Geomorphological and geophysical investigation of the effects of active tectonic deformation on the hydrogeology of North Culverden Basin, North Canterbury
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy (PhD)
This thesis examines the complex interaction between the tectonic evolution of Culverden Basin and the Late Quaternary sediments, which form the aquifer-bearing deposits, using geological and geomorphological mapping as well as near-surface geophysical investigations. Along the eastern margin of Culverden Basin, the deformation associated with the actively widening Australian-Pacific plate boundary zone, has resulted in the evolution of Culverden Basin and the progressive inversion of the basin floor. The eastern margin of the basin is structurally controlled by a NE trending, complexly segmented range-front fault system and associated thrust-propagated anticlines forming the basin boundary. Basin inversion is driven by the westward propagation of footwall imbricate thrusts and associated folds. The inversion of the basin floor lead to the creation of sub-basins within the larger basin, which have controlled the distribution and architecture of the Late Quaternary stratigraphy. The Late Quaternary sedimentary record documents periods of climatically induced aggradation during cold conditions and degradation in the intervening warmer times. The interaction between the sedimentation and ongoing tectonic deformation has resulted in complex lithological relationships between the locally sourced alluvial fans and the glacial outwash deposits of the major rivers entering the basin. The architecture of the aquifers is therefore controlled by the changing fluvial regime and its interaction with the evolving sub-basins. The progressive evolution of the sub-basins leads to increasing complexities in the facies relationships and to the confinement of the deposits into progressively smaller portions of the sub-basins. Once the basin boundaries become emergent, the basin becomes isolated, and potentially cut-off from its groundwater recharge source. Leonard Mound is an actively evolving imbricate thrust system along the eastern margin of Culverden Basin that has isolated the Wynyard sub-basin from the central portion of Culverden Basin, during the Late Pleistocene and present. The emergence of Leonard Mound is preventing the recharge to the Wynyard sub-basin from the high yielding aquifers of the central portion of the basin. In the central portion of Culverden Basin, high natural recharge combined with an irrigation scheme has allowed for transformation of the basin into a major dairy farming centre. In contrast, the Wynyard sub-basin is still subjected to frequent summer droughts, making it desirable to find a better source of groundwater for the eastern margin of the basin. The hydrogeological model provided by the Culverden Basin almost certainly has wider implications to the groundwater resources of other basins in similar active tectonic settings.