Messinian reef-building assemblages of the Salento Peninsula (southern Italy): palaeobathymetric and palaeoclimatic significance

Abstract

This paper mainly addresses the description and interpretation of different reef-building assemblages recognised within an early Messinian reef complex recently discovered along the eastern margin of the Apulia Platform (Salento Peninsula, southern Italy). It is the first Late Miocene reef recorded for the ‘Adriatic region’ and its location partly changes boundaries of coral reef distribution during this time in the Mediterranean. The Messinian reef complex (Novaglie Formation) is interpreted as a succession of fringing reefs accommodated in palaeo-reentrances or palaeo-embayments of the original Messinian rocky shore and overlying discordantly the underlying Cretaceous to Oligocene units. It consists of a discontinuous reef tract and associated clinostratified fore-reef slope. Relatively precise dating of the reef complex has been achieved using benthic foraminifera and ostracods associations. Three main different reef-building assemblages have been recognised: (1) Halimeda bioherms (2) Porites reef and (3) vermetid–microbial ‘trottoirs’. Each assemblage is described in detail according to its architecture and structure (setting, shape, quantitative estimation of the framework density), biotic components (taxonomic composition and relative abundance of the reef-builders, growth form, associated fauna), and intra-reef sediment (texture and fabric). Palaeoecologic analysis, based on physical observation within the margin-slope of the reef complex and in comparison with present-day analogues and their ecological demands, indicates that distribution and vertical succession of the three different reef assemblages are strictly depth-related, suggesting an ecological replacement consequent on small relative sea-level changes (fourth order), closely comparable with those already indicated for the early Messinian. Special attention is given to the remarkable abundance of vermetids that, together with microbial crusts, formed scattered ‘trottoirs’ along the shoreline. Vermetid occurrences have been extensively cited in the literature for the Late Miocene of the Mediterranean but poorly studied in detail. Here, their palaeoecologic significance is emphasised, indicating that these organisms can be used as reliable palaeobathymetric and palaeoclimatic indicators. Regarding the Miocene of the Mediterranean, development of vermetid–microbial ‘reefs’, so far recorded for the Messinian, is preferentially associated with low-diversity coral reefs and is interpreted as being mainly controlled by climatic constraints.