Facies and Cyclity of Barremian Peritidal Deposits, Southern Adriatic Platform, Croatia
The Jurassic-Cretaceous Adriatic Platform provides a window into tropical shallow-marine carbonate deposition in the western Tethys. The highly cyclic Barremian sediments are superbly exposed on the islands and mainland of southern Croatia. Five logged sections, ranging from 20 to 100 m thick, display superbly developed peritidal parasequences; the extensive Barremian microbial laminite facies likely contain the best preserved tidal flat facies compared to any Lower Cretaceous interval of the Adriatic Platform. The Barremian consists of 2 supersequences. The sequence boundary zone 1 in the Lower Barremian consists of up to 3 breccias. Supersequence 1 has at least 2 high frequency sequences. Sequence boundary zone 2 contains one to 2 breccias. Supersequence 2 has four high frequency sequences (HFS). Each HFS consists of shallowing upward succession with dominantly subtidal lower part, and laminated to fenestral upper part. Individual parasequences within each sequence are composed of shallow subtidal (lime mudstone and peloid-intraclast-skeletal packstone-grainstone) to intertidal (microbial laminites and fenestral lime mudstone) and subaerial exposure facies (greenish clay sheets or breccias with green clayey matrix). Presence of platform-wide subaerial exposure surfaces capping some cycles suggest relative sea level falls affected the platform over large areas. Most parasequences were formed by high-frequency sea level fluctuations perhaps related to orbital forcing; possible durations of the interval and its component parasequences are being evaluated to see if these are compatible with a precessional vs. longer term obliquity or eccentricity signals. Some parasequences probably also formed by auto cyclic processes and local tectonics associated with the impending (Aptian) collision between the Adriatic micro plate and Eurasia. Rapid thickness variations and facies changes over several tens of kilometers indicate that the synsedimentary differential subsidence (possibly over fault blocks) was a strong influence, with superimposed sea-level fluctuations generating the sequences and component cycles.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009