ABSTRACT

Anisotropy of magnetic susceptibility (AMS) measurements were performed on bioturbated intertidal sediments near Sapelo Island, Georgia, to observe the effects of burrowing organisms on experimental magnetic fabrics. Some bioturbated sediments exhibited primary fabric characteristics, typified by horizontal long and intermediate axial inclinations, near-vertical short-axis inclinations, and AMS parameters V > 45° and Q < 0.69. A primary magnetic foliation suggests that secondary physical rather than biological processes were responsible for the observed fabric.

Evidently, the activities of burrowing organisms initially expanded the sediments, permitting subsequent grain settling and readjustment. Both gravitational and hydrodynamic forces may reorient such grains, creating an improved but secondary magnetic fabric. These primary characteristics indicate that bioturbation per se does not necessarily result in a permanent, random, secondary fabric. Furthermore, some open burrows serve as sediment traps; repeated burrow excavation and passive filling results in a mosaic of individual, nonrandom depositional fabrics within the substrate.