Abstract The Lower Permian Irati Formation in the northeastern and central eastern Parana Basin (southern Brazil) was investigated in terms of bulk and molecular organic geochemistry in order to enlighten the complex depositional paleoenvironment during deposition of Irati black shales. The geochemical data reflect temporal and spatial variations of freshwater incursions promoting salinity stratification and high primary productivity in surface waters with the establishment of photic zone euxinia. Overall, highly concentrated C17 long-chain alkylnaphthalenes point to algal blooms as a result of freshwater inflows into the Irati Sea, mostly in the central eastern basin segment, and resemble concentration variations of pristane, phytane and nC17. The freshwater inflows were also retraced by increasing chroman ratios toward the top of the investigated units along with the general decrease of further palaeosalinity indicators, e.g., gammacerane, tetracyclic (C24), β-carotane, and the herein suggested γ-carotane and lexane indexes. The existence of a water column stratification promoting organic matter preservation is supported by the detection of tetrahydrophenanthrene at high concentrations, in addition to the known prominent occurrence of gammacerane. The detection of C10 to C31 aryl isoprenoids in addition to C16 and C18 pseudohomologue aryl isoprenoids points to the presence of photic zone euxinia. In general, samples from the central eastern basin were deposited in a deeper marine setting with lower salinity than samples from the northeastern basin, which displays signals of a shallower marine environment with reducing bottom water conditions, both deposited under freshwater influxes.

中文翻译：

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控制下二叠统 Irati 组（巴西巴拉那盆地）富有机质页岩盐度分层的淡水动力学的有机地球化学信号

摘要 为了揭示Irati黑色页岩沉积过程中复杂的沉积古环境，对Parana盆地东北部和中东部（巴西南部）下二叠统Irati组进行了体积和分子有机地球化学研究。地球化学数据反映了随着光区euxinia 的建立，淡水入侵促进了地表水中盐度分层和高初级生产力的时空变化。总体而言，高度浓缩的 C17 长链烷基萘表明由于淡水流入伊拉提海（主要在中东部盆地部分）导致藻华大量繁殖，类似于原始烷烃、植烷和 nC17 的浓度变化。随着进一步古盐度指标（例如伽玛蜡烷、四环（C24）、β-胡萝卜烷以及本文建议的γ-胡萝卜烷和莱克烷指数）的普遍降低，淡水流入量也随着向研究单元顶部增加色满比增加而回溯. 除了已知显着的伽马蜡烷外，检测到高浓度四氢菲也支持了促进有机物质保存的水柱分层的存在。除了 C16 和 C18 假同系物芳基异戊二烯外，C10 到 C31 芳基异戊二烯的检测表明存在光区 euxinia。一般来说，中东部盆地的样品沉积在更深的海洋环境中，盐度低于东北盆地的样品，