Re: The Great Lakes. What's the real deal?


brad wrote:
re: great lakes/real deal; "During much of the Wisconsonian glacial the
ice margin was well south of the state and all of Michigan was covered
by several thousand feet of ice" from Geology of Michigan by Dorr and
Eschman. when you consider that glaciers can carve grooves in bedrock
it isn't a stretch to see they can remove soft rock like gypsum, rock
salt ,and other precipitates , which if the lakes didn't exist would
outcrop in their place. the sedimentary rocks underlying the state look
like a stack of bowls ; a layer at the surface on the perimeter of the
state will be several thousand feet down at the center of the state. if
catasrophism was at the heart of their genesis you would expect some
deposits sorted according to the energy of the flow of the flood and a
channel, such as out west, no? where are they?

The lake basins were areas where fast currents caused erosion, so there
is not much sediment in them. It was removed by the currents and
redeposited. But there are some lag boulder accumulations in various
areas, for example at McKay's Harbour on the western side of Georgian
Bay. As for channels, a deep one was eroded in the floor of the lake
along the north end of the Bruce Peninsula where the current was
deflected by Cabot Head emerging from the water. It is shown on the
bathymetry map at:

http://vinyl2.sentex.ca/%7Etcc/GT/glaciers.html#Bathymetry

I have provided a link to the map source website from where you can
zoom in to get more detailed views.

There are several channels on the floor of Georgian Bay leading towards
the inlets between headlands of the Niagara escarpment. Currents swept
over the area, eroding the escarpment back to the SE. In the Bruce
Peninsula there are areas having patterns of giant current ripples on
the rock surface, transverse to current direction - no ice *** can
cause giant current ripples. There are also long, narrow drumlins near
Sky Lake on the Bruce peninsula that are down stream from an area with
these giant current ripples, and oriented normal to them. They show up
on the Google earth viewer. Patterns of ripples show up on topographic
maps.

In the main basin of Lake Huron there is a prominent submerged
escarpment, that like the Niagara Escarpment would present a barrier to
the movement of the hypothetical ice. Also, along the cliffs of the
Niagara escarpment on the Bruce Peninsula, there are pinnacles, and
stacks, and cliffs having big overhangs of 30 feet or more. These
features support the idea of erosion by fast currents that flowed SE,
generated by uplift of the Canadian Shield when the area was submerged,
rather than ice erosion.

The floor of the northern basin of Lake Huron is disected into numerous
channels and sumberged pinnacles, and looks like an area where the
drift cover has been eroded by currents. The bedrock surface under the
drift in southern Ontario has many features like those exposed in the
northern basin of Lake Huron. There are numerous buried valleys, the
one at Dundas being deeper than 1300 feet. They don't follow patterns
supporting erosion by former rivers, but follow joint patterns in the
bedrock. I suspect more studies on the channels at the floor of Lake
Huron will find examples of potholes. There are submerged potholes near
some of the islands of Georgian Bay off Tobermory.

in addition the weight
of the sheets of ice depressed the land beneath them and the drainage
initially was to the north,anyway. it was only recently that drainage
went to the south and east as crustal rebound raised the northern part
of the state and canada. what i find intriguing about the state's
geology is the reason why its a basin in the first place. for some
reason a bya (?) the mantle sagged and all the subsequent geology arose
from that.

Differential uplift and subsidence when the area was sumberged was the
driving force for the currents in my theory of the origin of the Great
Lakes.

Doug
http://www.sentex.net/~tcc/gtlakes.html

Doug

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