The original version of this article was published in the August 2020 issue of AAPG Explorer. This copy includes reference citations.
There is something about colored pencil crayons that we, as geologists, find impossible to resist. From geological maps to field sketches, to interpreting seismic on those never-ending rolls of paper taped to the longest corridor wall we can find. What more could any geologist want?
This is a source of much mirth amongst my non-geological friends and concern amongst management especially those having just purchased the latest expensive software.
Our need for powerful software, paper, and colored pencils reflects a fundamental problem in geology and especially exploration: how to manage, analyze and visualize the diversity and wealth of information required to solve exploration problems.
Figure 1. The nature of the problem: There is so much to take in. The view from the Castillo de Samitier north towards Ainsa.
There is simply so much to take in.
I am reminded of this each spring when Douglas Paton and I take the Leeds MSc Structural Geology with Geophysics students out to the central Pyrenees. This is an area familiar to many of you and highly recommended to those of you yet to visit.
As we look out from the Castillo de Samitier with the students, geological notebooks in hand, the challenge is always the same: how far should we, can we, 'stray' away from teaching only the structural geology?
If we only focus on the structures, we miss drawing student attention to the important interactions between deformation and the evolution of the turbidite transport pathways; something they will need to know if they ever look at deep-water West Africa or Equatorial South America. To fully understand those pathways requires knowledge of hinterland evolution and the whole source-to-sink story, a story that is heavily dictated by not only tectonic uplift, landscape dynamics, and drainage network evolution, but vegetation cover, bedrock and climate and how these impact weathering and erosion. When we talk about the contemporary climate, what climate? The 'background', 'average' (whatever that means) climate? Or a really 'bad day' in the Eocene? - the Castissent flood events of (Marzo, Nijman and Puigdefabregas, 1988; Mutti et al., 2000), and what does that do to submarine-channel architecture downstream and the interconnectivity, porosity, and permeability of potential reservoirs?...
...and suddenly we find ourselves discussing regional paleogeography, Earth System modeling, the PETM (Paleocene Eocene Thermal Maximum), the importance of extreme events, ala Derek Ager's catastrophic uniformitarianism (Ager, 1984; Ager, 1993) and plate tectonics, and we have lost most of the day and possibly our audience...
There is simply so much to take in.
So, what do we do?
Focus just on the structures? That is the MSc course title after all.
Or do we bring in the other parts of the story - the bigger picture?
The answer is, of course, the latter, and the reason is obvious.
To solve geological problems in exploration we need to consider all the components.
Explorationists, and therefore our students, need to know enough of the vocabulary of each part of the Earth system to know what questions to ask, where to look for answers, and how the components fit together to dictate source rock geometry and character, trap formation and timing, reservoir quality and all the other plethora of geological risks they will need to assess as explorationists.
Paleogeography as a solution
This is not a new problem. 200 years ago, the early geologists were faced with the same challenge, how to manage, analyze and visualize the rapidly expanding observations accumulating in the databases of the time – the world’s libraries and museums.
One solution was to map out (in color of course) the accumulated knowledge on reconstructions of the past distribution of land and sea such as those of Elie de Beaumont in France and Charles Lyell in Britain (Lyell, 1837). For the first time here were representations of what the Earth looked like in the geological past. But by the 1870s it was clear that more was needed, especially following the Pennsylvanian (1859) and Ontario (1858) discoveries and the birth of oil exploration (Sorenson, 2007).
Figure 2. Charles Lyell’s 1837 land-sea map of the Tertiary of NW Europe
It was one of the first petroleum geologists, Thomas Sterry Hunt, who saw the value of paleogeography in exploration, and who, in 1873, first coined the term 'paleogeography’ (Hunt, 1873). Hunt had worked in the Ontario discoveries (Hunt, 1862) and was one of several geologists who had simultaneously recognized the importance of anticlinal traps. It is probably this structural experience that led Hunt to realize that in order to reconstruct paleogeography (past landscapes) you first need to understand the underlying “architecture of the Earth”, the crustal architecture on which the landscapes are formed.
Despite the obvious benefits of mapping structural evolution and depositional systems spatially in geological time, Hunt's ideas were not immediately utilized. It is true, that over the following three decades there were a large number of paleogeographic maps drawn. From Alfred John Jukes-Brown’s Building of the British Isles (Jukes-Browne, 1888), in which he showed paleorivers, albeit only on a few maps, and somewhat schematically, to James Dana's first maps of North American paleogeography (Dana, 1863). By 1900 Albert August Cochon de Lapparent (Lapparent, 1900) felt confident enough to draw the first series of global paleogeographies, including a best guess at what was happening in the Atlantic and Pacific. But in all these cases the maps were still land-sea maps.
It was to be in Germany that geologists finally started to bring together crustal architecture and paleogeography as Hunt had originally advocated over 30 years before. From Franz Kossmat’s geological history of land and sea distributions (Kossmat, 1908), albeit heavy on text and light on maps, to Theodor Ardlts ‘Handbuch der Palaeogeographie’ (Arldt, 1917). But, with Alfred Wegener (Wegener, 1912), the potential to put together continental drift, palaeobiogeography, crustal architecture and Earth structure within paleogeography, seemed within reach. Indeed all of these elements were discussed in a single book by Edgar Dacqué in 1915 (Dacqué, 1915). The consequence should have been the first atlases of paleogeographies on plate reconstructions. “Should have been,” that is. Unfortunately, 1914-18 was a terrible time to be a German scientist trying to promote ideas to American and European audiences. And so, as a sad consequence of contemporary politics, there was no atlas, and development stopped and much of this literature was largely forgotten.
Or rather, almost forgotten.
The Yale View of Paleogeography
When in 1904 Charles Schuchert joined the faculty at Yale as Professor of Paleontology he was faced with a problem, how to teach the breadth of geology. His solution was to use paleogeographic maps to show how the Earth had changed over time. It was to become a life-long passion.
Schuchert knew the German work (his parents were German émigrés) and he was well versed in the 19th and early 20th-century geological literature, including that of Hunt. He was also a colleague of Joseph Barrell, one of the founders of modern stratigraphy. Consequently, Schuchert not only took Hunt's workflow, but also emphasized the importance of constraining time. For Schuchert, a paleogeographic map representing a large geological interval, such as the whole Cretaceous, was meaningless, given the major changes that occurred over even the shortest of geological intervals.
The resulting paleogeographic atlas of North America, first published in 1910, comprised 60 maps at much higher detail than before and set the tone for paleogeographic research for the rest of the 20th century. Considered together with paleo-climatology and -oceanography these paleogeographies could provide information on depositional systems. When this was linked with structure (it was Schuchert who first stressed the importance of understanding deformation by palinspastically reconstructing the past geography - deformable plates to you and me) this integrated view could have huge benefits for petroleum exploration (Schuchert, 1919).
Figure 3. Charles Schuchert’s paleogeographic map of the Turonian of North America
Missed Opportunities and Continued Frustration
And yet, 25 years after Schuchert's first maps, we find another petroleum geologist, John Emery Adams (1943), lamenting that paleogeography was still underutilized in the industry. Yes, there were more maps being drawn, but these were mostly local in extent, and more often than not more facies map than paleogeography. The standout exception was the work of Alexander Du Toit, another geologist familiar with the German literature and especially Wegener’s work. He had put all the components together to generate the first paleogeographic reconstruction of Gondwana back in 1937 (Du Toit, 1937) having already published a restored fit for South America and Africa (Du Toit and Reed, 1927). But hey, he was in South Africa and what did he know? Quite a lot as it turned out. But in North America and Europe little was done.
Adams suggested three reasons:
Having spent my career building paleogeographic maps, I empathize with Adams's frustration.
And yet, here was a great exploration opportunity, as Adams realized. Because if you put paleogeography together with reconstructions of climate and oceanography you could potentially predict source and reservoir facies, and what a great exploration advantage that would provide.
Plate Tectonics and the penny drops
Adams was to include some of these ideas in his eulithogeologic maps, which were very much a precursor to the play concept.
The importance of bringing paleogeography together with depositional systems, structure, paleo-climatology, and -oceanography was further developed by Marshall Kay a few years later (Kay, 1945).
But, it was to be another 30 years before the Industry realized what they had been missing when suddenly all the pieces fell into place, metaphorically and, as it happened, literally. This was the advent of plate tectonics. What the German workers had recognized and discussed at the turn of the century, now had observational support and a unifying mechanism (Heezen, 1960; Heirtzler, Pichon and Baron, 1966; Hess, 1962; Vine and Matthews, 1963; Wilson, 1963; Wilson, 1965).
Suddenly, geologists were rushing to plot their exploration data on the new plate reconstructions, together with paleo-coastlines and land-sea distributions. The result was an explosion in paleogeographic research with companies either generating their own maps internally or working with research groups to do so.
It was the late 1970s and exploration following the oil crisis of 1973 was in full swing. Great... But these were still land-sea maps (coastlines), and there was an increasing problem of how to deal with all the new data, especially now that this had to be rotated onto plate reconstructions which multiplied the volume of data created by orders of magnitude.
Paleogeography, Computers and big data in the Windy City
The Hinds Laboratory, home to the Department of the Geophysical Sciences at The University of Chicago, is one of those architectural 'wonders' that wins awards for architecture, and everyone 'wonders' why. In the 1970s and 1980s, the second floor was home to the leading figures in quantitative paleontology. Nothing short of the analysis of the entire fossil record. Big data indeed. The result was the discovery of the five great mass extinctions (Raup and Sepkoski, 1984; Sepkoski and Raup, 1985).
In another corner of the second floor, Fred Ziegler was also manipulating large datasets using early computer systems, this time to build paleogeographic maps (Ziegler et al., 1985).
Fred's background, like Schuchert’s, was Paleozoic paleobiology, especially the use of fossil assemblages to reconstruct paleobathymetry. It was to be this interest that was to differentiate the Paleogeographic Atlas Project and the students it spawned. Because Fred’s maps included reconstructions of paleo-bathymetry and paleo-elevation – the paleo-landscape. Schuchert had talked about this, and indeed there had been attempts to show paleolandscapes such as that of Pepper et al (1954), but those of the Atlas project were systematically constructed based on the underlying tectonics. They were also global in extent, constrained in time to stage level (probably the highest realistic resolution at a global scale), and took some account of palinspastic changes following the work of Kay (Kay, 1945) and Schuchert.
Fred's work had three immediate consequences.
First, the reconstruction of landscapes was key to understanding depositional systems because it was on these paleo-landscapes that the rock record was built. A particle sees topography, rivers, and oceans. It does not see mantle convection or hyper-extension, at least not directly. Weathering and erosion, transport, and ultimately deposition are a function of what happens at the surface.
Second, if you could model depositional systems, then you could model source, reservoir and seal facies, as Adams had suggested back in 1943. This led Judy Parrish, another of Fred’s students, to take the new paleogeographies, use these as the boundary conditions for her parametric climate modeling and then to take the results to retrodict (predict past events) the distribution of ocean upwelling and through this the areas of potential organic carbon accumulation - source facies (Parrish, 1982; Parrish and Curtis, 1982).
The third consequence was data management. Underpinning the new atlases of paleogeography were some of the first computer-based geological research databases. What Fred and his students realized as they built these was the need to better ‘know’ the data itself, specifically its provenance and reliability. ‘Big Data’ can be a very powerful resource, but only if the data is well-constrained. Unconstrained data is simply big bad data and that is worthless.
What Fred did was to find ways to qualify data quality and mapping confidence and provide an audit trail for interpretations. The confidence schemes Fred derived were simple (Ziegler et al., 1985), a categorization of 1-5 where “1” indicated caution and “5” represented the highest confidence. But that simplicity ensured clarity and, more importantly, that the databases would be populated. As Markwick and Lupia later wrote, having worked with Fred, “A database must be simple enough to be used, but comprehensive enough to be useful” (Markwick and Lupia, 2001). The Atlas Projects databases were then linked to the source data through a reference code to computerized reference database with physical copies of all papers stored alphabetically on shelves around the walls of Fred's workroom.
Figure 4. Fred Ziegler's Cenomanian map of North America. The use of computer databases and representation of paleotopography and paleobathymetry
Today, 50 years after plate tectonics, and 150 after Hunt, we are spoiled for choice by the plethora of maps that are readily available online such as those of Chris Scotese and the beautiful photoshopped images of Ron Blakey, which adorn many of the posters and presentations at AAPG each year.
The ideas of Hunt, Schuchert, Adams, Kay, and especially Ziegler have been developed and expanded, not least by Fred’s students, including Chris Scotese, who has perhaps done more than anyone else over the last 40 years to promote paleogeography. My own small contribution has been to build on Fred’s methods to improve paleogeographic boundary conditions for climate modeling (Markwick and Valdes, 2004), further developing the mapping workflow (Markwick, 2019) and then applying these methods to exploration through the development of the lithofacies prediction methodologies that ultimately became CGG Robertson’ Merlin and Getech’s Globe products, both of which used detailed global paleogeographies and Earth system models to retrodict depositional systems, as Adams had advocated back in the 1940s.
Figure 5. As Hunt, Schuchert, Adams, and Ziegler had all recognized, the greatest potential of paleogeography as an exploration tool has always been the ability to represent, analyze and understand all the components in the system. In this example to then use these to retrodict organic carbon and clastics for any time interval.
And yet, like Adams back in 1943, it feels that despite all this progress, for most explorationists paleogeographies are still only seen as backdrop images for presentations and montages rather than a key exploration tool. That is a great shame.
It is time to get out the colored pencils …
This article was first published in the August issue of AAPG Explorer. It is based on a talk I gave at last year's AAPG meeting in San Antonio. My thanks go to
Matt Silverman and Amanda Haddad who chaired the session, “Step Changes in Petroleum Geology: Historical Challenges and Technological Breakthroughs”, and especially to Matt for his kind invitation to write this article for Explorer. I am also indebted to Brian Ervin and Matt Randolph of AAPG in Tulsa who did such a great job with the layout.
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A pdf version of this blog is available here for download
This blog is co-posted on the Knowing Earth website (www.knowing.earth)
Paleogeographic maps come in a variety of forms. But it is as reconstructions of past landscapes that they are the most useful. Why? Because it is on these landscapes that the geological record is built. A particle sees topography, rivers, and oceans. It experiences rain and floods and the heat from the sun. It does not see mantle convection nor crustal hyper-extension nor differentiate between a compressional or extensional tectonic setting, at least not directly. How sediment is formed in the hinterland through weathering and erosion, transported and ultimately deposited is a function of what happens at the surface and therefore what that landscape is.
A Google search for the term "paleogeography" reveals a wide range of maps and images. From simple black and white sketches showing past shorelines to maps of depositional systems or the distribution of tectonic plates, to full-color renditions of paleo-elevation and -bathymetry. Many, if not most, are informative, some are aesthetically quite beautiful.
For most geologists, such maps need little introduction. They have a long history of usage in the literature, and today have become something approaching de rigueur for conference presentations and corporate montages.
But paleogeography is more than just images in presentations. It is or can be, a powerful tool for managing, analyzing and visualizing geological information, for investigating the juxtaposition and interaction of Earth processes, as well as acting as the boundary conditions for more advanced Earth system modeling with which to better understand how our planet works.
Over the next few months, I will present a series of blogs that will explore paleogeography.
It will be a journey that will take us through the history of paleogeography, a look at how maps are generated, a guide to some of the pitfalls and caveats of mapping, a review of some of the mapping tools available, as well as examples of how paleogeographic maps have been used to solve real-world problems, especially in resource exploration where I have the most experience.
It is a journey that I hope you enjoy and find useful.
In this first blog, I want to set the scene by addressing two simple questions. What is paleogeography? And why should you care?
The Nature of the Problem: there is simply so much to take in.
If we look at any landscape and the processes responsible for forming it and which are acting on it, such as in the central Pyrenees shown above, we are faced with something of a dilemma: There is simply so much to take in.
For example, if we are teaching field geology in such an area do we focus on the structural evolution, or the stratigraphy, or the depositional systems or the climate, or vegetation or any one of the many components that together comprise the Geological record and the Earth system in this view?
Or do we try and cover all the bases?
Ideally, we want to try and cover everything. But we have limited time. We also do not want to overwhelm all concerned with diverse technical vocabulary and concepts. The risk of losing our audience.
Consequently, we usually focus on a specific field of study.
The same is true in exploration. Whether we are assisting management to make strategic decisions about where to explore or are a member of an asset team identifying and evaluating blocks and then prospects. We need to understand all the components of the Earth system if we are to make informed decisions.
30 years ago, companies would have had an army of in-house specialists on whom they could call for help to do this, and even more academic experts on retainers. But, those days have long since gone.
Unfortunately, one thing that has not gone is the budget constraints of the commercial world.
Exploration is, by its very nature, a net cost to an energy exploration business.
So, in addition to the scientific challenges, in exploration, we are also faced with trying to extract the maximum value from limited budgets.
So, what do we do?
Finding solutions: Paleogeography as a key tool in the geologist’s toolbox
We need a tool with which we can bring together (gather), manage, visualize and interrogate diverse geological information, information which is often sparse (especially in frontier exploration areas), sometimes questionable, and often equivocal.
If we look to history for guidance, we find 19th-century geologists faced with the same problem. A growing volume of diverse geological information and how to deal with it.
Over the preceding 100 years, scientists had tried to encapsulate the contemporary knowledge of the Earth system into a single book or series of books. Humboldt's Cosmos or Lyell's Principles are examples. But this had become next to impossible by the middle of the 19th century due to the sheer volume of information, resulting in an exacerbation of the scientific specialism that we have today. Humboldt’s opus itself was unfinished at his death and completed based on his notes.
One solution to this problem was to use maps to distil visually this wealth of information. Ami Boué’s maps of the World, more commonly known through Alexander Keith Johnston's “Physical Atlas of Natural Phenomena” (Johnston, 1856) in the middle of the century., or Élisée Reclus’ excellent “The Earth” (Reclus, 1876)
Reclus’s book on the Earth (Reclus, 1876) included maps showing the distribution of mountains and volcanoes. With the distribution of seismicity and you have all the information necessary for plate tectonics.
With geology, the problem was exacerbated by the time dimension. This was not simply a matter of mapping the current physical state of the Earth and its processes but how this had evolved over time. The past geography of the Earth. This is Paleogeography.
It is no coincidence that Thomas Sterry Hunt, the author attributed with first coining the term “paleogeography”, was also one of the first petroleum geologists, looking for ways to manage and analyze geological data for exploration. (We will revisit this in a later blog).
Paleogeographic maps can summarise a wealth of geological information in a simple, visual way by distilling the record into representations of depositional environments and structures. This then allows additional information to be added and juxtapositions and relationships investigated.
Such maps can also show lithological distribution and character, although strictly speaking facies maps are distinct from paleogeography’s in that they represent the product of processes, i.e. the rock record (as do GDEs for that matter), whilst a paleogeography represents the environment and landscape in which and on which those processes act and upon which the geological record is built.
The late Ypresian paleogeography for the central Pyrenees showing one transport pathway that takes in the three outcrops shown. From Markwick (2019)
In practice, this definition of paleogeography has become blurred. Facies maps, GDEs (Gross Depositional Environments), and plate reconstructions are all frequently referred to as “paleogeography”.
The original definition of paleogeography proposed by Hunt was as a field within geology to describe the “geographical history” of the geological record, which to him included the depositional environments, such as deserts and seas (Hunt, 1873).
This view of paleogeography as being the representation of the depositional environments that comprise a landscape is useful for two important reasons.
First, because it allows us to distinguish between the landscape, the processes acting on the landscape, the processes that created the landscape, and the rock record that is the product of all of the above. This makes the Earth system more manageable. It also means that when building a map we can audit each step (something we will look at another time).
But second, it allows us to deconstruct what the rock record directly responds to. What is important to consider. Where we need to focus our time (and monies). If we think of a sedimentary particle formed in the hinterland through weathering and erosion, transported and ultimately deposited, what does it really ‘see’ (i.e. respond to – at the risk of personifying clastic particles too much). A particle sees topography, rivers, and oceans. It experiences rain and floods and the heat from the sun. It does not see mantle convection nor crustal hyper-extension nor differentiate between a compressional or extensional tectonic setting, at least not directly.
It responds to the contemporary landscape and the processes acting on it.
A particle eroded from the hinterland and transported to its depositional location responds on its journey to processes at the Earth surface
Paleogeography defined: the problem of time
We now need to add another component to our definition of what paleogeography is. And that is time.
This is something that was identified by Charles Schuchert, a professor at Yale and colleague of Joseph Barrell, one of the founders of modern stratigraphy.
Cenomanian – Turonian section, Steinaker Reservoir. What would a Cretaceous paleogeography meaningfully represent? The transgressive shales or prograding sands or any range of other units through the Cretaceous
The Earth is dynamic and landscapes and depositional environments and their products the rock record can change over relatively limited geographic distances and short temporal intervals. For Schuchert, a global Cretaceous map was meaningless, for the very simple reason of what exactly did it represent? A landscape at the beginning of the Cretaceous, the end, the maximum extent of marine conditions, or as more likely, a pastiche of lots of different parts of that Cretaceous record? Schuchert’s recommendation was to use the finest stratigraphic intervals possible, which for him were represented by stratigraphic formations.
Kay went further to suggest that ideally paleogeography should represent a “moment in time”. Rather like looking at a satellite image. In this definition, paleogeography was a snapshot of the depositional environment and the landscapes at a specific moment. That makes perfect sense, but there is a problem. In the absence of a global correlation tool that can pick out a moment in time, this is next to impossible to achieve, especially over large distances. But it is an aspiration. It is also a reminder to ask of a map, what does it represent? Again, this is something we will return to in a later blog.
What is paleogeography?
Paleogeography is the representation of the past surface of the Earth, at a ‘moment’ in time.
Why is it important and why should you care?
Because it allows us to bring together diverse information that will help us better understand the Earth system, whether we are teaching in Spain or faced with deciding on where to explore. Paleogeography gives us the spatial context for gathering, managing, visualizing and analyzing a wide array of geological information in a way that is easy to digest.
At the end of the day, paleogeography is far more than just an image in a presentation.
Maastrichtian paleogeography showing the distribution of DSDP and ODP sites (small red circles) and vertebrates (Markwick and Valdes, 2004; Markwick, 2007)
This blog is one of a series based on a lecture course on paleogeography. Readers are also directed to a new paper on paleogeography published in the Geological Magazine: https://www.cambridge.org/core/journals/geological-magazine/article/palaeogeography-in-exploration/444CC2544340A699A01539A2D4C6E92A
Hunt, T. S., 1873, The paleogeography of the North-American continent: Journal of the American Geographical Society of New York, v. 4, p. 416-431.
Johnston, A. K., 1856, The physical atlas of natural phenomena, London, William Blackwood & Sons, 137 p.:
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