Abstract The Serra da Saudade Formation is part of the Bambui Group, a cratonic cover from the western Sao Francisco craton. It is composed by siliciclastic sediments deposited in a foreland basin during a transgressive event. The Serra da Saudade Formation is mainly represented by rhythmites, siltstones (locally glauconitic) and rare sandstones. The glauconitic siltstone was deposited during a maximum flooding surface and sediment starvation, which allowed high concentrations of probable volcanic-sourced potassium. The interpretation of the depositional age of the Bambui Group had multiple turnovers in the last decades. Finding and dating synsedimentary volcanic rocks is essential to solve this conundrum. This paper presents the first U-Pb direct dating of the Bambui Group from zircon grains recovered from a volcaniclastic layer interbedded with glauconitic siltstones from the upper Serra da Saudade Formation. A total of 107 U-Pb ages were obtained by LA-ICP-MS and plotted into a Concordia diagram. The provenance signature comprises a wide range of detrital zircon ages (1.0–2.8 Ga). These data represent inherited zircon grains incorporated into the magma during magmatic activity that produced the volcanic sediment, or to dilution and reworking of volcanic ashes that mixed to fine-grained clastic sediments prior to deposition. A significant amount of 10 highly concordant, prismatic zircon grains clustered into a well constrained age of 520.2 ± 5.3 Ma, which represent the explosive volcanic eruption age, and by extent, the depositional age of the upper Serra da Saudade Formation. Since the currently final thrust stacking ages from the Brasilia Belt and the Aracuai Belt are dated ca. 600 and 540 Ma, respectively, one must carefully look for the real age of the deformation event that affected the Bambui Group over the Sao Francisco craton.

中文翻译：

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第一次火山碎屑岩层 U-Pb 定年支持巴西班布伊群上部寒武纪时代

摘要 Serra da Saudade 地层是 Bambui 群的一部分，Bambui 群是一个来自西圣弗朗西斯科克拉通的克拉通盖层。它由海侵事件期间沉积在前陆盆地中的硅质碎屑沉积物组成。Serra da Saudade 组主要以韵律岩、粉砂岩（局部为青光岩）和稀有砂岩为代表。青青质粉砂岩是在最大洪水表面和沉积物饥饿期间沉积的，这使得高浓度的可能来自火山的钾成为可能。在过去的几十年里，对 Bambui 群沉积时代的解释有多次更替。寻找和测年同沉积火山岩对于解决这个难题至关重要。本文介绍了从与 Serra da Saudade 组上部的青青质粉砂岩互层的火山碎屑岩层中回收的锆石颗粒对 Bambui 群的首次 U-Pb 直接测年。通过 LA-ICP-MS 获得了总共 107 个 U-Pb 年龄并绘制成 Concordia 图。物源特征包括广泛的碎屑锆石年龄（1.0-2.8 Ga）。这些数据代表了在产生火山沉积物的岩浆活动期间合并到岩浆中的继承锆石颗粒，或者在沉积之前混合到细粒碎屑沉积物的火山灰的稀释和再加工。大量 10 个高度一致的棱柱形锆石颗粒聚集在 520.2 ± 5.3 Ma 的良好约束年龄中，这代表了火山爆发的爆发年龄，并且在范围内，上 Serra da Saudade 组的沉积时代。由于目前来自巴西利亚带和 Aracuai 带的最终推力叠加年龄是大约 10 年。分别为 600 和 540 Ma，我们必须仔细寻找影响圣弗朗西斯科克拉通上的 Bambui 群的变形事件的真实年龄。