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首页> 外文期刊>Journal of African Earth Sciences >Foraminiferal assemblages and geochemistry for interpreting the incidence of Early Toarcian environmental changes in North Gondwana palaeomargin (Traras Mountains, Algeria)
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Foraminiferal assemblages and geochemistry for interpreting the incidence of Early Toarcian environmental changes in North Gondwana palaeomargin (Traras Mountains, Algeria)

机译：有孔虫的组合和地球化学用于解释北部冈瓦纳古边缘（阿尔及利亚的特拉拉斯山脉）早期Toarcian环境变化的发生率

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摘要

The Early Toarcian was characterised by important environmental changes and a mass extinction event usually related to a global oceanic anoxic event. The analysis of ecostratigraphic fluctuations of foraminiferal morphogroups, elemental geochemical proxies and C and O stable isotopes of the Mellala section (Tlemcen Domain, North Algeria) makes it possible to determine the incidence of the anoxic event in this sector of the north Gondwana palaeomargin. The end of the Pliensbachian is characterised by a diverse foraminiferal assemblage with equilibrium species suggesting good oxygen and nutrient availability. The beginning of the Toarcian (Polymorphum Zone) evidences major changes in foraminifera with the disappearance of species, decreasing proportions of epifauna and shallow infauna, and fluctuations in diversity and dominance of Lenticulina toarcense and Lingulina tenera confirming a perturbation in the palaeoecological conditions in the sea-bottom. Redox proxies (Co/Al, Cr/Al and V/Al) with local maximum values suggest a decrease in oxygenation degree. A negative excursion of δ~(13)C is recorded right at the Polymorphum/Levisoni Zone boundary, and the subsequent disappearance of epifauna, decreasing diversity and abundance of foraminifera (foram/100 g) would be related to the accentuation of stressing conditions. Also at the Polymorphum/Levisoni Zone boundary, suboxic waters at the sea-bottom indicate the maximum values of redox proxies (Co/Al, Cu/Al, Cr/Al and V/Al). The upper part of the Levisoni Zone is more calcareous, with increasing diversity of shallow infauna and a decrease in potentially deep infauna related to more favourable conditions. The incidence of the Toarcian Oceanic Anoxic Event in this context was very low in comparison with the Saharan Basin (Raknet El Kahla section, Saharan Atlas), where a ben-thic barren interval, higher total organic carbon and redox proxies are recorded. The low incidence of the biotic crisis and the rapid recovery of assemblages in the Tlemcen Domain is compared with the high incidence and delayed recovery in the Saharan Basin, where the palaeogeography determined restricted water circulation between the Saharan Craton and the Oran Massif.
机译：早期Toarcian的特征是重要的环境变化和通常与全球海洋缺氧事件有关的大规模灭绝事件。对梅拉拉剖面（北部阿尔及利亚特莱姆森域）的有孔虫形态群，元素地球化学代理以及C和O稳定同位素的生态地层波动的分析，使得确定该区域北部冈瓦纳古边缘缺氧事件的发生成为可能。 Pliensbachian的末端的特征是有孔虫的多样性与平衡物种的组合，表明良好的氧气和养分利用率。 Toarcian（Polymorphum Zone）的开始表明，有孔虫的主要变化是物种消失，表生动物和浅层动物的比例降低以及Lenticulina toarcense和Lingulina tenera的多样性和优势地位的波动，这证实了海洋古生态条件的扰动-底部。具有局部最大值的氧化还原代理（Co / Al，Cr / Al和V / Al）表明氧合度降低。 δ〜（13）C的负偏移恰好出现在多形/ Levisoni区边界，随后表生动物的消失，有孔虫的多样性减少和丰富度（孔/ 100 g）与胁迫条件的加重有关。同样在多形体/ Levisoni区边界，海底的低氧水域显示了氧化还原代理的最大值（Co / Al，Cu / Al，Cr / Al和V / Al）。 Levisoni区的上部是钙质的，浅层动物的多样性增加，而与更有利条件相关的潜在深层动物的减少。与撒哈拉盆地（撒哈拉阿特拉斯的Raknet El Kahla剖面）相比，Toarcian海洋缺氧事件的发生率非常低，在撒哈拉盆地记录了本性贫瘠的间隔，较高的总有机碳和氧化还原代理。生物危机的低发生率和特莱姆森地区组合的快速恢复与撒哈拉盆地的高发生率和延迟恢复相比，撒哈拉盆地的古地理学决定了撒哈拉克拉通和奥兰断层之间的水循环受到限制。

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