NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/talk/origins/15965

Text File | 1992-12-30 | 14.4 KB | 259 lines

Newsgroups: talk.origins
Path: sparky!uunet!nntp1.radiomail.net!fernwood!aurora!isaak
From: [e-mail] (Mark Isaak)
Subject: Response to the Response to the Flood FAQ
Message-ID: <[e-mail]>
Reply-To: [e-mail] (Mark Isaak)
Organization: The Aurora Group, Palo Alto, CA
Date: Wed, 30 Dec 92 17:05:25 GMT
Lines: 248


[The following is from Andrew MacRae ([e-mail]),
who cannot post himself.]

Response to the response to the Flood FAQ, part 1

1. MOUNTAINS AND SEDIMENTATION RATES
> Wayne Folta
>> [e-mail] (Mark Isaak)
>>   How were mountains formed?  Many very tall mountains are composed of
>>     sedimentary rocks.  If these were laid down during the flood, how
>>     did they reach their present height, and when were the valleys
>>     between them eroded away?

>As the land was raised up and the flood waters settled down into the ocean
>basins, mountains would be raised and great erosion would occur.

But what was the mechanism for "the land was raised up", and how is
it distinguished from the conventional, tectonic explanation?
    Also, 1) flood up - deposit sediments with marine fossils
        2) flood down - raise mountains, erode valleys
    Where did the sediments deposited in 1) erode from, since most of
the flood erosion apparently occurred during 2)?  You need something high to
erode to produce the sediments.  Sediments do not appear from nowhere.

>(This reminds me of the Mt. St. Helens video that Gish and company have.
>It shows a valley with a little stream running through it. The valley's
>walls show millions of fine layers of deposits. Three hundred years from
>now, people might assume that the layers had been deposited over millions
>of years and that the stream had taken hundreds of thousands of years to
>carve out the valley. In fact, the deposits occured in three days, and the
>valley was blown out by a huge steam/mud flood in half a day.)

    Wow!  Since you are dealing with a very high relief landscape with
little vegetation (a volcanic mountain), of course erosion rates are high.
I or any other geologist would _NOT_ assume the layers had been deposited
over millions of years, because volcanic terraines are _always_ areas of
high depositional and erosional rates, dominated by catastrophic events
(this is probably why creation "scientists" study modern environments there
:-).  Such events (e.g., debris flows, pyroclastic fallout deposits, surge
deposits, etc.) produce sedimentary structures quite distinct from slower
sedimentary processes.  It would be blatently obvious that the rock with the
"millions of fine layers" was volcanic in origin, especially if you looked
at the rock in thin section under the microscope.

Unfortunately for flood hypotheses, volcanic environments are very
distinctive, and make up a small part of depositional environments preserved
in the rock record.  Most of the environments preserved in the many
kilometres of sediment found in depositional basins is ocean bottom or
deltaic.  Do Morris et al. have a movie of the catastophic depositional
rates and erosion rates on the Mississippi Delta?  Sure, there are levee
breaches, but these are relatively infrequent, and quite small in scope
compared to the size of the entire delta complex.  Most of the deposition is
slow, at least in a vertical sense, because there are only a few metres of
accomodation between the sediment bottom and sea level.  You can deposit a
few metres of sediment to infill a bay, but once you are at sea-level,
deposition almost stops, because there is no "hole" to fill.

The Mississippi Delta complex has >5 km of sediment beneath it, deposited
over thousands of square kilometres.  Even if it was possible to deposit
huge volumes of mud overnight as at Mt. St. Helens, it would still take
thousands of years to equal the volume of sediment in the Mississippi Delta
basin alone.  Gosh, you could probably take _all_ the volume of Mt.  St.
Helens, and it would still take thousands of equivalent volumes to fill the
basin.  However, it isn't possible to deposit at the huge Mt. St.  Helens
rates anyway, since you would change the structure of the delta sediments
completely (no fine bedding, wave ripples, coal beds, oyster beds, in-place
tree stumps, paleosols (fossil soils), etc.).

Another strange problem of the flood model is how trees and other land
plants can form coal in areas that are now well below sea level.  Did the
flood waters also drop a kilometre below the current sea level so dry land
could form?  (The conventional explanation is that the weight of the
overlying sediments has caused the terrestrial sediments to subside well
below sea level after deposition).  I know, Morris et al. may have some
magical, catastophic explanation for coal; that claims it isn't composed of
terrestrial plants, or they claim that the plants accumulated in huge mats
of material during the flood.  Funny how the plants still managed to sort
themselves into stratigraphically distinct coal types (giant lycopod coals
in the Carboniferous, cypress coals in the Cretaceous, etc.).

>In Whitcomb and Morris, they speculate that the water level fell, on
>average, at 15 feet per day.

    Wow!  What an incredible rate of fall!  That water must have torn
into solid bedrock, excavating valleys thousands of metres deep and
producing thousands of cubic kilometres of sediment from solid rock - NOT!
Even if you scraped up _all_ the loose sediment now on the surface of the
Earth now, it would be a tiny fraction of the amount in the 10+ km deep
sedimentary basins of the world.  So you have to produce the sediment from
the bedrock - somehow.  I don't care how violent the flood was - you can not
turn granite into cubic kilometres of clay in a short amount of time.  The
process is limited by chemical reactions that are controlled by physics.

    According you the rate you quote, the rate of fall of the flood was
_less_ violent that the daily tidal flux in the Bay of Fundy, Nova Scotia,
which varies on the order of 15 _metres_ twice per day.  Wow.
What a cataclysm :-)

    If Whitcomb and Morris are claiming a rate of 15 feet per day, they
must have some evidence of how long it took for the water to fall.  How long
do they say there is to erode km deep valleys into _bedrock_ (not the
unconsolidated sediments on Mt. St. Helens flanks)?


2. ANGULAR AND OTHER UNCONFORMITIES

>>   How does a global flood explain angular unconformities, where one set
>>   of layers of sediments have been extensively modified (e.g., tilted)
>>     and eroded before a second set of layers were deposited on top?
>>     They thus seem to require at least two periods of deposition (more,
>>     where there is more than one unconformity) with long periods of
>>    time in between.

>Why long periods in between?

    Why long:
    1) Evidence for chemical weathering at the surface (i.e.  chemical
alteration of the underlying rocks).  Often paleosols (fossil soils) are
present.  The chemistry of the alteration process implies a long time (how
long does it take for a soil to form from bare bedrock?).
    2) _Rounded_ pebbles composed of the underlying rock deposited in
the overlying units.  Rounding in streams takes time.
    3) You must tilt the underlying rocks before (or while) eroding
them, then deposit near horizontal beds on top.  The deformation to produce
the tilting (i.e. mountain building) takes time, and must occur before
depositing the overlying units.
    4) Many angular unconformities are on top of igneous intrusive rocks
(e.g., granite) that imply a great deal of time because: A) the igneous rock
must be intruded kilometres below the surface (the kinematics of the
crystals in the rock constrain the pressure), B) they must cool slowly to
produce large crystals (calculate how long it takes many cubic kilometres of
rock at 600+ degrees Celcius to cool), C) then you must erode the kilometres
of rock off the top of the intrusive, _and_ D) erode the intrusive igneous
rock so you can deposit pebbles in the sediments overlying the unconformity.
This is observed at _many_ localities worldwide, of _different_ ages (see
below for an example).

>Does this assume that deposits made during the
>Flood would be from settling silt?

    No.  Any sedimentary rock.  An "angular" unconformity implies an
episode of deformation _before_ the erosion to produce the tilted beds; but
general unconformities can have any geometry.  The underlying rocks at an
unconformity do not have to be sedimentary on both sides.  The point is that
you have an older structure in the underlying rock that is cut by a younger
structure - the erosion surface or unconformity.  The unconformity divides
two sets of events - before the erosion, and after.  This is termed a
"cross-cutting" relationship, and is one of the principles of geology - the
structures that are "cut" are older than the structures doing the cutting
(in this case the erosion surface or unconformity).  You can't, for
instance, make the erosion surface first, then intrude the granite and put
pebbles of it in the overlying rocks.  It could not occur in this backwards
fashion.
    Do you see why finding unconformities causes problems for a
single-event flood?  There are plenty of unconformities in the rock record.
Every one of them implies 1 period of deposition before the unconformity, 1
period of erosion (sometimes subaerial), and 1 period of renewed deposition.
In the case of _angular_ unconformities, you must also fit a period of
deformation before the renewed deposition.
    Surely you can see that this would imply multiple "floods", or a
greatly complicated "flood history" that is at odds with the models "flood
creationists" have proposed.

>Surely deposits could be made by moving
>vast amounts of land much more quickly than that?

    You can create the geometry of an angular unconformity (intersecting
beds), but you will not find pebbles of the underlying rocks in the
overlying ones - and yes, this situation (incorporation of pebbles into the
overlying units) is very common.

>And how about the Colorado Plateau (Whitcomb & Morris, pg. 160), which
>occupies 250,000 square miles, and which has been uplifted multiple times
>(this believed because of disconformities in the stratigraphic sequences)
>and yet is nearly perfectly flat? This causes a problem for non-Flood
>geologies.

    Actually, the Coldoro Plateau is _relatively_ flat, but it it far
from "perfectly flat" or undeformed.  For instance, there are broad
structural domes and faulting in the vicinity of Moab and Canyonlands
National Park.  The Coldorado Plateau is cut by the Rio Grande Rift in the
east, and merges into the San Rafael Swell, another structural dome, to the
north, and to the west it merges into the broad deformation of the Basin and
Range Province.
    The Coldorado Plateau _is_ a sort of "window" of _reduced_
deformation.  It is very similar to the rest of the North American platform
to the east, but it has been "cut off" by the Rio Grande Rift.
    There are processes that can uplift an area without causing a great
deal of deformation.  One is to heat up the underlying mantle.  The Rio
Grande Rift, and other relatively recent volcanism in the Coldorado Plateau
area may be a partial indication of this process.
    Another factor that can produce the unconformities is sea-level
variations.  No, not "Biblical Flood"-style variations.  I'm talking about
sea-level variations on the order of 100m.  There is good evidence, for
instance, that the continental shelves were exposed, and therefore eroded,
during the latest glaciations.  Sea-level dropped because so much water was
trapped in the ice caps.  At the end of the last glaciation, the shelves
were "flooded".  There is some evidence for similar variations through most
of the Earth's history, although the mechanism may not be glacial alone.

Let's look at the effect of unconformities on the geologic history of an
area, and how they complicate a flood model:
    One area I am familiar with is the South Mountain Batholith, in
southern Nova Scotia.  It is an agglomeration of dozens of smaller
"granitic" bodies, and is approximately 100 X 40 km in surface dimensions.
It extends to at least a kilometre depth, probably more.  It occurs within
metamorphosed sedimentary rocks of the Meguma Group, itself at least a
kilometre or two thick, and composed of deep water marine sediments.  The
beds of the Meguma Group are extensively folded, in a similar fashion to a
carpet pushed on its edge.  The contact between the "granites" and the
Meguma Group cuts across the tilted bedding, and it is easy to see places at
the contact where the granite was injected into fractures, and where chunks
of the Meguma Group were wedged off the wall of the magma chamber, sank into
the melt, and were partly recrystallized.  These chunks are called xenoliths
or enclaves.  Clearly the structures support the interpretation that the
Meguma Group is older than the "granites", and since the "granites" are not
folded as well, the folding of the Meguma Group must have occurred before
the intrusion.
    On top of both the granites and the tilted beds of the Meguma Group
are sediments of the Horton Group.  The Horton Group contains plant fossils
of Carboniferous age, but the fossils do not really matter.  The basal
contact of the Horton Group is erosive, and occurs with both the tilted beds
of the Meguma Group (i.e. an angular unconformity) and the "granites" of the
South Mountain Batholith.  In the basal metre of the Horton Group, there are
abundant pebbles of both the Meguma Group and the South Mountain Batholith.
Often they are chemically altered, and rounded.  Higher in the Horton Group,
entire formations are composed of sandstones and conglomerates obviously
derived from granitic sources (they contain much feldspar, quartz, and
mica).  Clearly the sequence of events in this area is:
    1. deposit Meguma Group sediments in the ocean.
    2. fold and metamorphose the sediments.
    3. intrude the South Mountain Batholith (SMB).
    4. solidify the SMB (it takes a _long_ time to cool).
    5. erode the sediments on top, down to the level of the granites.
    6. deposit Horton Group sediments on top of the erosion surface
    7. fold and fault the Horton Group.

    And, there is yet another angular unconformity on top of the Horton
Group, followed by more sediments (with fragments of the South Mountain
Batholith, Meguma Group, and Horton Group), and basaltic lavas.
    Keep in mind that this is a great simplification of one corner of
the North American continent.  Geological history is very complex, even if
you ignore fossils and radiometric dating entirely.  Much more complex than
flood models can easily explain.

    -Andrew
    [e-mail]