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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 >Chemical stratigraphy of lake deposits from the Kalkkop Impact Crater, South Africa, and its palaeoenvironmental significance
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Chemical stratigraphy of lake deposits from the Kalkkop Impact Crater, South Africa, and its palaeoenvironmental significance

机译：kalkkop冲击火山口的湖泊沉积物化学层层，南非及其古环境意义

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摘要

The 650 m wide Kalkkop meteorite impact crater is situated in the Karoo, ~51 km southwest of Graaff-Reinet, South Africa. A core drilled through the centre of the crater passes through 89 m of variously laminated and massive, carbonates that overlie brecciated sandstone and shale of the Beaufort Group. Kalkkop has been previously dated at ~250 Ka using the U-Th method, similar in age to the Tswaing Crater, 40 km northwest of Pretoria. However, the inferred crater rim at Kalkkop has been almost entirely eroded and, given the low regional erosion rates (<4 m/million years), would appear to be much older than Tswaing. The carbonates are dominated by dolomite in the upper 35 m and by calcite below 35 m. Carbonate δ~(18)O values vary between -3.85 and 6.64‰ (relative to PDB), and generally increase upwards. These data are consistent with precipitation from water ranging in δ~(18)O between -3‰ (typical of meteoric water) at the base, and ~+5‰ (typical of highly evaporated water) in the upper part of the succession. The lower part of the succession shows a strong correlation between δ~(13)C and δ~(18)O values, suggesting non–equilibrium precipitation during periods of high evaporation rate. The upper part shows no correlation between δ~(13)C and δ~(18)O, which is consistent with equilibrium between the carbonates and the lake water, suggesting that recharge of water became more continuous. The Kalkkop Crater carbonates have great potential as a proxy for past climate, but first a detailed dating study is required.
机译：650米宽的Kalkkop陨石冲击枪口位于卡卢，南非格拉夫重新集团西南〜51公里。通过火山口中央钻的芯通过89米各种层压和巨大的碳酸盐，覆盖Beaufort群体的已封堵砂岩和页岩。 Kalkkop先前已经在〜250 kA日期使用了U-Th方法，同样在于TWAING CRATER，比勒陀利亚西北40公里。然而，Kalkkop的推断式火山口轮几乎完全被侵蚀，鉴于区域侵蚀率低（<4米/万年），似乎比TSWAING大得多。碳酸盐由白云石在上35米的含量和低于35米以下的核石石。碳酸盐δ〜（18）o值在-3.85和6.64‰之间（相对于PDB）变化，并且通常向上增加。这些数据与在碱基的-3‰（典型的Meeic水）之间的δ〜（18）O中的水沉淀，并且在继承的上部〜+ 5‰（典型的高度蒸发水）。继承的下部显示δ〜（13）C和δ〜（18）o值之间的强相关性，表明在高蒸发速率期间的非平衡沉淀。上部显示δ〜（13）C和δ〜（18）o之间的相关性，这与碳酸盐和湖水之间的平衡一致，表明水的充电变得更加连续。 Kalkkop Crater碳酸酯具有巨大的潜力作为过去的气候的代理，但首先需要详细的约会研究。

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