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Author Topic:   Formations really do match detailed lab expts of sorting under rapid currents
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Message 12 of 130 (25675)
12-06-2002 3:01 AM
Reply to: Message 11 by Tranquility Base
12-06-2002 2:25 AM

Sheesh TB, read this again -
From wehappyfew's message 6:
All three types of sediment are deposited simultaneously in a transgressive sequence. The shoreline at a particular place and time is the basal unit of the TS. It commonly contains conglomerates composed of the underlying sequence, and is always unconformable to it. At the same time the Tapeats sandstone is being deposited, farther offshore the tidal and beach sands grade into the silt and shale of the Bright Angel shale, just like passive margins today. Farther still, the water is deep enough and far enough from siliclastic sources to allow carbonate platforms to accumulate, like the South China Sea, for example.
As eustatic sealevel rises, the entire assemblage migrates uphill. Shales are deposited on top of sand, lime mud on top of shale, while the new shoreline cuts into higher ground pC basement rock, creating more siliclastic source material for the whole system.
This verbally explains the methodology of stratagraphic succession about as good as can be done - short of having some nice diagrams.
As sea level rises, what is deposited in the deeper waters is now deposited in the newly deepened waters, on top of what was deposited in more shallow waters. This results in the transgressive sequence - shallow water deposits on the bottom, deeper water deposits on the top.
A sea level fall causes the opposite vertical sequence - deeper water deposits on the bottom, shallower water deposits on top. That is a regressive sequence.
Perhaps you need to visit your local geology department, and have someone diagram lateral sedimentary facies changes, and the resultant vertical columns for a transgressive sea, and for a regressive sea.

This message is a reply to:
 Message 11 by Tranquility Base, posted 12-06-2002 2:25 AM Tranquility Base has replied

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Inactive Member

Message 20 of 130 (25781)
12-06-2002 7:34 PM
Reply to: Message 15 by wehappyfew
12-06-2002 10:56 AM

If you go to practically any passive margin today, you will find modern river delta deposits on top of shallow water silts on top of deep water shales. This is called a prograding delta. It is not the same thing as the Tonto trangressive sequence because the shallow water deposits are on top.
Just an added note - The prograding delta is for all practical effect the same as a regressing sea.

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 Message 15 by wehappyfew, posted 12-06-2002 10:56 AM wehappyfew has not replied

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