ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Saturday, July 20, 1996 TAG: 9607220132
SECTION: EDITORIAL PAGE: A-7 EDITION: METRO
SOURCE: ROBERT C. WHISONANT
I THOROUGHLY enjoyed the articles in your newspaper about Saltville - a truly unique and fascinating place. But in the July 14 article, "Holding ground," the brief paragraph or two devoted to this area's geologic history badly misrepresented the real story of the salt deposits. For example, no salt ever precipitated from a dried-up lake 1,700 feet above sea level in the Saltville Valley. And the big Ice Age mammals drawn to the region's natural salt licks came millions of years after the salt formed. In the interest of setting matters straight for your readers, I'd like to offer the following version of Saltville's geology.
The Saltville Valley is underlain by rocks belonging to the Maccrady Formation, a thick sequence of sedimentary strata deposited in the early Mississippian Period roughly 350 million years ago. At that time, the edge of present-day eastern North America collided with other tectonic units to begin elevating the Appalachian Mountains. To the west of these emerging mountains, in the continental interior, lay an extensive shallow sea. Great rivers carried mud, sand and gravel eroding from the northwestern slopes of the ancestral Appalachians into this ancient marine realm, forming deltas and coastal plains in Southwest Virginia where land met sea.
When the Maccrady sediments were deposited, Virginia was in a much different part of the world (thanks to tectonic plate movement), and thus had a climate radically unlike today's. Paleogeographically, the Old Dominion was located about 10 to 20 degrees south of the equator in the Trade Winds Belt and mostly on the leeward side of the developing Appalachian Mountains. This meant that, for much of the time, the Mississippian Coastal Plain in Southwest Virginia wasn't only hot but also dry. Modern regions similar to this are called "sabkhas," an Arabic word for wide tidal-flat complexes developed along a coastline in a hot, arid region such as the present Persian Gulf. In these areas, the salty waters trapped between the grains of sand and mud in the tidal flats become very saline, and abundant "evaporite" sediments - typically salt and gypsum - crystallize from the briny pore waters. Thus, the salt for which the Saltville area is so justly famous wasn't formed in a mountain-valley salt lake 1,700 feet above sea level, but in coastal sediments right at the water's edge of a long-vanished sea.
After deposition, the Maccrady sediments were deeply buried and compressed into rocks such as shale, sandstone, rock salt and gypsum. Eventually, powerful new tectonic forces folded and faulted these layers, gradually pushing them upward. This final mountain-building episode occurred over many millions of years, but culminated near the end of the Paleozoic Era around 250 million years ago. During this time, the converging North American and African plates crushed and uplifted the Appalachian Belt caught between them into a brand new mountain range. Since that time, erosion has slowly worn down these grand old mountains, at last uncovering rocks such as the Maccrady evaporite beds.
By about 14,000 years ago, the Saltville Valley topographically looked much as it does now - dotted with saline ponds and springs. These formed when fresh water from snow and rain seeped downward into the evaporite layers a few hundred feet underground, dissolved some salt, and returned to the surface as briny solutions issuing forth along faults, fractures and bedding planes. The great mammals of this time - including mammoths, mastodons, musk oxen, giant ground sloths, caribou, moose, deer and horses - flocked to these natural salt licks. With them came the Paleo-Indians who must have hunted these fabulously rich grounds for meat, bones and hides of the late Ice Age beasts.
In all likelihood, these early Native Americans also obtained salt for themselves by simply boiling it down from the region's naturally saline waters. Thus began human use of the Saltville Valley's evaporite resources, which goes on to this day. Although salt is no longer extracted, gypsum production, commenced in this area in the late 1700s, continues from the Maccrady rocks at the Locust Cove Mine located a few miles northeast of Saltville. A variety of wallboard products is made from gypsum, so it's possible that some of us may have a little piece of Smyth County in the walls of our homes!
Saltville is indeed one of the most unique sites in North America, thanks to its rare blend of geology, paleontology, archeology and recent history. Such a place certainly deserves to be much more widely known and appreciated than it is. I hope this brief sketch of the area's geologic history gives your readers a better sense of the vast expanses of time and the incredible earth forces required to create this very special part of Southwest Virginia.
Robert C. Whisonant is a geology professor at Radford University.
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