Tuesday, June 29, 2010

The Joys of Ground-Truthing

In past posts I have noted the importance that geophysical survey has played in our project. From the initial magnetic survey carried out in 2008 to our efforts to "ground-truth" the results by excavating where significant magnetic anomalies have been recorded, magnetic gradient survey has proven its value many times over. Its most spectacular success was the detection of the pit house, Feature 09-04, last season, but this year's work reveals how truly sensitive the instrument is, and, of course, the great proficiency of its operator and data-cruncher, Jarrod Burks.

In this post, I provide some of the results of our ground-truthing for a quite busy section of our current excavation area. The image below is a closeup view of the magnetic survey map for the western section of our bulldozer transect. The dark anomalies with feature numbers are those that mark prehistoric features. Note that every significant anomaly turned out to be a feature! No duds in the bunch. Pretty darn good and a great help to our efforts.

Probably the most indistinct feature is 09-18, a section of the oval enclosure ditch. It contained little of the oxidized soils, pottery, or fire-cracked rock that make for a strong anomaly. And it wasn't very easy to see when we dug into it! Feature 09-14 was a large but very thin lens of midden soil, charcoal and patches of burned earth. Still, the two small decorated pot sherds it contained proved very useful for placing its origin in the Late Prehistoric period. In contrast, Feature 09-26 was a large and deeper pit that contained nothing but charcoal, FCR, and a few flakes--very uninformative by comparison. Feature 09-34, shown below, was small but magnetically powerful since it was filled with fire-cracked rock.

Feature 10-13 was just opened today. It appeared as a rather indistinct, gray-brown feature stain in plan. Excavation of one half revealed a healthy amount of FCR, pottery, and charcoal-laden soil. A respectable amount of magnetic stuff but seemingly not that different from other features we have found that did not show up on the mag map. But we still have the other half to dig, so we will see.

Finally, there is what I have been calling "the big blob," a very large, somewhat irregular mag. anomaly, the north half of which lies within our transect. Now I suspected that this was more than one feature, but upon excavation it proved to be very complex. What we found were at least three overlapping pit features with some dark soil zones between them. We have spent the last several work days carving these features up in such a way as to sort them out. We are still

at it, but at least one we now know dates to the Middle Woodland period. I will have more to report on these interesting features later, but for now they reveal how complex the relationship is between the archaeological record and our high-tech methods of reading it.

Sunday, June 27, 2010

Soggy Site

A series of thunderstorms from Wednesday to Thursday dumped over an inch of rain on our beloved site. We were forced to 'bug-out' on Wednesday afternoon at 2:00 pm as an impressive thunderstorm approached us rapidly from the northwest. We were so busy packing up equipment and taking down our canopies that we didn't even feel the minor earthquake that came through about that time--what a dedicated crew!

We spent part of Thursday morning bailing water out of the units. This is a vital task that must be learned by all budding archaeologists; the trick is to get as little water on yourself as possible and to avoid slipping on the slick plastic tarps.

The upside of all this is that, because all but one of our currently open units were much too wet to excavate, we were forced to open up two new 3 x 3 meter units eastward along the transect. The wet remnants of the plow zone soil shoveled off rather easily and the weather was cool. Soon the subsoil was reached, and we were met with a wealth of possible post molds and some very interesting-looking feature stains (note some of the dark stains in the image above). One unit, 508N 515E came down on several distinct pit features that had shown up as half of a huge magnetic anomaly during the geophysical survey--mag anomaly no. 79 for those of you keeping score. More on this and other new discoveries later. A muddy time was had by all.

Saturday, June 26, 2010

Following the Stockade Line

Last Monday, we opened another 3 x 3 meter unit, but unlike the others, this unit was placed just to the north of our bulldozer transect at 514N 509E. This spatial deviation was designed to expose more of the eastern stockade line discovered last week. As expected, more of the distinct line of post molds were seen clearly on the floor of the unit and the line continued to the northeast. This particular segment of the line told us even more since it clearly ran across Feature 09-18, the filled ditch of the oval enclosure which was also exposed in this unit. Thus, we now know that the stockade line was erected after about 300 B.C., which is our current date for the filling of the enclosure ditch. How many years after is still uncertain.

The image below shows unit 514N 509E with the stockade post molds marked by red flagging tape. The line runs directly southwest (toward the corner where Jim and Debbie--with the fancy knee pads--are standing). You will notice that the line runs through an oval feature stain that is

partially excavated. This is Feature 10-11, a shallow pit or lens of dark soil that contained FCR and a few pot sherds. Interestingly, the post mold line disappeared at this feature, but upon excavation, the two missing post molds were exposed. As the image below shows, the post molds were 'hidden' under the pit (one is indicated by the arrow), which means that this small feature was constructed after the eastern stockade line came down. Unlike Feature 10-02, which also interrupted the post line, we recovered no good diagnostic artifacts from Feature 10-11 which could give us some chronological information. We will not chase this stockade line farther for the time being; we have much still to do in our main transect.

Tuesday, June 22, 2010

Beaver for Dinner?

So far this season animal bones are scarce and, when we do find them, poorly preserved. A few bits of deer bone and teeth have turned up along with the occasional fish bone. One interesting bone did turn up late last week as we excavated Feature 09-33, a small pit feature left over from last season's dig. It contained a relatively rich assortment of artifacts including a Madison triangular point and several pottery sherds that I believe belong to a Late Prehistoric period vessel, possibly Mixter Dentate. One oddly-shaped bone that was found amid the cluster of pot sherds was the femur (thigh bone) of a beaver (do beavers have 'thighs'?). The image below shows the beaver bone (about 9 cm long) among several pot sherds (the one in the upper left corner is decorated).

In my many years working in northern Ohio archaeology, I have run across numerous fragments of beaver incisors (front teeth which made good chiseling tools) but rarely post-cranial elements from this animal. To find one complete femur among pot sherds and other debris seems odd to me, but I am at a loss to explain it other than as a random bit of food remains. The bone is poorly preserved, but I think we can reconstruct it in the lab to see if it was indeed from an animal that was cooked for a meal. Beaver for dinner may have been tasty!

Sunday, June 20, 2010

More Pottery from the Oval Enclosure Ditch

As we moved eastward with our 3 x 3 meter excavation units, we once again encountered the oval enclosure ditch (Feature 09-18). As before, it appeared as a 1.5 to 2.0 meter wide, north-south oriented soil stain running along the eastern wall of unit 508N 506E. In the image below, you can see the enclosure ditch as a darker brown stain on the right (east) side of the unit. The horizontal dark streaks are plow scars and the pretty s-shaped curvy stain is a rodent burrow. The round spot at the west end of the curve is actually a small basin called Feature 10-01. Feature 10-02, described in the last post, can be seen in the upper left (northwest) corner of the image.

As this image shows, the fill of the oval enclosure ditch is relatively light in color, compared to other sections of the ditch. It contains a low density of artifacts with pottery being the most significant class of artifact found so far. One interesting rim sherd found this past week is from a grit-tempered, fabric impressed vessel. The rim measures about 6.0 cm wide and was found at 26 cm below datum. In the closeup shown below, the impression of an open weave, net-like fabric can be seen on the exterior surface. This impression could have been made by a net bag used for collecting plant material; its openings appear too small for it to have been used as a fishing net.

Fabric marked pottery such as this is less common in Early Woodland assemblages from northern Ohio than it is in the Ohio Valley and to the south. Still, there is no reason to think that this vessel was particularly unusual or maybe imported from parts south. It does point out the interesting range of variability in Early Woodland ceramic wares that were manufactured and used by the native peoples of northern Ohio.

A Western Stockade?

During our first week of the 2010 season, we made several interesting, and potentially very important, discoveries. The most revealing was the exposure of two parallel lines of what appear to be stockade posts situated just to the west of the oval enclosure. One of our objectives for this season was to look for any post structures that might have been associated with the oval ditch. Numerous Early Woodland enclosures in the Ohio Valley and elsewhere commonly consisted of a ditch and earthen wall embankment. Sometimes, an embankment was surmounted by a wooden post fence or screen which left behind one or more arcs of post molds. Strangely, the post mold lines we encountered on Monday appeared to run straight and at a northeast-southwest orientation. The two post lines are spaced at three meters apart, too close to represent house walls, and do not appear to be associated with the oval enclosure. The eastern line was most clear, and a section of it is shown in the image below. Selected post molds are indicated by the arrows.

As it turns out, this eastern line corresponds with a short section of very similar posts which were recorded last season in our most northwestern unit of the oval enclosure excavation. Exposure of more post molds on Tuesday filled the gap between these two segments to reveal a six meter-long line of posts. Near the center of this line, we discovered an oval pit (Feature 10-02) which contained one Madison triangular point and a Mixter Festooned type rim sherd (shown below).

Both these artifacts are indicative of the Late Prehistoric period and most likely date to around A.D. 1350. Excavation of this pit revealed no additional post molds from the eastern line, which indicates that this pit intruded into the already present post line and, thus, post-dates it. The precise time gap between the building of the line of posts and the digging of Feature 10-02 is unknown; however, it is certain that the posts themselves would have already been removed when the pit was constructed. When this occurred, we can't yet say. In any case, this discovery provides evidence of a wooden post enclosure that appears to be independent in time from the oval enclosure. Could this be a defensive enclosure for a later village occupation? More on this in a later post.

Wednesday, June 16, 2010

2010 Season Underway

On Monday, we began the 2010 field season in earnest by stripping a six meter wide by forty-five meter long transect across the location of the oval enclosure. We hired a local bulldozer operator to carefully strip the upper 15 to 20 cm of plow zone sediments across this transect in order to more efficiently look for features related to the enclosure.

Our plan is to shovel-shave the remaining plow zone deposits to expose the underlying subsoil, then search for features. Immediately after stripping, we covered the transect with sheet plastic to prevent the soil from drying out over the next few weeks.

Once the plow zone was completely removed, two three-meter by three-meter excavation units were laid out side by side at the west end of the transect. The floors of each excavation square were carefully troweled flat to reveal any organic feature stains.

Our first discovery was a clear line of post molds which ran in an oblique line across the eastern half of unit 508N 503E. This line could represent the wall of a structure or perhaps a stockade line. We were even more surprised to find a second line of post molds, running parallel to the first, in unit 511N 503 east. The image below shows the eastern line. More about these post lines later. Not a bad start for Week 1!

Sunday, June 13, 2010

New Dates on Heckleman Features

Over the winter, we submitted five organic samples from the 2009 excavations at Heckleman for radiocarbon dating. Each sample was selected from features that were thought to date to different occupations of the site, and this proved to be the case, for the most part. We were particularly interested in the age of the oval enclosure trench. Based on the rather thick, flat-bottomed vessel fragment and one knob handle that were found during excavation, we concluded that the trench was filled sometime during the Early Woodland period. A fragment of deer bone from this trench (Feature 09-10) returned a calibrated median date of 195 B.C., which is right on the mark. We also dated some deer bone from the nearby Feature 09-20, which contained similar forms of pottery and also a bladelet, and the result was nearly the same at 185 B.C.

I also was very interested in getting a date on Feature 09-19 which intruded into the fill of the enclosure trench. We dated a fragment of deer astragalus or ankle bone from this pit to 110 B.C., not terribly later than the other features but perhaps a generation or two later. So, based on this information, we have a good general sequence of events which began with the digging of the enclosure trench by about 200 B.C.—but who knows how much earlier—followed by a rather quick filling of the trench with debris (pottery sherds, a few used-up stone tools, a bit of animal bone, charcoal, and fire-cracked rock). The fill of the pit showed two to three distinct fill layers or strata which indicates that the filling took place in several episodes. Once the trench was filled, the folks that followed used the space for the construction of storage pits and other features. Perhaps this sequence reflects the use and then abandonment of the enclosure by Early Woodland people, but as yet, we still don’t know what the enclosure was used for or even when it was constructed.

The fourth radiocarbon date was run on a sample of charcoal from Feature 09-31, a small basin-shaped pit found inside the enclosure during the last week of the 2009 season. This is the pit that contained the fragmented siltstone gorget (see earlier post). The thick charcoal layer from which the dated sample was taken can be seen in the profile image shown below.

To my mild surprise, the median calibrated date on this sample was A.D. 525, significantly later than the Early Woodland occupation. This date marks the transition from Middle to Late Woodland societies in the region and shows that the former enclosure space was reused by much later inhabitants. The pit itself showed evidence of burning and, perhaps, use as a cooking pit. Numerous large and small post molds were recorded in the vicinity of this pit, which may indicate the presence of a structure; however, we cannot say at this time.

Finally, we dated the pit structure (Feature 09-04) using a carbonized hickory nut hull from a small concentration found near the floor of the house. The result was about what we expected, dating the structure to a mean calibrated date of A.D. 1535. The thin, well-made, grit-tempered pottery found in the fill of this structure, along with the Madison triangular points, could easily date to this era, the latter half of the Late Prehistoric period in northern Ohio. This final date most likely provides evidence of the last occupation of the Heckleman site, since no other sites in the Huron Valley date any later in time.