Sediments, sediments, sediments – what on earth are they and what to do with them? 

For many students of archaeology and the more general public, soils and sediments might just as well be one and the same. After all, most archaeologists go mindlessly through the layers and, at most, note down the changes in colour or texture only after being forced to do so by the supervisor – a dreaded moment for most beginners. Yet, often we do not know why we are recording any of this information and expect a specialist to magically tell us how the landscape looked at that particular point in time and space. Moreover, it is important to know how the artefacts ended up where they were discovered, and knowing the type of deposition is key to this information. In the process to recognising the mode of deposition, the geoarchaeologist is constantly considering a wide variety of possible scenarios based on the deposits’ qualities. For instance, the size of the grains or stones in a layer depends on the energy involved in the deposition, while the roundedness or angularity of the material in the deposit will reveal whether the material was deposited by gravity or water. The geoarchaeologist then uses this information to answer whether or not a certain layer is a soil or a sediment, a knowledge of which makes the world of difference, as discussed in the next section. 

But what then makes a soil and what is considered a sediment? How does a specialist differentiate between the two? Well, the short answer is that a sediment is the material that accumulates on top of the bedrock through various modes of deposition, while soils are formed in the sediment through chemical, physical and biological processes acting upon the earth’s surface. Among the specialists, sediments are commonly known as the parent materials for soils. Soils represent periods of inactivity in the deposition of material, and the length of time that the landscape has remained unaffected by outside forces can be inferred from the various stages of soil formation. For us archaeologists, identifying the formation stage at which the soil formation was interrupted by human activities, such as cultivation, can be a useful indicator of the kind of environment in which certain behaviours, including agriculture, first appeared. Furthermore, it is possible to go into more detail about the way in which the land was managed. For instance, it is possible to differentiate between slash and burn versus annual cultivation, as the more sedentary the agricultural community becomes, the more they have to depend on fertilising the soil as it becomes depleted from nutrients without fertilisation. 

Typical anthrosol, or human induced soil formation.

What about distant past?

In Palaeolithic archaeology, the importance of soils is slightly different from the archaeology dating to the Holocene. Soils still formed during the Palaeolithic, but today they are often either eroded or overlain by new sediments that subsequently formed soils. The soils that are still preserved and below a sedimentary deposit are called palaeosols. These are very important layers in Palaeolithic archaeology, as they represent stable conditions during which sedimentation processes halted, and thus allow us to infer that no vertical movement of artefacts have occurred. In addition, palaeosols are very good chronological markers. However, because palaeosols may have taken several thousand years to form, any artefact assemblage within a palaeosol is formed during that time period. What this then means is that in palaeosols, the differentiation between occupations is not possible, as the artefacts were simply dropped on the surface, resulting in large accumulations without any layering in between the various visits. In contrast, due to the continuous nature of sedimentation processes, if an artefact assemblage of ten artefacts with a vertical distance of ten centimetres from each other is found in, say, one metre deep sedimentary deposit, each of those individual artefacts may represent individual instances of deposition and therefore represent ten visits to the site. However, these ten artefacts might also represent either a single episode within a reworked deposit, or a secondary deposition of the artefacts by water or colluvium, depending on the mode of sedimentation. These hypotheses would have to be confirmed through micromorphological or fabric analysis. It is therefore easy to understand that recognising the presence of palaeosols and sediments in Palaeolithic sites is of importance, as the interpretation of whether the site was visited, or if the artefacts derive from somewhere else is highly dependent on the identification of sediments. 

 

Cave sedimentation

First, it is important to realise that there are two types of caves: exogene and endogene caves. Exogene caves are commonly known as rock shelters, and they are formed in a different manner than endogene caves, which are caves that have passages and/or chambers. Both types of caves act as natural depositional traps, in which the deposits are mostly protected from subaerial weathering and erosion. Because of this quality, caves represent longer time sequences than open air locations, they preserve human and faunal activities better, and they hold a higher quality climatic record. Studying several well dated cave sedimentary records may reveal changes in regional climate, while changes in local environments are discernible in practically all records. This allows us to reconstruct entire landscapes with or without human presence during the Palaeolithic. 

There are three main types of material contributing to cave sediments: clastic detritus, organic detritus, and precipitated carbonates. The term clastic detritus refers to all rock rubble, cave earth, and water-lain material within a sediment, while organic detritus refers to all organic matter within the sediment. Precipitated carbonates are essentially speleothems, or flow- and dripstones, which may cover entire walls and floors, protecting the artefacts from re-deposition. The proportions in which these three materials are represented in the cave sediment is related to the rock type, size of fissure, groundwater regime, as well as topographical, geological and geographical context. All of these materials can be analysed to reconstruct very fine detail palaeoenvironments and record climatic changes. Their origin is often exogenous, but faunal and human remains may also originate from the individuals who once occupied the cave, whilst the speleothems are always local formations. Organic deposits rarely make up the most of a sedimentary layer, although bone and artefact beds do occur. 

1. Breccias formation under a pitfall trap 2. and 3.Waterlain silts;  4. Den accumulation of bones;  5. Accumulation of bat remains beneath roosting area in the cave roof and accumulation of small mammals beneath owl roosting/nesting area in the cave roof; 6. Water transported mud from further inside the cave;  7. Speleothems; 8. Roof fall; Accumulation of bones of cave bear, died during hibernation in the deeper regions of the cave; 9. Former lower chamber of the cave that acted as a natural trap/ accumulation room of amalgamated debris flows. - See more at: http://historyofgeology.fieldofscience.com/2010/10/if-you-gaze-long-into-abyss-abyss-will.html#sthash.Baj7tbmO.dpuf

1. Breccias formation under a pitfall trap
2. and 3.Waterlain silts; 
4. Den accumulation of bones; 
5. Accumulation of bat remains beneath roosting area in the cave roof and accumulation of small mammals beneath owl roosting/nesting area in the cave roof;
6. Water transported mud from further inside the cave; 
7. Speleothems;
8. Roof fall; Accumulation of bones of cave bear, died during hibernation in the deeper regions of the cave;
9. Former lower chamber of the cave that acted as a natural trap/ accumulation room of amalgamated debris flows.
Taken from: History of Geology Blog - Taphonomy of Cave Environments

 

My research

In my research, I look at the differences between interglacial and glacial deposits. My research asks how do sedimentation processes vary according to the environment in south-western France? Are there any discernible differences between interglacial and glacial deposits? If so, what are they? In trying to answer these questions, my focus is not solely on micromorphological differences, but also macroscopic differences. This knowledge can then be used to determine whether taphonomic factors affect the interpretations of archaeological remains. Moreover, this information may reveal settlement patterns across the landscape if several sites with similar sedimentation processes and timeframes are noted. 

 

Further reading

Farrand, W.R., 2001. Sediments and Stratigraphy in Rockshelters and Caves: A Personal Perspective on Principles and Pragmatics. Geoarchaeology, 16(5), 537-557.

Karkanas, P., and Goldberg, P., 2013. Micromorphology of Cave Sediments. In: John F. Shroder (Editor-in-chief), Frumkin, A. (Volume Editor). Treatise on Geomorphology, Vol 6, Karst Geomorphology. San Diego: Academic Press, 286-297.

Lowe, J., and Walker, M., 2015. Reconstructing Quaternary Environments. 3rd ed. London: Routledge.

History of Geology Blog - Taphonomy of Cave Environments

White, W. B., 2007. Cave sediments and paleoclimate. Journal of Cave and Karst Studies, 69(1), 76-93.

 

Interdisciplinary Archaeology: The underestimated possibilities of geological practices 


 

It is well known that the importance of geological methods and theories within archaeological research is of upmost importance to understand the context of our findings. However, the further role geology could play within archaeological research is often underestimated. As archaeology is a rather young scientific discipline, and is formed by its interdisciplinary approaches, it is important to continue exploring the possibilities other disciplines might offer archaeology as a field of research. Every now and then, we (archaeologists) would do well to be reminded of this, and to re-explore other disciplines that may hold innovative and revealing approaches, methods and techniques that would benefit our own research.

The entanglement of archaeology with geology is deep, and though we might think we have learned all there is of geology and what it has to offer to archaeology, I think every self-respecting archaeologist should be open and willing to refresh, update, or even upgrade  its geological knowledge every once in a while. Therefore I have chosen to do a Geoarchaeological workshop at the VU (Amsterdam), provided by the ARCHON research school of archaeology. This three-day workshop has been refresehing and eye-opening to me, and has allowed me to reconsider and broaden my own thesis research. Don’t believe me? Let me explain to you why:  

The first day was all about re-excavating our geological knowledge as we kicked off with some very basic information about the origins of the dutch landscape. The influences of the Saalian glaciation, river and sea deposits, eolian (a.k.a. wind) deposits and peat formations have formed the landscape as we know it today. Apart from these sedimentary processes, soil formation processes provide us with information that sedimentary formations cannot: presence of well-developed soils for instance, indicate hiatuses (stable periods of no erosion/accumulation), different soil types may indicate different human activity as the kind of soil that is formed is dependent on its parent material, climatic factors, organisms, time and relief/drainage. Human activity found in relation to certain soils may thus help us understand why certain areas were preferred, as the soils are a proxy to reconstruct and understand the former landscapes. In addition, we got our hands dirty by examining actuals soils and determining their traits in order to understand their origin and formation processes.

To practice what we preached, the second day was devoted to a field-trip to two distinct types of areas that mark the dutch landscape: The Pleistocene formed hilly outskirts of the Wekeromse Zand and the flat landscape of Amstelveen. Here, we did some serious coring into the dwellings of these different areas. learning us to recognize, for instance, the naturally formed podzols (both completely and partly formed) and understand the locations of these soil types in relation to the relief, as was the case at the Wekeromse Zand, and to recognize the younger thickly accumulated sediments of the Holocene deposits at Amstelveen.

The third and final day has been the most eye-opening to me in terms of underestimated and not-often-enough-used methods: for this day kicked off with my first ever introduction to micromorphology. Of course, I knew of the existence of this technique, yet I never really realized how this exactly works and what this technique could actually offer archaeologists. Which is, actually, quite a lot. Thin sections of in-situ sediment samples were placed under the microscope, allowing the examination of traits within the composition of sediments and soils otherwise hardly visible to the naked eye. In addition, human influences or biologically created disturbances, such as worm-activity, could be recognized that otherwise may gone unnoticed. Micromorphology could also be really useful to understand the integrity of stratigraphy and allows the distinction between seemingly heterogeneous layers.    

But how has this workshop helped me with my own thesis research as I previously mentioned? My research focuses on the integrity of a techno-cultural assemblage, the so called Châtelperronian,  of which the authorship is unknown (Neanderthals or Anatomically Modern Humans) due to the possible high occurrence of post-depositional processes that may have resulted from the highly fluctuating climate during the times theses assemblages were deposited. I mainly try to reconstruct the possible post-depositional processes that have occurred by focusing on the artefacts themselves: their distribution within the site as well as the orientation of all elongated artefacts. certain patterns within these may be indicative of certain processes. However, the precise distinction between such processes are hard to observe. The geoarchaeological workshop has made me realize that it will we worth advising some geomorphological maps and micromorphological analyses to help me distinguish different types of post-depositional processes.

As this has convinced me that geoarchaeological implementations on archaeological research are very beneficial, I can imagine you may still not be fully convinced. And therefore I would like to tell you the following. Within the workshop, all the archaeologists, having different backgrounds and different specializations, were able to implement new methods, concepts, or approaches to a great variety of archaeological research.                     

Why is dirt fun?

It was my first year as an archaeology student. I invited both old friends from school and new ones from university to my birthday party. Amazed by the extensive chit-chat about sediments, soils and excavating -and clearly also fairly bored- a non-archaeologist friend asked me: “Why do you guys like dirt so much?” Here, I will briefly show why dirt is fun -both for the layman and the obsessed archaeologist– with the explanation of the geo-toolkit, applied on a Javanese, Pleistocene site, containing important fossils in the study of human evolution.

Video field report - Why dirt is fun

Equipment in the geo-toolkit

Archaeology exploits methods and data from a variety of disciplines, such as anthropology, biology and history. Fundamental applications come from geology, since archaeology explores material remains in the ground. By taking the geological toolkit with into the field ‑both actual tools and mental tools— an accurate context of site formation, dating and (post)depositional processes can be provided. In other words, it helps us, archaeologists, to understand how and when finds ended up where we found them. The toolkit contains an infinite number of instruments, of which many are yet to be developed. A few of those tools in the geo-box include studying old and new geographical maps, geomorphological studies through coring, micromorphology, which investigates contents of sediments and soils, and geochemical isotope analysis, which uses patterned variation in elements on earth in order to reconstruct ecology in the past. 

A Javanese site in need of the toolkit

Eugène Dubois was the first researcher to discover and recognise Homo erectus fossils, which were found in 1984 at the site Trinil on the island of Java, Indonesia. Homo erectus can be considered an essential species in studying the emergence of the modern human body, brain and behaviour. The Dubois collection – which is curated at Naturalis (click for collection history (Dutch) and for an extensive description of the collection) contains a great variety of faunal fossils from the context and the whole region, thus providing the archaeological and ecological context of Homo erectus. However, since geology and archaeology were not yet well-developed, documentation quality and quantity lacks significantly. New excavations might improve our understanding of past and future finds at Trinil.

Sundaland, the biogeographical region that contains Java, is a biodiversity hotspot, caused by tectonic activity and climate dynamics throughout the Pleistocene. With warmer and colder periods, level rising and dropping hid or exposed shelves of the marine continent, which served as (resp.) barrier or bridges and corridors (dis)connecting mainland to islands. See for descriptions and reconstructions Semah et al. 2010 and Bird et al. 2005

The Trinil shells

An environmental reconstruction of Trinil, based on aquatic fauna from the Dubois collection indicated that Homo erectus lived in a coastal and riverine environment. In addition, an abundance of large bivalves at the main palaeoanthropological layer suggested hominin activities for gathering, dexterously opening and consuming molluscs. Moreover, on shell showed to be a retouched tool and a second shell contained a geometric patterns of groove zigzags on its exterior. All three finds are important in the discussion of developments human behaviour, including fish consumption – related to big brains and an associated required high-quality diet, aquatic resource use as raw material - and interesting addition to the debate on the Movius Line, and possibly even symbolic behaviour in species other than Homo sapiens.

Applying the toolkit

Historical documentation and modern maps

Re-evaluation of old documentation by Eugène Dubois and a comparison with modern data can allow for a general image of what to expect if new fieldwork will occur. Dubois’ original drawings were simplistic and of brief description. Modern accessible maps, such as ONEGEOLOGY, often relate to larger geographical areas in lower resolution. However, by cafefull combining the data, pointing out lacking information and detail in the geological knowledge of the site, might actually be useful and provide precise recommenations for future fieldwork. 

 

Dirty shells and their significance

The assemblage of bivalves that included the perforated molluscs’ exterior and the modified shells, included some left-over sediments, which were subjected to micromorphological analyses. Other sedimantary remains within the Dubois collection, a hominin skull and a Stegodon skull, allowed for comparisons of the residues. These indicated that the contents of these sediments, matrices and micro-concretions, are very similar in all three types of fossils. In addition, volcanic materials in the sediments allowed for the first direct dates of the site, pushing the original estimations back with 500.000 years, to a date of 0.45-0.54 ka. Finally, observations of thin sections provided for more information on the depositional character of the layer that contained these fossils. Absence of soil formation and bioturbation (disturbance by animals or plants) indicated a quick infill of the shells, thus a quick covering of the fossils, sealing it well-preserved.

Conclusions

Careful studying of dirt -either as described on maps, fresh from cores, or tiny bits on long-excavated fossils- can teach us where we come from and how human cognition evolved. Dirt provides context of archaeological sites, possibilties for accurate age determination of the first occurance of human traits, landscape formation details trought time and, most importantly, a pandora's box of possibilities to develop new tools to understand remains of our distance past.

Day 1

On my way to the Archon course ‘Geoarchaeology – Theories and Practice 2015-2016’ in Amsterdam, I am starring out the window of a fully packed train. The sun is starting to rise over the by-passing landscape which makes for a pretty view. Still partially unknown to the heaps of information buried under the surface, I wonder what this course will bring. Led by dr. Sjoerd Kluiving (VU Amsterdam) and Prof. Ian A. Simpson (University of Stirling), we start the day with an introduction on the formation of the Quaternary geology in the Netherlands, and the associated processes. Next, the landscape and soil of the Netherlands and north-west Europe is discussed. Some important basic geological distinctions, like pedogenesis-geogenesis, alluviation-illuviation and sediment-soil, were highlighted and the process of podsolization was explained. 

The second part of the day was devoted to part of the geoarchaeological toolkit. Using a topographical map of Amersfoort, we looked at the different ways in which the geological characteristics given in the legend of the map, could be used to study archaeologically relevant questions, such as ‘What is the influence of the different types of soil/sediment on the way in which past societies arranged their agricultural allotments?’. Next, we went down under ground and examined the different structures of soil through several lacquers peels.

Dr. Kluiving holding our carbic podzol lacquer peelOur description of the lacquer peel

As can be seen, our carbic podzol contained enough food for the geoarchaeological brain. We ended our first day with what must be the favorite activity of every geo(archaeo)logist; seeing, feeling and perhaps even tasting actual soil samples. On the basis of the pocket version of the characteristics of soil, i.e. the ‘Munsell soil color charts’ and the ‘soil texture triangle’, we were able to distinguish between different types of soil. Seeing as I was still a geological newbie at this point, many questions arose regarding the connection between the toolkit and archaeological research. Luckily, dr. Kluiving and Prof. Simpson did not shy away for these, and the many more questions that were fired at them. 

Day 2

The day starts with a bumpy ride to the first location of our coring field trip, the Wekeromse Zand, since our tour bus gets stuck inside the muddy surface (pointed out by dr. Kluiving in the picture). This could however not stop us and we continued our path on foot.

Three cleverly chosen coring locations made sure that we would get a very good view on the difference in soil formations which can be present in one area, and the way in which these differences have been shaped over the decades. Since we started this day in one of the higher parts of the Netherlands (+ 25 NAP), the sandy soils introduced our muscles to the intensive part of the geoarchaeological toolkit. The hard part of the coring process was however still to come. 

Our first coring locationOur second coring locationOur third coring location

After waiting for one hour on a bus driver who was nowhere to be found, which gave us the time to discuss and evaluate on our past activities and future assignments, we traveled about 75 kilometers west-north-west and sunk 26 meters, ending up in the wet soils of Amstelveen which lie 1 meter below sea level. The is where the hardcor(e)(ing) started. Due to the fact that we ran behind on schedule, dr. Kluiving decided to bravely take upon himself the task of coring and showing us as much of the soil in the amount of time we had. It soon became clear why the Edelman auger, which we had used in Wekeromse Zand, was not suited for these wet and clayey soils. We therefor had switched to the gouge auger. The end score of the day was an impressive 7,10 meters deep (- 8.10 NAP), which was reached by dr. Kluiving and a courageous participant of the course. This meant that they were able to reach the Dutch basal peat layer (visible on the picture at the end of the drill core) and we had traveled back at least 5500 years in time. 

Day 3

The final day of the course started off with a practical lecture, given by Prof. Simpson, on thin section micromorphology. He showed us the many ways in which a small square of soil could reveal so much on the area from which it originates. Take for instance the three pictures below. Fltr: bone, manure, fungi spores. These indicators can be used to study the diet of past societies, the way they fertilized their agricultural soils and the grazing locations of their cattle, respectively.

Eager as we were, many questions were asked and Prof. Simpson did not hesitate to explain and discuss until everything was clear. 

The afternoon was devoted to a mini geoarchaeological conference in which each of the participants gave a 15 min presentation on the subject of their final paper for this course. Even though we had only had 2 days to think on this, dr. Kluiving and Prof. Simpson had been able to teach us enough to all come up with highly relevant geoarchaeological research questions. This was also noted by both teachers who applauded us for our broadmindedness. 

Coming up with a subject was not easy. I had started this course with a lack of knowledge on geoarchaeology and found it difficult to incorporate it into my own research. During my Research Master, I have specialized in (ethno)archaeobotany and had recently conducted research on the effects of carbonization on barley grain kernels. As my knowledge on geoarchaeology grew during the course, my mind was also opened up to the possibilities of incorporating geoarchaeology in archaeobotanical research, specifically into my previously conducted research. I have gotten curious to the effects of different types of soil and sediment on archaeobotanical macro-remains and the ways in which this information can be used to optimize sampling strategies. This is what I will be studying in my final paper. 

After the successful mini conference, we end this informative and pleasant course with an evaluation while enjoying a drink at a café nearby. Even though this is the first time this course is given in this format, it has taught me a lot on geoarchaeology and the possibilities of incorporating it in my future research. Satisfied, I travel back to Groningen, staring at a landscape from which I now know holds many secrets to be uncovered.