TABLE VIb
Particle-size fractions, in millimeters;expressed in percent of total weight of sample
Distribution (weight percent) of particle-size fractions for samples from Square J8, LoDaisKa site. Samples taken in continuous six-inch intervals from 38 inches below baseline.
Distribution (weight percent) of particle-size fractions for samples from Square J8, LoDaisKa site. Samples taken in continuous six-inch intervals from 38 inches below baseline.
The two levels represented in the section from M11 extend over the whole area of excavation and make up most of the deposits of the site. A late Pleistocene bouldery gravel, with which is included some variegated silty and clayey alluvium, is separated from the overlying dark-colored sandy and silty “alluvium” by a definite erosional break representing an unknown interval of time (Hunt, this report). There is a higher red sand layer and a younger bed of dusty brown fill which is found just below the surface; both of these are relatively quite thin and extend only over part of the area of the site. As the dark-colored homogeneous sands and silts made up most of the deposits of the site, and contained most of the cultural remains, they will be our particular concern.
The results of sieve analyses made on the samples from the front and back of the site have been summarized in Tables VIa and VIb; the breakdown into the various particle size fractions is by weight. This was done to 1) describe the physical nature of the deposits and 2) to determine the nature of textural variation of the samples.
Figure 67— Above: Size-distribution curves for typical samples of the deposits of the LoDaisKa Site, Square M11.Below: Size-distribution Curves for typical samples of the deposits of the LoDaisKa Site, Square J8.
Figure 67— Above: Size-distribution curves for typical samples of the deposits of the LoDaisKa Site, Square M11.Below: Size-distribution Curves for typical samples of the deposits of the LoDaisKa Site, Square J8.
Figure 67— Above: Size-distribution curves for typical samples of the deposits of the LoDaisKa Site, Square M11.
Below: Size-distribution Curves for typical samples of the deposits of the LoDaisKa Site, Square J8.
Local differences and variations in the parent rock and relief have a profound effect on soil characteristics (Thorp, 1941). In the present instance, there is no evidence of any appreciable change in the relief of the area immediately surrounding the site since the beginning of human occupation. The site is located towards one end of the relatively steep slope of outwash debris from the Fountain Formation which forms the overhang and extends upslope above the site. The deposits which make up the site are also the product of slope wash and of weathering of the overhang; they are some six feet above the level of the stream in Strain Gulch. The height of the deposits above modern stream level makes it seem most unlikely that the site was ever flooded in Recent times (Hunt, personal communication—Irwin and Irwin). Accordingly, the deposits would be a colluvium rather than alluvial in nature and would be derived from the overhang. Mechanical analyses of several samples of the Fountain Sandstone from the overhang suggest that the sandstone as it is found above the site is quite homogeneous, although it varies in color from white to maroon (see pg. 99 of this report):
These results compare closely with the analyses of the deposits making up the site, and suggest that weathering of the parent material was primarily dissolution, probably accompanied by some mechanical disintegration.
Figure 68— Above: Changes in relative importance (weight percent) of fine silt and clay fraction with depth below 38 inches below baseline, LoDaisKa site.Center: Changes in concentration of total calcium carbonate with depth below 38 inches below baseline, LoDaisKa site.Below: Changes in concentration of total soluble iron with depth below 38 inches below baseline, LoDaisKa site.
Figure 68— Above: Changes in relative importance (weight percent) of fine silt and clay fraction with depth below 38 inches below baseline, LoDaisKa site.Center: Changes in concentration of total calcium carbonate with depth below 38 inches below baseline, LoDaisKa site.Below: Changes in concentration of total soluble iron with depth below 38 inches below baseline, LoDaisKa site.
Figure 68— Above: Changes in relative importance (weight percent) of fine silt and clay fraction with depth below 38 inches below baseline, LoDaisKa site.
Center: Changes in concentration of total calcium carbonate with depth below 38 inches below baseline, LoDaisKa site.
Below: Changes in concentration of total soluble iron with depth below 38 inches below baseline, LoDaisKa site.
Representative particle size distributions of the deposits are shown in the cumulative curves inFig. 67. The median diameters and sorting coefficients, as we have already noted, suggest a uniform distribution of particle sizes, with the exception of the sample (W3) from depth 52-58 inches below baseline in front of the site. The median diameter of this sample is 1.32 mm., considerably larger than that (0.60-0.70 mm.) for the rest of the deposits. A line of much larger rocks at this level gives evidence of a period of rock fall, although this does not seem to extend to the very back of the shelter, and is not represented in the sample collected there. The human occupation of the site is uninterrupted, and there is no suggestion that this fall reflects any change in the mode of deposition or any change in climate. Increased aridity may have brought about an important increase in aeolian deposition in the area during some period of occupation, but the location of the site in a sheltered valley makes it unlikely that this would be indicated by the deposits. Any significant change in the relative importance of the coarse and fine fractions—suggesting perhaps such a change in deposition—would be reflected in the median diameters of the samples (Jenny, 1941). The similarity in the median diameters of the particles from the deposit gives evidence of a relatively uniform mode of deposition.
The amount of uncombined carbonate and “free” or acid-soluble iron oxide in the clay and silt fraction (finer than 0.062 mm.) of the samples from the back of the shelter (M11) was determined by chemical analysis. The results of these analyses have been summarized inFig. 68, where the percentage of the fines by weight has also been plotted. The uncombined oxides and carbonates (iron oxide and calcium carbonate) are present in the fine fractions especially in the form of an adsorbed coating on the surfaces of the particles, and also as precipitates acting as cementing materials to bind them together (Carroll, 1958; Deb, 1958; Barshad, 1958). The free iron oxides were obtained by dissolving the sample in 10% HC₁ (by volume) and digestion over a steam bath. It is assumed that any dissolution of the clay minerals is insignificant and that the amount of soluble iron determined is truly representative of the uncombined iron oxide in the sample (Barshad, 1958). The amount of carbonate was determined in the form of CO₂, by digesting the sample in 0.1N HCl; it is assumed that all of the carbonate occurred in the form of calcium carbonate.
A carbonate and iron oxide analysis was run on several samples of the Fountain sandstone which made up the roof of the rockshelter, in order to determine the amount of variation in the parent material:
The amount of soluble iron is quite variable in the parent material; it forms a coating on the primary minerals and gives the rock its red or maroon color. It is interesting to note that the soluble iron in the deposits, presumably derived from the Fountain sandstone, maintains a rather regular increase to a maximum at 102 inches below base-level. The amount of carbonate in the parent rock, by contrast, is certainly not enough to account for the variation which was found in the deposits and for the concentration of CaCO₃ at the particular levels. In the present instance there seems to be a definite independence in the movement and location of concentration of the soluble iron and of the fine silt and clay, which seem to be associated with concentrations of carbonate. The calcium carbonate occurs in the form of a coating on the fine particles and, more important, as a cement binding the particles together. This was particularly noticed on the artifactual and bone materials from the deposits from 70 to 94 inches below baseline.
The differential accumulation of calcium carbonate in the profile is due to either variations in the texture of the deposits, with the greater accumulations occurring in the zones of finer particle size, or to the processes of weathering of the deposits (Miller and Leopold, 1953). The present study suggests that changes in the distribution of calcium carbonate and the fine silt and clay fractions in the deposits cannot be related to variations in the parent material, relief in the immediate area, or the mode of deposition. Concentrations of calcium carbonate may be associated with changes in the depth of the water table or in drainage conditions. There is no evidence that the water table ever came close to the surface in this area in Recent times; at present it is something more than 150 feet below the level of the site. Internal and external drainage conditions of the deposits have probably not changed since the beginning of human occupation of the shelter, being largely determined by the nature of the relief and parent rock.
It is possible that the particular accumulation of calcium carbonate and of fine silt and clay between 68 and 96 inches below base-level are the result of downward migration and concentration of the fine fraction and CaCO₃ due to weathering processes—defining a paleosol. Some change in climatic conditions, perhaps just sufficient to modify to some extent the nature of the vegetation cover (Nikiforoff, 1937) seems to offer one logical explanation for the distribution of calcium carbonate, and of the fine silt and clay fraction—the products of soil development in semi-arid environments (Bryan and Albritton, 1943). It is hoped that x-ray and mineralogical analysis of the samples will definitely establish whether or not we are dealing with a buried soil.
If we do interpret the results of the chemical analyses as indicating a period of increased aridity over conditions as they now exist inthe area, one could establish aterminus post quemfor the archaeological complexes below approximately 64 inches below baseline. Accordingly, the artifactual materials with Great Basin influences and the earlier Duncan types may date from some time late in the Altithermal. This interpretation would not be completely out of keeping with a dating of the archaeological materials on typological grounds.
Acknowledgments
The author is particularly indebted to Dr. C. J. Rodden for his interest and assistance in the chemical analyses, and to Prof. John P. Miller for his suggestions and helpful criticisms of the preliminary draft of this manuscript.
References
Barshad, I., 1958Soil Development: Univ. of Calif., Berkeley, 69 p.Bryan, K. and Albritton, C. C., 1943, Soil phenomena as evidence of climatic change: Amer. Jour. Sci., 241, 469.Carroll, D., 1958, Role of clay minerals in the transportation of iron: Geochimica et Cosmochimica Acta, 14, 1.Deb, B. C., 1958, The movement and precipitation of iron oxides in podzol soils: reprint.Hunt, C. B., 1954, Pleistocene and Recent Deposits in the Denver Area, Colorado: U.S.G.S. Bull. 996-C, 140 p.Jenny, H., 1941, Factors of soil formation, a system of quantitative pedology. McGraw-Hill Book Co., Inc., New York.Knight, S. H., 1929, The Fountain and the Casper formations of the Laramie Basin: Contri. from Dept. of Geology of Columbia Univ., XL, No. 5, 82 p.Miller, J. P. and Leopold, L. B., 1953, The use of soils and paleosols for interpreting geomorphic and climatic history of arid regions: Res. Council of Israel. Spec. Publ. No. 2, 453.Miller, J. P., and Wendorf, D. F., 1958, The alluvial chronology of the Tesuque Valley, New Mexico: Jour. Geol., 66, 177.Nikiforoff, C. C., 1937, General trends of the desert type of soil formation: Soil Sci., 43, No. 2, 105.Simonson, R. W., 1954, Identification and interpretation of buried soils: Amer. Jour. Sci., 252, No. 12, 705.Thorp, J., 1941, The influence of environment on soil formation: Soil Sci. Soc. Amer. Proc., 6, 39.
Barshad, I., 1958Soil Development: Univ. of Calif., Berkeley, 69 p.
Bryan, K. and Albritton, C. C., 1943, Soil phenomena as evidence of climatic change: Amer. Jour. Sci., 241, 469.
Carroll, D., 1958, Role of clay minerals in the transportation of iron: Geochimica et Cosmochimica Acta, 14, 1.
Deb, B. C., 1958, The movement and precipitation of iron oxides in podzol soils: reprint.
Hunt, C. B., 1954, Pleistocene and Recent Deposits in the Denver Area, Colorado: U.S.G.S. Bull. 996-C, 140 p.
Jenny, H., 1941, Factors of soil formation, a system of quantitative pedology. McGraw-Hill Book Co., Inc., New York.
Knight, S. H., 1929, The Fountain and the Casper formations of the Laramie Basin: Contri. from Dept. of Geology of Columbia Univ., XL, No. 5, 82 p.
Miller, J. P. and Leopold, L. B., 1953, The use of soils and paleosols for interpreting geomorphic and climatic history of arid regions: Res. Council of Israel. Spec. Publ. No. 2, 453.
Miller, J. P., and Wendorf, D. F., 1958, The alluvial chronology of the Tesuque Valley, New Mexico: Jour. Geol., 66, 177.
Nikiforoff, C. C., 1937, General trends of the desert type of soil formation: Soil Sci., 43, No. 2, 105.
Simonson, R. W., 1954, Identification and interpretation of buried soils: Amer. Jour. Sci., 252, No. 12, 705.
Thorp, J., 1941, The influence of environment on soil formation: Soil Sci. Soc. Amer. Proc., 6, 39.