During the mid-Cretaceous times significant climatic-oceanographic changes are recorded. In the same time interval, both the eustatic oscillations and the tectonic events of the peri-Adriatic region produced localized emersions and deep physiographic alterations of the Apenninic carbonate platforms. Emersive phases that affected the Peri-Adriatic carbonate platforms resulted in reduced and discontinuous Albian-Cenomanian records in central-southern Italy. Exposure surfaces are often associated with palaeokarst networks and discontinuous bauxite covers. This supports the evidence of warm and humid climatic conditions. However, recent preliminary data suggest that dry and warm climatic conditions were active in the same time interval in different areas of the peri-Adriatic region (e.g.: Cilento area in southern Apennines, Tripolitza subzone of the External Ellenides, see Pomoni-Papaioannou F. and Zambetakis-Lekkas A., 2007; Bravi et alii, 2008). Detailed time and space constrains are needed in order to clarify their relationships with the hot and humid climatic conditions causing the intensive karst and bauxite development solving the above climatic discrepancy. The detailed analysis of a shallow-water carbonate succession cropping in the Campania Apennines (Southern Italy), has shown recurrent evidence of evaporitic depositional conditions. The related limestone has been dated early Albian up to late Cenomanian in age on the base of the presence of microfossil as Paracoskinolina tunesiana Peybernes and Sellialveolina viallii Colalongo in the lower part, and Cisalveolina fraasi (Gumbel) and Pseudolituonella reicheli Marie in the upper part. In-depth facies analyses of the basal interval of the succession, pointed out to a cyclic sedimentary pattern with shallowing upward cycles. The basal intervals of the cycles are made up of shallow water subtidal limestone followed by evaporitic levels (containing silica pseudomorphs after anhydrite/gypsum crystals), which in turn pass upward to marly layers including limestone nodules, barren or bearing a very poor biotic contain, few centimeters in diameter. Resting over this first interval, a middle Cenomanian “Platy Dolomite” interval occurs, in which remains of xerophytic megaflora (e.g. Sapindopsis sp., Frenelopsis sp.) have been found (Bravi et alii, 2004; Bartiromo et alii, 2008). Finally upper Cenomanian bioturbated limestone follows partly consisting of rudist coarsely grained biodetrital material and rapidly passing upward to thin muddy layers bearing planktonic microfauna. All the above suggests a deepening trend into an inner platform-restricted setting subject to dry climatic conditions. Palaeobotanical evidences both in the studied succession and in other carbonate sequences of the Campania region belonging to the same time span, further testify and confirms the prevailing dry and warm climatic conditions. In this frame, the evaporitic cycles witness repeated episodes of salinity shifting in paralic depositional settings. Salt, brackish or schizohaline ponds along with sabkha areas alternated in time and space repeatedly in the area likely following short-term climatic variations.

SABKHA-RELATED EVAPORITIC CYCLES IN THE “MIDDLE CRETACEOUS” LIMESTONE OF THE MONTEFORTE AREA (SOUTHERN APENNINES, ITALY).

CARANNANTE, GABRIELE;SIMONE, LUCIA
2009

Abstract

During the mid-Cretaceous times significant climatic-oceanographic changes are recorded. In the same time interval, both the eustatic oscillations and the tectonic events of the peri-Adriatic region produced localized emersions and deep physiographic alterations of the Apenninic carbonate platforms. Emersive phases that affected the Peri-Adriatic carbonate platforms resulted in reduced and discontinuous Albian-Cenomanian records in central-southern Italy. Exposure surfaces are often associated with palaeokarst networks and discontinuous bauxite covers. This supports the evidence of warm and humid climatic conditions. However, recent preliminary data suggest that dry and warm climatic conditions were active in the same time interval in different areas of the peri-Adriatic region (e.g.: Cilento area in southern Apennines, Tripolitza subzone of the External Ellenides, see Pomoni-Papaioannou F. and Zambetakis-Lekkas A., 2007; Bravi et alii, 2008). Detailed time and space constrains are needed in order to clarify their relationships with the hot and humid climatic conditions causing the intensive karst and bauxite development solving the above climatic discrepancy. The detailed analysis of a shallow-water carbonate succession cropping in the Campania Apennines (Southern Italy), has shown recurrent evidence of evaporitic depositional conditions. The related limestone has been dated early Albian up to late Cenomanian in age on the base of the presence of microfossil as Paracoskinolina tunesiana Peybernes and Sellialveolina viallii Colalongo in the lower part, and Cisalveolina fraasi (Gumbel) and Pseudolituonella reicheli Marie in the upper part. In-depth facies analyses of the basal interval of the succession, pointed out to a cyclic sedimentary pattern with shallowing upward cycles. The basal intervals of the cycles are made up of shallow water subtidal limestone followed by evaporitic levels (containing silica pseudomorphs after anhydrite/gypsum crystals), which in turn pass upward to marly layers including limestone nodules, barren or bearing a very poor biotic contain, few centimeters in diameter. Resting over this first interval, a middle Cenomanian “Platy Dolomite” interval occurs, in which remains of xerophytic megaflora (e.g. Sapindopsis sp., Frenelopsis sp.) have been found (Bravi et alii, 2004; Bartiromo et alii, 2008). Finally upper Cenomanian bioturbated limestone follows partly consisting of rudist coarsely grained biodetrital material and rapidly passing upward to thin muddy layers bearing planktonic microfauna. All the above suggests a deepening trend into an inner platform-restricted setting subject to dry climatic conditions. Palaeobotanical evidences both in the studied succession and in other carbonate sequences of the Campania region belonging to the same time span, further testify and confirms the prevailing dry and warm climatic conditions. In this frame, the evaporitic cycles witness repeated episodes of salinity shifting in paralic depositional settings. Salt, brackish or schizohaline ponds along with sabkha areas alternated in time and space repeatedly in the area likely following short-term climatic variations.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/364248
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