By Jack J Matthews, research fellow
On the southern shores of Newfoundland in Canada lie rocks containing the oldest known evidence of large, architecturally-complex life. Deposited within the Ediacaran Period, some 565 million years ago, these deep marine deposits have been the focus of palaeontological research since the first discovery of fossils there in 1967, and the locality – Mistaken Point Ecological Reserve – now sits in the UNESCO World Heritage list.
As part of my research on these rocks, alongside colleagues from Memorial University of Newfoundland, and the University of Cambridge, I created a new geological map of the area, covering 35 km of coastline in and around the Reserve. As well as providing new insights into the rocks themselves, and what environments they were deposited in, this mapping had an unexpected outcome – the discovery of some totally new fossil sites.
One site in particular, dubbed the ‘E’ surface, is the focus for Ediacaran fossils in Newfoundland. It is an area about the size of three Olympic boxing rings, containing more than 3,000 fossil organisms. Through the mapping we found a number of other outcrops of this same surface, but each shows slightly different types of fossils.
This is a mystery: if all the outcrops are from the same geological surface, why do they show different fossil assemblages?
The clue to the answer came while photographing the fossils and overlying volcanic ash at Mistaken Point, when I heard a loud, deep boom: a freak wave had struck the bottom of the cliff below the outcrop, sending a large splash of salty spray over much of the surface.
This got me thinking – how are processes such as weathering and erosion affecting the fossil surfaces now? Closer observation revealed those outcrops of ‘E’ with pristine beautiful fossils tended to be further from the sea, have a shallower dip, and the overlying ash tended to fall away in little flakes revealing beautiful, crisp, fossils. Other outcrops with scruffy fossils were usually close to the sea, battered by waves and rocks, steeply dipping, and the overlying ash, and often the fossils below it, would gradually abrade away as they are attacked by the sea.
Palaeontologists often discuss how changes during the fossil preservation of an organism can affect what we discover today, but they rarely discuss how processes occurring after preservation – metamorphism, exhumation, weathering, erosion, and even the time, manner, and conditions in which the fossil is recorded – might all affect how we analyse and interpret the original community of life which became fossilised.
Our new paper, published by the Geological Society of London, talks about these Post-Fossilization Processes, and recommends that when researchers are collecting fossil data they consider how their measurements might have been biased by such factors.
For 50 years now, the coastline of Newfoundland has yielded some of the most important finds in understanding the rise of the early life of the Ediacara, and through that the first evidence of animal life. Discoveries over the past few years show there is still much more to be found, and we’ll just have to hope that the post-fossilization processes fall in our favour to allow for many more significant discoveries.