Kath Grey: Building an Archean biostratigraphy from stromatolite paleontology

Kath Grey talks about the challenges and successes of her years devoted to using stromatolites to develop a Precambrian biostratigraphy for Australia.

Transcript

00:00 Kath

Near the top, I slipped and fell practically the whole way down the slope. When I  got to the bottom, I had a stromatolite tucked under each arm. I hadn't let go of them all the way down.

00:13 Julie

Welcome to The Rocks Beneath Our Feet. In this series, five geologists talk about their years devoted to working for the Geological Survey of Western Australia. From understanding early life, to the tectonic processes that shaped our planet, and making the maps that unearth our understanding of Western Australia’s geology, they reveal their shared passion for discovering the stories in the rocks beneath our feet.

I’m Julie Hollis.

In this episode, Kath Grey talks about the challenges and successes of her years devoted to using stromatolites to develop a Precambrian biostratigraphy for Australia.

00:49 Kath

When I joined the survey, geological mapping was usually carried out by a team that consisted of one geologist and one field assistant. And they usually were responsible for mapping a single one to 250,000 scale map sheet. That's an area of 150 kilometers by a hundred kilometers. And they visited as many outcrops as they could in the time available to them. And then if they found stromatolites or anything else they thought might be interesting, I then got called out and I would do a round trip of the various field parties and collect samples that I wanted to work on.

There were so many, I had to be very careful not to overload my vehicle. Usually I’d trundle into town when we came to the end of a traverse. And I would ship a load of samples off back down to Perth. Normally you move camp every night. You'd set your camp up to as the sun was going down and you'd be up before dawn and pack up and off you go again. Most of the time I was on much shorter trips than the geologists who were out doing the fieldwork. I did about six weeks on average, going around visiting the various parties. And that gave me enough time to collect more samples than I ever needed. About half the collection’s stuff I collected but never got time to look out when I got back to the office. So there's enough to keep me going forever. 

02:18 Julie

I should get you to explain what a stromatolite is.

02:22 Kath

They're actually the oldest forms of life we know about on Earth, but they're constructs from that life. The life itself is single-celled organisms that often form into linear chains, and then the whole lot forms a mat. So it's really a biomass or an ecosystem and it's a living mat. As the mat’s growing, sediment or precipitation accumulates on the top of it and the filaments push their way up through that accumulation. And it begins to build up in layer upon layer, often distinguishable because layers that are rich in organic material are dark and layers that aren't rich in organic material are light-colored. They're normally found in carbonates but there's no hard and fast rules about that. Some of them live in hot springs and can precipitate silica around themselves. There's also a broader group of structures – they’re closely allied to stromatolites – and the whole lot are sort of lumped under the category of microbialite, meaning rocks that are built by microbes. And that's probably the easiest way to think of them.

03:32 Julie

Yeah.

03:33 Kath

Although the early ones the fairly simple and just dome-shaped and you still get dome-shaped ones forming today, all the way through the Precambrian they were very, very complex and they produce very complicated branching structures, very much like some of the modern corals. Different shapes of laminae and you can look at the patterns that they form and identify them. It's worked very well in WA.

One of the problems with working on the Precambrian is that it's very difficult to date. If you've got volcanic rocks, then you can do geochronology on them. But there's so many areas where you haven't got good geochronological control. And in many of those areas the rocks are carbonates and have stromatolites in them. Until very late in the Precambrian, there aren't any other fossils around. Then after that you've got the big Cambrian explosion where the ancestors of everything we know about is beginning to develop on Earth.

04:35 Julie

From about 540 million years ago.

04:39 Kath

But in that interval between the rocks I've been talking about in the Pilbara and the Cambrian explosion,

04:46 Julie

A period of about 3 billion years.

04:49 Kath

there was hardly any life on Earth except the cyanobacteria and other bacteria that forms stromatolites, and then a bit later on, the algae. One of the easiest ways of thinking of this is to stretch out your arm. And if you think the Earth forming at your nose, your shoulder’s about where these very earliest stromatolites are. Your elbow is about where the first real algae appeared. They’re sort of next step up. And then your wrist is where the Cambrian explosion takes place. And dinosaurs occur between the last two knuckles. And one swipe of a nail file removes the record of human life on Earth. So it's a very, very long period of time with very, very little time control.

So the idea behind the work I was doing was, could I use these various shapes and forms to recognize particular periods of time, especially if the stromatolite rocks were sandwiched between ones that were well dated geochronologically. And I would go out and record what shapes occurred – it’s like doing a massive jigsaw puzzle and trying to build up a complete picture of what's going on in time and space. And of course on top of all that you have environmental changes going on. So you've got to take that into account as well, and the environment can control the shapes of the stromatolites in some cases. 

06:24 Julie

Right.

06:25 Kath

Again, that's another reason why some people don't believe you can use them. They think it's all environmentally controlled.

06:32 Julie

Right.

06:33 Kath

I don't think it is because I think I’ve got a good record. I must have been personally to about a thousand localities in Australia alone. And I've got a very big database that I've been building up, I've got over 4,000 records. And I can show from that database that you don't get repetition, I’m only talking here about more complex types. A dome is a dome and there isn't much you can say about it. There’s a few that have got characteristics you can recognize but, on the whole, they don't have identifiable features. But the more complex, particularly the branching types and the conical types, there are features that you can recognize. And you don't see that particular combination of features again through the rock record. 

So, the idea is that there is some sort of time control over what's happening with these various shapes and combinations. In order to prove that, you've got to do an awful lot of documentation. And I've been doing that for the best part of 40 years, I guess.

07:43 Julie

Yeah.

07:44 Kath

Now it looks pretty good at least in Australia. 

07:48 Julie

Why is there this resistance to the idea of using stromatolites to constrain the stratigraphy, when it’s such an accepted concept for other fossils?

07:59 Kath

Well, first of all, there's the problem of recognizing them. And there are certainly structures that look like stromatolites. You've only got to get a layered structure. Or if you look at something like a fold structure that's been pushed up almost into a cone, it vaguely looks like conical stromatolites. But when you look at the detail, the laminae are different.

They're difficult to work on. They really are. It’s time consuming. They're difficult to collect. I mean, I still have vivid memories of going out to Lake Nabberu with Malcolm Walter and another colleague, Stan Awramik. They were collecting microfossils and picking up little tiny bits of chert and walking around with two sample bags each across the lake. And I’d got a rucksack full of stromatolite samples and went in to my knees in the mud. So actually getting the material is difficult.

08:58 Julie

And if you were in any doubt of Kath’s commitment to getting the material.

09:03 Kath

Duck Creek Gorge within the Wyloo Group. It's a fantastic locality. It’s a very steep-sided gorge and one side of it’s been water washed. It's a lagoon with sandbars going up into deeper water and the cycles keep repeating. And you get different stromatolites in each cycle. We’d got their latest in the afternoon. So we’d barely had time to look at the gorge wall and realize how spectacular it was. And of course, I was itching to get at it the next day. But one thing was certain, that we shouldn't hammer this beautiful face because it would destroy the evidence. So the next day, next morning, I was still finishing off breakfast and Alan Thorne, who I was out with, suddenly started shouting, “Hey Kath, come over here, come over here.” And he was on the opposite wall of the gorge. Without thinking, I went rushing over to see what he'd found. And it was truly great. It was a very jumbled scree-covered slope, but there were the most perfect samples you could want to collect all the way up the gorge. And of course, I started scrambling up without thinking. And I'd still got my sandshoes on. I hadn't put my boots on. And somewhere up near the top, I slipped and fell practically the whole way down the slope, screaming as I went of course. And Alan was pretty horrified and wasn't sure whether he'd find me in one piece or not when he got to the bottom.

10:35 Julie

Yeah.

10:36 Kath

But I'd only managed to graze my knee rather badly. But what really impressed him was that I had a rucksack full of stromatolites still on my back. And a stromatolite tucked under each arm. And I hadn't let go of them all the way down. I still had them.

10:54 Julie

But back to why stromatolites are difficult to work on.

10:58 Kath

They’re very, very hard to cut and look at under the microscope. And you can't find organic material in the majority of stromatolites. There are few rare ones that have the microfossils preserved.

11:12 Julie

Right.

11:13 Kath

But in most cases the process of diagenesis has destroyed the organic material. So there's been a lot of resistance to even seeing some of these structures as being biogenic in formation, never mind having features that you can recognize.

11:30 Julie

But what is the relevance of using stromatolites for biostratigraphy for the mining industry?

11:35 Kath

The reason we were doing it was because we wanted to use it as a tool for the mining companies. They often put a drill hole down and they don't really know what age the rocks are. So if they want to go and explore in other rocks around, they've got no way of saying, well these the same age rocks.

So in principle, it works like any other paleontology. You find your commodity you’re looking for and then you find what fossils are above and below it and then you start drilling somewhere else and you try and match the fossils up and you can say well we've gone too deep, we don't need to drill anymore, or we've not going far enough down so keep drilling. And eventually I became sufficiently well versed in what these things look like to be able to recognize them in quite small sections of core because the I can still recognize the characteristics that tell me that that's that particular species.

12:35 Julie

Right.

12:36 Kath

In the Amadeus Basin, we've been able to use them very successfully matching drill core to outcrop. Two of the people at the survey, Heidi Allen and Peter Haines, were working on the bit of the Amadeus Basin in Western Australia, which hadn't been looked at for 50 years. From my work in central Australia and in the Officer Basin, which is very similar, I was able to predict which of the taxa they should find in their area and what order they should occur in. And that's more or less what happened.

13:11 Julie

Great.

13:12 Kath

It's a real test of it to show that the predictions are correct.

13:17 Julie

Yeah.

13:18 Kath

But, on most occasions it's turned out to be correct.

I worked on the Yerrida Basin, which originally was called the Nabberu Basin. And over the years I've kept going back to this, what was originally a very large basin. And we’ve slowly documented where the different stromatolites occur. And they're quite widespread. And there's a particular one, Segosia finlaysoniensis. That one I found in outcrop and I also recognized it in a previously drilled hole which unfortunately the company threw out because there were no minerals in it. And I'd slowly been mapping this thing across the basin as samples came in and then I got a call from a mining company and some emails and they said, “Do you think these things are stromatolites in our drill core?” And I wrote back and said, “Oh, yes, that's Segosia finlaysoniensis. It occurs in the base of the Yerrida Group and it's about 1.8 billion years old.” And I could give them a whole heap of information. They were quite amazed by it because they owned Degrussa, the big copper mine up north of Meekatharra, and really they'd been completely unsure what their copper mine was situated in. And this particular drill hole was sort of underneath the copper deposit. And they asked me to go and look at the core, which I did, and I was able to confirm the identification and I think I found another one similar from about the same age. So now we know where that underlying sequence of rocks fits in the stratigraphy and it's enabled them to make predictions. That was really critical information for them at that time.

15:07 Julie

That’s great.

15:08 Kath

There was another occasion where I gave a talk about stromatolites and I showed a slide from the Earaheedy Basin with some little digitate things with lead and emplaced between the columns. The hydrothermal fluids uses the channels between the columns and the lead became emplaced in that. I'd actually Illustrated it in a publication in 1984. This must have been about 10 or 15 years later. I can't remember which company it was now. But one of their geologists was in the audience and came storming down at the end of the thing ‘how dare you give our confidential information out about our exploration models’. And I said, “Well actually if you look at my slide of my publication, I think you'll find I showed that first.” They were quite upset about it. 

16:01 Julie

And where are we now in terms of the development of Precambrian paleontology?

16:07 Kath

I've noticed a distinct decline in paleontology as a subject over the years that I've worked at the survey. When I first joined the with three paleontologists and this was true of most institutions. I think the BMR 

16:23 Julie

The Bureau of Mineral Resources, an early precursor to Geoscience Australia.

16:29 Kath

had about 12. Nowadays, you’re lucky if there's one.

16:32 Julie

Wow.

16:33 Kath

Although the survey’s recently gone back to having two people working on paleontological subjects.

It's difficult to explain why, but I feel that a lot of people aren't being taught paleontology at university anymore. So there isn't much interest. And I've come across the sort of general attitude that people are frightened fossil names. And they can't pronounce them. So they tend to just ignore them. And it's sad really because there's so much data locked up in that information. If you only know how to use it and how to interpret it and what it means. So, we're not making the best use we can of paleontology. It's true it's time consuming and it's not an easy subject to deal with in all its shapes and forms. And the Precambrian stuff is particularly difficult. Many of the people who are working on Precambrian fossils are more interested in, looking at the biological evolution. They're not using it for biostratigraphy.

17:43 Julie

Yep.

17:44 Kath

And places like Russia and China have also lost many of their renowned stromatolite workers in recent years. I keep seeing, death notices for more and more of my colleagues as time goes by. And I'm quite afraid that some of the information might not get passed on.

So I was very relieved to be able to publish the handbook on microbialites that the survey put out, where my colleague, Stan Awramik, of Santa Barbara University, and I have been collecting stromatolite photographs for the best part of 45 years. Essentially it’s an atlas of different types of stromatolite, showing the different morphologies and introducing a standard terminology. It's free on the internet. So you can download it without a cost. There's a very nice hardback copy. I think it's going to be a very useful tool for anybody interested in looking at stromatolites.

18:48 Julie

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