September 8, 2008

I have immigrants!

Whilst not as cool as shouting, "I have syphilis!" upon studying ancient bones, I can exclaim that I have some immigrants. Surprisingly enough, the clearer evidence of immigrants right now is from Castellaccio, the site about 20km from the center of Rome. Casal Bertone, 1.5km from Rome, also appears to have immigrants, but the data aren't as conclusive yet. I can't wait to run all the rest of the teeth. It'll take for-freaking-ever (it took me, what, 8-10 weeks to get 35 samples done, and I have at least 70 more to go), but it might actually be worth it. In a sample of 9 individuals from Castellaccio, I have clear evidence of 2 immigrants - 2 female immigrants. And in a sample of 19 from Casal Bertone, I have 4 immigrants - 3 males and 1 female.

I have good strontium data from 30 people and 2 animals. Three samples didn't work - my errors are too high. Most of those people range from .709-.710, which is the 87Sr/86Sr ratio for young volcanic rock, the kind that composes most of the central coast of western Italy. Rome is located basically between two presumably dormant volcanoes, with two more just to the north. Around this area, extending down through the Alban Hills, there are strontium ratios with .709-.710 values. But I have 6 people so far who have .708 values (or 20% of my sample). This isn't quite low enough to put them into the older volcanic rocks in southern Italy near Vesuvius, which run around .705-.707. What .708 maps to are the cenozoic carbonates, which I believe includes travertine and limestones. The Romans used a lot of travertine in place of true marble and quarried it from Tivoli. But the published strontium data puts .708 around the Roccamonfina volcanic area, just north of Naples. This would make some sense, as the published strontium ratios tend to decrease moving south and .708 would fill a nice gap.

So it's possible my immigrants made their way from somewhere around Cassino, perhaps midway between Naples and Frosinone, which was well over 100km south of Rome. Even if there were decent roads, that trip easily could have taken a week. Or it's possible they came from an area as close as Tivoli, only about 30km to the east. The problem with strontium is that it gives you a data point consistent with local geology; and the geology in Italy is fairly complicated, with loads of older rock in the east and young volcanic rock in the west.

But just as it's possible to tell the difference between the Vesuvius area and the Alban Hills with strontium, in spite of their seeming similarity in geological composition, I might be able to scare up some articles that tease out more precision from the travertine/cenozoic carbonate so that I can say whether these individuals came from the east or the south. But it does seem to be relatively short-distance movement within the country. I hope I get some evidence of long-distance immigration soon.

Oh, and I totally want a giant wall-sized geological map of Italy for my office. Wonder where I could get one?

1 comments:

Newell said...

I think you could get a geological map from the USGS, but I don't know how much it would cost.

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