Paleomagnetic dating of ironstone nodules (‘nuts’) from the Yowah opal field, central southern Queensland
Paleomagnetic dating of ironstone nodules (‘nuts’) from the Yowah opal field, central southern Queensland
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昆士兰州中南部 Yowah 蛋白石田铁矿石结核（“坚果”）的古地磁测年
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发表时间：
2017
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通讯作者：
B. Dickson
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作者：
P. Schmidt;B. Dickson
为了确定澳大利亚蛋白石形成的年龄，我们对来自昆士兰州Yowah的氧化铁石“坚果”进行了古地磁研究。根据标准方法，我们计算出赤纬D = 191.4°，倾角I = 61.7°（α95 = 4.0°）的平均方向，表明在纬度λp = 71.3°S，经度ϕp = 119.4°E （A95 = 5.3°）处的古磁极位置。方向包括正极性和反极性，它们无法通过反转测试，很可能是由于受到最近/现在的小分量的污染。平均方向不应受到显著影响。通过与澳大利亚东部新生代岩石的古磁极、全球移动热点参考系的磁极和北美新生代磁极路径进行卡方比较，得出的平均年龄估计为35±7 Ma，即始新世晚期至渐新世早期。这被解释为铁石形成的年龄，这为珍贵的耶和华蛋白石的形成提供了最大的年龄。这一结果证实并确定了附近卡纳韦风化剖面的年龄。
ABSTRACT To constrain the age of Australian opal formation, we have undertaken a paleomagnetic study of oxidised ironstone ‘nuts’ from Yowah, Queensland. Following standard methods, we have calculated a mean direction of declination D = 191.4°, inclination I = 61.7° (α95 = 4.0°), indicating a paleomagnetic pole position at latitude λp = 71.3°S, longitude ϕp = 119.4°E (A95 = 5.3°). The direction comprises both normal and reverse polarities that fail a reversal test most probably owing to contamination by small recent/present-day components. The mean direction should not be significantly affected. A chi-square comparison with paleomagnetic poles for dated Cenozoic rocks in eastern Australia, poles derived from the Global Moving Hotspot Reference Frame and the Cenozoic pole path for North America, appropriately transferred to Australian coordinates, yields a mean age estimate of 35 ± 7 Ma, i.e. late Eocene to early Oligocene. This is interpreted as the age of the ironstone formation, which places a maximum age for the formation of precious Yowah opal. This result confirms and tightens the age for the nearby Canaway weathered profile.