Abstract In this study, we propose a new stratigraphic framework for a well-preserved Paleoproterozoic succession of the Carajas Basin (Amazonian craton) in northern Brazil. A core-based facies analysis is coupled with a critical review of previous data on this succession. We are proposing that the studied succession, which was previously considered as a single lithostratigraphic unit called the Aguas Claras Formation, consists of two different formations of Paleoproterozoic age (~2.37–2.06 Ga). The lower formation, which is composed of ~250-m-thick mudstone strata locally enriched with manganese, is formally proposed here and is designated as the Azul Formation, referring to the Azul mine, in which the type-section is described. The overlying Aguas Claras Formation is redefined as a stratigraphic unit composed exclusively of an ~800-m-thick succession of sandstone and conglomerate strata. The contact between these two formations is an easily recognizable surface; thus, these formations can be accurately mapped and distinguished within the basin. We suggest that the Azul and Aguas Claras formations are the stratigraphic record associated with a transgressive‒regressive sequence, in which these formations are limited one from the other by a maximum flooding zone. The Azul Formation was deposited during a marine transgression related to the latest incursion of the Azul sea towards the Carajas protocontinent. On the other hand, the overlying Aguas Claras Formation was deposited in a fluvial system that developed during a period of marine regression. Whereas the marine transgression may have been influenced by the deglaciation occurred aftermath the Siderian–Rhyacian Serra Sul glaciation, the subsequent marine regression was triggered, at least in part, by uplifting related to the Transamazonian cycle (~2.0 Ga). In addition to our results shed new light on the Carajas Basin evolution, they support the hypothesis that the Azul and Aguas Claras formations can be correlated with other Paleoproterozoic successions worldwide, mainly those registered in ancient landmasses that amalgamated and later formed the Columbia supercontinent during the Paleo-to Mesoproterozoic.

中文翻译：

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古元古代硅质碎屑岩层序的新地层学建议：对巴西亚马逊克拉通 Carajás 盆地演化的影响

摘要 在这项研究中，我们为巴西北部卡拉哈斯盆地（亚马逊克拉通）保存完好的古元古代序列提出了一个新的地层框架。以岩心为基础的相分析与对该系列之前数据的批判性审查相结合。我们建议研究的序列，以前被认为是称为 Aguas Claras 组的单个岩石地层单元，由古元古代（~2.37-2.06 Ga）的两个不同地层组成。下部地层由约 250 米厚的局部富含锰的泥岩地层组成，这里正式提出并命名为 Azul 地层，指的是 Azul 矿，其中描述了类型剖面。上覆的 Aguas Claras 组被重新定义为仅由约 800 米厚的砂岩和砾岩地层连续组成的地层单元。这两个地层之间的接触是一个容易识别的表面；因此，可以在盆地内准确地绘制和区分这些地层。我们认为 Azul 和 Aguas Claras 地层是与海进-海退层序相关的地层记录，其中这些地层彼此之间受到最大洪水区的限制。Azul 地层是在与 Azul 海最近一次侵入 Carajas 原大陆有关的海侵期间沉积的。另一方面，上覆的 Aguas Claras 组沉积在一个在海退期间形成的河流系统中。虽然海侵可能受到 Siderian-Rhyacian Serra Serra 冰川之后发生的冰消作用的影响，但随后的海退至少部分是由与跨亚马逊循环（~2.0 Ga）相关的隆升触发的。除了我们的结果为 Carajas 盆地演化提供了新的线索之外，他们还支持这样一个假设，即 Azul 和 Aguas Claras 地层可以与世界范围内的其他古元古代序列相关联，主要是在古代陆地上登记的那些，这些地块在 2006古至中元古代。0 加）。除了我们的结果为 Carajas 盆地演化提供了新的线索之外，他们还支持这样一个假设，即 Azul 和 Aguas Claras 地层可以与世界范围内的其他古元古代序列相关联，主要是在古代陆地上登记的那些，这些地块在 2006 年合并并后来形成了哥伦比亚超大陆。古至中元古代。0 加）。除了我们的结果为 Carajas 盆地演化提供了新的线索之外，他们还支持这样一个假设，即 Azul 和 Aguas Claras 地层可以与世界范围内的其他古元古代序列相关联，主要是在古代陆地上登记的那些，这些地块在 2006 年合并并后来形成了哥伦比亚超大陆。古至中元古代。