Geology and paleontology of Tresjuncos (Cuenca, Spain), a new diatomaceous deposit with Konservat-Lagerstätte characteristics from the European late Miocene.

Abstract

Purpose A new Iberian Konservat-Lagersta¨tte discovered in Tresjuncos (Cuenca, Spain) is described and interpreted based on geological and paleontological information. Methods The samples were studied using conventional mineralogical (powder X-ray diffraction), petrographic (optical and scanning electron microscopy) and geochemical (X-ray energy-dispersive spectrometry) techniques. Results Based upon geological context, stratigraphy, lithology, sedimentology and origin of the rocks, we describe and interpret the new fossil site as originated in a lacustrine environment. The micromammals found in the Tresjuncos 1 outcrop suggest that the main site is Turolian in age (uppermost Miocene), continental chronological unit MN13. The fossils are preserved in laminates comprising rhythmic, millimeterscale alternations of diatomites and calcareous diatomites. An analysis of the lake paleobiota includes amphibians, crustaceans, insects, plants, and diatoms. The diatoms are dominated by Cyclotella iris. The whole assemblage is indicative of a planktic community developed in somewhat alkaline waters. An extremely well preserved premetamorphic Pelobates (Pelobatidae) tadpole was discovered; it is remarkable because of its gigantic size. Its digestive tract predominantly contains the rare diatom Navicula halionata var directa, likely associated with the shore vegetation in which it presumably lived and fed. The arthropods form a typical lacustrine aquatic assemblage, lacking fish. This assemblage is made up of small filtering crustaceans and of both predator and nonpredator insects of diverse sizes. Conclusions The available evidence on Tresjuncos shows the extraordinary potential for paleontological information that can be expected from this new Konservat-Lagersta¨tte, which constitutes a significant finding that improves our understanding of continental late Miocene Mediterranean environments.