Geology Graduate Grace Fitzgerald describes her field trip to the Tabernas Basin in Spain.
Having arrived in the South of Spain four days previous, I was now standing out in the heat drawing a sketch of an astounding feature. Spanish sunshine in March was just the cherry on top of the cake. While most of Ireland was receiving threats of snow I stood in a sandy valley in the Tabernas basin looking at one of the most marvellous things I think I will ever see.
The amazing structure I was capturing in my field notebook had been aptly named the Gordo Megabed. Gordo when translated means fat, which is certainly a useful adjective to describe the magnitude of this gigantic slump structure. I remember thinking to myself that I had never before imagined something could be preserved in such remarkable detail millions of years after it happened.
We concluded the megabed was a massive underwater landslide thought to have been created by the action of six cubic kilometers of material cascading off the side of a mountain and plunging into the sea. The colossal failure of the mountain side and the disturbance it created was now almost fully exposed in a Spanish valley in front of me, having been uplifted out of sea as the African and European tectonic plates came together squeezing Southern Spain. I found it hard to visualize the force the impact of this event would have generated and was not surprised that it could have produced a tsunami. An avalanche of large chunks of schist (a type of metamorphic rock) falling into the sea would certainly have triggered massive wave action. The response to this disturbance had been preserved along the top of the megabed as a layer made of sand washed off beaches by the tsunami waves. This was only day four of our field trip and even more surprises were in store for us.
We were a small group (eleven students and two lecturers) sweeping through the Tabernas Basin in Almeria along valleys to completely alien landscapes chockablock full of the most remarkable secrets about the history of the area.
Each day had the same routine but the things we studied were always new and exciting. We would get up and get dressed at 8am. Slap suncream on (which was very important considering the combination of pale students and the baking hot Spanish sun) and venture out to see the geological wonders of the area. We mapped and drew sketches, we took measurements of the orientations of features to understand how they had been reshaped by stresses within the Earth. After a hard day in the field we would return to our hostel to a beautiful Spanish meal and some of the local wine to discuss everything we’d seen and learnt that day.
We saw valleys full of garnets, a mineral that provides evidence of the burial of rocks kilometers below the surface in their past, which were then brought back to the surface and subjected to weathering processes. Enough of these beautiful red minerals were present that we could scoop them up and fill our pockets.
The sedimentary rocks deposited in the basins include evidence for major changes in the environment. There were walls of gypsum (calcium sulphate closely associated with salt) due to the drying out of sea during an event called the Messinian Salinity Crisis about 6 million years ago, when the whole of the Mediterranean dried down due to intense evaporation.
We mapped out areas where carbonate reefs once sat teeming with life now raised far above their original home, the sea that surrounded them long gone but its presence forever marked in the rock record. We were shown stromatolites which are amazing mounds created by layer upon layer of single celled photosynthesizing bacteria. They are an important record of ancient life and are preserved because of the ability of sand to stick between layers of the bacteria.
Another day, we were brought to one area remarkably similar to the Giant’s Causeway. However, it was not upright like the Irish equivalent. This created a wall of columnar jointed basalts you could meet head on. We were also taken to ancient submarine volcanoes that were no longer active and had been lifted above sea level over time. Understanding how the volcanic systems in the area once operated was a fascinating journey.
We had the chance to create sedimentary logs by crawling along the face of marine deposits and reproducing the ebb and flow of the tides on paper to understand how the sea system once operated locally. Recording the rise and fall of sea level this way is a skill that creates a beautiful graphic record of changes to these systems.
Geology is an amazingly interdisciplinary field. You must learn to appreciate the Earth as a dynamic and ever changing system, which is a story the rocks will happily tell you if you learn to read them. My trip to Almeria taught me the beauty of learning to read rocks and how mind blowing and dynamic the Earth we live on really is.