Geosite: Duidduru fossiliferous quarry

A present-day tropical scenery

PALAEONTOLOGICAL SITE
The Genoni Geo-paleosite is truly unique in Sardinia. A geo-palaeontological gem, a must for lovers of cultural tourism or fossils and for schools.

The site’s origins
Sardinia offers precious fragments of its geological history in several areas of its territory.

In the territory of Genoni, a geological and palaeontological site of very important significance was discovered in the eighties.

A present-day tropical scenery can help us imagine how Duidduru might have been in the Miocene; the stratigraphy of the site and the wealth of fossils are some of the elements that make the site interesting from a scientific point of view.

The work of palaeontologists and geologists of the Superintendence for Archaeological Heritage of Sassari and Nuoro and Professors of the Department of Earth Sciences of the University of Cagliari has allowed the reconstruction of the Miocene environment.

Formation and development
The formation of Duidduru marks the beginning of the “1st sedimentary Miocene Cycle” Auct. in the territory we are looking at, where it surfaces with a thickness of about 50 meters.

It lies locally on the Paleozoic granite basement or on the Triassic dolomite and limestone formations or also on the Oligocene ignimbrites.

It is a terrigenous sequence consisting of arenitic and conglomeratic lithologies outcropping to the north-east (Arroleddu, N.ghe Addori, Pizzu Antoni Orrù, Sa Roia Manna) and west of Genoni (N.ghe Perdaligieri, Seddon Quaddaris, Duidduru).

In the Duidduru area, in particular, the meaningful geo-palaeontological site by the same name was established and equipped for the enhancement and protection of the rich fossil heritage contained in the layers of this geological formation.

The sandstones have average to fine grains, and are both inconsistent and compact according to the greater or lesser presence of carbonate cement; the colour varies from light brown to greenish brown. They are generally massive, although locally there is pseudostratification.

The presence of a volcanogenic component (tufitic sandstones) is constant, likely derived from a concurrent submarine magmatic activity of andesitic type, well known in Marmilla (Maccioni, 1969; 1974) and related to the “superior-type basic-intermediate volcanic sequence” or “Upper andesitic series” Auct ..

In its lower and medium part the formation appears poor of the macro-fossiliferous component, while in its medium-upper part there are very rich levels, especially of Clams and Echinoids.

In the Duidduru area and on the slopes on the left bank of the Riu Scraccadrixius, an arenitic carbonate cement bank, compact, of hazel colour, is characterized by the abundance of macro-fossils (shells and internal models), either whole or in fragments consisting of Echinoids (sand-dollar shells and Scutelleridae), Bivalves (Scallops and Clams) and rare Gastropods. These marine faunas have a sprawling arrangement indicating submarine mass transport.

In the Duidduru area, near Funtana Populis, under the N.ghe Perdaligieri and south-west of N.ghe Domu ‘e Birni, emerges a fine-grain arenitic bank, 70 cm to 2.5 m thick, consisting of Paleozoic lithology shale granules with abundant volcanic component, inconsistent and massive, distinguished both for the greenish-brown colour and, above all, for an abundance of fossils, mainly of calcified Turritellidae and rare Ostreidae (either whole or in fragments).

Revalorisation

The Superintendence for Archaeological Heritage of Sassari and Nuoro, the Department of Earth Sciences of the University of Cagliari and the Genoni Town Council strongly committed to the goal of preventing site deterioration. The acquisition of the site by the Municipality of Genoni has allowed the definition of the area to facilitate the work of palaeontologists and geologists. The importance of the Duidduru site necessitated its revalorisation, sanctioned in 2011 with the agreement between the Ministry of Culture and the Municipality of Genoni.

Discovery and recovery
The massive sandstone presence in the Duidduru territory had already hinted to the probable presence of finds in the area to fossil experts.

In the eighties, during quarrying to extract sandstone from the ground, the first fossil reefs were brought to light.

This discovery led to the closure of sedimentary rock sampling works and the beginning of the study of the site by the Superintendency for Archaeological Heritage of Sassari and Nuoro and the Department of Earth Sciences of the University di Cagliari.

Thanks to the work of palaeontologists and geologists, an important Miocene site was discovered.

Various levels of stratigraphy, the presence of many fossils, different palaeoenvironments were brought to light and can be admired by visitors.

Finds

The fossils in the area date back to the Miocene; the finds belong to marine animal species that still live in shallow tropical waters.

Their fossilisation took place by mineralization, and thanks to the sandstone the fossils have been preserved well.

Some exhibits were collected and studied; after a cleaning process by the palaeontologists of the Superintendence for Archaeological Heritage of Sassari and Nuoro, the fossils can be seen in the P.AR.C. exhibition hall.

The Site today
The site is like an open air museum, rich in geological and palaeontological information.
The rich stratigraphy shows various events that have taken place in the Miocene.
You can admire a fossilized seabed, rich in finds; in the central part is a turritella reef, the product of the encounter between sea and river, which created a lagoon. The wall also has two interesting examples of an earthquake in Sardinia about 5 million years ago: a visible fault and Neptune strands.