Understandable Earth Science

Posts tagged ‘Excavation’

So’a Basin Fieldwork, Part 2 – Life on the dig.

Welcome to Part 2 of my blog where I share some of my experiences of carrying out fieldwork in Indonesia as part of the So’a Basin Project . For this post, I am going to focus on the archaeological sites because I know that the workings of a large archaeological dig are a bit of a mystery to most people. To be fair, they are still a bit of a mystery to me – I was there mostly to take geological samples and to help constrain the stratigraphy of the area – but just being on the site, listening to the (very loud) chink of hammers and seeing a stegodon tusk slowly revealing itself a little more everyday was just fascinating.

The So’a Basin Project has various excavation sites scattered across the area, and thanks to the lack of vegetation, some of these show up really well on Google Earth.

Excavations from up high

Google Earth images of some of the excavations in the So’a Basin

The biggest of these excavations is a site called Mata Menge (the middle arrow on the above diagram), and it was near here that the So’a Basin team recently found hominid fossils. The site is a series of trenches, covered with tarpaulin to keep the sun (and very occasional rain shower) off both the workers and the trenches. These were very necessary as temperatures could easily reach 40 °C during the day.

As well as all of the archaeologists, geologists and other scientists visiting the site, the Project hired many people from the surrounding villages to help with the excavation. Each active trench had an experienced archaeologist as a manager, and a number of workers who had been trained to carefully excavate the sediment and rock in the trench, and identify whether a feature was archaeologically interesting (e.g. an artifact, fossil, or change in stratigraphy) and report it to the trench manager, who would note its location and investigate it further.

There were often dozens of people simultaneously using hammers and chisels to excavate the trenches; the first few times you hear this sound it is quite amazing, but it soon develops into a kind of musical background rhythm, that you only notice most when it stops as soon as the whistle blows for lunch break.

At the end of the day, the location of all of the finds (artifacts and fossils) needed to be measured and logged. This was a two-person job with one person taking a levelling rod to each find-location and placing it above each find, and another person manning the Total Station (a combined theodolite and EDM – electronic distance measurement) to measure (very precisely) the location of the find. This could easily add an extra 2-3 hours onto the end of the day if there were lots of finds that day.

Being very pale-skinned and a red-head (albeit out of a bottle), I am used to my appearance drawing a lot of attention when I visit hotter climates. This was exacerbated on my first trip to Mata Menge as I arrived near the end of the season, so was also the unusual newcomer. I lost count of the times I would be taking a sample from the wall of a trench and look up to realise that I had attracted an audience. Sometimes they were wondering if I needed any help, but other times they just wanted to watch whatever I was doing.

The trenches themselves were fairly free of local wildlife, but the wider area was grazed by local cattle and horses, and it wasn’t unusual to encounter a herd of buffalo or other exotic cattle while walking between sites.

Another site, about a 15 minute walk from Mata Menge, is Wolo Sege. It was here that Adam Brumm et. al. found some stone artefacts right below an ignimbrite deposit that was dated to ~ 1 million years ago. As a British, wannabe volcanologist, I was especially interested in this Wolo Sege Ignimbrite, because I don’t often get chance to look at ignimbrites that are younger than 450 million years old. It has everything a volcanologist could want – ash, pumice, accretionary lapilli and crystals (and when I say crystals, I mean shiny, 1 cm amphibole crystals – quite impressive!). The entire unit is about 3 m thick at Wolo Sege (the thickness varies where it has been identified at different sites across the region), and the top 2 m of that is ash (only the bottom part is shown on the photo below). There is a lot of ash mixed in with the pumice, and that, along with all the accretionary lapilli, suggests that there was a lot of water involved in this eruption – whether it was because of a rain storm, or erupting through a lake, we don’t yet know, though.

Wolo Sege Ignimbrite

Photo of the type-section of the Wolo Sege Ignimbrite, referenced to my stratigraphic log, and a close up of accretionary lapilli in the upper ash unit. Can you spot the accretionary lapilli clast in the ash below the pumice?

At the end of the excavation season, the trenches need to be protected to stop any partially-excavated, or as-yet-unexcavated finds being damaged by exposure. Exposed fossils are sealed in a protective gypsum plaster cast, after which plastic sheeting is laid at the base of the trench, and then all the material that has been dug out is used to fill the trenches back in again. This protects and preserves the site ready for the next season, while making it relatively easy to identify how far down you had excavated the year before.

So, that is life on an Indonesian excavation. However, I spent most of my time away from the excavation sites exploring the surrounding countryside, trying to correlate volcanic units, and I will tell you more about that in the next blog.

Mata Menge

Overview panorama of Mata Menge.