Molecular organic geochemistry of a proposed stratotype for the Oxfordian/Kimmeridgian boundary (Isle of Skye, Scotland)
Molecular organic geochemistry of a proposed stratotype for the Oxfordian/Kimmeridgian boundary (Isle of Skye, Scotland)
复制标题
牛津阶/启默里阶边界（苏格兰斯凯岛）拟议层型的分子有机地球化学
作者：
Apolline Lefort;Y. Hautevelle;B. Lathuilière;Vincent Huault
摘要首次报道了苏格兰斯凯岛牛津纪-基默里期浮游页岩段的可溶有机质组成。斯塔芬湾以北的岩石海岸上，连续不断地暴露着粉质粘土和多节石灰岩岩层。这一层序被认为是牛津期和基默里期之间界线的潜在层型。本文指出了有机质的特殊保存和极低的热降解。事实上，分子组成的特征是丰富的不饱和生物标志物(霍普烯和非甾烯)以及未受损的生物萜类化合物(铁锈醇和糖醇)。长链正构烷烃的丰度以奇偶优势为特征，表明大陆贡献占主导地位。相对较高的植物生物标志物(如铁锈醇、糖醇、杜仲烯和残烯)也证明了这一点，这表明在最近出现的陆地上，古植被主要由针叶植物组成，特别是柏科、杉科和白蜡草科。沉积环境的水柱上部为含氧水体，下部为缺氧水体。有机质的组成沿浮游页岩段变化不大。换句话说，不能从这些沉积岩的分子含量中推断出任何演化事件或古环境的剧烈变化，这也不允许我们支持牛津/基默吉期界线在序列中的准确位置。
Abstract The composition of the soluble organic matter of the Oxfordian–Kimmeridgian Flodigarry Shale Member (Isle of Skye, Scotland) is presented for the first time. A continuous succession of silty clays and nodular limestone beds is exposed on a rocky shore to the north of Staffin Bay. This succession is proposed as a potential stratotype of the boundary between the Oxfordian and Kimmeridgian stages. This paper points out the exceptional preservation and very low thermal degradation of the organic matter. Indeed, the molecular composition is characterized by the abundance of unsaturated biomarkers (hopenes and diasterenes) as well as undamaged bioterpenoids (ferruginol and sugiol). The abundance of long-chain n-alkanes characterized by an odd-over-even predominance reveals a dominant continental contribution. This is also attested to by the relatively high amounts of plant biomarkers (e.g. ferruginol, sugiol, cadalene and retene), which suggest a palaeovegetation largely composed of pinophytes, especially Cupressaceae, Taxodiaceae and Cheirolepidiaceae, on the nearest emerged lands. The water column of the depositional environment was oxic in its upper part and rather dysoxic in its lower part. The composition of the organic matter does not significantly change along the Flodigarry Shale Member. In other words, no evolutionary events or drastic change in palaeoenvironments can be deduced from the molecular content of these sedimentary rocks, and it does not allow us to support a precise location for the Oxfordian/Kimmeridgian boundary in the succession.