The second year field trip to Almeria, SE Spain by Jack Lacey

Posted by lcb14 at Sep 20, 2013 10:55 AM |
In September Geology students going into their second year attend a fieldtrip to Almeria in SE Spain for 7 days. During the trip they learn about geological field methods including advanced mapping, logging sedimentary successions and unraveling complex structures and tectonic histories. Here is a blog by PhD student Jack Lacey who was one of the demonstrators on the first trip (of two) this year…
The second year field trip to Almeria, SE Spain by Jack Lacey

Jack at the Carboneras Fault Zone

We arrived late Thursday in Almeria, and started our journey by coach to the Urra field center - our home for the next week. After a day of travelling the evening meal was well received and the lecture to follow on the local geology and regional context was, albeit at a late hour, listened to in full. The local (and onsite) drinking establishment – The Shady Grove – was the next port of call for a deserved beer, which saw out the rest of the night.

The first field day on Friday incorporated two activities in the area of Peñas Negras, to the south of the Sorbas basin. For the initial half of the day students looked at structural features and metamorphism in basement rocks and the other half was spent investigating a magnificent road section which shows an unconformity between the >200 million year old basement and the younger 8 million year old sediment infill. On top of this, literally, was a second unconformity with an overlying conglomerate. The students did an excellent job interpreting and recording data, later turning these observations into a generalised vertical section to present an overview of the geological sequence.   

Spain students logging
Students logging a sedimentary succession dominated by turbidites
Over the weekend we were in the Tabernas basin, southwest of Friday’s location near Sorbas, where students undertook the first assessed exercises of the trip. This was firstly to create a geological map of a complex structural area and secondly to construct two sedimentary logs through turbidite successions. Temperatures were high before we arrived at the field locality and continued to rise through both days; one could have fried an egg on the coarse grained sandstones! We found some interesting features including flame structures, soft-sediment deformation, trace fossils and current ripples, to name but a few. The detailed interpretation and commitment were mirrored from the previous day, in the field and also in the evening when completing work – a great effort all round.

The clouds rolled in on Monday morning and provided some relief from soaring temperatures, in the morning at least, as the group traversed the Rambla de Sierra canyon to create a cross section for the third assessment task. The rambla is located close to the weekend location in the Tabernas Basin, which has been used for scenes in several films, including Lawrence of Arabia, The Good The Bad and The Ugly and more recently Doctor Who. In the afternoon we visited the Carboneras Fault Zone where large-scale deformation can be seen in an amazing section near Sopalmo. The chemistry has been altered to produce a plethora of multi-coloured rocks – which are both geologically interesting and a pleasure to look at!

Spain Cerro del Hoyazo
On top of Cerro del Hoyazo, an extinct volcano fringed by reefs
On Tuesday we travelled to a locality close to Níjar, and after departing the coach trekked through a canyon into Cerro del Hoyazo. This extinct volcano has a dacite core with xenoliths of garnet-mica-schist (some over a meter wide!), and a coral reef that encircles the summit rim. The garnets readily weather out of the igneous rock and can be collected from dried streambeds in large volumes. Over the day students investigated various features including the limestone/igneous contact, large thrombolites and the structure/content of the reef. In the late afternoon we visited the town of Níjar, notable for its ceramics, for some touristic leisure time and a refreshing beverage.

Friday was another split day with two localities to visit, the first near El Pilar to look at metamorphic basement rocks and the second in Rambla de Gochar to investigate an amazing sedimentary succession. The basement rocks had recumbent isoclinal folding consisting of dolerites and marble, whose structure and composition suggests they had undergone regional metamorphism. Moving upwards, both topographically and stratigraphically, we then encountered an ophiolitic rock type (old oceanic crust) that contained serpentinite and exhibited a crenulation cleavage. In the afternoon we walked down Rambla de Gochar, logging through a sedimentary succession with stromatolitic limestones, conglomerates and fluvial sandstones. A sudden change in the weather meant we had to take cover under a bridge (since not everyone had waterproofs!) to watch a spectacular thunder and lightning show. Later that evening we had a marvelous paella washed down with homemade sangria – a fitting and extremely tasty meal on the last night.

The group outside the Shady Grove, a fine place to get some shade and a cool beer at the end of a long dayThat brings us to today… our last day in Spain, and the best is saved for last! We walked out from Urra through the dried bed of the Rio de Aguas to look at the result of the Messinian Salinity Crisis, where around 6 million years ago the Straight of Gibraltar closed and prevented the transfer for water from the Atlantic Ocean to the Mediterranean Sea. Reduced water input resulted in the Med evaporating and forming thick gypsum deposits that are revealed in an impressive cliff section, showing both thin layering and large cone-like structures. The coach will arrive imminently to transport us back to the airport to await the flight back to the UK, while at the same time Group B are travelling out for their week in Spain.

The past week has been a truly memorable field trip with enthusiasm and sustained intrigue from all of the 2nd year students throughout. Hopefully the weather will remain warm and dry for Group B!    

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