LATE VALANGINIAN TO EARLY BARREMIAN PERITIDAL FACIES OF THE ADRIATIC PLATFORM, CROATIA: EVIDENCE OF SUBAERIAL EXPOSURE

A continuous, 300-meters-thick Late Valanginian to Early Barremian section is exposed on Mljet Island, Croatia. It was deposited on the tectonically stable Adriatic carbonate platform interior. The Late Valanginian facies are massive to thick-bedded coarse sucrosic dolomudstone. Local dolowackestone-mudstone to floatstone interbeds with scattered gastropod molds are common; non-dolomitized wacke-mudstone containing gastropods and algal fragments are rare. Fenestral and planar lamination occur in rare peritidal laminites. Some shallowing-upward dolomudstone-to-laminite parasequences are capped by intraclast-paleosol layers a few centimeters thick.

The later Barremian and Hauterivian succession is cyclic with parasequences dominated by subtidal facies. The parasequences consist of, from bottom to top, 1) trangressive fenestral laminites resting on karstic rooted horizons or lags of microbial lump and pisoid wackestone-packstone to floatstone, or thin dark-colored, coarse ooid rudstone with broken-and-rehealed ooids; 2) well developed subtidal units of peloid floatstone with gastropods, clams, benthic foraminifera and calcareous algae, and branching, cm-wide peloid-filled burrows to peloid lime mudstone-wackestone; 3) regressive upper intertidal/supratidal fenestral laminites; and 4) incipient breccias of granule-to-pebble-size angular carbonate clasts in lime mudstone matrix or dolomitic green shale (emergence horizons) with karsified tops. Facies beneath karstic horizons contain leached mollusks, are commonly highly root-disrupted and branching rootlets infilled with green shaly dolomite. Rare upward deepening parasequences capped by paleosols are suggestive of Fischer’s Lofer cycles. Presence of roots and lack of evaporites suggests a dominantly humid climate. The major sequence boundary in the Early Barremian is marked by close-spaced amalgameted breccias.