朝鲜半岛中部的志留系特征及其地质意义

朝鲜半岛的志留系仅见于中朝克拉通东缘朝鲜半岛中部的平南盆地。该盆地志留系发育于谷山-新溪-遂安地区和法洞地区。谷山-新溪-遂安地区的志留系划分为碎屑碳酸盐岩组成的谷山组和碳酸盐岩为主的月阳里组,化石非常丰富,包括珊瑚类、腕足类、海百合类和腹足类等,该地区谷山组中部和月阳里组上部发育以床板珊瑚为主的生物礁。法洞地区志留系主要为碎屑岩,夹碳酸盐岩薄层,化石极少。将平南盆地志留系生物地层划分为5个组合带,自下而上依次为Striispirifer shiqianensis带、Palaeofavosites balticusCamarotoechia ubsuensis组合带、Favosites songrimensisLeptostrophia guizhouensis组合带、Parastriatopora coreanicusPleurorima granata组合带和Pentagonocyclicus monocostatusPentagonopentagonalis probus组合带。据此认为谷山组时代为兰多维列世,月阳里组时代为温洛克世-罗德洛世。     

磁铁石英岩铁运输沉淀的pH值条件约束:以朝鲜半岛龙渊铁矿床为例

前寒武纪时期铁矿形成过程中铁物质如何迁移的研究,已取得了众多科研成果,但仍有些问题未得到很好的解决。尤其是对陆壳来源性铁矿床(非Algoma类型)的成因,仍然具有诸多争议,焦点主要集中在铁迁移问题。笔者以朝鲜半岛龙渊铁矿床为例研究了铁介质形成和运输的问题。首先通过铁矿石的地球化学研究和前人研究结果的考察,发现此铁矿床不属于Algoma类型,而是在强酸性介质条件下陆壳物质风化、移动和沉积而形成的。那么为什么会出现如此强大的酸性环境条件呢？为了揭示这一点,对在当时环境下把水的性质能够变成酸性的物质进行了热力学计算。研究结果表明,当硫化物如黄铁矿风化时,形成了能够使铁源物质风化和迁移的介质。这些结果也符合这样一个事实,即目前从富含硫化物地层淋沥的水的pH值小于3.5,并且铁含量远高于非硫化物类型的地层。本次研究结果表明,陆壳来源的铁矿床形成过程中,不能忽视硫化物的风化作用。     

Validation of Sea Level Data in the East Asian Marginal Seas： Comparison between TOPEX／POSEIDON Altimeter and In-Situ Tide Gauges

In an effort to assess the reliability of satellite altimeter systems, the authors conduct a comparative analysis of sea level data that were collected from the TOPEX/POSEIDON (T/P) altimeter and 10 tide gauges (TG) near the satellite passing ground tracks. The analysis is made using datasets collected from marginal sea regions surrounding the Korean Peninsula at T/P cycles of 2 to 230, which correspond to October 1992 to December 1998. Proper treatment of tidal errors is a very critical step in data processing because the study area has very strong tide. When the T/P data are processed, the procedures of Park and Gamberoni (1995) are adapted to reduce errors associated with the tide. When the T/P data are processed in this way, the alias periods of M2, $2, and K1 constituents are found to be 62.1, 58.7, and 173 days repectively. The compatibility of the T/P and TG datasets are examined at various filtering periods.The results indicate that the low-frequency signals of the T/P data can be interpreted more safely with longer filtering periods (such as up to the maximum selected value of 200 days). When RMS errors for the 200-day low-pass filter period are compared with all 10 tidal stations, the values span the range of 2.8 to 6.7 cm. The results of a correlation analysis for this filtering period also show a strong agreement between the T/P and TG datasets across all stations investigated (e.g., p-values consistently less than 0.001). Hence according to the analysis, the conclusion is made that the analysis of surface sea level using satellite altimeter data can be made safely with reasonably extended filtering periods such as 200 days.     

Storm-influenced siliciclastic and carbonate ramp deposits, the Lower Ordovician Dumugol Formation, South Korea

The Dumugol Formation (Lower Ordovician) in the southern part of the Baegunsan syncline, South Korea, contains mixed siliciclastic and carbonate ramp deposits. The ramp sediments were frequently influenced by storm events resulting in tempestites of sandstone-mudstone couplets, bioclastic grainstones to packstones, flat-pebble conglomerates, a skeletal lag layer and laminated calcisiltites. All tempestites are characterized by an erosive to sharp base, poor grading and a transitional upper boundary. The difference in lithology of tempestites appears to have been controlled by the nature of substrates and by proximality. For example, laminated calcisiltites have developed on the shallow carbonate ramp, flat-pebble conglomerates are closely associated with nodular limestones on shallow and deep ramps, and thin skeletal lag layers from fossiliferous argillaceous sediments formed in a basinal setting. The stratigraphic succession of the Dumugol Formation represents an initial transgression followed by a regression. The vertical facies change records the transition from a shallow siliciclastic ramp to a deep carbonate ramp, to a basin, shallowing to a deep carbonate ramp, and to a shallow carbonate ramp. Storm effects are mostly well preserved in shallow to deep ramp deposits.     

TEM and XRD determination of crystallite size and lattice strain as a function of illite crystallinity in pelitic rocks

Average crystallite size and mean-square strain of illite in rock specimens and clay separates were measured independently in TEM images and by single-line Fourier (Voigt method) profile analysis of the c. 1 nm peak of XRD patterns for a prograde sequence of pelitic rocks (illite crystallinity indices=0.17–0.58°Δ2θ) from the Gaspé Peninsula, Quebec. The TEM-determined crystallite sizes in clay separates approximate those determined by Fourier profile analyses and those calculated from illite crystallinity indices by the Scherrer equation, with the exception of the diagenetic sample. The crystallite sizes and mean-square strains of illite in rock samples exhibit a trend similar to that determined by profile analyses, but the average crystallite sizes are up to five times larger than those measured for clay separates. TEM images show that all rock samples have a wide range of crystallite sizes, and the proportions of larger crystallites increase with metamorphic grade. The diagenetic illite is defect-rich, fine-grained (mean thickness by volume=c. 70 nm), 1M_d material. Anchizonal illite tends to occur as separate aggregates of small 1M_d and larger 2M₁ crystals (c. 200 nm), comprising arrays of subparallel coalescing packets. The epizone sample has thick (c. 400 nm), defect-free crystals of muscovite occurring in stacks of parallel layers, or subhedral crystals intergrown with large-angle boundaries. Cleaved crystals that are free of intracrystalline layer terminations are dominant in clay separates of all samples, having ranges of smaller sizes with volume-average thicknesses of c. 43, 43, and 81 nm (c. 14, 28, 67 nm by the Voigt method), respectively, for the three zones. The results suggest that illite crystallinity indices do not provide a direct measure of a single microstructural state of illite in rocks, although they yield consistent limits for average crystallite sizes for the anchizone (23 & 48 nm here). Therefore, they serve as a general parameter of the degree of recrystallization on a relative basis, in part because the contributions of all peak-broadening variables (mixed layering, size and strain) decrease regularly with prograde regional metamorphism of pelites. The microstructural changes caused by rock disaggregation are probably a function of those variables as well. The data collectively demonstrate a trend from metastable, defect-rich, small crystals towards a stable assemblage of larger, defect-free crystals, through dissolution of strained crystals and neocrystallization, consistent with the Ostwald step rule.     

SEDIMENT TRANSPORT CAPACITY -AN IMPROVED BAGNOLD FORMULA

This paper re-examines Bagnold’s theorem of sediment transport. Different from the stream power defined by Bagnold, i.e., τoV, this study shows that the total load of sediment-laden flow, gt, is related to near bed energy dissipation rate, i.e., τou*’. An attempt is made to explain the empirical relation. The ratio (=k) of measured total load, gt, to the product of near bed velocity, u*’, and energy dissipation rate, τou*’, is analyzed. It is found that k is independent of the Rouse number, Z, if Z is greater than 2.6, but the coefficient k decreases with the increase of Z when Z < 2.6. An empirical relation between k and Z is developed. A systematic and thorough analysis of 1,458 sets of data collected from 16 rivers and canals confirms that the proposed formula can be used to compute the total load with accuracy.     

2002年3月21—22日影响韩国的沙尘天气分析

利用气象卫星、天气形势场和NCEP/NCAR再分析资料,分析了2002年3月21—22日影响韩国沙尘天气的原因。结果表明:影响韩国沙尘天气的沙尘主要源地是蒙古国和中国内蒙古地区。沙尘天气发生在地面冷锋后部,高压伸展的前面;19日和20日沙尘暴发生后,沙尘沿着西北风输送,21日早晨影响韩国;PM10最高值达到2 778.2μg/m³,由于西北风较强,沙尘暴发生后很快影响到韩国,但在韩国持续的时间较短。     

A Maximum-Entropy Method for Estimating the Spectrum

Based on the maximum-entropy(ME)principle,a new power spectral estimator for random waves is derived in the form of S～(ω)=a/8H~2(2π)~(d 1)ω~-~((d 2))exp[-b(2π/ω)~n],by solving a variational problem subject to some quite general constraints.This robust method is comprehensive enough to describe the wave spectra even in extreme wave conditions and is superior to periodogram method that is not suitable to process comparatively short or intensively unsteady signals for its tremendous boundary effect and some inherent defects of FFT.Fortunately,the newly derived method for spectral estimation works fairly well,even though the sample data sets are very short and unsteady,and the reliability and efficiency of this spectral estimator have been preliminarily proved.     

Interaction of Streamwise and Wall-Normal Velocities in Combined Wave-Current Motion

The aim of this paper is to present an analytical expression for the streamwise velocity distribution in a non-uniform flow in the presence of waves; the correlation between the horizontal and vertical velocity components has been compreheusively examined. Different from previous researches which attributed the deviation of velocity from the classical log-law to the wave Reynolds stress, i.e. - ρ uv^- only, this study demonstrates that the momentum flux caused by mean velocities, i.e., u^- and v^-, is also responsible for the velocity deviation, and it is found that the streamwise velocity for a flow in the presence of non-zero wall-normal velocity does not follow the classical log-law, but the modified log-law proposed in this study based on simplified mixing-length theorem. The validity of the modified log-law has been verified by use of available experimental data from published sources for combined wave-current flows, and good agreement between the predicted and observed velocity profiles has been achieved.