The Geology of Malta consists of a sequence of

sedimentary rocks 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 t ...

of late

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

late Miocene The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million ye ...

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 is situated on the mainly shallow water continental platform between Sicily and North Africa that lies beneath the Sicily Channel, separating the Ionian Basin from the western

Mediterranean Basin In biogeography, the Mediterranean Basin (; also known as the Mediterranean Region or sometimes Mediterranea) is the region of lands around the Mediterranean Sea that have mostly a Mediterranean climate, with mild to cool, rainy winters and w ...

. The islands lie around 200 km to the south of the

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

boundary between the African 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 formed of three

graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...

s: the Pantelleria graben, that of Malta, and that of Linosa. The faults bounding these grabens are associated with most of the earthquakes that affect the archipelago, although some earthquakes with epicentres 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 Maltese archipelago, 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 (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentati ...

. 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'') a ...

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

The geological strata

The

stratigraphy Stratigraphy is a branch of geology concerned with the study of rock (geology), rock layers (Stratum, strata) and layering (stratification). It is primarily used in the study of sedimentary rock, sedimentary and layered volcanic rocks. Stratigrap ...

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 The Chattian is, in the geologic timescale, the younger of two ages or upper of two stages of the Oligocene Epoch/Series. It spans the time between . The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage ...

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, Malta, 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, Malta, Rabat. The vill ...

, and also along rifts, particularly near Mosta 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 is generally developed indicating a period during which the seafloor was exposed. It is this formation of which the Azure Window, 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 ICS geologic timescale, an age or stage in the middle Miocene Epoch/Series. It spans the time between 15.97 ± 0.05 Ma and 13.65 ± 0.05 Ma (million years ago) during the Middle Miocene.GeoWhen (2007) The Langhian was a ...

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 (cell biology), ectoplasm for catching food and ot ...

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 bed ...

. This rock has also been exported, and was used in the construction of the government palace of

Corfu Corfu (, ) or Kerkyra ( el, Κέρκυρα, Kérkyra, , ; ; la, Corcyra.) is a Greek island in the Ionian Sea, of the Ionian Islands, and, including its small satellite islands, forms the margin of the northwestern frontier of Greece. The isl ...

. The Maltese Lower Globigerina Limestone has been designated by the

International Union of Geological Sciences The International Union of Geological Sciences (IUGS) is an international non-governmental organization devoted to international cooperation in the field of geology. About The IUGS was founded in 1961 and is a Scientific Union member of the Inte ...

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

to Tortonian 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 characterist ...

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-bearing sandstone of Tortonian 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 The Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 Ma and 5.333 ± 0.005 Ma (million years ago). It follows the Tortonian and is followed by the Zanclean, the first ...

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 Malta ( , , ), officially the Republic of Malta ( mt, Repubblika ta' Malta ), is an island country in the Mediterranean Sea. It consists of ...

and in the east of

Gozo Gozo (, ), Maltese: ''Għawdex'' () and in antiquity known as Gaulos ( xpu, 𐤂𐤅𐤋, ; grc, Γαῦλος, Gaúlos), is an island in the Maltese archipelago in the Mediterranean Sea. The island is part of the Republic of Malta. After t ...

. 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 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 An oceanic or submarine plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides. There are 184 oceanic plateaus in the world, covering an area of or about 5.11% of the ...

of depths of less than 100 m. During different

marine regression A marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously-exposed land. Evidence of marine ...

s of the Mediterranean, Malta has been connected to Sicily by a surface isthmus by which animals have been able to cross, as evinced by the presence of island dwarfism ( 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 (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 t ...

References

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