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 During latest Aptian to latest Turonian time interval global changes triggered widespread crises that resulted in, among others, world-wide anoxic episodes and drastic variations in biogenic assemblages and lithofacies in carbonate sequences. The related carbonatedepositional systems changed as well. In this context, the Cenomanian represents one of the keys to understanding the turnover of faciesand biota observed in Cretaceous carbonate platforms. In particular, in this time interval, both the eustatic oscillations and the tectonicevents of the Periadratic region produced localized emersions and deep physiographic alterations of the Apenninic carbonate platforms.Emersion phases that affected the Periadriatic carbonate platforms resulted in reduced and discontinuous Cenomanian records in central-southern Italy. The Cenomanian strata generally show restricted peritidal deposits and more open lagoon facies, colonized by radiolitids, nerineids, and ostreids. These pass laterally into large, complex mosaics of molluscan bioclastic shoals, closely associated with smallcaprinid mounds. Despite the difficulty of interpreting the spatial relationships in the studied sections from the Apennine chain, outcropsof Cenomanian rudist-bearing limestones have been selected in the central-southern Apennines in order to show differences in thesedimentological and/or paleontological characterization. Particular attention was given to the evolution and interrelationships of thedifferent depositional areas that were characterized by shelf-margin or exposed conditions vs. areas which suffered restricted circulation.The lithofacies architecture indicates complex zonation corresponding to transitions from shelf-margin rudist patches and their relateddebris to semi-restricted areas and tidal flats. Sand-shoal-related deposits also occurred. These sediments built complex sand bodies or “small islands”. “Transition zones” between shelf-margin and semi-restricted environments were characterized by the intercalation ofskeletal sands with silty-mud deposits. Skeletal sands episodically washed back into the inner shelf from the high-energy shelf-margin beltand migrated across the colonized areas. Waves, currents, and/or storm-related events controlled the dispersion of the skeletal grains alongactive current pathways and/or tide-related small channel networks. In their evolution, the Cenomanian depositional settings had a strong pre-Cenomanian and synsedimentary tectonic control. Tectonicscontrolled the relationships between different areas and the creation of the related accommodation space. In addition, the presence of atectonically induced irregular topography resulted in the coexistence of areas with very different hydrodynamic conditions, allowingcolonization by different organic communities and complex distribution patterns of the skeletal debris. As a consequence, Cenomanianlithofacies architecture was significantly heterogeneous.

A bstract This paper characterizes a low-energy, open-shelf setting by focusing on the sedimentary processes and biofacies of a Late Cretaceous, temperate-type open shelf in the southern Apennine nappes of Italy. The facies evolution of the related rudist-rich limestonestakes into account the macrofossil characteristics and the microfaunal assemblages. The open-shelf depositional setting is interpreted by facies analysis. The facies are gradually transitional and the facies belts are broad, but wave-resistant biogenic frameworks are absent. Presumably the sea floor was characterized by a low bathymetric slope on which thewave energy was dissipated across a wide shelf, resulting in low-energy environments. Storm waves were damped by the wide, shallowbottom, and the fine fraction was not winnowed. Many rudists are in growth position, and those reworked are well preserved and commonly articulated. Different bathymetries and hydrodynamic conditions in two study areas, the Sorrento Peninsula and the northernCilento, resulted in different biofacies and stratal geometries. In the Cilento area, high-energy currents such as tidal currents created anetwork of small channel-like depressions. Different rudist species colonized these channels and their margins. Rudists in growth positionare rare, although reworked bivalves are commonly conjoined and the shells are pristine. In this subtidal facies key foraminifer species varyin abundance. The presence of marine open-shelf agglutinate forms supports the interpretation of a marine, high-energy shelf. In the Sorrento area, ephemeral subaerial exposure surfaces and pedogenic deposits indicate intertidal conditions and rudist faciesindicate subtidal sandy shelf. The rudists formed monospecific to paucispecific assemblages. The foraminiferal assemblages are much morediversified than those in the Cilento successions, indicating small but meaningful oscillations in sub-environments. The rudist shell beds exhibit great taphonomic variability. The foraminiferal assemblages are characterized by distinct taxa such asabundant conical and discoidal agglutinate forms ( Cuneolina and Dicyclina ), thick-shelled evoluted Soritidae (Murgella, Scandonea , and Pseudorhapydionina) , and larger, thicker ovoidal or subspherical Rotaliidae that indicate well-lit depositional environments with open watercirculation and normal salinity, characterized by medium values of the hydrodynamic energy with scarce or no evidence of traction currents.

Abstract Shallow-water foramol limestones have been studied from a locality in the southern Apennines in which outcrop conditions show an excellent overview of the lateral and vertical evolution of rudist bodies and allow their geometry and the dynamic aspects to be reconstructed. The lithofacies suggest open depositional settings characterized by peloidal silty-muddy sediments. Rudists inhabited well-defined sectors of these shelves, giving rise to wide biostromal bodies, and supplied most of the skeletal debris via bioerosion and minor physical breakdown. In particular, the characteristics of rudist lithosomes document the existence of a complex network of channel-like depressions. In such a depositional context, the evolution of rudist lithosomes was controlled by the environmental hydrodynamic conditions. The resulting composite rudist assemblages are characterized by often-toppled individuals, suggesting continuous sediment removal between the organisms. The good preservation of the shells and the common articulation of the valves, however, point to an absence of sustained transport but rather a slight sediment destabilization. The gross lenticular geometry of the shell beds could be related to the above-mentioned patterns of weak, perhaps channelized, pathways. In such a depositional context, rudist colonization on channel margins assumes particular importance as it documents the rudist ability to exploit a wide array of environments, comparable to that of oysters in Recent seas, and reflecting the probable opportunistic nature of rudists.

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.