Monthly archives of “March 2017

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New Zealand’s Hawks Crag Breccia – prelude to the drift from Gondwana

The New Zealand road network has some seriously quirky idiosyncrasies – little things we locals take for granted, but can cause some alarm to the ever-increasing number of tourists. There are, for example, hundreds of ‘one lane’ bridges. And about these,  I was once asked, in total exasperation by an American “Why don’t you just build two-lane bridges?!” (I dunno, cause they cost twice as much?). But on encountering one of those one lane bridges up near Hokitika – that also include the railway line, he was speechless.

Another quirky New Zealand road is that which claws its way around Hawks Crag, a steep bluff above the Buller River. You’ll encounter it if you drive from Westport towards Murchison. It’s one-way, and, in contrast to one-way bridges, because of the curve, you can’t see if there is on-coming traffic. There are now traffic lights, but a sign asks you that if the lights aren’t working (they weren’t last time I drove it) to be-careful.

The one-way road clawing its way around Hawks Crag, above the Buller River in New Zealand.

The one-way road clawing its way around Hawks Crag, above the Buller River in New Zealand.

The bluff that the road cuts around is’Hawks Crag’, and the rock its self is a ‘breccia’, composed of angular rock fragments in a finer matrix. Hence the formation that the road cuts through is called the Hawks Crag Breccia. It’s one of the more intriguing units of New Zealand geology.

The origin of the Breccia is relatively clear – it is the accumulation of material on a ‘fan’ – along the edge of an actively-growing mountain (this type of rock is sometimes called a ‘fanglomerate’). The rocks have not traveled far -rivers have not rounded or sorted the boulders. Material simply poured off active fault scarps into a basin. However, for many years the age of the Hawks Crag Breccia was unclear. Partially this was due to the nature of the breccia itself. It is largely devoid of fossils. But there are a few mudstone beds that would have been flood basins or swamps, and these did prove to have fossil spores. But many of these fossils were new – they were found no-where else, and thus could not be correlated elsewhere. From a variety of reasons, an early conclusions was that the Breccia was Jurassic (Couper, 1953, 1960). However, this was a problem, as the fledgling science of radiometric dating rocks at the same time concluded that the boulders in the breccia, were Cretaceous (Aronson 1965). The age of the rocks in the breccia of course, cannot be younger than the breccia itself. Either the radiometric date, or the date based on fossils, had to be wrong.

Detailed view of the Hawks Crag Breccia - an unsorted pile of sharp-edged rocks.

Detailed view of the Hawks Crag Breccia – an unsorted pile of sharp-edged rocks.

Eventually 30 species of plant fossils were found in the Hawks Crag Breccia (Norris 1968) – and fortuitously, at the same time, a detailed study of similar fossils in the Cretaceous of Australia became available (Dettmann and Playford 1968). This led to confirmation of a  mid Cretaceous age (late Albian, c. 105 Ma) of the Hawks Crag Breccia (Norris and Waterhouse, 1970; Waterhouse and Norris 1972; Raine 1984). There was no longer a problem with the age of the boulders – they were formed slightly before they entered the breccia. Several plant species that grew at Hawks Crag were also in eastern Australia. In some respects this is not surprising, as at the time, not only were they closer, but you could have walked from this part of New Zealand to Australia, or even Antarctica.  New Zealand was peripheral to, and only just breaking away from, the continent of Gondwana.

The plant fossils of the Hawks Crag Breccia (Norris 1968) are a diverse mix of lycopods, ferns (including tree ferns), podocarp and araucarian conifers, as well as the pollen of an extinct conifer family, the Cheirolepidiaceae. In some respects, the particular pollen and spore fossils are reminiscent of the cool and wet New Zealand vegetation today – but with one major difference – there were no flowering plants. These arrived in New Zealand very shortly (a million or two years or so) after the Hawks Crag Breccia accumulated.

The Hawks Crag Breccia is now understood to be one rock type in a broader system – the Porari Group. For example, the very different Bullock Formation is made up largely of mudstone. This has been interpreted as a lake, or series of lakes, into which the Hawks Crag fans flowed (Laird 1995). The Porari Group is now scattered over about 320 km of the West Coast, as well as there being similar deposits east of the Alps (Laird 1995). One could thus think of a ‘Porari Landscape’ or even a ‘Porari Ecosystem’.

In the broader picture the deposition of the Hawks Crag Breccia, and the whole Porari Group, was related to the Rangitata Orogeny – the period of mountainous upheaval that preceded the New Zealand region breaking away from the rest of Gondwana (Carter et al. 1974; Waterhouse and Norris 1972; Adams and Nathan 1978). The Rangitata Orogeny is one of New Zealand’s major periods of geological change where the regime went from compressional to extensional and eventually led to New Zealand drifting into the Pacific (Laird and Bradshaw 2004).

Schematic diagram (simplified from Schulte et al., 2014) to show the the Porari Group (including the Hawks Crag Breccia) forming on the flanks of a Metamorphic Core Complex.

Schematic diagram (simplified from Schulte et al., 2014) to show the the Porari Group (including the Hawks Crag Breccia) forming on the flanks of a Metamorphic Core Complex.

In detail, the Hawks Crag Breccia can also be placed into a more recent concept – the Metamorphic Core Complex (Tulloch and Kimbrough, 1989; Schulte, et al., 2014). These form in extensional environments, and consist of a central core of deeper, older rock that rises to the surface and is typically intruded by granites, while breccia-filled half-graben valleys develop on the flanks.

I wonder how long it will be before some local-Councillor gets it into his or her head to blast away this quirky stretch of road, to enable more people to get through, faster? In the meantime, just keep driving carefully, watch out for on-coming traffic. and the odd person having a closer look at the Hawks Crag Breccia.

References (links will take you to a downloadable pdf)

Adams, C.J.D., Nathan, S., 1978. Cretaceous chronology of the Lower Buller Valley, South Island, New Zealand. New Zealand Journal of Geology and Geophysics 21, 455-462.

Aronson, J.L., 1965. Reconnaissance rubidium—strontium geochronology of New Zealand plutonic and metamorphic rocks. New Zealand Journal of Geology and Geophysics 8, 401-423.

Carter, R.M., Landis, C.A., Norris, R.J., Bishop, D.G., 1974. Suggestions towards a high-level nomenclature for New Zealand rocks. Journal of the Royal Society of New Zealand 4, 5-18.

Couper, R.A., 1953. Upper Mesozoic and Cainozoic spores and pollen grains from New Zealand. New Zealand Geological Survey Palaeontological Bulletin n.s. 22, 77.

Couper, R.A., 1960. New Zealand Mesozoic and Cainozoic plant microfossils. New Zealand Geological Survey Paleontological Bulletin 32, 88 pp.

Dettmann, M.E., Playford, G., 1968. Taxonomy of some Cretaceous spores and pollen grains from eastern Australia. Proceedings of the Royal Society of Victoria 81, 69-93.

Laird, M.G., 1995. Coarse-grained lacustrine fan-delta deposits (Pororari Group) of the northwestern South Island, New Zealan: evidence for Mid-Cretaceous rifting. Special Publication of the International Association of Sedimentologists 22, 197-217.

Laird, M.G., Bradshaw, J.D., 2004. The Break-up of a Long-term Relationship: the Cretaceous Separation of New Zealand from Gondwana. Gondwana Research 7, 273-286.

Norris, G., 1968. Plant microfossils from the Hawks Crag Breccia, south-west Nelson, New Zealand. New Zealand Journal of Geology and Geophysics 11, 312-344.

Norris, G., Waterhouse, J.B., 1970. Age of the Hawks Crag Breccia. Transactions of the Royal Society of New Zealand. Earth Sciences 7, 241-250.

Raine, J.I., 1984. Outline of a palynological zonation of Cretaceous to Paleogene terrestrial sediments in west coast region, south island, New Zealand. New Zealand Geological Survey Report 109, 1-82.

Schulte, D.O., Ring, U., Thomson, S.N., Glodny, J., Carrad, H., 2014. Two-stage development of the Paparoa Metamorphic Core Complex, West Coast, South Island, New Zealand: Hot continental extension precedes sea-floor spreading by ~25 m.y. Lithosphere 6, 177-194.

Tulloch, A.J., and Kimbrough, D.L., 1989, The Paparoa Metamorphic Core Complex, New Zealand: Cretaceous extension associated with fragmentation of the Pacific margin of Gondwana: Tectonics, 8, 1217–1234.

Waterhouse, J.B., Norris, G., 1972. Paleobotanical solution to a granite conundrum: Hawks Crag Breccia of New Zealand and the tectonic evolution of the southwest Pacific. Geoscience and Man 4, 1-15.

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The Lost Forest of the Ashley River, Canterbury, New Zealand

A gem in the heart of Christchurch is Riccarton Bush (sometimes called Deans Bush). It’s a patch of original kahikatea forest, just a few hundred meters from the Riccarton shopping center (See Molloy,1995, for pretty much all you need to know about the forest).

As anyone who flies in or out of Christchurch, or drives that dead-boring road to Timaru can see, the Canterbury Plains are as ecologically-devastated as an area can get. Not just flat, but the native vegetation has simply been replaced with something else. There was, and remain, patches of native forest on the Banks Peninsula high-ground, and likewise where the foothills meet the plains, such as Geraldine and Oxford (Clark 1926). But for the Plains, Riccarton Bush is pretty much it. It really is a miracle that this one little patch has been preserved. Added to the data collated by Molloy and Brown (1995) of relict living trees, old stumps and charcoals, it is clear that there were once at least patches of forest on the good alluvial soils.  Without Riccarton Bush, it would be so much harder to believe that forest once grew on the Canterbury Plains.


The interior of Riccarton Bush.

Much of the ‘subfossil’ evidence for ancient forests comes from transient exposures in gravel pits or road works, but Benfield (2011)and Molloy (1995, Plate 9) illustrated stumps of a lost forest in a channel of the Ashley River. I don’t share Benfield’s views on 1080 poison, but his interest in the remains of the forest in the Ashley River fascinated me, and led me to have a look for myself.

As is so often the case (with me, anyway) I spent ages floundering around an overgrown, weedy area, along the river bank, then threading my way through a pile of blackberry (I made the most of this by eating lots and giving myself a stomach ache) before giving up, and finally finding some remains of the forest on the way back to the car.


A single large conifer stump in the Ashley River.

What I came across was one large tree stump, projecting from flowing water up to my thighs (see the featured image). It is one of the podocarp conifers, probably totara, or perhaps kahikatea or matai, although I haven’t worked out which yet. There were a few smaller stumps, totally submerged, a little downstream. The broad location is c. 28 km north of the center of Christchurch, and more precisely, 600 m  upstream of the bridge over the Ashley River near the right bank. A radiocarbon date on an Ashley River stump (NZ 14C No 7680) reported in Molloy and Brown (1995) provided an age of c. 870 years before 1950.

The radiating roots of a submerged stump in the Ashley River are just visible - and another stump is just upstream.

The radiating roots of a submerged stump in the Ashley River are just visible – and another stump is just upstream.

Benfield’s (2011) personal experience shows that even this small group of stumps was more extensive up until a few years ago. Development has either destroyed or re-buried much of it. Forests such as the one in the Ashley or Riccarton, owe their existence to the dynamic nature of braided rivers – with periodic fresh alluvial deposits or old channels becoming available for a new cohort of seedlings. The abruptly changing channels can also be their demise, or leave them standing in water as a ‘swamp forest’. Travelers down the West Coast will be familiar with the sight of semi-submerged kahikatea forests, for instance at Lake Wahapo or Ship Creek. These postcard examples help give rise to the belief that kahikatea prefers to grow in standing water, and in high rainfall areas.


Kahikatea trees in Lake Wahapo – with a c. 1m lower water level than normal.

However, it’s the Canterbury Plain evidence that helps confirm that kahikatea is also a tree of drier rainfall, provided the soils, and the groundwater table (Webb, 1995), suit. Ryan (1995) gives a figure of 668 mm as the average annual rainfall of the Christchurch Botanical Gardens – relatively low for New Zealand forests. These drier forests were most prone to being destroyed by fire once humans arrived on thee scene, thus distorting their apparent climatic preferences towards the wet end of the spectrum, Tellingly, Benfield (2011) observed that the Ashley River forest appeared to have been burnt.

A take-home message from this, is that the soils and the rainfall of the Canterbury Plains are fine for some of our native forests. Imagine a revived network of forest patches across the Plains – spaced within walking/cycling distance of Christchurch. Something to break that awful tedium of farms. It’s something I think about every time I drive past our ever increasing roadside plantings of natives. It can be done, and it just may have started.


Benfield, W.F. 2011. The Third Wave, Poisoning the Land. Tross Publishing, Wellington.

Clark, A.F. 1926. Canterbury’s native bush. TeKuraNgahere, New Zealand Journal of Forestry, 2, 15-22.

Molloy,  B. 1995. Riccarton Bush: Putaringamotu. The Riccarton Bush Trust, Christchurch.

Molloy, B. and Brown, L. 1995. Vegetation history. pp. 85-115 in: Molloy,  B. (Ed.) Riccarton Bush: Putaringamotu. The Riccarton Bush Trust, Christchurch.

Ryan, A. 1995. Climate & Weather. pp. 69-82 in: Molloy,  B. (Ed.) Riccarton Bush: Putaringamotu. The Riccarton Bush Trust, Christchurch.

Webb, T. 1995. Soils & Landforms.pp. 59-68  in: Molloy,  B. (Ed.) Riccarton Bush: Putaringamotu. The Riccarton Bush Trust, Christchurch.

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Phyllocladus fossils from the Miocene of New Zealand, and Cretaceous Protophyllocladus

A rare plant fossil in the Miocene Manuherikia Group of New Zealand, is Phyllocladus (the Celery Pine). This is a strange conifer which, instead of leaves, the adult plant has multi-veined flattened branches that are called phylloclades. With these phylloclades, the average person would scarcely believe Phyllocladus is a kind of conifer (very broadly, a pine). But it is common in some parts of New Zealand today (typically in ‘difficult’ places, cold, or with poor soils) and also in Tasmania and Malaysia.

Fossil pollen suggests Phyllocladus has been in New Zealand since the Eocene (Mildenhall 1980). There are somewhat similar, but older pollen records,  for example from New Zealand’s Late Cretaceous (Couper, 1953; Cookson & Pike, 1954) but these are likely to represent something distinct. Despite conifers being very diverse in the Miocene St Bathans Paleovalley sediments of the Manuherikia Group,  Phyllocladus appears to have been absent there (Pole 1992a, 1997, 2007). The climate may have been so warm, and the soils rich enough, to preclude it (Pole 2014). However, Phyllocladus is present in the Miocene Nevis Oil Shale (Pole 1992, see figured image), which was deposited in very different conditions (Douglas 1986). There are hints from the Nevis, including large fossil legumes (Pole et al. 1989, 1992b) that the climate may have had a distinct dry season. This may have favoured Phyllocladus. DNA evidence suggest the extant New Zealand species only radiated in the Late Cenozoic (Wagstaff, 2004), and there are certainly Phyllocladus fossils from this time (e.g. From Mataora, in the Coromandel. Pole and Moore, 2011).

Fossil Phyllocladus from Mataora, New Zealand.

Fossil Phyllocladus from Mataora, New Zealand.

Phylloclades appears to be a strategy to increase light-intercepting area beyond that of typical, simple, needle-like leaves ( e.g. Brodribb 2011). In essence, Phyllocladus is trying to become more like the broad leaves of typical flowing plants, in order to compete with them. Separate from that hypothesis, there seems to be an unstated assumption – that the world’s forests became darker, shadier places, with the evolution of broad-leaved flowering plants. But did they? Conifer forests can be damned dark under the canopy. An individual pine needle doesn’t create much shade, but a whole lot of them do.

Extant Phyllocladus IMG_0714

In one of the places I lived in for a few years in Brisbane, my neighbour on the opposite side of the street was Ray Specht. There was a big Eucalyptus tree growing between his house and mine. Ray happened to be one of the most influential people in Australian botany. For example, the various schemes of Australian vegetation classification mostly stem from him. On visiting Ray, the conversation would usually quickly go to the 1948 American-Australian Scientific Expedition to Arnhem Land, which was clearly a highlight of his life.   Ray would expound on the expedition until his wife would look up from her book and go “Oh Ray – shut up!”  Then, fascinating as the Expedition was, I could get him back to what I really wanted him to talk about – his views on how vegetation structure could be predicted from basic environmental properties.

One of Specht’s understandings was that the amount of shade under the canopy of a forest was fundamentally determined by the environment. Basically, closed canopy forests (like rainforests) are more open underneath the canopy, whereas open canopy forests (like Eucalyptus forests) have a denser zone of shrubs. Down near the ground, things even out. There are no doubt plenty of botanists who might take issue with the details, but I find it a valuable insight. At least in Specht’s view, given the right environmental conditions,  forests would have been just as dark and shady before flowering plants evolved, as after.

I’ve wondered if any other fossils might be helpful. In fact, there is a fossil plant with the intriguing name Protophyllocladus has long been known from Cretaceous rocks right across the Northern Hemisphere. In terms of gross morphology, it has phylloclades uncannily like Phyllocladus. However, their detailed structure,  and its affinities, have remained unclear up until very recently. But in 2014 the Russian scientists Natalya Nosova and Lena Golovneva from St Petersburg made a detailed study of the fossil epidermis of Protophyllocladus and compared it with Phyllocladus (Nosova and Golovneva 2014). They concluded Protophyllocladus was a conifer, and likely in the same family as Phyllocladus (the Podocarpaceae).  Protophyllocladus is much older than Phyllocladus, but it still comes from a time when flowering plant forests had spread across the Northern Hemisphere (see fig. 7 in Pole et al. 2016). In that respect, it is consistent with the idea that phylloclades evolved in response to the spread of flowering plants. If fossils of conifers with phylloclades turn up from pre-angiosperm times, then Spechts’ ideas should be looked at closely.

Extant Phyllocladus trichomanoides

Extant Phyllocladus trichomanoides

However, my feeling is that the epidermal morphology of Protophyllocladus is distinct from Phyllocladus or any of the extant related plants (the family Podocarpaceae). For instance the epidermal cells of Protophyllocladus  do not often occur in files. That is, I think the phylloclades of Protophyllocladus probably evolved quite independently of Phyllocladus.

Lightening, so it is said, never strikes the same place twice. But of course, we know this is wrong – lightening does hit some places multiple times and even the odd person has been struck more than once. I think of evolutionary developments as a bit like lightening striking a particular place (a new morphological feature evolves), but just occasionally, it strikes there again (and a similar feature evolves in another lineage. The technical term for this is ‘convergent evolution’. I suspect the phylloclades of Protophyllocladus and Phyllocladus are convergent evolution.

And that big Eucalyptus between my place and Ray Spechts’ ? According to him – it had been hit by lightening at least three times.


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

Brodribb, T.J., 2011. A functional analysis of podocarp ecology, in: Turner, B.L., Cernusak, L.A. (Eds.), Ecology of the Podocarpaceae in Tropical Forests, Smithsonian Contributions to Botany, No. 95. . Smithsonian Institution Scholarly Press, Washington, D.C., pp. 165-173.

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

Mildenhall, D.C., 1980. New Zealand Late Cretaceous and Cenozoic plant biogeography: a contribution. Palaeogeography, Palaeoclimatology, Palaeoecology 31, 197-233.

Nosova, N., Golovneva, L., 2014. The Mesozoic genus Protophyllocladus Berry (Pinopsida). Review of Palaeobotany and Palynology 210, 77–88.

Pole, M.S., 1992a. 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.

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

Pole, M., Moore, P.R., 2011. A late Miocene leaf assemblage from Mataora, Coromandel, New Zealand and its climatic implications. Alcheringa 35, 103-121.

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.

Pole, M., Wang, Y., Bugdaeva, E.V., Dong, C., Tian, N., Li, L., Zhou, N., 2016. The rise and demise of Podozamites in east Asia—An extinct conifer life style, . Palaeogeography, Palaeoclimatology, Palaeoecology.

Wagstaff, S.J., 2004. Evolution and biogeography of the austral genus Phyllocladus (Podocarpaceae). Journal of Biogeography 31, 1569–1577.