A power function model for the basic geometry of solution dolines: considerations from the classical karst of south‐central Slovenia     

France &#x;u&#x;ter&#x;i 《地球表面变化过程与地形》2006,31(3):293-302

Solution doline geometry is generally too complex to be expressed in terms of a few parameters. A methodology previously designed by the author, based on acquisition of specific field data and subsequent processing by various Fourier techniques, enabled doline geometry to be considered in its entirety. This paper sets out to investigate which simple rotational body (rotated power function) best fits the geometry of 38 dolines studied within the Classical Karst of Slovenia. It transpires that doline radius to depth ratio changes as a function of volume, whereas the mode of change remains stable regardless of the actual dimensions of individual dolines, and is basically the same at different locations. Doline volumes are very close of those of regular cones of the same dimensions, growing relatively deeper as the volume increases. Two poly‐segment models implied by the power function model and based on earlier work are discussed. It transpires that the studied dolines may be relict forms superimposed upon pre‐existing hidden shafts formed by epikarstic water. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

MIS11–19 pollen stratigraphy from the 250-m Choshi core, northeast Boso Peninsula, central Japan: Implications for the early/mid-Brunhes (400–780 ka) climate signals     

Masaaki  Okuda  Hiroomi  Nakazato  Norio  Miyoshi  Takeshi  Nakagawa  Hiroko  Okazaki  Saneatsu  Saito  Asahiko  Taira 《Island Arc》2006,15(3):338-354

Abstract   The 250-m Choshi core (CHOSHI-1), drilled from hemipelagic muds of the Inubo Group, has been physically, geochemically and tephrochronologically analyzed back to 1 Ma. We provide pollen results for the 19–169 m section of the core (400–780 ka) bracketed by the marker tephra Ty1 (equivalent to J4) and the Brunhes–Matuyama paleomagnetic boundary. The results show good agreement with the corresponding oxygen isotope (δ¹⁸O) profile, with high δ¹⁸O intervals dominated by boreal conifers Picea , Abies , Pinus (subgen. Haploxylon ) and Tsuga ( diversifolia ), whereas low δ¹⁸O intervals are dominated by temperate conifers Cryptomeria , Taxaceae-Cephalotaxaceae-Cupressaceae and Sciadopitys . In order to confirm pollen-climate relations for the relevant taxa, a modern surface pollen dataset for the Japanese archipelago was consulted. In this analysis, the ratios of Cryptomeria / Picea and temperate/boreal conifers serve as proxies for the 100-kyr glacial/interglacial cycle during the Middle Pleistocene. Distinct signals for marine isotope stages (MIS) 11, 12, 13–15, 16, 17 and 18–19 are recognized in accordance with the tephrochronology and δ¹⁸O of the same core. Application of the criteria to an independent pollen record from Lake Biwa provides an integrated pollen stratigraphy for mid-latitude Japan during the past 800 ky. Some degree of uncertainty remains in the chronology of the MIS13–15 interval, relating to the uncertainty in the eruption age of widespread tephra Ks11.  相似文献   

Effect of depositional processes on the origin and composition of organic matter: Examples from the Pleistocene sediments in the Choshi core, Boso Peninsula     

Akiko  Omura  Koichi  Hoyanagi  Satoko  Ishikawa 《Island Arc》2006,15(3):355-365

Abstract   Both marine and terrigenous organic matter are deposited in shelf and continental slope environments. In the present study, the relationship between environmental changes in the Choshi area and the sedimentation of organic matter was examined. The sediments of the Choshi core were deposited on a shelf environment and their lithology and ichnofacies, as well as the composition of the contained kerogen (insoluble organic matter) indicate a shallowing upward succession. The organic matter preserved in the sediments is of both marine and terrigenous origin, on the basis of C/N ratios (5.90–9.45), δ¹³C values (−21.6‰−24.6‰) and kerogen microscopy. The total organic carbon (TOC) content (0.39–1.08%) of the sediments shows a positive correlation with the increase of terrigenous organic matter before 500 ka, but decreases (0.26–0.61%) after 500 ka as the shelf environment becomes shallower because of dilution, caused by the input of terrigenous inorganic clasts, and oxidation. The variation in TOC contents was thus influenced by the increasing sedimentation rate of terrigenous materials, including both organic and inorganic particles as the basin filled.  相似文献   

Characterization of magnetic particles and magnetostratigraphic dating of shallow-water carbonates in the Ryukyu Islands, northwestern Pacific     

Saburo  Sakai  Mayumi  Jige 《Island Arc》2006,15(4):468-475

Abstract   Characterization of magnetic particles, and magnetostratigraphic dating, of Holocene and Pleistocene shallow-water carbonates (the Ryukyu Group) in the Ryukyu Islands was carried out to infer the age of reef formation. Magnetic particles from these strata are dominated by fine-grained, single-domain magnetite/maghemite (40–140 nm in length). The magnetite crystals exhibit the size and morphologies characteristic of the magnetite formed by magnetotactic bacteria. No large multidomain grains were seen in transmission electron microscopy observations. The widespread presence of single-domain magnetite in the Ryukyu Islands suggests that bacterial magnetites carry depositional remanent magnetization, which is stable enough for magnetostratigraphic dating and thereby for elucidating the evolution of shallow-water carbonates. The polarity-reversal sequence seen in a core taken from the Ryukyu Group correlates with the timescale of the Matuyama chron, including the Jaramillo subchron, Kamikatsura or Santa Rosa Excursions, through the Brunhes chron. These magnetostratigraphic results imply that the time of reef initiation in the Ryukyu Islands of the northwestern Pacific was earlier than in the Great Barrier Reef of the southwestern Pacific, where it started after the Brunhes–Matuyama boundary.  相似文献   

忻定盆地晚更新世晚期的一次构造运动          下载免费PDF全文

任俊杰  张世民 《地震地质》2006,28(3):487-496

忻定盆地是山西地堑系北部的一个张性断陷盆地,第四纪构造运动活跃。野外调查表明,盆地内晚更新世晚期经历了一次较强的构造运动,它使得断块山地进一步抬升,中止了末次冰期鼎盛期的一次河流加积过程,位于断裂上升盘的洪积扇扇顶部分也被抬升为洪积台地,山前形成了十几米到几十米的断层陡崖;构造运动还导致断层上升盘河流下切,形成了Ⅱ级阶地。黄土-古土壤时间标尺和多种方式的测年结果表明这次构造运动开始于距今2万年左右  相似文献   

五佛寺断层晚更新世活动段长度及活动方式研究     

张有龙  杨斌  周伶琦  柳煜  刘洪春 《地震研究》2006,29(3):269-275

通过野外地质调查，确定五佛寺、杨窝铺、窑洞水3条断层不构成左阶羽列；五佛寺断层晚更新世活动段展布于石板沟东一大台子北东，长度为8．3km，地质剖面中具有明显的宏观蠕滑特征，室内通过对断层泥进行扫描电镜等显微结构分析发现微观蠕滑特征，因此判断五佛寺断层晚更新世活动段活动方式为蠕滑，断层不会对小观音水库坝址造成影响。  相似文献   

A high-resolution late Pleistocene record of pollen vegetation and climate change from Jingning, NW China   总被引：2，自引：0，他引：2  

LI Chunhai  TANG Lingyu  FENG Zhaodong  ZHANG Hucai  WANG Weiguo  AN Chenbang 《中国科学D辑(英文版)》2006,49(2):154-162

During the late Pleistocene, a number of climatic fluctuations such as the Heinrich events were recorded in the climatic proxies in the Loess Plateau and in North China[1―7]. Most of these records were based on geophysical and geochemical evidence[1―4]. Therefore, more biologic evidence is necessary for explaining the regional ecosystems in response to climatic change in the Loess Plateau during this period since pollen re-cords in other areas presented strong evidence to cli-matic fluctu…  相似文献   

Paleomagnetism of Pleistocene widespread tephra deposits and its implication for tectonic rotation in central Japan     

Hiromi Iwaki  Akira Hayashida 《Island Arc》2003,12(1):46-60

Abstract   A single layer of widespread tephra deposits possibly can provide an instantaneous record of the past geomagnetic field and potentially can indicate even a small-scale tectonic rotation compared to a range of geomagnetic secular variations. We report paleomagnetic data of the Ebisutoge–Fukuda tephra, which is dated at approximately 1.8 Ma and is distributed in central Japan between the Osaka–Kyoto area and the Boso Peninsula. The Fukuda volcanic ash layer and its correlative ash deposits in the Osaka–Kyoto area, near Lake Biwa and in the Mie and Niigata areas yield identical site mean declinations of approximately −170° after tilt correction, whereas moderate inclination shallowing is observed in the upper unit at several localities. Anisotropy measurements both of low-field magnetic susceptibility and of anhysteretic remanent magnetization suggest that the inclination shallowing results from the biased alignment of magnetic grains, which were deposited in the fluvial environment. The source volcanic unit, Ebisutoge pyroclastic deposits in the Takayama area, yields a mean declination of approximately −155°, showing clockwise deflection from the magnetic directions of the correlative tephra deposits. These results suggest that no significant rotation occurred between the Osaka–Kyoto, Mie and Niigata areas, but that the Takayama area suffered a clockwise rotation in respect to the other areas during the Quaternary. This rotation might have been caused under an east–west stress field associated with the collision of the Okhotsk Plate with the Eurasia Plate.  相似文献   

青海唐古拉地区晚更新世湖相沉积特征、古植被及17.4 ka B.P.以来气候转型期的厘定     

邓中林  庄永成  韩海臣 《西北地质》2004,37(1):45-50

通过年代学研究、沉积特征与配套的植物学分析，确定出唐古拉地区晚更新世以来的古植被演化的3个阶段，相应的古气候经历了干寒-湿润-干寒旋回性的演变过程。同时，从晚更新世湖相沉积物中厘定出风成-水成的气候转型事件，大致发生在17．4ka B．P(TL)，而植被特征也出现了从草本、木本发育为主转变为以草本占绝对优势的阶段，并于17．4ka B．P(TL)后风成堆积物中出现植物花粉的低峰带。  相似文献   

River terraces of the Vltava and Labe (Elbe) system, Czech Republic, and their implications for the uplift history of the Bohemian Massif     

Jaroslav Tyrá?ek 《Proceedings of the Geologists' Association. Geologists' Association》2004,115(2):101-124

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