Monte Bolca is an Early Eocene-aged geologic site located near Verona, Italy. A Konservat-Lagerstätte, it contains an extremely well-preserved and diverse marine biota, including the most diverse fish fauna of any Cenozoic fossil site, as well as many of the earliest fossil occurrences of modern marine fish groups. It was one of the first fossil sites with high quality preservation known to Europeans, with studies of its biota dating back to the 18th century and earlier, and is still an important source of fossils.
History
Strictly speaking, the Monte Bolca site is one specific spot near the village of Bolca in Italy, known as the Pesciara ("The Fishbowl") due to its many extraordinarily well preserved Eocene fish fossils. However, there are several other related outcroppings in the general vicinity that also carry similar fossils, such as Monte Postale and Monte Vegroni. The term Monte Bolca is used interchangeably to refer to the one, original site, or to all the sites collectively.
The fossils at Monte Bolca have been known since at least the 16th century, though the first extensive research was conducted on them by Giovanni Serafino Volta in the late 18th century. This area represents a continuation of the Southern Alps. Though all of these sites have been put under a single name, there is not a place called "Monte Bolca". Due to the differences in the environment and stratigraphy, more recent authors have also called these sites the Bolca Lagerstätten. However, more recent work done at Monte Postale has not seen the presence of this supposed fault and has since been discarded.
Spilecco
Spilecco, also known as Spilecco Hill, is largely made up of poorly-exposed reddish marly and grey-green limestones. While the fossil content of the grey-green limestones is made up of various microfossils, macrofossils are found in the reddish marly limestones. The strata within Spilecco date from the Thanetian to lower Ypresian which make them the oldest shallow water deposits in the Lessini Shelf and would have been deposited after the first period of volcanic activity.
Pesciara
The Pesciara site of Monte Bolca is made up of a sheet-like limestone in the form of an olistolith which has an area of a few hundred square meters and is under 20 m thick. Throughout this bed, there are both reef and alveoline limestones which are medium-fine grained. The different limestone beds alternate between the fossiliferous laminites and more course-grained biocalcarenites and biocalcirudites. These more course layers are a lot less fossiliferous though still contain fossils such as foraminifera and mollusks. Most fossils within the Persciara site have been found within five of the levels with the 1st, 2nd, and 5th levels being the most productive. However, due to being completely excavated over the last four centuries, the 5th level is no longer accessible. Towards the south-east of the deposit, the limestone layers dip at a 24° angle which suggests that the beds slid towards the north-west when they were more plastic. Volcanoclastic rock surrounds the limestone beds and due to this isolation, there has been trouble in understanding the relationship between the Pesciara and Monte Postale sites. Though the site is largely known for the fish and plants found, Monte Postale is also well known for the molluscan fauna located at the uppermost section of the site. Just like Pesciara, the stata of Monte Postale have been dated to the late Ypresian with the upper-most portion of the beds being potentially correlated to the limestones seen at Pesciara. Additionally a cephalopod, crustaceans, jellyfish and polychaete worms have been found whole, but foraminifera, molluscs, and corals are found in fragments and may have been transported.