Holocene paleohydrology of playa lakes in northern and central Spain: A reconstruction based on the mineral composition of lacustrine sediments

The focus of this study is the reconstruction of Holocene limnic conditions of playa lakes in central Spain using inorganic components of their sedime nts. It is demonstrated that the mineralogical sediment characters provide valuable paleoenvironmental information: If dolomites originate from authig enic precipitation or early diagenetic dolomitization, the Mg-Ca-ratio of d olomites, derived from the position of dolomite's major X-ray diffraction l ine, turns out to be an indicator for the reconstruction of paleosalinity. In contrast, the concentrations of carbonates and sulphatic evaporites and their changing proportion to siliciclastic sediments point to changing depo sitional environments. The comparison of investigations from different play a lakes and drainage basin systems shows that the interpretation of mineral ogical sediment features always has to consider the petrographic, hydrologi c, and geomorphic features of the catchment. As for the lacustrine sediment s investigated there are no data available yet, a preliminary chronological Framework is derived by comparison with results from neighbouring areas. B ased on this the hypothesis is put forward that during the so-called Little Ice Age subhumid environmental conditions occurred over the central part o f the Iberian Peninsula, while today climatic conditions are dry-subhumid t o subarid. Also for times older than the Subatlantic distinct changes of en vironmental conditions are noticed, but various hiatuses in the sediments m ake correlation difficult. (C) 2000 Elsevier Science Ltd and INQUA. All rig hts reserved.