Geoarchaeology and Drinking Straw Technology

Jessi Halligan levels a core. - 2011 © Douglas Inglis

Sinkholes are unreasonably complex phenomena – those in rivers doubly so. If you can figure out their geological history, you have a better chance of figuring out how artifacts got there. As far as I can tell, this is not a straight forward task. As time goes by, sinks are subject to slumping, flood deposits, washouts and any number of interrelated sedimentary processes. When combined, they create a rather convoluted stratigraphic record. Sorting that record out was our primary task this excavation season.

Franklin pounds a core down through hard packed clay and peat. - 2011 © Douglas Inglis

To capture an exact record of sediments, we drove 3” aluminum core tubes down into the corner of each unit, invariably onto a rock, root, stump or other obstruction. We pounded them through the ground using a heavy hammer, brute force and dogged determination. To ease the process, we sharpened the end of the tubes so they would cut cleanly through the sediment. It was not as easy as we hoped. Driving a core through hard packed clay is a struggle on land – underwater, the mechanics get complicated! The diver has to be light enough to float at the top of the tube, but heavy enough so they won’t shoot to the surface every time they swing the hammer. Factor in a strong current, poor visibility and a SCUBA tank entangled with hookah hose and a relatively simple task suddenly becomes quite onerous!

SCIENCE! (Steve Spangler)

Cores operate on familiar drinking straw technology. If you place a straw in a Coke, cover the end, and then pull it out, the soda will stay inside. We capped our cores with a plastic lid and duct tape. When we pulled them out the resulting vacuum kept the soil sample inside long enough to cap the bottom. Back at the lab, we will cut each core in half (longwise) and have a perfect cross-section of the sink’s sediment layers. They also allow us to collect clean pollen, botanical and carbon samples. These will help us to date the site and understand what kind of plants grew in the area.

PS.

Coring is often full of surprises. In one unit, we drove the core into a subterranean spring. Cold water came spouting up from the base of the tube! As we continued to excavate the unit, the hole into the spring slowly widened. I dropped my trowel in. I thrust my arm in after, but could not find it. We dropped a high powered magnet on a string in and fished around. Alas, our only margin trowel was gone forever, lost in Florida’s labyrinthine subterranean drainages.