RE: Evaporites and rates

Karen G. Jensen (kjensen@calweb.com)
Wed, 17 Feb 1999 20:22:22 -0600

>>Alternating layers --
>>
>>Are you saying that yearly seasonal variation is the only possible
>>interpretation of the observation of alternating abundances of the
>>impurities?
>>
>><b>Perhaps you could present an alternative explanation which takes into
>>account the observed structure as well as the periodicities of several
>>hundreds of thousands of years ? Periodicities which match known processes
>>?</b>
>
>Drying lines around an evaporating puddle can exhibit cycles, even apparent
>"11-year cycles" which clearly have nothing to do with sunspots or with
>years. The observation of cycles does not necessarily mean multi-year
>periods, just as the observation of alternating layers does not necessarily
>mean seasonal variation within years.
>
>Please show how such drying lines can exhibit such cycles which all happen
>to match know cycles ? You are now saying drying puddles exhibit 11 year
>cycles ? Please support this with some evidence. Also the seasonal
>variations are 1) supported by observation 2) supported by the content of
>the layers.

This happened on a friend's front porch during the summer in Southern
California. We didn't take pictures. Perhaps you can observe it yourself
in a suitable place next summer.

>
>
>I don't know enough about these salt layers to propose a specific
>explanation, but would not assume that their alternations must be yearly
>seasons or that their cycles must be multi-year. What characteristics of
>
>That they are seasonal is based on a variety of evidence.
>
>the layers lead you to affirm that they are?

What are the evidences? Inferences from palynology?

I'm also intersted to hear
>your interpretation of rocks like the Castile formation (alternating CaCO3
>and CaSO4 -- Permian, near Capitan Reef). Looking at the structure of
>rocks like that, it is hard for me to believe that they were laid down over
>a long period of time.
>
I hoped to hear your read on the Castile formation, or another similar deposit.

>"Hard for you to believe" is not necessarily an convincing argument. It is
>even harder to believe that they were laid down in a short period of time.
>So please provide us with some features or reasoning which lead you to
>your conclusion ?

A specimen of Castile formation which I have in at hand here has the usual
whitish and greying more or less parallel stripes, showing the alternation
between the two salts. Most of the grey stripes are about 1 mm wide
(0.5-2mm); the white stripes vary much more, some being 4mm deep, some 2
mm, some 1mm or less, a few over 5mm. The lines are fairly straight, but
do undulate somewhat. There are about 20 alternations in about 9 cm, from
bottom to top of this specimen, possibly interpreted as 20 years'
deposition (in the midst of the hundreds of layers in the deposit as a
whole). That describes one end of the specimen.

The rest of the specimen is more revealing. Unlike most of the deposit, it
shows much soft-sediment deformation, including sections broken and turned
at various angles. A block of 11 alternations abuts against 15 horizontal
alternations, resting on the 16th and lower layers. Other blocks sit at
other angles, some with their layers bending under other blocks.

This tells me that the layers were still bendable when much of the
formation had been deposited, indicating rapid sedimentation of the entire
deposit rather than deposition and crystalization of individual layers, one
per year.

That is how I read it.

Karen