Abstract Post-Turonian (Late Cretaceous) rudist-bearing limestones of the Nurra region in northwestern Sardinia (northern Tethyan margin) and in the central-southern Apennines and Apulia (central Tethyan domain) have recorded relevant changes in the characteristics of the carbonate platforms following the “middle” Cretaceous crisis events which affected the peri-Tethyan region as well as other regions worldwide. Rudist bivalves became the dominant lithogenetic taxon owing to their proliferation in shallow-water environments and strong dominance of Late Cretaceous carbonate factories. Their inception, evolution, and demise were seemingly controlled by a complex interplay of environmental processes that, acting on a global scale, profoundly modified the Early Cretaceous hydrosphere-atmosphere system and forced Tethyan depositional systems to change their organization, internal architecture, and facies patterns. As a result, wide, open shelves developed where the almost ubiquitous mode of carbonate fixation was that of foramol factories. In this paper, evidence of the remarkable regional variability in the rudist-bearing carbonate platforms of the Mediterranean Tethys is presented. The analysis of the resulting shallow-water facies has demonstrated that, in spite of several stratigraphic similarities and common sedimentological features, some remarkable differences occurred between the northern Tethyan margin and the central Tethyan banks as regards the areal partitioning of the main paleoecologic controlling factors. This resulted in the deposition of rhodalgal successions in Sardinia (northern Tethyan margin) and rudist-rich foramol facies in the Apennine-Apulia (central Tethys) regions, respectively. Such Late Cretaceous carbonate systems can be viewed as geological products which have closely and coherently recorded the globally changing environmental conditions of the oceanic realm. In spite of this, the difference of the facies partitioning in different Tethyan regions according to a latitudinal gradient is interpreted as derived mainly from local variable paleoceanographic and paleoclimatic conditions.

Abstract: Carbonate platform sequences now located in Sardinia were originally located along the northern margin of the Mesozoic Tethys whereas similar platforms now outcropping in the southern Apennines-Apulia area developed along the southern margin of the Tethys. Upper Cretaceous limestones in both areas accumulated on temperate-type, ramp-like open shelves. Sediments are mostly bioerosion-derived bioclasts made up of rudists with variable proportions of benthic foraminifers, bryozoans and red algae. Non-skeletal grains are absent, and the skeletal components are indicative of the foramol sensu lato association, with clear rhodalgal characteristics in the Sardinian sequences. Lithofacies are dominated by fine- to coarse-grained skeletal grainstones and rudstones. They show evidence of storm and current winnowing. Rudists are rarely preserved in growth position and grew in loose sediment giving rise to limited and scattered rudist-rich bodies whose relief above the surrounding sea bed was slight and limited to the last generation of individuals which grew in a constratal pattern. No rigid frameworks were present in these rudist accumulations, and they did not develop into true reefs. No platform margin rims developed, and the bioerosion-derived finer fraction was swept off the resulting open shelves into deeper water areas, where the coarser skeletal debris accumulated by means of sediment gravity flows. Similar recent foramol deposits are spread over wide sectors of the continental shelves in temperate seas. Nevertheless, these deposits may also develop in tropical/subtropical regions under conditions of ecological stress. The Senonian peri-Tethyan platforms evolved from “warm-water” to relatively “cool-water” types. In the latter, complex interrelated factors may have been effective in controlling different environmental and depositional conditions, resulting in modified lithofacies on opposing margins of the Mediterranean Tethys.