-------------- Original message ---------------------- From: "Geary Schindel" <gschin...@edwardsaquifer.org> > This definition doesn't necessarily state that it's derived from > limestone but we may be nitpicking. Anyway, I've always thought that > they are mostly found on limestones so you would think that they would > be associated with the limestone weathering process. However, I've had > some pretty extensive discussions on the matter of Terra Rosa's in the > Mammoth Cave area with Jim Quinlan, former Mammoth Cave Park Geologist > about the soils and was surprised when he said that they were most > likely derived from overlying material as there was insufficient > insoluble material in the St. Genevieve Limestone to form the soils. If > that's the case, why are they red like every other limestone soil.
That all seems good up front. It seems that most (certainly not all) terra rossa has traditionally been associated with limestone by various sources. But perhaps their experience on a world scale is limited. Certainly not all limestone areas contain terra rossa--or at least it is not all red. Quinlan's assertion that its primary constituents came from the former overburden (some of it miles thick) seems to be too simple to have been missed by others. I would futher suggest that it could as easily have been transported hundreds of miles to the limestone either on the surface or underground where it was more or less trapped (lay in situ, at least) for some time within voids and was later exposed (and intensified or concentrated) through weathering. Or that the chemical composition of a particular limestone was capable of altering the chemical composition of a particular soil deposited on top of it--or vice versa. (I'm not proposing that, just suggesting that it could be as likely as any other speculation.) Further still, the shades and tones of redness (or lack of it) in the various soils and areas would almost certainly be attributed to "impurities" from the same or subsequent or even previous sources, in effect mechanically watering down or thinning of what is in some places very strikingly red soil--obvious terra rossa. The blackish clays and other sediments within most Texas caves definitely have enough or a red tint within them to leave white shirts pink, not gray, when washed after a caving trip. But a lot of the caves in Texas do have red mud--just not brilliantly red mud--and red soils can be found in non-limestone areas. Again, this is business too tricky for us mere dabblers to be dabbling in with any authority. --Ediger --------------------------------------------------------------------- Visit our website: http://texascavers.com To unsubscribe, e-mail: texascavers-unsubscr...@texascavers.com For additional commands, e-mail: texascavers-h...@texascavers.com
