This paper reports new integrated biostratigraphic and palaecological data from the upper Messinian to Zanclean succession exposed in the Moncucco quarry (Torino Hill, Tertiary Piedmont Basin, Northwestern Italy). The foraminifer, ostracod, and calcareous nannofossil assemblages have been studied in detail. In the Moncucco quarry the Vena del Gessi Formation is followed by post-evaporitic chaotic deposits (Valle Versa Chaotic Complex) and by continental and brackish water sediments, correlatable to the Lago-Mare deposits of the Mediterranean area. The latter are in turn followed by marine sediments of the Argille Azzurre Fm. (Zanclean) through an irregular surface that is overlaid by a 10-50 cm thick black arenitic layer very rich in organic matter. At the top of the bed an omission surface, evidenced by a network of firm ground burrows filled by the Zanclean sediments, has been observed. The ostracod assemblages recognised in the sediments just belo the black layer are referable to the Loxocorniculina djafarovi biozone (upper Messinian post-evaporitic interval). They indicate oligo-mesohaline shallow-water conditions and show the influx of Paratethyan faunas. Foraminifers and calcareous nannofossils in this interval are reworked. Microfaunas and calcareous nannofossils found in the sediments just above the black layer testify the MP11 foraminifer biozone and the MNN12 calcareous nannofossils biozone. However, the absence of the first sinistral coiling shift if Neogloboquadrina acostaensis and of Triquetrorhabdulus rugosus in the lowermost Pliocene samples suggests a short hiatus, further confirmed by the presence of the omission surface at the top of the black layer. The recognition of biostratigraphic markers along the section allows to identify the MP12, MP13, and MP14a foraminifer biozones and MNN13 and MNN14-15 calcareous nannofossil biozones, even if partially documented by the sedimentary record. The occurence of Agrenocythere pliocenica within the MP12 biozone, confirms the biostratigraphic importance of this taxon at the Mediterranean scale. Foraminifer and ostracod palaeoecological data suggest an upper epibathyal depositional palaeoenvironment in the MP11 biozone, a further deepening in the MP12 biozone and a progressive reduction of the water depth in the MP13 and MP14a biozones. On the whole, these data suggest that also in the Tertiary Piedmont Basin in the termination of the Messinian salinity crisis was abrupt, followed by the deep-sea Zanclean flooding event.
The Miocene/Pliocene boundary and the Early Pliocene micropalaeontological record: new data from the Tertiary Piedmont Basin (Moncucco quarry, Torino Hill, Northwestern Italy).
IRACE A
2008
Abstract
This paper reports new integrated biostratigraphic and palaecological data from the upper Messinian to Zanclean succession exposed in the Moncucco quarry (Torino Hill, Tertiary Piedmont Basin, Northwestern Italy). The foraminifer, ostracod, and calcareous nannofossil assemblages have been studied in detail. In the Moncucco quarry the Vena del Gessi Formation is followed by post-evaporitic chaotic deposits (Valle Versa Chaotic Complex) and by continental and brackish water sediments, correlatable to the Lago-Mare deposits of the Mediterranean area. The latter are in turn followed by marine sediments of the Argille Azzurre Fm. (Zanclean) through an irregular surface that is overlaid by a 10-50 cm thick black arenitic layer very rich in organic matter. At the top of the bed an omission surface, evidenced by a network of firm ground burrows filled by the Zanclean sediments, has been observed. The ostracod assemblages recognised in the sediments just belo the black layer are referable to the Loxocorniculina djafarovi biozone (upper Messinian post-evaporitic interval). They indicate oligo-mesohaline shallow-water conditions and show the influx of Paratethyan faunas. Foraminifers and calcareous nannofossils in this interval are reworked. Microfaunas and calcareous nannofossils found in the sediments just above the black layer testify the MP11 foraminifer biozone and the MNN12 calcareous nannofossils biozone. However, the absence of the first sinistral coiling shift if Neogloboquadrina acostaensis and of Triquetrorhabdulus rugosus in the lowermost Pliocene samples suggests a short hiatus, further confirmed by the presence of the omission surface at the top of the black layer. The recognition of biostratigraphic markers along the section allows to identify the MP12, MP13, and MP14a foraminifer biozones and MNN13 and MNN14-15 calcareous nannofossil biozones, even if partially documented by the sedimentary record. The occurence of Agrenocythere pliocenica within the MP12 biozone, confirms the biostratigraphic importance of this taxon at the Mediterranean scale. Foraminifer and ostracod palaeoecological data suggest an upper epibathyal depositional palaeoenvironment in the MP11 biozone, a further deepening in the MP12 biozone and a progressive reduction of the water depth in the MP13 and MP14a biozones. On the whole, these data suggest that also in the Tertiary Piedmont Basin in the termination of the Messinian salinity crisis was abrupt, followed by the deep-sea Zanclean flooding event.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
