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1.
In their comment, Park & Ree have raised several points against the interpretation by Park et al. , and argued that the remagnetization in the Jeongseon area was caused by the thermal effects of a Late Cretaceous pluton and/or associated short-range hydrothermal fluids, rather than by long-range fluids advocated by us.
We disagree with most points raised by Park & Ree and we make a case that these are invalid because of what we believe is incorrect geologic evidence. Hence, our model—that the fluids causing the chemical remagnetization might migrate through the fault system within the Ogcheon Fold Belt—is the most plausible scenario. We recognize that our model needs to be tested in a future study and we welcome new interpretations for or against our model based on reliable geologic or geophysical data. 相似文献
We disagree with most points raised by Park & Ree and we make a case that these are invalid because of what we believe is incorrect geologic evidence. Hence, our model—that the fluids causing the chemical remagnetization might migrate through the fault system within the Ogcheon Fold Belt—is the most plausible scenario. We recognize that our model needs to be tested in a future study and we welcome new interpretations for or against our model based on reliable geologic or geophysical data. 相似文献
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3.
The late Pleistocene geomagnetic field as recorded by sediments from Fargher Lake,Washington, U.S.A.
Measurement of the remanent magnetization of a 6.88-m oriented core of soft sediments and tephras from Fargher Lake near Mount St. Helens in southwestern Washington State shows that no significant geomagnetic reversals were recorded in the sediments of the lake. Radiocarbon and palynological dating of the tephra layers from the lake bed indicates deposition during the interval 17, 000–34, 000 years B.P. although geochemical correlation of a prominent tephra layer in the core with tephra set C of Mount St. Helens could mean that the maximum age of the sediments may be at least 36, 000 years B.P. The core was divided into specimens 0.02 m long, each representing approximately 55 years of deposition assuming a constant rate of sedimentation. Pilot alternating field demagnetization studies of every tenth specimen indicated a strong, stable remanence with median destructive field of 15 mT, and the remaining specimens were subsequently demagnetized in fields of this strength. The mean inclination for all specimens exclusive of the unstably magnetized muck and peat from near the surface is 56.1° which is 8° shallower than the present axial dipole field at this site, perhaps because of inclination error in the detrital remanent magnetization of the sediments, although because of the variability in the data, this departure from the axial dipole field may not be significant. The ranges of inclination and declination are comparable to those of normal secular variation at northern latitudes. Although three isolated specimens have remanence with negative inclination, these anomalous directions are due to sampling and depositional effects. Measurement of a second core of 6.86 m length also revealed only normal magnetic polarity, but this result is of little stratigraphic value as this core failed to penetrate the distinctive tephra found near the base of the former core.Studies of a concentrate of the magnetic minerals in the sediments by optical microscopy and X-ray diffraction indicate that the primary magnetic constituent is an essentially pure magnetite of detrital origin. The magnetite occurs in a wide range of grain sizes with much of it of sub-multidomain size (< 15 μm).As a whole, this study provides substantial evidence against the existence of large-scale worldwide geomagnetic reversals during the time interval of Fargher Lake sedimentation, a segment of geological time for which many excursions and reversals have been reported elsewhere. 相似文献
4.
Wonnyon Kim Seong-Jae Doh Yongjae Yu Jeong Jick Lee Dongwoo Suk 《Tectonophysics》2009,474(3-4):684-695
In order to better understand the tectonic environment of the Korean Peninsula since Cretaceous, a paleomagnetic study was carried out on the Jinan Basin located in southwestern Korea. From the demagnetization of 597 samples, we found that remanence is carried by pyrrhotite and/or magnetite (black siltstone) and hematite (red siltstone), which is a common magnetic mineral assemblage of the rocks remagnetized in Early Tertiary in Korea. All the rock units recorded identical ancient geomagnetic field directions. In particular, paleodirections were better clustered in geographic coordinates, indicating a secondary origin. The presence of abundant silicates as inclusions within Fe-oxides and Fe-sulfides confirms the authigenic origin of the magnetic carriers, precipitated by fluid mediated chemical processes. Compilation of the Korean Cretaceous and Tertiary poles indicates that the Jinan Basin was remagnetized in the Early Tertiary age. In addition, comparison of the Korean Cretaceous and Tertiary poles with those from adjacent major terrains including China and Siberia reveals that a dominant feature of tectonic motions in Korea was a vertical-axis rotation. Sense of vertical-axis rotation was time-dependent, with clear distinction between clockwise rotation in Cretaceous and counter-clockwise rotation in Early Tertiary. Such differences in the mode of vertical axis rotation might be caused by the activities of basin-bounding strike–slip faults in Korea, possibly driven by the changes of subduction regime of the Kula-Pacific plate in Early Tertiary. 相似文献
5.
Kim Y Cho S Kang HD Kim W Lee HR Doh SH Kim K Yun SG Kim DS Jeong GY 《Marine pollution bulletin》2006,52(6):659-665
The mineralogical effect on the (137)Cs reaction with marine sediment has not been systematically studied yet, even though illite has been known to adsorb Cs preferentially on its frayed edge sites in a low Cs concentration. Ninety-three marine sediment samples were collected near Yangnam, Korea for quantitative X-ray-diffraction (XRD), gamma-ray, and total organic carbon (TOC) analysis. Illite content was in the range of 0-23 wt.% and those of (137)Cs and TOC were minimum detectable activity (MDA) approximately 7.19 Bq/kg-dry and approximately 3.32%, respectively. The illite content in the marine sediment showed a good relationship with the (137)Cs content (R(2)=0.69), but with an increase in the illite content, the relationship became less linear. This trend can be clearly shown in two groups of samples with different size fractions (< and >5Mdvarphi). For the samples of larger particle sizes (low contents of illite), the relationship is linear, but for the samples of the smaller particle sizes (high illite content) it is less linear with a decreased slope, indicating that increase in illite content does not significantly contribute to the fixation of (137)Cs in marine sediment. Rather, the TOC has a more linear relationship with (137)Cs content with no slope change in all particle size ranges. This may indicate that humic materials in marine sediment block the access of (137)Cs to the frayed edge site and reduces the adsorption of (137)Cs on illite and that the organic materials in marine sediment play more important roles in adsorbing Cs than illite. 相似文献
6.
The accumulation of radiocesium in coarse marine sediment: effects of mineralogy and organic matter 总被引：1，自引：0，他引：1
The controlling factors affecting the accumulation of (137)Cs in marine sediment have not been investigated in detail, especially in coarse grained sediment. Eighty eight coarse marine sediment samples near Wuljin, Korea, were characterized by quantitative X-ray-diffraction (XRD), gamma-ray, and total organic carbon (TOC) analysis. Those factors were then compared. The grain size was in the range of -0.48 to 3.6Mdphi corresponding to sand grains. TOC content was in the range of 0.06-1.75%, and the concentration of (137)Cs was 相似文献
7.
Jeong Woo Kim Ralph R. B. von Frese Bang Yong Lee Daniel R. Roman Seong-Jae Doh 《Pure and Applied Geophysics》2011,168(5):815-826
The gravity-geologic method (GGM) was implemented for 2′ by 2′ bathymetric determinations in a 1.6° longitude-by-1.0° latitude
region centered on the eastern end of the Shackleton Fracture Zone in the Drake Passage, Antarctica. The GGM used the Bouguer
slab approximation to process satellite altimetry-derived marine free-air gravity anomalies and 6,548 local shipborne bathymetric
sounding measurements from the Korea Ocean Research and Development Institute to update the surrounding off-track bathymetry.
The limitations of the Bouguer slab for modeling the gravity effects of variable density, rugged bathymetric relief at distances
up to several kilometers, were mitigated by establishing ‘tuning’ densities that stabilized the GGM predictions. Tests using
two-thirds of the shipborne bathymetric measurements to estimate the remaining third indicated that the tuning densities minimized
root-mean-square deviations to about 29 m. The optimum GGM bathymetry model honoring all the ship observations correlated
very well with widely available bathymetry models, despite local differences that ranged up to a few kilometers. The great
analytical simplicity of GGM facilitates accurately and efficiently updating bathymetry as new gravity and bathymetric sounding
data become available. Furthermore, the availability of marine free-air gravity anomaly data ensures that the GGM is more
effective than simply extrapolating or interpolating ship bathymetry coverage into unmapped regions. 相似文献
8.
Twenty profiles of vertical electric soundings (VES) were obtained in a riverside alluvium at the Buyeo area, South Korea,
to examine the variations of subsurface geology and associated groundwater chemistry. The combination of the VES data with
the borehole data provided useful information on subsurface hydrogeologic conditions. The vestige of an ancient river channel
(e.g. oxbow lake) was identified on the resistivity profiles by the lateral continuation of a near-surface perched aquifer
parallel to the river. Such a perched aquifer is typically developed in the area with a clay-rich silty surface alluvium which
prohibits the infiltration of oxygen. Therefore, groundwater below the oxbow lake shows a very low nitrate concentration and
Eh values under the strong anoxic condition. The distribution of water resistivity is correlated with that of measured total
dissolved solids concentration in groundwater, while the earth resistivity of the aquifer shows a significant spatial variation.
It is interpreted that the earth resistivity of the aquifer is mainly controlled by the soil type rather than by the water
chemistry in the study area. 相似文献
9.
Deformation history inferred from magnetic fabric in the southwestern Okcheon metamorphic belt, Korea 总被引：2，自引：0，他引：2
Magnetic fabric and rock-magnetic studies have been carried out for the non-fossiliferous, low- to medium-grade metasedimentary rocks in the southwestern part of the Okcheon metamorphic belt (OMB). Two major metamorphic events in the study area were previously recognized: regional metamorphism (M1) in the late Carboniferous to early Permian and contact metamorphism (M2) due to the intrusion of granite in the middle Jurassic. The metamorphic grade of the study area increases from the biotite zone in southeast through the garnet zone to the staurolite zone towards the northwest. Magnetic fabrics of the study area are generally well defined and can be characterized according to the metamorphic zones. Magnetic foliation is the dominant magnetic fabric in the biotite zone, while magnetic lineation prevails in both garnet and staurolite zones. We interpret the metamorphism-related deformation history of the study area based on magnetic fabrics, magnetic mineralogy and previously reported metamorphic evolution as follows. Penetrative NW-dipping cleavage, represented by magnetic foliation, was formed in the study area by prevailing NW–SE shortening event during the M1 regional metamorphism in the late Carboniferous–early Permian. This shortening event is interpreted to be associated with the collisional event between the North and South China blocks. Cleavages dipping steeply to the southeast in the staurolite zone are attributed to the pressure exerted from the intrusion of Jurassic granite in the northwestern area. 相似文献
10.