Subaerial speleothems and deep karst in central Sweden linked to Hirnantian glaciations
Subaerial speleothems and deep karst in central Sweden linked to Hirnantian glaciations
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DOI：
10.1144/jgs2014-071
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发表时间：
2015-03
影响因子：
2.7
通讯作者：
B. Kröger;J. R. Ebbestad;O. Lehnert;C. Ullmann;C. Korte;R. Frei;C. Rasmussen
中科院分区：
文献类型：
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作者：
B. Kröger;J. R. Ebbestad;O. Lehnert;C. Ullmann;C. Korte;R. Frei;C. Rasmussen
瑞典中部西尔扬地区的上卡蒂安博达泥土丘（奥陶纪）的石灰岩是深裂的。这些裂缝部分是同沉积的，并且经常衬有叠层石状的结壳。这些结壳是迄今为止唯一已知的陆上奥陶纪洞穴沉积物。他们到达深度达30米以下的前土堆顶部。从宏观上看，结壳形成分米大小的锥形圆顶状集合体、钟乳石和石笋。微组构和形态学鉴定它们为在黑暗环境中微生物介导的洞穴沉积物。结合Sr和C同位素值表明，形成的洞穴沉积物从大气沃茨没有显着的土壤层的影响。洞穴沉积物的δ 13 C全岩和腕足动物壳同位素数据首次精确地将其年龄限制在Hirnantian中期。博达泥土丘在Hirnantian重复和/或长期的陆上暴露是显而易见的喀斯特表面和早期水泥的丘盖碳酸盐。在赫南阶同位素碳漂移的时间窗内，洞穴沉积物和岩溶表面记录了估计的海平面下降80-130米的范围。这种大规模的回归与从冈瓦纳西部的部分推断出的最大冰盖范围相吻合。补充材料：所选腕足动物外壳的87 Sr/86 Sr同位素比和能量色散X射线光谱分析结果可从http://www.geolsoc.org.uk/SUP18809获得
The limestones of the upper Katian Boda mud mounds (Ordovician) of the Siljan district in central Sweden are deeply fractured. The fissures were partly synsedimentary and are often lined with stromatolite-like crusts. These crusts thus far are the only known subaerial Ordovician speleothems. They reach depths of up to 30 m below the former mound top. Macroscopically the crusts form decimetre-sized, cone-shaped domal aggregates, stalactites and stalagmites. Microfabric and morphology identify them as microbially mediated speleothems in a dark environment. Combined Sr and C isotope values indicate a formation of the speleothems from meteoric waters without influence of a significant soil horizon. For the first time the age of the speleothems can be precisely constrained by δ13C whole-rock and brachiopod shell isotope data to the mid-Hirnantian. Repeated and/or prolonged subaerial exposure of the Boda mud mounds during the Hirnantian is evident from karst surfaces and early cements in the mound capping carbonates. The speleothems and the karst surfaces record an estimated sea-level fall in the range of 80–130 m within the time window of the Hirnantian Isotopic Carbon Excursion. This massive regression coincides with maximum ice sheet extent inferred from sections in West Gondwana. Supplementary material: 87Sr/86Sr isotope ratio of selected brachiopod shells and results of Energy-dispersive-X-ray spectroscopy are available from http://www.geolsoc.org.uk/SUP18809