Paleoenvironmental constraints influencing charophyte communities in an Early Cretaceous Karstic Lake, La Pedrera de Meià Konservat-Lagerstätte (Southern Pyrenees): combining geochemical and palaeoecological analyses.

Abstract

The combined sedimentological and palaeoecological analysis of charophyte-rich carbonate microfacies is proven to be a useful methodology for the palaeoenvironmental reconstruction of continental settings. However, the integration of these charophyte assemblages with geochemical proxies has not been explored, yet. In the present work, the charophyte-rich muddy carbonates of the Barremian La Pedrera de Meià Konservat-Lagerstätte (Southern Pyrenees, Spain) were studied from a taxonomic, taphonomic, and palaeoecological viewpoint, and the results were later integrated with previously published paleoenvironmental proxies (δ13C, δ18O, and elemental geochemistry). In the studied locality, monospecific Echinochara sp.–Charaxis spicatus meadows are only found in the temporary lakes recorded in the lower stages of lake infilling. The high Al, K, Fe and Ti concentrations and δ18O values previously described in these carbonates indicate meteoric infilling followed by evaporation periods. Freshwater and brackish communities are found in the upper stage of lake infilling. Freshwater settings had mixed meadows with Atopochara–Clavatoraxis, Clavatoroidae utricles–Clavatoraxis, and Ascidiella–Favargerella plants, while the brackish environments, that occurred laterally to freshwater, contain meadows dominated by porocharacean– Charaxis sp., and Echinochara sp.–Charaxis spicatus plants. Miliolids and broken dasycladaceans also occur in these facies. Sr/Ba ratios, REE + Y concentrations, and δ18O values previously reported in these lacustrine carbonates indicate prevalence of freshwater environments with occasional marine influence, which agrees with the occurrence of distinct brackish and freshwater charophyte assemblage and marine-affinity organisms, suggesting that during the last stage of lake evolution, the system was part of a coastal wetland. This work demonstrates that the integration of geochemical, palaeontological and palaeoecological datasets improves the understanding of the fossil continental carbonate settings and their evolution.