Salt of the Earth (on salt domes and beds)

FWIW, you can see one of these evaporite pans forming not far from here. Cedar Lake (sic) is a big white expanse of salt/gypsum near Seminole, Texas that was named probably by a land developer in a real wet year. It's only a couple of dozen square miles in extent, though. I have no clue how thick the salts are.

Sea water is about 3.4% by weight total salt, with sodium chloride making up a big majority of all the salts. A sodium chloride solution of 26% is saturated, meaning that's all the salt it can hold. So if you take eight liters of seawater and evaporate it down to one liter, sodium chloride will be starting to fall out of solution. (Other salts, like gypsum = calcium sulfate, will start dropping out before the table salt does. Magnesium chloride, for one example, will still be in solution at this point.)Sodium chloride has a density of 2.17 g/cc and seawater about 1.03. This lets us calculate that for each centimeter of salt deposited, you must evaporate about 62 centimeters equivalent of ocean. That would be tough if you were in open ocean or in a worldwide flood.

Seems entirely so to me, just based on seeing Cedar Lake. In wet years it's a lake, and in subsequent dry years it's solid and white, and with a thicker bottom than before.Heck, Jar, you have a few similar pans down in Kenedy County, if I'm not hallucinating again.

I can tell you one way it couldn't have happened, and it starts with an F. But I don't want to spoil things....

That's it. Those are oil wells - you can see the shadows (?) of pump jacks on some of the locations if you zoom in all the way on that photo. I'm betting that the splotchy shapes in the middle of all the white might be some water that hadn't evaporated at the time of the picture. I've never driven out onto the salt myself - just to the northeast edge. I'll have to revisit now that I know that there are lease roads out into the "lake" - they'll be maintained well enough that I won't fall through some sort of crust and be pickled for all time. Hey Anglagard - road trip??

One would need to know what sort of rocks are there - it might well be that an increased input of sediment into the salt seas/pans was responsible. It doesn't seem it could have gotten a bunch wetter, though - the salt already there would have dissolved with any significant movement of fresh water across it.

How did I miss this three years ago?I have always understood that salt domes like those along the Texas coast are emplaced from flat evaporite deposits that are overlain by denser sediments. The salt's bouyancy and plasticity let it "float" up through the rock. There are domes in Iran that come to surface and even form "glaciers" of salt. (Lot's wife, anyone??)The strata near the Texas domes are pretty obviously broken from below - there have been about four zillion oil wells drilled into the edges of salt domes over around Beaumont, and well logs and seismic surveys mapped out the shapes pretty accurately several decades ago.

Maybe not that impressive. From the Halliburton Services Cementing Technology Manual, 1993 edition, we find the following solubilities for salt:
at 0 degrees C - 26.28% by weight
at 50 C - 26.83%
at 200 C - 31.6%
at 400 C - 46.4%So let's do some cocktail-napkin calculations, assuming that the heat capacity of salt solutions is the same as that of fresh water (which it ain't - it will drop with increasing salt):100 tons of 400-degree salt -saturated water + 100 tons of zero-degree fresh water will yield 200 tons of 200-degree water with 23.4% (46.4 tons divided by two hundred) salt. That will all stay dissolved, as 31.6% is saturation.100 tons of 400-degree salt-saturated water + 700 tons of zero-degree fresh gives 800 tons of 5.8% brine at 50 degrees C. Still all soluble. And 50 C is still on the warm side for fish.Also, the solubility of calcium sulfate (gypsum) actually increases a bit as water gets colder. This would make it pretty tough on the "precipitite" mechanism as a way to explain all the mixed salt/gypsum beds out here in West Texas.Note: sorry for the obscure citation. I worked for Halliburton back then, and I can assure you that they probably copied the table they published from somewhere, perhaps the International Critical Tables, with no attribution at all.

Sure, mixing brines can cause all kinds of precipitation. I deal with exactly that every day in oil field brines, and they don't have to be all that concentrated to cause problems from that precipitation. I see barium sulfate, calcium carbonate, and gypsum all the time that formed that way. And you are correct: "mixing two mineral-filled water solutions" is devilishly complicated, and there are some pretty elaborate computer programs based on hundreds of man-years of lab work to help predict what falls out of solution when.But that's not what you are trying to explain, Slevesque: you have posited hot, very salty water that mixes with cold water and drops fairly pure sodium chloride, and then ends up resembling sea water after the solids have dropped out. Seawater has even less salt than my 50-C example above. Saturated hot brine meeting cold something-like-seawater may well precipitate something - gypsum, calcium carbonate, strontium and barium sulfate - but halite = sodium chloride is not going to be what falls out.

From that abstract:
"These criteria are based on (1) comparison of observed evaporite fabrics with similar fabrics in modern and other ancient examples, and (2) interpretation of how observed evaporite processes would effect fabrics in different settings."- my emphasis