Monthly archives of “March 2016

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Miocene Nothofagus in New Zealand’s Manuherikia Group

Perhaps the most surprising thing about Nothofagus leaf fossils in New Zealand is – not finding them. Nothofagus is another name for the southern beech trees that form forests in New Zealand, as well as Australia, Patagonia, New Caledonia and New Guinea.

As a group, the beeches are certainly an old element in New Zealand, with at least some of them being around since Gondwana-times. This is not the same thing as saying that the Nothofagus in New Zealand today have an unbroken lineage back to Gondwana, but they are something you might  expect  to find as fossils.

Miocene Nothofagus leaf fossil from Bannockburn,New Zealand

Miocene Nothofagus leaf fossil from Bannockburn,New Zealand

When I collected plant fossils for my PhD on the Miocene Manuherikia Group, I noticed an striking pattern in the Nothofagus remains. Fossil beech leaves were common in some beds – but only the lower, older ones. This was the same whether it was the lower beds in the Bannockburn area, several hundred meters away on the banks of the Kawarau River near the Bannockburn bridge, or several kilometers down the Kawarau River, near Cromwell. Even tens of kilometers away, in St Bathans, where the sediments are the oldest of the Manuherikia Group, fossil Nothofagus leaves were common.

The distribution of Nothofagus leaf fossils in Miocene Manuherikia Group sections.

The distribution of Nothofagus leaf fossils in Miocene Manuherikia Group sections.

In each of these localities, Nothofagus was the most common leaf fossil, up to perhaps 40 % or so of the total. It’s safe to say that in the forests provided these leaves, the beeches would have made up about the same amount of the biomass. Higher beds of rock had leaf fossils – they include some diverse and large-leaved ones. The supplejack vine (Ripogonum) was there, palms, and even Eucalyptus, but no Nothofagus (there was a single exception where I found a Nothofagus leaf with a Eucalyptus). What was going on?

Miocene Nothofagus leaf fossil from Nevis Valley, New Zealand

Miocene Nothofagus leaf fossil from Nevis Valley, New Zealand

The distribution of beech forests now gives a big clue. In New Zealand today, the beeches can form forests from sea level to the tree-line in the South Island. In the North Island, they tend to make forests only at higher altitude. In other countries, the trend is similar. The attitudinal zone of Nothofagus forests rises from Tasmania in the south, until it skims the mountain-tops in the Border-Ranges of northern NSW and southern Queensland. There is then a gap,  before they appear again, high in the mountains of New Guinea. From Tierra del Fuego at the southern tip of South America, the story is the same. The further north – the higher the zone of Nothofagus.

The Nothofagus Zone (green) between Tasmanian and New Guinea (pretty sure I adapted this figure from someone else's a long time back. I'll add the credit when I find it)

The Nothofagus Zone (green) between Tasmanian and New Guinea (pretty sure I adapted this figure from someone else’s a long time back. I’ll add the credit when I find it)

It should be clear from this distribution that Nothofagus forests prefer cooler conditions. You won’t find beeches in the lowland tropical forests like in the Daintree. But it’s not simply temperature – cooler can also mean wetter. For instance in the Border Ranges, the cloudiest conditions are on the tops. Perhaps heavier rain falls occur in the lowlands, but the frequent clouds on the ridge tops means they hardly ever get very dry.

I think this is what the Manuherikia Group Nothofagus leaf fossils are telling us. In the lower, older beds, the earlier Miocene climate was optimal for beeches to dominate the forests. It was relatively cool and wet. Then, later in the Miocene, there was a climate change. It got warmer, and the rain would have evaporated more quickly, and perhaps it fell more seasonally. This tipped the balance from temperate conditions to more subtropical. Nothofagus never left – there are always their pollen grains around. Perhaps it just became rare, or even the crests of the low hills of the time were enough of a refuge.

Scientists love to say “Absence of evidence is not evidence of absence”. But in this case, its not simply lack of evidence. There are nice beds with  fossil leaves, higher in the Manuherikia Group., It’s just that they don’t have Nothofagus. Sometimes not finding something is important.

Technical Stuff.
The Manuherikia Group refers to the fluvial-lacustrine muds, sands and coal that accumulated on top of the schist in Central Otago (and probably further afield too), New Zealand, in the Miocene, and before substantial mountain-growth. See Douglas (1986) below for detailed description.

 

References

Links will take you to a downloadable pdf.

Douglas, B. J. 1986. Lignite resources of Central Otago. New Zealand Energy Research and Development Committee Publication P104: Volume one, Volume 1.

Douglas, B. J. 1986. Lignite resources of Central Otago. New Zealand Energy Research and Development Committee Publication P104: Volume one, Volume 2.

McGlone, M.S., Mildenhall, D.C., Pole, M.S., 1996. History and paleoecology of New Zealand Nothofagus forests., in: In:Veblen, T.T., Hill, R.S., Read, J. (Eds.), The ecology and biogeography of Nothofagus forest. Yale University, Yale, pp. 83-130.

Mildenhall, D.C., 1989. Summary of the age and paleoecology of the Miocene Manuherikia Group, Central Otago, New Zealand. Journal of the Royal Society of New Zealand 19, 19-29.

Pole, M. S. 1993a: Early Miocene flora of the Manuherikia Group, New Zealand. 5. Smilacaceae, Polygonaceae, Elaeocarpaceae. Journal of the Royal Society of New Zealand 23: 289-302.

Pole, M. S. 1993b: Early Miocene floras of the Manuherikia Group, New Zealand. 7. Myrtaceae, including Eucalyptus. Journal of the Royal Society of New Zealand 23: 313-328.

Pole, M.S., 1993. Early Miocene flora of the Manuherikia Group, New Zealand. 8. Nothofagus. Journal of the Royal Society of New Zealand 23, 329-344.

Pole, M. S. 1993: Early Miocene flora of the Manuherikia Group, New Zealand. 10. Paleoecology and stratigraphy. Journal of the Royal Society of New Zealand 23: 393-426.

Pole, M., 2014. The Miocene climate in New Zealand: Estimates from paleobotanical data. Palaeontologia Electronica 17, 1-79, palaeo-electronica.org/content/2014/2780-miocene-climate-of-new-zealand.

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Interdistributary drifters – a Miocene bay in New Zealand

One of the more evocative Miocene fossils you might pick up near Bannockburn, New Zealand, are she-oak ‘cones’ (see the featured image). The Latin name is Casuarina (but see ‘Technical Details’, below). This is a plant that no-longer grows naturally in New Zealand, but is a  tree in much of Australia. It’s cones, and sometimes its brush-like foliage, are one of the more common fossils in a unit of shale. The shale is a sedimentary rock that was deposited around 16-20 million years ago (Mildenhall, 1989; Mildenhall and Pocknall, 1989).  Its beds are dipping towards the road, but when it was forming, they would have been lying flat, and under water.

Shale Bannockburn 78412

The shale.

There are quite a range of fossils in this shale – mostly leaves. Some of the more common are beeches (Nothofagus), a kind of hoop pine (Araucaria),  perhaps some fragments of palm fronds, and even pea pods. Many of these fossil leaves await to be named.

Miocene beech (Nothofagus) leaf fossil

Miocene beech (Nothofagus) leaf fossil

Geologist Barry Douglas recognised this shale as having formed in an ‘interdistributary bay’. This is a term used for the quiet parts of a river delta (think of the Mississippi), in between the mouths of the narrow channels and their levees. Deltas are where rivers enter a standing body of water, and their channels split. Often the only areas above water are the narrow levees on either side of the channels. Flanking these was probably marsh, with little-more than extensive growth of reeds. These leaves and fruits were more likely from trees on the higher ground – growing on the levees. They would have blown into the channels, washed down them, drifted around to the bay, then settled into the mud on its bottom.

Schematic diagram illustrating the kind of interdistributary bay that would have existed at Bannockburn in the Miocene.

Schematic diagram illustrating the kind of interdistributary bay that would have existed at Bannockburn in the Miocene.

The bay had its own life. New Zealand’s first ever crayfish fossil comes from here. There are also the shells of fresh water mussels, and quite frequently fish-bones.

A Miocene freshwater mussel fossil

A Miocene freshwater mussel fossil

Miocene fish vertebrae fossils

Miocene fish vertebrae fossils

Miocene crayfish fossil

Miocene crayfish fossil

Collect enough of the leaves and you can work out their average length – and this can tell you something about the climate that they grew in. Go to a forest in the Catlins today, and the average length of the leaves on the forest floor will be around 50 mm. In the shale at Bannockburn, it’s closer to 60 mm. The average temperature was most likely a degree or two warmer than in forests at this latitude today. It may even have been four or five degrees higher or more.

 

Technical Stuff.
The shale is part of the Manuherikia Group. See Douglas (1986) below for an original description.
She-oaks all used to be called Casuarina, but a name-split means these ones are more likely Allocasuarina, or perhaps even Gymnostoma.

 

References

A link will take you to where you can download a pdf.

Douglas, B. J. 1986. Lignite resources of Central Otago. New Zealand Energy Research and Development Committee Publication P104: Volume one, Volume 1.

Douglas, B. J. 1986. Lignite resources of Central Otago. New Zealand Energy Research and Development Committee Publication P104: Volume one, Volume 2.

Feldmann, R., Pole, M.S., 1994. A new species of Paranephrops White, 1842: a fossil freshwater crayfish (Decapoda: Parastaciadae) from the Manuherikia Group (Miocene), Central Otago, New Zealand. New Zealand Journal of Geology and Geophysics 37, 163-167.

McGlone, M.S., Mildenhall, D.C., Pole, M.S., 1996. The History and Paleoecology of New Zealand Nothofagus forests., in: Veblen, T.T., Hill, R.S., Read, J. (Eds.), Nothofagus: Ecology and Evolution. Yale University Press, Yale.

Mildenhall, D.C., 1989. Summary of the age and paleoecology of the Miocene Manuherikia Group, Central Otago, New Zealand. . Journal of the Royal Society of New Zealand 19, 19–29.

Mildenhall, D.C., Pocknall, D.T., 1989. Miocene–Pleistocene  spores  and  pollen  from  Central  Otago, South Island, New Zealand. New Zealand Geological Survey Palaeontological Bulletin 59, 1–128.

Pole, M.S., 1993. Early Miocene flora of the Manuherikia Group, New Zealand. 8. Nothofagus. Journal of the Royal Society of New Zealand 23, 329-344.

Pole, M. S. 1993: Early Miocene flora of the Manuherikia Group, New Zealand. 10. Paleoecology and stratigraphy. Journal of the Royal Society of New Zealand 23: 393-426.

Pole, M., 2014. The Miocene climate in New Zealand: Estimates from paleobotanical data. Palaeontologia Electronica 17, 1-79, palaeo-electronica.org/content/2014/2780-miocene-climate-of-new-zealand.

 

Podozamites fossil from New Zealand Jurasic
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Podozamites – a multi-veined conifer in New Zealand’s Jurassic

Most conifer leaves have just one vein, whether they be the needles of pines, or the much broader leaves of some tropical conifers. This limits their size and shape (they mostly stay small and can’t do fancy stuff like many flowering plant leaves). Just two kinds of conifer have several veins in their leaves – some of the ‘Monkey Puzzles’ or ‘Bunya Pines’ (Araucaria) and the kauris (Agathis). All of these are evergreen.

In the past, things were rather different. My Chinese and Russian colleagues have just put out a paper reviewing Podozamites – a sort of ‘catch-all’ term for fossil multi-veined conifers. We limited out study to what is now East Asia – it has a nice latitudinal spread of plant fossil localities going all the way from the Late Triassic to the Late Cretaceous.  Early in this time Podozamites was a very widespread in mid-latitudes, and at times it probably formed an almost mono-specific kind of swamp forest. It also seems to have been deciduous, rather like the Ginkgo, which in some respects, is probably the most similar thing around today.

Chinese Podozamites

A slab of Early Jurassic rock from China covered with leaves and shoots of Podozamites.

We documented how, through the Jurassic and Cretaceous periods, Podozamites lost its dominance and often became just one of several conifers in a forest. It also retreated in to higher latitudes, towards the north before finally going extinct sometime in the Cretaceous. Over this period it had to deal with the appearance of something quite new – the flowering plants. Like Podozamites, many of these in East Asia were also deciduous and with relatively large leaves. They may have been the death-knell for Podozamites. We don’t know, but it’s curious that the plants with the leaves that may have been most able to hold their own against the ‘invasion’ of flowering plants, were the very ones to vanish. The East Asian Podozamites were not closely related to any conifer today. When they died out, it wasn’t just the end of a lineage, it was the end of a whole life-style.

New Zealand Podozamites

A Podozamites shoot from the New Zealand Jurassic.

New Zealand has Podozamites fossils from the Jurassic (see featured image) but these are quite unlike the typical East Asian ones. The New Zealand ones are possibly the narrowest Podozamites of all, with just a few veins. And they were probably evergreen. They are more likely to be related to those multi-veined conifers that still live in the region (Araucaria and Agathis).

But why were there never (as far as we know) vast swamp forests dominated by deciduous Podozamites in New Zealand? Was our climate just not right? If so – what was our climate? And why are our Podozamites so narrow?

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Podozamites shoot from the New Zealand Jurassic.

As they say in the trade – these are questions for future research….

Reference

This will take you to a link to pdf of our Podozamites paper:

POLE, M., WANG, Y., BUGDAEVA, E.V., DONG, C., TIAN, N., LI, L., ZHOU, N., In Press. The rise and demise of Podozamites in East Asia – an extinct conifer life style. Palaeogeography Palaeoclimatology Palaeoecology

Miocene leaf fossil from Blue Lake, St Bathans, New Zealand
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Blue Lake, St Bathans – the most biodiverse Miocene fossil plant locality

The biodiversity of Blue Lake, at St Bathans, New Zealand, is precisely zero. It is an artificial lake partly filling a hole blasted out in the search for gold in the 19th century. The hole is directly in front of one of St Bathan’s and New Zealand’s gems – the Vulcan Hotel. If you ran out the front door and forgot to stop at the cliff marking the edge of the old workings – you would land in one of the most biodiverse fossil plant sites anywhere on the planet.

Blue Lake, St Bathans, New Zealand

Blue Lake, St Bathans, New Zealand

The gold miners were sluicing quartz-rich gravel and sands. But in among those are thinner beds and lenses of mud. These are often full of plant fossils of Miocene age – say around 17-18 million years. Sometimes these are amazingly-preserved whole leaves – the featured image and one below show fossil leaves that have been floated out of the mudstone and then set in glycerine jelly between sheets of plastic. But often the fossils are just a hash of leaf fragments. This looks like a handful of compost at first, but it’s this hash, plus the extremely good preservation of that hash – that can make just a single handful of mud rich with fossils.

On the slope marking the edge of the Blue Lake digging and in front of the Vulcan Hotel there used to be a pine tree. It was my marker to locate a lens of mud remarkable by itself for its fossil plant content. In a few handfuls of mud from that lens were seven genera of conifers and at least 48 flowering plants. The conifers included some of our familiar New Zealand trees – like matai (Prumnopitys) and rimu (Dacrydium). But there were also surprises. There was Acmopyle – unique as a ‘hairy’-leaved conifer, and only growing in Fiji and New Caledonia now. Also Retrophyllum, a conifer with a distinctive paired arrangement of leaves along its shoot, but now found only in New Caledonia, Melanesia and South America.

Miocene leaf fossil from Blue Lake, St Bathans, New Zealand

Miocene leaf fossil from Blue Lake, St Bathans, New Zealand

And that little lens was just the start of it. Blue Lake has many such lenses, and over the hill is a ‘sister-lake’ – one of the local names being ‘Grey Lake’. It has a similar kind of geology. The sands and mud exposed in these lakes were deposited in an ancient river flowing along what geologist Barry Douglas (1986)  has called the ‘St Bathans PaleoValley’. It came from uplands in the west, to the coast somewhere to the east. In both Blue and Grey Lake muds I’ve now recorded a total of 13 conifers, 144 flowering-plant types and a further two cycad-like ones. To put this biodiversity in context, As a comparison, today there are around 215 species of tree in the entire New Zealand region (including the subtropical Kermadec Island; McGlone et al., 2010) and nine genera of conifers. So in an area of just a few hectares – there are more fossil conifer types than in all of New Zealand today. This is one of the most biodiverse, and perhaps the most, Miocene plant fossil localities anywhere.

What caused this high biodiversity? It was certainly warmer – the climate was warm temperate or even subtropical. Average temperatures would have been at least 6-7 degrees warmer than today. But perhaps more importantly, the cooler temperatures would have been much warmer. The harsh frosts and snow that St Bathans gets now, would have been entirely unknown. The kinds of rainforest plant fossils found at Blue Lake prove that rainfall too, would have been higher and more consistent, quite unlike the low and drought-ridden climate that the area has now. On top of that, Douglas considered that the ancient river was ‘braided’. This is a type of river that has many channels, and switches between  them from time to time. This process keeps vegetation in various stages of ‘succession’, allowing many species a chance to find their niche.

Vulcan Hotel, St Bathans, New Zealand

Vulcan Hotel, St Bathans, New Zealand in the snow. There would have been no snow, or even frosts, during the Miocene when biodiverse rainforest grew here.

The Miocene plant fossils of Blue and Grey Lakes are a treasure -trove and much remains yet to be understood. Many of the fragmentary plant fossils are still unidentified. They are clearly not plants living in New Zealand today – but where will similar plants turn-up? New Caledonia? Patagonia? Madagascar? And just what were the plant communities that lived in the St Bathans Paleovalley? How many new fossils wait to be found?

And that first lens of mud? The one beside the pine tree? Pine trees are an introduced, often invasive conifer in New Zealand. Their spread across parts of New Zealand is causing problems (they shade out smaller natives, acidify the soil and are a fire hazard) and so the Department of Conservation is doing their best to control the pines. That pine, one of the few trees in an otherwise naturally vegetation-free spot, was removed, and along with it, much of that biodiverse fossil lens. In fact, with the pine tree gone and the disturbance that created, I’ve had trouble re-locating it.

Something very ironic there!

References

Links will take you to a site to download pdfs of the papers.

Douglas, B. J. 1986. Lignite resources of Central Otago. New Zealand Energy Research and Development Committee Publication P104: Volume one, Volume 2.

Pocknall, D.T., 1982. Pollen and spores from Blue Lake, St Bathans (H41) and Harliwichs Lignite Pit, Roxburgh (G43), Central Otago, New Zealand. Palynology Section, NZGS, Lower Hutt.

Pole, M.S., 1992. Early Miocene flora of the Manuherikia Group, New Zealand. 2. Conifers. Journal of the Royal Society of New Zealand 22, 287-302.

Pole, M.S., 1997. Miocene conifers from the Manuherikia Group, New Zealand. Journal of the Royal Society of New Zealand 27, 355-370.

McGlone, M. S., S. J. Richardson, et al. 2010. Comparative biogeography of New Zealand trees: species richness, height, leaf traits and range sizes. New Zealand Journal of Ecology 34: 1-15.

Pole, M., 2007. Conifer and cycad distribution in the Miocene of southern New Zealand. Australian Journal of Botany 55, 143-164.

Pole, M., 2008. Dispersed leaf cuticle from the Early Miocene of southern New Zealand. Palaeontologia Electronica 11 (3) 15A:, 1-117.

Pole, M., 2014. The Miocene climate in New Zealand: Estimates from paleobotanical data. Palaeontologia Electronica 17, 1-79, palaeo-electronica.org/content/2014/2780-miocene-climate-of-new-zealand.

 

Fossil pea pod (legume) from the Miocene of New Zealand
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Giant Pea Pod fossils in New Zealand’s Miocene

Pea pod fossils in New Zealand were first found by Aline Holden, a pioneer of New Zealand plant fossil research. She found the first ones at Bannockburn in 1981, while working on her PhD, and then found more in the Nevis Valley.

In 1987, my PhD professor, J.D. Campbell and his wife, Anne, dropped in unexpectedly in Alexandra (my home). They were on their way to the Nevis Valley and wanted to know if I would come too. The Nevis Valley has a well-known oil shale deposit, and this includes fossil leaves and scattered fish bones of Miocene age (c. 18-17 million years). Once in the area, ‘JDC’ focussed on shale near the track, while I set off to explore up a shrubby side valley. I was on the way back when I spotted a likely outcrop up on the valley side. It was solid gold – to a fossil plant person that it is. Technically it was mudstone, but stuffed full of not only fossil leaves, but pea pods as well. I worked out as large a chunk as I could, strapped it to my pack frame, and then staggered back to the car with it.

Back in the lab, chipping away the overlying mudstone, revealed fossil pods (legumes) up to 130 mm long, and with 14 peas (seeds).

Fossil pea pod (legume) from the Miocene of Nevis Valley, New Zealand

Fossil pea pod (legume) from the Miocene of Nevis Valley, New Zealand (length c. 130 mm)

Today New Zealand has just four groups of peas (the legume family). There’s kowhai (Sophora), Kakabeak (Clianthus), the scree pea (Montigena) and the many brooms (Carmichaelia). All of these are part of the legume family that have classic ‘pea flowers’. One of the technical terms for this group is (or was) the Papilionoideae (think of the French word for butterfly – ‘papillion’).

But traditionally, there are also two other large groups of legumes. One is the Caesalpinioideae – with quite showy flowers (think Bauhinia), then the Mimosoideae. These have very reduced flowers, looking a bit like pom-poms (think of the wattles/Acacia).

Fossil pea pod (legume) from the Miocene of Bannockburn, New Zealand

Fossil pea pod (legume) from the Miocene of Bannockburn, New Zealand

The lucky find in the Nevis that day was not just the large fossil pea pods, some with the seeds (peas) in them, but some scattered leaves that were surely produced by the same plant. Based on the combination of evidence, the legume expert Dr Les Pedley, suggested most likely identification of the fossils was Serianthes. This plant is now found in New Caledonia, Fiji, and French Polynesia.

Fossil legume leaflet from the Miocene of Bannockburn, New Zealand

Fossil legume leaflet from the Miocene of Bannockburn, New Zealand

Serianthes is one of the Mimosoideae group. The Mimosoideae was already known in New Zealand based on fossil pollen, although in those cases, Acacia was considered the more likely parent plant (Pocknall and Mildenahll 1984; Mildenhall and Pocknall 1989).

Together, the pods, leaves and pollen make a nice addition to what used to grow in New Zealand. But what do these fossil mean? Based on where Serianthes grows today, the average annual temperature may have been more than 20 C. That’s about twice what it is now. Also a suspicion that the vegetation it was growing in was relatively dry.

I seem to spend half my life staggering kilometres with a pile of rock, either on my back or worse, carrying it in my arms. But in this case, it was well worth it.

References

Links will take you to my academia.edu site where you can download a pdf.

Mildenhall, D.C., Pocknall, D.T., 1989. Miocene-Pleistocene spores and pollen from Central Otago, South Island, New Zealand. New Zealand Geological Survey Palaeontological Bulletin 59, 1-128.

Pocknall, D.T., Mildenhall, D.C., 1984. Late Oligocene -Early Miocene spores and pollen from Southland, New Zealand. New Zealand Geological Survey Paleontological Bulletin 51, 1-66.

Pole, M.S., 1992. Fossils of Leguminosae from the Miocene Manuherikia Group of New Zealand, in: Herendeen, P.S., Dilcher, D.L. (Eds.), Advances in Legume Systematics: Part 4. The Fossil Record. The Royal Botanic Gardens, Kew, pp. 251-258.

Pole, M.S., Holden, A.M., Campbell, J.D., 1989. Fossil legumes from the Manuherikia Group (Miocene), Central Otago, New Zealand. Journal of the Royal Society of New Zealand 19, 225-228.