T42 Sedimentary Geology of the Next Generation: Student Posters (Posters)

Sunday, 18 October 2009
9:00 AM - 6:00 PM
Hall A

PERITIDAL AND SUBAERIAL EXPOSURE FACIES OF LATE VALANGINIAN TO LATE HAUTERIVIAN PLATFORM-INTERIOR CARBONATES, MLJET ISLAND, CROATIA

Paper number: T42-14
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

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. Some shallowing-upward dolomudstone-to-laminite parasequences are capped by few-centimeter-thick reworked intraclast, paleosol layers.

The Hauterivian parasequences are dominated by subtidal facies and consist of, from base to top, (1) transgressive fenestral laminites (rare, resting on rooted horizons with karstic tops) or transgressive 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 lime mudstone-wackestone to floatstone with gastropods, clams, benthic foraminifera and calcareous algae, and branching, cm-wide peloid-filled burrows; (3) regressive fenestral laminites (upper intertidal/supratidal); and (4) karstified tops with incipient breccia of granule-to-pebble-size angular clasts in lime mudstone matrix or dolomitic green shale (emergence horizons); underlying facies commonly are rooted-disrupted and may have branching rootlets and leached mollusks infilled with green shaly dolomite. Some parasequences are completely dolomitized. Some upward deepening parasequences capped by paleosols are suggestive of Fischer’s original Lofer cycles. The facies strongly suggest deposition under dominantly humid climate, and the abundant paleosols suggest significant repeated exposure events.