Abstract The Toarcian Oceanic Anoxic Event (TOAE) is characterised by a perturbation of the global carbon cycle and the widespread deposition of organic matter (OM)-rich strata/sediments in the northern areas of the West Tethys Shelf, in several northern European epicontinental basins. Contrariwise, in the southern areas of the West Tethys Shelf such as western and southern Iberian, and northern Gondwana margins, OM-rich strata/sediments are spatially and temporally restricted. To better understand the relationship between OM production, depositional conditions, and palaeoceanographic controls on the occurrence of OM-rich facies in the northern Iberian margin, we collected and analysed 18 samples from the Rodiles section (Asturian Basin) for geochemical (total organic carbon-TOC, total sulfur-TS, δ13CKerogen, and δ13CWood) and palynofacies analysis. The studied upper Pliensbachian–lower Toarcian succession has TOC values reaching up to 2.9 wt%. The relative dominance of non-opaque phytoclasts and the δ13CKerogen values (average of ~ −24‰) in the lowermost Toarcian (Tenuicostatum Zone) agrees with previous interpretations indicating that this area was located in a dominantly winter-wet climate zone. A change in the kerogen assemblages is observed at the Tenuicostatum/Serpentinum zones boundary (onset of TOAE), related to an increase in amorphous OM (AOM). A slight increase in non-opaque phytoclasts and terrestrial palynomorphs, and a negative δ13CKerogen excursion (reaching −31.5‰) is recorded in the same interval. These observations suggest a increase in continental weathering and fluvial runoff associated with more humid conditions, likely resulting in increased superficial productivity and deposition and preservation of OM under, at least, suboxic conditions. Above the TOAE interval, the δ13CKerogen record (values around −24‰) and the drastic drop in TOC and AOM content indicate that bottom water oxygenation improved after the TOAE. Our results demonstrate a link between early Toarcian climate dynamics and the deposition of OM-rich strata/sediments.

中文翻译：

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阿斯图里亚斯盆地（西班牙北部）最上层 Pliensbachian-Lower Toarcian 序列的干酪根组合和 δ13CKerogen

摘要 Toarcian 大洋缺氧事件 (TOAE) 的特点是全球碳循环的扰动和西特提斯大陆架北部地区的富含有机质 (OM) 的地层/沉积物的广泛沉积，在几个北欧大陆盆地. 相反，在西特提斯大陆架的南部地区，如伊比利亚西部和南部以及冈瓦纳大陆边缘，富含 OM 的地层/沉积物在空间和时间上受到限制。为了更好地了解 OM 产生、沉积条件和古海洋学控制与伊比利亚北部边缘富含 OM 相的发生之间的关系，我们收集并分析了来自 Rodiles 剖面（阿斯图里亚斯盆地）的 18 个样品的地球化学（总有机碳- TOC、总硫-TS、δ13CKerogen、和δ13CWood）和孢粉相分析。研究的上 Pliensbachian-下 Toarcian 序列的 TOC 值高达 2.9 wt%。Toarcian (Tenuicostatum 区) 最低处的非不透明植株的相对优势和 δ13CKerogen 值（平均 ~ -24‰）与先前的解释一致，表明该地区位于主要的冬季潮湿气候区。在 Tenuicostatum/Serpentinum 区域边界（TOAE 开始）观察到干酪根组合的变化，这与无定形 OM (AOM) 的增加有关。在同一时间间隔内，非不透明植株和陆生孢粉体略有增加，δ13CKerogen 负偏移（达到-31.5‰）。这些观察结果表明，与更潮湿的条件相关的大陆风化和河流径流增加，可能导致至少在缺氧条件下增加表面生产力以及 OM 的沉积和保存。在 TOAE 间隔之上，δ13CKerogen 记录（值约为 -24‰）以及 TOC 和 AOM 含量的急剧下降表明，TOAE 后底水氧合有所改善。我们的结果表明，早期托阿尔克纪气候动力学与富含有机质的地层/沉积物的沉积之间存在联系。