The Holocene sedimentary record in southeastern Australia is present in a range of landscape
settings, such as upland swamps (dells), internally drained lake basins, alluvial fans, and mid-catchment
and lowland floodplains. An assessment of the best-constrained basal radiocarbon dates in valley-fill locations
between 30 and 42°S and upstream of last-glacial eustatic influences yields an intriguing pattern. The
record for fluvial sites with catchment areas30km2 exhibits a distinct gap in the alluvial record between
8 and 4 ka BP (10–4.5 ka). In contrast, data for eleven upland-swamp sites with catchment areas50km2
exhibit a broader spectrum of basal ages, albeit with some reduction of activity during the alluvial gap.We
suggest that the period 8–4 ka BP in the sedimentary record at the fluvial sites reflects the early to mid-
Holocene climatic optimum independently recognized in proxy climate data in the region. It was a period
of enhanced water discharges, stable well-vegetated catchments and low sediment yields, and therefore
greatly limited sediment sequestration, and it has been termed the Nambucca Phase. In upland swamps,
however, threshold-driven processes produce an episodic landscape responses during much of the Holocene.
Contrasting results in upland compared with middle and lower basin locations demonstrate the nonuniform
landscape response to climatic changes during the Holocene in southeastern Australia.