Geohistory
five centuries of geological research in the Apuan Alps
 

The morphological rarity of the Apuan Alps has always been an attraction for naturalists-travellers, or at least, it has been so since the 16th century, when a scientific investigation on the mountain range was carried out to understand its nature and find natural products useful for economy.
In the modern age famous geologists used to match excursions with the pleasure of naturalistic knowledge. Famous is the excursion by Andrea Cesalpino (1525-1603), who focused on a firestone "stone by ovens", described as “invincible to fire”, found in Cardoso di Stazzema.

In the 17th century the bohemian Daniel Meisner (1585-1625) and the dutch Jan Jansson (1588-1664) visited the area and drew the valley of Seravezza, pinpointing the sites for marble excavation and silver extraction.
The Apuan Alps, visible from western Florence, were particularly fascinating for its citizens, who grew up surrounded by Renaissance culture and, therefore, naturally inclined to discover nature from an aesthetic and scientific point of view.
 

Daniel Meisner (1629): Apuan Alps as natural space of the aesthetic and scientific discovery of the nature
 

The visits were already numerous in the 18th century. In those years, several naturalists showed their growing interest in the Apuan Alps which had become a privileged research field for hydrogeological studies and geo-mineral research in Italy.
Here, Antonio Vallisnieri senior (1661-1730) developed and tested the new theory on the underground water cycle (1704-1715), thanks to the close relation between water springs and karst cavities.
Meanwhile, explorations of mines and studies on mineralization took off, with the active participation, among others, of Giovanni Arduino (1714-1795) and Lazzaro Spallanzani (1729-1799).
As a result, the first geological descriptions of the Apuan Alps was produced, based on Arduino’s chronostratigraphic approach and pointing out the ancient core of the mountain range consisting of schist “primitive rocks” covered by “secondary rocks”. moreover, the description of the naturalistic voyage of Giovanni Targioni Tozzetti (1712-1783) in 1743 is rich in content as he described not only Apuan rocks and minerals, but also physical landforms and morphogenetic agents.

Antonio Vallisneri (1714): on the origin of springs, based on an exploration in the Apuan Alps and Apennines

click on image to start movie
(created by Marco Yais)

Paolo Savi (1833): "cut" of the Apuan Alps (cross-section for a first 'plutonist' interpretation of the apuan elipsoid)
 

In 1833, for the first time the Apuan Alps are shown in a geological cross-section in a work by Paolo Savi (1798-1871) who gives a ‘Plutonic’ interpretation of the mountain range. According to him, it was raised by the intrusion of a deep magma body and became a remnant of an ancient orographic ridge – called “metalliferous chain” – originally situated in the area from La Spezia to Mt. Argentario.
For almost half a century, literature on geology was dominated by the scientific contributions of Italian and foreign geologists (Coquand, Pareto, Puggard, Simi, Cocchi, De Stefani) who used to support the well-established theory of the Apuan Alps as a single anticline of Plutonic origin. Research is, nevertheless, rich in surprises and important discoveries. In 1872, Antonio Stoppani (1824-1891) and Igino Cocchi (1827-1913) in two different studies found the first morainic deposits in the Apuan Alps and presented them to the scientific community as the first Apennine marks of the Quaternary Glaciations.
 

Modern geology began with a systematic survey of the Apuan Alps completed between 1879 and 1890 by Bernardino Lotti (1847-1933) and Domenico Zaccagna (1851-1940). The two engineers of the Geological Royal Committee belonged to the ‘autochthonist’ school of thought assigning the Apuan rocks to a single stratigraphic sequence excluding any possibility of nappe overlapping. Therefore, they proposed a folding tectonics characterized by regular folds with double vergence without dealing with the existence of faults.

Domenico Zaccagna (1881): Mt. Sagro natural section

The map drawing was completed by Domenico Zaccagna alone, who retrieved and developed the contemporary studies by Igino Cocchi (1827-1913) and Carlo De Stefani (1850-1924), in compliance with the geological survey project presented at the Second International Congress in Bologna in 1881. These are the first examples of modern geological cartography in Italy.
 

The scientific commitment was matched with the institutional interest of the Geological Committee, which aimed at providing the Apuan marble mining industry with an useful instrument in a historic moment of remarkable spreading of quarrying activities beyond the traditional basins of Carrara, Massa and the area of Versilia.
In 1917, despite their sheer ‘autochthonist’ approach, the Zaccagna and Lotti’s geological map enabled, Stanislaw Lencewicz (1889-1944) to reinterpret the structure of the mountain range from an ‘allochthonist’ perspective, showing the tectonic duplication of the Tuscan sequence.

Domenico Zaccagna (1880-1886): Mt. Sagro's geological map - scale 1:25.000

For the very first time in the history of the Apuan Alps and Apennines the allochthonous origin of nappes was recognized, though it had already been proposed by Lugeon and Argand for the Pennine Alps (1905) on the basis of the overthrusting of two equivalent stratigraphic sequences. In the following two decades the geological studies, especially by experts from the central European school and culture, enabled the identification of a ‘tectonic window’ in the central part of the Apuan range. In particular, in 1926, Norbert Tillman (1883-1947) described the Apuan Alps as a complex structure of folded sedimentary sequences which are overturned, faulted and tectonically overlapped. After the Second World War the main subject of geological studies was the gravitational sliding of nappes, which led Carlo Migliorini (1891-1953) to formulate the theory of ‘composite wedges’ (1948), according to which nappes may gradually slip for hundreds of kilometres through different and subsequent phases thanks to a limited number of inclined surfaces. The interpretation was then retrieved and developed by Giovanni Merla (1906-1983) and Livio Trevisan (1909-1996), who, shortly afterwards, described a gravitational sliding of nappes progressively moving from the Tyrrhenian to the Adriatic area thanks to the upthrust of subsequent tectonic ‘ridges’ or ‘wrinkles’. In the same period, Felice Ippolito (1915-1997) carried out geological-petrographic studies on the Apuan Alps and Pisani Mountains assigning the Apuan rocks to three superposed sequences. The ‘Autochthonous’ sequence is the deepest one and is overthrusted by an equivalent lithological sequence, called ‘Tuscan Nappe’ which is in turn topped by the ‘Ligurian Unit’.
 

In the 1960’s the Apuan Autochthon is described, especially by Enzo Giannini (1919-1992), as the most remarkable part of a structural high (geoanticline) which divides the two main basins, the ‘inland’ (eugeosyncline) and the ‘outer’ one (miogeosyncline). The Apuan tectonic ridge was allegedly overthrusted by the Tuscan and Ligurian units because of tangential pushes by the oceanic area towards the foreland, thus leading to the late formation of rigid structures such as horsts (Apuan) and grabens (Serchio Valley).
The quality leap in the interpretation of the evolution of the Apuan Alps and Northern Apennines was made thanks to the theoretical support of ‘plate tectonics’ or ‘global tectonics’ with the identification of the physical “engine” able to provide the necessary push for large translations of nappes. After 1975, a series of studies on the geometry of polyphase deformations, created by the superposition of different tectonic phases, took place within a framework consistent with the Cenozoic paleographic evolution and crustal movements of the western Mediterranean area.