Integrated sedimento logica! and micropaleontological (foraminifera, ostracods, pollen) analyses of eight continuously-cored boreholes, 150 to 270 m deep, reveal the depositional history and the paleoclimatic evolution of southeastern Po Plain· (northern ltaly) during the last 150 ky. Facies analysis, carried out through identification of 20 facies associations and 12 microfossil assemblages, and detailed stratigraphic correlations across severa! tens of km show a cyclic stacking pattern of facies (including continental, littoral and shallow-marine deposits ), which defines two fom1h-order sequences deposited during the last two glacial-interglacial cycles. Two prominent stratigraphic markers, corresponding to wedge-shaped coastal sand bodies, are recorded between 0- 30m and l 00-125m core depths. These bodies were deposited during the twç> major transgressive pulsations and subsequent sea-level highstands of the las t 150 ky, assigned to the Tyrrhenian ( oxygen isotope substage Se) and the Holocene, respectively. Stratigraphic architecture of both cycles shows similar patterns of còastal evolution withchanging sea leve!. Hiatal surfaces, characterized by basinward shifts of facies and paleosol development, mark sequence boundaries, overlain by alluvial plain deposits. The transgressive deposits invariably reflect the onset of a coastal plain and the landward migration of barrier-lagoonestuary systems, whereas highstand deposition was characterized by extensive delta and strandplain progradation. The key surfaces for sequence-stratigraphic interpretation are identified readily by lithofacies changes and/or important variations in the micropalaeontologic associations. The transgressive surfaces are considerably easier to identify than the other key surfaces and display diagnostic pollen . signatures. Pollen assemblages in the transgressive (TST) and highstand (HST) deposits of both Tyrrhenian and Holocene age indicate warm periods, characterized by the development of interglacial mixed deciduous broad-leaved forests. A characteristic four-steps evolution of vegetation is recognized in the TST and HST of three long~cored pollen seri es, providing evidence for synchronous changes in climatic conditions between glacial-to-interglacial and interglacial-to-glacial transitions. By contrast, abrupt shifts to very Jow pollen concentrations and pollen spectra dominateci by Pinus and non-arborea! pollen types at the base of stratigraphic intervals dominated by alluvial deposits (fallingstage and lowstand systems tracts), are interpreted to reflect the onset of glacial periods. The good match between facies architecture, pollen distribution and global sea-level evolution strongly suggests that late Quaternary sedimentation in the Po Basin developed under a predominantly glac~o-eustatic contro!. Stratigraphic architecture of the Po Basin thus can provi de a useful analog for interpretation and correlation in the stratigraphic record of very rapid glacio-eustatic (fourth-order) cycles with frequencies of about l OOky.

Paleogeographic and paleoclimatic evolution of the Po plain from 150-KY core records

SARTI, GIOVANNI
2001

Abstract

Integrated sedimento logica! and micropaleontological (foraminifera, ostracods, pollen) analyses of eight continuously-cored boreholes, 150 to 270 m deep, reveal the depositional history and the paleoclimatic evolution of southeastern Po Plain· (northern ltaly) during the last 150 ky. Facies analysis, carried out through identification of 20 facies associations and 12 microfossil assemblages, and detailed stratigraphic correlations across severa! tens of km show a cyclic stacking pattern of facies (including continental, littoral and shallow-marine deposits ), which defines two fom1h-order sequences deposited during the last two glacial-interglacial cycles. Two prominent stratigraphic markers, corresponding to wedge-shaped coastal sand bodies, are recorded between 0- 30m and l 00-125m core depths. These bodies were deposited during the twç> major transgressive pulsations and subsequent sea-level highstands of the las t 150 ky, assigned to the Tyrrhenian ( oxygen isotope substage Se) and the Holocene, respectively. Stratigraphic architecture of both cycles shows similar patterns of còastal evolution withchanging sea leve!. Hiatal surfaces, characterized by basinward shifts of facies and paleosol development, mark sequence boundaries, overlain by alluvial plain deposits. The transgressive deposits invariably reflect the onset of a coastal plain and the landward migration of barrier-lagoonestuary systems, whereas highstand deposition was characterized by extensive delta and strandplain progradation. The key surfaces for sequence-stratigraphic interpretation are identified readily by lithofacies changes and/or important variations in the micropalaeontologic associations. The transgressive surfaces are considerably easier to identify than the other key surfaces and display diagnostic pollen . signatures. Pollen assemblages in the transgressive (TST) and highstand (HST) deposits of both Tyrrhenian and Holocene age indicate warm periods, characterized by the development of interglacial mixed deciduous broad-leaved forests. A characteristic four-steps evolution of vegetation is recognized in the TST and HST of three long~cored pollen seri es, providing evidence for synchronous changes in climatic conditions between glacial-to-interglacial and interglacial-to-glacial transitions. By contrast, abrupt shifts to very Jow pollen concentrations and pollen spectra dominateci by Pinus and non-arborea! pollen types at the base of stratigraphic intervals dominated by alluvial deposits (fallingstage and lowstand systems tracts), are interpreted to reflect the onset of glacial periods. The good match between facies architecture, pollen distribution and global sea-level evolution strongly suggests that late Quaternary sedimentation in the Po Basin developed under a predominantly glac~o-eustatic contro!. Stratigraphic architecture of the Po Basin thus can provi de a useful analog for interpretation and correlation in the stratigraphic record of very rapid glacio-eustatic (fourth-order) cycles with frequencies of about l OOky.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/191417
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