The Legnagnone section (North-eastern Apennines) represents one of the few shallow water records of theonset of the Messinian salinity crisis. Here we present a detailed description of a ~200 kyr time intervalencompassing the pre-/syn-evaporitic transition based on a multidisciplinary approach, integrating sedimentological,bio-magnetostratigraphical, palaeontological and stable isotope data. Such a shallow water settingis potentially more sensitive to the palaeoenvironmental change leading to the MSC than the more oftenstudied deeper Mediterranean basin. The aquatic palaeoenvironmental reconstruction proposed here isbased on the study of foraminifer, ostracod and mollusc assemblages. It depicts a change from infralittoral(20–50 m) to inner circalittoral environment (60–100 m) that, since 6.12 Ma, was progressively affectedby a reduction of oxygen at the sea floor punctuated by short-lived anoxic events. At least three coolingevents have been recognized on the basis of relative abundance data in mid to high altitude pollen, which,before 6.03 Ma, are in phase with abundance peaks of Turborotalia spp., a taxon indicating eutrophic andcool surface waters. The absence of stress-tolerant benthic foraminifers during these peaks points to strongventilation episodes triggered by a generally cooler climate. The proximity of a deltaic system and the consequentriverine input probably caused a salinity decrease of the surface waters, hindering the proliferation ofplanktonic foraminifers in the water column, which prevalently occur in short influxes and disappear at ca.6 Ma. Our results suggest that the onset of the crisis occurred during a phase of relative sea level highstand, whereas no evidences of sea level drop can be envisaged. The palaeoclimatic reconstruction basedon palynological data indicates the dominance of a “subtropical humid forest” vegetation type, where freshwater swamps are well represented. From 6.03 Ma onward, the transition to the salinity crisis is markedby more pronounced cyclical expansions of the temperate broad-leaved deciduous forest, along with herbaceoustaxa. The establishment of the strongly evaporative condition at the crisis onset is not associated withmajor vegetational changes towards drier conditions, but linked to a sudden increase of δ18O and the disappearanceof benthic foraminifers just prior to the deposition of the 1st laminated carbonate, which representsthe base of the Primary Lower Gypsum unit.

A shallow water record of the onset of the Messinian salinity crisis in the Adriatic foredeep (Legnagnone section, Northern Apennines).

ROSSO, Maria Antonietta;
2013-01-01

Abstract

The Legnagnone section (North-eastern Apennines) represents one of the few shallow water records of theonset of the Messinian salinity crisis. Here we present a detailed description of a ~200 kyr time intervalencompassing the pre-/syn-evaporitic transition based on a multidisciplinary approach, integrating sedimentological,bio-magnetostratigraphical, palaeontological and stable isotope data. Such a shallow water settingis potentially more sensitive to the palaeoenvironmental change leading to the MSC than the more oftenstudied deeper Mediterranean basin. The aquatic palaeoenvironmental reconstruction proposed here isbased on the study of foraminifer, ostracod and mollusc assemblages. It depicts a change from infralittoral(20–50 m) to inner circalittoral environment (60–100 m) that, since 6.12 Ma, was progressively affectedby a reduction of oxygen at the sea floor punctuated by short-lived anoxic events. At least three coolingevents have been recognized on the basis of relative abundance data in mid to high altitude pollen, which,before 6.03 Ma, are in phase with abundance peaks of Turborotalia spp., a taxon indicating eutrophic andcool surface waters. The absence of stress-tolerant benthic foraminifers during these peaks points to strongventilation episodes triggered by a generally cooler climate. The proximity of a deltaic system and the consequentriverine input probably caused a salinity decrease of the surface waters, hindering the proliferation ofplanktonic foraminifers in the water column, which prevalently occur in short influxes and disappear at ca.6 Ma. Our results suggest that the onset of the crisis occurred during a phase of relative sea level highstand, whereas no evidences of sea level drop can be envisaged. The palaeoclimatic reconstruction basedon palynological data indicates the dominance of a “subtropical humid forest” vegetation type, where freshwater swamps are well represented. From 6.03 Ma onward, the transition to the salinity crisis is markedby more pronounced cyclical expansions of the temperate broad-leaved deciduous forest, along with herbaceoustaxa. The establishment of the strongly evaporative condition at the crisis onset is not associated withmajor vegetational changes towards drier conditions, but linked to a sudden increase of δ18O and the disappearanceof benthic foraminifers just prior to the deposition of the 1st laminated carbonate, which representsthe base of the Primary Lower Gypsum unit.
2013
Messinian; multiproxi-palaeoenvironmental reconstruction; palaeoclimate, palaeoceanography
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11769/53609
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