Early Cretaceous dendritic shrub-like fabric in karstified peritidal carbonates from southern Italy

Abstract

Lower Cretaceous (Valanginian) dendritic microfabrics occur in karstic cavities within fine-grained shallow-marine platform carbonates at San Lorenzello, southern Italy. They form dense micritic masses and clusters, generally oriented perpendicularly to cavity surfaces, surrounded by layered sparry cement. Individual dendrites, typically sub-millimetric in size, have highly irregular margins and form distinctive shrub-like masses ranging from compact and squat, to elongate and highly branched. The centimetric and irregularly elongate cavities appear to have formed through subaerial exposure, and are almost entirely filled by the micritic dendrites and associated sparry crusts. In size, shape and micritic composition, the dendrites broadly resemble a variety of similar fabrics, including hot spring travertine shrubs and calcified microfossils such as Cambrian Angusticellularia, which has analogs in present-day lacustrine calcified cyanobacteria. However, the San Lorenzello dendrites differ in occupying small cavities. This cryptic microkarstic dripstone setting, together with the often regular spacing and appearance of these dendritic fabrics, may be more consistent with an abiotic origin. These comparisons underscore the challenge of interpreting microdendritic carbonates fabrics in general.