Within the colluvial clastic deposits of the Crati Basin, near the village of Tarsia, a decimetre to metre thick volcaniclastic stratum outcrops interbedded within poorly structured sandy-pelitic deposits. The volcaniclastic stratum is structureless, powdery, pinkish grey or yellowish brown, slightly pedogenized towards the top and characterized at the base by centimetre-sized clasts of crystalline rocks. The depositional and textural features suggest a primary fall-out of volcanic ash during a period when the climate-favoured modification of the landscape and re-mobilization of the ash as mud flows with the first rainy episode. This area was subjected to strong uplift (0.7 mm/yr) and climatic effects of the Last Glacial Maximum, and the preservation of this volcaniclastic stratum represents an unusual and exceptional event. The volcanic ash, representing the principal component of the deposit, is composed of shards and pumices of phonolithic composition with millimetre-sized phenocrysts of sanidine. The non-volcanic component consists of quartz clasts and, to a much lesser extent, feldspars and fragments of metamorphic rocks. Thermal (TL) and optical stimulated luminescence (OSL) techniques were used to date the potassium feldspar crystals of volcanic origin and the quartz crystals from the non-volcanic component. The stratum contains sediments of different origins. The feldspar fraction was subjected to high temperatures at the moment of volcanic emission, zeroing the internal luminescence clock. The quartz fraction was exposed to light probably only at the moment of sedimentation, with the possibility of only partial bleaching of luminescence signal. OSL ages are chronologically undistinguishable between the quartz and feldspar fractions. The quartz and feldspar fraction ages obtained by OSL are, respectively, 2873 ka and 2772 ka. TL measurements reveal an age of 4173 ka for the quartz fraction and 3373 ka for the feldspar fraction. The age and chemical and mineralogical composition of the volcanic fraction indicate the source for the large explosive eruptions occurred in the Campanian area (Ischia-Flegrei, southern Italy) between 42 and 25 ka.
Thermal (TL) and optical stimulated luminescence (OSL) techniques for dating Quaternary colluvial volcanoclastic sediments: an example from the Crati Basin (Northern Calabrian)
DE ROSA, Rosanna;
2006-01-01
Abstract
Within the colluvial clastic deposits of the Crati Basin, near the village of Tarsia, a decimetre to metre thick volcaniclastic stratum outcrops interbedded within poorly structured sandy-pelitic deposits. The volcaniclastic stratum is structureless, powdery, pinkish grey or yellowish brown, slightly pedogenized towards the top and characterized at the base by centimetre-sized clasts of crystalline rocks. The depositional and textural features suggest a primary fall-out of volcanic ash during a period when the climate-favoured modification of the landscape and re-mobilization of the ash as mud flows with the first rainy episode. This area was subjected to strong uplift (0.7 mm/yr) and climatic effects of the Last Glacial Maximum, and the preservation of this volcaniclastic stratum represents an unusual and exceptional event. The volcanic ash, representing the principal component of the deposit, is composed of shards and pumices of phonolithic composition with millimetre-sized phenocrysts of sanidine. The non-volcanic component consists of quartz clasts and, to a much lesser extent, feldspars and fragments of metamorphic rocks. Thermal (TL) and optical stimulated luminescence (OSL) techniques were used to date the potassium feldspar crystals of volcanic origin and the quartz crystals from the non-volcanic component. The stratum contains sediments of different origins. The feldspar fraction was subjected to high temperatures at the moment of volcanic emission, zeroing the internal luminescence clock. The quartz fraction was exposed to light probably only at the moment of sedimentation, with the possibility of only partial bleaching of luminescence signal. OSL ages are chronologically undistinguishable between the quartz and feldspar fractions. The quartz and feldspar fraction ages obtained by OSL are, respectively, 2873 ka and 2772 ka. TL measurements reveal an age of 4173 ka for the quartz fraction and 3373 ka for the feldspar fraction. The age and chemical and mineralogical composition of the volcanic fraction indicate the source for the large explosive eruptions occurred in the Campanian area (Ischia-Flegrei, southern Italy) between 42 and 25 ka.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
