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Papers by Alessandro Lanfranchi
… , A. Lanfranchi, F. …, 2008
Quantitative analysis of sediment composition was performed on a kilometre wide section of Upper ... more Quantitative analysis of sediment composition was performed on a kilometre wide section of Upper Tithonian low relief (up to 70 m), gently inclined (3°to 15°), sigmoidal carbonate clinoforms (eastern Sardinia) to identify changes in sediment composition along the slope and across the studied succession. These changes may reflect modifications of the carbonate factory and of processes responsible for sediment transport. Point-count analysis of carbonate microfacies, Q-mode/R-mode cluster analysis and Spearman's rank provided a composition-based classification of microfacies and highlighted relationships among sediment components. The studied clinoforms are mainly composed of non-skeletal grains (70%), such as peloids and lithoclasts, together with micrite and cements and only a limited contribution from coated grains (2%). Among skeletal grains (28%), the greatest contribution derives from a coralstromatoporoid-encruster reef that provided 15% of the components. Crinoids, brachiopods and other along-slope thriving biota provided nearly 5% of the allochems, whilst fragments of molluscs (gastropods, bivalves and diceratids) from the backreef sourced another 2%. The contribution of platform interior biota is negligible (1%). The association of composition-based facies varies along the slope. The upper slope beds consist of coral-stromatoporoid grainstone to rudstone; the middle slope deposits are dominated by encrusterlithoclast grainstone and packstone. At the lower slope, peloidal lithoclastic packstone as well as brachiopod-crinoidal wackestone prevail. Also the association of skeletal grains changes along the slope. The encruster-frame builder association typifies the upper slope whilst encrusters characterize the middle slope sediments. In the lower slope encrusters are equally represented as the brachiopod-crinoid association. Along-slope compositional changes evidence a scarce downslope transport of frame builders and a progressive enrichment in along-slope thriving biota. Quantitative analysis of microfacies allowed the sigmoidal clinoforms to be grouped into six sets. Each set gathers sigmoids with a similar sediment composition. Coated grains are dominant in the first set whilst they are lacking in the overlying sets reflecting a change in the carbonate factory. Other major compositional changes among the sets concern the relative amounts of peloids, micrite, frame builders (corals and stromatoporoids) and encrusters. The contribution of peloids varies inversely to that of cements and micrite as evidenced in the third and fifth sets which, respectively, record the highest occurrence of peloids or cement and micrite. Variations in the amount of frame builders and encrusters are instead nonlinear. High percentages of both frame builders and encrusters, as recorded in the second and fifth sets, are related to low amounts of peloids and lithoclasts Sedimentology 1 that probably reflect episodes of reduced background sedimentation. This study demonstrates that quantitative analysis of carbonate microfacies represents a powerful tool that can improve the reconstruction of the stacking pattern in carbonate slope successions both in outcrop and in subsurface settings.
Sedimentary Geology, 2011
The Upper Anisian to Early Carnian succession of the Middle Val Brembana-Pegherolo Massif (Centra... more The Upper Anisian to Early Carnian succession of the Middle Val Brembana-Pegherolo Massif (Central Southern Alps of Italy) records a complete depositional cycle from platform inception to growth, demise and rebirth. The depositional architecture of this system reflects different evolutionary stages: an inception stage which postdates a previous drowning of an Anisian carbonate platform with progradation of the carbonate platform from the nucleation areas, an aggradational stage with increasing water depth in the basins, a progradational stage where steep slopes composed of margin-derived breccias develop and a final crisis corresponding to the subaerial exposure of the platform top, followed by the deposition of shales in the basin before the rebirth of a different type of carbonate factory. The record of this evolution reflects the effects of the change in accommodation space (interplay of subsidence and eustacy), which controls the type and storage sites of the sediments produced by the carbonate factory. The effects of the changes in accommodation space are recorded in the shallow water platform as well as in the intraplatform basins, where the sediments, delivered at different rates from the platform top are stored. As a consequence, the aggradational stage corresponds to reduced sedimentation in the basins (i.e. sediments are stored on the platform top) whereas during progradation resedimented limestones are more common in the basin. Subaerial exposure rapidly halted the carbonate production on the platform top, while a major input of shales (probably reflecting a climate change and/or lowering of the base level) is recorded in the basin, where shales onlap the slope of the previous carbonate system. The rebirth of the carbonate factory after subaerial exposure of the platform top is characterized by a different composition of the carbonate factory, probably reflecting changes of the environmental conditions. The step-by-step recording of the evolution of the carbonate system represents a unique opportunity to record a seismic-scale complete evolutionary cycle of a carbonate system in its different sub-environments, from the platform top to the basin.
…, 2007
... BERRA, FABRIZIO,; JADOUL, FLAVIO,; ERBA, ELISABETTA,; LANFRANCHI, ALESSANDRO,; CASELLATO, CRI... more ... BERRA, FABRIZIO,; JADOUL, FLAVIO,; ERBA, ELISABETTA,; LANFRANCHI, ALESSANDRO,; CASELLATO, CRISTINA EMANUELA,; GALLI, MARIA TERESA,; F. Jadoul, A. Lanfranchi, C. Casellato, F. Berra, E. Erba, MT Galli, G. Liveriero Lavelli,; FIST. Abstract. ...
… , A. Lanfranchi, F. …, 2008
Quantitative analysis of sediment composition was performed on a kilometre wide section of Upper ... more Quantitative analysis of sediment composition was performed on a kilometre wide section of Upper Tithonian low relief (up to 70 m), gently inclined (3°to 15°), sigmoidal carbonate clinoforms (eastern Sardinia) to identify changes in sediment composition along the slope and across the studied succession. These changes may reflect modifications of the carbonate factory and of processes responsible for sediment transport. Point-count analysis of carbonate microfacies, Q-mode/R-mode cluster analysis and Spearman's rank provided a composition-based classification of microfacies and highlighted relationships among sediment components. The studied clinoforms are mainly composed of non-skeletal grains (70%), such as peloids and lithoclasts, together with micrite and cements and only a limited contribution from coated grains (2%). Among skeletal grains (28%), the greatest contribution derives from a coralstromatoporoid-encruster reef that provided 15% of the components. Crinoids, brachiopods and other along-slope thriving biota provided nearly 5% of the allochems, whilst fragments of molluscs (gastropods, bivalves and diceratids) from the backreef sourced another 2%. The contribution of platform interior biota is negligible (1%). The association of composition-based facies varies along the slope. The upper slope beds consist of coral-stromatoporoid grainstone to rudstone; the middle slope deposits are dominated by encrusterlithoclast grainstone and packstone. At the lower slope, peloidal lithoclastic packstone as well as brachiopod-crinoidal wackestone prevail. Also the association of skeletal grains changes along the slope. The encruster-frame builder association typifies the upper slope whilst encrusters characterize the middle slope sediments. In the lower slope encrusters are equally represented as the brachiopod-crinoid association. Along-slope compositional changes evidence a scarce downslope transport of frame builders and a progressive enrichment in along-slope thriving biota. Quantitative analysis of microfacies allowed the sigmoidal clinoforms to be grouped into six sets. Each set gathers sigmoids with a similar sediment composition. Coated grains are dominant in the first set whilst they are lacking in the overlying sets reflecting a change in the carbonate factory. Other major compositional changes among the sets concern the relative amounts of peloids, micrite, frame builders (corals and stromatoporoids) and encrusters. The contribution of peloids varies inversely to that of cements and micrite as evidenced in the third and fifth sets which, respectively, record the highest occurrence of peloids or cement and micrite. Variations in the amount of frame builders and encrusters are instead nonlinear. High percentages of both frame builders and encrusters, as recorded in the second and fifth sets, are related to low amounts of peloids and lithoclasts Sedimentology 1 that probably reflect episodes of reduced background sedimentation. This study demonstrates that quantitative analysis of carbonate microfacies represents a powerful tool that can improve the reconstruction of the stacking pattern in carbonate slope successions both in outcrop and in subsurface settings.
Sedimentary Geology, 2011
The Upper Anisian to Early Carnian succession of the Middle Val Brembana-Pegherolo Massif (Centra... more The Upper Anisian to Early Carnian succession of the Middle Val Brembana-Pegherolo Massif (Central Southern Alps of Italy) records a complete depositional cycle from platform inception to growth, demise and rebirth. The depositional architecture of this system reflects different evolutionary stages: an inception stage which postdates a previous drowning of an Anisian carbonate platform with progradation of the carbonate platform from the nucleation areas, an aggradational stage with increasing water depth in the basins, a progradational stage where steep slopes composed of margin-derived breccias develop and a final crisis corresponding to the subaerial exposure of the platform top, followed by the deposition of shales in the basin before the rebirth of a different type of carbonate factory. The record of this evolution reflects the effects of the change in accommodation space (interplay of subsidence and eustacy), which controls the type and storage sites of the sediments produced by the carbonate factory. The effects of the changes in accommodation space are recorded in the shallow water platform as well as in the intraplatform basins, where the sediments, delivered at different rates from the platform top are stored. As a consequence, the aggradational stage corresponds to reduced sedimentation in the basins (i.e. sediments are stored on the platform top) whereas during progradation resedimented limestones are more common in the basin. Subaerial exposure rapidly halted the carbonate production on the platform top, while a major input of shales (probably reflecting a climate change and/or lowering of the base level) is recorded in the basin, where shales onlap the slope of the previous carbonate system. The rebirth of the carbonate factory after subaerial exposure of the platform top is characterized by a different composition of the carbonate factory, probably reflecting changes of the environmental conditions. The step-by-step recording of the evolution of the carbonate system represents a unique opportunity to record a seismic-scale complete evolutionary cycle of a carbonate system in its different sub-environments, from the platform top to the basin.
…, 2007
... BERRA, FABRIZIO,; JADOUL, FLAVIO,; ERBA, ELISABETTA,; LANFRANCHI, ALESSANDRO,; CASELLATO, CRI... more ... BERRA, FABRIZIO,; JADOUL, FLAVIO,; ERBA, ELISABETTA,; LANFRANCHI, ALESSANDRO,; CASELLATO, CRISTINA EMANUELA,; GALLI, MARIA TERESA,; F. Jadoul, A. Lanfranchi, C. Casellato, F. Berra, E. Erba, MT Galli, G. Liveriero Lavelli,; FIST. Abstract. ...