Monday, September 27, 2010

The Saginaw Bay Impact Hypothetis

Like many Google Earth afficionados I have pondered the origin and meaning of the Carolina Bays, those shallow teardrop ovals which can be miles wide, and whose longer axes seem to point back towards the American midwest.  The Atlantic coastal pain is just lousy with them, but there also is a swath through Kansas and Nebraska.  They resemble impact craters from above, but on the ground they are quite shallow and bear small semblance to Meteor Crater in Arizona.

What puzzled me most was why we hear so little about this earth impact forensic evidence, with no plausible hypothesis for their origin, even though they tell a story of devastation across our land and apparently date from within the time of mankind, unlike the celebrated Chicxulub comet that nuked the Yucatan at the end of the Cretaceous, which certainly ended the dinosaurs in North America, if not the entire world.

Then I found a website that offers a plausible scenario, Perigree:Zero at  Now if you go and examine this website, you may note it goes beyond explaining geography, and falls prey to the ambition of explaining everything.  A warning bell goes off when on the Dedication page it names Immanuel Velikovsky, whose books made great reading when I was a teenager, but whose ideas about the wandering of Venus and Mars completely misunderstand the orbital reality of those two huge solar bodies.  Also the pages are full of misspellings and typos!   Okay, I know these people aren't scientists, just web-era online diggers, but maybe they really have something here.  They aren't scientists, but they have leveraged other people's research into the Wisconsinan glaciation, geology, hydrology, soils, the behavior of 'ejecta' from impacts.

The central thesis of the Perigree: Zero website and its companion site is that there was an impact event circa 12500 years BP whose impact crater is now Saginaw Bay.  At the time this area was covered with a mile or two of glacial ice.  The low-angle impact upon the icesheet kicked out mountain-sized slush balls into the atmosphere and the Carolina Bays are the resulting splatter.  So the reason these Carolina Bays are shallow and such regularly shaped teardrops is the material of their formation is muddy slush.

The traditional explanation of Saginaw Bay is that there was a Saginaw Lobe in the Laurentian Ice Sheet which dug it out, the way glaciers dug out the Finger Lakes.  But glaciers are more successful at digging when the rock is soft, like the shale around the Finger Lakes; when they hit something hard like the Precambrian Adirondack rocks they go over or around.  Well, central Michigan has a big slab of sandstone that doesn't seem to have breached anywhere but up through the Saginaw Bay region, and Saginaw Bay is no fjord, it is a big wide open bay.

The authors, Michael and Jeanette Davias, have done their homework.  Michael's experiments with splattering things is in the best tradition of practical science, like Franklin and his kite.  The assembled collection of scholarly papers strongly braces their ideas. It is like a fusillade of smoking guns.  There are buried soils and organic material.  The "Saginaw Lobe" disappeared long before the Michigan and Huron lobes.  The glacial till has Precambrian pebbles.  There are anomalous heavy metal and salt concentrations around Saginaw.

For example, they cite a paper called "Fractured hydrothermal dolomite reservoirs in the Devonian Dundee Formation of the central Michigan Basin" published in the American Association of Petroleum Geologists Bulletin in November, 2006, which concluded that the Dundee rocks have such incongruous inclusions that they must have been reheated, but the authors of that paper can offer no explanation of how this could have happened.  That's where scientists must leave off, inside the box, and inspired amateurs, who do not have careers to ruin, must take over.

I'm still savoring the excitement of this leap to conclusions. Velikovsky never marshalled quite so much hard science to his point, he fatally relied on ancient writings, legends express the desires of storytellers and their listeners, not data.

But the Davias's are not immune to trying to explain ancient historical egnimas using their new ideas about impacts, and I would like to separate this over-reaching from the basic hypothesis which has so much value.  They are right to be proud and excited about what they've cobbled together from the evidence at hand, and they've understandably fallen prey to trying to use their new ideas to explain everything.

One really funny thing they point out which is not obscure is that the temperatures during the Holocene, which is the latest interglacial warming period, have remained fairly stable for the last 10K years, while during earlier interglacial periods there was a spike of high temperatures, and then a falling.  They say the comet might have something to do with this.  Maybe or not, it is another cause to ponder.  Maybe our agriculture was altered the climate so the temperatures have not fallen as before.

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