CONICET | Buscador de Institutos y Recursos Humanos

Field studies in a mesotidal flat in Bahia Blanca estuary, Argentina, reveal the presence of extensive areas with microbial mats, covering the upper-intertidal and lower-supratidal areas. Studies of recent environments with microbial mats increased considerably during the last years, not only because their unique sedimentologic and ecologic characteristics, but also because they provide important implications for the understanding of fossil environments and paleocommunities. The main purpose of this research was to evaluate the role of microbial mats in the preservation of biogenic structures. We recorded the distribution of recent traces all over the tidal-flat, although focused the analysis on the preservation of large bird tracks. Several footprints were selected and photographed, recording the morphological modifications they experienced during four months. During this time, most of the footprints showed resistance to tide- and wind-erosion, and also to heavy rains and storms that affected the tidal-flat. This resistance was clearly associated to the presence of the microbial mats, which are known to biostabilize the sediment. Also, microscopic analysis of the tidal-flat sediment revealed the presence of zeolites and calcite, suggesting early cementation, which may have favored the consolidation of the footprints. Mat-thickness also affected the morphology of the footprints; in areas with thick microbial mats overlying soupy sands, the tracks were deeply impressed and did not show fine details. On the contrary, in zones with thin microbial mats overlying relatively stiff muds, the traces were shallow and preserved details such as skin impressions and skid-marks. Also, both types of footprints were affected by mat growth, although in the shallow traces the modification was faster, and the fine details were progressively obliterated. This study yields valuable insights into the relationship between microbial mats and morphology of the footprints, and provides key information for the analysis of fossil tracks in equivalent paleoenvironments.