The Triassic to Lowermost Jurassic mudrocks from continental redbeds of the Longi-Taormina Unit (Calabria-PeloritaniArc; southern Italy) have been mineralogically, chemically and petrographically analyzed, in order to reveal their complexhistory, which record an important phase of the geological evolution of the Mediterranean area.The Late Triassic corresponds with a low first-order sea level stand and a time of high continental emergence whereasthe Early Jurassic was the time of the initiation of the first-order sea level rise in the mid-Mesozoic, generally marked bya transgressive trend.The mineralogical assemblage, dominated by the occurrence of illite and illite/smectite mixed layers, coupled to theCIA index and to the A-CN-K plot, indicates post-depositional K-enrichments.Palaeoweathering indices (CIW and PIA ratios) suggest that the source experienced intense weathering and that theylikely record a recycling effect from their metasedimentary basement rocks. A recycling effect is also suggested by thedistribution of Al2O3, TiO2, and Zr. In the Zr/Sc vs. the Th/Sc plot the redbeds are not clustered along the primarycompositional trend but fall along a trend involving zircon addition and thus sediment recycling. Recycling could significantlyaffect the weathering indices which likely monitor a cumulative effect including a first cycle of weathering at thesource rocks. Weathering occurred under hot, episodically humid climate with a prolonged dry season. Wet-humid conditionsfavored the formation of stream channels that eroded the soil profiles, whereas the dry season promoted the sedimentation.The climate alternation in the Early Jurassic favored recycling.An additional provenance terrane occurring in the basement, including metavolcanic rocks having mafic compositioncannot be excluded, since the Eu anomaly is slightly higher than the PAAS value. Although the effects of recycling onREE distribution are uncertain, the Eu/Eu* should increase, as more feldspar is destroyed during weathering and diagenesis.This involves that the Eu/Eu* ratio could monitor a supply of low Eu/Eu* mafic detritus which compensate for the recyclingeffect by reducing Eu/Eu*. Eu released during the dissolution of feldspar could be retained by clay minerals contributingto minimize the recycling induced increase of the Eu-anomaly. This may involve that the recycling effect on the Euanomalywas minor and that the low Eu/Eu* mafic detritus supply was also minor. The subordinate importance of a maficsupply is confirmed also by other provenance proxies including the La-Th-Sc plot and the Cr/V and Y/Ni ratios.The proportions of illitic layers in I/S mixed layers coupled with the illite crystallinity values, expressed as KüblerIndex (KI), suggesting an estimated temperature experienced by the Longi Units in the range of 100–150°C. Starting fromthis range the diagenetic/tectonic evolution should correspond to a lithostatic/tectonic loading of about 4–5 km.

Sedimentary recycling, provenance and paleoweathering from chemistry and mineralogy of Mesozoic continental redbed mudrocks, Peloritani mountains, southern Italy

CRITELLI, Salvatore;PERRI F;SONNINO, Maurizio
2006-01-01

Abstract

The Triassic to Lowermost Jurassic mudrocks from continental redbeds of the Longi-Taormina Unit (Calabria-PeloritaniArc; southern Italy) have been mineralogically, chemically and petrographically analyzed, in order to reveal their complexhistory, which record an important phase of the geological evolution of the Mediterranean area.The Late Triassic corresponds with a low first-order sea level stand and a time of high continental emergence whereasthe Early Jurassic was the time of the initiation of the first-order sea level rise in the mid-Mesozoic, generally marked bya transgressive trend.The mineralogical assemblage, dominated by the occurrence of illite and illite/smectite mixed layers, coupled to theCIA index and to the A-CN-K plot, indicates post-depositional K-enrichments.Palaeoweathering indices (CIW and PIA ratios) suggest that the source experienced intense weathering and that theylikely record a recycling effect from their metasedimentary basement rocks. A recycling effect is also suggested by thedistribution of Al2O3, TiO2, and Zr. In the Zr/Sc vs. the Th/Sc plot the redbeds are not clustered along the primarycompositional trend but fall along a trend involving zircon addition and thus sediment recycling. Recycling could significantlyaffect the weathering indices which likely monitor a cumulative effect including a first cycle of weathering at thesource rocks. Weathering occurred under hot, episodically humid climate with a prolonged dry season. Wet-humid conditionsfavored the formation of stream channels that eroded the soil profiles, whereas the dry season promoted the sedimentation.The climate alternation in the Early Jurassic favored recycling.An additional provenance terrane occurring in the basement, including metavolcanic rocks having mafic compositioncannot be excluded, since the Eu anomaly is slightly higher than the PAAS value. Although the effects of recycling onREE distribution are uncertain, the Eu/Eu* should increase, as more feldspar is destroyed during weathering and diagenesis.This involves that the Eu/Eu* ratio could monitor a supply of low Eu/Eu* mafic detritus which compensate for the recyclingeffect by reducing Eu/Eu*. Eu released during the dissolution of feldspar could be retained by clay minerals contributingto minimize the recycling induced increase of the Eu-anomaly. This may involve that the recycling effect on the Euanomalywas minor and that the low Eu/Eu* mafic detritus supply was also minor. The subordinate importance of a maficsupply is confirmed also by other provenance proxies including the La-Th-Sc plot and the Cr/V and Y/Ni ratios.The proportions of illitic layers in I/S mixed layers coupled with the illite crystallinity values, expressed as KüblerIndex (KI), suggesting an estimated temperature experienced by the Longi Units in the range of 100–150°C. Starting fromthis range the diagenetic/tectonic evolution should correspond to a lithostatic/tectonic loading of about 4–5 km.
2006
mudrocks; provenance; Mesozoic continental redbeds
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11770/141164
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 156
  • ???jsp.display-item.citation.isi??? 141
social impact