Micromorphological Observations of Selected Samples Received from Dr. Gary Huckleberry from Kennewick Site

Paul Goldberg
Department of Archaeology
Boston University
675 Commonwealth Ave.
Boston, MA 02215

Sample Kennewick 230 [The upper half of the slide is a bit too thick making it difficult to observe.]
Overall, the material in the slide is comprised of medium to coarse silt sized grains of predominately quartz and other minerals (e.g., biotite, weathered clay aggregates, hornblende and other heavy minerals) in a calcareous fine silty matrix. A rounded granule of welded tuff containing quartz and feldspar inclusions was also observed.

The structure of the material is comprised of sub-parallel plate-like fissures interspersed with irregularly shaped, millimeter size voids (vughs). The origin of these vughs appears to be related to biological activity, likely roots. Other evidence of biological activity is shown by small, millimeter size burrows and aggregates of the matrix.

Additional postdepositional modification is shown by localized calcium carbonate cementation of the matrix primarily in areas encasing voids (called hypocoatings), but these are not very well developed. In addition, the upper surface of this sample appears to be slightly more compact and cemented than the material below; as such, it appears to form a thin crust about 200 µm thick.

Sample Kennewick 231
This sample is quite similar to Sample 230, although this is not completely clear because this is a smaller sample. Nevertheless, it is somewhat finer grained than Sample 230, having slightly less quartz silt. Secondary cementation appears slightly better developed, although certain irregular but sharply defined domains of non-calcareous silty material can be recognized. These non-calcareous domains appear to be a result of localized decalcification of the matrix. The presence of some aggregates also point to biological activity that affected the sediments.

Sample Kennewick 245
This sample is different from Sample 230 and 231 in a number of ways:

• Quartz, silt, and other heavy mineral grains of silt size are noticeably more abundant, with a concomitant decrease in the fine silt calcareous fraction. Consequently, this sample is overall less calcareous than the others.
• Remains of hypocoatings are evident, but the carbonates are clearly being dissolved. In other words, we can see only remnants of what was once a more calcareous sample.
• The porosity in this sample is much lower, and the moderately sorted silt fraction is quite compact. The silt fraction appears to have a higher proportion of heavy minerals, but this observation could result from the decalcification to some extent .
• Some irregular vughs and channels can be observed, but these are much less abundant than in the other samples.
• Aggregation and other evidence for biological activity are not particularly evident.

Sample Kennewick 246
This sample is very similar to Sample 245, although vughs are more abundant. In addition, locally there are a few centimeter size areas that have a more open and less compact fabric rich in coarser silt. These areas appear to be burrow infillings. Hypocoatings are also well represented here, but again these appear to be remnants of a more calcareous sample. Finally, some of the vughs - including those with hypocoatings - appear to exhibit thin (~5 µm) incipient impregnations of iron/manganese.

Sample Kennewick 250 [Sample is slightly too thick.]
This sample is similar to Samples 245 and 246, but is just ever so slightly finer grained than they are.

Sample Kennewick 251
This sample is predominantly silt size mineral material as above, with some interstitial fine grained carbonate that is in the process of being dissolved. This dissolution also includes calcium carbonate that appears to have been precipitated within some of the voids. In other words, the secondary carbonate here is not in the form of hypocoatings -which are produced by carbonate solutions which penetrate from the void into the matrix - but rather these are carbonates that have been precipitated within the empty space of the void itself. In any case, the overall makeup of this sample is not dissimilar from that of Samples 245, 246, and 250. It is difficult to definitively assess this sample in light of its very small size and the fact that it is being decalcified.

Sample Kennewick 251a
Similar to Sample 251 but somewhat less decalcified. There is no evidence for carbonate precipitation in the voids, but again, this is a very small sample.

Comments
In terms of general gross lithological similarity, it is evident that Samples 230 and 231 are quite similar to each other but are distinct from the remaining samples, which are coarser grained and have been subjected to decalcification. It should be pointed out that all the samples (with the exception of Samples 251 and 251a) exhibit secondary hypocoatings which are a pedogenic feature. The ultimate textural difference between Samples 230 and 231 and the others could simply relate to slightly different energies that one might find in overbank flood deposits, for example. Similarly, all of them could easily fit within a fluvial or colluvial setting in which loess-like material could have supplied the basic components.