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Author Topic:   Geology- working up from basic principles.
Percy
Member
Posts: 22393
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 126 of 156 (542208)
01-08-2010 10:20 AM
Reply to: Message 125 by stewartreeve
01-08-2010 10:09 AM


Re: Coagulation and Flocculation
stewartreeve writes:
Oh, and a note, someone brought up recently that i was using the notion of flocculation to disprove the Lake Shigetsu varve interpretations - i actually did not such thing...i merely corrected a comment previous to that original correction, which asserted that clays necessarily settled slowly. That's it. I did not comment on the Lake Shigetsu info at all, initially.
Uh, not that coagulation and flocculation aren't fascinating, but unless you can tie them into evidence for your position, such as how they affect the interpretation of the Lake Suigetsu (not Shigetsu) varves, discussion of them doesn't really belong in this thread.
--Percy

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 Message 125 by stewartreeve, posted 01-08-2010 10:09 AM stewartreeve has replied

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 Message 128 by stewartreeve, posted 01-08-2010 10:29 AM Percy has seen this message but not replied

  
Percy
Member
Posts: 22393
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 135 of 156 (542614)
01-11-2010 9:04 AM
Reply to: Message 133 by petrophysics1
01-11-2010 7:56 AM


Re: On the timelyness of replies and focus on the topic
petrophysics1 writes:
Formations and their boundaries ARE NOT time lines. In special instances they could be, but in general they are not.
Isn't this overstated when you say "special instances"? You used the example of the Mississippi and the Gulf of Mexico, but isn't the area around the margins of the Gulf dwarfed by the area of the Gulf itself? Aren't the intersections of major rivers like the Mississippi with major bodies of water like the Gulf of Mexico the exception rather than the rule? And if we're talking about millions of years rather than thousands of years, aren't a great many formations and their boundaries fairly useful time lines?
So if we're looking at sandstone deposits that formed just off the coast of a continent then as we move further and further way from the old continental margin we're looking at newer and newer sandstone deposits, but how many years are we talking about per horizontal mile? Not millions, surely.
And if we're looking at limestone deposits that formed in shallow seas far from the coast then they were pretty much deposited all at the same time, and limestone deposits are not "special instances."
--Percy

This message is a reply to:
 Message 133 by petrophysics1, posted 01-11-2010 7:56 AM petrophysics1 has replied

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 Message 138 by petrophysics1, posted 01-11-2010 12:02 PM Percy has replied

  
Percy
Member
Posts: 22393
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 139 of 156 (542636)
01-11-2010 1:26 PM
Reply to: Message 138 by petrophysics1
01-11-2010 12:02 PM


Re: On the timelyness of replies and focus on the topic
Hi Petrophysics1,
You seem to be addressing yourself to the larger discussion in this thread rather than to my rather minor point, namely that when you said, "Formations and their boundaries ARE NOT time lines. In special instances they could be, but in general they are not," that it was overstated. Nothing you've said here changes my mind, because nothing you've said here addresses what I said.
petrophysics1 writes:
Ash falls, or all the diatoms dying the in winter and settling out are very close to a time line,but almost everything else you look at is either prograding/regressing or transgressing.
But, as I asked already (see where I concluded with, "Not millions, surely."), how much vertically compared to how much horizontally? For example, the vertical thickness of the layers in the Grand Canyon represent ten, twenty, sometimes more, millions of years. Only at most a few hundred feet thick, the horizontal extent of these layers is for miles and miles and miles. Obviously the horizontal transgressing is far, far faster than the vertical deposition rate, and so these layers, especially at the precision of millions of years, represent pretty clear time lines.
This doesn't have anything to do with the Gilbert Delta or RAZD or some poor schmuck from Australia. I was just making a minor point that when you say that layers could only be considered time lines under special circumstances that in my opinion you were overstating the case.
--Percy

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 Message 138 by petrophysics1, posted 01-11-2010 12:02 PM petrophysics1 has replied

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 Message 141 by petrophysics1, posted 01-11-2010 5:36 PM Percy has seen this message but not replied
 Message 142 by edge, posted 01-11-2010 7:59 PM Percy has seen this message but not replied

  
Percy
Member
Posts: 22393
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 143 of 156 (542679)
01-11-2010 8:23 PM


To Edge and Petrophysics1
I think if you guys go back to my posts you won't be able to find where I object to anything about transgressions and so forth. I understand it, I agree with it. You can stop trying to convince me.
I had a different and somewhat minor point. Petrophysics1 said that layers are not time lines except in special circumstances. But on a scale of millions of years the vast majority of layers are timelines. The Grand Canyon is one giant gallery of such time lines, and the Grand Canyon is not a special circumstance. In fact, it is probably where most laypeople get their best impressions of the geologic column and the succession of geological eras.
I made the point because I was afraid that some might conclude that Petrophysics meant that layers that laypeople are actually likely to see are not actually much like timelines with dates that we have confidence in, that, for example, the Coconino sandstone layer of the Grand Canyon is not really from around 260 million years ago, but actually varies in age a great deal as you go from one end of the canyon to the other. I very much doubt that the age of such layers varies by more than a couple percent across hundreds of miles.
--Percy

Replies to this message:
 Message 146 by edge, posted 01-11-2010 10:15 PM Percy has seen this message but not replied
 Message 147 by petrophysics1, posted 01-11-2010 10:30 PM Percy has seen this message but not replied

  
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