Re: Hypothesis Involving Planetoid Impacts

Christof Kuhn wrote:
> Professor Gauss wrote:

> > 3) The relatively highly curved crust relieved itself on the now less 
> > highly
> > curved surface by distorting.  Massive cracks may have given rise to long
> > rivers such as the Mississippi.  In other places, more stress relief 
> > may have
> > caused the formation of wrinkling and faulting to produce various 
> > types of
> > mountain ranges.  The cracking process, in addition to the impacts 
> > themselves,
> > may have caused the crust to break up into continents.
> You got the distortion thing right (in contrast to most Earth 
> Expansionists), but as I said, the crust is younger than the impact era.
> And the Mississippi formed only a twinkling of an eye ago in relation to 
> the Earth's history...
> And I cannot recall any crack in the whole run of the Mississippi - if 
> you would consider the African Rift valley, that's a different thing, 
> but it's because of plate tectonics.

Christof is correct in saying the modern Mississippi is only tens of 
thousands of years old, but the story is a bit more complex than that.

The rocks beneath the Mississippi at St. Louis are lower Carboniferous 
limestones in age, thus putting a lower age limit on that part of the 
river basin. A river must flow downhill. The New Madrid Rift Zone is 
considered a failed rift arm of a triple point junction related to the 
Ouachita uplift/subsidence zone, and weakness along that zone is at 
least 200 million years old (From Cape Girardeau, Mo south, down the 
current river valley then angling west to Marked Tree, Arkansas). Some 
people think there was earlier vertical movement in that section of the 
country, related to the Ozark uplift. Most geologists believe the 
sedimentary dip around the Ozarks combines initial dip, (3-7 degrees 
from the Ozarks to the Mississippi) with later subsidence along the 
river, related to New Madrid/Reelfoot zone movement.
    At the same time, it is generally believed that the Midwest, 
including the Mississippi and Missouri drained to a proto-Hudson bay in 
the north until the last ice age. It is also well-supported that the 
Mississippi was once much shorter, entering the proto-Gulf of Mexico 
around Cape Girardeau, Missouri, (the Mississippi Embayment) which 
deposited Jurassic and Cretaceous rocks, as well as Tertiary and 
Quaternary unconsolidated sediments from Southern Missouri to the 
present Mississippi delta. The Mississippi has also done a fair amount 
of thrashing about in its bed, through present day western city of St. 
Louis, along Crowley's Ridge, with some incursion into southern 
Illinois, western Tennessee and western Kentucky. (Not to mention south 
of there, including the current delta.)

     In short, what this means is: the concept of the Mississippi River 
as a big trench towards which everything drains is relatively recent, 
though the basin itself has functioned as a river going several 
directions on several occasions over the millenia. There is even some 
evidence that the proto-Missouri flowed a)to the west, draining into the 
Red River system somewhere east of Wichita, Kansas; b)north, towards the 
proto-Hudson; and c)the Missouri was eventually pushed south along the 
ice sheet, and was captured eastward, eventually draining into the 
Mississippi at St. Louis.

I don't think the Mississippi is good evidence for this accumulatory 
hypothesis.


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