[meteorite-list] The so-called "impactite bed"

[Paul]

Mr. Grondine wrote:



“Yes. Here you go:



http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=109768&org=NSF&from=news



drtanuki <drtanuki at yahoo.com> wrote:



“http://www.youtube.com/watch?v=f1GCgOI3B1o



The black impactite layer is pretty amazing – I

never expected it to be that dense or clearly 

obvious to the naked eye - my guess is that it 

extends throughout other sandstone formations

 in the region –“



What is seen there is ***not*** a layer of impactite. The “black 
mat,” as archaeologist call this layer, is organic-rich sediment, 
which was deposited in a low-energy cienega (stream or creek 
bog) environment. "Black mats" have been known to archaeologists 
for decades. What these black mats represent, along with wet-
meadow soils and pond deposits that include diatomite and marls, 
are periods of higher water tables and increased ground water 
discharge. They are not all of the same age.



Haynes (2003) stated:



"Younger Dryas (YD) age "black mats" (YDBM), 

while variable, represent moister conditions 

than before or after deposition. 



Higher water tables, some perched, are indicated by 

Wet meadow soils, algal mats, and pond sediments

Including marls and diatomites, some of which are 

white. Geochronological study of over 50 localities 

from Arizona to Canada reveal that YDBMs contain 

the earliest post-Clovis archaeological evidence and 

overlie the last Rancholabrean faunas.



Upland or lowland YDBMs occur sometimes as facies 

Or catenas. Regional YD paleosols include the Brady 

Of  Nebraska and the Leonard of the Dakotas. On 

uplands these are darker and thicker in swales and 

may reflect perched groundwater or poor drainage. 

In lowlands they occur deeply buried beneath 

floodplains; in some colluvial settings multiple black 

bands are separated by lighter colored slope wash. 

Some YDBMs are related to springfed meadows and 

ponds formed during increased-discharge periods."



and Huckleberry et al. (2004) stated:



"After ca. 11,000 14C yr B.P., sandy and finer 

alluvial muds commonly contain a dark organic 

zone or "black mat." These black mats are related 

to elevated water tables and increased spring 

activity and cluster in age at 9,500 to 10,500 

14C yr B.P. (Quade et al., 1998). Quade et al.

(1998) suggest these black mats and associated 

spring-fed channels formed in response to 

moister conditions during the Younger Dryas 

and preserve the last episode of increased spring 

discharge before substantial drying occurred in 

the early Holocene."


Also, other "black mats" can be found in sediments both post-

dating and predating the Clovis Culture all over the United States. 

For example, in the Lake King basin in Trans-Pecos Texas, black 

mats have been dated at 17,200, 19,000, 22,600, and 24,700 

radiocarbon years BP. Quade et al. (1998) decribes several "black 

mats", which have been dated as being much younger than Clovis, 

i.e. 1450 , 2320, 6670, 7920, and 7230 BP. In Figure 11, they show 

a picture of a "modern black mat marginal to a small spring-fed 

channel below Indian Springs Ranch in Steptoe Valley, northeast 

Nevada". Black mats are unique neither to Clovis Sites nor times. 

All the black mats indicates is that they occupying locations 

adjacent to spring-fed wet meadows and channels during periods 

of high ground water table and discharge. All they do is indicate 

that dramatic climate change  occurred during the Younger Dryas. 

Of course, that is well known and the significant question is what 

caused it.



The black layers, which are seen in photographs are **not** 

composed of impactite. These black mats, which occur at some 
Paleo-Indian sites are only hypothesized to contain microscopic 

impactites. It is quite impossible to see such impactites in any

photographs. the see the alleged impactites, a person has to
conduct a detailed microscopic analysis of the material.



When I worked at the Lubbock Lake Site in Lubbock Texas,

I actually excavated bison bones and artifacts from the “black 
mats”, which occur at that site. If only I had known the 
controversy, which they would cause, I would have copies of
the slide, which I took before giving them to the Lubbock Lake
Site Museum.

Given all of the fuss about these black mats, I should contact my 
archaeologists friends to get some samples to look at for myself.



References Cited



Haynes, C. V. Jr, 2003, Younger Dryas "Black Mats"

and other stratigraphic manifestations of climate change in 

North America. XVI INQUA congress; Shaping the Earth; a 

Quaternary perspective. Congress of the International Union 

for Quaternary Research, 2003, vol. 16, pp. 191. [gsa.confex.com]



Huckleberry, G., C. Beck, G. T. Jones, A. Holmes, M. Cannon

S. Livingston, and J. M. Broughton, 2001, Terminal Pleistocene/

Early Holocene Environmental Change at the Sunshine Locality, 

North-Central Nevada, U.S.A. Quaternary Research. vol. 55, 

no. 3, pp. 303-312.



Quade, J., R. M. Forester, W. L. Pratt, and C. Carter, 1998, Black 

mats, spring-fed streams, and lateglacial-age recharge in the southern 

Great Basin. Quaternary Research. vol. 49, pp. 129-148.



Other discussion of paleoenvironmental significance of 

 “Black Mats” can be found in:



Mehringer, P. J., Jr., and C. V. Haynes, Jr., 1965, The Pollen 

Evidence for the Environment of Early Man and Extinct 

Mammals at the Lehner Mammoth Site, Southeastern Arizona

American Antiquity. vol. 31, no. 1, pp. 17-23.



Waters, M. R., 1991, The Geoarchaeology of Gullies and Arroyos 

in Southern Arizona. Journal of Field Archaeology. vol. 18, no. 2,

pp. 141-159.



Waters, M. R., 2000, Alluvial stratigraphy and geoarchaeology 

in the American Southwest. Geoarchaeology. Vol. 15, no. 6, 

pp 537-577.



Waters, M. R., and D. D. Kuehn, 1996, The Geoarchaeology of 

Place: The Effect of Geological Processes on the Preservation 

and Interpretation of the Archaeological Record American 

Antiquity. vol. 61, no. 3, pp. 483-497.



Yours,



Paul



       
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