Widespread loess-like deposit in the Martian northern lowlands identifies Middle Amazonian climate change
Widespread loess-like deposit in the Martian northern lowlands identifies Middle Amazonian climate change
复制标题
火星北部低地广泛的黄土状沉积物表明亚马逊中部气候变化
作者：
J. Skinner;Kenneth L. Tanaka;T. Platz
在火星低地，一致的可映射单元对于区分地质过程的风格和相互作用至关重要。这项研究确定了一个以前未映射的中亚马逊河（约。1 Ga）单位（中亚马逊低地单位，mAl），晚于晚期西方和早期亚马逊低地平原>2 b.y.该单元在区域上由边缘陡坎和斜坡组成，平均厚度为32 m，在北纬35° ~ 80°之间延伸面积大于3.1 × 106 km 2。基座型火山口和嵌套的弧形脊（拇指纹地形）往往出现在单位mAl露头附近，这表明目前的露头是更广泛的存款的遗迹，以前覆盖16 × 10 6 km 2。暴露的地层、地表坑和地表地貌的披覆暗示着沉积成因，可能是通过大气沉降物有节奏地侵位的黄土状存款。我们建议，单位铝积累coevally，并在牺牲，北极基底单位的侵蚀，确定一个主要的情节中亚马逊河流域的气候驱动的沉积在低地。这项工作将古代沉积过程与气候变化联系起来，而气候变化发生在目前的轨道和自旋轴模型所暗示的气候变化之前。
Consistently mappable units critical to distinguishing the style and interplay of geologic processes through time are sparse in the Martian lowlands. This study identifies a previously unmapped Middle Amazonian (ca. 1 Ga) unit (Middle Amazonian lowland unit, mAl) that postdates the Late Hesperian and Early Amazonian lowland plains by >2 b.y. The unit is regionally defined by subtle marginal scarps and slopes, has a mean thickness of 32 m, and extends >3.1 × 10 6 km 2 between lat 35°N and 80°N. Pedestal-type craterforms and nested, arcuate ridges (thumbprint terrain) tend to occur adjacent to unit mAl outcrops, suggesting that current outcrops are vestiges of a more extensive deposit that previously covered ∼16 × 10 6 km 2 . Exposed layers, surface pits, and the draping of subjacent landforms allude to a sedimentary origin, perhaps as a loess-like deposit emplaced rhythmically through atmospheric fallout. We propose that unit mAl accumulated coevally with, and at the expense of, the erosion of the north polar basal units, identifying a major episode of Middle Amazonian climate-driven sedimentation in the lowlands. This work links ancient sedimentary processes to climate change that occurred well before those implied by current orbital and spin axis models.