The Colorado basin in the SW Atlantic is one of the key exploratory frontier basins along the Argentine shelf. The stratigraphy shows a typical rift basin, divided into two major seismic successions, a Jurassic-Lower Cretaceous synrift followed by an Upper Cretaceous to Cenozoic postrift. They represent, respectively, the breakup of Gondwana and passive margin evolution. While the synrift basin formation was associated with the development of structural grabens, the preservation of thick (thousands of meters) postrift sequences are still debated because they cannot be accounted for only by thermal subsidence. In this work, we conducted a multimethodological subsidence analysis across the Colorado basin, including part of the continental slope. We performed a 1D backstripping analysis on 10 hydrocarbon exploration wells and 32 pseudo-wells, covering the whole basin area and a uniform stretching model, which were supported using dynamic topography data from the study region. From the backstripping analyses, considering the six major postrift sedimentary successions described in the literature, we could recognize three subsidence stages. An initial rapid subsidence stage during the post-rift (125–83 Ma), which is restricted to the main depocenters, followed by a stage of generalized and low subsidence focused on the main axis of the basin (83–33 Ma), with an increase in the last 33 my (33–0 Ma). The stretching models exhibit a typical asymptotic curve, depicting significant subsidence at the onset of the postrift stage, gradually diminishing to minimal values within a few tens of millions of years. Upon comparing the backstripping curves with the stretching subsidence models, particularly during the final flat segments, a residual negative value emerges over time (locally exceeding −500 m), indicating considerable residual subsidence during the Cenozoic postrift evolution along the Colorado Basin. This could be interpreted as dynamic subsidence. This residual sinking in the Argentina shelf matches with dynamic topography numerical models in the study region as well as the occurrence of accumulated slabs in the mantle detected by seismic tomography studies. We propose that the accumulation of slabs along this segment of the South American subduction zone might be the drivers of dynamic subsidence, which assisted to the preservation of a large thickness of post-rift strata along the SW Atlantic margin.

中文翻译：

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科罗拉多盆地、阿根廷近海、南大西洋的动态沉降


西南大西洋的科罗拉多盆地是阿根廷陆架沿线重点勘探的前沿盆地之一。地层学显示了一个典型的裂谷盆地，分为两个主要的地震序列，侏罗纪-下白垩统同裂谷，随后是上白垩纪至新生代后裂谷。它们分别代表冈瓦纳大陆的分裂和被动边缘演化。虽然同裂谷盆地的形成与构造地堑的发育有关，但厚（数千米）的裂谷后层序的保存仍然存在争议，因为它们不能仅用热沉降来解释。在这项工作中，我们对科罗拉多盆地（包括部分大陆坡）进行了多方法沉降分析。我们对10口油气探井和32口拟井进行了一维反剥离分析，覆盖整个盆地区域，并采用均匀拉伸模型，并利用研究区的动态地形数据进行支持。从回剥分析中，考虑到文献中描述的六种主要的裂谷后沉积层序，我们可以识别出三个沉降阶段。裂谷后的初始快速沉降阶段（125-83Ma）仅限于主要沉积中心，随后是集中在盆地主轴的普遍低沉降阶段（83-33Ma），最后 33 my (33–0 Ma) 有所增加。拉伸模型表现出典型的渐近曲线，描绘了裂谷后阶段开始时的显着沉降，并在几千万年内逐渐减小到最小值。 将回剥曲线与拉伸沉降模型进行比较，特别是在最后的平坦段期间，随着时间的推移会出现残余负值（局部超过-500 m），这表明科罗拉多盆地新生代裂谷后演化过程中存在相当大的残余沉降。这可以解释为动态沉降。阿根廷陆架的残余下沉与研究区域的动态地形数值模型以及地震层析成像研究检测到的地幔中堆积板的出现相匹配。我们认为，沿着南美俯冲带这一段的板片堆积可能是动态沉降的驱动因素，这有助于保存沿西南大西洋边缘的大厚度裂谷后地层。