engleski

The Late Jurassic Tithonian, a greenhouse phase in the Middle Jurassic-Early Cretaceous "cool" mode: evidence from the cyclic Adriatic Platform, Croatia

Well-exposed Mesozoic sections of the Bahama-like Adriatic Platform along the Dalmatian coast (southern Croatia) reveal the detailed stacking patterns of cyclic facies within the rapidly subsiding Late Jurassic (Tithonian) shallow platform-interior (over 750 m thick, ca 5-6 Myr duration). Facies within parasequences include dasyclad-oncoid mudstone-wackestone-floatstone and skeletal-peloid wackestone-packstone (shallow lagoon), intraclast-peloid packstone and grainstone (shoal), radial-ooid grainstone (hypersaline shallow subtidal/intertidal shoals and ponds), lime mudstone (restricted lagoon), fenestral carbonates and microbial laminites (tidal flat). Parasequences in the overall transgressive Lower Tithonian sections are 1-4.5 m thick, and dominated by subtidal facies, some of which are capped by very shallow-water grainstone-packstone or restricted lime mudstone ; laminated tidal caps become common only towards the interior of the platform. Parasequences in the regressive Upper Tithonian are dominated by peritidal facies with distinctive basal oolite units and well-developed laminate caps. Maximum water depths of facies within parasequences (estimated from stratigraphic distance of the facies to the base of the tidal flat units capping parasequences) were generally <4 m, and facies show strongly overlapping depth ranges suggesting facies mosaics. Parasequences were formed by precessional (20 kyr) orbital forcing and form parasequence sets of 100 and 400 kyr eccentricity bundles. Parasequences are arranged in third-order sequences that lack significant bounding disconformities, and are evident on accommodation (Fischer) plots of cumulative departure from average cycle thickness plotted against cycle number or stratigraphic position. Modelling suggests that precessional sea-level changes were small (several metres) as were eccentricity sea-level changes (or precessional sea-level changes modulated by eccentricity), supporting a global, hot greenhouse climate for the Late Jurassic (Tithonian) within the overall "cool" mode of the Middle Jurassic to Early Cretaceous.

Adriatic Platform; Croatia; greenhouse; Late Jurassic; precession

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