Fine-grained rhythmites are a recurrent sedimentary facies in glacially influenced marine and lacustrine sequences throughout geological time. Paleoenvironmental interpretation of these ancient deposits has been a challenge, because similar rhythmites may have formed in different depositional contexts. In the Paraná Basin, the Itararé Group contains numerous successions of fine-grained rhythmites, deposited in the Carboniferous during the Late Paleozoic Ice Age (LPIA). The described rhythmites are characterized by the intercalation of fine-grained sandstones and siltstones with clay and clayey siltstones. We have identified two distinct types of rhythmites based on the contact between couplets, couplets thickness, sedimentary structures, and geochemical proxies. Type 1 rhythmites are characterized by intercalation of very fine-grained sandstone–siltstone (60–90%) with claystone (40–10%) and normal grading. Type 2 rhythmites are characterized by couplets of siltstone (50%) and claystone (50%), with a sharp contact within couplets. Type 1 rhythmites are interpreted as turbidity-current deposits, and Type 2 as distal deposits of hypopycnal flow. Geochemical proxies suggest deposition of the rhythmites under marine conditions, in a period of rising temperature and humidity, and with intensified chemical weathering. These paleoenvironmental characteristics are in agreement with the interglacial period. The preservation of thick rhythmite successions of the Itararé Group in the southern part of the basin was controlled by the constant creation of accommodation space inside paleovalleys.

中文翻译：

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巴拉那盆地最南端的晚古生代冰期节律：沉积学和古环境分析

在整个地质时期中，细粒节律是受冰川影响的海洋和湖相层序中反复出现的沉积相。这些古沉积物的古环境解释一直是一个挑战，因为相似的旋律可能在不同的沉积环境中形成。在巴拉那盆地，伊塔拉雷群包含许多连续的细节律，在晚古生代冰河时期（LPIA）沉积在石炭纪。所述的节律植物的特征在于细粒砂岩和粉砂岩与粘土和黏土粉砂岩的夹层。根据couple联，thickness联厚度，沉积结构和地球化学代理之间的接触，我们确定了两种不同的节律类型。1型节律的特征是，将非常细粒度的砂岩-粉砂岩（60-90％）与粘土岩（40-10％）插入，并进行正常分级。2型节律的特点是粉砂岩（50％）和粘土岩（50％）的couple联，在couple联中有强烈的接触。类型1的节律被解释为浊度-电流沉积，类型2的被解释为是次流的远端沉积。地球化学代理表明，在海洋条件下，在温度和湿度升高的时期，以及化学风化加剧的情况下，节律动物的沉积。这些古环境特征与间冰期一致。盆地南部伊塔拉雷群厚厚的节奏性演替的保存受到古河谷内部不断形成的居住空间的控制。