Impact of the MECO (Middle Eocene Climatic Optimum) on shallow-water carbonate systems: a case study from the Apulia Carbonate Platform (Gargano Promontory and Tremiti Islands, Italy)

Over geological time, climatic fluctuations and hyperthermal events profoundly influenced carbonate systems and the related marine ecosystems. During the Eocene, approximately 40.1 Ma, a significant warming phase, the Middle Eocene Climatic Optimum (MECO), occurred persisting for around 500,000 years. Within this context, the composition and calcification rates of marine organisms, such as corals and larger benthic foraminifera (LBF), were shaped by variations in global CO2 levels and oceanographic conditions, exerting a profound influence on photic-zone carbonate factories.

The Middle Eocene Monte Saraceno sequence (Gargano Promontory) and the San Domino Formation (Tremiti Islands), cropping out along the eastern margin of the Apulia Carbonate Platform (southern Italy), represent case studies to explore the carbonate factory responses to climatic variations as the MECO event. In this areas, Middle Eocene deposits are mainly characterized by two distinct intervals with different modes of carbonate production. In particular, a well-exposed section belonged to the Monte Saraceno sequence reveals a lower interval with clinostratified, thick beds of rudstone to floatstone, predominantly formed by LBF belonging to the genus Nummulites, indicating an early Bartonian age (Shallow Benthic Zone 17). The upper interval, separated from the lower by a sharp boundary, is characterized by branching coral floatstone to rudstone with a packstone matrix associated with bivalve, gastropods, and rare, small LBF. Here, the Heterostegina sp. and Glomalveolina ungaroi occurrences define a late Bartonian age (Shallow Benthic Zone 18). Likewise, in the Tremiti Islands, the San Domino Fm is characterized by abundant LBF in the lower intervals covered by coral-rich facies exhibiting a great diversity in coral species and morphologies.

Integration of biostratigraphy, stable-isotope, and sedimentological evidences of the Monte Saraceno sequence indicates that the lower clinostratified interval, featuring abundant Nummulites and an absence of corals, corresponds to the MECO event. Conversely, the abrupt transition in the late Bartonian to a coral-dominated carbonate factory, accompanied by a marked decline in LBF abundance and size, is likely attributable to a temperature drop that fostered conditions more favorable for coral growth. Analogously, the coral factory flourishing, occurred within upper interval of the San Domino Fm, is associated to colder environments probably reaching the late Bartonian-Priabonian ages.

Therefore, this study provides compelling evidence of how the environmental changes can impact on marine carbonate production, highlighting how these studies can be a powerful tool in understanding the relationship between climate dynamics and carbonate systems across geological timescales, including the past, present, and future.