Sediment

Core blimey! Jason Stewart and the Sediment Core Samples

The best thing about working as a geoarchaeologist at MOLA is the variety; one day I could be watching a machine ripping through the odorous remains of a 19th century gas works, the next day could find me wrestling with the implications of a newly returned set of radiocarbon dates.

Today however finds me in the lab examining sediment cores retrieved from an evaluation. The site is in Dartford within the Thames estuary and has early prehistoric peat forming on top of the cold climate landsurface with various phases of being mudflat, marshland or flooded.

The cores are carefully laid out with the top of the borehole at one end of the lab and the base at the other. As there is 16m of sequence and the cores are 1.5m long and filled with heavy sediment this can take longer than you would think.  The cores are then methodically cleaned and the colour texture, inclusions and nature of the boundaries are recorded.  This detailed cleaning and logging allows me to think about the depositional environment of the site and the nature and rate of the changes that occur.

The next task is to select the locations from which to take samples, we take samples for radiocarbon dating, this enables us to places the changes in environment in some kind of chronological framework allowing us to compare the developments onsite with other work we have done in the surrounding area.  We also sample for things which will tell us about the environment in the past (usually pollen, diatoms, ostracods and plant remains).  These are carefully sliced from the core and sealed in labelled bags to be sent off to the various specialists.  The cores are then re-wrapped and returned to their climate controlled environment, the lab surfaces cleaned and the results typed up.

Jason Stewart

Virgil Yendell: Geoarchaeologist and his lovely sediments

Here are some shots of a trial pit under a former pub in Victoria. The lovely sediments from the base show c. 10,000 yr old fluvial gravels over lain by sandy deposits of a substantial tributary of the Thames, possibly the Tyburn, running through Victoria. During the prehistoric this river appears to have silted up and a waterlogged woodland is evident from the brown peaty deposits, which later developed into possible clayey water meadows that would have been used for pasture during the historic period.