Geological characteristics and topographic configuration of the edge of the Vastitas Borealis Formation: Implications for a Hesperian ocean on Mars

我们研究的主要目标是对整个北部平原内北部瓦斯蒂塔斯组(VBF)外缘的地质背景、平面形状、地层和地形形态进行系统的追踪、测绘和分析。这项研究的结果对于测试北冰洋和火星长波地形的存在和演化模型至关重要。这项研究的一阶结果将是描述沿VBF接触的长波长地形起伏的长度尺度、幅度和空间关联的特征。受这些起伏影响的单位的地层位置和绝对模型年龄的估计将有助于确定火星上长波长地形变化的时间。无论过去有没有海洋，对VBF边界地形形态的表征将为理解火星地形的演化提供必要的线索。我们对北瓦斯蒂塔斯地层外边界的研究旨在解决与火星海洋假说的各个方面密切相关的下列科学问题：VBF外边界的整体地形形状是什么？乌托邦和平地岛上绘制的VBF外接触部分的地形分布是否代表了更广泛的地形趋势的部分？沿VBF边界选定区域的陨石坑计数结果如何限制VBF就位的时间间隔？我们研究区域的哪些特征(如果有的话)提供了VBF由一系列连续单元组成的证据，表明它有多个侵位事件？VBF与周围地质单位之间的地层关系是什么？VBF边缘附近的地形地貌特征是什么？它们与对VBF的解释是否一致，认为它是以前海洋的升华残留物？VBF及其外围区域的特征(例如，幽灵陨石坑，TPT)是否不仅出现在乌托邦和Asidalia Planitiae，而且也出现在VBF外接触的其他地方？

The primary goal of our study is a systematic tracing, mapping, and analyses of the geological settings, planform, stratigraphy, and topographic configuration of the outer edge of the Vastitas Borealis Formation (VBF) within the entire northern plains. Results of this research are crucially important in testing models of the existence and evolution of both the northern ocean and long wavelength topography on Mars. The first-order results of this study will be a characterization of the length scales, amplitudes, and the spatial associations of long-wavelength topographic undulations along the VBF contact. The stratigraphic position and estimates of the absolute model age of units affected by these undulations will permit determination of the timing of the changes of the long-wavelength topography on Mars. Regardless of the presence or absence of the ocean in the past, the characterization of the topographic configuration of the VBF boundary will provide necessary clues to understand the evolution of the Martian topography. Our study of the outer boundary of the Vastitas Borealis Formation is aimed to address the following scientific questions closely related to various aspects of the Martian ocean hypothesis: What is the overall topographic configuration of the outer boundary of the VBF? Does the topographic distribution of the portions of the outer contact of the VBF mapped in Utopia and Acidalia Planitiae represent segments of broader topographic trends? How do the results of crater counts in selected areas along the VBF boundary constrain the time interval of the VBF emplacement? What features (if any) in our study area provide evidence that the VBF consists of a series of sequential units suggesting multiple episodes of its emplacement? What are the stratigraphic relationships between the VBF and the surrounding geologic units? What are the morphologic and topographic characteristics of the VBF near its edge? Are they consistent with the interpretation of the VBF as a sublimation residue of a former ocean? Do features that characterize the VBF and its peripheral zone (e.g., ghost craters, TPT) occur not only in Utopia and Acidalia Planitiae, but also elsewhere along the outer contact of the VBF?