Seminar Sum-Up: Hutton Club 28/9/18


On Thursday 28th of September 2018 I attended a seminar on Sediment Routing Systems in Extreme Climates taken by Sébastien Castelltort from the University of Geneva. The seminar primarily focused on the response of sediment systems to climate change with a case study from the North of Spain, in the Pyrenees. Focusing on the Tremp-Graus basin near Aren and Roda situated in the South Pyrenean foreland basin.

The seminar sought to highlight how powerful sediment supply and processes can be and how they can dominate stratigraphic signals. Also, the seminar demonstrates how sensitive climate is to temperature change and how future global warming may be affected by this.

The sedimentology of the Tremp-Graus basin was focused on first by Sébastien – due to the presence of a thick conglomerate layer at the Palaeocene-Eocene boundary, known as the Claret Conglomerate. It was deposited during the Paleocene-Eocene Thermal Maximum 'PETM' – where warming of 5-8⁰C occurred so a hypothesis can be put forward: An increase in temperature leads to seasonal extreme precipitation and high energy flooding causing transportation of huge clasts and deposition of a vast braid plain - the Claret conglomerate. Techniques such as grainsize measuring were exemplified to quantify paleodischarge. The results showed grainsize was consistent – all fine-grained floodplain material is gone, and the channel width dramatically increased in the PETM. The hypothesis can be accepted on this evidence inferring a huge flood due to seasonally increased precipitation into the floodplain deposited thick gravel and flushed the fine-grained floodplain material away.

The sedimentology of Roda was then highlighted as this was the delta in the foreland basin of the South Pyrenees. During the PETM there were climate fluctuations within, categorised as Hyperthermals – when it was warmer and Hypothermals – when it was colder. The Roda succession displays cycles of clastics and limestones alternating, and this can be explained by the upstream sediment changes which were affected by the hyper and hypo thermal climate fluctuations imposed on the PETM. Supply forced regression occurred during hyperthermals due to increased weathering and higher river transport leading to this conglomerate braid and clastic deposition. Colder hypothermals resulted in a starved sediment supply resulting in the Roda carbonate accumulation.

This seminar showed how climate controls the source of the river sediment and impacts the sink sediment – exemplified by the stratigraphy of the Tremp-Graus basin and the Roda succession. This proves the stratigraphic signal can dominate over sea level and tectonic change. Current global warming is moving faster than conditions in the PETM and so this seminar enhances our knowledge on how the climate and seasonality may change in the future and how weathering and sediment processes might respond.

 - Meg

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