Fieldwork on an ancient seafloor
While the majority of the Centre for Deep Sea researchers have gone out to the Norwegian Sea this summer to study seafloor processes and hydrothermal vents, Desiree Roerdink flew to the other side of the world to do exactly the same thing – in rocks that are more than three billion years old.
“We have just returned from fieldwork near Marble Bar in Western Australia, where winter temperatures are still around a comfortable 27 degrees. Not only is this part of Australia a great place to escape the Bergen summer, we also find some of the oldest rocks on Earth here that can help us to understand what our early planet looked like.
Surprisingly, some of the rocks look very similar to what we would find in the field today. Three-and-a-half billion year old fossilized wave ripples may remind of you of a beach walk on a summer afternoon, pillow lavas look like they just erupted on the seafloor, and microbial mats (stromatolites) closely resemble their modern cousins found on the Western Australian coast. You would almost forget that the early Earth was a planet without oxygen in the atmosphere, no life other than micro-organisms, and oceans rich in iron and silica with widespread hot springs. Understanding these ancient environments is still a key target for us geologists working on the first two billion years of Earth’s history.
Our fieldwork in Australia focused on one specific type of environment, where large barite and silica deposits formed in seafloor hot springs. It’s a combination of minerals that we also find in modern white smokers and in the low-temperature area of the Loki’s Castle vent field, but the Australian deposits are of a much larger scale than what we find in today’s oceans. Unvaluable for the lithium and gold prospectors near Marble Bar today, but very valuable for us scientists as the barite hosts some of the oldest evidence for life and records the chemistry of the earliest oceans.
During the two weeks of fieldwork, we made several drone maps and collected tens of kilos of carefully picked samples – the high density of barite makes you think twice about carrying that large block back home! Now the red dust has been washed from our field clothes, we are heading back into the lab to analyze these samples for their geochemical and isotopic compositions. Together with work that we previously did on barite deposits in South Africa, this will hopefully enable us to finally solve the puzzle on how these bedded barite deposits formed in a world that was very low in sulfate.”
The fieldwork of #TeamBarite (Paul Mason, Mark van Zuilen, Desiree Roerdink and Dylan Wilmeth) was funded by grants from the Dr. Schürmann Foundation and the Meltzer Research Fund.