Abstract

Four new high-precision U–Pb ash bed dates constrain the timing and rate of coal measures deposition in Tasmania and, combined with new palynological data, allow improved numerical age calibration of eastern Australian Late Triassic spore-pollen biozones. Felsic ashfall tuff beds are numerous in the middle and upper parts of the 400 m-thick Mount Nicholas Coal Measures of northeast Tasmania. Our four U–Pb CA-TIMS dates on zircon span 99 m of section and range from 222.52 to 217.84 Ma. All four dates are closely associated with palynomorph assemblages belonging to the Craterisporites rotundus Assemblage Zone. Our data indicate an age of at least 223 Ma, and likely several million years older, for our earliest observed C. rotundus Zone assemblages, whereas the base of the Polycingulatisporites crenulatus Zone may be ca 217 Ma (and no older than 217.84 Ma).

1. KEY POINTS

2. Felsic ash beds are common in the middle and upper parts of the Upper Triassic Mount Nicholas Coal Measures.

3. The ash beds have yielded four new U–Pb CA-TIMS dates on zircon that span 99 m of section and range from 222.52 to 217.84 Ma.

4. The new dates all lie within the upper part of the Craterisporites rotundus Assemblage Zone.

摘要

四个新的高精度 U-Pb 灰床日期限制了塔斯马尼亚煤沉积的时间和速率，并结合新的孢粉学数据，改进了澳大利亚晚三叠世东部孢粉生物区的数值年龄校准。塔斯马尼亚东北部 400 米厚的尼古拉斯山煤系的中部和上部有许多长英质凝灰岩层。我们在锆石上的四个 U-Pb CA-TIMS 日期跨越 99 m，范围从 222.52 到 217.84 Ma。所有四个日期都与属于Craterisporites rotundus组合区的孢粉组合密切相关。我们的数据表明，对于我们最早观察到的C. rotundus Zone 组合，它的年龄至少为 223 Ma，可能还要早几百万年，而Polycingulatisporites crenulatus区可能是CA 217马（与年龄不超过217.84 MA）。

1. 关键点

2. 长英质灰层常见于上三叠统尼古拉斯山煤系的中上部。

3. 灰层已经在锆石上产生了四个新的 U-Pb CA-TIMS 日期，跨越 99 m 的截面，范围从 222.52 到 217.84 Ma。

4. 新日期都位于Craterisporites rotundus Assemblage Zone的上部。