Reinterpreting the age of the uppermost 'Old Red Sandstone' and Early Carboniferous in Scotland
Reinterpreting the age of the uppermost 'Old Red Sandstone' and Early Carboniferous in Scotland
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重新解释苏格兰最上面的“老红砂岩”和早石炭世的年龄
DOI：
10.1017/s1755691018000968
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发表时间：
2019
影响因子：
1.2
通讯作者：
MARSHALL J
中科院分区：
文献类型：
--
作者：
MARSHALL J
在苏格兰，传统上将巴拉甘组的底部置于相邻的晚泥盆世至石炭纪序列中的第一层灰色泥岩处。该惯例将泥盆纪-石炭纪界线置于老红砂岩（ORS）Kinnesswood地层内。这一位置的结果是，来自巴拉根组的四足动物被确定为晚图尔奈期，而在金尼斯伍德组发现的典型泥盆纪鱼类的范围一直持续到石炭纪。Pease Bay的Remigolepis鱼标本来自Kinnesswood地层。与格陵兰岛的范围相比，以孢子为标准，显示它的年龄是法门期的。在伯恩茅斯从Ballagan组底部采集的详细的孢粉学样品证明存在早期Tournaisian孢子带（VI和HD + Cl 1）。在大部分演替过程中出现的Schopfites物种是Schopfites delicatus而不是Schopfites claviger。后者的物种定义晚Tournaisian CM孢子带。在Ballagan组（普雷斯顿，Whiteadder Water）下的上'ORS'地层中发现的第一个孢子组合包含Retispora lepidophyta，来自早最晚的Famennian LL孢子带。孢子样品与火山碎屑互层，这表明凯尔索火山岩组的部分年龄是最晚的早期法门期。这些发现表明，Ballagan组包括大部分的Tournaisian与泥盆纪-石炭纪的边界定位接近Kinnesswood组的顶部。皮斯湾第6阶段的钙质结砾岩可以与Carham的相应剖面相关联，表明它代表了一个相当于最新法门期冰川作用的时间间隔。重要的是，最近描述的一些巴拉甘组四足动物比以前的年龄更老，现在填补了罗默缺口的关键早期部分。
In Scotland, the base of the Ballagan Formation has traditionally been placed at the first grey mudstone within a contiguous Late Devonian to Carboniferous succession. This convention places the Devonian–Carboniferous boundary within the Old Red Sandstone (ORS) Kinnesswood Formation. The consequences of this placement are that tetrapods from the Ballagan Formation were dated as late Tournaisian in age and that the ranges of typically Devonian fish found in the Kinnesswood Formation continued into the Carboniferous. The Pease Bay specimen of the fish Remigolepis is from the Kinnesswood Formation. Comparisons with its range in Greenland, calibrated against spores, show it was Famennian in age. Detailed palynological sampling at Burnmouth from the base of the Ballagan Formation proves that the early Tournaisian spore zones (VI and HD plus Cl 1) are present. The Schopfites species that occurs through most of the succession is Schopfites delicatus rather than Schopfites claviger. The latter species defines the late Tournaisian CM spore zone. The first spore assemblage that has been found in Upper ‘ORS' strata underlying the Ballagan Formation (Preston, Whiteadder Water), contains Retispora lepidophyta and is from the early latest Famennian LL spore zone. The spore samples are interbedded with volcaniclastic debris, which shows that the Kelso Volcanic Formation is, in part, early latest Famennian in age. These findings demonstrate that the Ballagan Formation includes most of the Tournaisian with the Devonian–Carboniferous boundary positioned close to the top of the Kinnesswood Formation. The Stage 6 calcrete at Pease Bay can be correlated to the equivalent section at Carham, showing that it represents a time gap equivalent to the latest Famennian glaciation(s). Importantly, some of the recently described Ballagan Formation tetrapods are older than previously dated and now fill the key early part of Romer's Gap.