Crater-Exposed Intact Stratigraphy Blocks and Volcanogenic Origin

Introduction: Typical terrestrial uplift and exposure of layered and stratified rocks are usually not oriented at a high enough tilt to easily infer their geometries from aerial or orbital remote sensing techniques. However, when layers are brought to the surface in crater central stratigraphic uplifts, they are tilted at such high orientations (>45) as to be useful for such determinations as thickness, strike, dip, etc. Here we use a variety of Martian datasets to identify (THEMIS IR, MOLA) and classify (CTX and HiRISE) these unique bedrock exposures and textures in Martian craters [1]. A global survey of 868 Martin craters reveals three distinct classifications of bedrock textures, which includes uplifted and overturned strata that are exposed from depth. Crater-exposed bedrock provides a unique opportunity to not only understand the underlying mineral compositions within the Martian crust, but also gain insight into past geologic processes of Mars. Of the 868 craters surveyed, 210 have bedrock outcroppings that are sufficiently exposed and extensive enough to determine their overall textures. Of these, we classified 39 as Intact layered Stratigraphy (IS) (i.e., uplifted and inverted bedrock consisting of strongly layered and intact blocks of stratigraphy with layers ranging from meter to decameter scales in HiRISE images as seen in Figure 1). As seen in Figure 2, a strong correlation exists between the location of IS craters observed and the major volcanic provinces and mapped Hesperian flood lavas and ridged plains (purple units), generally interpreted as flood lavas [2]. Here we couple the geologic context and textures observed from depth with the measurable thickness and cyclicity of the layers, which alternate between competent and less competent layers within a given uplifted megablock, to better understand and relate past geologic events and processes across vast regions of Mars.