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Sequence Stratigraphy and Oxygen-Carbon Isotope Signal from Albian Platform-Interior Carbonates, Southern Croatia

Oates, Amelia C.*1; Husinec, Antun 1; Read, J. Fred 2
(1) Geology, St. Lawrence University, Canton, NY.
(2) Geological Sciences, Virginia Tech, Blacksburg, VA.

The Albian succession of Adriatic platform in southern Croatia is an overall shallowing upward supersequence more than 400 meters thick. Based on detailed bed-by-bed analysis of three sections (Korcula and Mljet Islands), the supersequence is composed of four large, 20 to 210-m-thick third order sequences. The sequences are composed of highly cyclic peritidal carbonate facies and bounded by emergence breccias. Albian sequence Alb1 is characterized by abundant diagenetic dolomites and post-Mesozoic cave fill deposits, whereas the base of sequence Alb2 lithology is predominately limestone. Sequences Alb2, Alb3 and Alb4 represent mixed lithologies, with thick sections of limestone and dolomite as well as some dolomitized limestone. The meter-scale shallowing-upward cycles that make up the sequences typically consist of, from bottom to top: (a) skeletal lime mudstone, locally heavily burrowed, with clams and oncoids; (b) pellet-skeletal wackestone with oncoids; (c) peloid-skeletal-intraclast wacke-packstone with scattered rudists and gastropods; (d) intraclast-peloid-skeletal grainstone; (e) gastropod-rudist-oncoid floatstone to rudstone with lime mudstone, skeletal-peloid, or coarse dolomite matrix; (f) barren lime mudstone with rare gastropod moulds; (e) fenestral laminite; (d) emergence breccias represented by lime clast floatstone-rudstone or dolomite. Major skeletal components are calcareous algae and benthic foraminifera.

The two logged sections were sampled at 1 meter intervals for carbon and oxygen isotopes. The overall mean values for carbon are +0.55‰ PDB, and -1.96‰ PDB for oxygen. The values of δ18O for the Albian limestones range from -4.60‰ PDB to +2.11‰ PDB with an average value for oxygen at -2.00‰ PDB. The values of δ13C for limestone lithology ranges from -6.43‰ PDB to +2.19‰ PDB with an average carbon value at +0.40‰ PDB. Dolomite lithology varies slightly from limestone with the δ18O values ranging from -4.85‰ PDB to +2.71‰ PDB and an average value of -1.31‰ PDB. The δ13C values were also determined for dolomites in the Albian succession and range from -5.45‰ PDB to +1.93‰ PDB with an average of +0.10‰ PDB. The δ18O values for both limestone and dolomite lithologies are very close in value whereas the δ13C values have a wider range for limestone lithologies than that of dolomites. The secular variability in the carbon stratigraphy versus sequence boundaries is tested.  

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California