quote:
The Geo Column idea assumes that each layer is a "landscape" taht endured for a very long period of time. I keep coming to the Mississippian period because it seems simplest: Only one kind of sediment, redwall limestone, and the period is said to have lasted some 50 million years. ONLY redwall limestone made up that "environment," that "landscape" for fifty million years? How long was it in the sedimentary form? Was this underwater? Did it lithify during those 50 million years before the next layer / era began?
The problem here is that you need to actually appreciate the data that is to be explained.
This webpage makes a good start:
http://www.geocities.com/earthhistory/grandb.htm
Some relevant quotes are:
The Redwall is divided into four members: the Whitmore Wash, Thunder Springs, Mooney Falls, and Horseshoe Mesa members. The Whitmore Wash is nearly pure calcium carbonate (98% pure). The Thunder Springs member consists of alternating layers of chert and carbonate. The Mooney Falls member is once again almost totally pure calcium carbonate (99.5%). The Horseshoe Mesa member consists of thinly-bedded carbonate with occasional chert lenses.
So much for "one type of sediment".
The Surprise Canyon formation is also Mississipian, and so that must also be included in any discussion of the "types" of sediment.
Though only a few million years are thought to seperate the end of Redwall deposition and the begginning of Suprise Canyon deposition, the surface of Redwall Limestone was altered considerably during this time. During this time, a series of westwardly-deepening channels were incised into the surface of the Redwall, up to 400ft thick in some places. Blocky knolls and small erosional "mesas," up to 40ft high, are present on the upper surface of the Redwall, buried by basal Supai sediments
So much for there being no erosion.
I would also suggest that the question "over what extent of planet earth did this Mississippian era stretch" is rephrased. As written it makes about as much sense as asking what portion of the Earth is currently in the year 2005AD by the Gregorian calendar.
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