Abstract The objective of this study is to investigate the relationship between early Toarcian climatic events and the composition of kerogen assemblages in the Lusitanian Basin (Portugal). In particular, we aim to understand how the Pliensbachian–Toarcian Event (Pl–Toa Event) and Toarcian Oceanic Anoxic Event (TOAE) affected the continental areas of the western Iberian margin and how possible variations in continental sources of organic matter (OM) were expressed in marginal-marine and hemipelagic depositional environments during the early Toarcian. We present here a characterisation [total organic carbon (TOC), total sulphur (TS), δ13C in kerogen concentrate (δ13CKerogen), and palynofacies] of kerogen assemblages from several uppermost Pliensbachian (emaciatum ammonite Zone)–lower Toarcian sections in the Lusitanian Basin (western Iberian margin), including the Peniche section, which contains the Toarcian GSSP. In all sections, TOC concentration is low (average 0.4 wt.%), with the highest values reaching up to 2.1 wt.% in a discrete level located approximately 10.5 m above the base of the levisoni Zone at Peniche. The TOAE negative carbon isotope excursion is observed in kerogen concentrate at the base of the levisoni Zone throughout the basin. Palynofacies analysis demonstrates that the kerogen assemblages are mostly of terrestrial affinity, with the dominance of the Phytoclast Group and terrestrial palynomorphs, and with punctual increases in amorphous organic matter, freshwater (e.g. Botryococcus sp.) and marine microplankton (dinoflagellate cysts, acritarchs, and prasinophyte algae) in specific stratigraphic intervals. A change in palynofacies assemblages associated with the TOAE is observed around the base of levisoni Zone. Although with slight differences between sections, the TOAE interval records an increase in non-opaque, translucent, phytoclasts (NOP) and cuticle fragments, and is also associated with an increased contribution of terrestrial palynomorphs (increase in sporomorphs and Classopollis in tetrads and agglomerates) and decrease in marine palynomorphs. The increases in NOP and terrestrial palynomorphs support the postulated enhancement of the hydrological cycle and increased export of terrestrial OM into marine environments during the early Toarcian, especially during the TOAE, in the western Iberian margin. Understanding the impact of the early Toarcian climatic events on land-based ecosystems may provide important insights into current climate change.

中文翻译：

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卢西塔尼亚盆地（葡萄牙）的沉积有机质与托阿尔阶早期环境变化

摘要 本研究的目的是调查早期托阿尔克纪气候事件与卢西塔尼亚盆地（葡萄牙）干酪根组合组成之间的关系。特别是，我们旨在了解 Pliensbachian-Toarcian 事件（Pl-Toa 事件）和 Toarcian 海洋缺氧事件（TOAE）如何影响伊比利亚西部边缘的大陆地区，以及大陆有机质来源（OM）的可能变化是如何发生的。 Toarcian 早期在边缘海洋和半远洋沉积环境中表达。我们在此展示了一个表征 [总有机碳 (TOC)、总硫 (TS)、干酪根精矿中的 δ13C (δ13CKerogen)，和孢粉相] 来自 Lusitanian 盆地（伊比利亚西部边缘）的几个最上层 Pliensbachian（emaciatum 菊石带）-下 Toarcian 剖面的干酪根组合，包括包含 Toarcian GSSP 的 Peniche 剖面。在所有剖面中，TOC 浓度都很低（平均 0.4 wt.%），最高值在位于 Peniche levisoni 区底部上方约 10.5 m 的离散水平上达到 2.1 wt.%。在整个盆地 levisoni 带底部的干酪根浓缩物中观察到 TOAE 负碳同位素偏移。孢粉相分析表明干酪根组合大多具有陆生亲和性，其中植株群和陆生孢粉体占优势，无定形有机物、淡水（如葡萄球菌属）的准时增加。) 和海洋微型浮游生物（甲藻囊肿、acritarchs 和 prasinophyte 藻类）在特定的地层间隔。在 levisoni 带底部周围观察到与 TOAE 相关的孢粉相组合的变化。尽管各部分之间略有差异，但 TOAE 间隔记录了非不透明、半透明、植株破碎 (NOP) 和角质层碎片的增加，并且还与陆地孢粉形的贡献增加有关（四分体和团聚体中孢子形和 Classopollis 的增加）和海洋孢粉型的减少。NOP 和陆地孢粉体的增加支持了水文循环增强和陆地 OM 在早期 Toarcian 期间向海洋环境的输出增加的假设，特别是在 TOAE 期间，在伊比利亚西部边缘。