Thank you for answering all these.
>>> 4. How does one get thick halite (salt) or gypsum layers in the middle
>>> of Paleozoic sedimentary rocks?
>>
>> How do you get halite layers on the surface? They are usually not pure
>> halite, and not very thick. You would have to evaporate many feet of sea
>> water to get layers like we find in the column, and it wouldn't be pure
>> halite -- or pure gypsum.
>>
>>> How exactly do evaporite minerals form in flood waters?
>>
>> I don't pretend to know exactly! To get pure deposits, you would have to
>> have pure precipitates from pure brines. Brines still come out from the
>> ocean floor. Temperature changes and other factors induce supersaturation
>> and precipitation. This suggests some interesting experiments.
>
> Armchair theorizing is not science. Maybe someone could actually DO the
>experiments and then we'll talk!
Our "experiments" include observations of existing salt flats, trona (etc.)
mines, and mineral deposits at seafloor vents. Looking at these, I would
say that the past processes that deposited thick vast horizontal layers of
pure salt deposits were very different from the processes we observe at the
surface or undersea today. The present is the key to the past here telling
us that the past conditions included much greater volumes of pure brines
and conditions for ideal precipitation.
Do you know anyone who could do some larger-than-a-fishtank scale
experiments on this? Maybe Colorado State University where they did those
great flume experiments showing that micro-laminations form in seconds,
before your eyes, during sediment flow.
>
>>> Oh, and also please explain mud cracks, scour channels, and ripple
>>> marks in adjacent shales to some of these deposits (I have photos from
>>> a gypsum mine under Grand Rapids if you'd like to see them).
>>
>> I would expect scour channels and ripple marks (and other paleocurrent
>> indicators). Are the mud cracks in the same area? Mud cracks do form
>> underwater by chemical shrinkage.
>
> The mud cracks are in the shale directly overlying the gypsum.
Just what would be expected! Water and other minerals would be pulled from
the mud into the very concentrated CaSO4 solution adjacent to the
precipitate!
>
> Mud cracks far more commonly form in subaerially-exposed mud than underwater
>by chemical shrinkage. Mudcracks are also often associated with other
>sedimentary structures indicating exposure.
>
Of course. That is what we usually see in a mudpuddle.
>>> Since you mentioned rapid sedimentation, please explain how long it
>>> takes to precipitate, say, 100 feet of halite from flood waters.
>>
>> I don't know how rapid. But if it were slow, even mm per hour, I would
>> expect a lot of impurities in it. The purity we observe would indicate
>> to me a much faster rate.
>
> I disagree. Nothing I've seen in salt or gypsum mines indicates any
>exceptional purity or fast rates.
What do you see as sure evidence for slow rates?
>
>>> How much heat would be released by such a rate?
>>
>> Is the amount of heat affected by the rate?
>
> If I remember my thermodynamics, the amount of heat released is proportional
>to the amount of material precipitated but the rate is important because that
>heat has to be carried away at some finite rate (water can only transport heat
>away so fast before it starts boiling).
>
Right. The same as with the batholiths. No special problem if the heat
production and dissipation is slow, but a challenge if it is fast. Faster
moving water could carry away more heat than trapped water, but how fast
could water move without sweeping up the precipitate beneath it? I don't
know what flow rate, or other process, would balance between heat
production and dissipation. Opportunity for more aspects to the proposed
large scale experiments.
Karen