Sarah’s search for Jurassic charcoals

The presence of fossil charcoal within rocks indicates that wildfires have occurred in Earth’s ancient past. Variations in the amount of charcoal found in rocks are suggested to indicate changes in the frequency of palaeowildfires.

The Peniche coastline in Portugal hosts a unique rock outcrop, which exposes one of the most complete sections of sedimentary rocks of Jurassic age (the rocks are between 201 million years old and 145 million years old !). Throughout this long tract of time major climatic and atmospheric changes are believed to have occurred which likely had the ability to influence the frequency of wildfires.

amir chiselling

The sediments deposited here are made up of rocks known as marls (silty-clayey calcium carbonate rich sediments formed by loose clay/silt deposits under the sea) and limestones (hard, calcium carbonate rich rocks formed from ancient skeletal fragments of marine organisms e.g. corals). These sediments indicate that the past environment in which these rocks formed was likely to be a shallow carbonate ramp (nearshore setting). Due to its past nearshore setting, high preservation characteristics and complete record, Peniche offers one of the best places to study variations in fossilised charcoal that were deposited throughout the Early Jurassic period (approximately 174 to 182 million years ago).

Between the 19th and 22nd of May 2014 Sarah Baker, Dr Luis Duarte and field assistant Amir Abbasi ventured to Peniche, collecting samples from the rock section at Praia do Abalo (on the north coast) ready to be analysed for their charcoal content.  Rock samples were chiselled out of the rock section at regular intervals and then bagged. These samples are to be analysed for their charcoal content by Sarah Baker for her PhD thesis in an attempt to assess how fire frequency may have varied throughout the Early Jurassic period (Pliensbachian (182.7 to 190.8 million years old) to the Toarcian (174.1 to 182.7 million years old)).

Blogged by Sarah Baker