摘要:
滇中地区中元古代昆阳群因民组以碎屑岩为主,内发育典型的风暴沉积构造 (包括渠铸型、丘状交错层理和洼状交错层理、递变层理等 )。风暴沉积主要包括 4种岩相类型 :A -具口袋构造的递变层理砂岩段。B -具丘状或洼状交错层理的砂岩段。C -具均质层理的粉砂岩、泥质岩段。D -具水平层理的泥质岩段。上述岩相A、B、C分别代表风暴流作用 -风暴浪作用 -风暴后期的快速悬浮沉积 (事件沉积 ),D代表风暴过后缓慢悬浮沉积 (背景沉积 ),它们组合成不同的风暴沉积序列。滇中地区昆阳群风暴沉积的发现表明中元古代大气圈、水圈及其相互作用与现今近似;中元古代滇中地区位于低纬度 (5 - 30°)的风暴作用带。该沉积对于解释因民组递变层砂岩的成因、证实昆阳群的地层层序也具有重要意义。
关键词:
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风暴岩 /
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风暴沉积 /
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中元古代 /
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昆阳群 /
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云南省
Abstract:
Kunyang Group of Mesoproterozoic in central Yunnan province consists of 4 Formations: Yinmin Formation, Luoxue Formation, Etouchang Formation and Luzhi j iang Formation. Yinmin Formation is composed of clastic stone with the sedimenta ry structures developed characteristically in storm deposits, which includes gut ter casts, hummocky or sunken cross bedding, and graded bedding. The storm depos its consist of 4 types of lithofacies: a-sandstone with gutter casts and graded bedding, b-sandstone with hummocky or sunken cross bedding, c-siltstone and muds tone with homogeneous bedding, and d-argillite with horizontal bedding. These l ithofacies represent respectively deposits of storm current (a), deposits of sto rm wave(b), rapid suspended sediment (event deposits, c) and slow suspended sed iment (background deposits, d). These lithofacies constitute various sedimentary sequences of storm deposits. Sequence 1 is an assemblage upward of graded sands tone with gutter casts, sandstone with hummocky or sunken cross bedding, siltsto ne and mudstone with homogeneous bedding, and argillite with horizontal bedding. Sequence 2 is of graded sandstone with scouring casts, sandstone with parallel bedding, sandstone with wave ripple cross bedding and siltstone and mudstone wit h homogeneous bedding and horizontal bedding. Sequence 3 is of sandstone with hu mmocky or sunken cross bedding, fine sandstone with wave ripple cross bedding, a nd siltstone and mudstone with homogeneous bedding and horizontal bedding. The d iscovery of tempestite in Yinmin Formation, Kunyang Group of Mesoproterozoic in central Yunnan province reflects that the atmosphere, hydrosphere and their inte raction in Mesoprotozoic are similar to those in nowadays. The central Yunnan Pr ovince in Mesoprotozoic located in the area of low latitude（5°～30°） where deve loped storm. Meanwhile,the discovery of the storm deposits has important significance to explain the genesis of the sandstone with grade bedding and interpret the sequence of Kunyang Group.
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