Evidence for rapid and widespread emplacement of volcanic plains on Venus: Stratigraphic studies in the Baltis Vallis Region
Geological mapping of the area around Baltis Vallis, the longest (6,800 km) canali-type channel on Venus, has led to the determination of stratigraphic relations which appear to be consistent over this entire region comprising ∼20×106 km² or ∼5% of the total surface of Venus. The most abundant unit in the study area, plains with wrinkle ridges (Pwr), consists of two subunits separated by the formation of Baltis Vallis, a feature which is interpreted by most workers to have formed essentially geologically instantaneously. The wrinkle ridges deform both subunits of Pwr, while ridge belts are embayed by the Pwr plains. Consistent age relationships between the Pwr subunits, wrinkle ridges, Baltis Vallis and ridge belts along the entire 6,800 km channel length is evidence that unit Pwr is a real stratigraphic marker unit and not a mosaic of plains emplaced at significantly different times, at least in the ∼5% of the surface of Venus comprising the study area. The Baltis stratigraphic sequence was compared with stratigraphic relations found in earlier studies of thirty-six 1,000×1,000 km sites randomly distributed over the surface of Venus [Basilevsky and Head, 1995] and was found to be comparable. This supports the interpretation that these stratigraphic units represent generally globally quasi-synchronous geologic events rather than the products of geologic activity in different areas of the planet at different times.