Tumbledown Formation (original) (raw)

The Tumbledown Formation is a Precambrian geologic formation found in the vicinity of Van Horn, Texas. The formation consists of volcaniclastic rock (sedimentary rock composed of fragments of volcanic rock) interbedded with basalt lava flows. It is notable as part of an almost undeformed sequence of ancient rock beds in the otherwise highly deformed orogenic belt of the Grenville orogeny, which gives geologists a window on conditions on Earth around 1200 to 1100 million years ago.