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Lateral variability of shelf-edge and basin-floor deposits, Santos Basin, offshore Brazil
Journal of Sedimentary Research ( IF 2 ) Pub Date : 2020-10-06 , DOI: 10.2110/jsr.2020.14
Michael J. Steventon 1 , Christopher A-L. Jackson 1 , David M. Hodgson 2 , Howard D. Johnson 1
Affiliation  

Construction of continental margins is driven by sediment transported across the shelf to the shelf edge, where it is reworked by wave, tide, and fluvial processes in deltas and flanking clastic shorelines. Stalling of continental-margin progradation often results in degradation of the outer shelf to upper slope, with resedimentation to the lower slope and basin floor via a range of sediment gravity flows and mass-movement processes. Typically, our understanding of how these processes contribute to the long-term development of continental margins has been limited to observations from broadly two-dimensional, subsurface and outcrop datasets. Consequently, the three-dimensional variability in process regime and margin evolution is poorly constrained and often underappreciated. We use a large (90 km by 30 km, parallel to depositional strike and dip, respectively) post-stack time-migrated 3D seismic-reflection dataset to investigate along-strike variations in shelf-margin progradation and outer-shelf to upper-slope collapse in the Santos Basin, offshore SE Brazil. Early Paleogene to Eocene progradation of the shelf margin is recorded by spectacularly imaged, SE-dipping clinoforms. Periodic failure of the outer shelf and upper slope formed ca. 30-km-wide (parallel to shelf-margin strike) slump scars, which resulted in a strongly scalloped upper-slope. Margin collapse caused: 1) the emplacement of slope-attached mass-transport complexes (MTCs) (up to ca. 375 m thick, 12+ km long, 20 km wide) on the proximal basin floor, and 2) accommodation creation on the outer shelf to upper slope. This newly formed accommodation was infilled by shelf-edge-delta clinoforms (up to 685 m thick), that nucleated and prograded basinward from the margin-collapse headwall scarp, downlapping onto the underlying slump scar and/or MTCs. Trajectory analysis of the shelf-edge deltas suggests that slope degradation-created accommodation was generated throughout the sea-level cycle, rather than during base-level fall as would be predicted by conventional sequence-stratigraphic models. Our results highlight the significant along-strike variability in depositional style, geometry, and evolution that can occur on this and other continental margins. Coeval strata, separated by only a few kilometers, display strikingly different stratigraphic architectures; this variability, which could be missed in 2D datasets, is not currently captured in conventional 2D sequence stratigraphic models.

中文翻译:

巴西近海桑托斯盆地陆缘和盆地底沉积物的横向变化

大陆边缘的建设是由沉积物跨过陆架运至陆架边缘而驱动的,在三角洲和碎屑海岸线的两侧,海浪,潮汐和河流冲刷过程对其进行了修复。大陆边缘扩展的停滞通常会导致外架子退化为上斜坡,并通过一系列沉积物重力流和质量运动过程重新沉积到下斜坡和盆地底部。通常,我们对这些过程如何促进大陆边缘长期发展的理解仅限于从广泛的二维,地下和露头数据集中进行的观测。因此,工艺状态和裕度演变的三维可变性受到的约束很少,而且常常被低估。我们使用大型(90公里乘30公里,平行于沉积走滑和倾角,分别)叠后时间迁移的3D地震反射数据集,以调查巴西东南部桑托斯盆地沿陆架演化和外架到上斜坡塌陷的沿走向变化。早期的古近纪至始新世的陆架边缘发育是通过成像壮观的,浸有SE的斜型记录的。外部架子和上斜坡的周期性破坏形成了约。30公里宽(平行于货架边缘的罢工)坍落的疤痕,导致强烈的扇形上坡。造成边际塌陷的原因有:1)在近岸盆地底板上安置了附有坡度的运输复合体(MTC)(厚约375 m,长12+ km,宽20 km),以及2)外层架到上坡。这个新形成的住处被架子边缘的三角斜形(最大685 m厚)填充,从边缘塌陷的头壁陡峭带向核形发展,并向下塌陷到潜在的坍落性瘢痕和/或MTC上。大陆架边缘三角洲的轨迹分析表明,在整个海平面周期内,而不是在常规层序-地层学模型所预测的基础水平下降期间,产生了由坡度退化所产生的适应作用。我们的研究结果突显了在该大陆边缘和其他大陆边缘可能发生的沿沉积带样式,几何形状和演化的重大沿线变化。相距仅几公里的远古地层显示出截然不同的地层结构。目前在常规2D层序地层模型中并未捕获到2D数据集中可能遗漏的这种可变性。叠加到潜在的低迷疤痕和/或MTC上。大陆架边缘三角洲的轨迹分析表明,在整个海平面周期内,而不是在常规层序-地层学模型所预测的基础水平下降期间,产生了由坡度退化所产生的适应作用。我们的研究结果突显了在该大陆边缘和其他大陆边缘可能发生的沿沉积带样式,几何形状和演化的重大沿线变化。相距仅几公里的远古地层显示出截然不同的地层结构。目前在常规2D层序地层模型中并未捕获到2D数据集中可能遗漏的这种可变性。叠加到潜在的低迷疤痕和/或MTC上。大陆架边缘三角洲的轨迹分析表明,在整个海平面周期内,而不是在常规层序-地层学模型所预测的基础水平下降期间,产生了由坡度退化所产生的适应作用。我们的研究结果突显了在该大陆边缘和其他大陆边缘可能发生的沿沉积带样式,几何形状和演化的重大沿线变化。相距仅几公里的远古地层显示出截然不同的地层结构。目前在常规2D层序地层模型中并未捕获到2D数据集中可能遗漏的这种可变性。大陆架边缘三角洲的轨迹分析表明,在整个海平面周期内,而不是在常规层序-地层学模型所预测的基础水平下降期间,产生了由坡度退化所产生的适应作用。我们的研究结果突显了在该大陆边缘和其他大陆边缘可能发生的沿沉积带样式,几何形状和演化的重大沿线变化。相距仅几公里的远古地层显示出截然不同的地层结构。目前在常规2D层序地层模型中并未捕获到2D数据集中可能遗漏的这种可变性。大陆架边缘三角洲的轨迹分析表明,在整个海平面周期内,而不是在常规层序-地层学模型所预测的基础水平下降期间,产生了由坡度退化所产生的适应作用。我们的研究结果突显了在该大陆边缘和其他大陆边缘可能发生的沿沉积带样式,几何形状和演化的重大沿线变化。相距仅几公里的远古地层显示出截然不同的地层结构。目前在常规2D层序地层模型中并未捕获到2D数据集中可能遗漏的这种可变性。我们的研究结果突显了在该大陆边缘和其他大陆边缘可能发生的沿沉积带样式,几何形状和演化的重大沿线变化。相距仅几公里的远古地层显示出截然不同的地层结构。目前在常规2D层序地层模型中并未捕获到2D数据集中可能遗漏的这种可变性。我们的研究结果突显了在该大陆边缘和其他大陆边缘可能发生的沿沉积带样式,几何形状和演化的重大沿线变化。相距仅几公里的远古地层显示出截然不同的地层结构。目前在常规2D层序地层模型中并未捕获到2D数据集中可能遗漏的这种可变性。
更新日期:2020-11-17
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