Friday, April 04, 2014

White Sands

I try to stick to a fairly standard theme in this blog. Posts are places (not issues or topics or events, and only occasionally people). They are built around photos I've taken myself (usually within days or sometimes weeks). The subject material is usually a blend of coasts and physical geography. Occasionally, I post photos of a shoreline with little geologic or geographic narrative. And sometimes I even post photos of something geologic with only a very tenuous connection to the coast.

A few days in New Mexico left me with a particularly tenuous connection to the coast and the next two posts are a bit of a stretch for Gravel Beach.  My editor may object - but wait, this is a blog, there is no editor!

White Sands National Monument is a large dune field in the Tularosa Basin of south central New Mexico. The white sands are gypsum crystals, not the quartz sand we usually encounter in dune environments. The gypsum originated in a shallow Permian Sea that may have resembled the warm Persian Gulf of today. This 250-million year old Permian Sea is a recurring theme in southern New Mexico, one that gets visited again in the next post. Repeated drying up of the sea left thick deposits of gypsum.


These gypsum-rich rocks were buried for most of their history, but were then uplifted and exposed 70 million years ago during the Laramide Orogeny (formation of the Rocky Mountains) and erosion and chemical dissolution carried the gypsum into the isolated Tularosa Basin. The gradual drying up of Pleistocene Lake Otero further concentrated the gypsum and now the winds blowing across the dry lake beds of Lake Lucero and nearby playas carry the gypsum crystals up into the dunes.

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