Coring is not boring

By Dr. S. David Webb

The Aucilla River Prehistory Project (ARPP) committed the first two months of 1997 to recov-ering sediment cores from three key research areas on the river. The purpose of coring was to get a broad overview of the sedimentary types, ages and distributions in areas targeted for excavation during our summer field season. This gave ARPP scientists a huge headstart in knowing where to excavate. We estimate that each well-placed core saved, on average, a week of exploratory excavation. There are two reasons for doing our coring in the winter months: first, because we have relatively few other commitments during that time of year; and secondly, because that gives sufficient lead time to get laboratory results back in time for the major summer field season. The biggest drawback to this schedule is that the water is at its coldest, but as we discovered, divers can be fairly efficient under such circumstances.

The ARPP is deeply indebted to Dr. Joe Donoghue of the Geology Department at Florida State University for loaning us his vibracoring rig and to Jim Hunt of Perry, Florida for providing his large block and tackle for retrieving the cores. We began by modifying the projectís 21-foot aluminum pontoon boat by cutting a six-inch hole in the deck amidships. This allowed ample working room for the tripod frame, the vibracore engine and at least three crew-members to drive the core at a balanced entry point. We spent one long weekend on each of the three research areas. For each area the scientific field director selected and prioritized up to six core sites. We purchased enough thin-walled four-inch aluminum coring tube in 30-foot lengths. The first weekend was scrubbed due to a stripped gear in the vibracore rig. Subsequently we succeeded in each of the target areas, with three cores at Nutall Rise, six in the upper end of Little River, and seven cores down-river in the West Run.

Divers were employed first to spot the precise river bottom locations for the cores. They were needed again after the core was driven and partly retrieved, to cap the bottom of the aluminum tube. This was essential to prevent loss of sediments that were not well consolidated. Some cores encountered hard bottom prematurely and therefore required relocation to an adjacent location. Such cases required divers to remobilize on an unpredictable schedule. Survey and depth data were recorded for each core.

When the cores were returned to the ARPPís field headquarters at the river, they were placed horizontally on a wooden rack designed by Ed Green and then cut in half longitudinally with a metal-cutting circular saw. The core sediments were then photographed while freshly exposed. Next, they were measured and described. From one half of the core, samples were bagged and wood fragments or other carbon-datable samples were taken. For most cores, at least the bottom carbon sample was sent off for dating. As the dates came back and the core logs were compared, a general three-dimensional view of the sediment stacks in each research area were developed.

We are pleased that the coring season was so successful. For a total of four long weekends of coring, and an almost equal time doing analyses, we obtained very valuable advance knowledge of the field areas to be excavated that summer. For Matt Mihlbachler and Lance Carlson at Nutall Rise, for Mark Muniz at Little River Rapids, and for Andy Hemmings in the West Run, the coring results offered a sophisticated perspective on where to focus their scientific excavation plans. Ultimately the core data will be integrated into the fabric of the entire research area. One feature of good science is learning how to develop testable hypotheses from limited data. ARPPís winter 1997 coring operations on the Aucilla River exemplify the early stages of developing a sound prehistoric framework on which to base more detailed work.

Editorís note: Reprinted with permission from the Summer 1997 issue of The Dive Log, UF Diving Science and Safety Program.