St. Michael’s Hill, which is part of the Cagliari hill system, has an interesting geological history that begins at least 15 million years ago, in the Middle Miocene (Tertiary Era period).
The first studies on the geology of this area date back to General Alberto La Marmora (1857) and Domenico Lovisato (1885).
The latter was Professor of Geology at the University of Cagliari; from then to now, there are numerous scholars (geologists and paleontologists) of the geological formations outcropping in this area. These formations, consisting of sedimentary rocks (sandstones, marls and calcarenites), are very rich in fossil remains of marine organisms that testify to the fact that in the Miocene the entire territory of Cagliari was affected by prolonged marine ingression.
The marine sediments of St. Michael’s Hill are called, from the oldest to the most recent, “Pirri sandstones,” “Pietra Cantone,” “Tramezzario,” and “Pietra Forte,” according to the jargon of stone quarrymen.
Their abundant fossil content consists of Bivalves, Gastropods, Echinoids, Corals, Crocodiles, Sharks’ teeth, etc.
The study of these organisms makes it possible to reconstruct the marine paleoenvironment and its paleoclimatic conditions.
The sediments that are at the base of the hill indicate for that ancient Miocene sea a paleoprobability of about 50 meters, while those at the top of the hill report a sea about 10 meters deep. These paleoclimatic conditions are comparable to those of today’s warm, tropical seas.
