Jurassic fern Piazopteris from the Girón Group, Colombia: A taxonomic and paleoenvironmental evaluation

This study investigates a new set of fossil tree ferns from the Late Jurassic Girón Group in the Eastern Cordillera of Colombia. Located on carbonaceous mudstones from the La Honda Creek, we analyzed six specimens tentatively identified as Piazopteris cf. branneri (Matoniaceae). Using thin-section petrography, scanning electron microscopy (SEM), and carbon geochemistry, including total organic carbon (TOC) and stable carbon isotope analyses (δ¹³C_org), we characterize the sedimentological context and paleoenvironmental conditions associated with these fossil remains. The lithofacies, primarily composed of dark-gray mudstone, reveal significant organic matter accumulation and suggests a low-energy depositional environment with fair organic matter preservation, likely a swampy and humid setting. Geochemical analyses, including δ¹³C_org values are consistent with this interpretation, and suggest conditions in a tropical to subtropical climate typical of the Jurassic. These findings provide new insights into the Mesozoic paleoenvironments and flora of the circum-Caribbean region and underscores the importance of the Girón Group to develop future paleobotanical studies in Colombia.