Fossil hunting lured paleontologist Mike Pole to Benhar this week.
Pole, who has studied New Zealand plant fossils for most of his life, was hoping to find samples in the old Benhar clay pits.
He said the coal mine at nearby Kaitangata, which was part of broader coal field, had proved a rich source of plant fossils in the past, although no one seemed to realise that until a field trip in the 1980s.
"The beauty is they don't necessarily look like fantastic specimens in the field, but if you break down the mud or coal and sieve it, you can get a perfectly preserved plant fragment."
He gave the examples of leaf cuticles or conifer shoots, which had been discovered in Kaitangata.
Pole had spent a lot of time working in Kaitangata, but was keen to explore the clay soil in Benhar after finding a report in a 1958 manual from the New Zealand Geological Society that mentioned good leaf samples had been found there.
"I'm looking for mud with flecks through it which are basically bits of plant hash."
He collected the mud samples in a sandwich bag before transporting them back to the lab for analysis.
Once in the lab, the samples were broken down and sieved, which left just the plant material to be cleaned with hydrofluoric acid.
There were three main reasons for studying plant fossils, Pole said: To work out what plant life used to be in the area, to identify what the climate used to be like and to see what the carbon dioxide levels were millions of years ago.
The fossils previously collected at Kaitangata dated back to the late cretaceous period about 67 to 68 million years ago, he said.
They showed conifers which were all extinct, along with a mix evergreen and flowering deciduous plants, which meant the area may well have been above the polar circle, he added.
"It's the only part of the southern hemisphere that has plant fossils that well preserved."
The Benhar area was younger than the seam mine at Kaitangata and he was hoping it would prove a similar sort of fertile hunting ground.
"I'm really hoping to find something new."
It was a matter of trying to put together the ecology of the place, he said.
Pole started studying plant fossils in 1971 and said it grabbed him because most people were researching shell fossils at that time.
"No-one was really doing leaves then," he said.
Formerly based at the University of Queensland, Pole was still an honorary curator of the Queensland Herbarium.
- Clutha Leader
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