A major debate in Mars science is the nature of the early Mars climate, and the availability of precipitation and runoff. Observations of relict erosional valley networks have been proposed as evidence for extensive surface runoff around the Noachian‐Hesperian boundary. However, these valley networks only provide a time‐integrated record of landscape evolution, and thus, the timing, relative timescales and intensity of aqueous activity required to erode the valleys remain unknown. Here, we investigate an ancient fluvial sedimentary system in western Arabia Terra, now preserved in positive relief. This ridge, “Aram Dorsum,” is flat‐topped, branching, ~85 km long, and particularly well preserved. We show that Aram Dorsum was an aggradational alluvial system and that the existing ridge was once a large river channel belt set in extensive flood plains, many of which are still preserved. Smaller, palaeochannel belts feed the main system; their setting and network pattern suggest a distributed source of water. The alluvial succession is up to 60 m thick, suggesting a formation time of 10⁵ to 10⁷ years by analogy to Earth. Our observations are consistent with Aram Dorsum having formed by long‐lived flows of water, sourced both locally, and regionally as part of a wider alluvial system in Arabia Terra. This suggests frequent or seasonal precipitation as the source of water. Correlating our observations with previous regional‐scale mapping shows that Aram Dorsum formed in the mid‐Noachian. Aram Dorsum is one of the oldest fluvial systems described on Mars and indicates climatic conditions that sustained surface river flows on early Mars.

中文翻译：

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Aram Dorsum：火星阿拉伯Terra中广泛的中挪亚时代河流沉积系统

火星科学界的一个主要辩论是火星早期气候的性质以及降水和径流的可用性。已经提出了对遗迹侵蚀性山谷网络的观测，作为围绕Noachian-Hesperian边界的广泛地表径流的证据。但是，这些山谷网络仅提供了景观演化的时间积分记录，因此侵蚀山谷所需的时间，相对时间尺度和水活动强度仍然未知。在这里，我们研究了阿拉伯西部Terra的古代河流沉积系统，该系统现已保存为正浮雕。该山脊“ Aram Dorsum”是平顶的，分支的，长约85公里，保存得特别好。我们证明了Aram Dorsum是一个集积冲积系统，而现有的山脊曾经是一个位于广阔洪泛平原的大型河道带，其中许多仍被保留。较小的古河道带进入主系统。它们的设置和网络模式表明存在分布式水源。冲积层厚达60 m，表明形成时间为10 比地球大⁵至10 ⁷年。我们的观察结果与长期存在的水流形成的Aram Dorsum一致，该水流是本地和区域性的，是阿拉伯Terra较广泛的冲积系统的一部分。这表明经常或季节性降水是水的来源。将我们的观察结果与先前的区域规模图进行对比，可以发现Aram Dorsum形成于Noachian中部。Aram Dorsum是火星上描述的最古老的河流系统之一，它指示了在火星早期持续地表河流流动的气候条件。