La reconstrucción de paleoambientes cuaternarios: ideas, ejemplos y una síntesis de la evolución del Holoceno en el NW de la Península Ibérica

This paper is the consequence af an invited presentation given at the Facultade de Letras do Porto during lhe II Jornadas do Quaternário «Quaternary, Natural and Cultural Heritage» held at Porto (Portugal). It deals wiith a personal view on how to reconstruct Quaternary palaeonvironments, based on the experience gained during lhe last fifteen years collaborating with researchers of many disciplines, although I have to aknowledge lo archaeologists and prehistoricians for triggering my interest. Present environment can be considered as a dynamic system of emergent complexity, product of the many interactions -feedbacks, couplings, perturbations, inductions, metachronicities, ... – stablished amongst its constituent parts -basically the lithosphere, the atmosphere, the hydrosphere and the biosphere; playing humans an increasing role among biota-. So have to be considered past environments or palaeoenvironments. This complexity demands an integrated, interdisciplinary view of research for a reasonable reconstruction. The object of analysis is the archive, an entity that contains a record of environmental changes -polar and glacier ice and snow, lake and ocean sediments, peat bogs, tree rings, ... - While any property resulting from a change that can be measured and interpreted can be considered as a signal -biotic or abiotic-. Natural archives are the memory of the geosystem. Under the influence of environmental conditions superficial formations of the lithosphere undergo processes that are responsible for their properties - physico-chemical, mineralogical, biological, etc, ... - In this sense, palaeoenvironmental reconstruction tries to follow the inverse intinerary: from present observed properties to stablish the processes related to their genesis and from those we try to uncover the past environments that governed them. Nevertheless, we have to be aware of the fact that progressive and regressive pathways are both likely to have ocurred, so information was sometimes stored and sometimes deleted from the archives. In fact, the further we go back in time the less information we are able toobtain. It is also important to remind that reconstruction is always partial, as it is impossible to obtain cluesof all the complexities, and even some past environments may have had conditions which are not comparable to any present environment. With these ideas as background framework I briefly introduce here some aspects on the properties of archives and signals, propose an approach to Quaternary palaeoenvironments reconstruction, give some insights on the relationships between human activities, archaeological sites and past environments, put some examples of archives we have been using and results obtained, and end up with a synthesis of the Holocene evolution of Northwestern Spain.