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481.
Stefan H. Doerr Rob R. Davies Alexander Lewis Graham Pilkington John A. Webb Peter J. Ackroyd Owen Bodger 《地球表面变化过程与地形》2012,37(3):253-261
The Australian Nullarbor Plain, one of the world's largest limestone platforms (~200 000 km2), has few distinctive surface karst features for its size, but is known for its enigmatic ‘blowholes’, which can display strong barometric draughts. Thousands of these vertical tubes with decimetre–metre (dm–m) scale diameter puncture the largely featureless terrain. The cause and distribution of these has remained unclear, but they have been thought to originate from downward dissolution and/or salt weathering. To elucidate blowhole distribution and mode of formation we (i) correlated existing location data with Shuttle Radar Topography Mission (SRTM) data, which distinguishes the subtle undulations (< 10 m per km) of the landscape, (ii) surveyed blowhole morphology and (iii) determined their rock surface hardness. Over a sampled area of 4200 km2, the distribution of 615 known blowholes is not correlated with present topography. Blowholes are often connected to small or, in some cases extensive, but typically shallow cavities, which exhibit numerous ‘cupolas’ (dome‐shaped pockets) in their ceilings. Statistical arguments suggest that cavities with cupolas are common, but in only a few cases do these puncture the surface. Hardness measurements indicate that salt weathering is not their main cause. Our observations suggest that blowholes do not develop downwards, but occur where a cupola breaks through the surface. Lowering of the land surface is suggested to be the main cause for this breakthrough. Although cupolas may undergo some modification under the current climate, they, as well as the shallow caves they are formed in, are likely to be palaeokarst features formed under a shallower water table and wetter conditions in the past. The findings presented have implications for theories of dissolutional forms development in caves worldwide. The environmental history of the Nullarbor platform allows testing of such theories, because many other factors, which complicate karst evolution elsewhere, have not interfered with landform evolution here. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
482.
从瘤体与基质的矿物组成、岩石的结构构造出发,深入探讨了滇西施甸地区保山组瘤状灰岩的沉积环境及其形成机理。研究表明,滇西施甸地区上寒武统保山组瘤状灰岩存在3种成因:一种是呈互层状的泥质和灰质沉积物在半固结或弱固结状态下,经差异压实-压溶作用而形成瘤状构造,岩石中各组分含量及后期压溶作用强度的差异导致了瘤状灰岩不同的存在形式;另一种是泥质和灰质沉积物在半固结或弱固结状态下经斜坡滑塌作用形成串珠状、砾屑状灰岩;第三种则是泥灰质沉积层间歇性地暴露干裂,移位磨蚀,并被后期沉积物充填胶结形成瘤状灰岩。 相似文献
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484.
Gary Kocurek Rowan C. Martindale Mackenzie Day Timothy A. Goudge Charles Kerans Hima J. Hassenruck‐Gudipati Jasmine Mason Benjamin T. Cardenas Eric I. Petersen David Mohrig Daniel S. Aylward Cory M. Hughes Caroline M. Nazworth 《Sedimentology》2019,66(3):808-837
The Middle Jurassic Todilto Member of the Wanakah Formation is a carbonate and gypsum unit inset into the underlying aeolian Entrada Sandstone in the San Juan Basin. Field and thin section study of the uppermost Entrada and Todilto at Ghost Ranch, New Mexico, identified Todilto facies and their relationship to remnant Entrada dune topography. Results support the previous interpretation that the Entrada dunes, housed in a basin below sea level, were rapidly flooded by marine waters. Mass wasting of the dunes gave rise to sediment‐gravity flows that largely buried remnant dune topography, leaving ca 12 m of relief that defined the antecedent condition for Todilto deposition. Previously interpreted as seasonal varves deposited in a stratified water body, the Todilto is reinterpreted as a microbial biolaminite. Most diagnostic are organic‐rich laminae with structures characteristic of filamentous microbes and containing trapped aeolian silt, and clotted‐texture laminae with a fabric associated with calcification of extracellular polymeric substances. The spatial arrangement of Todilto facies is controlled by the dune palaeotopography. A continuous basal laminated mudstone thickens over the dune crest, reflecting the optimum conditions for microbial mat development, and is interpreted to have been deposited when marine waters submerged the topography. Subsequent drying caused emergence of the crestal area, and formation of tepee structures and a dissolution breccia. Gypsiferous mudflats and periodic ponds occupied the dune flanks and interdune area, with gypsum concentrated within the interdune area. Entrada sands remained unstable during Todilto deposition with common injection structures into the Todilto, and a remnant slope caused the downslope movement and folding of Todilto strata on the upper lee face. Although some expansion of the gypsum occurred in the subsurface, facies architecture fostered development of a dissolution front adjacent to the interdune gypsum body with section collapse of gypsiferous limestone on the dune flanks. 相似文献
485.
上扬子地区晚二叠世晚期及早三叠世早期异常碳酸盐岩可以按成因分为3大类:A类-生物成因
的异常碳酸盐岩,B类-非生物成因(化学及水动力成因) 的异常碳酸盐岩,C类-生物、水动力及化学等复
合成因的异常碳酸盐岩;还可进一步识别出8个具体类别,包括微生物岩、角砾状灰岩、扁平砾屑灰岩、条带
状灰岩、薄板状、纹层状泥质灰岩、鲕粒碳酸盐岩及a、b型蠕虫状灰岩。近乎极端的古海洋环境和古气候条件
是P/T转换时期以错时相为主的异常碳酸盐岩得以发育并作为早三叠世重要沉积类型的基础;P/T生物大灭绝
事件发生以后,底栖动物对海相沉积层表面的破坏几乎停止,海洋洋流近乎停滞,与此同时表层海水饱受季风
与飓风风暴的侵扰,分布在生物礁或浅水碳酸盐岩台地之上的透光带菌藻生态系统生长为具有一定抗浪能力的
微生物岩,频繁的风暴对海底的影响使得同生期弱固结的碳酸盐软泥被打碎而形成同生砾屑,一定的古地形坡
度又加剧了风暴为诱因的碳酸盐沉积物重力流的发育;此外,碳酸钙过饱和的海水可以使得碳酸盐直接化学沉
淀于海底,同时巨型季风带来的黏土和粉砂与碳酸盐化学沉积共生,这一系列的过程发生于早三叠世早期特殊
的古环境中,造成了上扬子地区多种多样的异常碳酸盐岩沉积。 相似文献
486.
487.
488.
在综合分析假白榴正长岩物相组成的基础上,以碳酸钠为助剂,分解假白榴正长岩中主要矿物相,对其进行热力学分析,并与石灰石烧结法进行比较。烧结反应实验结果表明,采用碳酸钠为助剂,假白榴正长岩粉体在760~880 ℃条件下反应10~15 h,矿石中主要矿物的分解率可达971%。热力学计算结果表明,纯碱烧结法处理1 t假白榴正长岩矿石,消耗Na2CO3 065 t,且约95%的Na2CO3可以回收循环利用,消耗标准煤19097~20682 kg,排放CO2 077~081 t,一次性资源消耗量、标准煤耗、温室气体CO2排放量分别比石灰石烧结法分别减少了65%、63%、65%。纯碱烧结法具有一次性资源消耗低、能耗低和温室气体CO2排放量少等优点,工业化应用前景十分广阔。 相似文献
489.
高温状态下加载速率对石灰岩力学效应研究 总被引:3,自引:0,他引:3
采用美国MTS810电液伺服材料试验机,对200 ℃高温状态下的石灰岩试件进行了5级不同加载速率下的单轴压缩试验,考察了石灰岩的全应力-应变曲线,给出了其峰值强度、峰值应变、弹性模量E随加载速率的变化特征。研究结果表明,(1) 石灰岩的峰值强度、弹性模量在加载速率v = 0.000 5~0.005 mm/s内,随加载速率增大呈急剧上升现象;当v = 0.005 0~0.5 mm/s内,随加载速率增大呈下降趋势;当v >0.5 mm/s后,呈现上升趋势。(2) 石灰岩的峰值应变在v = 0.000 5~0.005 mm/s内,随加载速率增大呈下降趋势;在v = 0.005~5.0 mm/s加载速率区段,峰值应变呈现缓慢上升现象。研究结果可为相关岩体的爆破效应及评价岩石工程的稳定性提供参考。 相似文献
490.
四川盆地下侏罗统自流井组大安寨段一亚段(大一亚段)灰岩是元坝地区主要产气层。岩心、薄片、物性资料、试油、录井、测井、地震资料综合研究表明,大一亚段灰岩主要为介壳灰岩和含泥介壳灰岩,介壳灰岩平均孔隙度236%,平均渗透率为002×10-3 μm2,含泥介壳灰岩平均孔隙度为459%,平均渗透率为021×10-3 μm2。介壳灰岩为浅湖亚相高能滩微相沉积,含泥介壳灰岩为浅湖亚相次高能滩微相沉积。地震波形分类上,以介壳灰岩为主的高能滩微相为高连续低频中强波谷反射,以含泥介壳灰岩为主的次高能滩微相为高连续低频中弱振幅波谷反射。高连续低频中强振幅波谷反射和高连续低频中弱振幅波谷反射以SW-NE向分布于研究区中央地带。以伽马值大于46 API为门槛值剔除泥岩、泥质粉砂岩等,得到介壳灰岩和含泥介壳灰岩的伽马数据体。精细刻画了高能滩微相介壳灰岩和次高能滩微相含泥介壳灰岩的分布范围,新增天然气有利区面积518 km2,为元坝地区大安寨段天然气储量和产量的增加奠定了坚实的基础。 相似文献