Through the analysis of the sedimentary indicators present inside some caves at Circeo frequented by the Neanderthal man, the ancient position of the sea level on the Lazio coast has been reconstructed as a result of the oscillations linked to the alternation of glacial and interglacial periods . The results of the INGV study show that the sea level was different from that previously estimated by physical-mathematical models
A study conducted by a group of researchers from the National Institute of Geophysics and Volcanology (INGV), just published in the journal Quaternary International, indicates that the geological traces of sea level during the oscillations of 100.000 and 79.000 years ago are found at significantly higher than those estimated so far by current models.
The results of the work, which examined a set of caves that open onto the slopes of the cliffs that form the Circeo promontory, are the result of the analysis of sedimentary indicators, such as the ancient lagoon deposits of the marine terraces, and those all inside the caves at Circeo frequented by the Neanderthal man.
"The earth", explains Fabrizio Marra, researcher at the National Institute of Geophysics and Volcanology and co-author of the research, "behaves like a rubber ball crushed at the two poles by the weight of the ice: when these melt, the deformation "adjusts" and the lands at the poles rise, while those at the equator, due to the conservation of volume, sink. The melting of ice causes the sea level to rise at different rates at different latitudes, depending on the regional lowering or rising of the earth's surface. This phenomenon is not simple and homogeneous and to predict it, various computer models have been proposed which simulate the behavior of the earth and the seas”.
In the last 250.000 years the Lazio area has gradually risen by more than 50 metres. This phenomenon has created the so-called. marine terraces, or platforms that are now found at gradually higher altitudes depending on their age and which represent the remaining edges of the ancient beaches and coastal plains. It is a sort of large stairway along the entire central Tyrrhenian coast, now reconstructed in detail thanks to the geomorphological study of topographic maps and the use of modern satellite surveying techniques (Digital Terrain Model, or DEM).
“This suite of terraces” - continues Fabrizio Marra - “has been rebuilt and dated. To define the positions of the ancient sea level we have examined, among other indicators, a set of caves that open onto the slopes of the cliffs that form the Circeo promontory. The research highlights the link between the Neanderthal presence in Rome and Lazio and the oscillations in sea level linked to the alternation of glacial and interglacial periods. In the Circeo caves, in fact, numerous testimonies of human occupation of the Paleolithic have been found, among which an almost complete Neanderthal skull found in Grotta Guattari is the most important.
A large quantity of tools both in flint and made by Neanderthal man using the valves of a shell, known as "fasolaro", still typical of the beaches of the Lazio coast have been found. Precisely thanks to the presence of elements such as shells, holes of "lithodome" organisms that live in holes dug in the cliffs, and shoreline furrows engraved in the rock by the tide, these caves provide important information on the oscillations of the sea level linked to the last two glaciations " .
The study has highlighted new elements that profoundly change the notions of sea level in the Mediterranean during the penultimate interglacial period (the last is the current one), characterized by three successive oscillations that occurred around 125.000, 100.000 and 80.000 years ago .
“By putting together the reconstruction of the marine terraces with the indications of the sea level taken from the sedimentary indicators, three paleo-levels of the sea have been identified at progressively lower altitudes. The highest one, which is now found at an altitude of around thirty-five meters above current sea level, corresponding to the oldest terrace whose age has been established to be around 125.000 years, thanks to the presence of volcanic levels which have been dated with the method of 'radioactive argon. The lowest, around ten metres, identified by the shell deposits, the lithodomus holes and the foreshore furrow in the Guattari cave and in other caves of the Circeo, corresponds to the most recent marine terrace. Until now, this terrace was considered to be that of 125.000 years ago, which new research instead identifies as much as twenty-five meters higher. On the lower terrace a Glycimeris shell dating was done which gave an age of 79.000, allowing this terrace to be correlated with the last positive sea level fluctuation at the end of the last interglacial. The intermediate sea level, identified by a "furrow of the shoreline" currently at about twenty-two meters above sea level in the Circeo cliffs, is consequently correlated with the oscillation of about 100.000 years ago. Even taking into account the uplift of the Lazio Tyrrhenian margin which occurred in the last 125.000 years, which explains why the terrace corresponding to this era is so high, the sea levels of 100.000 and 79.000 years ago are in any case significantly higher than previously estimated on the basis of global models”, explains Fabrizio Marra.
Furthermore, these results are in agreement with analogous data of marine terraces studied in the Balearic Islands which, until now, the scientific literature had considered unreliable, indicating their regional significance for the Mediterranean.
“The implications of the results of the study”, concludes the researcher, “are evident and important even for the present era. In fact, these new data on the Mediterranean will have to be taken into account in future projections on the rise in sea level caused by global warming. Furthermore, the reconstruction of paleogeography at the time when the Circeo caves were frequented offers an insight into the environment in which the Neanderthals lived. Unlike today, where the caves are located several meters above the sea or far from it, 79.000 years ago these caves opened onto beaches which facilitated their attendance and offered unusual but very suitable materials, such as shells, for build small artefacts and tools”.
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Picture 1 - The reconstruction of the marine terraces with the indications of the sea level taken from the sedimentary indicators
Picture 2 - The photo taken from the volume Geosites of the Territory of Rome, edited by the Italian Society of Environmental Geology, shows the gravel pit of Saccopastore, next to the outcrop where in 1929 the first of two skulls was found (Saccopastore I), belonging to a female Neanderthal, indicated by the red circle. A few years later, in 1935, on the same site, a second skull of a Neanderthal male (Saccopastore II), indicated by the orange circle, was found in the gravel level above the one where the first one was discovered. The two skulls, of which the casts shown in the photographs are faithful reproductions, constitute the most ancient direct evidence of the presence of Neanderthal man in Italy, today dated 240.000 years, against the 125.000 previously attributed to the finds, thanks to the revision of the geology of the site
