Palynological studies in the Lower Namoi catchment, Australia, show that there was a transition from a relatively wet climate in the mid-late Miocene to a drier climate in the Pleistocene. These data are, however, of relatively low resolution. The link between catchment rainfall and depositional processes is well established, thus past climate change information is recorded in the alluvial architecture of palaeovalley filling alluvial sequences. The impact of climate change during the Neogene is examined for the ~140 m thick alluvial sequences in the Lower Namoi catchment Australia. By combining the insights from the sparse palynological data with a 3D analysis of lithological logs and groundwater hydrograph data, a 3D conceptual model of the sediments that fill the palaeovalley is constructed, and this architecture is linked to changes in the climate. The compressive conceptual model of the sedimentary and hydrostratigraphic architecture of the palaeovalley filling alluvial alluvium is developed by statistically analysing the lithological sequences in 278 boreholes. Palaeochannels are mapped in 3D by interpolating the coarsest units in the borehole logs. Further details on the hydrostatigraphy are mapped by examining groundwater head fluctuations due to seasonal groundwater extractions, which are in the order of 100,000 ML/year. These results are then examined in the context of palynological climate change indicators. From the interpolated lithological logs it is observed that near the base of the sequence there was a dominant single channel belt. Progressing upwards through the sequence this channel belt migrates ~40 km southwards. At approximately 150 m.a.s.l. anabranching channels are observable. This shift occurs near the Pleistocene/Pliocene boundary and the boundary between the unconfined and semi-confined aquifer system. There is no discernible catchment wide aquitard, but there is an increase in the relative portion of clay which is most pronounced in the Holocene vertosols at the surface of the alluvial plain. The hydrostratigraphic boundary is a complex architecture of truncated palaeochannels and flood plains. The resolution of the borehole logs provides greater detail than obtained to date on the variability of past climates and their impacts on rivers in southeastern Australia. Only two major climatic changes are recorded in palynological data. However, catchment wide quantification of the borehole lithological statistics indicates six major shifts in the depositional setting, which are likely to correspond to major shifts in the Eastern Australian climate since the mid-late Miocene.
Neogene Climate Change and the Impact on the Hydrostatigraphy of the Lower Namoi Catchment, Australia
GIAMBASTIANI, Beatrice Maria Sole;
2011
Abstract
Palynological studies in the Lower Namoi catchment, Australia, show that there was a transition from a relatively wet climate in the mid-late Miocene to a drier climate in the Pleistocene. These data are, however, of relatively low resolution. The link between catchment rainfall and depositional processes is well established, thus past climate change information is recorded in the alluvial architecture of palaeovalley filling alluvial sequences. The impact of climate change during the Neogene is examined for the ~140 m thick alluvial sequences in the Lower Namoi catchment Australia. By combining the insights from the sparse palynological data with a 3D analysis of lithological logs and groundwater hydrograph data, a 3D conceptual model of the sediments that fill the palaeovalley is constructed, and this architecture is linked to changes in the climate. The compressive conceptual model of the sedimentary and hydrostratigraphic architecture of the palaeovalley filling alluvial alluvium is developed by statistically analysing the lithological sequences in 278 boreholes. Palaeochannels are mapped in 3D by interpolating the coarsest units in the borehole logs. Further details on the hydrostatigraphy are mapped by examining groundwater head fluctuations due to seasonal groundwater extractions, which are in the order of 100,000 ML/year. These results are then examined in the context of palynological climate change indicators. From the interpolated lithological logs it is observed that near the base of the sequence there was a dominant single channel belt. Progressing upwards through the sequence this channel belt migrates ~40 km southwards. At approximately 150 m.a.s.l. anabranching channels are observable. This shift occurs near the Pleistocene/Pliocene boundary and the boundary between the unconfined and semi-confined aquifer system. There is no discernible catchment wide aquitard, but there is an increase in the relative portion of clay which is most pronounced in the Holocene vertosols at the surface of the alluvial plain. The hydrostratigraphic boundary is a complex architecture of truncated palaeochannels and flood plains. The resolution of the borehole logs provides greater detail than obtained to date on the variability of past climates and their impacts on rivers in southeastern Australia. Only two major climatic changes are recorded in palynological data. However, catchment wide quantification of the borehole lithological statistics indicates six major shifts in the depositional setting, which are likely to correspond to major shifts in the Eastern Australian climate since the mid-late Miocene.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
