Visiting the Brushy Basin
Brushy Basin Member, Colorado Plateau
Morrison Formation 153-145Ma.
A lone sauropod dinosaur visits the shores of a lake in what will one day become a part of the Colorado Plateau. Volcanic dust hangs in the air, huge fire-blackened logs, similar to the extant redwood, rot at the lake shore, whilst tall cycads are blown about in the warm afternoon wind.
The Brushy Basin Member is the youngest of four recognised sub-divisions of the Morrison Formation exposed on the Colorado Plateau. The Morrison Formation is an extensive unit of sedimentary rock deposited over a period of approximately ten million years during the Late Jurassic period and underlies several states in western North America, covering an estimated 1.5 Million square kilometres.
For several million years prior to the deposition of the Morrison Formation, a series of marine transgressions from the Arctic Ocean covered the western United States, finally regressing with the uplift of highlands to the west. These rocks, known as the Sundance Formation, underlay the Morrison formation, contributing toward the flat semi-arid landscape that would follow.
The rocks of the Brushy Basin Member are composed of fine silt mudstones layered with volcanic ash, and represent a time when great braided rivers bordered by riparian forests, analogous to the modern Mississippi floodplain, meandered across a flat alluvial landscape into a basin containing a vast saline lake.
Printmaking and graphite on paper.
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