GLOBAL MAPPING OF VENUS' RIBBON TESSERA TERRAIN, DISTRIBUTION PATTERNS, AND IMPLICATIONS FOR RESURFACING HYPOTHESES

Venus, Earth's sister planet, displays a rich variety of exogenic and endogenic structures that provide clues to its history. Currently, the widely accepted hypothesis that dominates textbooks and popular science calls upon 1 to 3 km of catastrophic volcanic flooding in order to bury ~80% of Venus' surface in 10 to 100 Ma. Flooding would create a fresh global surface in the form of lowland plains, erasing (through burial) the recorded geologic history prior to flooding at ~750 Ma. Later, colliding bolides would create the ~970 'pristine' impact craters which display little evidence of tectonism or flooding. This hypothesis predicts that ~80% of Venus' surface (the extensive lowlands) should have been buried to a depth of >1km. This hypothesis can be tested because a distinctive tectonic fabric, ribbon tessera terrain, is widely accepted as representing a pre-catastrophic flooding surface, and as such, represents a base to the proposed flood layer.

Using NASA Magellan SAR imagery we have begun high-resolution geologic mapping of ribbon tessera terrain at a global scale. Using this global data set in an ArcGlobe GIS environment we can analyze the distribution and spatial relations of ribbon tessera terrain outcrop in order to constrain, at a global scale, the estimated thickness of the proposed low viscosity flood layer. Ribbon tessera terrain occurs in large tracts, preserved in the highlands, and in moderate to small sized exposures across the lowlands. The close proximity of numerous small outcrops, with distribution over extensive regions, places first order constraints on the thickness of the proposed flood layer. Ribbon terrain distribution indicates that most of Venus cannot be covered in an extensive layer >1 km thick. Two tracts of the southern hemisphere, 0-25S/160-240E and 50-82S/45E-360E, contain little to no ribbon terrain tessera. In these two regions ribbon tessera terrain could be buried to a depth greater than 1 km, or alternatively ribbon tessera terrain might not have formed there.

The distribution of ribbon tessera terrain does not does support catastrophic resurfacing. Mapping of structural trends within ribbon terrain may provide critical clues to tessera terrain formation. It seems clear that Venus preserves a geologic record that extends further back in time than widely appreciated.