The Kyonggi Shear Zone of the Central Korean Peninsula: Late Orogenic Imprint of the North and South China Collision     

Kim J  Ree J  Kwon S  Park Y  Choi S  Cheong C 《The Journal of geology》2000,108(4):469-478

The crustal-scale Kyonggi shear zone of central Korea has been identified as a major boundary between the Precambrian Kyonggi massif in the south and the Imjingang belt in the north. The latter is an eastward extension of the Qinling-Dabie-Sulu collisional belt of China. Field observations and microstructural analysis indicate that the extensional shear zone evolved from a deep crustal ductile regime to a shallow crustal brittle regime, associated with a rapid uplift of the Kyonggi massif following the Late Permian-Early Triassic collision between the Sino-Korean and Yangtze cratons. A Rb-Sr muscovite age (226+/-1.2 Ma) of the mylonite suggests that the extensional ductile shearing occurred during the Late Triassic.  相似文献   

Effects of atmospheric circulation and boundary layer structure on the dispersion of suspended particulates in the Seoul metropolitan area     

H. Choi  M. S. Speer 《Meteorology and Atmospheric Physics》2006,92(3-4):239-254

Summary A three-dimensional non-hydrostatic numerical model and lagrangian particle model (random walk model) were used to investigate the effects of the atmospheric circulation and boundary layer structure on the dispersion of suspended particulates in the Seoul metropolitan area. Initially, emitted particulate matter rises from the surface of the city towards the top of the convective boundary layer (CBL), owing to daytime thermal heating of the surface and the combined effect of an onshore wind with a westerly synoptic-scale wind. A reinforcing sea-valley breeze directed from the coast toward the city of Seoul, which is enclosed in a basin and bordered by mountains to its east, disperses the suspended particulate matter toward the eastern mountains. Total suspended particulate concentration (TSP) at ground level in the city is very low and relatively high in the mountains. Radiative cooling of the surface produces a shallow nocturnal surface inversion layer (NSIL) and the suspended particulate matter still present near the top of the CBL from the previous day, sinks to the surface. An easterly downslope mountain wind is directed into the metropolitan area, transporting particulate matter towards the city, thereby recycling the pollutants. The particulates descending from the top of the NSIL and mountains, combine with particulates emitted near the surface over the city at night, and under the shallow NSIL spread out, resulting in a maximum ground level concentration of TSP in the metropolitan area at 2300 LST. As those particles move toward the Yellow Sea through the topographically shaped outlet west of Seoul city under the influence of the easterly land breeze, the maximum TSP concentration occurs at the coastal site. During the following morning, onshore winds resulting from a combined synoptic-scale westerly wind and westerly sea breeze, force particulates dispersed the previous night to move over the adjacent sea and back over the inland metropolitan area. The recycled particulates combine with the particulates emitted from the surface in the central part of the metropolitan area, producing a high TSP and again rise towards the top of the CBL ready to repeat the cycle.  相似文献   

Freeze thaw cycles in Toronto, Canada in a changing climate     

E. Ho  W. A. Gough 《Theoretical and Applied Climatology》2006,83(1-4):203-210

Summary Freeze thaw cycles are examined in Toronto Canada. Using data from 1960 to 1989 for three Toronto area weather stations, trends in freeze thaw activity, the relationship to mean monthly temperature and projections of freeze thaw activity are examined. For downtown Toronto the annual frequency of freeze thaw cycles is decreasing significantly, most notably in the shoulder months of October and April. At the Pearson International Airport and the Toronto Island Airport similar annual trends were not found, however there was evidence of decreased freeze thaw activity in April and October. Polynomial curve fitting provided functional relationships between mean monthly temperature and freeze thaw activity. These relationships enabled the assessment of freeze thaw activity under synthetic warming conditions. The results of this analysis show that the warming of the magnitude typically projected for the rest of this century will not likely generate a significant change in the freeze thaw activity although there are indications that the freeze thaw season will contract.  相似文献   

Dating of lower terrace sediments from the Middle Rhine area, Germany     

Sung-Won Choi  Frank Preusser  Ulrich Radtke 《Quaternary Geochronology》2007,2(1-4):137-142

Modern and known-age Pleistocene fluvial sediments were investigated by optical dating of quartz to test the suitability of the approach for dating deposits from the deeply incised Middle Rhine Valley. Samples from modern flood sediments revealed skewed distributions indicating different residual levels of equivalent dose (D_e) within the different aliquots. Nevertheless, a substantial number of aliquots from the modern deposits reflect D_e values close to zero. For the Pleistocene samples, optical ages are in general consistent with age control given by the presence of the Laacher See Tephra and radiocarbon dating. However, some samples overestimate the known age by a few thousand years when using the arithmetic mean. This is apparently explained by including aliquots in the determination of mean D_e where the optical signal was incompletely bleached at deposition. The most difficult issue in this context is identifying a suitable approach that can distinguish between the variability of D_e due to partial bleaching and microdosimetry. However, even when considering these limitations it appears that optical dating will by a quite suitable method to date Pleistocene sediments from such a complex fluvial environment, especially when focusing on a precision scale beyond a few thousand years.  相似文献   

The effect of weathering on optically stimulated luminescence dating   总被引：2，自引：0，他引：2  

Gi Young Jeong  Chang-Sik Cheong  Jeong-Heon Choi 《Quaternary Geochronology》2007,2(1-4):117-122

Optically stimulated luminescence (OSL) dating was applied to quartz samples recovered from the gravel sediments of deformed marine terrace at the Suryum site, southeastern Korea, but has yielded stratigraphically inconsistent ages. Micromorphological, chemical, and mineralogical analyses of the gravels indicate the possible influence of chemical weathering on the apparent OSL ages. In the course of weathering after emerging from beach environments, originally permeable gravels underwent infilling by halloysite-rich clays in their voids, export and import of radioactive elements, and loss of mechanical strength with the creation of a porosity within pebbles. Calculation based on the evolution of the weathering profile showed a severe fluctuation of dose rate caused by the change of water content and radioactive element concentrations. Samples recovered from the weathering profile inevitably include quartz grains derived from mechanically weakened pebbles or illuviated from the upper layer, making it difficult to determine the equivalent dose (D_e) values of exclusively depositional quartz sands. Quantitative evaluation of the change of fabric and chemistry of the sediments on the basis of pedologic insight significantly aids in the derivation of OSL ages consistent with geomorphology and other independent age controls.  相似文献   

Characteristics of tephra in Holocene lake sediments on King George Island, West Antarctica: implications for deglaciation and paleoenvironment     

Yong Il Lee  Hyoun Soo Lim  Ho Il Yoon  Andrzej Tatur 《Quaternary Science Reviews》2007,26(25-28):3167-3178

Several reworked tephra layers in gravity-flow deposits are present in lacustrine core sediments collected from Hotel and Rudy Lakes on King George Island, South Shetland Islands, maritime sub-Antarctica. This study tests the values of tephra for establishing regional tephrochronologies for lakes in ice-covered landscapes in the vicinity of volcanoes. The tephra record is more abundant in a long Hotel Lake core (515 cm long). This study uses volcanic glass samples from five tephra layers of Hotel Lake and from one tephra layer of Rudy Lake. Morphologically, tephras are mixtures of basaltic and pumice shards, both having various degrees of vesicularity. Major element analyses of glass shards reveal that the majority of the glass fragments belong to basic glass (<60 wt% SiO₂), compositionally ranging from basalt to low-silica andesite and subalkaline series medium-K tholeiites, probably sourced from Deception Island located 130 km southwest of King George Island. Less than 20% of tephra belongs to silicic glass and occurs in three tephra horizons E of Hotel Lake. However, source volcano(es) for about 10% of basic tephra and silicic tephra are not readily identified from nearby volcanic centers. Except for the studied tephra in Rudy Lake, all tephra samples in Hotel Lake are not ashfall deposits but reworked and redeposited pyroclasts derived from retreating ice sheet, resulting in the occurrence of geochemically equivalent tephra samples in different tephra horizons. The dating of the studied tephra horizons represents the timing of deglaciation rather than that of volcanic eruptions. The result of this study implies that combined with sedimentological information more chemical criterion is necessary to study tephrochronology and regional correlation and to understand paleoenvironmental changes using tephra.  相似文献   

Impact of adsorbed petroleum hydrocarbons on marine organisms     

C.L. Ho  H. Karim 《Marine pollution bulletin》1978,9(6):156-162

Adsorptions of south Louisiana crude oil from seawater by clays, non-clay minerals and sediments were conducted in the laboratory. Effect of sediment-adsorbed and water dispersed crude oil on adult oysters were investigated in aquaria. Hydrocarbons in oyster tissues and surrounding water were identified by gas chromatography. Field specimens from an area of a new oil spill and an area five months after an oil spill were also analysed. Evidence of secondary chemical effect of aged oil in sediments on oyster mortality is presented. Oil coated asbestos surfaces severely reduced recruitment of sedentary larval organisms.  相似文献   

Madagascar     

Ming-Hung Wong  Kin-Chung Ho  Tim-Tak Kwok 《Marine pollution bulletin》1980,11(2):36-40

Untreated domestic and industrial wastes are discharged into Tolo Harbour via several major streams entering the harbour. These untreated wastes will cause a harmful effect because Tolo Harbour is a land-locked sea with only a narrow outlet and an ever-decreasing volume caused by the construction of Plover Cove Reservoir and the reclamation of Shatin New Town. In order to study the effect of polluted water discharged into the harbour, water samples and sediments near the mouths of the major rivers were collected. The analysis of the total organic carbon, total nitrogen, and water soluble phosphate contents of the samples showed that Lam Tsuen River, Tai Po Kau River, and Shing Mon River were grossly polluted by organic and inorganic wastes. Blue Snake River which passes through the iron ore tailings accumulated high contents of metal contaminants.  相似文献   

贵州中三叠世生物礁   总被引：13，自引：0，他引：13       下载免费PDF全文

贺自爱  杨宏  周经才 《地质科学》1980,15(3):256-264

贵州中三叠世生物礁,早在六十年代中期,殷鸿福、杨遵仪就已提出线索。作者在六十年代初研究贵州三叠纪地层时,已对三叠系相变带的特征和规模,以及板庚碳酸盐岩体有了初步认识。七十年代初,作者又到花江进行调查,发现一套壮观的藻礁灰岩。  相似文献   

Importance of no‐rain measurements on the comparison of radar and rain gauge rain rate     

Chulsang Yoo  Kyoungjun Kim  Jeongho Choi  Eunho Ha 《水文研究》2010,24(7):924-933

This study evaluated four possible cases of comparing radar and rain gauge rain rate for the detection of mean‐field bias. These four cases, or detection designs, consider in this study are: (1) design 1‐uses all the data sets available, including zero radar rain rate and zero rain gauge rain rate, (2) design 2—uses the data sets of positive radar rain rate and zero or positive rain gauge rain rate, (3) design 3—uses the data sets of zero or positive radar rain rate and positive rain gauge rain rate and (4) design 4—uses the data sets of positive radar rain rate and positive rain gauge rain rate. A theoretical review of these four detection designs showed that only the design 1 causes no design bias, but designs 2, 3 and 4 can cause positive, negative and negative design biases, respectively. This theoretical result was also verified by applying these four designs to the rain rate field generated by a multi‐dimensional rain rate model, as well as to that of the Mt Gwanak radar in Korea. The results from both applications showed that especially the design 4, which is generally used for the detection of mean‐field bias of radar rain rate, causes a serious design bias; therefore, is inappropriate as a design for detecting the mean‐field bias of radar rain rate. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献