Central Otago fossil beds reveal their secrets

A parasitic wasp millions of years old lies entombed in kauri amber. It was one of many specimens found at Harliwich’s coal mine at Coal Creek, near Roxburgh. Photo: University of Otago
A parasitic wasp millions of years old lies entombed in kauri amber. It was one of many specimens found at Harliwich’s coal mine at Coal Creek, near Roxburgh. Photo: University of Otago
Research into Central Otago’s geological history is unearthing discoveries of international significance. Yvonne O’Hara looks at the scientific past of the region and future discoveries expected to be made.

Three insects never before recorded in Australia or New Zealand have been found in fossil beds at Bannockburn.

And more discoveries are ‘‘in the pipeline’’, Associate Professor Daphne Lee, of Otago University’s department of geology, says.

Prof Lee said the discoveries of a plant hopper no longer found in New Zealand, a weevil now only found in New Caledonia and a caddisfly, which is still here, were announced in June.

Central Otago has rich fossil beds near Roxburgh, St Bathans and Bannockburn.

The fossils were laid down during the time of Lake Manuherikia, a vast Miocene-era (23 million to 5.3 million years ago) freshwater body which covered about 5600sq km from the Maniototo to Roxburgh, the Nevis Valley and Wanaka, and possibly extending up into southern Canterbury about 18 million years ago.

Associate Prof Daphne Lee, of the University of Otago’s geology department, displays an example of a frond found in a fossil at Bannockburn. Photo: Yvonne O'Hara
Associate Prof Daphne Lee, of the University of Otago’s geology department, displays an example of a frond found in a fossil at Bannockburn. Photo: Yvonne O'Hara
‘‘This is the first time we have found insects in the lake’s mudstone,’’ Prof Lee said.

Earlier this year, fossil remains of insects and nematodes found in kauri amber at the Harliwich lignite mine near Roxburgh were identified as species that had never been found in the southern hemisphere before.

‘‘Lake Manuherikia was larger than all the present day lakes [in New Zealand] added together,’’ Prof Lee said.

‘‘It has the some of the most amazing fossil deposits we have in New Zealand.’’

It was thought to be 100m to 300m deep and formed when the country’s climate was warmer and more temperate.

There is fossil evidence of many birds, tuatara, frogs, lizards, moa, many species of fish, bats and a freshwater crocodile, living in and around the lake.
Prof Lee said Harliwich’s mine was an important site for plant and insect fossils.

As the Roxburgh amber is opaque, samples were sent to the University of Gottingen in Germany to be analysed using new techniques.

These revealed complete and partial remains of insects, including pseudo-scorpions found for the first time in New Zealand, spiders (and a spider web), and even scales of butterflies or moths.

Other tiny fossils include mites, springtails — which are new species for Australia and New Zealand — beetles, parasitic wasps, fungus gnats, and bark lice.
Prof Lee said more fossil species were expected to be found and described in the future.

‘‘As fossils that are so rare and unusual they have been sent for study to experts throughout the world and the work is continuing.’’

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