What is macrobotanical analysis?
Carbonized (burned) plant remains are considered useful to archaeologists, as once carbonized, these remains can preserve for thousands of years. Although carbonized seeds, wood, and other plant parts can be considered macrobotanicals (visible to the naked eye), their recovery requires the application of additional techniques used by archaeologists in the field. In the case of macrobotanicals, flotation is usually necessary.
Flotation basically serves the purpose to separate the soil matrix from plant remains, which will float to the surface. This is made possible as dirt itself does not float, while carbonized (and uncarbonized) plant remains usually do as they are less dense than rocks. This simple, yet effective technique has made it possible for archaeologists to understand the past from a completely different perspective. Flotation can be carried out using manual or mechanized systems, and both have their advantages and disadvantages.
Below I discuss both manual and mechanized systems, as well as the basic laboratory procedures.
Flotation basically serves the purpose to separate the soil matrix from plant remains, which will float to the surface. This is made possible as dirt itself does not float, while carbonized (and uncarbonized) plant remains usually do as they are less dense than rocks. This simple, yet effective technique has made it possible for archaeologists to understand the past from a completely different perspective. Flotation can be carried out using manual or mechanized systems, and both have their advantages and disadvantages.
Below I discuss both manual and mechanized systems, as well as the basic laboratory procedures.
Manual Water Flotation: Bucket Flotation
Bucket flotation at La Corona, 2011
The most basic manner to recover botanical remains is to use bucket flotation. Here the soil is placed in a bucket, water is added, contents are swirled around, and then carefully poured into a sieve. This sieve will catch the lighter particles, while the heavier plant remains will stay in the bucket.
Manual water flotation is usually easier to set up, especially in the field, and inexpensive. However, it can be time consuming and labor intensive, and usually does not make sense for processing very large samples of soil.
Link to excellent video on bucket flotation by Dr. Dorian Fuller: click HERE.
Manual water flotation is usually easier to set up, especially in the field, and inexpensive. However, it can be time consuming and labor intensive, and usually does not make sense for processing very large samples of soil.
Link to excellent video on bucket flotation by Dr. Dorian Fuller: click HERE.
Machine-Assisted Flotation
The machine used for my own flotation in Guatemala City.
Since the development of machine-assisted flotation, modifications have been made to various machines. The one shown here (right) is a modified SMAP (Shell Mound Archaeological Project) machine. The water is not being recycled, and therefore this particular machine is best suited for places where access to water is not an issue.
This particular machine relies on water rising from below, and therefore allowing the lighter materials to float to the surface and gently pour into a sieve. The material which ends up in the sieve is the lighter fraction, while the materials remaining inside the large tank is the heavy fraction.
Although this allows for much larger samples to be processed than manual flotation, it does require the expertise of a welder, and access to parts such as storage tanks and shower parts.
Some flotation machines, for example the Flote-Tech, allows for water to be recycled (whereby the water doesn't need to be changed after each sample). This machine is rather expensive to build, yet can last a long time and process large amounts of soil.
Each method and machine will have its appeals and drawbacks, and the key is knowing which modifications can be made to suit a projects budget and the conditions in the field, all while being able to effectively gather the data in accordance with the research objectives.
This particular machine relies on water rising from below, and therefore allowing the lighter materials to float to the surface and gently pour into a sieve. The material which ends up in the sieve is the lighter fraction, while the materials remaining inside the large tank is the heavy fraction.
Although this allows for much larger samples to be processed than manual flotation, it does require the expertise of a welder, and access to parts such as storage tanks and shower parts.
Some flotation machines, for example the Flote-Tech, allows for water to be recycled (whereby the water doesn't need to be changed after each sample). This machine is rather expensive to build, yet can last a long time and process large amounts of soil.
Each method and machine will have its appeals and drawbacks, and the key is knowing which modifications can be made to suit a projects budget and the conditions in the field, all while being able to effectively gather the data in accordance with the research objectives.
Drying Samples
Heavy and light fractions are hung to dry in the shade. El Perú-Waka', 2012.
Following the flotation of the soil sample, one is left with 2 types of samples, the Heavy Fraction (which usually consists of rocks, large bones, and other heavier materials), and the Light Fraction (which should consist of lighter plant remains, such as wood, seeds, small bones, etc).
The samples are dried in the shade, and once dry, can be packaged and sent to a laboratory for analysis.
The samples are dried in the shade, and once dry, can be packaged and sent to a laboratory for analysis.
Microscope Work
Sorting samples using a light microscope.
La Corona laboratory.
Laboratory work is composed of several steps and long hours working with the microscope. Here I include a basic overview of the procedures.
1. Weigh the entire sample
2. Enter information on appropriate analysis sheet
3. Pass the sample through nested sieves
4. Weigh contents of each sieve separately and place in separate labeled containers
5. Materials in sieves greater than 2.00 mm will be entirely separated, weighed and labeled. Below 2.00 mm, carbonized seeds and other plant remains of interest will be selected and reported on the analysis sheet. It is important to note that not all seeds or other carbonized remains in the samples can always be identified, and these usually remain as "unknowns" or "unidentified seeds"
6. Plant remains are quantified using for example ubiquity, percent frequency, density, comparison ratios, and diversity indices
7. Photos of select seeds and other plant remains are taken
8. Results are interpreted, published, and/or presented at conferences and talks
1. Weigh the entire sample
2. Enter information on appropriate analysis sheet
3. Pass the sample through nested sieves
4. Weigh contents of each sieve separately and place in separate labeled containers
5. Materials in sieves greater than 2.00 mm will be entirely separated, weighed and labeled. Below 2.00 mm, carbonized seeds and other plant remains of interest will be selected and reported on the analysis sheet. It is important to note that not all seeds or other carbonized remains in the samples can always be identified, and these usually remain as "unknowns" or "unidentified seeds"
6. Plant remains are quantified using for example ubiquity, percent frequency, density, comparison ratios, and diversity indices
7. Photos of select seeds and other plant remains are taken
8. Results are interpreted, published, and/or presented at conferences and talks
Creating a Comparative Collection
Fruit of huevos de caballo (Stemmadenia donnell-smithii)
Creating a reference collection is extremely important in order to compare the archaeological material found in the samples, to then be able to identify the genus or species to which the plant remains in the samples belongs to.
Collecting seeds and plant parts is best done in the region where the archaeological project is being carried out. Other possibilities include requesting seeds from botanical gardens and exchanging with other research institutions.
Creating voucher specimens is also an important part of making a good reference collection.
Collecting seeds and plant parts is best done in the region where the archaeological project is being carried out. Other possibilities include requesting seeds from botanical gardens and exchanging with other research institutions.
Creating voucher specimens is also an important part of making a good reference collection.
Experimental Charring
Carbonized seed of chile pepper (Capsicum sp. )
Not all plant parts will react in the same manner when exposed to heat and charring. Therefore, charring select seeds and other plant parts, and analyzing these under a microscope, can help in understanding how certain seeds are affected by different degrees of heat, and how this changes their appearance. This further aids the paleoethnobotanist with the identification of archaeological material.
Additional References
Fritz, Gayle J. 2005. Paleoethnobotanical Methods and Applications. In Handbook of Archaeological Methods, edited by Herbert D.G. Maschner and Christopher Chippindale, pp. 771-832. Altamira Press, Walnut Creek, CA.
Hastorf, Christine A., and Virginia S. Popper. 1989. Current Paleoethnobotany: Analytical Methods and Cultural Interpretations of Archaeological Plant Remains. University of Chicago Press.
Pearsall, Deborah M. 2000. Paleoethnobotany: A Handbook of Procedures, 2nd Edition. Academic Press, San Diego, CA.
van der Veen, Marijke. 2011. Consumption, Trade and Innovation: Exploring the Botanical Remains from the Roman and Islamic Ports at Quseir al-Qadim, Egypt. Journal of African Archaeology Monograph Series, Vol. 6. Africa Magna Verlag, Frankfurt.