Middle and Late Jurassic record of sea-level, sequence development, and carbon-isotope fluctuations, Tethyan Adriatic Carbonate Platform, Croatia

Abstract

The Adriatic Platform, Croatia is a large isolated carbonate platform that developed under a warm greenhouse climate interspersed with cooler episodes in western Tethys. However, the δ13C record and high-resolution sequence stratigraphy of the Middle and Upper Jurassic portion generally is poorly known. The ~1900 m thick (30 Myr duration) mainly Middle to Upper Jurassic succession of the platform was studied bed-by-bed to track the fluctuations of δ13C, facies stacking into bundles, superbundles, and sequences and potential sea-level changes within ongoing studies of evidence of astronomical forcing of the units. The study interval consists of cyclic subtidal intervals (upper Toarcian-lower Aalenian, lower Callovian, Oxfordian, lower Kimmeridgian, and lower Tithonian) interspersed with highly cyclic peritidal units (upper Bajocian-lower Bathonian, upper Kimmeridgian, and upper Tithonian-basal Berriasian). Ages were constrained by biostratigraphy and δ13C chemostratigraphy. The absolute δ13C values obtained from the shallow-marine bulk carbonate matrix are similar to those from coeval pelagic carbonates and exhibit similar trends, are characterized by overall little data spread (<2‰), and generally show little resetting associated with disconformities and/or burial. This rock-buffered record likely preserved at least relative marine δ13C values with several major excursions, including the BjBaE (Bajocian-Bathonian), CaOxBE (Callovian-Oxfordian boundary), EOxE, and MOxE (Early and Middle Oxfordian). The studied interval provides a detailed record of Milankovitch induced platform-flooding and exposure at scales from ~1Myr to ~20 kyr. The study suggests that detailed research of similar thick Jurassic isolated platform successions could provide valuable records of δ13C, climate, and sea-level changes over relatively long geological intervals.