Apart from several other processes (biological influence, change in pH of lake water, etc.), evaporation is one of the cause for calcite-aragonite precipitation in the lake water.
In several literature, the sequence of carbonate precipitation b evaporation process is is well explained. My question is that, is there any way by which we can quantify the evaporative process between calcite and aragonite minerals.
Sorry for the confusion......I mean is it possible to make a relative curve for evaporation based on the carbonate mineral %.
e.g. Aragontie precipitates in more evaporative condition relative to calcite. So using this concept can we able to make a plot for relative evaporation for the core profile.
Are you asking if you can use the presence of Aragonite vs. Calcite to quantify the rate of evaporation?
If so I haven't come across anything like that in the literature, and don't think it's possible as Aragonite vs. Calcite precipitation isn't governed by the rate of evaporation. It is governed by the ratio of Mg+ : Ca2+ as well as other environmental factors as Kenneth above has mentioned.
dear Joshua,
I can understand its very hard to do that.....but we should keep in mind that apart from other process (as mention by Dr. Kenneth), evaporation factor can also govern the Mg/Ca ratio in the lake water which may influence the aragonite concentration.
The process of evaporation itself does not influence the Mg/Ca ratio. Evaporation can only concentrate the dissolved constituents, but each chemical species will remain in the same proportional concentration to one another; i.e. a two-fold evaporation of water containing 2Ca and 3Mg will result in a brine containing 4Ca and 6Mg. Both chemical species are doubled in their individual concentration, but they remain in the same ratio of 2mCa : 3mMg.
If evaporation continues, eventually one or other of the dissolved constituents will become supersaturated and this may cause the precipitation of a mineral - which mineral is dependent on the molar ratios of the chemical species within the brine, and the precipitation will change the molar ratios as more of one species may be required to precipitate a mineral than another.
The ratio may also be changed if another mineral is dissolved into the water, or if cation exchange with surrounding minerals occurs.
Water-rock interactions or another biophysical process may impact the molar ratios, but evaporation itself cannot directly affect molar ratios, only the lead on effects resulting from the concentration of water (such as mineral precipitation) can do this.
Therefore, I do not think that you can directly calculate evaporation rates from the amount of Aragonite vs. Calcite.
What you could potentially tell from the presence of Aragonite over Calcite would be a number of other environmental factors at the time of deposition, because Aragonite only precipitates in preference to calcite under certain conditions.
that is why i like this discussion forum.......a healthy discussion gives you lot of information....
thanks Mr. Kenneth and Joshua for such a nice discussion.....
Now I can understand the only based on calcite and aragonite we can not quantify evaporation process, for this we need some other factors also, which may influence the aragonite precipitation over calcite.
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