Sequence analysis, cyclostratigraphy and palynofacies of early Anisian carbonate ramp deposits, NW Bulgaria

A sequence- and cyclostratigraphic interpretation of early Anisian (Aegean) shallow-marine carbonate ramp deposits, exposed in outcrop sections west of Tserovo village, NW Bulgaria, is presented. The hierarchical pattern identified can be interpreted in terms of Milankovitch cyclicity with elementary sequences representing the precession (20-kyr) cycle, small-scale sequences the short eccentricity (100-kyr), and medium-scale sequences the long eccentricity (400-kyr) cycle. Palynology provides a robust stratigraphic framework. The study of sedimentary organic matter, revealing variations of terrestrial input, sorting and fragmentation of phytoclasts, and prominent acritarch peaks, allows the interpretation of environmental changes and contributes to the cyclostratigraphic and sequence-stratigraphic framework. The detailed documentation of syndepositional soft-sediment deformation structures confirms their laterally traceable distribution within the depositional sequences and makes them good palaeoenvironmental indicators. Anisian ramp systems of the western Tethyan realm thus were subjected to highly dynamic regimes, recording the interplay between sea-level changes in tune with orbital cycles and ramp morphology.