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Peritidal and Subaerial Exposure Facies of Late Valanginian to Late Hauterivian Platform-Interior Carbonates, Mljet Island, Croatia

The 240-meter-thick Late Valanginian to Late Hauterivian roadcut section on Mljet Island, Croatia was deposited in a tectonically stable Adriatic carbonate platform interior. The Valanginian is dominated by massive to very-thick-bedded cream, coarse sucrosic dolomudstone. This subtidal facies locally contains scattered gastropod molds and/or interbeds of gastropod-mold dolowackestone-mudstone to floatstone ; non-dolomitized gastropod-algal wackestone-mudstone is very rare. Peritidal laminites are rare ; fine-scale faint lamination in coarse sucrosic dolomite is fenestral and planar. Shallowing-upward dolomudstone-to-laminite parasequences are infrequently capped by few-centimeter-thick reworked intraclast, paleosol-like layers. The Hauterivian is dominated by well developed subtidal cycles with basal rooted horizons and mainly fenestral laminite caps suggesting humid subtidal to emergent conditions. The most common facies is peloid lime mudstone-wackestone to floatstone with branching, up to 1-cm-wide root burrows ; some horizons are heavily root-disrupted with green dolomitized shale fills, or completely dolomitized and represented by olive-gray, root-disrupted sucrosic dolomudstone. This facies also contains gastropods, clams, benthic foraminifera and calcareous algae, as well as pockets of peloid packstone ; clams and gastropods are locally leached and molds are filled with green shale. Root-disrupted horizons sporadically exhibit highly irregular and karstified tops with incipient breccia composed of granule-to-pebble-size angular clasts in lime mudstone matrix or dolomitized green shaly interstices. Laminated facies (upper intertidal to supratidal) commonly overlies rooted horizons and is distinguishable by fenestral peloid packstone and mudstone, frequently with sharp tops. Locally, fenestral laminites are transgressive ; they overlie rooted horizons with karstified tops and grade up into massive, rooted mudstone-wackestone. Transgressive, deepening parts of subtidal cycles are less frequently characterized by transgressive lags of microbial-lump and pisoid wackestone-packstone to floatstone, and thin dark-colored, broken-and-rehealed coarse ooid rudstone.

Valanginian; Hauterivian; Platform Carbonates; Croatia; Mljet

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