Evidence for Pulsed Flooding Periods from a Series of Terraces along the Burdekin River in Northeast Queensland, Australia, during the Late Quaternary: Implication for Climate Change

This study characterizes Quaternary terraces along one of the largest river systems in tropical north Queensland, Australia. Four stacked terraces, each up to ~4 m thick, occur along a road cut near Battery Crossing (19º 26' 13.8'' S, 145º 51' 42.2'' E) that represent overbank flood deposits of the upper Burdekin River. The terraces are the highest positioned flood sediments and the modern riverbed is found ~17 m below the top of the uppermost Terrace 1 (basal age of 10,500 cal BP). Geochemical, mineralogical, CNS, and particle size analyses were done in order to obtain information about variability of source and composition of the flood sediments through time. Dating of the sediments was done using ¹⁴C AMS for charcoal fragments and OSL for quartz grains.

Characteristic trends occur within the terrace deposits including sediment composition, color, organic carbon and geochemistry. All terraces have fining upward cycles comprised of medium to coarse silt and each is capped by a 30-50 cm thick paleosol horizon. Some thin layers of coarse sand and granules also are found within Terrace 2 and 3. Color variation in each terrace ranges from light yellowish brown (2.5 YR 6/3) near the base to strong brown (7YR 4/4) at the top. Carbon content is <1% in all terraces with most values < 0.6 wt-%. C:N ratios indicate that organic material contribution came primarily from soil algae with terrestrial contribution most pronounced within the lowest 80 cm of T1 and T4. Trends in major and trace elements show depletion above the boundaries of T3 and T2, and near the upper boundary between T2 and T1. The ages of the terraces imply that several larger than Holocene wet-phases occurred during the Late Quaternary which led to the deposition of these deposits.