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1.
Subsurface large-scale patterned ground structures, observed as crop-marks in cereal fields with spring-barley and oats have been detected in southwestern Jutland. It is assumed that the structures revealed are fossil ice-wedge polygons. Mode of origin, time of formation and palneoclimatic significance of ice-wedge casts are discussed. Texture of poorly layered wedge-fill materials can be distinguished from that of the stratified materials transected by the wedges, causing stress conditions in crop, in dry summers, seen as differential growth and cereal ripening. The water-holding capacity is highest in wedge-fill materials. Plants growing above the ice-wedge casts arc able to withstand a certain deficiency in precipitation during spring and early summer. Cereals growing outside ice-wedge casts suffer owing to lack of available moisture, and growth may be restricted, even to the extent that the plants can wither. Consequently, crop-marks of variable growth appear in the fields. A growth season with high precipitation makes it difficult to trace crop marks. 相似文献
2.
Significance of pot and gutter casts in a Middle Triassic carbonate platform, Betic Cordillera, southern Spain 总被引：3，自引：0，他引：3
A. Pérez-López 《Sedimentology》2001,48(6):1371-1388
Pot casts and gutter casts are described for the first time in the lower part of the Majanillos Formation, a Middle Triassic carbonate unit located in the External Zones of the Betic Cordillera (southern Spain). Their identification, as well as their relation to tempestites, enables the better interpretation of the depositional environments and the shoreline-to-offshore facies transition on the Anisian muddy carbonate ramp of the southern Iberian Massif. The Majanillos Formation contains three members, which become progressively more marly towards the top. Well-preserved pot and gutter casts and thin intercalations of calcarenite, which are interpreted as tempestites, are abundant in the lowest member. Above the pot and gutter casts, thicker calcarenite beds, which locally contain hummocky cross-stratification, predominate. Bioturbated nodular limestones are prevalent at the top of the member. The remaining succession, which records a long-term Triassic transgressive cycle, consists mostly of fine-grained limestones deposited in very shallow-marine environments. Calcarenitic sediments only accumulated within potholes and gutters in the nearshore. They developed during storms when strong currents transported sediment to the outer shelf, where it was deposited as tempestite beds. Pot and gutter casts characterize sedimentation in the bypass zone. It is concluded that storm deposits provide important constraints for the interpretation of palaeobathymetry; it is proposed that gutter casts display a trend of increasing width/thickness ratios towards the outer shelf. The identification of these structures in marine successions elsewhere should prove useful in the interpretation of depositional environments. 相似文献
3.
内蒙古中部地区古冰缘研究 总被引：1，自引：0，他引：1
在描述和分析内蒙古中部地区古冰缘基本特征的基础上，对砂多边形的成因，时代及反映的古环境进行了深入探讨，确认研究区内广泛发育的砂多边形为古冰楔，古冰楔可划分为两期，它们是末次冰期两个冰缘阶的产物，时代分别为距今３６０００－３８０００ａ和４１０００－４５０００ａ，古冰楔的存在说明研究区在末次冰期时处理于严寒的冰缘环境中。 相似文献
4.
Troy L Péwé 《Geoforum》1973,4(3):15-26
Ice wedge casts are the most accurate and widespread indicators of past permafrost. Many ice wedge casts exist in Alaska, some in areas of existing ice wedges. In addition to indicating paleotemperature conditions and a wider distribution of permafrost in Wisconsinan time than now, casts in Alaska also indicate permafrost in Iliinoian and pre-lllinoian time. Hundreds of ice wedge casts are now known in temperate North America and are described from about 22 widespread localities coast to coast in Canada and United States. Permafrost existed in late Wisconsinan time, 20,000 to 10,000 years ago, along the glacial border in temperate United States. Later permafrost formed north of the glacial border as the continental ice sheet withdrew exposing drift to the rigorous periglacial climate. Ice wedge casts indicate that the ? 7 °C mean annual air isotherm was about 2000 km farther south in late Wisconsinan time than now. 相似文献
5.
冰楔假型是反映古气候环境的重要标志,其蕴涵的气候地层信息对地貌演化过程具有重要的指示意义。通过对黄土高原北缘中部环江T1阶地上新发现的冰楔假型群特征的研究和光释光(OSL)测年,结果显示这些发育在冲积砂砾石中的冰楔假型的充填砂体的年代为 (30.01±3.31) ka B.P.,形成环境推测当时的年平均地温比现今要低17.7 ℃。该冰楔假型的发现也为末次冰期阶段性冻土南界的位置和变迁提供了证据。另外,据冰楔与阶地冲积物的关系推测,在冰楔形成的冰冻期河流阶地的堆积缓慢甚至停滞,在(28.64±3.13) ka B.P.之后的气候温暖期河流快速下切、T1阶地形成。这为河流阶地成因机制的探讨提供了依据,反映了气候波动对阶地发育的控制。 相似文献
6.
Giant groove casts have been found in the upper Proterozoic to Lower Cambrian Phe Formation (Haimanta Group), a siliciclastic sandstone/shale succession in the Tethyan Zone of the Higher Himalaya tectonic unit. The grooves are among the largest linear erosion structures related to submarine mass-movements observed in the geologic record. They are up to 4 m wide, about 0.2 m deep and can be traced for more than 35 m without changing their character. The grooves are straight, subparallel to cross-cutting striations with shallow semi-circular cross-sections and well-defined superimposed minor ridges and grooves. Groove casts exist on the soles of several sandstone beds within a 73 m thick logged section, commonly associated with flute casts. Their characteristics were compared with several other types of ancient and modern submarine linear erosion structures. A sand-rich, non-channelized basin floor depositional environment is inferred from the lithofacies, the combination of sedimentary structures, the lack of coarse-grained pebbly facies, the lateral continuity of beds, and the lack of channel structures. The grooves probably formed by laminar debris flows/concentrated density flows dragging blocks of already lithified sediment across the basin floor. When the bedding is structurally rotated back to horizontal, the groove casts show consistent North–South oriented palaeocurrent trends, with South-directed palaeocurrent directions indicated by flute casts. These palaeocurrent orientations contrast with previous palaeogeographic reconstructions of this area, which propose sediment delivery from the South. We therefore suggest a new “double provenance” model for the spatial relationship of late Proterozoic to Early Cambrian strata of the Himalaya, in which Lesser and Tethyan Himalayan age-equivalent sediment was deposited in a connected basin, where the former received detritus from the South, and the latter from a hitherto unknown source in the North. One possible candidate for this northern source is the South China Block and an associated Neoproterozoic volcanic arc. 相似文献
7.
Sedimentary structures in the Miocene fluviatile deposits of the Lower Rhine Basin, lying immediately beneath the lignite formations have been studied at Tagebau Frechen near Cologne. The structures investigated include slump structures, load casts, clay breccia, cross-bedding, sand fabric and orientation of driftwood. The slump structures are composed of alternating laminae of clay and silt and have resulted from sub-aquatic sliding of a sedimentary sheet over a surface of erosion or of a foreset bed of 10–20° inclination. The slumping has caused folding or brecciation of the strata involved. The base of a sand bed is difficult to obtain as the sediment is weakly consolidated. Load casts, therefore, have been studied exclusively in their internal structure. It is considered that the load casts of smaller dimensions have suffered a diminution of relief through settlement after the process of load casting had ceased. Two types of clay breccia have been recognised, namely those which have undergone erosion and transportation by water and those which have resulted from slumping. In an exposure, tabular- and trough-type of cross-bedding alternate with each other in geological succession. From these examples sand fabrics have been studied. Both in tabular- and trough-type of cross-bedding the apparent long axes show two maxima. In the former case, these maxima are disposed to each other at an acute angle, in the latter case, however, they are perpendicular to each other. Imbrication, after tilting the Sf-to original position, is down-current in tabular cross-bedding. In trough type, on the contrary, it may be upcurrent or the long axes of the grains dip symmetrically in up- and down-current direction. 相似文献
8.
上海地区既有建筑的节能改造,大幅减少了建筑能耗,使老建筑焕发了青春。同时又美化了城市景观。通过对既有建筑的关键部位进行的节能设计和综合改造,实现了降低50％能耗的节能目标,增加了室内环境的舒适性,延长了建筑的使用年限,是既有建筑可持续发展的有效途径。 相似文献
9.
中国北方地区保留了晚更新世以来大量的冰缘遗迹. 在气候变化背景下, 在寒区和干旱区分别出现冰缘地貌、正逆向沙化等问题, 综合不同区域的地质遗迹, 从时间上的对应关系可进一步分析气候环境变化问题. 2008年5-7月调查中, 在鄂尔多斯和大同地区分别发现了新的砂楔和土楔;在大兴安岭生态定位研究站设立了8个钻孔和2套自动气象站, 开启了冻土、湿地、 积雪研究以及现代陆面过程对下伏冻土影响的研究;在黄岗梁地区新发现了一个冻融褶皱;调查了松嫩沙地古沙丘及古土壤活动与冻土进退的关系;发现小兴安岭地区冻土退化显著, 岛状冻土散布于海拔相对较高的地区;三江平原西部农业开发强烈改变了地表覆盖, 冻土温度升高显著, 冻土上限下降明显, 甚至厚度较薄的冻土消失. 后期工作希望通过综合、集成分析以上结果, 探讨我国北方地区晚更新世/全新世的冻土南界及环境变迁. 相似文献
10.
The experiments reported here show that a range of early diagenetic clay minerals can develop within ingested sand in the guts of creatures at a rate that is at least 2 or 3 orders of magnitude greater than in an abiotic environment. Early diagenesis in marine environments may be strongly influenced by the occurrence of sediment ingestion and excretion by animals. Using a set of artificial marine experiments and the common lugworm Arenicola marina , it is shown that sediment ingestion by macrobiota represents a new way in which to precipitate clay minerals or 'bio-clays'. Significant quantities of clay minerals can be the product of biological interaction within sediment. Tanks were constructed with artificially layered sediment and natural seawater. The experiments were conducted at room temperature for a total duration of 9 months. The silicate material fed to the worms was an unweathered, and thus clay mineral-free, basalt from Iceland. Less than 2 μ m fractions from original, control and faecal samples were periodically analysed using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Faecal casts underwent mineral alteration as denoted by loss of primary minerals, especially plagioclase. New minerals in faecal casts from the lugworms included, kaolinite, illite, quartz and possibly chlorite. Inorganic weathering of similar parent basalt would probably produce an identical mineral assemblage but many more times slowly than with the macrobiotic mechanism demonstrated here. 相似文献
11.
12.
ELSE KOLSTRUP VAGN MEJDAHL 《Boreas: An International Journal of Quaternary Research》1986,15(4):311-321
Excavations for an oil pipeline in western Jutland provided the opportunity to study geological features in the trenches. Among these were ice wedge casts, composite wedge casts, and wedges with primary infilling of eolian sand. In this paper the characteristics of three wedges with a high proportion of primary infill of eolian sand are described in some detail. Thermoluminescence (TL) dating was made on the eolian sand using 0.1–0.3 mm grains of quartz and potassium feldspar. The TL ages are: 39,000 ± 5,000, 24,000 ± 3,000, and 17,000 ± 3,000 years B.P. These ages are discussed and compared with indirect datings. Palaeoenvironmental conditions at the time of maximum cold during the upper part of the Weichselian are briefly considered. 相似文献
13.
一、地质概况福建下三叠统溪口组主要出露于闽西南地区,北起将乐,南至永定,西部见于清流,东部延至长泰、德化一带,以龙岩、永定、漳平、永安、大田等地最为发育。溪口组主要是一套细碎屑沉积组合,局部地区出现碳酸盐岩夹层。最大厚度可达到1484m,可分为三个岩性段:下段以泥岩、含粉砂泥岩和粉砂质泥岩为主,局部夹薄层粉砂岩。东南部的安溪、长泰尚见有钙硅质胶结的细粒石英杂砂岩夹层。大部分地区岩石具不同程度的角岩化。具有 相似文献
14.
Rebecca M. Briant G. Russell Coope Richard C. Preece David H. Keen Steve Boreham Huw I. Griffiths Mary B. Seddon Philip L. Gibbard 《第四纪科学杂志》2004,19(5):479-495
Little is known about the impact of Late Devensian (Weichselian) aridity on lowland British landscapes, largely because they lack the widespread coversand deposits of the adjacent continent. The concentration of large interformational ice‐wedge casts in the upper part of many Devensian fluvial sequences suggests that fluvial activity may have decreased considerably during this time. The development of optically stimulated luminescence (OSL) dating enables this period of ice‐wedge cast formation to be constrained for the first time in eastern England, where a marked horizon of ice‐wedge casts is found between two distinctive dateable facies associations. Contrasts between this horizon and adjacent sediments show clear changes in environment and fluvial system behaviour in response to changing water supply, in line with palaeontological evidence. In addition to providing chronological control on the period of ice‐wedge formation, the study shows good agreement of the radiocarbon and OSL dating techniques during the Middle and Late Devensian, with direct comparison of these techniques beyond 15 000 yr for the first time in Britain. It is suggested that aridity during the Late Devensian forced a significant decrease in fluvial activity compared with preceding and following periods, initiating a system with low peak flows and widespread permafrost development. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
15.
纹层是组成层理的基本单位,既可以是低能深水沉积环境的产物,也可能形成于高能环境中。在受风暴影响的区域,微小的泥质颗粒能够在流动过程中发生絮凝形成絮粒并沉积下来形成纹层。贵州习水吼滩剖面下奥陶统桐梓组碳酸盐岩纹层发育,纹层中风暴沉积构造丰富,包括风暴侵蚀面和渠模等。基于细致的野外观察和室内沉积学研究,将在风暴作用影响下形成的纹层划分为5个类型:平行厚纹层、单向交错薄纹层、平行薄纹层、波状厚纹层和水平厚纹层。采用EDS元素面扫描方法,发现亮、暗纹层中都含有铝、硅和镁元素且分布都比较均匀,而暗纹层所含黏土矿物稍多,所以暗纹层中3种元素的含量比亮纹层的稍高。利用开尔文—赫姆霍兹不稳定性解释了亮、暗纹层的形成机制,即絮粒与未发生絮凝的微小颗粒在开尔文—赫姆霍兹不稳定性作用下交替沉积,其中以絮粒为主的纹层更容易发生重结晶形成亮纹层。根据各纹层不同的垂向结合序列划分出3种风暴序列,且从Ⅰ型到Ⅲ型风暴作用逐渐减弱。 相似文献
16.
Two new tetrapod burrow casts from the Naobaogou Formation （Middle or Late Permian） of Nei Mongol,China are described.It marks the first pre-Cenozoic tetrapod burrow from China,and one of the earliest records of tetrapod burrows.Comparison to other Permian and Triassic burrows suggests that these burrows were created by tetrapod slightly smaller than Lystrosaurus.Deduced from the morphology and sizes of two burrows and known tetrapods of the Naobaogou Formation,the burrow should be the production of a therapsid,most likely a dicynodon.These burrows indicate a seasonal climate and this area was semiarid or arid during that time. 相似文献
17.
三峡库区泄滩滑坡滑带土特征研究 总被引：7，自引：2，他引：7
在滑坡地质灾害勘察过程中,如何准确地辨识滑带土的特征和确定滑动面的具体位置,是让大多数工程技术人员都感到头痛的问题。本文以三峡库区泄滩古滑坡为例,较为详细地介绍了泄滩滑坡滑体的结构特征,以及通过勘探平硐、钻孔岩芯和地表露头等多种手段揭露的滑带土的基本特征。研究结果表明,泄滩滑坡滑带土中不仅可见明显的擦痕、镜面以及碎块石印模,而且在个别钻孔可见滑带土呈糜棱岩化现象,地表露头还可见到滑带土在地下水和高速下滑过程中被碾压、搓揉原有结构被破坏后又重新胶结的痕迹。同时,在滑带以下还存在一层特殊的滑坡影响带。泄滩滑坡滑带土特征非常典型,具有一定的代表性,可供同行在实际工作中确定滑面时参考。 相似文献
18.
广西来宾蓬莱滩及合山马滩两地的晚二叠世地层中发育有典型的重力流沉积构造,如粒序层理、包卷层理、槽模、重荷模、碟状构造和滑塌褶皱等。通过对蓬莱滩合山组和大隆组以及马滩剖面的大隆组岩相特征的详细研究,提出来宾蓬莱滩晚二叠世合山组和大隆组以及合山马滩晚二叠世大隆组形成于海底扇环境,划分出具碟状构造的块状砂岩(B１)、块状砂岩(B2)、近基浊积岩(C)、远基浊积岩(D)、不规则互层的砂泥岩(E)、滑塌褶皱层(F)及含浮游生物化石的页岩、硅质岩(G)等岩相类型,同时归纳出外扇相组合、中扇舌状体相组合、中扇水道相组合、斜坡相组合及深切谷水道相组合等,还对这些海底扇浊积岩系的古地理意义做了讨论。桂中碳酸盐岩台地相区和云开古陆之间在晚二叠世为一发育海底扇浊积岩的深水盆地,其中来宾-合山一带在大隆组沉积期处于水深约300～1 000 m的深水盆地环境,合山一带火山活动提供的火山物质及来自东侧云开古陆的陆源物质构成该区浊积岩的主要物源。 相似文献
19.
《International Geology Review》2012,54(8):736-753
Subtidal, intertidal, and supratidal carbonate facies are recognized in the Upper Jurassic (Kimmeridgian)-Upper Cretaceous (Cenomanian) peritidal carbonates of the Fele area (Western Taurides, Turkey). Vertical stacking patterns of these facies are of a cyclical character; shallowing upward is the trend of the cyclicity in these carbonate facies. In-situ karstic breccias, collapse breccias, caliche (laminar calcrete), “Microcodium” accretion, and root casts are structures commonly indicative of third-order sequence boundaries. However, mud cracks, solution pores or vugs, sheet cracks, loferites, and birds-eye structures are commonly delineated by parasequence boundaries. In-situ or collapse breccias can be genetically derived from sheet cracks, mud cracks, solution pores or vugs, and birds-eye structures with increasing exposure time. The use of such sedimentary structures in the recognition of sequence boundaries is highly practical in the ancient carbonate platforms of the world, inasmuch as the sequence boundaries, as demonstrated in this study, correlate with the eustatic sea level curves. 相似文献
20.
Pierre Gangloff 《Geoforum》1981,12(3):273-280
Evidence of villafranchian permafrost has been found at the southern end of the Rhine graben, 20km west of Basel. Two syngenetic ice-wedge casts were discovered in the “alluvions du Sundgau”. From a stratigraphical point of view, these coarse gravels were deposited after the Miocene and before the Günz glaciation. The occurrence of syngenetic periglacial structures shows that they must be of Pleistocene (Villafranchian) age. A SEM study of sand from the infilling of one of the cryogenic structures showed numerous marks of glacial origin on the quartz grains. They are indicative of a pre-Günz glaciation in the Alps. It is suggested that permafrost in villafranchian time developed only on the fringe of the alpine glaciation, but further studies will be needed for a better picture of villafranchian palaeogeography. 相似文献