The present study used shallow high-resolution seismic surveys to characterize the architecture and stratigraphic evolution of the last depositional sequence of the São Francisco Delta (SFDS). The sequence was accumulated within a bathymetric low (BL) on the shelf located in front of the São Francisco river. This antecedent topography provided additional accommodation of tens of meters in comparison with the rest of the shelf. The BL and its sediment-trapping effect allowed the accumulation of a complete stratigraphic record of the eustatic sea-level rise since the Last Glacial Maximum (LGM). The SFDS comprises six stratigraphic units. Because cores and radiocarbon dates are not available for this study area, the depth of occurrence of the top and base of each unit and their lateral relationships with wave-cut terraces carved into the BL walls were used in an effort to tentatively tie the mapped units to known eustatic sea-level curves available in the literature. Results suggest that major episodes of accumulation occurred during intervals of reduced rates in sea-level rise. The lower five units mapped accumulated in a large bay-estuarine protected environment, which resulted from the inundation of the BL. Only the topmost unit (the present clinoform) accumulated in an open ocean environment when sea level reached approximately its present position after 8 ka and the whole shelf was flooded. The most important delta backstepping event was probably associated with Meltwater Pulse 1B, which followed the Younger Dryas and produced one of the most significant stratal surfaces of the SFDS. Among the existing wave-dominated deltas in the Brazilian coast only, the São Francisco was able to construct a well-developed sigmoidal muddy clinoform in an otherwise very shallow shelf subjected to high wave-energy levels. This was only possible because of the existence of a bathymetric low in front of the river mouth, which illustrates the role that antecedent topography might play in providing larger amount of available accommodation space called in this paper of additional accommodation.

中文翻译：

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先行地形控制了最新更新世-全新世海侵记录的保存和斜面发育：以圣弗朗西斯科三角洲（​​巴西东部）为例

本研究使用浅层高分辨率地震勘测来表征圣弗朗西斯科三角洲 (SFDS) 最后沉积序列的结构和地层演化。该序列在位于圣弗朗西斯科河前的陆架上的一个测深低 (BL) 内积累。与货架的其余部分相比，这种先行地形提供了数十米的额外空间。BL 及其沉积物捕获效应允许积累自末次盛冰期 (LGM) 以来海平面上升的完整地层记录。SFDS 包括六个地层单元。由于无法获得该研究区域的岩心和放射性碳日期，每个单元顶部和底部的发生深度及其与刻在 BL 壁上的波浪切割阶地的横向关系被用于尝试将映射单元与文献中已知的海平面曲线联系起来。结果表明，主要的积累事件发生在海平面上升速率降低的间隔期间。下方的五个单元在大型海湾河口受保护环境中积累，这是由于 BL 的淹没造成的。当海平面在 8 ka 后达到大约现在的位置并且整个大陆架被淹没时，只有最顶层的单元（现在的斜面）在开阔的海洋环境中积累。最重要的三角洲反推事件可能与 Meltwater Pulse 1B 相关，紧随新仙女木之后，产生了 SFDS 最重要的地层表面之一。仅在巴西海岸现有的以波浪为主导的三角洲中，圣弗朗西斯科能够在受到高波浪能水平的其他非常浅的陆架上建造一个发育良好的 S 形泥质斜坡。这是唯一可能的，因为在河口前面存在一个测深低点，这说明了先行地形可能在提供更多可用住宿空间方面发挥的作用，在本文中称为额外住宿。圣弗朗西斯科号能够在受到高波浪能水平影响的非常浅的陆架上建造一个发育良好的 S 形泥质斜坡。这是唯一可能的，因为在河口前面存在一个测深低点，这说明了先行地形可能在提供更多可用住宿空间方面发挥的作用，在本文中称为额外住宿。圣弗朗西斯科号能够在受到高波浪能水平影响的非常浅的陆架上建造一个发育良好的 S 形泥质斜坡。这是唯一可能的，因为在河口前面存在一个测深低点，这说明了先行地形可能在提供更多可用住宿空间方面发挥的作用，在本文中称为额外住宿。