I DEPOSITI ALLUVIONALI OLOCENICI DI CAMPO IMPERATORE (MASSICCIO DEL GRAN SASSO – ABRUZZO)

Abstract

The Campo Imperatore Holocene alluvial sediments (Gran Sasso Massif – Central Italy)
The detailed geological and geomorphological survey carried out on Campo Imperatore alluvial sediments and terraces enabled some
Holocene depositional phases to be recognised. The chronological framework has been obtained through radiocarbon datings on
palaeosols and lacustrine sediments and shows that alluvial deposition took place, even if with some interruptions, during most of the
Holocene period.
The deposition of the alluvial unit forming the first terrace took place between 12.100±100 BP (14.410÷13.770 Cal BP) and a period
more recent than 7060±70 BP (8120÷7910 Cal BP) and older than 5420±80 BP (6400÷5950 Cal BP). The second terrace alluvial
sequence has been dated between 7060±70 BP (8120÷7910 Cal BP) and 4070±70 BP ( 4830÷4410 Cal BP). The deposition of the
alluvial sediments forming the third terrace occurred between 4070±70 BP (4830÷4410 Cal BP) and a period following 2130±50 BP
(2190÷1990 Cal BP) and preceding 1410±40 BP (580÷689 Cal AD).
The alluvial sediments forming the fourth terrace were deposited between 1410±40 BP (580÷689 Cal AD) and a period following
1440÷1640 Cal AD. The fifth terrace has been formed by very recent alluvial activity.
Thanks to the dating of the sediments one can observe a correlation between alluvial sedimentation at Campo Imperatore and in other
Central and Northern Apennine sites, and between the start of the alluvial phases and the advance of the Calderone Glaciers (on the
Gran Sasso Massif) and some Alpine glaciers.
The Campo Imperatore alluvial sedimentation appears strongly linked to the environmental impact produced by climatic oscillations,
which affected both Mediterranean and Alpine areas, also affecting glaciers that cannot be changed by human activity. Even if there is
proof of fires that developed during prehistoric times, the data available show that the human impact was not able to produce any instability of the slopes and alluvial sedimentation phases not linked to the climatìc variations.
The large, thick alluvial units outcropping at Campo Imperatore seem strongly linked also to the presence of cataclastic rocks on the
slope surrounding the northern boundary of the plain; the gullies affecting the cataclasites were inactive only during short periods,
when morphological stability prevailed and soils developed.
The considerable detail regarding phases of sedimentation and pedogenesis preserved on the deposits (younger than the VI-VII centuries AD) forming the IV terrace seems due to the morphology of the site: the place is very flat and the water in the streams loses its energy, the sediments are mainly thin and between them lie gentle erosion surfaces.
The same detail was not found in the older alluvial units lying in different places where the streams flowed with greater energy, the
grain size was larger and erosional phases stronger.