Sediment accumulation and Holocene - OzCoasts

Sediment accumulation and Holocene evolution of the Fitzroy River lower floodplain
sclerophyll arboreal taxa, although there is some influx from aquatics, and
minimal input from gymnosperms, rainforest taxa, pteridophytes and mangroves.
There is a reduction in the concentration of grains between 40 and 50 cm, which
appears to correlate with the time of Brigalow clearing in the catchment (Kuhnen,
2004) and possibly indicates an increase in total sediment, which may have
diluted the concentration of pollen grains. At the base of the core the
concentration of pollen grains is very small, but there is a large concentration of
mangrove pollen compared with the rest of the samples. This significant change
in mangrove pollen correlates with the distinct change in facies to a grey clay. It
is possible that this grey clay is a relict surface, which was once part of the tidal
system and there were mangroves proximal to what is now the position of the
lagoon. An alternative hypothesis is that the mangrove pollen was transported
into the lagoon during a flood, prior to the barrage, when mangroves colonized
further upstream from Rockhampton.
Geochemistry
Geochemical analysis of samples from core FK406B was originally undertaken
by Kuhnen (2004) and then extended by Smith et al. (2005) and Douglas et al.
(2005). Using Bayesian statistical techniques it has been possible to determine
the contributions of sediments from different rock types in the Fitzroy River
catchment to the lagoon deposit (Kuhnen, 2004; Douglas et al., 2005).
Sediments are deposited in Crescent Lagoon during flood events when the river
flow is greater than 6 000 000 megalitres. Results for FK406B suggest that under
high flow conditions the majority of the sediment deposited in Crescent Lagoon is
from the Bowen and Surat Basins in the catchment (Figure 21). The other main
contribution of sediment is from the New England Fold Belt, with some
contribution also from the Tertiary basalts (