Cretaceous cyclic peritidal carbonates of the Apulia Carbonate Platform (Apulia, southern Italy) in a hierarchical sequence-stratigraphic perspective: A case study from the Murge area (the Giovinazzo sea-cliff section)

Cretaceous cyclic peritidal carbonates form the bulk of the Apulia Region in Italy and represent the vestiges of the Apulia Carbonate Platform. To show from a sequence stratigraphic perspective the architecture of peritidal carbonates, the 17 m thick Albian Giovinazzo sea-cliff section was studied at a centimetre detail, aiming to: (i) describe cyclic facies organisation in beds and bedsets; (ii) reconstruct the relative sea-level curve and its evolution over time; (iii) interpret the long-term evolution of the accommodation space in terms of sequence stratigraphy. The hierarchical stacking pattern of facies in beds and bedsets reveals Milankovitch cyclicity. As a working hypothesis, elementary sequences are assumed to represent the precession cycle (ca 20 kyr) and small-scale and medium-scale sequences the short (ca 100 kyr) and long (ca 400 kyr) eccentricity cycles, respectively. Four different types of elementary sequences (condensed, catch-down, catch-up and give-up) are recognised and interpreted in terms of relative sea-level changes to reconstruct the relative sea-level curve of the entire succession. The envelope of the reconstructed relative sea-level curve is used to represent the long-term accommodation change on the platform, which covers a time span of approximately 1.8 Myr. Most of this time was spent in subaerial exposure, as approximately 1.2 Myr was predicted to be condensed in a stratigraphic interval encompassing both the sequence-boundary zone/falling stage deposits and the lowstand deposits. Moreover, it was interpreted that about two-third of the total thickness of the succession was formed in only 280 kyr and consisted of both transgressive and maximum-flooding deposits. The main implication of this study is that unconformities do not necessarily correspond to single surfaces but, rather, to very amalgamated intervals or unconformity zones. Moreover, based on biostratigraphic constraints, there is a correlation between the unconformity zone of the studied succession and the third-order KAl4 sequence boundary of the Cretaceous eustatic cycle chart.