The Sergipe–Alagoas Basin, in northeastern Brazil, has extensive exposures of carbonate rocks that may be studied as analogues to hydrocarbon reservoirs. The outcrops are equivalent to the pre-salt and post-salt reservoirs of the Campos and Santos basins, the most important hydrocarbon exploration targets nowadays in Brazil. Outcrops and well logs of the Riachuelo Formation, the most important for analogue studies of Cretaceous marine carbonate reservoirs of the Campos Basin due to the great variability of facies, are described and interpreted to identify the depositional cycles and stratigraphic sequences. Three unconformities formed during the initial drift phase of the basin are recognized. The depositional setting of the studied section changes from a siliciclastic-dominated continental to shallow-marine mixed siliciclastic-carbonate at the base to a shallow-marine carbonate platform in the upper part. The transgressive–regressive (T–R) sequence model was used for the stratigraphic analysis, leading to a stratigraphic framework of three third-order T–R sequences, with an estimated duration of approximately 2.0, 4.5 and 1.5 Ma, respectively. Consequently, the higher frequency cycles identified in the well logs represent a timing of circa 140,000 years, and are interpreted as fourth-order depositional cycles.

中文翻译：

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巴西东北部塞尔吉佩-阿拉戈斯盆地白垩纪混合硅质碎屑-碳酸盐台地层序的高分辨率层序地层学

Sergipe-Alagoas 盆地位于巴西东北部，有大量碳酸盐岩暴露，可以作为类似油气藏进行研究。露头相当于目前巴西最重要的油气勘探目标坎波斯和桑托斯盆地的盐前和盐后储层。Riachuelo 组的露头和测井是对 Campos 盆地白垩纪海相碳酸盐岩储层的类比研究最重要的，因为相的巨大变异性，被描述和解释以识别沉积旋回和地层序列。识别出盆地初始漂移阶段形成的三个不整合面。研究剖面的沉积环境由以硅质碎屑为主的陆相转变为浅海相混合的硅质碎屑-碳酸盐岩基底，再到上部浅海相碳酸盐台地。海进-回归（T-R）层序模型用于地层分析，导致三个三阶 T-R 层序的地层框架，估计持续时间分别约为 2.0、4.5 和 1.5 Ma。因此，测井中确定的较高频率周期代表大约 140,000 年的时间，并被解释为四阶沉积周期。估计持续时间分别约为 2.0、4.5 和 1.5 Ma。因此，测井记录中确定的较高频率周期代表大约 140,000 年的时间，并被解释为四阶沉积周期。估计持续时间分别约为 2.0、4.5 和 1.5 Ma。因此，测井中确定的较高频率周期代表大约 140,000 年的时间，并被解释为四阶沉积周期。