Unsolved Geologic Dilemma

The Dolomite bedrock common in the Eleven Point District of the Oz-Arks is riddled with caves, underground streams, and springs like this one off highway 19 near Greer, Missouri.

The Irish Wilderness Notebook:

The Dolomite Mystery

The woodsy descent through the ridge ravine and downward toward the caulfloweresque creekboil at Greer Springs is patched with poison ivy. We stay close to the trail, only veering aside to inspect some carbonate rock resembling miniature cityscapes erupting out of the dense ivy undergrowth.

These rocks, which we now realize form the bed over which we have been walking, are chalked full of oceanic fossils from the Cambrian--algae, sponges, worms, bryozoans, brachiopods, trilobites, cephalopods, and crinoids.

Limestone and dolomite are formed by microscopic showers of needle-thin aragonites and calcite crytstals rained upon the ocean floor, burying shells and other remnants of life in limy ooze. But only dolomite contains a substantial amount of magnesium. Few creatures incorporate magnesium carbonate in their tissues, so the presence of this mineral cannot be explained by the skeletal remains of Cambrian life-forms. Nor does magnesium carbonate crystalize and settle out of water with the ease of calcium carbonate. Even though magnesium is found in seawater alongside calcium, it never accumulates in sediments as readily as calcium.

Where did the thousands of feet of magnesium-rich dolomite we are now standing on come from?