Dig this! A reflection on three days of geoarchaeology 

 

Three days of an intensive goarchaeology course does something to a human being. One is altered in a way that one can never look at the landscape again with a mind that is blank, naïve, oblivious. Landscape, like beauty, is in the eye of the beholder. I feel like a novice hunter that has been taught how to see, and to pick up signals so that the landscape reveals a layer of itself that I have not layed eyes on before (see Ingold, 2000). Whether this change inside me and my fellow students is for the better, I could not tell you.

 

One has to see a sol to know a sol

Everything has a context. In the case of archaeology, the space-time continuum (FitzPatrick, 1983) of soil gives context to what we find, or what we don’t find. Archaeology will always have a soil and sediment record surrounding it which is like a story of what happened in the past. If someone walks the soil, ploughs it, manures it, or digs it: it affects the underlying soils and sediments. Archaeologists try to read this thick book through an extensive set of tools. Describing features like color, texture, structure, organic contents, and the nature of the lower transition from one soil horizont to another, are a prerequisite for a geo-scientific approach to understanding soils and sediments. The landscape can be understood subsequently, but understanding has to be built op by describing before combining soil features to an analytical conclusion.

 

However, before one can describe a soil, one has to see a soil. One can see a soil profile in the form of a lacquer peel, and one can see a soil in real life. Both could be done in this course and both leave different impressions on novice hunters or on, of course, me and my fellow students. On day 1 of this geoarchaeology course we got confronted with an extensive range of laquer peels that didn’t smell or didn’t taste quite as good as, we discovered the next day, real life soils, but anyways could be described for different abovementioned soil features. Me and my partner-in-crime hit checkpot directly because we were describing a so-called ‘Vaaggrond’ (if directly translated to English a ‘vague soil’, which mostly leaves the layman with utter confusion) (Fig. 1). Following is an account of the process of describing the soil and its features (Fig. 2). I will go more deeply into the features that I found particularly interesting and will only mention the others briefly.


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Fig.  1. Our Vaaggrond: you can see the greyish and brownish colors and limited soil formation.


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Fig. 2. The description of the soil features.

  

 

 

Firstly we drew the soil profile and divided it into several ‘layers’ that we could distinguish (or at least we thought so), and ended up with 15 layers which we later refrained to only 4 distinct soil horizonts. We described the color through comparement with the Munsell color chart and discovered that most colors in our profile were shades of greyish brown or brownish grey. Mostly the top layer(s) were browner and darker and the following layers lighter with more grey. These colors can give indications of drainage, leaching of the soil, and organic components and are thus very useful. Next thing to describe is the texture of the soil: how fine or coarse is it ranging from silt to gravel? This gives indications regarding the depositional process, fertility of the soil, and drainage possibilities. I found our profile particularly interesting for this feature because we had a so-called ‘fining upward sequence’. Dr. Sjoerd Kluiving explained to me and my partner that we had an alluvial deposit for which the rivers ‘stroomdraad’ changed over time.  Later, we evaluated the texture which can tell us for example about the presence of clay or silt. Following this, the organic compound of the soil is described. This is of interest because it can give an indiciation of vegetation. Next we described the presence of iron oxide, clay skins, and the nature of the boundary between one horizont and the next.

            Now came the part we highly awaited: the final analysis in which I could finally make conclusions and check my skills in pattern recogniton. With some illuviation of knowledge from prof. Ian Simpson and Dr. Sjoerd Kluiving into the brains of me and my partner, we could conclude that our soil showed evidence of a plowed Anthrosol, an illuviated plowed Anthrosol, followed by an illuviated sol, and finishing it off with a thick layer of parent material. Translating these horizonts we came to our Final Judgement: a Vaaggrond. A Vaaggrond – which has no literal translation in the World Reference Base for Soil Resources but can either be classified as an Arenosol or a Regosol, depended upon texture – is a soil that hasn’t developed clear horizonts, which is mostly due to the young age of the soil.

 

Real life soils going wild!

A fieldtrip of any kind brings joy to the hearts of archaeologists. Even more so if a friendly busdriver makes sure everyone stays safe by giving you a firm hand around your underarm by every disembarkment. Even more so if one is to get dirty. And even more so if one sees fellow students getting dirty while observing in amusement. I would happily write about the social and soily dynamics but I will contain myself as I am not an anthropologist but an archaeologist. Armed with gouges, cores (an ‘Edelmanboor’ in our case), gouge knives, tapelines, paper and pencil, Dr. Sjoerd Kluiving and prof. Ian Simpson showed us the places of interest for the second day of the course. Coring we went through 4 observation points near and on the Wekeromse Zand, culling a Vaaggrond, a Micropodzol, a Podzol, and a Carbic Podzol. Unable to control our soil rage, subsequently we gouged at 2 observation points in Amstelveen. Two Gleysols were slaughtered that afternoon.  

            The Gleysols in particular left most students in amazement because of the endless layers of peat and clay. Especially when we were told that each 1 meter of sediment approximates a 1000 years of sedimentation: how could our young brains ever comprehend this magic? At the second observation point in Amstelveen we already had to physically descend to around 4 to 5 meters below NAP (Normaal Amsterdams Peil, describing the average sea level - originally calibrated to the geoid). We gouged (Fig. 3) out firstly a disturbed layer of around 20 centimeters, whereafter only about 50 centimeters of peat. This was not surprising because the rest of the peat has already been removed to be used as fuel in earlier times (remember our descend to around 4 to 5 meters below NAP?). Subsequently we came into endless layers of clay; blueish clay, sandy clay, greish clay, compact clay, and shelly clay. This went on for about 5 meters before Dr. Sjoerd Kluiving and Prof. Ian Simpson decided this was enough. Dr. Sjoerd must have seen the bewildered faces of me and my fellow students because he explained:

 

            The peat that formed developed in a closed habitat, which is an indication of the closed circumstances of the coast because of shore formations. This peat is lying on top of this very open marine system, where shells could live and people couldn’t. On one point below this there would be a based peat layer, which developed because of   rising ground water tables which in turn were due to rising sea levels. Only later the Netherlands would actually flood because of the sea level rise. Below this based peat layer there would be a layer of Pleistocene substrate. This could have been river deposits or a sandy soil, or there is even the possibility of a podzol having developed   there. This was possible because before the Pleistocene substrate became flooded by the sea, this soil had thousands of years to develop and to form horizonts. Even hunter-gatherers could have lived on this surface.

 
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 Fig. 3. Endless layers of clay in our gouge at the second observation point in Amstelveen. 

Thin sections of rubbish

Looking through a microscope is always fun. Actually it doesn’t really matter what you are looking at because the colors and shapes under different lights are beautiful anyways. However, I have to admit that knowing that the multi-colored slide you are looking at is kitchen-waste makes you think slightly different about rubbish. At the third and last day of our geoarchaeology course we got confronted with thin section micromorphology. In micromorphology it’s possible to take a closer look at the stratigraphy and is an analysis of the undisturbed soil and sediments under the microscope. It gives insight into how the soil and sediments are organised, which gives clues about how the soil is related to each other and thus formed. My first moments behind the microscope made me feel mentally disoriented (not the first time I experienced that mental state in the last couple of days), but prof. Ian Simpson came to our rescue with examples and explanations. We managed (I say ‘we’ and not ‘I’ because prof. Ian Simpson rescued me many times) to partly untangle 1 thin section – from an agricultural layer at Tofts Ness, Sanday – which I will briefly describe in the following alinea.

            In the thin section from Tofts Ness (Fig. 4) we could discover a microstructure of chambers. The related distribution, which explains the relationship between coarse and fine material was porphyric with a coarse/fine ratio of 30/70. Porphyric means that the coarse and fine material is totally mixed with each other. Of the coarse mineral material that was present, quartz was very frequent, sandstone was only present in traces, and clacareous sands only in small amounts. This coarse material was moderately sorted, which means that it was not all of the same size, but also didn’t show big size differences. Regarding the fine mineral material, this thin section dominantly showed organic material, very few rubified material, and a speckled and random B-fabric. Linear patterns of the B-fabric could indicate an agricultural layer, but in this thin section there didn’t seem to be a particular organisation to it. Futhermore, we saw shell fragments, bone fragments, and fungal spores (Fig. 5).

 
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Fig. 5. Micromorphology in the thin section from Tofts Ness. A: a shell fragment under cross polarized light. B: a bone fragment under polarized light. C: the same bone fragment under crossed polarized light. D: fungal spore under polarized light.

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Fig.   4. Thin section from Tofts Ness.

Prof. Ian Simpson explained to us that the thin section of Tofts Ness gave us a look into a kitchen-waste layer that is used to mend with the soil. The soil predominantly existed out of wind-blown calcareous sands which was freely drained. People tried to farm in the area and it was a difficult environment to work with. Mending kitchen-waste with soil gave it the opportunity to be cultivated. This was an interesting insight and made me think about what ‘rubbish’ or ‘waste’ actually means in a world where maybe everything gets a second purpose.

 

Of blank minds and stuffed brains: geoarchaeology ain’t bringing sand to the beach

All in all I have to say that this course changed the way in how I look at landscape. Whether I like to have a blank mind when I look at the landscape surrounding me or one stuffed with questions and theories depends a bit on the day. From experience I can tell you however: one does not simply switch the geoarchaeology switch off! A couple of days have passed and my mind is still not back to normal yet…

            - No longer is this a ‘just whatever augmentation’ in the Dutch landscape. This, before, uninteresting augmentation has changed into a push moraine; a relic from the second last ice age during which big icecaps smoothed along the Dutch landscape, pushing softer sediments like river deposits into hillish features. During the last ice age wind-borne cover sands were deposited on top of this push moraine, for then this part of the landscape was a vast polar desert. After that, finer sands like driftsand could be deposited. Then, during the Middle Ages or later, humans found ingenuitive ways to fertilize this sterile soil. They augmented the push moraine even more through depositing heath sods mingled with dung from livestock. These and later generations plowed the soil and precipitation drained through it to leach minerals and organic matter from the topsoil into earlier deposits, like the cover sand. I have learned that this cover sand lost its clean color when approaching the layer of plaggen; now being a darker …... Down, brain! Down! … Good girl. -

 

            I did learn a lot, and the course also gave me insight in how I could use geoarchaeology for my own research (which mostly revolves around reindeer and circumpolar communities – what about reconstructing migratory patterns of domesticated reindeer through different properties of soil and its stratigraphy?). Knowledge can definitely be a burden, but it does open ones eyes for sure.

 

 

References

 

FitzPatrick, E.A., 1983. Soils. Their formation, classification and distribution. Longman: London.

 

Ingold, T., 2000. The perception of the environment: Essays on livelihood, dwelling, and skill. Routledge: London.