ONE TRACE, TWO TRACE, OLD TRACE, NEW TRACE: GEORADAR APPLICATIONS IN ZOOGEOMORPHOLOGY AND ICHNOLOGY

Numerous near-surface geophysical images have undoubtedly captured a rich variety of biogenic structures, however the interpretation of discordant or point-source subsurface features is overwhelmingly in favor of primary physical structures or other geological anomalies. Over the past decade, ground-penetrating radar (GPR) imaging has been increasingly utilized for characterizing and cataloguing a spectrum of biogenic features. These efforts are not only aimed at shedding light as specific traces of behavior (neoichnology) or diverse aspects of pedoturbation and landscape engineering (zoogeomorphology), but will hopefully provide the framework for recognizing biogenic structures in radargrams. Here, a spectrum of bioturbation features and surface traces (tracks) are reviewed using both traditional 2D (B-scan) sections and horizontal depth slices (quasi-3D amplitude visualization) at center frequencies between 250-2300 MHz, with 800 MHz emerging as the most useful compromise for near-surface penetration and resolution. In addition to continuous (odometer wheel-triggered) mode, applications of real-time imaging are discussed. Examples span siliciclastic, carbonate, and evaporite media and an assortment of features produced by plants (root systems, buried trees) and animals (ungulates, rodents, turtles, squamates, and crustaceans). With continuous technological advances and new post-processing algorithms for attribute analysis, GPR will continue to serve as an indispensible non-invasive technique in field and laboratory research aimed at documenting and quantifying the rates and magnitude of beiogeomorphic agents.