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The Permian Sea that dominated this part of Pangaea 250 million years ago left the gypsum rich deposits that have now been recycled to form the dunes at White Sands (previous post). This sea (or some smaller connected seas) also gave rise to large carbonate reefs, one of which has been subsequently uplifted and exposed by erosion as the current Guadalupe Escarpment (Guadalupe Mountains National Park).
AERIAL VIEW
Guadalupe Peak is the highest point in Texas (8751'). El Capitan, the distinctive prow immediately to the south, marks the southern end of the Guadalupe Escarpment. Carlsbad Caverns was carved (dissolved, actually) into the core of the reef much later, aided by the presence of hydrocarbons in the adjacent basin that leaked hydrogen sulfide and produced sulfuric acid, a much more effective cave-forming agent than the more common carbonic acid.
The Capitan Reef faced eastward across the Delaware Sea (an arm of the larger Permian Sea). The Delaware Basin and the Midland Basin farther east are now both major oil and gas fields and driving south towards Carlsbad I was reminded of this by the pump jacks and well heads, the pipe yards, and the lines of red Halliburton trucks. I spent the fall of 1981 in Schlumberger's training program in Midland and spent weekends exploring west Texas in my new little pickup truck. That was a long time ago!
I suppose there may have been beaches on the shores of this Permian ocean - but the environment behind these reefs was probably pretty quiet and the shores were probably muddy and perhaps vegetated (although I suspect they didn't look like the mangroves or salt marshes you might find in similar settings today).
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.
AERIAL VIEW
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.
