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jlhredshift
2013-Jun-20, 11:26 PM
The following paper became available on May 21, 2013. Its twenty eight authors travelled the world, revisited sites, and used advanced methodologies to produce this paper. I am personally sure it will reignite the controversy and study of the comet impact theory at the Younger Dryas (YD) transition. This is my second foray into this subject that I have been studying since 2007.

Wittke et al 2013:

Evidence for deposition of 10 million tonnes of impact spherules across four continents 12,800 y ago (http://www.scribd.com/fullscreen/142399184?access_key=key-2c9s2py30l8cpxhhn8wm)

I have been absent from this board for a while, but I have not been idle. I have accumulated a mass of information including Archaeological, Paleontological, and Geological on this subject, both hard copy and digital.

http://farm9.staticflickr.com/8459/8071704912_ccbab2ee78_z.jpg

From page nine of the paper is the following:


Beneath the flight path of the impactor fragments, thermal radiation from the air shocks was intense enough to melt Fe-rich and Si-rich surficial sediments, transforming them into lechatelierite-rich melt-glass and spherules at >2,200 C. Multiple airbursts/impacts over a wide area can account for the heterogeneity of the melt materials. In addition, high temperatures may have produced spherules and melt-glass by incinerating vegetation within the fire-balls and shock fronts. High-velocity winds and attenuated airshocks lofted the melted material into the upper atmosphere, where high-altitude winds transported them over a wide area. As previously suggested (7), nanodiamonds potentially formed from vaporized carbon within localized, transiently anoxic regions of the shock front. This impact model is speculative because the exact nature of air-bursts is poorly constrained. For example, the complexity of airburst phenomena is only hinted at by the recent hydrocode modeling of Boslough and Crawford (65), who concluded that more realistic airburst simulations are needed to understand the phenomenon.

I take this to mean that they do not expect to find a crater because, like Tunguska, only the fireball and shock front intersected the ground.

My speculation is that the impacting body may have been solely formed from the ices of carbon dioxide, ammonia, and water, if it existed at all.

This is not over.

Certainty is not at hand.

The cause of the climate shift at the YD has not been pinned down, lots of theories.

The cause of the 14C plateaus at the YD have not been determined.

The cause of the mega-mammal extinctions, which include the Clovis people, have not been explained, lots of theories.

Though, the authors of the cited paper, think they have a clue.

dgavin
2013-Jun-21, 02:01 AM
It sounds like great research!

But I have a question for you, how do you reconcile this with Missoula Glacial Lake Flood, of which there are Native American legends about, dating back about 12800 years ago as well? Which basically means the Clovis people descendants are still with us.

Related events maybe? the Impactor broke apart the glacial dam maybe?

jlhredshift
2013-Jun-21, 02:26 AM
It sounds like great research!

But I have a question for you, how do you reconcile this with Missoula Glacial Lake Flood, of which there are Native American legends about, dating back about 12800 years ago as well? Which basically means the Clovis people descendants are still with us.

Related events maybe? the Impactor broke apart the glacial dam maybe?

To my knowledge the people in the northwest had a different toolkit than the Clovis. The Manis Mastodon and Paisley cave are the search terms for the northwest. If memory serves the timing of the Missoula floods were not at the YD boundary, but before. Edit: People were there pre YD. The Manis Mastodon had a bone point embedded in its ribs ca 13800 cal yr ago.

For the location of people at that time see:

The Effect of the Younger Dryas on Paleoindian Occupations in Southeastern North America from PIDBA

http://pidba.org/content/AGU2008_small.pdf

dgavin
2013-Jun-21, 07:23 PM
Hmm I wonder if some of the thunderbird legends, not from the NW area, might be impact related.

The Sioux believed that in "old times" the thunderbirds destroyed monsters called the Unktehila. That could tie into the YD event you are discussing. While the Thunderbird legends in the NW seem to be related to subduction megathrust quakes, there are many thunderbird legends that can't be attributed to that, in central and eastern American. And the Sioux's legend specifcally mentions an extinction in relation to thunderbirds.

It's probably subjective at best, but the Souix's thunderbird legend does seem to support an impactor, minimmaly perhaps.

jlhredshift
2013-Jun-22, 11:39 AM
At best, legends may be entertaining to think about, but they are not a rabbit hole that I investigate.

jlhredshift
2013-Jun-22, 01:50 PM
The following paper by Meltzer and Holliday (2010) has been updated in 2011. I see them as the major opposition to the Comet theory.

Would North American Paleoindians have Noticed Younger Dryas Age Climate Changes? (http://www.argonaut.arizona.edu/articles/2011_Update/Meltzer_Holliday2010_JWP.pdf)

Also, a recent book titled "Hunter-Gatherer Behavior: Human Response during the Younger Dryas" edited by M. I. Eren (2012) covers the current thinking on YD as it relates to populations and any behavioral changes, or not, observed in the archaeological record during this time. [I was able to get it from the public library, its contents are not currently available on the web in its entirety.] The general conclusion from all the authors is that the YD was not as dramatic as originally thought, and particularly in the southern hemisphere. Meltzer points out that even W. Broecker has changed his mind.

dgavin
2013-Jun-24, 07:35 PM
So if I unserstand the high level idea behind that opposition (Meltzer and Holliday) paper you posted, they are attributing the YD to a change in the north atlantic current.

Isn't there a tell tale ejecta (Iridium) layer in geologic terms at the lowest part of YD boundry, including in Greenland's Ice Core records?

Not to pick nit's but even Meltzer and Holliday's less drasctic model could have still been partillay triggered by an impact event it seems.

LookingSkyward
2013-Jun-26, 10:15 AM
I have nothing to contribute to this thread, but very much appreciate the postings... this is a topic of interest to me. Thank you both.

jlhredshift
2013-Jun-26, 02:38 PM
So if I unserstand the high level idea behind that opposition (Meltzer and Holliday) paper you posted, they are attributing the YD to a change in the north atlantic current.

Isn't there a tell tale ejecta (Iridium) layer in geologic terms at the lowest part of YD boundry, including in Greenland's Ice Core records?

Not to pick nit's but even Meltzer and Holliday's less drasctic model could have still been partillay triggered by an impact event it seems.

Yes

Yes, but the resolution of the timing is poor and, is the amount of enhancement significant or a random perturbation; eg Gabrielli, 2004.

Unknown

Currently (no pun) it is unclear whether the AMOC changed significantly or not, the debate and research continues. The several proposed routes for freshwater influx all have issues with both timing and amounts; eg Fisher, Murton, Broecker.

One question that is unclear to me is whether the Be10 signal, as a proxy for solar activity, does or does not show an enhancement or not for the increase in C14, at the time period in question with high enough resolution to be conclusive one way or the other ( not my area of knowledge)?

jlhredshift
2013-Jun-26, 02:58 PM
What Firestone et al are proposing would have happened in a geological instant, the timing of data is crucial!

It appears that the Mastodon may have survived longer into the YD, there are several C14 dates in the 10,192 C14 (Ogden and Hay, 1967) area, but they are older research that I would like to see redated with AMS; i.e. Johnstown Mastodon.


Links to Johnstown Mastodon

https://journals.uair.arizona.edu/index.php/radiocarbon/article/download/3363/2955

https://kb.osu.edu/dspace/bitstream/handle/1811/5422/V68N06_257.p?sequence=1

http://www.dnr.state.oh.us/Portals/10/pdf/newsletter/Winter90.pdf

Solfe
2013-Jun-26, 10:58 PM
Subscribe. I love this stuff. :)

jlhredshift
2013-Jun-28, 12:57 AM
Well, here is more to love.

There is an archaeological site known as Jake Bluff (Bement et al; 2010; American Antiquity), that is a Clovis Bison kill. The next older Clovis site is the Domebo Mammoth kill site, the last mammoth kill known. At Jake bluff directly above the Clovis is a Folsom deposit that remains undated. Wittke et al do not mention Jake Bluff at all, yet it lies in the center of their "YBD Field" on page 2. Also, there is no "black mat" at Jake Bluff; but, in fairness, the site has not been tested for micro spherules. Below is a snip from Bement et al:


When calibrated, the four dates (excluding the outlier) yield a [1 sigma] average range of 12,825-12,850 cal BP with an intercept point at 12,838 cal BP. The Jake Bluff age postdates the Domebo mammoth kill, which is the latest southern plains mammoth kill with an age range of 12,873 to 12,917 cal BP. The recent reevaluation of Clovis radiocarbon ages (Waters and Stafford 2007) places Jake Bluff at the terminus of Clovis.

So, no mammoth at Jake Bluff, no black mat, the Clovis tool kit was present, and Folsom above, it seems to me to be a perfect site for testing for spherules.

Jake Bluff: Clovis Bison Hunting on the Southern Plains of North America (http://saa.metapress.com/content/c6355755w573k1q5/)

Link is to abstract only, I gained access to the paper through library affiliation.

Solfe
2013-Jun-28, 01:34 AM
I can't read it using my college library account. No related fields at ECC, I would think. I have a different university account I can try with tomorrow.

jlhredshift
2013-Jun-29, 01:41 AM
This came out today and I just printed it, I'll get back after I've read it.

New Evidence from a Black Mat Site in the Northern Andes Supporting a Cosmic Impact 12,800 Years Ago (http://www.jstor.org/discover/10.1086/670652?uid=3739840&uid=2134&uid=2&uid=70&uid=4&uid=3739256&sid=21102414084971)

jlhredshift
2013-Jun-30, 04:11 PM
I am going to refrain from any comments on the above "paper", other than to quote a line from "Star Wars" episode IV:


These aren't the droids we are looking for. Move along. Move along.

dgavin
2013-Jul-02, 07:03 PM
I can't read the full paper, but the summary indicates the black mat matches the know mat's from thee other continents. I assume the issue with an impact event of the magnitude needed, is the impact site can't be found? Even if it hit a glacier 2km thick there would still be some evident below in the crust? I'm assuming your reaction the paper though put the paper in doubt.

Anyway, what about a terrestrial cause such as a large methane-hydrate release triggered event? That might also leave a black mat in some conditions, if the methane release was extended, and was ignited by lightning early on. It might also explain the sudden cold ocean current's occurring right before the YD, it might of been near an ice sheet and caused hyperactive melting, that led to an influx of cold melt water into the cold currents.