Sedimentary Processes and Biofacies of Late Cretaceous Low-Energy Carbonate Ramp Systems (Southern Italy)
Published:January 01, 2007
Daniela Ruberti, Gabriele Carannante, Lucia Simone, Giuseppe Sirna, Maurizio Sirna, 2007. "Sedimentary Processes and Biofacies of Late Cretaceous Low-Energy Carbonate Ramp Systems (Southern Italy)", Cretaceous Rudists and Carbonate Platforms: Environmental Feedback, Robert W. Scott
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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.
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Cretaceous Rudists and Carbonate Platforms: Environmental Feedback
Sedimentologists, stratigraphers and paleontologists will find new data in SP 87, "Cretaceous Rudists and Carbonate Platforms: Environmental Feedback". The papers of the Proceedings of the Seventh International Congress on Rudists are organized into three themes: (1) Depositional Environments of Cretaceous Carbonates has been an overarching theme of the Working Group on Cretaceous Carbonate Platforms, Study of rudists, which produced great volumes of carbonate sediment, is central to understanding processes and reservoir prediction. Some of the world's great hydrocarbon reservoirs are rudist debris beds. (2) The Origins, Events, and Demise of Rudist Paleocommunities signal significant local and even global events in Earth systems. Rudist communities responded to oceanic anoxic events and to complex factors that lead to oxygenation of deep ocean water masses. (3) Theme Towards Rudists Taxonomy, Biogeography, and Phylogeny focuses on the paleobiology and systematics of rudists. The foundation of all interpretations of biogeography and paleoecology is solid taxonomy that is agreed upon by the majority of specialists. This is a core, ongoing scientific pursuit.