Abstract The Canadon Asfalto continental Basin preserves terrestrial deposits interbedded with volcanic rocks, providing a unique opportunity for palaeoenvironmental reconstructions of the Jurassic continental realm. This study presents a sedimentological, mineralogical, and geochemical analysis of three lacustrine successions in the Cerro Condor area of the Canadon Asfalto Basin, Argentina. New CA ID-TIMS U–Pb data from tuffaceous deposits indicate a late Toarcian age (179.481 ± 0.059, 179.41 ± 0.13, and 177.27 ± 0.40 Ma), suggesting that the palaeolakes developed contemporaneously to the Chon Aike volcanic activity. The sedimentary successions are composed of carbonate, organic matter-rich mudstone — with up to 8 wt% total organic carbon (TOC) content — sandstone and conglomerate, all with an important contribution of volcanic and volcanogenic material. The clay mineral assemblage dominated by corrensite (chlorite-vermiculite mixed layers), smectite and vermiculite is likely related to hydrothermal activity and alteration of volcanic material, rather than to change in weathering processes and climate. Organic matter preserved in the sedimentary successions has a lacustrine and terrestrial/reworked origin. Changes in the source of carbon dioxide (CO2) and in the type and/or degree of preservation of the organic matter had a major impact on the δ13Corg values. This further exemplifies the necessity to evaluate the influence of the depositional environment before interpretation of the organic carbon isotope records. The combined high phosphorus and TOC contents suggest that episodes of increased nutrient availability into the basin enhanced lacustrine primary productivity, which favoured the development of oxygen-depleted conditions bottom waters and ultimately organic matter preservation and burial. High Corg/Ptot ratios indicate that phosphorus was likely released back into the water column in a positive feedback loop, further sustaining primary productivity. This study provides an important clue to understand the palaeoenvironmental conditions prevailing on land during the late Toarcian and on how volcanism exerted a control on the depositional conditions.

中文翻译：

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Toarcian 晚期大陆古环境条件：以阿根廷南部 Cañadón Asfalto 组为例

摘要 加拿大阿斯法尔托大陆盆地保存着火山岩互层的陆相沉积，为侏罗纪大陆域的古环境重建提供了独特的机会。本研究对阿根廷 Canadon Asfalto 盆地的 Cerro Condor 地区的三个湖泊系列进行了沉积学、矿物学和地球化学分析。来自凝灰质沉积物的新 CA ID-TIMS U-Pb 数据表明晚托阿尔世时代（179.481 ± 0.059、179.41 ± 0.13 和 177.27 ± 0.40 Ma），表明古湖泊与 Chon Aike 火山活动同时发育。沉积层序由碳酸盐、富含有机质的泥岩 — 总有机碳 (TOC) 含量高达 8 wt% — 砂岩和砾岩、所有这些都具有火山和火山成因物质的重要贡献。以柯伦石（绿泥石-蛭石混合层）、蒙脱石和蛭石为主的粘土矿物组合可能与热液活动和火山物质蚀变有关，与风化过程和气候变化无关。沉积层序中保存的有机质具有湖泊和陆地/再加工成因。二氧化碳 (CO2) 来源的变化以及有机物质的类型和/或保存程度对 δ13Corg 值产生了重大影响。这进一步说明了在解释有机碳同位素记录之前评估沉积环境影响的必要性。结合高磷和 TOC 含量表明，进入盆地的养分供应增加的事件提高了湖泊初级生产力，这有利于缺氧条件的底水的发展，并最终有利于有机物质的保存和掩埋。高 Corg/Ptot 比率表明磷可能以正反馈循环释放回水体，进一步维持初级生产力。该研究为了解托阿尔世晚期陆地上盛行的古环境条件以及火山作用如何控制沉积条件提供了重要线索。高 Corg/Ptot 比率表明磷可能以正反馈循环释放回水体，进一步维持初级生产力。该研究为了解托阿尔世晚期陆地上盛行的古环境条件以及火山作用如何控制沉积条件提供了重要线索。高 Corg/Ptot 比率表明磷可能以正反馈循环释放回水体，进一步维持初级生产力。该研究为了解托阿尔世晚期陆地上盛行的古环境条件以及火山作用如何控制沉积条件提供了重要线索。