#bioturbation

Forces : Bioturbation 2020, felted lamb's wool, 150 x 180 cm

Bioturbation

It is a process in which living organisms (animals or plants) disturb the sediment record. Pictured here is a perfect example of this.

A thin layer of sediments can accumulate over thousands of years or within few hours. Once it is buried by more sediment, it becomes preserved in sedimentological record. Just like when you borrow a book from a library, and a record of what and when you have borrowed the book is added to your card, in a similar way such layers preserve a record about the event that deposited that layer.

However, such record can be disturbed by living organisms, and a lot of preserved information can be lost. As sea creatures burrow through the sediment in search of food or making a temporary home, or a plant growing its roots through sediments in search of nutrients, the result is the same, sediment is mixed and original relationships between sand grains are forever lost in the process of bioturbation.

On the other hand, bioturbation tells sedimentologist (sediment historian) something about life that occupied this space, and this can be very interesting in itself, especially when one looks at rock record that is millions of years old. However, it can be difficult to know when or what living organism disturbed the sediment.

The example above is from over 250 million year old rocks. Bottom stripped layer on this picture is consists of sandy and undisturbed sands. The gray-black middle layer contains more mud and organic matter (hence the black colour) and is heavily bioturbated. Presence of organic matter is likely the reason why the bioturbation is so extensive, as sea floor dwelling creature were chewing through this sediment in search of organic particles they can feed on. And as a result, we have this messy and chaotic layer that is strongly mixed. Above, is another layer of sands that do not contain much organic material, and so, sea creatures do not burrow through it and all sedimentary features are preserved.

Bioturbation //  Superstimulus @ a&o Kunsthalle, Leipzig, 2019

Bioturbation–Worms at Work

from Wim von Egmond

Bioturbation is the mixing of (plant) residues into soils and sediments by biotic activity. It is one of the fundamental processes in ecology, as it stimulates decomposition, creates habitats for other (micro) fauna and increases gas and water flow through the soil.

This time lapse movie shows bioturbation by 3 earthworms species:

Lumbricus terrestris (an ’anecic’ earthworm, feeding on leaves and living in deep vertical burrows; 2 individuals present)

Lumbricus rubellus (an ’epigeic’ earthworm, feeding on leaves and living in shallow, non-permanent burrows; 2 individuals present)

Aporrectodea caliginosa (an ‘endogeic’ earthworm, feeding on decomposed organic matter and living deeper in the soil; 3 individuals present).

Poplar leaves were applied on top of the soil as food for the earthworms. Different soil layers were simulated by mixing a topsoil (rich in organic matter) with quartz sand in various ratios.

Several articles have been published which point to evidence of Neanderthals burying their dead, but conflicting viewpoints have also pointed out that the evidence could rather be from other forces, such as bioturbation. Did Neanderthals deliberately bury their dead, even using symbols such as flowers and grave goods? And if so, what can this mean when thinking of their mental capacities?

Further Reading: Gargett, Robert H. 1989 Grave Shortcomings: The Evidence for Neandertal Burial. Current Anthropology 30(2):157-190.

Pettitt, Paul 2011 The Palaeolithic Origins of Human Burial. New York: Routledge.

Solecki, Ralph S. 1975 Shanidar IV, a Neanderthal Flower Burial in Northern Iraq. Science 190(4217):880-881.