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Sunday, 26 August 2007

The so-called "impactite bed"

The so-called "impactite bed"

Paul bristolia at
Sun Aug 26 10:39:13 EDT 2007

Mr. Grondine wrote:

“Yes. Here you go:

error [[[drtanuki wrote: ]]] error
Note: this was not Dirk Ross`s quote; quote by E.P. Grondine-- later corrected in later post by Paul H.

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. []

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.



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