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Jim Bradshaw: An old well offered clues about the Gulf's formation

Savinien Cart found out for himself that practically all of south Louisiana was once beneath the sea. He dug a well 40 feet deep at his place at Pointe-aux-Loups in what was then western St. Landry Parish (Acadia today) in spring 1879.
At 35 feet, he struck a pine log “in a tolerable state of preservation,” according to a report in the Opelousas Courier. Two and a half feet deeper, he struck what the newspaper said were Salurian-era shells which, if I remember my Geology 101 correctly, would make them several hundred million years old. The layer of shells was “over one foot in depth resting upon a bed of grey blue clay.”
When Savinien dug through the clay, “he took out more than a barrel of these marine fossils, of almost every shape and size found on our sea-shore.”
I’m not sure that the newspaper’s got the dates right, but it is a fact that Pointe-aux-Loups and lots of other places were once beneath the Gulf of Mexico. Scientists know that its waters once stretched nearly to Oklahoma, but there is some argument about how the basin that became the Gulf was formed.
One theory is that about 500 million years ago it was part of a land mass that gradually began to sink along a crack in the earth that stretched from central Texas to Mobile Bay. Some other scientists argue that the Gulf basin began as a depression created when the earth’s crust first began to form.
Another idea is that the it was formed when a huge continent called Pangea began to fall apart. According to this theory North America, South America, Europe, and Africa were all part of one big continent until about 250 million years ago, when for some reason they split apart. The space left between them filled with water, part of which is the Gulf
That has a certain appeal to me. The curves on the east coast of South America and the west coast of Africa look to my untrained eye like they would make a snug fit if the continents were pushed back together,
The answer to the question of when the Gulf permanently filled with water depends, at least in part, on which theory is correct, if any of them is.
The most popular scenario seems to be that water from the Pacific Ocean poured into the depression, however it was formed, when gaps were opened from time to time by earthquakes or other events in what is now Mexico.
Geologists say the Gulf filled permanently probably between 250 million and 350 million years ago, perhaps bringing the shells that ended up in Savinien Cart’s well.
At least, I think that’s what the geologists say. The Courier’s editors noted in their article, “We are not sufficiently acquainted with the geology to speculate upon the age of the deposits. … This is a question for our scientists — not a country newspaper.”
Nothing has changed about that.
A collection of Jim Bradshaw’s columns, "Cajuns and Other Characters" is now available from Pelican Publishing. You can contact him at jimbradshaw4321@gmail.com or P.O. Box 1121, Washington LA 70589.

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