Stratigraphy, Sedimentology and Palaeontology

Alena Ebinghaus

After graduating at the University of Bonn in 2010, Alena Ebinghaus took up a PhD project at the University of Aberdeen, examining inter-lava sedimentation and plant ecosystem development in the Columbia River Flood Basalt Province, Washington State. Following her graduation in 2014, Alena joined the University of Aberdeen as a post-doctoral researcher. In her current research, Alena focuses on the understanding of continental environments during past rapid climate warming, such as the Early Danian Dan-C2 event and the Palaeocene-Eocene Thermal Maximum. Since 2017, Alena has served as the Early Career Scientist (ECS) representative of the SSP division.

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


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.

Famous geological sites: Delicate Arch, Utah

Famous geological sites: Delicate Arch, Utah

Delicate Arch is probably the most spectacular natural arch in Arches National Park, Utah. Delicate Arch is made of the Middle Jurassic Entrada Sandstone, which was deposited in various environmental settings, particularly beaches, tidal mudflats and deserts. Arches National Park attracts more than 1.5 million visitors per year.

The world about pollen

The world about pollen

Pollen – for many people rather an irritant across spring, summer and autumn when trees and flowers are in bloom. Individual pollen grains are between a few µm (micrometre, which is one thousandth of an mm) and >130 µm in diameter. This size range is impossible to see with the naked eye unless the pollen grains are clumped together, or when pollen is dispersed as powder into the air on a dry summer day. When observed under the microscope, pollen display a complex and beautiful surface patterns (called sculpture) specific to each plant species. The study of pollen is also referred to as palynology.

Despite causing sore throats, sneezing and itchy eyes, pollen may be of great scientific and forensic importance! Pollen is the male part of the reproductive system of seed plants. During pollination, the pollen grows a tube down the ovary of the female part of the flower, and sends male sperm cells to the ovule (egg). Each plant species produces its very own type of pollen of distinctive size and shape. The number of pollen grains produced by a plant during the flowering season is immense. For example, it is estimated that the flower head of an average grass produces up to 10 million pollen grains.

Pine pollen dust dispersed through wind.

While numerous plants are widely distributed there are plants that have a distinctive local occurrence. These pollen easily gets stuck at our clothing. This is where pollen becomes a useful tool in tracking down people or objects in forensics. Despite forensic palynology, pollen are widely used in biology, archaeology, and palaeontology, to better understand vegetation patterns, dynamics and ecosystems. The field of palynology, however, does not only include pollen, but all types of “palynomorphs”, such as spores (produced by ferns, mosses, algae and fungi), and dinocysts, which form part of the lifecycle of dinoflagellates (marine and freshwater plankton).

As a palaeopalynologist, I am interested in the fossil record of palynomorphs. In my research, I am looking at the palynological record of Cenozoic fluvial and lacustrine strata. In our palynological lab at the University of Aberdeen we use a range of acid treatments, particularly hydrofluoric acid treatment, to extract palynomorphs from the rock samples. The resultant solution is pipetted onto a slide, dried up and covered up to produce a palynological slide for examination under the microscope.

The examination of such palynological slides may be time consuming, however, systematic recording of the various abundant palynological taxa produces a great data set that allows me to reconstruct ancient vegetation patterns, communities and habitats. I commonly combine the palynological data with sedimentological and geochemical data to analyse how the vegetation interacted with its surrounding environment. Studying such palaeo-environments gives us the opportunity to get insights in how ecosystems developed over long-term, geological time scales.

For instance, as part of my post-graduate studies of the Columbia River Flood Basalt Province (CRBP) in Washington State, USA – a large volcanic terrain that was active between 17 and 6 My ago, I assessed how the ancient plant ecosystem was affected by volcanic eruptions and lava flow emplacement. The CRBP, however, has a particular geological setting, and is associated with more explosive volcanism of the adjacent Yellowstone hotspot and Cascade Range volcanism. In particular ancient Yellowstone volcanoes have spread large amounts of volcanic ash towards the CRBP over millions of years. Integrating the palynological record from the CRBP sedimentary intervals with analyses of volcanic ash deposits, we concluded that the ecological succession of CRBP plant communities was frequently disrupted by the external Yellowstone ashes, rather than internal CRBP volcanism (Ebinghaus et al. 2015*).

Basaltic lavas of the Columbia River Flood Basalt Province, Washington State.

Large igneous province (LIP) volcanism like the CRBP is understood to have had significant impact on the environment within the vicinity of the volcanic centre. However, in comparison to other large igneous province, such as the Deccan LIP (India) and Siberian Traps (Russia), which are considered to have triggered major mass extinction events, the CRBP is a relatively “small” LIP. This may explain why the geologically continuous CRBP volcanism did not disrupt the plant ecosystem in such an extent as the more instant and explosive Yellowstone volcanism, thus causing less ecological impact.

Although not widely taught in undergraduate geoscience programmes, palynology is a useful tool to not only study past plant ecosystems, but also how environments responded to major stress factors such as volcanism. Its application in forensic science demonstrates the wider applicability of pollen studies. And maybe during the next flowering season one may imagine (hopefully without hay fever!) the transport and depositional history millions of pollen and spores have ahead and what they may tell about our environment sometime in the future.

*Ebinghaus, A; Jolley, D.W., and Hartley A.J. (2015): Extrinsic forcing of plant ecosystems in a large igneous province: The Columbia River flood basalt province, Washington State, USA. Geology, v. 43, no. 12, p. 1107 – 1110. doi:10.1130/G37276.1.