Microbialites and trace fossils from a Middle Triassic restricted carbonate ramp in the Catalan Basin, Spain: evaluating environmental and evolutionary controls in an epicontinental setting

The timing of recovery after the end-Permian mass extinction has been a matter of debate, with some authors favouring a more rapid faunal recovery during the Early Triassic and others considering a more protracted biotic reestablishment spanning until the Middle Triassic. In this work, we investigated the lowermost Middle Triassic (Ladinian) carbonate deposits in the Catalan Basin to evaluate the potential environmental mechanisms and evolutionary constrains involved in the kilometre-scale predominance of microbialites and the low-diversity and high-density Planolites association in a low-latitude epicontinental setting. The studied sedimentary succession records the development from a low-gradient, homoclinal microbial-dominated carbonate ramp evolving towards a slightly inclined swell-dominated type. Sedimentological analysis suggests that facies heterogeneity was controlled by pulses of syn-rift tectonic activity, which compromised Peri-Tethyan basin connectivity, reducing palaeobathymetry gradients. Although the monospecific nature of the studied trace-fossil association may reflect the delayed recovery after the end-Permian mass extinction, this is inconsistent with widespread, relatively high-diversity ichnofaunas in carbonates elsewhere in the region. Since other Ladinian basins were characterized by the recurrence of microbial carbonates, low-diversity ichnoassemblages and limited skeletal production, we hypothesize that shallow and restricted carbonate ramp settings harboured limited ecological complexity and widespread opportunistic colonization of the sediment when compared to coeval open marine locations.