Stratigraphy, Sedimentology and Palaeontology

Stratigraphy, Sedimentology and Palaeontology

Slimy Landscapes

When we think about how our landscapes evolve and change we probably tend to go straight for the big stuff, things like the climate, tectonics or geology, and in my previous blog I looked at how rainfall contributes to changing the planet’s surface. However, it is not just the big stuff which controls these changes, smaller things do as well, for example changes in land cover (ie, from grasses to trees, or the other way round) results in changes in the patterns of erosion and deposition, not just in the areas where the land cover changed but also further along a system.

There are also several examples of how animals can influence the processes driving landscape changes too. In Yellowstone Park, USA, the hydrological conditions in the area changed when the main predator, the grey wolf, disappeared from the area causing a knock-on effect on grazers removing sapling trees which in turn stops woodland reaching maturity resulting in a change in land cover. To try and reverse this the grey wolf was reintroduced but so far has not been successful returning the system to its former state. Recently it has been shown how spawning Pacific salmon can make localised changes to river channels and increase the ability of flows to erode the river, impacting the whole river profile.

But let’s get even smaller, right down to the smallest living things on Earth. Surely things like bacteria cannot influence how landscapes evolve over long periods of time? Well, think again. Serena Teasdale is an Early Career Researcher who works with me at the University of Hull, and she is researching how bacteria can change the erosion rates of shorelines.

“Often when we consider the role of biology, our initial assumption is that of vegetation.  However, studies have begun to highlight the fundamental importance of EPS [technical way of saying slime, more on this later – Chris] on driving sediment behaviour, notably stabilising sediment and enhancing the erosion threshold.  This occurs as the EPS matrix, secreted by microorganisms, forms bridging structures between sediment particles which prevent them from moving freely” she tells me.

Serena has developed a really neat demonstration to show the impact this slime can have on the resilience of sediment – she uses sandcastles. It’s simple but highly effective. One sandcastle is made using normal sand and a second has been mixed with xanthan gum, a proxy for this slime and it is commonly used as a binding agent in fat free mayonnaise. She pours water from a watering can over both and times how long it takes for them to fall apart – it is clear that the one full of slime takes much longer to collapse.

This slime is actually called Extracellular Polymeric Substances (EPS) and whilst this might sound like something made up for the Ghostbusters’ franchise it exerts huge influence over landforms. Physical experiments have shown that mixing sand and mud with different volumes of the xanthan gum proxy, and you only need a tiny amount, can shift river bed landforms from dunes, to ripples, to flat beds. It means our current models of interpreting past environments from buried bed forms might be wrong as these have not considered the effects of the bacterial slime.

The slime therefore can impact changes in sand castles and on river beds, but what about the evolution of landscapes? I spoke to another Early Career colleague, Josh Johnson, about his research –

“The extra stickiness causes deltas to form with fewer distributaries but these are larger and more stable.”

Comparisons of two deltas – both the same discharge but the right has low cohesion (stickiness) and the left high.

Josh has created an interactive display using animations of his modelling to show the impacts of river discharges and ‘stickiness’ on the developing shape and channel networks on deltas. In it you can choose low, medium and high levels of both and it shows you the result. Above we can see a low stickiness and high stickiness delta for medium discharges.

So next time you are out in the pristine landscape and considering just how it came to be, don’t just dwell on the big stuff, it might be all because of bacteria snot. Isn’t nature beautiful?

You wouldn’t go in the early basement during the upper afternoon, don’t you?

I remember it perfectly. It was 13 years ago, while writing my first manuscript, I was first confronted with that thing that challenges a lot of junior stratigraphers, especially when they are not a native English: Geochronology vs. Chronostratigraphy! Or to simplify, how to properly distinguish time and time-rock units in your writings.

Several papers have been published on this subject, out of which I would recommend the recent Zalasiewicz et al. (2013). But, although these papers do provide a very clear scientific explanation on this subject, I always remember myself 13 years ago and how difficult it was for me back in those days to understand these concepts!

So, is it that difficult? Or is there an easy way to spot the light at the end of the tunnel? Well, if you have spotted the oddness in the title of this blog, the good news is that you have already made 3/4 of the way. Of course, the trick is in the use of early/late vs. lower/upper, that is to say on the distinction between time (geochronology) and space (chronostratigraphy), respectively.

Let’s have a little test to check that. Which of the following five sentences are wrong?
1. The late Bajocian is 500m-thick in this region.
2. The upper Bajocian can be correlated throughout this region.
3. The lower Bajocian has experienced environmental changes.
4. A carbon cycle perturbation occurred during the early Bajocian.
5. The lower Bajocian carbon isotope excursion.

Without having too much suspense: it’s the sentences 1 and 3 that are wrong.
In sentence #1, the term “late” is used whereas the sentence makes reference to time-rock unit, i.e. chronostratigraphy. Here, Bajocian refers to the thickness of the sedimentary sequence, so one should use the term “upper”. However, if you insist on using “late”, then you should write the sentence as following: “The thickness of the sedimentary succession dated from the late Bajocian is 500m”.
In sentence #3, we have the opposite case, i.e. the use of “lower” while referring to time, i.e. geochronology. It is as odd as “having a meeting in the upper afternoon”.

There you go, you have done 3/4 of the way. What about the last quarter? The answer is in sentence #5. It is indeed correct, and refers to the carbon isotope excursion you have measured in the Lower Bajocian, i.e. in the section you have worked on. But writing “the early Bajocian carbon isotope excursion” is also correct, but this time it refers to the carbon cycle perturbation that has occurred during the early Bajocian. You know… the one that is recorded in the lower Bajocian! But never say that it is recorded in the early Bajocian, that would be wrong.

Zalasiewicz, J., Cita, M.B., Hilgen, F.J., Pratt, B.R., Strasser, A., Thierry, J. and Weissert, H. (2013) Chronostratigraphy and geochronology: A proposed realignment. GSA Today 23, 4–8.

Author: Dr. Stéphane Bodin, University of Aarhus


Tiny but powerful

Oceans are “populated” by millions of specimens of microscopic organisms which constitute the phytoplanktonic communities (e.g. diatoms, dinoflagellates, cyanobacteria and coccolithophorids). These tiny organisms are important indicators of the “health” of present oceans and their remains constitute important tracers of past paleoenvironmental conditions. The ocean is in fact the oldest and largest ecosystem on Earth and best records global changes in climate and atmospheric composition, as well as major variations in physical, chemical and trophic parameters. This is particularly important since recent environmental changes, pose urgent questions regarding biota ability to cope with rapid and progressive climatic changes accelerated by anthropogenic emissions of greenhouse gases. A major issue of present global environmental perturbations, regards the impact of rapid warming and climate instability on ecosystems. Concerns are therefore addressed to the possibility that biodiversity loss will soon derive from biota failure in sustaining such profound alteration of ecosystems.



It is well known that increasing COis inducing pH lowering. This has an effect on CaCOsaturation state and calcite compensation depth in the oceans with consequent problems for calcifying organisms such as corals and microplankton: these groups become vulnerable and unable to produce their shells-skeletons if the acidity passes a critical level. At present, decreased calcification could have negative impacts not only on marine ecosystems, but also on marine food chain (and resources) at global scale.

Coccosphere of E. huxleyi (


One phytoplanktonic group which can provide important information regarding past and present response to environmental perturbations is constituted by coccolithophorids. Coccolithophores are golden-brown algae (phylum Haptophyta) which live in the upper photic zone and that developed the ability to secrete tiny calcite crystals and arrange them to build an exoskeleton called coccospheres.

Although these algae are extremely tiny (a few microns), they are important primary producers. The biocalcification process made coccolithophores rock-forming organisms during the Jurassic and Cretaceous and they were/are directly involved in the total carbon budget by influencing the carbon cycle via photosynthesis and biocalcification. We understand how these organisms are widespread in the oceans and, consequently, important for the carbon cycle by looking at blooms of the coccolithophore E. huxleyi which are visible from space!

Under certain conditions, Emiliania huxleyi can form massive blooms which can be detected by satellite remote sensing. The white could is  the reflected light from billions of coccoliths floating in the water-column. Details: Landsat image from 24th July 1999, by Steve Groom.

One commonly used approach to derive projections of how ecosystems will look in the future is to perform experiments on living forms. The data obtained from several experiments over the last decades, evidenced a direct impact of increasing COemissions on coccolithophores but several questions are still open regarding the mechanisms involved during biocalcification and the role of combined high CO2 with other stressing factors. Scientists have to work to understand the capability (and velocity) of coccolithophores to adapt to these environmental changes as well as to understand the interaction of different parameters on biocalcification and their effect on the ocean/atmosphere system.

Additional methods of investigation can be applied to model the evolution of the ocean from the recent past to the near future, as for example presented in a published work based on satellite observations. The dataset indicates that the Arctic Ocean and its surrounding shelf seas are warming much faster than the global average, potentially opening up new distribution areas for temperate‐origin marine phytoplankton. The data already show that increased inflow and temperature of Atlantic waters in the Barents Sea resulted in a striking poleward shift in the distribution of blooms of E. huxleyi (Neukermans& Fournier 2018).

Fossil coccosphere of Watznaueria barnesiae (Black) Bukry 1969 (


Last but not least, geologists can obtain important information which cannot be acquired via laboratory experiments. For example, it is not possible to capture the ability of organisms to migrate or to select and evolve. Experiments are often limited to a select few species and cannot represent the complexity of ‘real’ ecosystems. Moreover, “environmental scientists” deal with time scales of day to decades but geoscientists work on records of thousands to millions of years and look at the largest “natural laboratory” on earth captured in sedimentary rocks and their fossil content. Only through the combination of the information that can be gained via experiments, via new techniques and the study of microfossils, scientists will be able to help understanding the Earth system at longer time scales (than human observations) and make prediction about the response of our planet to profound climatic perturbations.

Outdoor water-based ceramic sculpture ‘Coccolithophores’ by Michelle Maher at Sculpture in the Gardens 2010 at Brigit’s Garden, Co. Galway. The piece was inspired by a microscopic algae organisms the Coccolithophore.


Griet Neukermans and Georges Fournier, Optical Modeling of Spectral Backscattering and Remote Sensing Reflectance From Emiliania huxleyi Blooms, Frontiers in Marine Science, 10.3389/fmars.2018.00146, 5, (2018).

When lava meets water…

When lava meets water…

Pillow-palagonite complex forming as a result of hot lava entering a former river channel or lake in the Columbia River Flood Basalt Province, Washington State, USA (c. 15 My). Individual sediment packages were picked up from the bottom of the water body and trapped within the lava complex (see white arrow). Orange-brown palagonite is a type of clay which forms through the break-down of volcanic glass that surrounds the basaltic pillows.