Evolving coralline platform geometries – Oligocene to Holocene of the Maltase Platform

Abstract

<p>The Maltase Platform in the Central Mediterranean has hosted carbonate production dominated by coralline algae at least since the Oligocene. Through this period a wide range of parameters has changed including the amplitude and wavelength of sea level change, oceanographic connectivity of the Central Mediterranean, nutrient state and many more. As such the Maltase Platform offers a unique location to examine how the light dominated coralline algae carbonate factory had respond to these changes.</p><p>The Maltase Platform hosts three main units of coralline algae deposits: the middle to late Oligocene Lower Coralline Limestone (LCL), the late Miocene Upper Coralline Limestone (UCL) and the Pleistocene-Holocene corallines offshore. The Pleistocene-Holocene deposits are characterized by three main modes: coralline sand, rhodolith and mounds. Both the rhodoliths and mounds occur in mesophotic depths, the mounds along ancient terraces and the rhodoliths on the outer shelf. Coralline sand on the other hand can be found in nearly all locations and water depths. With the exception of special localities, none of these form accumulations of more then a few meters in thickness with nearly no accumulations at the shores or near shore. The UCL deposits are characterized by massive bioherms, mostly comprised of interbedded modes of crustose corallines and coralline sands, as well as coralline sands deposits. These accumulations are several meters to tens of meters (offshore). The coralline sands building large prograding clinoform bodies as well as deposits of cross bedded deposits to intertidal depth. The bioherms are mostly align along a SE-NW line on the south of the platform with the clinoforms extending from them. The LCL deposits are characterized by large platforms built to several tens of meter. These deposits form large clinoform bodies which exhibit, progradation aggradation and in some cases degradation. Multiple small platforms are distributed across the platrform with handover of production and export between one platform to the other observed in some locations. Corals are not common but present in all three units, both the UCL and the LCL host intervals of tropical corals while the Pleistocene-Holocene hosts only rare Mediterranean corals.</p><p>The change in the oceanographic state in the Central Mediterranean had diminished the production intensity of the light dominated coralline algae carbonate factory in this region since the Oligocene. Accumulation to accommodation space do not appear to occur in the Pleistocene-Holocene and most of the production is limited to the mesophotic depth where accumulation rates are slower. Similarly, the changes from the late Oligocene to the late Miocene resulted in less active production within this factory at that time. Sea level amplitude and frequency, water temperature and nutrient states are likely parameters that lead to this change with ongoing global cooling and restriction of the Mediterranean through this period. </p>