NEOICHNOLOGICAL EXPERIMENTS WITH MEIO- AND MACROFAUNA IN FINE-GRAINED MEDIA: PRELIMINARY RESULTS

The purpose of this study is to document meio- and macrofauna burrows in fine-grained media and resulting sedimentary fabrics. Of particular interest is the documentation and comparison of cryptobioturbation, a form of bioturbation that is difficult to observe owing to small size of burrows and lack of contrast from surrounding media. Clay and silt collected from a salt marsh near Savannah, GA were used in the neoichnological experiments. These sediments contained several organisms such as polychaetes and copepods. Clay and silt from Savannah was added to a tank with water salinity of 30 ppt and allowed to settle completely. Kaolinite or illite was blended with water prior to being added to the tank and allowed to settle completely while one side of the tank was videotaped. The experiments ran for several days, typically adding more kaolinite or illite layers as time progressed. Organisms usually began to burrow through the new clay within minutes after new sediment was added. Organisms moved quickly through the sediment creating open vertical to horizontal burrows. Sediment layer boundaries often became blurrier with continued bioturbation. Multiple experiments had mounds of basal sediment lying on top of the most recent layer created by organisms removing the sediment after a couple hours. After 24 hours the sediment was bioturbated thoroughly and the thickness of clay layers was reduced owing to clay fabric destruction; however, individual newly generated burrows could still be observed. After a few days of settling, burrows with a sinusoidal morphology resembling the ichnogenera Cochlichnus became visible. Once the sediment settled completely, new open burrows remained open unless destroyed by other organisms. The first burrows created in basal sediments often collapsed as a result of the additional weight of overlying sediment and were difficult to observe because lack of contrast in the sediment and because of further bioturbation. Sediment was preserved using a water-acetone-epoxy-exchange method. Samples were cut and scanned to be digitally enhanced and decompressed to observe burrows and sediment contacts. Cut samples show bioturbation is very subtle owing to lack of contrast. Sediment layer contacts and horizontal banding created by bioturbation can look like planar lamination when digitally compressed.