EXPERIMENTALLY DEPLOYED WOOD ON THE SEA FLOOR: IMPLICATIONS FOR UNDERSTANDING THE TEREDOLITES ICHNOFACIES

Analysis of wood, which was experimentally deployed in the Gulf of Mexico and the Bahamas at shallow to intermediate depths (Gulf of Mexico: 60 – 572 mbsl; Bahamas: 15 – 267 mbsl), as a part of SSETI (Shelf Slope Experimental Taphonomy Initiative), provides new insight into the Teredolites ichnofacies. Teredolites are tubular or clavate burrow fills, formed due to the activity of wood-eating molluscs (teredinids and pholads). Although lignitized and permineralized logs containing in situ Teredolites do occur, most Teredolites are found disaggregated, in reworked concentrations at the base of transgressive sequences. Savrda outlined a model for the formation of in situ and reworked Teredolites, which stressed the role of transgression in: 1. increasing the supply of wood to the sea floor, 2. hydraulic concentration of buried wood by ravinement, and 3. condensation related to sediment starvation.

Deployed wood consisted of kiln-dried lumber (Magnolia, Quercus, Araucaria, Sequoia and Pinus) and Quercus branches aged in a humid terrestrial environment for five years prior to deployment. Although Pinus and Magnolia generally experienced higher rates of attack than other wood types, and wood disappeared more quickly in siliclastic than carbonate environments, over two years most unburied wood had completely disappeared, regardless of type or substrate. Preservation of in situ Teredolites requires extremely rapid rates of sedimentation, and may not depend on increased wood supply to the shelf. Both ‘large, deep’ molluscan burrowers (teredinids and pholads) and small surface tunnelers (limnorid isopods) contributed to the destruction of wood. Over two years, molluscan burrowers consumed all of the wood in most blocks, except for a thin surficial layer. At all Bahamian sites and shallow Gulf sites, limnorids excavated sinuous, shallow tunnels about 1 mm deep in the surface of the blocks. Limnorid tunnels expose the calcite-lined burrows of teredinids, making them vulnerable to predation by boring organisms and mechanical breakage. These processes lead to sediment infilling and disaggregation of the lined burrows to form reworked Teredolites. Although limnorids have an extremely sparse fossil record, limnorids and other surficial wood feeders probably contribute to the formation of reworked Teredolites.