Short-term colonization trace-fossil assemblages in a carbonate lacustrineKonservat-Lagerstatte (Las Hoyas fossil site, Lower Cretaceous, Cuenca, central Spain)

Rhythmically laminated fine-grained lacustrine carbonates of the Cretaceous La Huerguina Limestone Formation at Las Hoyas fossil site, central Spain, contain not only a spectacular body fossil fauna, but also vertebrate and i nvertebrate trace fossils. The study of the Las Hoyas invertebrate ichnofau na provides valuable taphonomic, paleoecological and paleoenvironmental inf ormation and represents one of the first attempts to study in detail a lacu strine trace-fossil assemblage in carbonate rocks. The Las Hoyas ichnofauna includes Cruziana problematica, Helminthoidichnites tenuis, Lockeia isp., Palaeophycus tubularis, and Treptichnus pollardi. This assemblage is charac terized by low ichnodiversity and small burrow size, and it is dominated by surface trails and extremely shallow burrows produced mostly by detritus f eeders. The Las Hoyas ichnofauna indicates low to moderately low energy, pe rmanently submerged, shallow-lacustrine areas. The ichnofauna is suggestive of environmental stress, most likely oxygen-depleted conditions in interst itial waters. Occurrence of traces in event beds indicates opportunistic co lonization by epifauna and very shallow infauna during brief periods of imp roved oxygenation related to the passage of density underflows and dilute t urbidity currents. The Las Hoyas ichnofauna resembles other shallow lacustr ine trace-fossil assemblages of the archetypal Mermia ichnofacies and diffe rs significantly from the archetypal Scoyenia ichnofacies. It is therefore best regarded as a proximal, depauperate example of the Mermia ichnofacies. The Las Hoyas assemblage is similar to the slightly older lacustrine Monts ec ichnofauna, but it is remarkably different from marine ichnocoenoses of other Mesozoic konservat-lagerstatten in lithographic limestones such as th ose of Cerin, Solnhofen and Nusplingen.