Naslov
High-resolution sequence stratigraphy of a Late Jurassic Adriatic platform: carbonate isotopic signature and greenhouse vs transitional eustasy

Autori
Husinec, A. ; Read, J. Fred

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, ostalo

Skup
27th Regional Meeting of the International Association of Sedimentologists

Mjesto i datum
Alghero, Italija, 20.09.2009. - 23.09.2009

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
Sequence Stratigraphy; LAte Jurassic Adriatic Platform; Stable Isotopes; Greenhouse; Transitional Eutasy

Sažetak
Late Jurassic carbonates, Adriatic platform, Croatia are being studied to evaluate their paleoclimate signal. The Kimmeridgian supersequence has 2 major sequences bounded by breccia. The lower sequence contains 2 high frequency sequences separated by a breccia. Parasequences are 0.5 to 3 m thick, dominated by lump-oncoid wackestone-mudstone capped by lime mudstone and microbial laminite ; packstone-grainstones are rare. In the lower Kimmeridgian sequence, lump-skeletal wackstone and mudstone cap most parasequences ; microbial laminite caps parasequences in late highstands of the Kimmeridgian sequences. The Tithonian supersequence has 4 smaller scale sequences. The lower Tithonian is dominated by subtidal parasequences and the upper Tithonian by peritidal and oolitic parasequences. Parasequences are 1 to 5 m thick units of basal subtidal skeletal-oncoidal wackestone-mudstone, up into intraclast-peloid packstone grainstone. In more interior areas, bases of parasequences have transgressive ooid grainstone ; regressive oolitic units are rare. Lime mudstone caps most parasequences near the platform margin, while elsewhere microbial fenestral laminites cap cycles. Clayey breccias occur at sequence boundaries in the interior of the platform. The cyclic facies suggests greenhouse low amplitude sea level changes within the precessional band, crudely based on the duration of the Tithonian and number of cycles. Carbon and oxygen isotopes were obtained from carbonate mud matrix of the Lower Tithonian dasyclad-oncoid mudstone-wackestone (shallow lagoon) ; one set at 5 m intervals from a 200 m thick section closer to the platform margin, and the other from 1 m intervals from a 200 m thick section in the more inboard part of the platform. Isotope values PDB of dolomite are compatible with semi-arid tidal flat origin with δ18O values 2 to 4 ‰ heavier than the calcite mudstones that have average values of marine calcite (0.0 to -3.0 ‰). Many of the small positive excursions in C isotopes appear to correlate with the high relative sea level stands, suggesting that carbon is being sequestered during high frequency high stands of sea level (100 k.y.?), or that organic productivity in the photic zone is high during the high frequency highstands, perhaps related to the large area of platform that is shallowly submerged ; effects of diagenesis are also being evaluated.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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