In situ investigations by the Mars Science Laboratory Curiosity rover have confirmed the presence of an ancient lake that existed in Gale crater for up to 10 million years. The lake was filled with sediments that eventually converted to a compacted sandstone. However, it remains unclear whether the infilling of the lake was the result of background sedimentation processes or represents punctual flooding events in a largely isolated lake. Here, we used the X-ray diffraction data obtained with the Chemistry and Mineralogy instrument onboard the Curiosity rover to characterize the degree of disorder of clay minerals in the Murray formation at Gale crater. Our analysis shows that they are structurally and compositionally related to glauconitic clays, which are a sensitive proxy of quiescent conditions in liquid bodies for extended periods of time. Such results provide evidence of long periods of extremely low sedimentation in an ancient brackish lake on Mars, the signature of an aqueous regime with slow evaporation at low temperatures. More in general, the identification of lacustrine glauconitic clays on Mars provides a key parameter in the characterization of aqueous Martian palaeoenvironments that may once have harboured life.

火星科学实验室好奇号火星车进行的原位调查证实，盖尔陨石坑中存在一个古老的湖泊，其存在时间长达 1000 万年。湖中充满了沉积物，最终转化为压实的砂岩。然而，尚不清楚湖泊的填充是背景沉积过程的结果，还是代表了一个基本上孤立的湖泊中的准时洪水事件。在这里，我们使用好奇号火星车上的化学和矿物学仪器获得的 X 射线衍射数据来表征盖尔陨石坑默里地层中粘土矿物的无序程度。我们的分析表明，它们在结构和组成上与海绿石粘土有关，后者是液体长时间处于静止状态的敏感指标。这些结果提供了火星上一个古老的咸水湖长期极低沉降的证据，这是低温下缓慢蒸发的含水状态的标志。更一般地说，火星上湖相海绿石粘土的鉴定为表征曾经存在生命的火星水古环境提供了一个关键参数。