The so-called "impactite bed"Paul bristolia at yahoo.com
Sun Aug 26 10:39:13 EDT 2007
Mr. Grondine wrote:
“Yes. Here you go:
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
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
Given all of the fuss about these black mats, I should contact my
archaeologists friends to get some samples to look at for myself.
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,
Waters, M. R., 2000, Alluvial stratigraphy and geoarchaeology
in the American Southwest. Geoarchaeology. Vol. 15, no. 6,
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.