排序方式： 共有25条查询结果，搜索用时 15 毫秒
11.
TONY WALTHAM 《Geology Today》1998,14(2):67-70
Standing isolated on the barren Tibetan Plateau, the gleaming white snow-clad pyramid of Mount Kailas is a remnant of massive conglomerates formed within the Himalayan orogeny. Reached by an approach walk through the Himalayas in western Nepal, the circuit of Kailas on the pilgrims' kora path offers some views of the impressively exposed geology. 相似文献
12.
就中国以外已发现的26个天坑的特征和成因进行了一般性的描述和讨论.此外,对其它类型的一些特大型塌陷漏斗也与天坑进行了比较. 相似文献
13.
The Role of Tourism in the Economic Transformation of the Central West Queensland Economy 总被引：1，自引：0，他引：1
Central West Queensland's predominantly pastoral sector experienced considerable hardship in the decade to 1996 as the consequence of drought and low commodity prices. The social and economic consequences were both large and spatially diverse. Those often remoter shires, characterised by few people and services, experienced sharp decline on both dimensions. In contrast, some of the larger and more accessible towns managed to stabilise or even increase both population and services, assisted by the development of the tourism sector. This, in turn, reflects the region's unique geographical character, features of which include strong historical associations, harsh and seasonably variable climate, vast distances, and sparse populations. Unsurprisingly, the tourist industry has been developed by small-scale local entrepreneurs, focuses on distinct market segments--especially the elderly and adventurous, and is highly seasonal. 相似文献
14.
15.
TONY WALTHAM 《Geology Today》1994,10(3):105-111
The rose-red city half as old as time is an incredible series of monuments carved out of Cambrian sandstone, which offers more than a little geological interest. Both the site of Petra and its approach canyons are tightly controlled by the geology, and the sandstone itself is mineralized and coloured on a surprising scale. 相似文献
16.
17.
D. WALTHAM 《Geophysical Prospecting》1992,40(3):343-358
A method is presented for developing and/or evaluating 2D filters applied to seismic data. The approach used is to express linear 2D filtering operations in the space-frequency (x–ω) domain. Correction filters are then determined using plane-wave constraints. For example, requiring a vertically propagating plane wave to be unaffected by migration necessitates application of a half-derivative correction in Kirchhoff migration. The same approach allows determination of the region of time-offset space where half-derivative corrections are correct in x–t domain dip moveout. Finally, an x–ω domain dip filter is derived using the constraint that a plane wave be attenuated as its dip increases. This filter has the advantage that it is significantly faster than f–k domain dip filtering and can be used on irregularly spaced data. This latter property also allows the filter to be used for interpolation of irregular data onto a regular grid. 相似文献
18.
PETER NIELSEN PHILIPPE MUCHEZ WOUTER HEIJLEN A. E. TONY FALLICK† EDDY KEPPENS‡ DOMINIQUE WEIS§ RUDY SWENNEN 《Sedimentology》2005,52(5):945-967
In topographic flat areas, sedimentary settings may vary from one outcrop to another. In these settings, calcite precipitates may yield macroscopically similar columnar features, although they are products of different sedimentary or diagenetic processes. Three columnar calcite crystal fabrics, i.e. rosettes, palisade crusts and macro-columnar crystal fans, have been differentiated near and at the contact between Upper Tournaisian dolomites and limestones along the southern margin of the Brabant-Wales Palaeohigh. Their petrographic characteristics, and geochemical and fluid inclusion data provide information on the (dia)genetic processes involved. Rosettes composed of non-luminescent columnar calcite crystal fans (1–5 cm in diameter) developed on top of one another, forming discrete horizons in repetitive sedimentary cycles. The cycles consist of three horizons: (I) a basal horizon with fragments from the underlying horizon, (II) a micrite/microspar horizon with incipient glaebules, (III) an upper horizon consisting of calcite rosettes, with desiccation features. The petrographical features and δ18O signatures of −10·0 to −5·5‰ and δ13C values of −5·5 to −3·2‰ support either evaporative growth, an evaporative pedogenic origin, or overprinting of marine precipitates. Palisade crusts, composed of a few to 10 mm long non-luminescent calcite crystals, coat palaeokarst cavities. Successive palisade growth-stages occur which are separated by thin laminae of micrite or detrital quartz, displaying a geopetal arrangement. Palisade crusts are interpreted as intra-Mississippian speleothems. This interpretation is supported by their petrographic characteristics and isotopic signature (δ18O = −8·7 to −6·5‰ and δ13C = −4·8 to −2·5‰). Macro-columnar crystals, 1–50 cm long, developed mainly perpendicular to cavity walls and dolomite clasts. Crystal growth stages in the macro-columnar crystals are missing. δ18O values vary between −16·4 and −6·8‰ and δ13C values between −5·2 and −0·9‰. These features possibly support a late diagenetic high temperature precipitation in relation to hydrothermal karstification. 相似文献
19.
This article explores the emergence and persistence of crisis narratives in the policy environment of twentieth century Nigeria. It finds that environmental crisis narratives have a well-established and traceable historical lineage, initially, as continuity between colonial and post-colonial policy discourse, but more recently with donor agencies gaining increasing importance in influencing and shaping debate. Counter-narratives are identified, but these lack historical 'legitimacy', and often sit uncomfortably alongside donor-funded initiatives. In light of weak governance systems that impede the development and maintenance of robust data-sets, the article argues that flawed 'conventional wisdom' regarding environmental processes and people–environment linkages will combine to produce a policy environment that could actually constrain rather than enable the improvement of rural livelihoods. 相似文献
20.
TONY WALTHAM 《Geology Today》1995,11(6):228-233
The 1980 eruption of the Mount St Helens volcano produced a huge crater, massive debris flows and truly remarkable blast effects. All the features are still very visible, and the site offers easy access for an unforgettable visit. 相似文献