Mishev Ivan G, Smith Isaac B, Quantin Cathy, Thollot Patrick, Putzig Nathaniel E, Viviano Christina, Chojnacki Matt, Campbell Bruce
York University Toronto ON Canada.
Planetary Science Institute Tucson AZ USA.
J Geophys Res Planets. 2024 Dec;129(12):e2024JE008425. doi: 10.1029/2024JE008425. Epub 2024 Dec 19.
Layered deposits are found on the plateaus surrounding the western portion of Valles Marineris, mantling the chasmata rims. These rim deposits exhibit intricate layering and are described as light-toned layered deposits (LLDs) in previous studies. Light-toned layered deposits are thought to be composed of pyroclastic ash that was emplaced during volcanic eruptions and later chemically altered. Using Shallow Radar (SHARAD) observations to map radar reflections from what appears to be the base of these deposits, we discovered two additional types of rim deposits that are contiguous with the well-known LLDs; weakly layered deposits (WLDs) that exhibit less obvious stratification and completely unstratified deposits designated as nonlayered deposits (NDs). Complementing the SHARAD data with imagery from Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) and with narrow-angle imagery from the Mars Global Surveyor Mars Observer Camera (MOC-NA), we mapped the full extent of all rim deposits and present the finished map within this study. We hypothesize that all three deposits originate from pyroclastic ashfall but experienced different degrees of modification due to the variable presence of liquid water. This hypothesis requires a source of volcanic depositional material and past aqueous environments in regions with LLDs and WLDs. We discuss the potential for several large Tharsis volcanoes and a hypothesized degraded volcano within Noctis Labyrinthus as sources of the ash, and we examine the evidence for past aqueous environments.
在水手号峡谷西部周围的高原上发现了层状沉积物，覆盖着峡谷边缘。这些边缘沉积物呈现出复杂的分层，在先前的研究中被描述为浅色层状沉积物（LLD）。浅色层状沉积物被认为是由火山喷发期间堆积并随后发生化学变化的火山碎屑灰组成。利用浅层雷达（SHARAD）观测来绘制这些沉积物底部似乎反射的雷达图像，我们发现了另外两种与著名的LLD相邻的边缘沉积物类型；分层不太明显的弱层状沉积物（WLD）和被指定为非层状沉积物（ND）的完全非分层沉积物。通过火星勘测轨道飞行器的高分辨率成像科学实验（HiRISE）和上下文相机（CTX）的图像以及火星全球勘测者火星观测相机（MOC - NA）的窄角图像对SHARAD数据进行补充，我们绘制了所有边缘沉积物的完整范围，并在本研究中展示了完成的地图。我们假设所有这三种沉积物都源自火山碎屑灰降落，但由于液态水的存在情况不同而经历了不同程度的改造。这一假设需要在有LLD和WLD的地区存在火山沉积物质来源和过去的水环境。我们讨论了几个大型塔尔西斯火山以及夜迷宫中一个假设的退化火山作为灰烬来源的可能性，并研究了过去水环境的证据。
