SSP
Stratigraphy, Sedimentology and Palaeontology

Stratigraphy, Sedimentology and Palaeontology

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.

Blame it on the Weatherman

Blame it on the Weatherman

I like rain. Being British, this is a useful trait. It’s also what led me to do a PhD in Hydrometeorology. Since then, I have researched in hydrology, hydraulics, geomorphology, and more recently I have dabbled in sedimentology. Yet, the common theme through all of my research has been rain.

I think it’s often underappreciated by those of us more interested in dry stuff like sediment and rocks, but speak to any hydrometeorologist or hydrologist and they will be able to tell you at length just how troublesome the wet stuff is. For starters there is no accurate way to even tell how much is falling over an area, and this has led to some creative methods of measuring it, mainly from EGU stalwart, Rolf Hut.

Rain is a big theme in my SeriousGeoGames

Another issue is that it doesn’t just come in one type and each can have a different impact on sediments. Frontal rain is miserable and can bring day after day of rain, adding a lot of water to the land but spread out over a long time this is often not enough to have an impact the land surface. Convective rainfall can be extremely heavy, extremely localised, and can have huge impacts on the land – just look at the recent flooding in Coverack, UK.

This complicates things – we like to lump rainfall together and climatically we think about mean annual totals. However, by shifting the balance from low- to medium-intensity frontal rain to high-intensity convective rain it is possible that with no change in the mean annual totals there will be an increase in geomorphic activity. It is even possible that the mean annual rainfall total could decrease, but if summer convective storms increase in frequency and magnitude, the sediment yields of catchments will increase.

To try and simplify this, the variability of rainfall often has a greater impact on sediment processes than the amount of rainfall. This can also influence the shapes of landscapes and how they develop – in my work with Professor Tom Coulthard we showed how using the same rainfall totals at different spatial and temporal resolutions impacted the sediment yields predicted by the CAESAR-Lisflood model. We found that when using the finest resolution, the sediment yields could be more than double those using a daily total and spatial homogenous rainfall rates – this could be taken as analogous of the same rainfall totals applied as convective and frontal. Over 1000 years of simulation the convective higher-resolution data produced more erosion higher up in the catchment, and increase deposition in the valley floors.

The CatchyRain Team setting up their next experiment

I wanted to follow this up by seeing if we could get similar results using a sediment flume. However, I’ve been beaten to it by the CatchyRain group from Wageningen University who have been conducted experiments via the Hydralab+ programme. Fortunately, they conducted their experiments using the Total Environment Simulator at my University, Hull, and they kindly let me visit and film some of it on my 360 camera – in the video below I speak to Dr Jantiene Baartman, Assistant Professor from Wageningen University. You will also see others involved in the test, such as Dr Martine van der Ploeg, and Hull’s Dr Hannah Williams and Dr Wietse van de Lageweg. To get the best effect out of this video, view it on a mobile device via the YouTube app.

What the Wageningen and Hydralab+ team will hopefully show is that even the same volume of rainfall falling on a catchment will produce different patterns of sediment processes due to the variability in intensities. I am really looking forward to seeing the results presented at EGU 2018, for example this Highlight presentation by Hannah.

This is just the tip of the iceberg in terms of how complicated rainfall is and how its variations and variability can influence landscapes. I haven’t had chance to open the Pandora’s Box of how the uncertainty in rainfall estimations can cascade through modelling processes – maybe another blog for another time. In the meantime, I hope I will have inspired you to think about rain a little more and for EGU 2018 I would highly recommend a visit to the HEPEX sessions.

Picture of March

Picture of March