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Author Topic:   Introduction To Geology
Taq
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Posts: 7997
Joined: 03-06-2009
Member Rating: 3.9


Message 92 of 293 (658419)
04-04-2012 4:18 PM
Reply to: Message 91 by Artemis Entreri
04-04-2012 3:58 PM


Re:
Not sure if you haven't got to it yet or if you are going to cover it, but…Do you have anything on Sand dunes? I realize you mentioned them in the Deserts (evap exceeds precip) section, but it seemed very brief. I realize that your topic and interest is due to your acceptance of Uniformitarianism, and that Sand Dunes may not always apply to this assumption, but I think they are important to understanding how natural forces (wind) affect the earth (as in soil and rocks).

Our understanding of sand dunes in the fossil record comes from our study of sand dunes in the present. That is uniformitarianism.

To start off, I would suggest the wiki page for cross-bedding. It includes pictures of cross-bedded sandstones which are preserved wind blown (eolian) sand dunes.

http://en.wikipedia.org/wiki/Cross-bedding


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 Message 91 by Artemis Entreri, posted 04-04-2012 3:58 PM Artemis Entreri has responded

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Taq
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Posts: 7997
Joined: 03-06-2009
Member Rating: 3.9


Message 99 of 293 (658490)
04-05-2012 12:36 PM
Reply to: Message 97 by Artemis Entreri
04-05-2012 9:37 AM


Re: On Holiday
I don't really have any suggestions, other than maybe a brief explanation on the various types of dunes (for some reason crescent dunes get all the love),

Indeed, they do. However, I happen to live within a very short drive of these wonderful dunes:

http://en.wikipedia.org/wiki/Bruneau_Dunes_State_Park

They are reportedly the tallest dunes in North America at 470 feet. Interestingly, they do not move and are not the classic mobile crescent shaped dunes. They have remained in their current position since the end of the last Ice Age because the area acts as a trap for windblown sand.


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Taq
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Posts: 7997
Joined: 03-06-2009
Member Rating: 3.9


Message 100 of 293 (658492)
04-05-2012 12:41 PM
Reply to: Message 96 by Artemis Entreri
04-05-2012 9:30 AM


Re:
thanks. That is very interesting. Some sand dunes are old (not geologically speaking though), and are constantly changing form and shape.

What doesn't change are the laws of physics which underlie the mechanisms that produce wind blown (eolian) sand dunes. We can look at modern sand dunes and use that knowledge to detect wind blown sand dunes in the geologic record. This is uniformitarianism.

What is interesting is that some creationists claim that the deposits seen in the Grand Canyon were produced by a recent global flood. One of those deposits is the Coconino Sandstone. This deposit has all of the markings of eolian deposits. IOW, there had to be a desert with wind blown sand dunes during the flood. This seems very problematic, at least to me.

{Careful - Starting to head off-topic. This topic is a geology course, not a critique of creationist alternatives - Adminnemooseus}

Edited by Adminnemooseus, : Note in red.


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Taq
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Posts: 7997
Joined: 03-06-2009
Member Rating: 3.9


Message 103 of 293 (658800)
04-09-2012 6:09 PM
Reply to: Message 102 by Artemis Entreri
04-06-2012 12:40 PM


Re: On Holiday
hmm never hear of that state park before, my ID experience consists of Pocatello

I live on the West side of the state. Absolutely wonderful geology in the area. My personal favorite is the amazing weathered tuffs at Leslie Gulch (just across the border in Oregon):

http://www.blm.gov/or/resources/recreation/site_info.php?...

Near Pocatello is the Craters of the Moon national park where you can check out massive lava fields:

http://en.wikipedia.org/...on_National_Monument_and_Preserve

In between west and east Idaho you can check out a number of massive and very beautiful canyons that are cut through flood basalts such as this one in Twin Falls (the canyon that Evel Knievel couldn't seem to get across):

http://www.idahoreporter.com/...s/2012/01/Perrine-Bridge.jpg

I am not a geology expert by any means, but the local geology has always interested me. That is why threads like this one always interest me.


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 Message 102 by Artemis Entreri, posted 04-06-2012 12:40 PM Artemis Entreri has responded

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Taq
Member
Posts: 7997
Joined: 03-06-2009
Member Rating: 3.9


Message 109 of 293 (659611)
04-17-2012 11:43 AM
Reply to: Message 108 by Dr Adequate
04-17-2012 2:12 AM


Re: Reefs
Corals are constrained by their biology to be shallow-water organisms. Some can grow as deep as 50 meters, some will perish in depths greater than 1 meter, but all require relatively shallow water.

There are deep water corals:

http://en.wikipedia.org/wiki/Deep-water_coral

However, they are different from shallow water reefs.


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 Message 108 by Dr Adequate, posted 04-17-2012 2:12 AM Dr Adequate has responded

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Taq
Member
Posts: 7997
Joined: 03-06-2009
Member Rating: 3.9


Message 111 of 293 (659630)
04-17-2012 2:57 PM
Reply to: Message 110 by Dr Adequate
04-17-2012 12:28 PM


Re: Reefs
You're quite right. I can't think how I managed to avoid finding that out. I shall amend the article accordingly. Thank you.

It is true that shallow water corals do depend on sunlight because they carry endosymbionts called zooxanthellae. These are photosynthetic flaggelated protozoans that provide the host with energy (e.g. glucose). However, corals are in the phylum Cnideria which also includes jellyfish, hydrozoa, and sea anemones. They are capable of producing energy of their own, and that is exactly what deep sea corals do by feeding on zooplankton and small invertebrates. Like jellyfish and hydrozoa, they have stinging nematocysts that they use to stun their prey.

It would be accurate to say that specific species of coral can only live within the daylit portion of the ocean due to their dependence on photosynthesis.


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