Precise U–Pb age constraints for end-Triassic mass extinction, its correlation to volcanism and Hettangian post-extinction recovery
Precise U–Pb age constraints for end-Triassic mass extinction, its correlation to volcanism and Hettangian post-extinction recovery
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DOI：
10.1016/j.epsl.2007.11.031
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发表时间：
2008-03
影响因子：
5.3
通讯作者：
U. Schaltegger;J. Guex;A. Bartolini;B. Schoene;M. Ovtcharova
中科院分区：
文献类型：
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作者：
U. Schaltegger;J. Guex;A. Bartolini;B. Schoene;M. Ovtcharova
提出了三叠系—侏罗系（rhetian—hettangian）和hettangian—sinemurian界线的锆石U-Pb精确年龄。通过对秘鲁北部Utcubamba山谷Aramachay组Pucara组火山灰层中单个化学磨损锆石的ID-TIMS定年获得了年龄。位于确定边界的菊石最后一次和第一次出现之间的灰分层产生的206pb /238U年龄分别为201.58±0.17/0.28 Ma （95% c.l，不确定度分别为无/有衰变常数误差）和199.53±0.19 / 0.29 Ma （hettan - sinemurian界线）。前者建立在三叠纪最上层chistoceras属最后一次局部产状的1 m以上的凝灰岩上，而Hettangian属Psiloceras则位于5 m以下。后者的样品来自加拿大八斗峡地层中采集的凝灰岩。我们的新时代记录了赫塔纪的总持续时间不超过2万年，这对解释三叠纪最顶端灭绝后菊石恢复的意义具有根本意义。U-Pb年龄比中大西洋岩浆省（CAMP）洪水玄武岩的40ar - 39ar年龄老0.8±0.5%。考虑到人们普遍接受的假设，即40k衰变常数或物理常数的不准确性在两种测年方法之间造成了类似的偏差，我们对T/J边界的新的U-Pb锆石年龄测定证实了CAMP是在同一时间放置的假设，并且可能是主要气候转换和大灭绝的原因。T/J界锆石206pb /238U年龄略早于北山玄武岩（Newark Supergroup, Nova Scotia, Canada）的201.27±0.06 Ma [Schoene et al., 2006]。Geochim。Cosmochim。[j].中国科学：自然科学。重要的是寻找更早的CAMP喷发，并通过U-Pb技术精确地确定它们的日期，同时解决所有系统性不确定性的来源，以进一步验证火山引起的气候变化导致灭绝的假设。这种高精度、高精度的数据将有助于在100万年的水平上限制地质事件的同时代性。
New precise zircon U–Pb ages are proposed for the Triassic–Jurassic (Rhetian–Hettangian) and the Hettangian–Sinemurian boundaries. The ages were obtained by ID-TIMS dating of single chemical-abraded zircons from volcanic ash layers within the Pucara Group, Aramachay Formation in the Utcubamba valley, northern Peru. Ash layers situated between last and first occurrences of boundary-defining ammonites yielded206Pb/238U ages of 201.58±0.17/0.28 Ma (95% c.l., uncertainties without/with decay constant errors, respectively) for the Triassic–Jurassic and of 199.53±0.19 / 0.29 Ma for the Hettangian–Sinemurian boundaries. The former is established on a tuff located 1 m above the last local occurrence of the topmost Triassic genus Choristoceras, and 5 m below the Hettangian genus Psiloceras. The latter sample was obtained from a tuff collected within the Badouxia canadensis beds. Our new ages document total duration of the Hettagian of no more than c. 2 m.y., which has fundamental implications for the interpretation and significance of the ammonite recovery after the topmost Triassic extinction. The U–Pb age is about 0.8±0.5% older than40Ar–39Ar dates determined on flood basalts of the Central Atlantic Magmatic Province (CAMP). Given the widely accepted hypothesis that inaccuracies in the40K decay constants or physical constants create a similar bias between the two dating methods, our new U–Pb zircon age determination for the T/J boundary corroborates the hypothesis that the CAMP was emplaced at the same time and may be responsible for a major climatic turnover and mass extinction. The zircon206Pb/238U age for the T/J boundary is marginally older than the North Mountain Basalt (Newark Supergroup, Nova Scotia, Canada), which has been dated at 201.27±0.06 Ma [Schoene et al., 2006. Geochim. Cosmochim. Acta 70, 426–445]. It will be important to look for older eruptions of the CAMP and date them precisely by U–Pb techniques while addressing all sources of systematic uncertainty to further test the hypothesis of volcanic induced climate change leading to extinction. Such high-precision, high-accuracy data will be instrumental for constraining the contemporaneity of geological events at a 100 kyr level.