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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 >Unusual speleothem formation in the Thabazimbi mine cave, Limpopo Province, South Africa, and its chronology
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Unusual speleothem formation in the Thabazimbi mine cave, Limpopo Province, South Africa, and its chronology

机译：Thabazimbi矿山，林帕省，南非及其年表的不寻常的斯派比姆形成

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摘要

An unusual cave is located in the hills southeast of the town of Thabazimbi in the Limpopo Province. This cave, a Vshaped shallow chamber measuring 110 x 40 m, was discovered serendipitously when an adit was driven into the hill in connection with iron ore mining. It has no natural entry point and no externally derived sediment is found in it. It is situated within the upper part of the Malmani Subgroup and although it was formed as a solution cavity, requiring a phreatic environment, dripwater flow must subsequently have been low: no large speleothems (stalactites, stalagmites or flowstones) were ever formed in the cave. Instead, evaporation produced crystallictitic frostwork bushes consisting of aragonite (metastably grown due to enhanced Mg-content) which were in part redissolved followed by the secondary formation of calcite corals and encrustations. This sequence of events can be understood in the context of an enclosed cave where the CO_2 content of the air is high. U/Th disequilibrium dating of two aragonite frostwork samples from the cave yielded two very different ages (155.1 ± 7.4 and 67.2 ± 3.4 ka), thus showing that the formation of this type of frostwork occurred (probably episodically) over a long period of time. The two dates broadly coincide with the waning stages of periods of low total inorganic carbon (TIC) as well as high clastic input in the Tshwaing crater sediment record, both indicating enhanced rainfall at that locality. The younger age coincides with a brief negative excursion in chlorine content and a positive potassium anomaly at Tshwaing, both also indicating high rainfall. However, both ages are also coeval with glacial maxima, thus underlining earlier observations from the Tshwaing record that in southern Africa, wet periods are not necessarily coeval with northern hemisphere interglacials.
机译：一个不寻常的洞穴位于林帕齐省塔巴尼亚省镇东南部的山丘。该洞穴，在与铁矿石开采的山上被驱动到山上时，在山上被发现了一个v鱼浅腔室。它没有自然的入口点，它没有发现外部衍生的沉积物。它位于Malmani亚组的上部，虽然它形成为溶液腔，但需要潜水环境，随后必须低：在洞穴中没有形成大的Spelehems（钟乳石，石笋或流动石） 。相反，蒸发产生的结晶霜衬衫，其由基石（由于增强的Mg含量导致的长期生长）组成，其部分重新溶解，然后是方解石珊瑚和结壳的二次形成。在封闭洞穴的上下文中可以理解这种事件序列，其中空气的CO_2含量高。来自山坡的两个玻璃石霜样品的U / Th不平衡约会产生两个非常不同的年龄（155.1±7.4和67.2±3.4 ka），从而在很长一段时间内发生这种类型的霜工厂（可能是剧本）的形成。这两个日期与低总无机碳（TIC）的衰退阶段宽泛一致，以及TSHWAING火山口沉积物记录中的高碎屑输入，两者都指示该地方的降雨增强。较年轻的年龄与氯含量的短暂消极偏移和Tshwaing的阳性异常，两者也表明降雨量。然而，两年龄段也是冰川最大值的群体，从而强调了从Tshwaing记录中的早期观察，即在南部非洲，潮湿的时期不一定与北半球外夹的共同。

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