Quantitative modal analysis of sandstones represents a useful stratigraphic tool for correlation, revealing major heterochroneities in the largely unfossiliferous fluvial to coastal terrigenous succession of the Austroalpine Domain. Besides its petrostratigraphic significance, sandstone composition provides a wealth of useful information for paleogeographic interpretation. A fundamental step to interpret modal data correctly is the assessment of various factors which control sandstone mineralogy. This case history shows how the relative importance of tectonic evolution of source areas versus effects of sedimentary processes and grain size may drastically change even within single stratigraphic intervals in the same stratigraphic succession. In various Austroalpine nappes, Permian to Anisian siliciclastic wedges represent the base of the post-Hercynian sedimentary cover. Even though each thrust-sheet is characterized by a notably different paleotectonic and sedimentary history, and in spite of lateral facies changes, coeval terrigenous packages maintain a common petrographic signature ("petrologic intervals"). The mineralogy of the metamorphiclastic "Verrucano" exposed in the Livigno area records an unroofing sequence within a single sedimentologically monotonous unit; largely epimetamorphic detritus is progressively replaced upwards by detritus from deeper-seated basement rocks as documented by superposition of distinct petrofacies. Mineralogy of the overlying volcaniclastic "Buntsandstein" and Val Pila Formation, which record a long-term fining-upward trend during transgression in the first part of the Triassic, testifies the overwhelming importance of sedimentary differentiation and grain size effects. Various grain size classes are in fact characterized by markedly different modal compositions, even though the Gazzi-Dickinson method was followed scrupulously. No methodological approach is thus effectively able to minimize grain size control on composition.

Garzanti, E., Vezzoli, G., Senna, P., Berra, F. (2002). Discriminating source rock and environmental control from detrital modes of Permo-Triassic fluvio-deltaic Sandstones: II. Austroalpine Domain (Livigno,Italy). In R. Valloni, A. Basu (a cura di), Memorie descrittive della carta geologica d'Italia. Volume LXI. Quantitative provenance studies in Italy (pp. 85-98). Roma : Istituto Poligrafico e Zecca dello Stato.

Discriminating source rock and environmental control from detrital modes of Permo-Triassic fluvio-deltaic Sandstones: II. Austroalpine Domain (Livigno,Italy)

GARZANTI, EDUARDO;VEZZOLI, GIOVANNI;
2002

Abstract

Quantitative modal analysis of sandstones represents a useful stratigraphic tool for correlation, revealing major heterochroneities in the largely unfossiliferous fluvial to coastal terrigenous succession of the Austroalpine Domain. Besides its petrostratigraphic significance, sandstone composition provides a wealth of useful information for paleogeographic interpretation. A fundamental step to interpret modal data correctly is the assessment of various factors which control sandstone mineralogy. This case history shows how the relative importance of tectonic evolution of source areas versus effects of sedimentary processes and grain size may drastically change even within single stratigraphic intervals in the same stratigraphic succession. In various Austroalpine nappes, Permian to Anisian siliciclastic wedges represent the base of the post-Hercynian sedimentary cover. Even though each thrust-sheet is characterized by a notably different paleotectonic and sedimentary history, and in spite of lateral facies changes, coeval terrigenous packages maintain a common petrographic signature ("petrologic intervals"). The mineralogy of the metamorphiclastic "Verrucano" exposed in the Livigno area records an unroofing sequence within a single sedimentologically monotonous unit; largely epimetamorphic detritus is progressively replaced upwards by detritus from deeper-seated basement rocks as documented by superposition of distinct petrofacies. Mineralogy of the overlying volcaniclastic "Buntsandstein" and Val Pila Formation, which record a long-term fining-upward trend during transgression in the first part of the Triassic, testifies the overwhelming importance of sedimentary differentiation and grain size effects. Various grain size classes are in fact characterized by markedly different modal compositions, even though the Gazzi-Dickinson method was followed scrupulously. No methodological approach is thus effectively able to minimize grain size control on composition.
Capitolo o saggio
Permian, Triassic, Austroalpine Domain, Stratigraphy, Sandstone Petrography, Petrofacies
English
Memorie descrittive della carta geologica d'Italia. Volume LXI. Quantitative provenance studies in Italy
Presidenza del Consiglio dei Ministri. Servizio Geologico
Garzanti, E., Vezzoli, G., Senna, P., Berra, F. (2002). Discriminating source rock and environmental control from detrital modes of Permo-Triassic fluvio-deltaic Sandstones: II. Austroalpine Domain (Livigno,Italy). In R. Valloni, A. Basu (a cura di), Memorie descrittive della carta geologica d'Italia. Volume LXI. Quantitative provenance studies in Italy (pp. 85-98). Roma : Istituto Poligrafico e Zecca dello Stato.
Garzanti, E; Vezzoli, G; Senna, P; Berra, F
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/10281/7212
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