0400 - The geophysics of a new one

Here is a new image of geophysics for a Portuguese Prehistoric Enclosure, just finished few days ago. A twin of Xancra, just a bit more complex.

0388 - Preparing for excavating Tomb 4 at Perdigões

Click on the image to enlarge

To prepare the excavation of Tomb 4 at Perdigões Era team did some more geophysics to improve the available image. Here you may compare the previous image (on the left) of the monument with the new one (on the right, over the previous one). The difference is remarkable and a lot of useful information about the architecture is provided.

We will starting to adopt this procedure to other specific areas of the enclosures to get more detailed information.

0254 – Knowing what method to choose

At Perdigões two methods of geophysics were tested. First georadar. Slower and needing a considerable cleaned soil (for the radar runs a few inches over the surface), this method was totally disappointing. 

Georadar image of the center of Perdigões enclosures

On the contrary, magnetometry, not just is faster in the measurements, but provided excellent results. In Perdigões, but also in Xancra, Moreiros 2, Monte do Olival 1, Luz 20, Montoito, Monte da Contenda, images that you can see all through this blog. Or you can search in the net for tens of European examples.

Image of the same area done by magnetometry 

For negative structures, like pits and ditches, magnetometry is the method that provides best results. Of course the quality depends of several circumstances (like the bedrock or the proximity of highly magnetic material) that need to be taken into consideration.  But the results leave no doubt.

0227 - Montoito is (partially) done

We finished yesterday this year campaign of geophysics at the ditched enclosure of Montoito, just 8 klms north of Perdigões. 

Cleaning the field so Helmut Becker could measure was a hard task. 

I would like to thank Rui Mataloto and the Municipality of Redondo for their support and also to the volunteer students of FLUL that collaborated in this arduous ”archaeological” task. Without these collaborations the work simply couldn’t have been done.

Now we just have to wait for the first layout of the measured area to confirm that our “google eye” is sharp. 

0225 - Monte da Contenda is done

Measuring Monte da Contenda 

The geophysics of Monte da Contenda had just been done. A project of NIA-ERA Arqueologia, directed by me and with Helmut Becker responsible for the geophysics, as usual. The results, I've just been told, are very interesting. Next week, if possible, we will be doing Montoito, just 8 klms north of Pedigões.

0222 - Geophysics at Monte da Contenda

Next week, a project of NIA-ERA coordinated by me will promote a geophysical survey at Monte da Contenda, one of the sites located in Google Earth and presented in the poster of the previous post. The geophysics will be done by Helmut Becker, as usual. Expectations are high.

Aerial image of Monte da Conteda ditched enclosures. Now we are going to try to get a better image of what is there.

0181 – Luz 20 ditched enclosure

Location: Mourão municipality, Évora district, Alentejo, South Portugal.
Chronology: Chalcolithic
Bibliographic references: Valera, 2006; Becker & Valera, 2012.

Surveyed by Era company in 2004, in the context of the construction of Alqueva dam, Luz 20 is a double ditched enclosure with stone structures inside. Those works will be published next month included in a monographic study of several interventions done there in the same process.

Later, in 2010, it was submitted to geophysical survey (caesium magnetometry) in the context of NIA’s research project “Plans of ditched enclosures and Neolithic cosmologies: a landscape, archaeoastronomical and geophysical approach” financed by Calouste Gulbenkian Foudation.

The results confirmed the existence of the two ditched enclosures, of circular and concentric tendency, several circular pits and a large perfectly circular chamber of a possible tholoi structure.

Above is the magnetogram with the survey areas overlaid, showing the inside ditch and part of the outside, matching the areas were they were identified in the archaeological excavation.

However, in Portugal, geophysics continues not to be use as a regular tool in these kinds of infrastructure projects.  And they keep bumping into enclosures.

0170 - Poster on Moreiros 2

Poster presented to the IX Iberian Congress of Archaeometry. Lisbon, 2011.

0115 - New papers on Portuguese ditched enclosures

With free download here.

Helmut Becker e António Carlos Valera

LUZ 20 (MOURÃO, ÉVORA): RESULTADOS PRELIMINARES DA PROSPEÇÃO GEOFÍSICA (MAGNETOMETRIA DE CÉSIO)
Luz 20 (Mourão, Évora): preleminary results of geophysical survey (caesium magnetometry)

Helmut Becker, António Carlos Valera e Patrícia Castanheira

MONTE DO OLIVAL 1 (FERREIRA DO ALENTEJO, BEJA): MAGNETOMETRIA DE CÉSIO NUM RECINTO DE FOSSOS DO 3º MILÉNIO AC.
Monte do Olival 1 (Ferreira do Alentejo, Beja). Caesium magnetometry in a ditched enclosure from the 3^rd millennium BC.

António Carlos Valera

“ÍDOLOS ALMERIENSES” PROVENIENTES DE CONTEXTOS NEOLÍTICOS DO COMPLEXO DE RECINTOS DOS PERDIGÕES.
“Almeriense Idols” from Neolithic contexts of the enclosures complex of Perdigões

0112 - Interpreting geophysics

Here is the image of the magnetogram of the ditched and palisade enclosure of Monte do Olival 1 with Helmut Becker’s interpretation of the negative structures present at the site. This interpretation will be published next month in the electronic journal Apontamentos de Arqueologia e Património (a free download journal).

One of the things we learn with Helmut is that having a magnetogram is not enough. We also need good interpretation, based on the knowledge of geophysics, but also of the type of contexts we are dealing with.

0107 - The small enclosure of Carrascal (Porto Torrão)

It was a project developed by Era Arqueologia, and the geophysics was, of course, done by Helmut Becker with the results he usually provides.

Just 800 meters way from Porto Torrão traditional limits, and associated to a large area of necropolis, here is a small and perfectly circular ditched enclosure, with just 20m diameter.

A gate is visible at NW, possible orientated to sunset summer solstice.

At Porto Torrão things are much more complex than everybody expected and, I would argue, still expect.

0103 - The importance of good geophysics

The importance of good geophysics is evident. It can provide a global image of a site (that we can only have by traditional archaeological excavation after at least some decades) allowing the development of the scientific inquiry and research, it is not intrusive, so it doesn’t rise the problems that an excavation does, and provides a powerful planning tool (in research or impact assessment contexts).

At Perdigões, the geophysics done by Helmut Becker (Márquez-Romero et al. 2011; Valera et al., in press) is important, not just for the general interpretation of the site, but because it allows the contextualization of the excavated areas in a broader picture. Now we know exactly where we are in the site. But also important, we can plan where we want to be.

And in this year campaign, this is one of the places we want to be: the area inside Late Neolithic Ditch 6, where the geophysics showed two tiny lines that might correspond to palisades.

Fragment of the geophysics of Perdigões with the location of the area to survey

Well, we prepared the excavation by removing the ploughed upper level, and there it was: Ditch 6 and inside two smaller parallel ditches corresponding to the geophysical image (with an extra: a small pit between Ditch 6 and the first inside line). The goals, now, are characterize these structures, try to determine their functionality and date them.

Survey area, confirming the presence of the structures.

References:

Márquez, J.E.; Valera, A.C.; Becker, H.; Jiménez, V. & Suárez, J. (2011), “El Complexo Arqueológico dos Perdigões (Reguengos de Monsaraz, Portugal). Prospecciones Geofísicas – Campaña 2008-09.” Trabajos de Prehistoria, Madrid.

Valera, A.C, Márquez, J.E., Becker, H., Jiménez, V. & Suárez, J. (in press B), “O Complexo Arqueológico dos Perdigões: nova imagem e novos problemas proporcionados pela prospecção geofísica” Actas do 8º Encontro de Arqueologia do Algarve, (2010), Silves.