MAY 25, 2005

From: Scott Beld
Sent: Thursday, May 26, 2005
To: Oxbow Archaeologists
Subject: Riverbank Testing - 5-25-05 and this Weekend

Hi Oxbow Archaeologists,

I’ve given a rather lengthy description of what an A-horizon is below, so I’ll reverse my normal order for the updates and give you the plans for this weekend (in case your not interested in A-horizons for some reason – I can’t imagine why). This weekend we’ll plan on digging on both Saturday and Monday (Memorial Day). John O. and I are planning on digging on Monday and I should be at the site (Riverbank) about 9:00 both days. Right now the weather I’ve seen doesn’t look like it should be too bad on Saturday and should be quiet nice on Monday. If it should rain on Saturday, we’ll be in the Resource Building.

Yesterday, we made it out to the site in the afternoon and evening and opened a new unit, 85W-North2, adjacent to the two units already open (Photo 1). Dave, Nik and I excavated this unit to about 60 cm. We also had a photographer from the Midland Daily News come out to take pictures for an article in the newspaper.

The new unit had some bone fragments, fire cracked rock, and flakes (including one of Upper Mercer chert). There was also a shattered fragment of a biface (probably Upper Mercer chert) in the upper levels (0-50 cm). The other debitage was Bayport chert – we found about a half dozen flakes. We encountered the buried A-horizon at about 55-60 cm and stopped for the evening at the top of it.

Some of you have asked what an A-horizon is, so I’ll try to give an explanation.

First, soils can start to form when sediment is deposited at a location. This is “unaltered sediment” or the “parent material.”

Once a parent material is deposited, there are four general processes that transform the parent material into a soil: 1) the addition of material from the surface and atmosphere, such as the decay of surface vegetation and animals and the addition of dissolved and solid particles during rainfall; 2) the transformation of substances in the soil, such as decomposition of organic material (leaves, roots, etc.) into humus and minerals chemically altered into clays and dissolved chemical constituents (ions and oxides); 3) the vertical transfer of material downward through the soil – this is where very small particles, organic matter and chemical constituents are carried down through the voids between soil particles by water and gravity; and 4) the removal of chemical constituents from the soil by leaching.

These soil formation processes form a sequence (soil profile) of distinctive zones or layers. These zones or layers are called horizons. There are six major kinds of soil horizons designated by capital letters O, A, E, B, C, and R. Well-developed soils commonly consist of three main horizons, from top to bottom, A, B, and C. The A-horizon, at the top, is a mineral horizon where decomposed organic material (humus) accumulates and is the source for the solid and soluble constituents that move downward through the soil profile. Typically the A-horizon is darker than the horizons below it. The B-horizon forms below A, E or O horizons and is where clay particles, humus and various chemicals and minerals (iron, aluminum, carbonates, gypsum, and silica) accumulate as water moves through the soil. The C-horizon is located below the other horizons and is unaltered or slightly altered parent material. In less developed soils, A-horizons can be located directly on the C-horizon. For the other three horizons – an O-horizon is dark colored organic material at the surface (leaf litter, etc.) and an R-horizon is bedrock below the soil. An E-horizon normally is located between an A and B-horizon and is where organic matter, clay, iron and aluminum have been completely leached out leaving quartz and weather-resistant minerals.

Technically, we don’t actually know (yet) that our “buried A-horizon” is actually a buried A-horizon (or paleosol). It could possibly be a midden or flood deposit unaffected by soil formation processes (see Photo 2 to see the layers I’m talking about). In order to determine this we need to dig deeper and see more of the profile as well as get a better understanding of the deposition of sediment by the river on the site. My hunch is that this is actually a buried ground surface and that it isn’t just limited to this location. In fact the profiles from the Cater site that were done in the 1970’s show a similar layer at about the same level across the river (though they only found it in stratigraphic tests and didn’t excavate). This weekend we will be excavating the units on the riverbank deeper and hopefully get a better understanding of what we’re finding. In case you want to learn more about soil formations, I took most of the information from Michael R. Waters, Principles of Geoarchaeology (The University of Arizona Press, Tucson, 1992). Also there is a new book on buried sites in Michigan that Michigan State University has just published – G. William Monaghan and William A. Lovis, Modeling Archaeological Site Burial in Southern Michigan that deals with exactly the type of site we’ve found on the riverbank. While this book is so new that I haven’t had a chance to read it yet, glancing through, it looks like it has an excellent discussion of late Pleistocene and Holocene geology and environments in Michigan as well as a good summary and discussion of Michigan prehistory.

Hope to see you at the site Saturday and/or Monday.

Scott

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Scott G. Beld, Ph.D.
Research Associate II
The University of Michigan Museum of Paleontology
1109 Geddes Road
Ann Arbor, Michigan 48109-1079
Phone: 734-764-0489 (UMMP Main Office)
734-763-9253 (My Office)
Fax: 734-936-1380
Email: sbeld@umich.edu
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