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Magnitude of global contraction on Mars from analysis of surface faults: Implications for martian thermal history 总被引：1，自引：0，他引：1
Faults provide a record of a planet’s crustal stress state and interior dynamics, including volumetric changes related to long-term cooling. Previous work has suggested that Mars experienced a pulse of large-scale global contraction during Hesperian time. Here we evaluate the evidence for martian global contraction using a recent compilation of thrust faults. Fault-related strains were calculated for wrinkle ridges and lobate scarps to provide lower and upper bounds, respectively, on the magnitude of global contraction from contractional structures observed on the surface of Mars. During the hypothesized pulse of global contraction, contractional strain of −0.007% to −0.13% is indicated by the structures, corresponding to decreases in planetary radius of 112 m to 2.24 km, respectively. By contrast, consideration of all recognized thrust faults regardless of age produces a globally averaged contractional strain of −0.011% to −0.22%, corresponding to a radius decrease of 188 m to 3.77 km since the Early Noachian. The amount of global contraction predicted by thermal models is larger than what is recorded by the faults at the surface, paralleling similar studies for Mercury and the Moon, which suggests that observations of fault populations at the surface may provide tighter bounds on planetary thermal evolution than models alone. 相似文献
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Wook-Hyun Nahm Gyoo Ho Lee Dong-Yoon Yang Ju-Yong Kim Kenji Kashiwaya Masayoshi Yamamoto Aya Sakaguchi 《Journal of Paleolimnology》2010,43(3):489-498
This paper describes mean grain-size data from the 137Cs- and 210Pb-dated sediment core BS-3 (33-cm long) recovered from Jinheung Pond, located in the southwestern part of the Korean Peninsula.
Grain-size analysis of the Jinheung Pond sediments shows a clear signal for changes in annual precipitation over the past
60 years. Instrumental records of annual precipitation (AP) and the annual summation of the precipitation of >50 mm per day
(AP50), which reflects the energy available for sediment transport, correlate well with the mean grain-size distributions
measured in the core. The most plausible mechanism for this response in mean grain size is variations in the annual amount
and intensity of precipitation. Heavy precipitation enhances soil erosion over the catchment area and increases the transport
capacity of streams and rivers. Thus, coarser mean grain size should reflect higher precipitation, and smaller mean grain
size should reflect lower rainfall. In the data from core BS-3, however, grain-size peaks attributed to increased annual precipitation
are not prominent. This is because a dam prevents removal of fine particles from the pond via the outflow. Therefore, the
mean grain-size value represents somewhat larger sediments together with fine clays. The results of this study show that sediments
of dammed lakes and ponds are well suited for high-resolution environmental investigations, especially for records of changes
in precipitation over time. 相似文献
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Accumulation of heavy metals in the lacustrine sediment of Longgan Lake, middle reaches of Yangtze River, China 总被引：1，自引：0，他引：1
Haijian Bing Yanhong Wu Wook-Hyun Nahm Enfeng Liu 《Environmental Earth Sciences》2013,69(8):2679-2689
Spatial and temporal distribution of heavy metals (Chromium, Copper, Nickel, Lead, and Zinc) in the sediment of Longgan Lake, middle reaches of Yangtze River, China were analyzed to discuss their enrichment characteristics and history in combination with geochronological data and to identify anthropogenic effects. The results showed that the enrichment state of heavy metals was higher in the western versus eastern lake area, although their concentrations behave in the opposite case, which demonstrated that stronger human activities existed in the western lake catchment. The enrichment history of heavy metals pointed out that prior to 1950, the enrichment state was lower in the ambient lake areas illustrating the natural effect on the lake; thereafter the human activities in the catchment enhanced markedly causing an increasing heavy metal enrichment. The increase of heavy metal enrichment in the 1970s occurred in the central lake areas. The temporal difference between the ambient and central areas elucidated that the heavy metal accumulation might be buffered by the lake before they entered the sediment. Correlation analysis revealed that there was a significant correlation between heavy metals in the sediment suggesting their similar sources. Heavy metals were distinctly related to aluminum, calcium, lithium, iron, and organic matters, which could denote their forms in the sediment. 相似文献
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Kee-Bom Nahm 《GeoJournal》1999,49(3):289-299
In recent years, central Seoul has been experiencing a dynamic transformation. In the process of reorganization of the urban
industrial structure including tertiarization and quaternarization of the economic base of Seoul, business services are growing
very rapidly and large scale urban renewal projects are quickly implemented. Downtown office activities become a nucleus for
economic performance of Seoul and high-rise office buildings steer the landscape transformation of central Seoul. Even though
there appears to exist some evidence that office districts have dispersed to several subcenters, major office activities are
still concentrated in central Seoul. This paper redefines office industry in a narrow sense comprising only relevant economic
sectors and office buildings as office activity-functioning units. It then explores the industrial networking and territorial
specialization of office activities focusing on the dual process of concentration and dispersion in Seoul. The changing characteristics
of the downtown linkages of office activities in this post-industrial era transforms the spatial economy of central Seoul
into a more flexible and volatile system, while territorial concentration of power and control functions are fortified at
the same time. Finally, the paper addresses the development of manufacturing- tertiary-quaternary industrial complexes, which
can be regarded as emerging industrial clusters, producing the cultural economy of urban space and images for clients and
customers, in relation to urban competitiveness and territorial specialization of large metropolitan areas.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Holocene salinity fluctuations of the East Korean lagoon related to sea level and precipitation changes 
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下载免费PDF全文 Detailed diatom records within core sediments from Maeho Lagoon along the Eastern coast of South Korea revealed that the ecological dynamics of the lagoon during the Holocene were associated with relative sea level and regional precipitation. Accelerator mass spectrometry (AMS) 14C dating indicates that sediment accumulation began prior to 8300 cal. year BP, and that the lagoon formed around 8000 cal. year BP. The salinity level of the lagoon increased until 5000 cal. year BP, and then decreased. Long‐term trends in salinity were dependent upon changes in sea level: periods of high salinity in the lagoon were generally coincident with periods of high sea levels along the east coasts of Korea and Japan. On the other hand, multicentennial‐scale fluctuations in diatom assemblages and magnetic susceptibility (MS) suggest that a 400 year fluctuation in salinity was regulated by changes in precipitation in the area of this lagoon. Changes in the westerly jet stream, controlled by variation in solar irradiance, had an important influence on precipitation volume in South Korea, suggesting that the patterns of the westerly jet stream fluctuate on a 400 year cycle. 相似文献
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