HEAVY MINERALS ADD WEIGHT TO NEOICHNOLOGICAL RESEARCH

Abstract

Vertebrate tracks offer important paleobiological and paleoenvironmental insights as indicated in the increasing number of studies of modern and fossil tracks in recent decades (Laporte and Behrensmeyer, 1980; Loope, 1986; McKeever, 1991; Platt and Hasiotis, 2008; Milan et al., 2007; and references therein). Whereas fine-grained sediments typically preserve the greatest detail, a track record of many organisms is archived in sand-rich strata representing paleo-shorelines, river banks, and dunes (Frey and Pemberton, 1986; Lockley, 1986). Despite the dynamic nature and coarse texture of sandy media ( = substrates), many studies report abundant vertebrate and invertebrate tracks, from Paleozoic sandstones to Cenozoic depositional sequences (McKeever, 1991; Lea, 1996; Loope, 2006; Lucas et al., 2007). Aside from a few cursory investigations of vertebrate tracks in recent beach and dune environments, little research has focused on their distribution and preservation in unconsolidated sand-rich media (McKee, 1947; Loope, 1986; Lea, 1996). This is largely due to the difficulty of preserving the tracks and even greater challenge of detecting biogenic structures in coarse-grained sediments. New neoichnological research is underway that addresses this long-standing problem, making use of the combination of natural selective mineral sorting and the ability to image small-scale structures using geophysical techniques. In many coastal and eolian settings, such lithological anomalies as heavy-mineral concentrations (HMCs) represent density lag formation during episodes of increased wave or wind activity (Komar and Wang, 1984; Smith and Jackson, 1990; Buynevich et al., 2007; Mange and Wright, 2007). Such lithological anomalies not only act as environmental indicators, but also accentuate vertebrate and large invertebrate tracks due to their darker color (Fig. 1; …