The Cretaceous shallow water limestone cropping out in central-southern Apennines (Matese – Camposauro- Monte Maggiore Mountains, Italy) records significant climatic and tectonic events that affected the peri-Tethyan Region during Cretaceous times. The lower Cretaceous limestone documents healthy carbonate systems, which grew bearing mainly chlorozoan assemblages and non-skeletal grain-rich deposits although minor crisis moments in the growth of the carbonate factories have been recognized. Mid-Cretaceous tectonics and the resulting complex palaeotopography dramatically controlled the Albian-Turonian evolution of the analysed area; the related carbonate factories experienced repeated crisis events presumably also related to global oceanographic changes. In particular, following late Aptian-Albian crisis events, highlighted by unhealthy platform conditions inferred by the flourishing of cyanobacterial consortia (Lithocodium-Bacinella-type) and other mesotrophic-tendentially eutrophic condition-adapted assemblages, the reconstructed shallow-water domains were forced to change sediment production modes, depositional patterns and internal sedimentary architecture. These events were also accomplished by the progressive reduction of the previous mainly aragonitic-shelled chlorozoan assemblages and an increase of calcite-dominated skeletal components among which rudists with calcitic outer shell layer. The main turnover of facies has been registered in the Cenomanian time. Like in the other carbonate platform domains, pertaining to the southern Tethyan belt, in the central-southern Apennines Cenomanian platforms, repeated variations of the sea level were superimposed on tectonic-related, morphologically articulated substrata thus contributing to the creation of the complex scenario in which the rudist-bearing carbonate lithofacies accumulated. Mostly calcitic, elevator and clinger rudists flourished but were associated to the large recumbent forms, which had still aragonitic inner shell and colonized the high energy, outer shelf settings. Tectonics controlled the relationships between different areas and the creation of the related accommodation space. In addition, the presence of a tectonically induced irregular topography resulted in the coexistence, in a relatively short distance, of areas with very different hydrodynamic conditions, allowing colonization by different organic assemblages and complex distribution patterns of the skeletal debris. As a consequence, Cenomanian lithofacies architecture was significantly heterogeneous. The Cenomanian sediments were arranged in a complex way; they built up patchily distributed “sedimentary bodies” controlled by the growth and the type of the rudists. 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 small caprinid mounds. The rudists colonized irregular bottom surfaces; in particular, they have also been found in growth position on inclined surfaces that delimit sigmoidal sandy bodies. These surfaces bordered small incisions that were filled with well-washed and sorted sediment consisting mainly of rounded, locally imbricated, coarse rudist debris. The overall characteristics of the sandy belts suggest active current pathways or small tidal channel networks along which extended transport of the skeletal debris occurred, although outcrop discontinuity does not allow a thorough reconstruction of the depositional geometries. The associated fenestral laminites as well as the immature pedogenic profiles (from which black clasts likely were derived) are typical of the intertidal–supratidal portions of the channel levees and interchannel ponds; the current-related sands suggest lateral-bar deposits, and mollusc-shell coquinas point to lag deposits of channel-like depressions. As a consequence, in the studied shelf successions the repetitive intercalation of coarse skeletal sheets as well as of intertidal laminites and/or black-clast-rich layers suggests channel migration on a morphologically differentiated shelf, in which slightly elevated sand bodies and anastomosed current pathways contributed to create a complex depositional setting resulting in the aforementioned significant heterogeneity in the Cenomanian lithofacies architecture. Although often missing, the Turonian sediments covering the Cenomanian strata document restricted conditions and the wide presence of cyanobacterial consortia (thaumathoporellaceans and Aeolisaccus s.p.), associated with grazing or detritivorous gastropods (nerineids and acteonids). Recumbent rudist forms reduced up to disappear, whereas the calcitic elevator and clinger ones became more and more dominant. These characteristics call for carbonate factory unhealthiness, known also in other peri-tethyan carbonate platforms and correlatable with early-middle Turonian atmospheric-oceanic perturbations. The onset of latest Turonian-Coniacian p.p. renewed suitable environmental conditions is documented by recovering of the carbonate factories, whereas controlled by changed oceanographic conditions that resulted in a shift toward foramol depositional systems with sciophilous and mesotrophic condition-adapted assemblages.

MID CRETACEOUS CARBONATE RUDIST-BEARING SHELF BETWEEN MAJOR CRISIS EVENTS: CASE HISTORIES FROM THE CENTRAL-SOUTHERN APENNINES (ITALY)

SIMONE, LUCIA
2009

Abstract

The Cretaceous shallow water limestone cropping out in central-southern Apennines (Matese – Camposauro- Monte Maggiore Mountains, Italy) records significant climatic and tectonic events that affected the peri-Tethyan Region during Cretaceous times. The lower Cretaceous limestone documents healthy carbonate systems, which grew bearing mainly chlorozoan assemblages and non-skeletal grain-rich deposits although minor crisis moments in the growth of the carbonate factories have been recognized. Mid-Cretaceous tectonics and the resulting complex palaeotopography dramatically controlled the Albian-Turonian evolution of the analysed area; the related carbonate factories experienced repeated crisis events presumably also related to global oceanographic changes. In particular, following late Aptian-Albian crisis events, highlighted by unhealthy platform conditions inferred by the flourishing of cyanobacterial consortia (Lithocodium-Bacinella-type) and other mesotrophic-tendentially eutrophic condition-adapted assemblages, the reconstructed shallow-water domains were forced to change sediment production modes, depositional patterns and internal sedimentary architecture. These events were also accomplished by the progressive reduction of the previous mainly aragonitic-shelled chlorozoan assemblages and an increase of calcite-dominated skeletal components among which rudists with calcitic outer shell layer. The main turnover of facies has been registered in the Cenomanian time. Like in the other carbonate platform domains, pertaining to the southern Tethyan belt, in the central-southern Apennines Cenomanian platforms, repeated variations of the sea level were superimposed on tectonic-related, morphologically articulated substrata thus contributing to the creation of the complex scenario in which the rudist-bearing carbonate lithofacies accumulated. Mostly calcitic, elevator and clinger rudists flourished but were associated to the large recumbent forms, which had still aragonitic inner shell and colonized the high energy, outer shelf settings. Tectonics controlled the relationships between different areas and the creation of the related accommodation space. In addition, the presence of a tectonically induced irregular topography resulted in the coexistence, in a relatively short distance, of areas with very different hydrodynamic conditions, allowing colonization by different organic assemblages and complex distribution patterns of the skeletal debris. As a consequence, Cenomanian lithofacies architecture was significantly heterogeneous. The Cenomanian sediments were arranged in a complex way; they built up patchily distributed “sedimentary bodies” controlled by the growth and the type of the rudists. 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 small caprinid mounds. The rudists colonized irregular bottom surfaces; in particular, they have also been found in growth position on inclined surfaces that delimit sigmoidal sandy bodies. These surfaces bordered small incisions that were filled with well-washed and sorted sediment consisting mainly of rounded, locally imbricated, coarse rudist debris. The overall characteristics of the sandy belts suggest active current pathways or small tidal channel networks along which extended transport of the skeletal debris occurred, although outcrop discontinuity does not allow a thorough reconstruction of the depositional geometries. The associated fenestral laminites as well as the immature pedogenic profiles (from which black clasts likely were derived) are typical of the intertidal–supratidal portions of the channel levees and interchannel ponds; the current-related sands suggest lateral-bar deposits, and mollusc-shell coquinas point to lag deposits of channel-like depressions. As a consequence, in the studied shelf successions the repetitive intercalation of coarse skeletal sheets as well as of intertidal laminites and/or black-clast-rich layers suggests channel migration on a morphologically differentiated shelf, in which slightly elevated sand bodies and anastomosed current pathways contributed to create a complex depositional setting resulting in the aforementioned significant heterogeneity in the Cenomanian lithofacies architecture. Although often missing, the Turonian sediments covering the Cenomanian strata document restricted conditions and the wide presence of cyanobacterial consortia (thaumathoporellaceans and Aeolisaccus s.p.), associated with grazing or detritivorous gastropods (nerineids and acteonids). Recumbent rudist forms reduced up to disappear, whereas the calcitic elevator and clinger ones became more and more dominant. These characteristics call for carbonate factory unhealthiness, known also in other peri-tethyan carbonate platforms and correlatable with early-middle Turonian atmospheric-oceanic perturbations. The onset of latest Turonian-Coniacian p.p. renewed suitable environmental conditions is documented by recovering of the carbonate factories, whereas controlled by changed oceanographic conditions that resulted in a shift toward foramol depositional systems with sciophilous and mesotrophic condition-adapted assemblages.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/364245
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