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 in [Fig. 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 in [Fig. 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:
| Sample | Percent Carbonate (by weight) | sol. | Percent Iron (by weight) insol. | total |
|---|---|---|---|---|
| Light | ||||
| No. 1 | 0.34% | 0.43% | 0.14% | 0.57% |
| No. 2 | 0.31% | 0.38% | 0.13% | 0.51% |
| Red | ||||
| No. 1 | 0.08% | 4.95% | 0.62% | 5.57% |
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.