The Geology of Malta consists of a sequence of sedimentary rocks of late Oligocene to late Miocene age cut through by a set of

extensional fault An extensional fault is a fault caused by stretching of the Earth's crust. Stretching reduces the thickness and horizontally extends portions of the crust and/or lithosphere. In most cases such a fault is also a normal fault, but may create a ...

s of

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58

Tectonics

The

Maltese archipelago Malta ( , , ), officially the Republic of Malta ( mt, Repubblika ta' Malta ), is an island country in the Mediterranean Sea. It consists of an archipelago, between Italy and Libya, and is often considered a part of Southern Europe. It lies ...

is situated on the mainly shallow water continental platform between Sicily and North Africa that lies beneath the

Sicily Channel (man) it, Siciliana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Ethnicity , demographics1_footnotes = , demographi ...

, separating the

Ionian Basin Ionic or Ionian may refer to: Arts and entertainment * Ionic meter, a poetic metre in ancient Greek and Latin poetry * Ionian mode, a musical mode or a diatonic scale Places and peoples * Ionian, of or from Ionia, an ancient region in western ...

from the western Mediterranean Basin. The islands lie around 200 km to the south of the subduction boundary between the

African Plate The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plate ...

and the

Eurasian Plate The Eurasian Plate is a tectonic plate that includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent and ...

. The platform is crossed by a

rift zone A rift zone is a feature of some volcanoes, especially shield volcanoes, in which a set of linear cracks (or rifts) develops in a volcanic edifice, typically forming into two or three well-defined regions along the flanks of the vent. Believed t ...

formed of three grabens: the

Pantelleria Pantelleria (; Sicilian: ''Pantiddirìa'', Maltese: ''Pantellerija'' or ''Qawsra''), the ancient Cossyra or Cossura, is an Italian island and comune in the Strait of Sicily in the Mediterranean Sea, southwest of Sicily and east of the Tunisi ...

graben, that of Malta, and that of

Linosa Linosa (; scn, Linusa; ar, نموشة, ''Nammūša'') is one of the Pelagie Islands in the Sicily Channel of the Mediterranean Sea. The island is a part of the Italian comune of Lampedusa e Linosa, part of the province of Agrigento in Sicily, ...

. The faults bounding these grabens are associated with most of the earthquakes that affect the archipelago, although some earthquakes with

epicentre The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Surface damage Before the instrumental pe ...

s in Sicily may have damaging effects, such as the

1693 Sicily earthquake The 1693 Sicily earthquake struck parts of southern Italy near Sicily, Calabria, and Malta on January 11 at around 21:00 local time. This earthquake was preceded by a damaging foreshock on January 9. The main quake had an estimated magnitude of 7 ...

.Galea, P. pp.725–740

Formation of the islands

The

, situated between

Sicily (man) it, Siciliana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Ethnicity , demographics1_footnotes = , demographi ...

and

Tunisia ) , image_map = Tunisia location (orthographic projection).svg , map_caption = Location of Tunisia in northern Africa , image_map2 = , capital = Tunis , largest_city = capital , ...

, was created through the uplift of

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s. This uplift dates from the late Miocene to the Pliocene. Malta forms the crest of a tilted block on the edge of the Malta Graben.Catalano, R. The isle of

Lampedusa Lampedusa ( , , ; scn, Lampidusa ; grc, Λοπαδοῦσσα and Λοπαδοῦσα and Λοπαδυῦσσα, Lopadoûssa; mt, Lampeduża) is the largest island of the Italian Pelagie Islands in the Mediterranean Sea. The ''comune'' of L ...

is made up of an identical structure on the southwest side of this rift.

Nature of the sub-soil

The rocks are exclusively

sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

. There is a lot of

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

, which has contributed to the construction of the ancient buildings of the island. These rocks come from marine deposits (essentially from

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') ...

s) dating from between 25 and 5 million years ago.Samut Tagliaferro, John

The geological strata

The stratigraphy of the Maltese islands consists of five

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

s, ranging in age from late Oligocene to late Miocene.Sultana, J., et al.

Oligocene

Lower Coralline Limestone Formation

The oldest exposed rock layer of Malta is the Lower Coralline Limestone Formation ( mt, Żonqor), which is of Chattian age (~28–23 million years old) with a maximum thickness of 162 m. The unit is exposed on the lower parts of cliffs in the south-west of the archipelago such as at

Dingli Dingli ( mt, Ħad-Dingli) is a village in the Northern Region of Malta, with a population of 3,865 as of 2021. It is from the capital Valletta and two kilometers () from the nearest town, Rabat. The village lies on a plateau some 250 metre ...

, and also along rifts, particularly near

Mosta Mosta ( mt, Il-Mosta) is a small but densely populated city in the Northern Region of Malta. The most prominent building in Mosta is the Rotunda, a large basilica built by its parishioners' volunteer labour. It features the world's 3rd largest ...

and

Naxxar Naxxar ( mt, In-Naxxar) is a small city in the Northern Region of Malta, with a population of 14,891 people as of March 2014. The Naxxar Church is dedicated to Our Lady of Victories. The annual village feast is celebrated on 8 September. Naxx ...

. This is a hard limestone which is pale grey in colour, and comparable to the Upper Coralline Limestone. At the top of this unit a

hardground Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor (Wilson and Palmer, 1992). A hardground is essentially, then, a lithified seafloor. Ancient hardgrounds are found in limestone ...

is generally developed indicating a period during which the seafloor was exposed. It is this formation of which the

Azure Window The Azure Window ( mt, it-Tieqa Żerqa, italic=no), also known as the Dwejra Window ( mt, it-Tieqa tad-Dwejra, italic=no), was a natural arch on the island of Gozo, located just off the shores of Malta. The limestone feature, which was in Dw ...

, a spectacular coastal rock arch, popular with tourists and film-makers, was composed, prior to its final collapse in 2017.

Miocene

Globigerina Limestone Formation

The Globigerina Limestone ( mt, Franka) is a soft, gold-coloured limestone of Aquitanian to

Langhian The Langhian is, in the International Commission on Stratigraphy, ICS geologic timescale, an age (geology), age or stage (stratigraphy), stage in the middle Miocene epoch (geology), Epoch/series (stratigraphy), Series. It spans the time between 15 ...

age (~23–14 million years old), ranging in thickness from 23 m to 207 m. It contains many

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s, especially those of the

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

Globigerina ''Globigerina'' () is a genus of planktonic Foraminifera, in the order of Rotaliida.Glo ...

'' that give it its name. It is divided into three members, the lower, middle and upper, with the boundaries between them being hardgrounds, representing the effects of further seabed exposure. Since prehistoric times, this limestone has constituted the majority of building material used in Malta. Exposed to the air, the stone takes on a rosy colour, which browns with the formation of a protective patina. Lesser quality rocks can erode easily however, and can show

honeycomb weathering Honeycomb weathering, also known as honeycombs, honeycombed sandstone, is a form of cavernous weathering and subcategory of tafoni that consists of regular, tightly adjoining, and commonly patterned cavities that are developed in weathered be ...

. This rock has also been exported, and was used in the construction of the government palace of Corfu. The Maltese Lower Globigerina Limestone has been designated by the International Union of Geological Sciences as a

Global Heritage Stone Resource The Global Heritage Stone Resource (GHSR) designation seeks international recognition of natural stone resources that have achieved widespread utilisation in human culture. Details of the “Global Heritage Stone Resource” proposal were first pr ...

. .

Blue Clay Formation

The Blue Clay ( mt, Tafal) is a blue-gray mudstone of

Tortonian The Tortonian is in the geologic time scale an age or stage of the late Miocene that spans the time between 11.608 ± 0.005 Ma and 7.246 ± 0.005 Ma (million years ago). It follows the Serravallian and is followed by the Messinian. The Torto ...

in age (~15–10 million years old) measuring up to 65 m thick. It shows major thickness variations and is missing completely from most of the eastern parts of the islands. It was deposited in a deepwater environment. It forms an impermeable layer beneath the Greensand and Upper Coralline Limestone formations. It is most visible in the northwest of Malta and the northeast of Gozo. It allows the capture of rainfall and the creation of

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteris ...

s. Water is extracted through wells or escapes through occasional springs when the topsoil has been eroded.Blouet, B.

Greensand Formation

The Greensand ( mt, Ġebla s-Safra) is a

glauconite Glauconite is an iron potassium phyllosilicate ( mica group) mineral of characteristic green color which is very friable and has very low weathering resistance. It crystallizes with a monoclinic geometry. Its name is derived from the Gre ...

-bearing sandstone of

age (~10–7 million years old). Yellow-green in colour, it takes on an orange tint when it comes into contact with the air. It is generally very thin, a few tens of centimetres in most areas, with a maximum thickness of 11 m. It is friable and therefore unsuitable for building purposes. Its permeable nature and its position immediately above the Blue Clay allow for the infiltration of rainwater.

Upper Coralline Limestone Formation

The top layer, the Upper Coralline Limestone ( mt, Qawwi ta' Fuq), is the youngest formation of Messinian age (~7–5 million years old) and is around 140 m thick. It is mainly present on the islands of

Malta Malta ( , , ), officially the Republic of Malta ( mt, Repubblika ta' Malta ), is an island country in the Mediterranean Sea. It consists of an archipelago, between Italy and Libya, and is often considered a part of Southern Europe. It lies ...

Comino Comino ( mt, Kemmuna) is a small island of the Maltese archipelago between the islands of Malta and Gozo in the Mediterranean Sea, measuring in area. Named after the cumin seed, the island has a permanent population of only two residents and ...

and in the east of Gozo. The Coralline Limestone is a hard, pale-grey limestone. It was used frequently in constructions requiring great strength, and in fortifications in particular.

Faults

The rock layers in Malta are relatively flat-lying, with the exception of zones where the rock has been folded close to faults. The faults have two main orientations, with the largest faults being northwest-southeast trending, parallel to the line of islands, although these faults are only locally exposed, and a second set that are WSW-ENE trending, with generally small displacements that dominate the topography of the islands. The largest of the second set are the

Victoria Lines The Victoria Lines, originally known as the North West Front, are a line of fortifications that spans 12 kilometres along the width of Malta, dividing the north of the island from the more heavily populated south. Location The Victoria Lines ru ...

Fault on northern Malta and the Qala Fault on southern Gozo. The fault is around long. Overall, the islands of the archipelago are tilted towards the northeast, with cliffs on the southwest coast and descending gradients towards the northeast.

Recent geological history

The Maltese archipelago is linked to Sicily by an underwater plateau of depths of less than 100 m. During different marine regressions of the Mediterranean, Malta has been connected to Sicily by a surface

isthmus An isthmus (; ; ) is a narrow piece of land connecting two larger areas across an expanse of water by which they are otherwise separated. A tombolo is an isthmus that consists of a spit or bar, and a strait is the sea counterpart of an isthmus ...

by which animals have been able to cross, as evinced by the presence of

island dwarfism Insular dwarfism, a form of phyletic dwarfism, is the process and condition of large animals evolving or having a reduced body size when their population's range is limited to a small environment, primarily islands. This natural process is disti ...

( Maltese dwarf hippopotamus and

dwarf elephant Dwarf elephants are prehistoric members of the order Proboscidea which, through the process of allopatric speciation on islands, evolved much smaller body sizes (around ) in comparison with their immediate ancestors. Dwarf elephants are an example ...

fossils),Courtin, J. as well as

island gigantism Island gigantism, or insular gigantism, is a biological phenomenon in which the size of an animal species isolated on an island increases dramatically in comparison to its mainland relatives. Island gigantism is one aspect of the more general Fos ...

(fossils of the Maltese Giant Dormouse,

Leithia melitensis ''Leithia'' is a genus of extinct giant dormice from the Mediterranean islands of Malta and Sicily. It is considered an example of island gigantism. ''Leithia melitensis'' is the largest known species of dormouse, living or extinct, being twice ...

References

* * * * * * {{Portal bar, Geology, Malta