Miocene-Holocene river drainage evolution in Southland, New Zealand, deduced from fish genetics, detrital gold and geology

ABSTRACT

We integrate multidisciplinary observations to provide a regional-scale synthesis of river drainage reconfiguration in Southland (New Zealand) between the Miocene and the Holocene. Distributions of sedimentary clasts, including alluvial gold, garnets and chromite, are combined with freshwater fish genetics, surface geomorphology, and basement geology to constrain river drainage directions and interconnections through time. River evolution in much of the South Island has been dominated by localised tectonic uplift linked to distant Alpine Fault tectonism. In the southeast, the rise of ranges between Central Otago and Southland severed initial long-distance southward drainage and gold transport and isolated fish species. Plio-Pleistocene range uplift caused the recycling of older alluvial gold deposits into the new Southland river systems. The most significant Southland drainage reorientations have occurred through the Pleistocene, in parallel with similar processes in Central Otago. In particular, the Pomahaka River has evolved geomorphologically from a Southland-linked catchment to become a major tributary of the Clutha catchment, with associated biological evolution of distinctive endemic freshwater fish.

KEYWORDS:

• Geomorphology
• tectonics
• structure
• stratigraphy
• gold
• fish
• genetics

Acknowledgements

This study was facilitated by Noel Becker of Waikaia Gold Ltd, who provided samples of gold and heavy mineral concentrates from Waikaia and Waikaka, and Tony Baker, who provided access to his Waimumu mine site. Discussions with Donna Falconer, Jon Lindqvist, and John Youngson were helpful in developing ideas expressed herein, although they may not agree with all the conclusions. Brent Pooley assisted with sample preparation, Steve Read helped with image preparation, and Gemma Kerr assisted with the XRD mineral identification and hand-held XRF analysis. The final manuscript was substantially improved in response to a thorough review by Phaedra Upton and editorial comments from James Scott.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

All data relevant to this synthesis study are included within this paper and within cited references.

Additional information

Funding

This research was funded partially by the Royal Society of New Zealand via the Marsden Fund. Additional financial support was provided by the University of Otago and NZ Ministry of Business, Innovation and Employment (MBIE) via a research contract to CRL Energy (now Verum Group).