Internal waves as controlling factor in the development of stromatoporoid-rich facies of the Apulia Platform margin (Upper Jurassic-Lower Cretaceous, Gargano Promontory, Italy)

Abstract

During the Late Jurassic, stromatoporoid-rich buildups were developed in south and intra-Tethys realms. These stromatoporoid buildups are mainly characterized by the high percentage of intraclastic-bioclastic debris, as main components of buildup bodies. However, the source of hydrodynamic energy resulted in debris production, is still a matter of debate. This study examines the Upper Jurassic-Lower Cretaceous stromatoporoid-rich buildups of Monte Sacro Limestones (MSL), Apulia Carbonate Platform (ACP), in order to describe the main carbonate facies along the study area, as well as the possible source of turbulence. Three main lithofacies have been distinguished: LF1 — stromatoporoid-rich facies with two subfacies (LF1-S1: floatstone with wackestone to fine-grained packstone, LF1-S2: rudstone-floatstone with intraclastic-bioclastic packstone-grainstone), LF2 — stromatoporoid-coral facies distributed in wackestone to packstone matrix (LF2-S1) and tabular stromatoporoid-corals surrounded by wackestone matrix (LF2-S2) and, LF3 — stromatoporoid-microbial facies. These facies were deposited along the mid part of a distally steepened ramp. The in-situ form of stromatoporoids was developed in a mud-dominated matrix (LF1-S1) under low-energy conditions while the intraclastic-bioclastic rich facies (LF1-S2) were deposited under a high-energy condition. The distribution of LF2 and LF3 in muddy matrix suggests occurrence of these lithofacies in quiet environments.The biotas were influenced by several factors including nutrient and light availability as well as by hydrodynamism. The stromatoporoid-rich buildups in ACP can be categorized as phototrophic-heterotrophic reefs generated in a pure carbonate environment. The light penetration was confined, resulted in the high development of light-independent micro-encrusters (Tubiphytes morronensis), in a mesophotic condition, where the environment was not ideal for light-dependent microencrusters (Lithocodium-Bacinella) to grow.We suggest that debris-dominated stromatoporoid-rich lithofacies (LF1) thrived in meso-oligophotic setting, along the nutricline and were affected by more than episodic high-energy events in a context where the surface waves were not effective. In such environments, internal waves can be an effective candidate to explain the episodic turbulences to produce the debris-rich facies of LF1-S2. Moreover, internal waves can pump the nutrient-rich waters to the buildups, and create an ideal setting where these metazoan communities thrived.