Until today, the most detailed description of the Messinian succession of the TPB was that provided by STURANI (1973), at the western border of the Langhe Basin (Alba). He described a "normal" succession, characterized by: a lower "pre-evaporitic" deep-water marine interval, (uppermost part of the S.Agata Fossili Marls=SAF); an intermediate "evaporitic" shallow water interval (Gessoso-solfifera Fm.=GS); an upper "post-evaporitic" brackish interval ("Strati a Congerie"), mapped in the southern TPB as the Cassano Spinola Conglomerates. However, the analysis of geological maps of remaining sectors of the TPB shows that large sectors of it are composed of a chaotic interval, with a "blocks-in-matrix" texture, that has been informally named "Valle Versa Chaotic Complex" (CTV). Owing to these different results, geological mapping and stratigraphic analysis of the Messinian succession of the northeastern edge of the Langhe Basin and of the southern margin of the Torino Hill has been carried out. The recognition and correlation of main regional unconformities has allowed to obtain an updated physical-stratigraphic scheme of the Piedmont Messinian succession. The main prominent results of this contribution can be summarized as follows: 1) The recognition of the limited areal extent of the "Alba-type" normal succession, only preserved in the north-western border of the Langhe Basin. 2) The subdivision of the Messinian succession into three mappable unconformity bounded stratigraphic units, separated by two important disconinuity surfaces (D1 and D2), that record regional phases of tectonic deformation. The lower (Tortonian-Messinian) unit groups the SAF and terrigenous and evaporite (both selenite and "balatino-like" laminated facies) well bedded deposits, that represent the lateral equivalent of the "evaporitic" interval of Alba. For historical reasons, we continue to refer the primary evaporites to the GS. The intermediate unit (upper Messinian) is bounded at the base by the D1, that corresponds to an erosional surface, associated with an angular unconformity, cutting first into the GS and down to the SAF and pre-Tortonian sediments. This unit is entirely represented by the chaotic sediments of the CTV, that consist of resedimented pieces of the GS, and of a wide range of carbonate blocks, floating within a poorly exposed fine-grained matrix. The CTV forms an irregular body, several kms wide and with a maximum thickness of about 250-300 m, that is referable to the "post-evaporitic stage" of the Messinian. The uppermost unit (upper Messinian) is floored by the D2 and consists of fine to coarse-grained terrigenous sediments, correlatable to the "Lago-Mare" deposits, that are here reported for the first time also in the Torino Hill domain. In conclusion, the presented data depict a new sketch for the TPB Messinian stratigraphy, that seems to be better comparable to that reconstructed by ROVERI et al., (2001) in the Apennine foredeep, than to the classical scheme proposed by STURANI (1973), that anyway is still valid for the western marginal sector of the TPB.
The Messinian sediments of the Tertiary Piedmont Basin (TPB): new data from recent geological mappings.
Irace A;Dela Pierre F;
2005
Abstract
Until today, the most detailed description of the Messinian succession of the TPB was that provided by STURANI (1973), at the western border of the Langhe Basin (Alba). He described a "normal" succession, characterized by: a lower "pre-evaporitic" deep-water marine interval, (uppermost part of the S.Agata Fossili Marls=SAF); an intermediate "evaporitic" shallow water interval (Gessoso-solfifera Fm.=GS); an upper "post-evaporitic" brackish interval ("Strati a Congerie"), mapped in the southern TPB as the Cassano Spinola Conglomerates. However, the analysis of geological maps of remaining sectors of the TPB shows that large sectors of it are composed of a chaotic interval, with a "blocks-in-matrix" texture, that has been informally named "Valle Versa Chaotic Complex" (CTV). Owing to these different results, geological mapping and stratigraphic analysis of the Messinian succession of the northeastern edge of the Langhe Basin and of the southern margin of the Torino Hill has been carried out. The recognition and correlation of main regional unconformities has allowed to obtain an updated physical-stratigraphic scheme of the Piedmont Messinian succession. The main prominent results of this contribution can be summarized as follows: 1) The recognition of the limited areal extent of the "Alba-type" normal succession, only preserved in the north-western border of the Langhe Basin. 2) The subdivision of the Messinian succession into three mappable unconformity bounded stratigraphic units, separated by two important disconinuity surfaces (D1 and D2), that record regional phases of tectonic deformation. The lower (Tortonian-Messinian) unit groups the SAF and terrigenous and evaporite (both selenite and "balatino-like" laminated facies) well bedded deposits, that represent the lateral equivalent of the "evaporitic" interval of Alba. For historical reasons, we continue to refer the primary evaporites to the GS. The intermediate unit (upper Messinian) is bounded at the base by the D1, that corresponds to an erosional surface, associated with an angular unconformity, cutting first into the GS and down to the SAF and pre-Tortonian sediments. This unit is entirely represented by the chaotic sediments of the CTV, that consist of resedimented pieces of the GS, and of a wide range of carbonate blocks, floating within a poorly exposed fine-grained matrix. The CTV forms an irregular body, several kms wide and with a maximum thickness of about 250-300 m, that is referable to the "post-evaporitic stage" of the Messinian. The uppermost unit (upper Messinian) is floored by the D2 and consists of fine to coarse-grained terrigenous sediments, correlatable to the "Lago-Mare" deposits, that are here reported for the first time also in the Torino Hill domain. In conclusion, the presented data depict a new sketch for the TPB Messinian stratigraphy, that seems to be better comparable to that reconstructed by ROVERI et al., (2001) in the Apennine foredeep, than to the classical scheme proposed by STURANI (1973), that anyway is still valid for the western marginal sector of the TPB.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
