BASIN FRAMEWORK AND PEAT ARCHITECTURE INFERRED FROM GROUND PENETRATING RADAR SURVEYING – IMPLICATIONS FOR CLIMATE AND CARBON SEQUESTRATION

Wetlands are recognized as important environments due to their roles as breeding grounds and nurseries, in storage of carbon and water, and for their economic resources. Previous research has primarily focused on coastal salt marshes, ombrotrophic peat bogs and mangrove swamps. A series of unique, fire resistant and resilient peatland have been recognized in the southeast coastal areas of Queensland, Australia. The peatlands appear to take three forms: 1) former coastal/estuarine environments; 2) former fluvial environments; and 3) former lacustrine environments. In each, restricted decomposition of different types of vegetation has resulted in the accumulation of peat.

In November 2023 an interdisciplinary team collected nearly 10 km of 160 MHz and 80 MHz ground penetrating radar (GPR) over peatlands that appear in former fluvial and lacustrine environments. GPR lines were orientated perpendicular to former fluvial structures and radially in circular to sub-circular lacustrine basins. Survey lines were acquired to understand the basin architecture and elucidate the infilling history.

In formerly fluvial wetlands, GPR data revealed the presence of an asymmetric surface beneath layers of peat that exceeded 5 m. This surface is consistent with a paleo channel of a river system incised into the surrounding sediments. The channel was then back-filled by sediments and finally peat as the stream responded to changes in base level during sea level rise. The present day streams are now tightly confined by peat deposits.

In formerly lacustrine wetlands, GPR data revealed the presence of a strong concave up, continuous reflection that was interpreted as the base of the former lacustrine system. The overlying ponded then draped series of reflections are suggestive of infill of the basin by lacustrine then palustrine sediments as the accommodation space lessened. Changes in surface vegetation are reflected in the GPR data as interfingering boundaries on the margins that relate to water depth and saturation of sediments.

This survey will be used to begin to elucidate the evolutionary history of these unique peatland systems developed on well-drained, sand substrates. Further, the data will inform a coring campaign to sample infill sequences to relate changes in infill sediments and sediment rates to the regional climate.