BORINGS NOT BORING: TRYPANITES ICHNOFACIES FROM THE BAY OF FUNDY, NOVA SCOTIA

Cobequid Bay represents the easternmost arm of the Bay of Fundy and it suffers the most extreme tidal range in the system (up to 14m). As such, the intertidal zone is wide and unusually high (tidal) energy deposits are commonly exposed. A remarkable bored surface (Trypanites Ichnofacies) is present on the north margin of Cobequid Bay near Economy, Nova Scotia. The surface is the result of tidal ravinement, which has eroded the local Triassic sandstone and exposed it to boring and encrusting organisms.

The borings are exclusively the work of the boring bivalves Petricola pholadiformis Lamarck and Zirfaea pilsbryi Lowe. However, several encrusting organisms are present, including barnacles, Mussels, kelp, algae, bryozoans, foraminifers, and rare sponges and anemones. Several squatters are also present: these are amphipods, gastropods, various worms, and two species of bivalve.

Although the distribution of borings is patchy, the population density is highest in or near pools and at the bottom of rock-floored tidal channels. The largest continuously burrowed zone is 300m by 80m. Smaller patches are common. Boring density locally exceeds 1250 borings/ square meter, suggesting that Petricola and Zirfaea can be agents of intense bioerosion in the area.

Finally, animal relationships, discerned colonization patterns, and simple taphonomy reveal that: (1) the largest surface represents about 40 years of colonization; (2) at least 15cm of erosion into the bedrock has occurred over that time span; and, (3) standing water, flowing water, or salt spray is necessary for the activities of the animals. All of the above show that rock record Trypanites surfaces probably represent dynamic biomes that have a discernible temporal significance and can be linked to sedimentary processes and, to a lesser degree, bathymetry.