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

点击翻译按钮获取中文摘要

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?