排序方式： 共有2条查询结果，搜索用时 0 毫秒
1
1.
A unique instance of Holocene estuarine phosphogenesis has been investigated in Raglan Harbour, on the west coast of North Island, New Zealand. Nodular calcareous concretions, which formed within surficial estuarine muds between 6500 and 3600 years BP, were superficially impregnated by carbonate fluorapatite between 3600 and 1600 years BP. The phosphatized nodules lie beneath a late Quaternary shore platform, which is reinforced by a mass of intertwined bioturbation structures and tubular rootlet casts impregnated by limonite and goethite. Large polygonal cracks, indicative of a desiccatory regime, are locally conspicuous on the platform surface and in the immediately subjacent muds. The phosphogenesis in Raglan Harbour is here related to an episode of lowered sea-level, during which a paludal environment succeeded the estuarine, to be followed, in turn, by a positively and interlude. The subsequent rise of sea-level to its present position over the last 1600 years or so has reinstated the shore platform in its present intertidal situation. 相似文献
2.
High-temperature contact metamorphism at the contact of an alpine-typeultramafic intrusion is described. Permian spilitic volcanicsand tuffs within a zone about 750 yards in width are convertedto amphibolites and pyroxene hornfelses. In the amphibolitesthe colour of the amphibole changes from green to brown-greenand finally to deep brown at the contact. Two-pyroxene hornfelsesare developed at the contact, together with wollastonite, grossular,and hydrogrossular. Chemical changes in the amphiboles acrossthe contact aureole are: increase in (Na+ K) and (Al(6) + Fe+3+Ti) approaching the contact, and progressive decrease in thewater content. Similar chemical changes are noted in a lensof country rock included within the main ultramafic intrusion. It is considered that original high-temperature-contact effectsare often obscured by later Ca-metasomatism during serpentinizationof the ultramafic rocks, or by later tectonic deformation ofthe rocks which may involve movement of the ultramafic mass,as a relatively cold solid intrusion, to higher levels. 相似文献
1