The Petrography and Chemistry of Fossil Burrow Margins

Abstract

<p>A great deal of information may be attained from trace fossils. Burrow margins represent zones of complex interactions, which may be recognized in the rock record. Sediment deformation results during organism penetration and reoriented particles tend to align with the burrow structure. Sixty-five percent of all elongate grains show less than 10° tangential deviation parallel to burrow length, and 82% less than 20° tangential deviation for grains measured around the circular burrow cross-section. As suggested by fluid dynamic theory, fluctuation in burrowing velocity appears to induce grain rotation. Sediment type and fluidity, in conjunction with the nature of burrowing, will control the preservation of reoriented grains.</p> <p>Burrow walls are sites of metal accumulation. Metal cations become complexed to metabolites associated with decomposition of marginal organics, or to clay minerals entering the burrow. Some of these metals may also "scavenge" additional cations out of irrigated seawater. Concentrations are preserved as oxides or metal-rich cements within the marginal zone; characteristic of only those structures which are organically induced. Electron probe scans across burrow structures produce high relative peaks for Fe, Al, Cu and Ni in the wall region.</p> <p> These analyses may allow valuable interpretations, expanding the realm of Ichnology.</p>