Geosciences Journal

Lim, Seonmi; Cheong, Daekyo

doi: 10.1007/s12303-022-0005-2pmid: N/A

Previous studies about tectonic events in the Ulleung Basin have been performed using diverse methods, but the deformation history of the Ulleung Basin is still controversial. In the Ulleung Basin, the Dolgorae and Gorae I structures were formed by basin deformation I (northwest-southeast compression) and the Gorae V structure was formed by basin deformation II (east-west compression). Since the quality of seismic data of the Dolgorae structures is not good, it is more difficult to reveal the basin deformation history through structural analysis of the seismic data. Thus, we traced the change in paleo-shelf breaks and studied provenance using image logs as indirect tectonic evidence and analyzed the growth strata of the Dolgorae and Gorae structures using seismic data for analyzing basin deformation. The shape of the paleo-shelf break has changed from linear to curved shape since 12.5 Ma, and the progradation rate of the paleo-shelf break was the fastest during 10.6–12.5 Ma. Before 12.5 Ma, sediments were supplied in the southwest direction, but after 12.5 Ma, they were supplied in the southeast direction originated from uplifted Dolgorae thrust fault zone. This evidence imply that basin deformation occurred in 12.5 Ma. During basin deformation I, the Gorae I structure was formed later than the Dolgorae structures due to the propagation of compression, and during basin deformation II, the Gorae V structure was formed from 5.33 Ma based on analysis of growth strata.

Rhee, Hyun Hee; Seong, Yeong Bae; Lee, Min Kyung; Jeong, Ara; Dash, Chinmay; Lee, Jae Il; Yoo, Kyu-Cheul; Yu, Byung Yong

doi: 10.1007/s12303-022-0003-4pmid: N/A

This study documents spatial variations in authigenic 9Be and 10Be concentrations and 10Be/9Be ratios in different glacial settings in the Weddell and Ross seas, Antarctica. Weddell Sea surface sediments have the lowest 10Be and highest 9Be concentrations, and most depleted 10Be/9Be ratios, as compared with other regions, indicating 9Be enrichment from the recently collapsed Larsen Ice Shelf (LIS) B and reduction of 10Be supply due to blockage by the un-deglaciated LIS C. Local 10Be deposition varies across the open marine Ross Sea, which is more affected by seasonal sea ice persistence than ocean currents. Higher 10Be/9Be ratios in the western Ross Sea and higher 10Be concentrations in the eastern Ross Sea correlate with higher sea ice concentrations and changes, and vice versa in the central Ross Sea. The higher sea ice concentration not only blocks atmospheric 10Be and dust deposition during the frozen season, but increases the dust flux and supply of Be isotopes during the sea ice melting season. Thus, the spatial distribution of Be isotopes in surface sediments of the Antarctic oceans can be used as a proxy for sea ice dynamics and sedimentary environments.

Lee, Jungchul; Yoo, Yongwook

doi: 10.1007/s12303-021-0045-zpmid: N/A

This article introduces palaeolithic assemblages from the South Han River Area (SHRA) of South Korea and examines their ages in the geoarchaeological context. This task will be a starting point to discuss major factors responsible for the relatively late predominance of seemingly simple-and-crude Mode 1 toolkits in East Asia. Eight palaeolithic sites of the SHRA are covered and formation processes of their assemblages are examined based on geological features and published chronometric dates as well as additional proxy data. The ages of SHRA assemblages are roughly Late Pleistocene from MIS 5c to MIS 2. The lithic type variability of the SHRA is of typical Mode 1 technology which is principally composed of pebble-tools and minimally modified flakes. The issue of such a simple technology flourished in a limited area of East Asia during a quite late temporal range is discussed. A hypothetical explanation is that stone tools in the SHRA served as complementary items for making perishable primary living items out of organic materials and that local hominins were not obliged to be sedulous on such subsidiary items as stone tools. As a result, the nature of the SHRA assemblage looks apparently unlabored and expedient; this nature of lithic technology tends to be timeless and even survive anywhere anytime in East Asia, which can be recognized as retarded and not advanced.

Kim, Seok-Jin; Choi, Jeong-Heon; Lim, Hyoun Soo; Shin, Seungwon; Yeo, Eun-Young; Weon, Hyo-Jeong; Heo, Seoyoung

doi: 10.1007/s12303-022-0002-5pmid: N/A

In the last few years, substantial amount of archaeological remains, which belong to the Bronze and the Iron Ages, has been excavated in Jungdo, central part of Korean peninsula, indicating that the prehistoric (partly, early historic) cultures had been flourished in this area. Particularly, more than 150 dolmens were found during the excavation campaign, and they have drawn keen attentions because dolmens are controversially regarded as being the representative remains for the Bronze Age in Korean peninsula. Despite their archaeological importance for understanding the ancient cultural and social aspects in Korean peninsula, the chronology of the dolmens has largely been dependent upon sensory tests using concomitant artifacts while numerical dating has been scarce and limited to the case when organic materials for radiocarbon dating were available. Recent advances in luminescence dating, however, allow direct dating of stone structures, like dolmens, by measuring OSL (Optically Stimulated Luminescence) signals in phosphor minerals underneath the stone structures. In this paper, we performed OSL dating of quartz collected from underneath the stones making up dolmens in Jungdo. For OSL dating, we chose three dolmens and six sediment samples were collected from them. Using multiple grain aliquots, consisting of ∼300 quartz grains, the OSL ages of ∼4.3–3.2 ka were obtained. These ages, however, appear to be older than previously reported radiocarbon ages in Jungdo and a radiocarbon age (2119–1750 cal yr BP) of a human bone sample excavated from one of the dolmens. On the contrary, single grain OSL dating yielded MAM-3 (Minimum Age Model with three parameters) ages consistent with the radiocarbon age, ranging ∼2.9–2.2 ka. Our results suggest that Jungdo has been the place either for burial plots or habitation of the ancient humans up to early Iron Age in the central part of Korean peninsula.

Jung, Yunsun; Woo, Jeong-Ung; Rhie, Junkee

doi: 10.1007/s12303-021-0043-1pmid: N/A

As a fundamental task in observational seismology, accurate hypocenter determination is crucial for seismic hazard analysis, delineating faults, and elucidating seismic source characteristics. However, hypocenters determined using an inaccurate velocity model can exhibit significant deviations from the actual hypocenter. In this study, we investigated how a 3-D velocity model results in a better constraint than a 1-D model for the hypocenter determination problem associated with the 2017 MW 5.5 Pohang earthquake. This study determined the hypocenter of the Pohang earthquake sequence using a 3-D velocity model of 32 events including the mainshock that occurred on November {vn15}, 2017, in South Korea. The S wave velocity model, based on an ambient noise tomography, was combined with the average Vp/Vs ratio of the crust of the Korean Peninsula to construct a 3-D velocity model; additional 1-D velocity model was used to compare the results. The hypocenters were determined via a nonlinear method, which allowed the calculation of the posterior probability density of the source via a direct search method, confirming that the accuracy improved when using the 3-D model compared with the 1-D model. We observed that our 3-D velocity model enables hypocenters to be consistently determined, less affected by station configuration, or a lack of adjacent seismic stations. Further numerical investigation showed that complex basin geometry and the heterogeneity of the crustal thickness, which cannot be considered in 1-D model, are critical for hypocenter determination.

Kim, Gyoo-Bum; Son, Young-Chul; Hwang, Chan-Ik

doi: 10.1007/s12303-021-0044-0pmid: N/A

South Koreas National Groundwater Monitoring Network (NGMN) was installed during the early 1990s to detect the trends in groundwater levels; however, a revised NGMN plan is required in consideration of climate change and human activities. Linear trend analyses of the groundwater levels, Cl concentration, and NO3-N concentration of 521 monitoring wells were conducted to define the downward and upward trends. The attributes of 14 items relating to topography, stream proximity, land use, soil, hydrogeology, and well density were extracted from thematic maps for each monitoring site. An artificial neural network (ANN) model for groundwater level trends was developed using these 14 input variables to predict the downward (output variable: 1) and non-downward (output variable: 0) trends at any grid point in a standard watershed. Candidate sites for new groundwater monitoring wells were suggested based on the probability of the existence of two trends for groundwater levels. Candidate sites were excluded if they showed upward trends of Cl and NO3-N because the primary objective of the NGMN was not to observe changes in water quality but to observe the background conditions of water quality. It was proposed to install a total of 1475 groundwater monitoring wells (existing plus new wells) by 2045, and the percentage contributions of non-downward and downward trends of groundwater levels to the total number of trends (i.e., wells) were projected to be 61.5% and 38.5%, respectively. The NGMN will play an important role in recognizing climate change, observing groundwater level declines caused by human activities, and assessing the relationship between surface water and groundwater in standard watersheds.

Wang, Dejian; Qian, Jiazhong; Zhao, Weidong; Hou, Xiaoliang; Wang, Wei; Ma, Lei

doi: 10.1007/s12303-022-0004-3pmid: N/A

To disclose the distribution characteristics, the situation of flow and storage, and processes along flow paths of shallow groundwater in Tan-Lu fault zones, nine hundred and seven groundwater table elevations data and one hundred hydrochemical samples of shallow groundwater were taken from the Tan-Lu fault zone in Anhui province to analyze the characteristic of groundwater distribution. The geographic information system (GIS) method was used to analyze the spatial distribution characteristics of groundwater tables, total dissolved solids (TDS) and chloride ion (Cl−). Geophysical prospecting, drilling material and regional hydrogeological survey were utilized to disclose groundwater storage and flow regime in the fault zone. The results show that the Tan-Lu fault zone in Anhui province has controlled groundwater flow into the Jiashan basin, Hefei basin, Chaohu area and Qianshan basin, which developed from north to south in this area. Groundwater in theses basins have recharged from surrounding areas to form a water storage space. Geophysical prospecting and drilling technology revealed that the Tan-Lu fault zone provided a flow channel and storage space for ground-water. Faults provide preferential channels in some areas for the groundwater flow and circulation, eventually deep hot-water flows upward and discharges in the form of hot-springs. The identification of the groundwater flow pathway can help to provide a reliable scientific basis for regional spatial development and utilization of groundwater resources.