What is lurking behind and around the fossils of your palynology slide? Is it a black amorphous goop, or angular brown and black pieces?
For most palynologists, this background material is of little interest. Despite a superficially uninteresting appearance, these kerogens offer an insight into palaeoenvironments and depositional settings.
Welcome to the “Dark Side” of Palynology; the study of palynofacies. Our palynofacies wizard, Nick Miles, is always on hand to guide us.
When I said I wanted to do more palynofacies the company bought me this:
After all, when you have things like this to look at:
Who would want to look at things like this:
But a mess of kerogen like this has a tale to tell for palynologists as well as geochemists.
The Tyson Ternary Plot – Making sense of kerogens for palynofacies analysis
The world of marine palynofacies was brought into the age of numerical data by the Tyson Ternary diagram. At last the basic data became quantifiable and consistently interpretable. It was no longer witchcraft, no more jokes about the dark side of palynology. No wands, no red light sabres, just plottable data.
So, what do the fields on this ternary diagram mean and how do we identify them?
Apices of the Ternary plot – The Kerogen types
Rather than our usual pursuit of fossil spores, pollen and algae within the organic fraction of a rock sample, palynofacies tries to take in the whole organic residue. This can be reduced to three easily identified components:
Phytoclasts: effectively fragmented plant debris, often showing structure.
Amorphous organic matter (AOM): structureless, very fine grained material
Palynomorphs: things like spores, pollen dinocysts and acritarchs. Learn more about palynomorph groups on our Palynology page
Tyson showed that the proportions of these groups of organic material varied in a systematic way throughout a Jurassic marine depositional system. Subsequent work has shown the same features can be seen from Devonian to Recent depositional systems too. The general principle behind the Tyson ternary plots is that redox, sorting and proximity to fluvial source determine the kerogen content of a sample. Where oxygen availability is low, AOM is preserved. Where oxygen availability is high, AOM is not preserved. In very proximal settings phytoclasts (plant debris) dominate, whilst, in more distal settings, more buoyant palynomorphs are preferentially sorted and sedimented.
So, the hapless palynologist can make counts (preferably based on hundreds of specimens) of the kerogen particles, derive percentages of the three key ingredients and plot them on ternary diagram. Stratabugs charting software can take care of the maths and create the charts for us.
The Roman Numerals – Palynofacies Fields and Depositional environments
Within the ternary plot there are fields, each with a Roman numeral. These are the depositional environments defined by the relative proportions of the kerogen types.
Here are the fields that Tyson defined in his seminal work:
|I||highly proximal shelf or basin|
|II||marginal dysoxic-oxic basin|
|III||heterolithic oxic shelf (proximal shelf)|
|IV||Shelf to basin transition|
|V||Mud-dominated oxic shelf (distal shelf)|
|VI||Proximal suboxic-anoxic shelf|
|VII||Distal dysoxic-anoxic “shelf”|
|VIII||Distal dysoxic-anoxic shelf|
|IX||Distal suboxic-anoxic basin|
Putting theory into practice – Examples of kerogens under the microscope
Looking down the microscope, how distinctive are these palynofacies? Here are some examples below.
Example of Palynofacies Field I
Here is how Palynofacies Field I looks – full of nicely structured plant debris but lacking spores.
Example of Palynofacies Field III
Palynofacies Field III adds good numbers of spores to the mix.
Example of Palynofacies Field VII
In more suboxic settings AOM predominates over the structured plant debris and spores, as in Palynofacies Field VII.
Example of Palynofacies Field IX
And once we are into a distal marine anoxic facies there is the messy look of Palynofacies Field IX, with barely a spore or plant debris fragment in sight. The cauldron of oil generation.
What do we do with all this data?
What do we get for working our way through all these slides full of organic gloop? In the following diagram there is an example of a palynofacies plot for an onshore UK Carboniferous section. Even though there is a very inconvenient scarcity of marine palynomorphs during the Carboniferous, the palynofacies clearly show the progradation of deltaic systems into an anoxic basin.
What are the industrial applications of palynofacies to the oil and gas sector?
At PetroStrat, we can include optional palynofacies analysis as part of our Palynology Service. Palynofacies can provide additional information on;
- Thermal maturity
- Source rock potential
Palynofacies formed a key part in our extensive Namurian Shales Study. In this study.
A bright and shiny future for palynofacies analysis?
Is there a future for the dark little sideshow of palynofacies? I like to think so! There have been some starter attempts to identify kerogens using the truly dark art of Artificial Intelligence – algorithms have already been composed (or whatever you do to get an algorithm). These use automated microscope and camera systems. Once they bear fruit (probably a very dark fruit) then pesky palynologists can be put to one side and palynofacies can enter the world of cheap Big Data.
Want to learn more? Here is a reading list where you can learn more about the world of kerogens and palynofacies.
- Carvalho, M. de A., Cabral Ramos, R.R., Crud, M.B., Witovisk, L., Kellner, A.W.A., Silva, H. de P., Grillo, O.N., Riff, D. & Romano, P.S. R. 2013. Palynofacies as indicators of palaeoenvironmental changes in a Cretaceous succession from the Larsen Basin, James Ross Island, Antarctica. Sedimentary Geology, 295: 53-66.
- Heal, S. & Clayton, G. 2008. The palynology of the Hannibal Shale (Mississippian) of northeastern Missouri, U.S.A. and correlation with western Europe. Palynology, 32: 27-37.
- Kuncheva, L.I, Charles, J.J., Miles, N.H., Collins, A., Wells, B., Lim, I.S. 2008. Automated Kerogen Classification in Microscope Images of Dispersed Kerogen Preparation. Mathematical Geosciences, 40: 1-14.
- Makeen, Y.M., Hakimi, M.H. & Abdullah, W.H. 2015. The origin, type and preservation of organic matter of the BarremianeAptian organic-rich shales in the Muglad Basin, Southern Sudan, and their relation to paleoenvironmental and paleoclimate conditions. Marine and Petroleum Geology, 65: 187-197.
- Mueller, S., Veld, H., Nagy, J. & Kurschner, W.M. 2014. Depositional history of the Upper Triassic Kapp Toscana Group on Svalbard, Norway, inferred from palynofacies analysis and organic geochemistry. Sedimentary Geology, 310: 16-29.
- Roncaglia, L. & Kuijpers, A. 2006. Revision of the palynofacies model of Tyson (1993) based on recent high-latitude sediments from the North Atlantic. Facies, 52: 19-39.
- Tyson, R.V. 1995. Sedimentary Organic Matter: organic facies and palynofacies. Chapman and Hall: 615pp.