I depositi alluvionali olocenici di Campo Imperatore (Massiccio del Gran Sasso – Abruzzo)

Il rilevamento geologico e geomorfologico di dettaglio eseguito sui sedimenti e sui terrazzi alluvionali di Campo Imperatore ha permessodi distinguere varie fasi di sedimentazione risalenti all’Olocene. La scansione cronologica dell’attività alluvionale, ottenuta per mezzodi datazioni radiocarbonio su paleosuoli e sedimenti lacustri, dimostra come il trasporto solido nei corsi d’acqua sia avvenuto, seppurecon diversa energia e con brevi fasi di interruzione, lungo gran parte dell’Olocene.La fase di sedimentazione alluvionale olocenica che forma il primo terrazzo è avvenuta tra 12.100±100 BP (14.410÷13.770 Cal BP) eun periodo successivo a 7060±70 BP (8120÷7910 Cal BP) e precedente a 5420±80 BP (6400÷5950 Cal BP). La sedimentazione delcorpo alluvionale che forma il secondo terrazzo si è verificata tra 7060±70 BP (8120÷7910 Cal BP) e 4070±70 BP ( 4830÷4410 CalBP). Le alluvioni che formano il terzo terrazzo si sono deposte in un periodo compreso tra 4070±70 BP (4830÷4410 Cal BP) e unmomento successivo a 2130±50 BP (2190÷1990 Cal BP) e precedente a 1410±40 BP (580÷689 AD).La sedimentazione delle alluvioni che formano il quarto terrazzo è avvenuta tra 1410±40 BP (580÷689 AD) ed un periodo più recentedegli anni 1440÷1640 AD. Il quinto terrazzo è stato formato dall’attività alluvionale recentissima. Appare poi evidente la correlazione tra fasi di sedimentazione alluvionale individuate a Campo Imperatore e quelle riconosciute in altrelocalità dell’Appennino Centrale e Settentrionale; inoltre vi è una notevole coincidenza cronologica anche con le fasi di espansione del Ghiacciaio del Calderone e di alcuni ghiacciai alpini.

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 onpalaeosols and lacustrine sediments and shows that alluvial deposition took place, even if with some interruptions, during most of theHolocene 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 periodmore recent than 7060±70 BP (8120÷7910 Cal BP) and older than 5420±80 BP (6400÷5950 Cal BP). The second terrace alluvialsequence has been dated between 7060±70 BP (8120÷7910 Cal BP) and 4070±70 BP ( 4830÷4410 Cal BP). The deposition of thealluvial 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 otherCentral and Northern Apennine sites, and between the start of the alluvial phases and the advance of the Calderone Glaciers (on theGran 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 isproof 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 theslope 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 centuriesAD) forming the IV terrace seems due to the morphology of the site: the place is very flat and the water in the streams loses itsenergy, 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, thegrain size was larger and erosional phases stronger.