Boggy Test Pit

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In the Lake Mälaren area of Sweden, you rarely find any large pieces of Bronze Age metalwork in graves or at settlement sites. When the beautiful larger objects occur – axe heads, spear heads, swords, neck rings, belt ornaments – they almost exclusively come from odd find contexts that I for one feel comfortable with terming sacrificial deposits. My current main project aims to find out the rules that decided where people made sacrificial deposits. This entails looking at the finds we already know of and trying to trace the find spots, which is difficult as most finds were made about 1900 by members of the public. This strange time framing has to do with the fact that most of the sacrifices were made in wetlands, and the wetlands of the Lake Mälaren area were mainly messed with by the public during the decades to either side of 1900.

I want to be able to predict where these sites are and dig them in their untouched state, thus helping to reinvigorate a field of study that has languished for lack of new data for half a century.

This far into my studies, I’m not very optimistic about finding any useful regularities regarding the dry land sacrifices. They are a minority of the finds, and dry land occupies a great majority of the area involved. I’m afraid that any rules I may be able to propose will be too vague to tell me where to dig. But with wetlands, it may be another thing. Far more finds and a far smaller percentage of the area.

In the past weeks I have finished primary data collection on the known finds and run some simple numbers. Looking at finds that are at least potentially from wetlands by parish, Skogs-Tibble near Uppsala leads the field. And a closer look showed me that the numbers represent a belt of finds scattered through three parishes, from Österunda through Skogs-Tibble to Vänge, with some peripheral occurrences in parishes to the sides. So at this point in the evolution of my model, it’s basically like this:

Look in the Skogs-Tibble scatter. In wetlands. About 1.5 km from burnt mounds and rock-art sites.

And that’s what I did Friday. Near the site scatter’s centre of mass is an oblong lake basin in Skogs-Tibble that has steadily been silting up since getting cut off from the Baltic some time in the Neolithic (current surface 37 m a.s.l.). Only at the centre is there still a small area of open water, while the rest is all bog. In 1891, someone found a bronze flanged-axe head of c. 1400 BC while digging at an unspecified point in the eastern half of the basin. Most likely the digging had something to do with drainage, that is, reclaiming strips of dry land along the basin’s edges to improve forestry. I fought through the undergrowth at the basin’s edge, had a look around, and then settled for a spot to sink a test pit.

You’ll have to understand that I’m pretty new to wetland archaeology, which has never been a big pastime among my colleagues in the region. We don’t really have a tradition. Opening that test pit was a first step for me in learning about how these places really look under the spongy ground surface. And I made a stupid mistake that I could have saved myself if I had remembered what I learned while digging at Djurhamn and Finnestorp in recent years. Maybe you’ll laugh at me, but anyway:

A lake basin is usually deepest at the centre. And my pit was almost as near the centre of this basin as I could get without diving into the lake. I had to remove 1.5 metres of finely layered Phragmites australis reed-root peat before I reached open-water sediment. When I was finished, that pit was deeper than my wife is tall, and it was surrounded by an embankment of turves. And I was grimy from head to toe.

So, what did I learn? Well, in the reed peat were a few well-preserved (though very soft) sticks and other pieces of wood that showed no sign of human modification. They suggest drier woodland episodes. I only went beneath the peat on a 0.5 sqm surface, stooping in the shaft. There was no identifiable organic lake sediment, just a thin layer of coarse sand and sharp-edged gravel, then clean grey glacial clay that was laid down long before the Bronze Age. No artefacts. The spot has been a reed belt for thousands of years, probably since before the basin became landlocked.

Next time I’ll spend comparable labour digging several shallower pits instead, closer to the respective basin’s edge where the sediment pillar above the Bronze Age level is lower. Live & learn.

Comments

  1. #1 Steven Blowney
    July 11, 2011

    Two questions: 1. How did you pick where to dig? 2. Considering the situation, can relative chronology be determined?

  2. #2 Mu
    July 11, 2011

    So what you’re really saying is you’d like a Bobcat with a core drilling attachment for Christmas?

  3. #3 Martin R
    July 11, 2011

    Steve,

    1. I was looking at the crappy map in my GPS unit and forgot that it has no shading for boggy ground. The ditch that drains the lake into the bog looked like it drained onto dry land. One look at an air photo and I would have understood immediately. (The lake water oozes through the bog and then exits it via another ditch 500 m farther east at the end of the basin.)

    2. Please rephrase.

    Mu, I’ve thought about coring. It would be useful along with unlimited funding for radiocarbon, to find the Bronze Age levels at various spots. But a drill core is too small to tell me if there is any archaeology around down there.

  4. #4 Steven Blowney
    July 11, 2011

    On question #2: My mistake: I apologize. What interests me is how is a date determined? Through comparison with what? It seems to me that there’s a possibility that a bog accumulates layers differently than other sites. Is organic material preserved, and does it affect the layers in question?

  5. #5 Martin R
    July 11, 2011

    How is a date determined for what? Each layer of reed roots in the peat has its own date. Peat is mainly an organic substance.

  6. #6 Birger Johansson
    July 11, 2011

    Peat is a wonderful substance. Nowhere else can you find well-preserved wood dating all the way back to the end of the ice age.

    (OT) Regarding vertical descent into a damp environment:
    A medieval ship has been found outside Gotland.
    http://www.dn.se/webbtv/nyheter/se-dykarnas-bilder-inifran-vraket/
    The claim that it belonged to Danish king Valdemar Atterdag should be taken with a grain of salt.

  7. #7 dustbubble
    July 12, 2011

    What was this lesson you say you learned? Anything to do with shoring at >0.5m, and spoil placement? Or did the rain hold off?
    Good project, looks like healthy fun. Over here various agencies would have had kittens about sondaging into places like that, “Site of Special Scientific Interest” or some other protected environment.
    Mind you, we’re not even allowed to cut down trees, or light a fire for a brew.

  8. #8 Martin R
    July 12, 2011

    This is July, Sweden’s driest month. That’s why I’m doing wetland fieldwork now. The peat wasn’t collapse-prone, it was like carving in a stack of wet cardboard boxes.

    There’s no protected archaeological site in the bog as the exact find spot isn’t known. (And perhaps because info about the find is buried in an old museum ledger.) As for what any environmental agency might say, umm, I may have forgotten to ask them.

  9. #9 Mu
    July 12, 2011

    But a drill core is too small to tell me if there is any archaeology around down there.
    True, but it would have told you where to put the dynamite to remove the overlaying layers ;).

  10. #10 Tor
    July 15, 2011

    “This is July, Sweden’s driest month.”

    For `driest’, read `wettest’.
    http://www.smhi.se/klimatdata/meteorologi/nederbord

  11. #11 Martin R
    July 15, 2011

    Yes, measured in mm precipitation, July is actually the Stockholm area’s wettest month, not its driest. But it is also the warmest month and follows upon the driest six months of the year, and so this is the time of year when the wetlands are driest and easiest to dig without a bail pump.

  12. #12 Tor
    July 15, 2011

    My faith in Swedish archaeology is restored.

  13. #13 Tenerife Property
    July 17, 2011

    I was thinking maybe the artefacts maybe on higher ground but then you said there was no lake sediment where you dug your test pit. Presumably the discovery of sand means that area was once the shore of the lake but can you estimate the time period that would have been?

  14. #14 Martin R
    July 17, 2011

    The basin was an inlet of the sea until ~5000 years ago. Then post-glacial land uplift isolated it from the sea and it became a lake. A bronze axe head was either dropped into the lake or buried on its boggy edge ~3400 years ago.

    The spot I dug the above-mentioned test pit at has little or no open-water sediment before the reeds move in and start accumulating reed-root peat. I believe the sand and small stones represent the sea-floor before the basin became cut off.

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