As discussed here repeatedly before, the eastern coast of Sweden is in continual flux because of post-glacial shoreline displacement. Since the inland ice melted away and relieved its pressure on the land over 10 000 years ago, the dent made by the ice has been rebounding: first very quickly, then slower and slower. This land upheaval is however only half the explanation for where the shoreline has been at a certain time: the water level in the Baltic basin has also varied. This means that while the general trend has been for the shoreline to recede, there have been periods when it has stood still for centuries or even moved upwards.
Now, imagine shore-dwelling people with sloppy habits, whose settlements are littered with various kinds of garbage. The archaeological sites they leave behind will be easy to sort chronologically: the ones on mountaintops are really old, the ones near today’s shoreline really young. And when the shoreline stops moving for a while, then there will be uncommonly many sites at that level. Nicklas Björk (with whom I had the pleasure to dig in the season of 1992) demonstrated this clustering on certain levels above the sea for the Gästrikland coast in work published during the 1990s.
Neolithic shorebound sites along the Baltic coast of Sweden are rich in decorated pottery. With the aid of shore displacement, the chronology of this pottery should be easy to investigate. A certain pottery style should always be found on the same level above the sea, right? Unfortunately, no: because land upheavel isn’t uniform across the area once covered by the ice. It proceeds really quickly near the ice’s original centre of gravity, somewhere in Middle Norrland, and then becomes slower and slower as one approaches the edge of the ice. Outside the glaciated area, there is a zone where the land actually recedes. So it’s been very hard to make sense of the Neolithic pottery chronology. Axel Bagge published important studies in the inter-war years, but he could only really study the development within individual sites such as Säter and Fagervik. There was no way for him to find out whether a certain level on one site was older or younger than a certain level on another site, unless they were located very close to each other. And worse, the pottery is rich in long-lived or local traits that aren’t useful for interregional chronology. And Bagge didn’t have access to the stringent typological methodology developed by Mats Malmer around 1960. So things have long been fuzzy with the Neolithic pottery, despite the introduction of radiocarbon dating. But a brand new piece of work seems to have nailed it down.
My buddy Niklas Ytterberg has done something absolutely audacious. He started with Björk’s level clustering concept and extended it to the entire Baltic coast of Sweden, looking at hundreds of sites. Everywhere, he found the same number of clusters, though the actual levels they sat on varied widely. Then he turned to quaternary geology, where people have been busy for decades refining regional shore displacement curves using radiocarbon. (They drill cores in lake sediments, identify the level where seawater diatoms are replaced by freshwater ones, and date organics from that level.) Using the geologists’ regional shore displacement models, Niklas figured out which level clusters in the various regions’ Neolithic site record are coeval. And in a final step, he sorted through insane amounts of pottery from each level cluster and identified traits that were shared all along the coast at that time. Presto — we have an interregional Neolithic pottery chronology with stringent type definitions, absolute dates from radiocarbon and huge interdisciplinary relevance for quaternary geology. Thanks, Niklas!
Ytterberg, N., 2007. Östsvensk neolitisk keramik i Bagges efterföljd. In: Stenbäck, N. (ed.). Stenåldern i Uppland — uppdragsarkeologi och eftertanke. Arkeologi E4 Uppland — Studier 1. SAU/Raä UV. Uppsala.
[More blog entries about archaeology, pottery, Sweden, Neolithic, shoredisplacement; arkeologi, keramik, sverige, neolitikum, stenåldern, strandlinjeförskjutning.]