Sovere: Fossil Lake Park
The site, known as the “Pianico-Sèllere natural archive”, tells a 45,000-year-long story of the environment and climate in the Alps: a deep lake formed here between about 800 and 755,000 years ago, preserving an exceptional deposit of fossil leaves and pollen.
The site, also known as the “Pianico-Sellere natural archive”, provides an insight into the nature and environment that characterised the Val Borlezza area between 755 and 800,000 years ago. Before the glaciations that disrupted the climate and life here, a deep lake formed, which accumulated deposits on its bottom for a long time. The weight of the layers of sediment and water slowly compressed and dried out the underlying debris, which over time hardened and turned to rock. Today, their fossilisation allows us to observe and study the weathering of this distant era, the species of plants and animals that were trapped at the bottom of the lake, and much more.
The importance of the site was first perceived in 1858 when, during mining excavations, bone remains of a cold-blooded rhinoceros (Rhinoceros merkii Jaeg.) were brought to light. Later, leaves of maple, boxwood, elm and other species typical of temperate climates were found. This led to the conclusion that the lake in question was probably formed in the glacial period, but continued to exist and accumulate sediments in the interglacial period that followed.
The area has been internationally recognised as one of the most important for the reconstruction of the plant and animal presence in the Alps thanks to the immense number and variety of species it allows us to observe. Over the last twenty-five years, the importance of this place has attracted the attention of scholars from all over the world.
The currently visible and studied wall is ten metres high and consists of 41˙600 layers that have been deposited two at a time every year for twenty thousand years. The pairs of layers can be recognised by their different colours: dark for layers deposited in winter and light for those deposited during the warm season.
Among the many deposits are some particularly interesting ones, including t21d, a dark layer of volcanic ash from an eruption hundreds of kilometres from the lake. Another important deposit is the perfectly preserved specimen of Cervus acoronatus, which is the most complete existing skeleton of the fossil species and was found in one of the highest, and therefore most recent, layers of the deposit. In addition, many pollen grains have been found in the numerous layers of varvae, which have survived thanks to their strong walls: more than 250,000 grains have been identified, amounting to more than 100 different species.
The story told by the fossil wall was interrupted around 750,000 years ago by the passage of the glacier, which eroded the last layers and replaced them with glacial deposits.
The site remained the object of study only for experts for many years, until, in 2000, the discovery of the fossil deer increased the attention; around 2013 the Park was created, equipped with illustrative panels, QR Code and suitably trained guides. In 2021, after several years of closure due to a landslide that had made it unfit for use, the site underwent extensive safety work, which allowed it to reopen to the public.
In general, the sediments of the Banco Varvato Carbonatico (Carbonate Varve Bank) appear almost white, because the varves, the annual layers, are composed of a light-coloured lamina, deposited in summer, which is much thicker than the black, winter lamina. In the last 3,800 varves, laid in as many years of warm temperate climate, there are also numerous blackish layers, usually produced by underwater mudflows. However, it was noted that a grey level (t21d15) turned red in contact with the air, due to its high iron content: this is a very fine level of volcanic ash (called ‘tephra’), composed of glass and volcanic minerals, resulting from the fallout of an eruptive cloud carried by atmospheric currents. Radiometric dating of the glass and feldspar contained in the ash layer has made it possible to establish the age of the eruption: 779 ± 13 thousand years ago. The volcano responsible has not yet been identified with certainty, but this ash can travel in the direction of the winds for hundreds of kilometres and the most plausible candidate is located in the French Massif Central.
A second particularly dark layer (t32) was deposited about 755,000 years ago and is evidence of another grandiose explosive eruption. Based on the chemical composition, the volcano that dispersed these ashes into the air was located in the volcanic province of Central Italy, probably an extinct volcano in the Sabatini Mountains, north of Rome.
On 19 February 2000, while searching the banks of the Borlezza stream, two students spotted a bone sticking out of the wall of the ‘Arnie section’. Technicians from the Museo Civico di Scienze Naturali of Bergamo and the University of Ferrara later established that these were the heel bones of a large vertebrate, a deer. We know that whole mammal carcasses, with lungs full of air, can float on the surface of lakes before they sink to the bottom. Fortunately, the erosion of the stream had not yet affected the paw and the rest of the carcass was preserved in the sediment. The Museum therefore organised an extensive excavation to recover the animal, which is now on display in Bergamo.
The skeleton belongs to an adult male of the species from which today’s deer originated: the antler has only two terminal daggers, whereas the species living today in Eurasia has a crown of several daggers, which is why scholars have named it ‘Acoronate Deer’. Thanks to the study of fossil pollen, we know that this specimen lived 762,000 years ago, when the mountains of the Val Borlezza were covered with mixed deciduous and coniferous forests, before the onset of a cold phase.
Deer remains had already been found along the Borlezza in the 19th century, but the one on display in the Bergamo Museum is the most complete existing skeleton of the fossilised species.
for the visit
the Fossil Lake Park is freely accessible all year round; guided tours for groups can be arranged by prior reservation and for a fee, from 1st of April to 30th of November 2022.
wide parking at the football field of the village, near the site entrance. It is recommended to wear comfortable clothes and suitable for unpaved trails. Walking time: 2 hours. Not suitable for people with motor disabilities.