Transient Electromagnetic Data form the North Adelaide Plains

We collected the TEM data using a Zonge Engineering NanoTEM system. The NanoTEM is a low-power, fast-sampling time-domain TEM system that was specifically designed to provide high resolution images of the near-surface (~50 metres depth). The NanoTEM data were collected using a 20 m x 20 m square transmitter loop with a 5 m x 5 m, single-turn receiving loop. The transmitter coil had an output current of 2 A and a turnoff of ~ 2 µs. The receiving loop sampled at 625 kHz, stacking 256 cycles at a repetition rate of 32 Hz. The stacks were averaged and then inspected to remove noisy data in the late times. The NanoTEM data were inverted using the Aarhusinv program, run using “smooth model” settings (Auken et al., 2006, 2015). The 1D inversion assumes laterally homogeneous layers. All NanoTEM soundings were inverted separately (i.e. there were no lateral constraints,) and placed next to one another and interpolated to generate pseudo 2D profiles of bulk electrical conductivity. The quality of the inversion is determined by a misfit value between the observed and modelled voltages.