Craig S. Feibel

Where giants trod: The geology and geochronology of East Africa

Geological context is a critical component in the broader understanding of fossils and sites in East Africa. From Olduvai Gorge to the Turkana Basin, field geologists have explored the geology and geochronology of the Human Cradle and their broad shoulders provide a solid platform upon which future generations will continue to discover new and exciting perspectives on the past.

FULL TRANSCRIPT

Some of you may recognize I borrowed my title from Monty Brown's wonderful book about the peoples around Lake Turkana who lived there and the explorers who have sort of brought us into understanding that part of the world. And as I was sort of charged with speaking on geology and geochronology, I thought this would be sort of self-suggested both Richard himself as one of the giants who brought in a tremendous cohort of geologists. And particularly I wanted to pay tribute to both Frank Brown and Ian McDougall, who really were critical to advancing us to the stage where we can do really, really wonderful things in understanding the geology, particularly of the Turkana Basin. I first met Richard in 1981 and when I was starting my graduate career, and I ended up in Nairobi with another graduate student on the way to Koobi Fora and Richard, one of his characteristics was being incredibly welcoming and supportive of students and we were in a rather odd situation, but we ended up trundled up to Koobi Fora and left there for six months to investigate the geology, which was a wonderful opportunity. 

But we never could have survived without the tremendous support that Richard brought to us. And I have to say that I think through his career and particularly the work in Turkana, Richard May have been vexed at times by geologists, and certainly they brought him a lot of consternation and troubles. But this is in part the sort of the history of how Richard managed to find the right solutions and bring in the right people at the right times to ultimately overcome some of those obstacles. It's hard not to start any story of geology in East Africa away from Olduvai Gorge because really that's where the first steps are taken. And particularly this milestone 1965 is the first time we had numerical age control on sequences in East Africa that we're interested in. And so, the ever and Curtis paper put Olduvai Gorge on the map in time with a date of 1.85 million years on the basalt at the base of Bed I. 

And this becomes a critical milestone for understanding everything else. And Olduvai Gorge, of course, takes the lead in sort of not only timing, but the directions that Geology will go. In particular, Richard Hay who for years did the geological work for Louis and Mary at Olduvai Gorge. And I want to call out two things that Richard Hay did that were really critical in setting the tone for later explorations in Turkana. And the first was that although he was primarily interested in mineralogy and the funny minerals that formed in Olduvai Lakes, he became a litho-stratigrapher. He did rock stratigraphy, and he produced a series of wonderful sections and profiles around Olduvai Gorge. But the real strength of Richard Hay in doing this work was that each year he'd go to Olduvai, he would produce new sections, new maps, and he would publish them right away. 

And he'd go back the next year and he would discover he had made a mistake, he had found something new, and he was always willing to correct himself and to advance the science with step-by-step moving things along. And this has become sort of the hallmark of stratigraphy, large and small. It's constantly evolving and self-improving. The other thing that Dick Hay did was to think about Olduvai in broader spatial terms and to create these paleogeographic maps of what Olduvai lakes would look like. And this will come back later on when we talk about advances made in Turkana in trying to think about Turkana on a basin spatial scale. 

We've heard a lot about the early expeditions and Richard's sort of discovery and involvement, first at East Rudolf and then around the Turkana Basin. And I want to go through some quick major milestones in the geological discoveries that are made there. And of course, this all starts in the lower Omo Valley with the Omo expedition. But what's perhaps most salient about the Omo expedition was that Clark Howell had the mindset to send his geologist a year ahead of time. Frank Brown went out alone in 1966 to figure out the stratigraphy and as himself a starting graduate student on his own, he did it. He figured it out. 

He used lithostratigraphic tools. And this is critical that in the early years, the tools available essentially limited in the technological sense. And he was aided by the fact that almost stratigraphy is relatively straightforward, but he simply walked and walked and walked mapped and mapped and constructed the sections that would become sort of the measure of almost stratigraphy. But later in his career, as you'll  see, he was able to adapt new tools and take new perspectives to continually broaden our understanding of the geology of the Turkana Basin. As I said, the Omo Valley was in a sense the easy case because it's relatively continuous, relatively unfolded. And lithostratigraphy as a tool worked extremely well there. And the initial efforts never needed major revision or improvement. And so that seminal contribution that Frank was able to make there stood the test of time. And so this is Clark Howell's version of the early column that Frank produced. 

And I want to point out right up this thing right up in here. Frank found a tuff in his first year that eventually became known as Tuff H-2, and it was important as a stratigraphic marker, lithostratographically and also Frank found pumices in it, and that would ultimately contribute to the complex dating story that was about to evolve. Meanwhile, down at East Rudolf as it was then known, this motley crew, fossil hunters were finding all sorts of spectacular specimens. And of course, the geology of that part of the world needed to be worked out in its sort of self. And East Rudolf as it was then known Koobi Fora, as we would say today, is much more complicated, heavily faulted, discontinuous outcrops, and a stratigraphy that is not a simple layer cake story, but very, very complicated. And that's going to unravel very quickly into a series of problems which Richard would have to address with finding the right tools and the right individuals to solve those particular problems. 

So first and foremost, Kay Behrensmeyer as a student went to the field and produced the first stratigraphic column from Koobi Fora and made a couple of really critical contributions, not the least of which was discovering another important tuff, this one that would come to be known as the KBS Tuff because the site, the artifacts in that tuff became the Kay Behrensmeyer site. But Kay worked in a relatively limited geographic area, and as things expanded spatially, they're going to get more complicated. But the first steps in that sense proved very, very successful and made sort of a key contribution, not only finding KBS Tuff, but discovering that in fact not only contained artifacts but contained pumices, which again would be fodder for the dating machines. So, the Oldowan artifacts in the KBS site, which were discovered 1969 within the tuff, one of the rare instances where we can actually date the materials we're interested in, and within a few years, 1470 would be discovered nearby and stratigraphically lower than the KBS Tuff. 

So, the age of that tuff became the critical sort of element in the East Rudolf story and of correspond what came to be known as the KBS controversy. But there's actually two major problems that spun out of control very early on. One of them was what we classically call the KBS controversy, which primarily relates to the dating of the pumices that Kay found at the KBS site. But there was a parallel set of problems with correlation because tying together the disparate sections around East Rudolf was not straightforward as it had been in the Omo. So, the KBS controversy is well documented, and Roger Lewin's book on this is really wonderful. The initial steps is probably what in sports you would call an unforced error. They literally got the wrong number and we still haven't figured out how that happened. 

That's a head scratcher. But something went wrong from the outset in spite of the fact that we were using the newest technology argon/argon step heating method to get the best possible dates. So that's kind of a flyer. But what happened from here, and one of the reasons this spins out of control is sort of certain stubbornness to  admit defeat and realize that this was a problem. And the problem was really in the pigs. And after learning about this problem and studying for years, I come to say that always trust the pigs. The pigs know. And Basil Cooke who worked on the pigs immediately pointed out a faunal mismatch between the biostratigraphy and the Omo sequence associated with that tuff that Frank had found. Tuff H-2 and fossils associated with the KBS at Koobi Fora. And in the Omo, there was an age of 1.8 million years that came out on Tuff H-2, the Fitch and Miller date, more than half a million years older, simply didn't work with biostratigraphy. 

So, the next step in this saga from East Rudolf was as Kay moved on to greener pastures and a team under Carl Vondra from Iowa State University came in mostly actually Carl's students who did all the groundwork, but a new stratigraphic team, which explored wider, expanded the stratigraphic column, but ran into some really key problems. And this was the fact that lithostratigraphy was no longer a sufficient tool to solve the problems at East Rudolf the way they solve the problems in the Omo. It was a limitation of the method and probably unsolvable given the tools of the time. And the way this played out was, as you can see here in the Bowe and Vondra’s column from 1973, they used what we call the four-tuff model, which is an oversimplification, but there were four major markers in the East Rudolf region. The lowest one was the thing they called the Suregei Tuff, this big white band. 

 It's actually not even a tuff, it's a diatomite, but it was a good stratigraphic marker. But the lithostratigraphic approach said anything that's big and white must be the Suregei, tuff. Stratigraphically above It was a big gray tuff. And this was traditionally the Tulu Bor tuff. And there is a Tulu Borr tuff locality, but anything gray was being called the Tulu Bor tuff, such as this example here in Area 102, which is nearly a million years or a million and a half years younger, the Lorenyang Tuff, the KBS Tuff was central to the story. Unfortunately, the KBS behaves itself reasonably well, although there were a couple of other tuffs very close in the sequence that were mistaken for it. And then finally there was this thing called the Chari Tuff near the top of the sequence, which was big good stratigraphic marker and again, would ultimately be dateable. 

So the KBS controversy is springing out of control with different approaches trying to redate and confirm ages and deal with this faunal mismatch Garniss Curtis's lab, same lab that dated the Olduvai material in the earliest dates came up with a 1.8 million year date for that Tuff H-2 in the Omo, fission track ages attempted to sort of resolve the discrepancy, but they came back in support of the Fitch and Miller ages rather than challenging them. And a series of other tools constantly sort of kept putting Richard back in the position of, well, we tried something new. And it still seems to say that those old ages are right. So this became a dilemma through the seventies. And right up until the very end, as I said, the pigs were very unhappy and there was a lot of work on those particular guide fossils, and particularly by John Harris and none other than Tim White and their work had sort of worked out their own phylogeny of pigs and what was going on in pig biostratigraphy and applying that to the East Turkana sequence came up with what is the most godawful stratigraphic correlation chart ever published.

Because it was area by area, tuff by tuff, it was a total mess. And even a geologist can't really follow what was going on here. But that was literally the state of the art by about 1979. Now enter at this stage, Thure Cerling and Frank Brown and Thure had been working in his dissertation on problems around Turkana, mostly on geochemistry. And he had done some analysis of the glass components of tephra and Frank Brown had been doing the same sort of thing based on his samples from the Omo. And in the late 1970s, they got together and solved the first of those two problems. The problem of correlation by demonstrating that you could actually geochemically match that is fingerprint tephra. And so, this 1979 paper, among other things, demonstrated that the KBS tuff at Koobi Fora was geochemically identical. That is the product of the same eruption as that H-2 Tuff up in the Omo. 

So they proved that they were the same thing. It didn't resolve the question of how old they really were. And that came from an independent arbiter. And this is again, Richard realizing that there were two camps fighting it out over the age of things in Turkana. And so he brought in Ian McDougall from ANU in Australia, and Ian was meticulous, persistent, and he produced a whole series of ages. And he ended up saying the KBS was one of the easiest things he ever dated because he could get the same numbers over and over again. And he came up with initially, okay, 1.89, which got revised to 1.88, but this was the number that finally sort of put the nail in the coffin of the early Fitch and Miller dates and really resolved the KBS controversy. And interestingly enough, none other than Richard Hay wrote the discussion in Nature that the KBS controversy maybe ended. 

But it did resolve that. And what it meant was that for the next decades, these sorts of controversies would not emerge. And perhaps the biggest outcome of the KBS controversy, one of the problems with the Fitch and Miller work was that we never saw the data. They simply produced results, the numbers. And that's why every time we read a scientific paper these days, we have to go through pages and pages of tables on those horrible isotopic dates because everyone has to produce the data these days. Okay? So since then, geologists have been playing a little bit of catch up, but ultimately are getting ahead, I think, of the paleontological game and being able to understand the Turkana basin and tie things together. So once again, Frank and Ian working together on both the geochemical correlation and the dating of layers were able to expand the network. 

And in Frank's case, just massive, massive amounts of work, huge numbers of samples in his sort of throughput with undergraduate laborers to produce a huge dataset that finally tied things together. And it had huge implications for our understanding of the Basin. So, he produced lots of understanding of the geochemical variation of individual tephra lots and lots of data points to go into these sorts of things, understand them in a stratigraphic sequence and be able to place them in a temporal framework. So, the Koobi Fora story expanded because of this, because all of those tuffs that were being sort of pigeonholed into one of those initial four tuffs turned out to be closer to 300 tuffs, and a lot of complexity suddenly became very obvious. So, the Koobi Fora column got taller, more time, more sediment, and a whole lot more tephra added to both the correlation framework as well as the dated timescale for working on these sorts of things. 

So, you see over on the left-hand side here, the Nachukui Formation was added in a relatively straightforward, easy addition because of what had come before from the Shungura and from Koobi Fora, what does this mean now? Where can we go with problems in Turkana? And how does this whole framework of geology that's been constructed allow us to think about things? Well, one of these avenues comes back to what Richard Hay started back at Olduvai Gorge thinking spatially about basin scale problems. And this is where we can look at modern Lake Turkana satellite view today and say, okay, what did this Basin look like 4.1 million years ago? And using the tephra markers and the correlations along with basic lithostratigraphy, understanding sedimentary faces, we can map out this huge lake, the Lonyumun lake that existed at 4.1 million years and literally put hominids, for example, the Kanapoi assemblage that is in this delta association down here at the south end of the lake, things that are happening at South Turkwel. 

Well, at the same time from the Turkwel Delta and things that are happening up north the Koobi Fora or in the Omo into a geographic, a paleogeographic perspective. And fortunately, I had a wonderful undergraduate who is an artist who is able to basically make false satellite images from 4.1 million years ago, or the more complicated problem, what happens when that lake fills in and a big fluvial system takes over the basin. This was Frank's big leap when he tried connecting the dots of all of his tuffs and saying, how do you get the same tuff in a river channel on the east side of the lake and the west side of the lake? The only way to do that is if there's no lake there. And initially he didn't understand the problem of the geometry, but that funny back and forth pattern is actually a signature of the tectonic underpinnings, the alternating [inaudible] in the structure that controls the Turkana Basin. 

And so, it all came together very beautifully in the 1980s and 1990s to understand actually spatially what was going on in the Basin based upon these frameworks of time and correlation that Frank and Ian had constructed. One of the important points about time is we can think about it in a number of different ways and we can think about it numerically, which is wonderful. And David Phillips's team at Melbourne, and now they just have a paper coming out where they've got ages on the KBS down to about plus or minus a few thousand years. And that precision is really wonderful, but that's dating an eruptive event, and we have to move that to a deposition event and then put it into a context of a sequence through time into which the things we are interested in, particularly the fossils or the archeology can be fit. 

And so it may be time to sort of switch gears and say, numbers are great, numerical time is wonderful. But what's really important is more sort of the stratigraphic evolution in the environmental record where the Turkana Plio-Pleistocene story is one of lakes alternating with floodplain systems. These are the ecological units, the environmental units that actually probably are more significant to the sorts of records that we're studying. And it's nice to be able to put numbers on things, but putting these things into a bigger framework is also much more important. Thinking about time in a very different sort of way, the mapping story has just made a huge hurdle forward. Frank was always frustrated that there wasn't really a vehicle for producing the huge maps, which you've seen outside that Bob has created, but particularly to make it accessible to workers. And Bob has jumped this hurdle incredibly with integrating all of the preexisting mapping, new mapping, putting it all together into a single platform that is now something I can download onto my phone and walk around in the field and know where I am stratigraphically.

So that's perhaps one of the biggest technological jumps that's allowed us in the next generation to do all sorts of things we couldn't have done before. And a final advance in the geological work is that moving from outcrop studies to core studies with scientific drilling is opening up new avenues to understand continuous records, high resolution stories to look at the history. And so, we did a core in West Turkana back in 2013 at Kaitio, and it produced an incredible record on 216 meters of core. So it was about half a million years in time. We thought we were drilling out in the lake, the paleo lake, and we get this nice long continuous lacustrine record, and it was punctuated by more than 130 soils. And what it demonstrated to us is that this system is incredibly dynamic over short timeframes. And while the big talk is about astronomical forcing and the big cycles that are 120 and 40, 20,000 years, we've got cycles that are operating on about a 4,000 years frequency. 

So very, very high-resolution stuff and a whole new frontier in understanding the environmental dynamics is actually probably much closer to the scales that are significant for evolutionary problems and other sorts of things that are going on in the Basin. Much of this work was done by my former student, Kat Beck, who's now at Hamilton, and the big step out for the future is that she's coordinating a project called Deep Drilling in the Turkana Basin, where we're going to jump from that half million year record that we recovered to trying to go for 4 million years of Plio-Pleistocene time. And it's a huge lift. We had a drilling workshop in Nairobi last summer, but we're planning on sort of a two phase project to look at a series of cores staggered on the west side, which get us from about four and a half million down to roughly a half a million years. 

But to get the last and most sort of precious unknown part of the story, we're going to have to go out onto the lake for a coring campaign out there. So this is something that to sort of close up, Richard was incredibly supportive of. He was a little leery of the oil company connections and public perception, but once he understood what this sort of scientific drilling and particularly bringing in the knowledge of the oil companies, their seismic information, core information, in integrating this with the sorts of scientific problems that we've been advancing, once again, Richard was leading the way in bringing the science and particularly the geological sciences right up to the present day and into the future. So that's a precede of some of Richard's interactions with, and I'd really like to say again, Richard was incredibly supportive of geologists and particularly of student geologists, and it was one of the most important things. I think the return on that investment was incredible, but Richard has always been someone who really made it not only possible, but really wonderful to work in the Turkana Basin. So thank you.

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