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首页> 外文期刊>South African Journal of Geology: Being the Transaction of the Geological Society of South African: Syndie die Verhandelinge van die Geologiese Vereniging van Suid-Afrika >Early diagenetic signals archived in black shales of the Dwyka and Lower Ecca Groups of the southern Karoo Basin (South Africa): Keys to the deglaciation history of Gondwana during the Early Permian, and its effect on potential shale gas storage
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Early diagenetic signals archived in black shales of the Dwyka and Lower Ecca Groups of the southern Karoo Basin (South Africa): Keys to the deglaciation history of Gondwana during the Early Permian, and its effect on potential shale gas storage

机译：早期成岩信号存档在Dwyka的黑色Shales和南方卡卢盆地（南非）的下射群组：初级久坐地区的击晕历史，其对潜在页岩储气的影响

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During the final glaciation and following melting across the Carboniferous/Permian boundary, southern Gondwana experienced an icehouse to greenhouse transition at a relatively high palaeolatitude (ca. 60°). Sediments deposited from around 300 to 280 Ma in the southern Karoo Basin are archives of this transition, but the evolution of their links to the flanking oceans is still a matter of debate. The aim here is to detail the deglaciation history by simulating early diagenetic processes both under melt and marine water conditions. For this, black shale core samples from three wells, which were drilled in the 1960s through the Lower Ecca Group into the Dwyka Group,were analysed for TOC contents, mineralogical composition and textural properties. The data allow extrapolations about the depositional mineralogy and early diagenesis that in turn serve as input parameters for hydrogeochemical models. The imaging and modelling results reveal that the organic carbon-lean shales associated with, and directly overlying the diamictite beds of the Dwyka Group (known as the Prince Albert Formation) can be interpreted as rhythmites (varves?) deposited under freshwater conditions in response to the deglaciation across southern Gondwana during the latest Carboniferous (~300 to 280 Ma). Thereafter, in the early Permian (~280 Ma) the first notable marine influence is revealed by the occurrence of Mg-bearing carbonate precipitates in black shales of the Whitehill Formation of the overlying Lower Ecca Group; and from the hydrogeochemical models. Preferential preservation of organic matter in these shales is interpreted to be due to marine water fluctuations from the south that created stratified water columns of dense anoxic cold bottom systems overlain by lighter freshwater. Directly above the Whitehill Formation, Mn-siderite in rhythmites of the Collingham Formation points to a recurring influx of fresh water from the north. Today, the black shales of the Lower Ecca Group are tight,
机译：在最终冰川期间和在融化石炭系/二叠纪边界之后，南吉瓦纳经历了冰水屋在相对较高的古代壮观（约60°）的温室过渡。沉积物在南方卡卢盆地沉积在大约300至280 mA中，是这种过渡的档案，但他们与侧翼海洋的连接的演变仍然是一个辩论的问题。这里的目的是通过模拟熔融和海水条件下的早期成岩工艺来详细说明亡血史。为此，分析了来自三个孔的黑页岩核心样本，在20世纪60年代钻入DWYKA组，分析了TOC含量，矿物学组成和纹理性质。数据允许关于沉积矿物学和早期成岩的外推，这反过来用作水文地造型模型的输入参数。成像和建模结果表明，与淡水条件下沉积的节奏（变化α）解释为有机碳 - 瘦菌，并直接覆盖DWYKA组（称为亚伯特王子粒子）的有机碳瘦蚊子（称为亚伯特王子粒子）。最新的石炭系（〜300至280 mA）期间，南部南部南部的令人沮丧。此后，在早期的二叠纪（〜280mA）中，第一个显着的海洋影响通过覆盖的下ECCA组的白蓟填充的黑色页岩中含有Mg的碳酸盐沉淀物的发生;并从水文层上的模型。这些节宝中有机物质的优先保护被解释为由于南部的海洋水波动，由较轻的淡水覆盖着偏心的贫砷冷底部系统的分层水柱。直接在白蓟地层上方，Collingham形成的节奏中的Mn-Siderite指向从北方的淡水的重复涌入。今天，下ECCA组的黑色HALES紧张，

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