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首页> 外文期刊>Global and planetary change >Low post-Cenomanian denudation depths across the Brazilian Northeast: Implications for long-term landscape evolution at a transform continental margin
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Low post-Cenomanian denudation depths across the Brazilian Northeast: Implications for long-term landscape evolution at a transform continental margin

机译：巴西东北部的后塞诺曼时期剥蚀深度低：对转型大陆边缘的长期景观演变有影响

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摘要

The Brazilian Northeast affords good opportunities for obtaining reliable timings and rates of landscape evolution based on stratigraphic correlations across a vast region. The landscape formed in the context of an episodically fluctuating but continuously falling base level since the Cenomanian. After formation of the transform passive margin in Aptian times, landscape development was further driven by a swell-like uplift with its crest situated ～300 km from the coastline. The seaward flank of this swell or broad monocline between the interior Araripe and coastal Potiguar basins was eroded, and currently forms a deeply embayed plain bordered by a semi-circular, north-facing erosional escarpment. The post-Cenomanian uplift caused an inversion of the Cretaceous basins and generated a landscape in which the most elevated landforms correspond either to resistant Mesozoic sedimentary caprock, or to eroded stumps of syn-rift Cretaceous footwall uplands. Denudation in the last 90 My never exceeded mean rates of 10 m·My~(-1) and exhumed a number of Cretaceous stratigraphic unconformities. As a result, some topographic surfaces at low elevations are effectively Mesozoic land surfaces that became re-exposed in Cenozoic times. The Neogene Barreiras Formation forms a continuous and mostly clastic apron near the coast. It testifies to the last peak of erosion in the hinterland and coincided with the onset of more arid climates at ～ 13 Ma or earlier. The semi-circular escarpment is not directly related to the initial breakup rift flanks, which had been mostly eroded before the end of the Mesozoic, but the cause and exact timing of post-Cenomanian crustal upwarping are poorly constrained. It could perhaps have been a flexural response of the low-rigidity lithosphere to sediment loads on the margin, and thus a slowly ongoing process since the late Cretaceous. Uplift could instead be the consequence of a more discrete dynamic event related either to Oligocene magmatism in the region, or to continental-scale far-field stresses determined by Andean convergence.
机译：巴西东北部地区为基于广阔地区地层相关性的可靠时间和景观演化速率提供了良好的机会。自塞诺曼尼亚以来，地势在波动的基础上不断下降，但不断下降。在Aptian时代形成了被动过渡边缘之后，景观的发展进一步受到了隆起的推动，其隆起距离海岸线约300 km。在内部Araripe盆地和沿海Potiguar盆地之间的这种隆起或宽阔的单斜线的海侧被侵蚀了，目前形成了一个深陷的平原，以一个半圆形的北向侵蚀悬崖为界。后新生代的隆升引起白垩纪盆地的倒转，并产生了一个景观，在该景观中，最高的地貌要么对应于中生代的抵抗性沉积盖岩，要么对应于同裂谷期白垩纪底盘高地的侵蚀树桩。最近90 My的剥蚀从未超过10 m·My〜（-1）的平均速率，并发掘出许多白垩纪地层不整合面。结果，一些低海拔的地形表面实际上是中新生代陆面，并在新生代重新暴露。 Neogene Barreiras组在海岸附近形成一个连续的且大部分为碎屑的围裙。它证明了内陆地区侵蚀的最后一个高峰，并与〜13 Ma或更早的干旱气候的发生相吻合。半圆形悬崖与最初的裂谷纵裂侧面并没有直接关系，后者在中生代末期之前已被侵蚀，但是在后新生代地壳隆升的原因和确切时机上却受到了很大的限制。这可能是低刚性岩石圈对边缘沉积物载荷的挠曲响应，因此是自白垩纪晚期以来一个缓慢进行的过程。相反，隆起可能是与该地区渐新世岩浆作用或由安第斯辐合确定的大陆范围远场应力有关的更离散的动力学事件的结果。

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