UNDERGRADUATE FIELD EXPERIENCE IN L'AINSA, HUESCA, SPAIN: PIGGY-BACK BASINS, PARALICS, AND THE PYRENEAN OROGENY

The Sam Houston State University (SHSU) geology program has offered variations of a biennial, spring break trip to the Spanish Pyrenees for more than two decades. The trips have been, by necessity, limited to a small number of participants – generally eight to ten upperclassmen and one or two faculty. The field experience is based out of L’Ainsa, Spain. L’Ainsa is a small, medieval village (pop. ~2,180) that dates from the 11^th century and is ideally located in the heart of the Sobrarbe Geopark – one of fifty-nine European Geoparks designated by UNESCO. The Ainsa-Sobrarbe region covers more than 2,200 km² and has a population of just 7,000 inhabitants. Geologically, L’Ainsa is located just south of the Paleozoic metamorphic core of the Pyrenees, known as the Axial Zone. The Axial Zone is flanked on the north and south by younger Mesozoic rocks that formed dual foreland-fold and thrust belts during the collision of the Iberian and European plates 50 – 29 mya. The Mesozoic rocks are interpreted to have been deposited in an aulacogen developed during the break up of Pangea that effectively isolated the Iberian micro-plate and formed a deep sedimentary basin during the Late Jurassic to Early Cretaceous. During the maximum uplift of the Pyrenees (Eocene to Oligocene), a number of piggy-back basins formed parallel to the orogenic front as thrust sheets propagated into the foreland and were filled by molasse shed from the Axial Zone and deposited by large deltaic complexes. As the foreland-fold and thrust belts formed, large antiformal stacks were exposed subaerially that lead to a number of angular conformities as the piggy-back basins formed. Students are given a field guidebook and an extended bibliography prior to spending ten days exploring the geology and culture of the Ainsa-Sobrarbe region. The field experience is not run as a ‘for credit’ course, but all participants have the option of completing directed research for credit. Cost per student during the Spring 2014 trip was approximately $775 plus airfare, which includes ground transportation, lodging, and meals.