Late Cretaceous astrochronology, organic carbon evolution, and paleoclimate inferences for the subtropical western South Atlantic, Espírito Santo Basin

Cyclostratigraphy has revealed the quasi-periodic nature that globally distributed sedimentary succes- sions present through the Phanerozoic. This is mainly the case of the strong eccentricity-related greenhouse climate of the Cretaceous period, a time interval in which the long-eccentricity 405-kyr cycle has been routinely used to constrain high-resolution astronomical time scales. Despite the importance of the South Atlantic opening to the evolution of the Cretaceous climate and carbon cycle, few investigations have applied the modern cyclostratigraphic analysis to explore the eventual orbital pacing of the Cretaceous South Atlantic successions. We use geophysical and geochemical data analysis from the Petrobras well ES-1 (offshore Espírito Santo Basin to develop a floating and anchored astro- nomical time scale (ATS) and infer the relation between sedimentation rate and TOC accumulation. Additionally, we estimate the net primary productivity (NPP) during intervals of high TOC accumulation. Our results show a pervasive orbitally-driven forcing imprint according to the Milankovitch spectral peak ratio as predicted to Cretaceous times, with a prominent occurrence of a 405-kyr long-eccentricity cycle, being used to constrain the elapsed time. An abrupt shift in the GR data likely associated with the Cretaceous e Paleogene boundary was used to anchor our floating ATS. The evolutionary Average Spectral Misfit (eASM) and Correlation Coefficient (COCO/eCOCO) tests demonstrate that the sedimen- tation rate can have contrasting effects over the organic matter burial, which is likely related to the large- scale paleogeographic configuration. Our study exemplifies that orbitally-driven sedimentation can be used to build high-resolution chronology for Brazilian marginal basins旋回地层学（Cyclostratigraphy）的研究揭示了显生宙（Phanerozoic）以来全球分布的沉积序列普遍具备准周期特性。其中尤以白垩纪（Cretaceous period）与强偏心率相关的温室气候背景为典型，该地质时段内，长偏心率405千年周期（long-eccentricity 405-kyr cycle）常被用于约束高分辨率天文年代标尺（astronomical time scale, ATS）。尽管南大西洋的张开对白垩纪气候与碳循环演化具有重要意义，但鲜有研究运用现代旋回地层学分析方法，探究白垩纪南大西洋沉积序列是否受轨道周期调控。本研究依托巴西石油公司（Petrobras）ES-1井（位于近海圣埃斯皮里图盆地（Espírito Santo Basin））的地球物理与地球化学数据，构建浮动式且锚定的天文年代标尺，并厘清沉积速率与总有机碳（Total Organic Carbon, TOC）富集之间的关联。此外，本研究还估算了总有机碳高富集时段的净初级生产力（net primary productivity, NPP）。研究结果显示，依据白垩纪时期的米兰科维奇频谱峰值比（Milankovitch spectral peak ratio），沉积记录普遍受轨道驱动作用影响，其中405千年长偏心率周期尤为显著，该周期被用于约束研究时段的流逝时间。伽马射线（GR）测井数据中的一次突变事件，极可能对应白垩-古近纪界线（Cretaceous-Paleogene boundary），被用于锚定本研究的浮动天文年代标尺。演化平均频谱失配（evolutionary Average Spectral Misfit, eASM）与相关系数（Correlation Coefficient, COCO/eCOCO）测试表明，沉积速率对有机质埋藏的影响存在显著差异，这大概率与大规模古地理格局有关。本研究证实，轨道驱动的沉积作用可用于构建巴西边缘盆地（Brazilian marginal basins）的高分辨率年代地层序列。