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Author Topic:   Geological question. (Sea floor sediment accumulation)
bdfoster
Member (Idle past 4869 days)
Posts: 60
From: Riverside, CA
Joined: 05-09-2007


Message 15 of 38 (400256)
05-11-2007 6:38 PM
Reply to: Message 14 by anglagard
05-05-2007 3:59 PM


Re: California's Coast Range
Well of course there are no references in the original argument so it's impossible to check the numbers. But it assumes that subduction is the only process that removes sediment from the ocean basins. But subduction of sediments is actually fairly insignificant. The numbers sound right; about a 20th of all sediment being subducted. And once it's subducted you never see it again, except in it's geochemical signature in arc magmas. But California's Great Valley has over 50,000 feet of sediment that was never subducted. The stratigraphic thickness of sediments exposed in the mountains of the western U.S is substantially more than this. The total stratigraphic thickness of sediments deposited and then metamorphosed to form the Appalachians is staggering to even imagine. Accretion (that is closing of ocean basins, scraping off sediment, adding it to the continent) is the primary plate tectonic process that removes sediment from the ocean basins.
Edited by bdfoster, : No reason given.

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bdfoster
Member (Idle past 4869 days)
Posts: 60
From: Riverside, CA
Joined: 05-09-2007


Message 33 of 38 (400438)
05-13-2007 8:03 PM


Thanks for the welcome Coragyps! As for the Grand Canyon, it has experienced much greater uplift than the Miss. hence the greater depth. And the canyons at St Helens were carved in a unique type of material, volcanic ash. Because it's unconsolidated, it has very little resistance to erosion. But the interlocking grains give it the strength to support a steep face. Some YECs have said that the Grand Canyon was carved rapidly in soft sediment, but just a quick look at Grand Canyon stratigraphy shows this is impossible. Grand Canyon has vertical cliffs in sandstone and gentle slopes in the shales, like most natural landscapes. But this is the opposite of what is seen in unconsloidated sediment. Anyone familiar with construction sites will know you can't dig a trench in wet sand. Wet sand won't hold a face for 5 minutes much less 5,000 years. Wet clay OTH has cohesion, and will hold a vertical face.

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 Message 34 by jar, posted 05-13-2007 8:55 PM bdfoster has replied

  
bdfoster
Member (Idle past 4869 days)
Posts: 60
From: Riverside, CA
Joined: 05-09-2007


Message 35 of 38 (400441)
05-13-2007 9:15 PM
Reply to: Message 34 by jar
05-13-2007 8:55 PM


Re: Glad you are here so let's put you to work
Oh no! I don't want to work! Just kidding. That sounds like a great idea for a thread. I'm no expert on the Grand Canyon, and I'm sure I would learn more from a thread like that than I could ever contribute. I will definitely check it out. Thanks.
Brent

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