Montenero Quarry, Onano, Viterbo Province, Lazio, Italyi

Regional Level Types
Montenero Quarry	Quarry
Onano	Municipality
Viterbo Province	Province
Lazio	Administrative Region
Italy	Country

In the Montenero quarry (Onano, Làtera volcano, Viterbo, Lazio) pyroclastic fall, flow, and surge deposits and deposits of scoria flows crop out.

The sequence includes the Onano Formation at the base and the Pitigliano Formation at the top.

From bottom to top, we can distinguish:

— deposits of scoriaceous lapilli followed by several flow units covered by levels of lapilli and ash;

— levels of pisolithic ash and pumice with crossed structures delimited at the roof and base by paleosols;

— lapilli level with a chaotic deposit (lahar) subjected to a vesiculated tuff;

— level of scoriaceous lapilli with surge deposits on the roof with crossed structures;

— alternating levels of fall, flow, and surge deposits;

— level of minute pumices;

— levels of lapilli and ash interbedded with paleosols.

Various syn- and post-depositional deformational structures are visible, such as the load imprints left by the falling blocks and the erosion channels filled in turn by pyroclastic material.

Within these stratified formations, mostly made up of black and grey scoria, there are numerous inclusions of pre-volcanic and sedimentary rocks, mostly marine clays and limestones. These were transformed by the heat of the volcanic conduit into metamorphic rocks quite different from those of the Pitigliano formation.

Large xenoliths are very abundant in the scoria and tuffs, mostly leucitic tephrites and trachytes, which in some cases reach considerable dimensions, together with fragments of mafic rocks, partly reabsorbed, with particular recrystallizations within them; of notable mineralogical interest are the metasomatic, metamorphic and intrusive rocks. The volcanological-stratigraphic and mineralogical study has been the subject of several works.