The Silurian Ockerkalk of Sardinia (Italy): Stratigraphy, palaeontology, mineralogy and geological significance
Ferretti, Annalisa; Malferrari, Daniele; Corriga, Maria Giovanna; Corradini, Carlo
Newsletters on Stratigraphy (2026)
95 references
published online: Oct 22, 2026
manuscript accepted: Oct 15, 2026
manuscript revision requested: Oct 1, 2026
manuscript received: Aug 20, 2026
DOI: 10.1127/nos/0937
Abstract
The Ockerkalk is an informal ochre-coloured calcareous unit widely distributed across Europe and represents a key upper Silurian (Ludlow–Přídolí) stratigraphical interval, occurring in Thuringia (Germany), Sardinia (Italy), the Pyrenees (Spain), and the Czech Republic. Among these regions, the Silius–Gerrei area of southeastern Sardinia preserves one of the most complete and continuous Ockerkalk successions, where exceptionally well-exposed stratigraphical sections provide a unique record of late Silurian marine environments. The abundance of conodont faunas, together with the excellent preservation of sedimentary structures, makes this area particularly valuable for reconstructing late Silurian palaeoenvironmental conditions within a high-resolution biostratigraphical framework. Despite its wide geographical distribution, the overall stratigraphical significance and broader geological importance of the Ockerkalk have never been comprehensively evaluated. This study addresses this gap by integrating current knowledge of the unit’s lithostratigraphy, palaeontological content, and depositional architecture within a broader geological framework. A detailed mineralogical investigation is also carried out to identify the compositional and diagenetic factors responsible for the distinctive ochre coloration of the Ockerkalk and to assess their variation throughout the succession. By integrating lithostratigraphical observations, biostratigraphical constraints, and mineralogical and geochemical analyses, this study refines the stratigraphical framework of the Ockerkalk in Sardinia and clarifies its relationships with coeval peri-Gondwanan carbonate facies. The Ockerkalk records low-energy carbonate deposition in a moderately deep pelagic to hemipelagic setting with intermittent siliciclastic input, while its conodont biozones provide a robust high-resolution chronostratigraphical framework from the upper Gorstian to the upper Přídolí, demonstrating that the unit does not extend to the Silurian–Devonian boundary. Mineralogical and geochemical data show that the unit is strongly calcite-dominated (83.5–95.5 wt%), with subordinate illite and quartz and minor Fe-rich amorphous material concentrated in coatings and veins, indicating a significant post-depositional overprint related to thermal alteration and structurally controlled fluid circulation.
Keywords
Late Silurian • Peri-Gondwana • Biostratigraphy • Chronostratigraphy • Mineralogy • Diagenesis