How the world’s largest known volcanic event helped create the world’s largest delta
Albina Gilmullina
I have been advising a team of researchers led by Dr. Albina Gilmullina of Bergen University, Norway, looking into Triassic sedimentation rates and patterns in the Greater Barents Sea. The results were published in the GSA Bulletin this year.
During the Triassic, this remote Arctic province saw the emplacement of a thick and extensive Triassic succession – up to 4.5 km thickness over an area of quarter of a million square km (more than ten times the area of the UK). The sediment loads are larger than those of any other known river, past or present, and comparable with the entire output of rapidly eroding continental margins like the southern Himalayas.
Why we did it
The Triassic is an important economic unit in the Barents Sea, containing both source and reservoir facies. In addition, the anomalously high sedimentation rates at the beginning of the Triassic, and later in the period, record a major global upheaval and one of the most radical episodes of climate change and extinction in the Earth’s history. Understanding this succession has relevance to modern-day climate change, and to understanding high-output depositional systems through geological time. The scale of the Triassic depocenter has direct relevance to the paleogeography of the Arctic at a time before the present-day Arctic Ocean existed.
Triassic paleogeographic reconstructions of the Greater Barents Sea
Triassic sediment flux compared to modern river systems
What did we do?
Observational data on the Barents Triassic section from seismic and wells were combined with statistical modelling of source and catchment areas, to determine sediment flux through time, and the scale of the probable provenance area. The results were compared with modern day river systems, for example those supplied by rapidly-eroding orogens.
What did we find?
During the Early Triassic, sediment supply was at its peak. It was larger than those of the biggest modern-day river systems, and comparable to modern-day margins supplied by tectonically active orogens. The Middle Triassic sediment load was significantly lower but still comparable to that of the top 10 largest modern rivers. During the Late Triassic, sediment load increased again. Significant bypass took place, meaning that sediments from the eastern source area will have been distributed more widely in the greater Arctic.
The Early Triassic sediment supply was a direct and indirect result of emplacement of the Siberian Traps Large Igneous Province, the most extensive known volcanic episode in Earth’s history. This event caused reactivation and uplift of both cratons and adjacent orogens, and a global temperature increase that probably led to the collapse of most onshore vegetation, leading in turn to extreme weathering and runoff into the adjacent seas. Triassic sediments in the Greater Barents Sea have typically been attributed to erosion from the developing Ural mountain chain. However, the sediment supply was so large that a much bigger provenance area is needed. The area probably included large parts of what is now the huge West Siberia Basin and the East Siberian platform.
I’m thrilled that this talented researcher and her back-up team wanted me to participate in this exciting study. A follow-up paper, coming soon, will demonstrate the signature and significance of the episode in the wider Arctic area.
