Facies-Stacking Patterns in a Late-Jurassic Bahama-Type Platform Interior, Dinaric Platform, Croatia

Antun Husinec¹ and J. Fred Read^2
1 Institute of Geology (presently Virginia Tech), Zagreb, Croatia
² Virginia Tech, Blacksburg, VA

The immense, several kilometers thick Bahama-type carbonate platform of the Dinarides was initiated in the Permo-Triassic as a portion of a land-attached Tethyan platform. It developed into the Jurassic-Cretaceous isolated platform following breakup of the Adria microcontinent. Well exposed Mesozoic sections along the Dalmatian coast (S Croatia) reveal the detailed stacking patterns of facies within the Late Jurassic (Tithonian) shallow platform interior (over 700 m thick). Facies include deeper lagoon dasyclad wackestone, oncoid wackestone, shoal-water skeletal packstone and grainstone, restricted lagoon lime mudstone, tidal flat microbial laminites and fenestral carbonates, and transgressive, periodically emergent radial-ooid grainstone. Sections consist of 40-60 meter thick parasequence sets roughly 400 ky duration based on long-term accumulation rates. Lower Tithonian sets are dominated by thick subtidal parasequences passing up into thin, more shallow water parasequences. Upper Tithonian sets also have thick subtidal parasequences in lower parts passing up into thin muddy peritidal parasequences with oolitic bases and microbial laminite caps. Roughly 10-15 parasequences make up the 400 ky parasequence sets suggesting incompletely recorded obliquity-precessional forcing. Emergence near the Jurassic/Cretaceous boundary formed extensive sequence-bounding subaerial clayey limestone breccia horizons interstratified with lowermost Cretaceous (Berriasian) cyclic carbonates. The striking 400 ky packaging in the Late Jurassic has also been observed in the Early Cretaceous elsewhere by others, and ascribed to presence of some polar ice. The Jurassic-Cretaceous sections of the Dinaric platform in Croatia may provide important paleoclimatic data for this time interval during which some of the world's major petroleum reservoirs were generated.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005