. From the mineralogical analyses, main minerals of dolostone were dolomite with calcite, quartz, talc, amphibole, and pyroxene. From SEM/EDS analyses, tremolite-actinolite asbestoses were observed in dolostone and their shapes were prismatic and fibrous (less than $1{\mu}m$ in width). Non-asbestos prismatic forms were also found and they would transfer to asbestos particles resulting from the cleavage and fracture of the prismatic particles. Overall results suggest that asbestoses in Ungdo dolosotnes were mainly tremolite-actinolite and they were originated from the hydrothermal alteration of Ca-Mg rich dolostone.

• Korean journal of applied entomology
• /
• v.55 no.2
• /
• pp.129-138
• /
• 2016

Eicosanoids are a group of C20 oxygenated polyunsaturated fatty acids (PUFAs). To monitor biosynthetic precursors of these PUFAs, this study extracted fatty acids from different tissues of the beet armyworm, Spodoptera exigua, and assessed their compositions using GC/MS. Fifth instar larvae were dissected to isolate different tissues of gut, fat body, hemocytes, and integument. From each tissue, total lipids were extracted and fractionated into neutral lipid (NL), glycolipid (GL), and phospholipid (PL). Most tissues contained palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2), and linolenic acid (18:3). However, their compositions were different among tissues and lipid types. Fat body and hemocytes possessed other type of fatty acids such as myristic acid (14:0) and three unknown fatty acids. Among lipid types, PL contained relatively high levels of linolenic acid than NL and GL, while it had lower saturated fatty acids. Total unsaturated fatty acid composition was varied among tissues and lipid types. PL was rich in unsaturated fatty acids in fat body, gut, and hemocytes. There was a significant influence of calcium-independent phospholipase $A_2$ ($iPLA_2$) on maintaining fatty acid composition because RNA interference of $iPLA_2$ expression significantly modified fatty acid compositions in NL and PL. However, this study did not detect arachidonic acid, a main eicosanoid biosynthesis precursor, in all tissues. This suggests an alternative biosynthesis of eicosanoids in insects, which is distinct from the biosynthetic pathway of mammals.

• Geophysics and Geophysical Exploration
• /
• v.10 no.4
• /
• pp.393-398
• /
• 2007

Seismic traveltime tomography technique was conducted at a site composed of black shale. It is well known that black shale has strong anisotropic property. Therefore, the anisotropic property of black shale has to be considered to obtain the appropriate subsurface velocity model by an inversion process. To estimate the anisotropic constant of the velocity of the black shale in the survey area, the relation between the velocity, which is calculated by the straight ray path and the first arrival time, and the angle of the ray propagation was examined. The elliptically shaped relation was found and it reveals that the black shale contains the anisotropic property of velocity. It was also noticed that the horizontal velocity is faster than the vertical velocity. When the estimated anisotropic constant was applied in the process of the velocity inversion for three sets of field data, we could obtain the appropriate velocity structures of the site that is consistent with the result of the geological survey.