THE PLIOCENE BASIN AND THE LOWER PLEISTOCENE BASIN

THE PLIOCENE BASIN

The oldest part of the oldest lake, formed in the Pliocene more than 2,500,000 years ago, has left its traces in part of the sediments of the so-called “Aielli Complex”. These fragments constitute the backbone of the reliefs of the north-eastern sector of the Colle Caprino-La Selvotta basin; and also the middle-upper part of the relief, on which the town of Aielli stands, emerging between this and the nearby town of Cerchio.

The succession of sediments is represented by clays, silts and sands generally gray or yellowish, sometimes rich in the shells of pulmonate gastropods in the lower part.

The grain size gradually increases upwards, becoming more gravelly-sandy, until it presents, at about 900 meters above sea level, lenses of limestone breccias emerging along the road that connects Aielli to Aielli Stazione.

It is also possible to find individual limestone elements, with volumes of hundreds of cubic meters, linked to landslide repair mechanisms.

Likely, calcareous fragments, included in the Pliocene sediments, are also to be considered whole clods of the order of millions of cubic meters, such as Colle Dora, surfaced in another sector of the basin, north of Castelnuovo.

From the point of view of the depositional environment, it should be noted that in the lower and intermediate part of the “Aielli Complex” there are completely no limestone clasts. The carbonate contribution, even with large blocks, becomes more significant in the upper part.

This indicates that the paleo slopes, which fueled the sedimentation in ancient times basin, were originally made up of terrigenous deposits (clayey and arenaceous marine sediments Miocene) and only after a long erosion phase, concomitant with uplift of the mountainous reliefs, came to day the limestone slopes whose erosion – sometimes with landslide mechanisms – it is witnessed by the accumulation of the part high of the “Aielli Complex”.

Basically, it is in the course of the sedimentation of this first cycle of positional, which passes from a general

presumably dominated landscape from mild clayey and arenaceous ridges, to steep carbonate slopes, more similar to those who dominate in the sector the current edge of the Fucino in the north.

However, the paleogeographic and geological picture original was certainly different from today. In fact, the Pliocene sediments did not were found only between Aielli and Cerchio, but also in the areas of I Tre Monti, Castelnuovo, Antrosano, Alba Fucens and Magliano dé Marsi.

This continuity and their presence to in the nearby Valle del Salto they suggest that the Pliocene lake basin was very large and included the northern sector of the Fucino and a large depression towards the present basin of Rieti.

The lower Pleistocene basin

During the Lower Pleistocene, after the intense erosion of the sediments of the “Complex of Aielli “, contemporary to the uplift in the western sector of the current Apennine chain, the gravels were deposited with mainly sandy intercalations, of an environment from fluvial to lake (“Complex of Cupoli”), clearly visible between Celano and Aielli, in correspondence with the relief of the Cupoli Valley.

These sediments have a generally different position of the layers from that of most ancient deposits, with a gentle slope towards the basin.

White or white-yellowish limestone can also be attributed to the “Complex of Cupoli” extensively emerging between Collarmele and Pescina and referable to a more depositional environment frankly lacustrine.

Simultaneously with the lake and river sedimentation, the slopes mountainous were characterized by the placement of limestone breccias, often well stratified and cemented with a micritic matrix of pink color.

These are ancient slope deposits, with rather characteristic appearance (the pinkish matrix), widespread in the Abruzzo Apennines, which can reach a considerable thickness of 120-130 meters.

In the basin area del Fucino, these breaches were found along the southern slope of I Tre Monti, on the western one of the Serra di Celano (between Celano and Ovindoli), on the eastern one of Gole di Celano (at an altitude between about 1,300 and 1,500 m), on the south-western side of  M. Velino and especially along the southern slope of the Magnola Mountains.

Here in correspondence of Colle del Pidocchio, the succession of breaches is well exposed thanks to the sub-horizontal arrangement of the strata, above all in the upper part of the relief.

Note that the breaches they emerge on this mountainous ridge even at high altitudes altitude, around 1,950 meters, between Monte Cocurello and Il Sasso.

The stratigraphic and sedimentological characteristics, as well as the plano-altimetric distribution of the deposits of the “Complex of Cupoli” indicate that the basin of sedimentation about 1 million years ago was supposed to be very different from that of the Pliocene.

Basically, the landscape began to approximate the current one, since the presence of the aforementioned breaches clarifies that many of the slopes and valley engravings, which still characterize the Fucense physiography, (eg Monti della Magnola, Gole di Celano, southern side of I Tre Monti, but also Vallelonga and Giovenco valley) were already present about 1,000,000 years ago.