A BRIEF GUIDE TO
GEOLOGY OF CAPRI ISLAND
Filippo BARATTOLO and Marcello SCHIATTARELLA
The Island of Capri (Bay of Naples, Italy) represents, from a morpho-structural point of view, the continuation toward the sea of the carbonate horst of the Sorrento Peninsula. Therefore it constitutes the western extremity of the Southern Apennines.
The south-apenninic chain is an Adriatic-verging nappe edifice formed during Neogene tectogenesis. Structural units result prevalently by the deformation of palaeogeographical domains belonging to the African continental margin and, in a subordinate amount, forming the covers of the Tethyan oceanic floors. Detachment and emplacement of all those terrains occurred during the Miocene and Lower to Middle Pliocene. During the Upper Pliocene and the Middle Pleistocene, the post - nappe tectonic history of the chain led to the genesis of an internal Tyrrhenian belt, strongly subsiding but interrupted by counter - apenninic structural high zones (i.e. Sorrento Peninsula - Capri Island and Mt. Massico horsts), and of an external apenninic sector, roughly parallel to the first one, affected by progressive uplift from West toward East, with offsets over one thousand meters. In the same period counter - apenninic regional faults were generated. Quaternary tectonic evolution of the Southern Apennines is characterized by a, common, marked uplift mainly controlled by longitudinal structures. During the uplift stage the transversal (i.e. counter - apenninic) brittle structures were reactivated on a regional scale, bordering sectors with differential vertical displacement sometimes show strike-slip movements.
In the modern scientific literature the Island of Capri is considered, from a palaeogeographical view point, as part of the internal (i.e. western) edge of a wide bahamian - type Mesozoic carbonate platform which outcrops from Calabria to Southern Latium. This huge depositional system was called by geologists from the University of Naples as the "Campania-Lucania Platform" and it forms the south - apenninic chain consisting of the Alburno - Cervati (central bulk), the Bulgheria - Verbicaro (internal margin) and the Foraporta - Maddalena (external margin) units. In a classical geological model, Capri is related to the Bulgheria - Verbicaro unit even if recent studies still debate this problem.
Several formations of different ages, lithologies and facies outcrop at Capri: it is possible to recognize neritic dolostones, reef boundstones, cherty limestones as well as other transitional or pelagic terrains, terrigenous sediments, slope breccias and pyroclastic products. The tectonic framework of the island is very complex, resulting from interference of several deformational stages, characterized by folds, thrusts and normal faults. The central zone ("Tossa di Capri") has been interpreted as a graben-type structure or as a zone bordered by a NE-SW trending normal fault on the eastern side and by a thrust zone to the west, along the Mt. Solaro - Mt. S. Maria slopes or maybe as a relict of a piggy-back basin. The geometric relationships between Capri and Anacapri zones are not yet fully understood, although many tectonic studies have been carried out since the beginnings of this century. At present most geologists, who have studed the area, think that the western part of the island is tectonically overthrusted onto the eastern part and that Mesozoic bulks lie on Miocene flysch, but the kinematic evolution is unknown and the structural patterns have not been well defined.
Mesozoic terrains of Capri Island are constituted prevalently by platform margin, slope and batial carbonate rocks. Lagoonal and littoral facies are restricted to dolostones, sometimes with stromatolithic texture, Early Lias in age, and to Neocomian limestones with Rudists. In order to explain the arrangement of the formations, the territory of Capri has been divided into five letter-marked zone (A, B, C, D and E), as shown in figure 1 (BARATTOLO & PUGLIESE, 1987).
For every single zone, one or several stratigraphic sections are illustrated. The A zone is included among Punta Campetiello, Caprile, La Migliara and Punta Carena. The B zone westward borders on the A zone, it joins northward Anacapri outskirts and it is delimited by Mt. S. Maria and Mt. Solaro cliffs respectively to east and south. The C zone southward borders on A and B zones, while eastward it borders on the Barbarossa Castle cliff, and it is delimited by northern and western coastlines. The D zone includes almost the entire eastern part of the island, save the little area of Cala del Fico, which belongs to the E zone. Terrains outcropping in these five zones have been grouped into eleven formations. They are (from the bottom, but not in a continuous sequence):
1. CALA VENTROSO DOLOMITE(Lower Lias) - Grey, saccharoidal, sometimes stromatolithic, layered dolostones.
2. GROTTA DELLE FELU BIOCLASTIC LIMESTONE(Middle-Upper Lias) -Bioclastic calcarenites and calcirudites, sometimes dolomitized, stratified, with Palaeodasycladus mediterraneus, Amiiella amiji and Pelecypods ("Lithiotis facies").
3. TORINA OOLITIC LIMESTONE(Aalenian-Bathonian) - Grey to avana oolitic, stratified limestones, with Lucasella bizonorum, Archeosepta platierensis, Protopeneroplis striata, Conicospiriffina basiliensis.
4. MIGLIARA CHERTY LIMESTONE(MiddIe Lias-Kimmeridgian p.p.) Grey to dark brown, stratified cherty calcilutites and dolostones, with re-sedimented Protopeneroplis striata, Nautiloculina oolithica, Conicospiriffina basiliensis, Kurnubia palastiniensis, Labyrinthina mirabilis and Salpingoporella pygmaea.
5. CAPRI ELLIPSACTINIA LIMESTONE(Callovian-Valanginian) - Grey to whitish massive calcirudites and calcarenites with Kurnubia palastiniensis, Labyrinthina mirabilis, Salpingoporella pygmaea, Protopeneroplis striata, Protopeneroplis trochangulata, Tubiphytes morronensis, Ellipsactinia, Chaetetids and Corals.
6. CAPO LIMESTONE(Neocomian) - Hazel to grey calcilutites and subordinate calcarenites, with Nerineids and Rudists, and with Protopeneroplis trochangulata, Conicospirillina basiliensis, Miliolids, Textularids, Dasicladaceae.
7. LIMMO WHITE LIMESTONE(Aptian) - White massive to stratified calcirudites and calcarenites with Palorbitolina lenticularis and fragments of Ostreids and Radiolitids.
8. TIBERIO RUDITE(Aptian-Cenomanian) - Matrix-depleted calcareous breccias, with rare Orbitolina. Graded calcareous breccias, more or less rich in Aptian fossils-bearing matrix (Salpingoporella dinarica, Ovalveolina reicheli). Calcareous breccias, poor in matrix, with clastic elements containing Cenomanian microfauna (Orbitolina conica, Praealveolina cf. osimoi).
9. PUNTA CARENA SCAGLIA(Upper Turonian - Coniacian p.p.) - Scaglia-type cherty limestones with Dicarinella scheegansi, D. concavata, Marginotruncana linneiana.
10. FARO CONGLOMERATE(Maastrichtian) - Calcareous polygenic conglomerate with Globotruncanids in the matrix and occasionally Siderolites cf. calcitrapoides in the pebbles.
11. MOUNT S. MICHELE LIMESTONE(Maastrichtian-Paleocene ?) - Whitish sub-crystalline limestones with Hellenocyclina beotica and Siderolites calcitrapoides.
On the grounds of stratigraphic studies and with regard to the schematic zoning proposed in BARATTOLO & PUGLIESE 1987), the following environmental and sedimentary evolution may be restorea for the Mesozoic.
During the Early Lias lagoonal conditions, testified by the Cala Ventroso Dolomite Fm., were established in part of the Capri palaeoenvironment. In the Middle Lias, marginal facies was dominant in the B zone (Grotta delle Felci Bioclastic Limestones Fm.). This facies laterally passes (A zone) to slope sediments of, the Migliara Cherty Limestone Fm.; in the B zone, during the Dogger and starting from the Aalenian, an oolitic sequence (Torina Oolitic Limestone Fm.) was deposited: also this formation laterally passes (A zone) to the slope facies of the Migliara Formation. During the Bathonian the cherty limestones were deposited in the B zone too. Later (Callovian), in that area shallower environmental conditions and marginal facies, represented by the Capri Ellipsactinia Limestone Fm., were restored. They will remain the same at least until the PortIandian. As a matter of fact, starting from Kimmeridgian to the Portlandian, Ellipsactinia limestones extend on the whole A zone and they are present in the C and D zones too, dating respectively Kimmeridgian - Berriasian and Portlandian-Valanginian.
The upper part of the Capri Ellipsactinia Limestone Fm. is covered by Cretaceous sediments in the whole island. Along the contact surface it is possible to recognize a stratigraphic gap between the two formations, due to pre-Aptian emersion. Certainly both in the A and B zones the transgression is related to the Aptian, age of the Limmo White Limestone Fm., which probably indicates an environment along the margin-slope boundary. Cretaceous transgression also seems to be Aptian in age (C and D zones) where the Tiberio Rudite Fm. (Aptian-Cenomanian) outcrops.
Mesozoic terrains younger of the Cenomanian are present prevalently in the south-western part of Capri (A zone) and in a lower amount also in the D zones (Castiglione). In the A zone they overlay with a hiatus the Limmo limestones and are represented by the batial facies of the Punta Carena Scaglia Fm. (Turonian-Coniacian p.p.). On this formation lie breccias of the Faro Conglomerate Fm. (Maastrichtian), maybe depending on tectonic controls, like it seems to be occurred for the deposition of Aptian conglomerates of the Tiberio Rudite Fm. outcropping in the E zone (Cala del Fico). Mount S. Michele Limestone perhaps may represent an eteropic deposit just of Faro Conglomerate.
Cenozoic terrains also outcrop at Capri. One can observe pelagic and transitional facies of Punta del Capo, represented by scaglia-type limestones and dark cherty limestone (Paleocene-Eocene), besides the synorogenic silico-clastic sediments ("flysch", Miocene in age). Quaternary formations are constituted by both marine and continental Pleistocene detritical deposits. Pyroclastic rocks, frequently reworked and maybe of Phlegraean origin, are recorded too.
A GEOLOGICAL ITINERARY
STOP 1- One of the most important site to understand the tectonic framework of Capri, certainly is the zone around Punta del Capo. In that area it is possible to observe the tectonic superimposition of a thick carbonate bulk (prevalently formed by Ellipsactinia limestones) on Miocene terrigenous rocks, consisting of marly clays and sandstones with intercalated Bryozoans bearing calcareous levels. Along the shear zone, dark-grey limestones with chert and pinky limestones with Globigerinidae, Paleogene in age, are present too. Different deformational features characterize the outcropping terrains. The carbonate hanging-wall is typically affected by brittle deformation both on the meso and larger scales, with faults and fracture systems showing several preferred orientations. Those limestones form altogether a north-verging plicative structure, maybe originated as ramp fold. The terrigenous foot-wall shows ductile structures on different scales: on the mesoscale, recumbent isoclinal folds associated to boudinage of more competent levels and cleavage conjugate systems are recognized; on entire outcrop scale, silico-clastic sediments are isoclinally folded accordíng to the sense of shear of the thrusting, as testified by geometries of minor structures besides the attitude of the limbs, roughly parallel to the thrust surface.
STOP 2- On the eastern side of the island, at Cala del Fico, the Tiberio Rudite is recognizable in well-exposed outcrops. This heterogeneous formation, grouping different breccias, Aptian in age, probably lies on Ellipsactinia limestones. Deposition and evolution of the Tiberio Rudite may be related to tectonic activity along p form margins.
STOP 3- The oldest formations of Capri are outcropping along the Cala Ventroso-Mt. Solaro zone. A thick sequence ranging from Early Lias to Bathonian is formed by (from the bottom) Cal entroso Dolomite, Grotta delle Felci Bioclastic Limestone and Torina Oolitic Limestone.
STOP 4- In the Punta Carena-Limmo-Migliara zone (south-west side of the island), five different formations are recorded. Here one can observe terrains belonging to (from the bottom) Migliara Cherty Limestone, Capri Ellipsactinia Limestone, Limmo White Limestone, Punta Carena Scaglia and Faro Conglomerate. Ages range from Middle Lias to Maastrichtían, while facies may vary from marginal to batial environments.
STOP 5- Mount S. Michele Limestone Fm. outcrops at the eastern extremity of Marina Grande. In this site, calcareous megabreccias with elements certainly Cretaceous in age (e.g. wackestones with Salpingoporella dinarica) have been recognized. Other samples show a rich fossil association with Cymopolia, Jodotella, Solenoporaceae (Elianella elegans) and Melobesíoideae.
STOP 6- Going up toward Capri, near Tragara it is possible to observe outcrops belonging to Capri Ellipsactinia Limestone Fm., containing Tubiphytes morronensis, an incertae sedis species, typical of Malm shelf-margin facies.