GROUND PENETRATING RADAR APPLICATION TO RESOLVE BURROW COMPLEXITY IN MODERN MARMOTA MONAX BURROWS: IMPLICATION FOR THE RECOGNITION OF MAMMAL BURROWS IN THE ROCK RECORD

Specific criteria permit the assignment of burrows in the rock record to mammal or non-mammalian digging behavior. These criteria revolve around mammalian burrow complexity that contrasts with simple burrows of non-mammalian excavators, typically amphibians or reptiles. Modern large burrow systems lack study because of the extensive disruption of the land surface required to determine the true extent of the system. Ground Penetrating Radar (GPR) provides a non-invasive technique that has the potential to expand our understanding of burrow systems. Surveys were conducted at 3 locations of known Marmota monax burrows using a SIR 3000 GPR system from GSSI with 400 and 900 MHz antennas and upper reaches probed with an endoscope.

The 400 MHz antenna was used to identify positions of possible subsurface burrow features in clay-rich soils in surveys performed with a line spacing of 25-50cm. Burrow positions were ground truthed with an endoscope; abrupt turns in the burrow tunnels hampered intrusion of the total burrow length. Burrows were further examined with a 900 MHz antenna with a line spacing of 10 cm. The 900 MHz traverses resolved the burrow position more accurately in 3D space and revealed features which have been interpreted as additional offshoots from the main tunnel. Both antennas resolved a flat, dipping reflector suggestive of a ramp in the middle of the tunnel and a possible terminal chamber of that burrow. The 900MHz antenna constrained the tunnel width. Endoscopic examination showed tunnel deflection around roots that was not resolved by GPR. The observed burrow geometry is consistent with the criteria proposed to identify mammal burrows in the rock record.