PETROGRAPHIC AND GEOCHEMICAL COMPARISON OF LIMESTONE AND CARBONATE BRECCIA FROM CALA MADONNA WITH THE CLASSIC TRIASSIC SHALLOWING-UPWARD CYCLES OF THE CAPO RAMA RESERVE (SICILY, ITALY)

This petrographic and stable isotope study compares Triassic (upper Norian) subtidal limestone and carbonate breccia from the Cala Madonna site at the Capo Rama Reserve in Sicily, Italy to better understand their formation and diagenetic histories in relation to the previously documented peritidal cycles of the classic Capo Rama succession. Examination of four pairs of samples from an irregular erosional contact at Cala Madonna indicates that the subtidal limestone above the contact consists of peloidal packstone and grainstone with some skeletal (ostracod, benthic foraminifera, algae and sponge) fragments. The limestone breccia below the contact mainly consists of clasts (2mm-7cm in diameter) of similar peloidal-skeletal packstone-grainstone in addition to wackestone and mudstone and less common clasts of sparite and laminated fenestral microbialite in hematitic matrix. All deposits are severely fractured and have veins filled with multiple generations of carbonate cement.

These calcitic Cala Madonna deposits differ from those of the previously described mainly dolomitic Capo Rama succession. Although both have been interpreted as cyclic tidal flat deposits, the Cala Madonna limestone examined here is indicative of subtidal carbonate platform interior deposition (i.e., back reef lagoon). Documented petrographic and stable isotope differences between the Cala Madonna subtidal limestone and carbonate breccia suggest that: 1) not all breccia clasts resemble the subtidal deposits from the base of the cycle; 2) breccia clasts are likely derived from subtidal to intertidal deposits from higher up in the cycles; 3) deposits from the basal vs. the upper parts of cycles differ in composition due to shallowing upward and environmental restriction. The origin of Cala Madonna carbonate breccia remains unclear, as it could represent periodic short-term exposure, tectonism (e.g., fault breccia), or platform-wide, longer-term exposure during the Late Triassic that resulted in a regional unconformity and karst formation. Future studies should include continuous sampling within and across multiple sedimentary cycles of both the Capo Rama and Cala Madonna successions to improve the interpretations of their depositional and diagenetic history and regional stratigraphic relationships.