FACIES STACKING PATTERN, SEQUENCE STRATIGRAPHY AND CARBON-ISOTOPE SIGNATURE OF ALBIAN PLATFORM-INTERIOR CARBONATES, SOUTHERN CROATIA

The Albian succession of Adriatic platform in southern Croatia is an overall shallowing upward supersequence reaching more than 400 meters. Based on detailed bed-by-bed analysis of two 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. These meter-scale shallowing-upward cycles 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 intra/lithoclast floatstone-rudstone or dolomite. Major skeletal components are calcareous algae and benthic foraminifera.

The two logged sections from southern Croatia were sampled for carbon and oxygen isotopes at 1 meter intervals. The mean values for carbon are +0.55‰ PDB, and -1.96‰ PDB for oxygen. The base of the Albian sequence Alb1 corresponds to the oceanic anoxic event OAE1b and is characterized by a stepwise negative excursion of δ¹³C, reaching a minimum value of -6.52‰ PDB. Sequence Alb2 begins with a positive δ¹³C excursion, followed by carbon isotope values varying within the range -6.52‰ PDB to +2.19 ‰ PDB; Sequence Alb3 represents a low period of δ¹³C values, with the minimum value of -5.54 ‰ PDB. Sequence Alb4 encompasses both the highest and lowest values of δ¹³C within the Upper Albian part of the supersequence, +2.19‰ and -4.77‰ PDB, respectively. Carbon chemostratigraphy and its possible relationship to sequence stratigraphy is tested.