Geological Map of the Maltese Islands

Geological Map of the Maltese Islands

The Continental Shelf Department acts as the Geological Survey of Malta. The main functions of the Survey are to upkeep and revise at a more detailed scale the geological map of the Maltese Islands which is under the custodianship of the Continental Shelf Department, to participate in EuroGeoSurveys (EGS) directors, national delegate meetings and expert group meetings on various geological themes and to participate in EGS and European Union geology related projects.

During 2016, the Continental Shelf Department produced, using Geographic Information Systems (GIS) technology, a digital version of the geological map of the Maltese Islands that was published in 1993. The map was resurveyed at a scale of 1:10,000 by the British Geological Survey in 2021-2022 through a contract awarded by the Continental Shelf Department.  

The entire geological information is now organised under 7 themes/layers: bedrock geology, superficial geology, artificial geology, fault features, fold features, solution subsidence features and bedding measurements. They are available on a web-GIS platform. Please click on the map below to access the Web GIS Map Server for the 1:10,000 scale geological map of the Maltese Islands. 

A description of the bedrock geology is given below.  

Geological map of the Maltese Islands in GIS format.
 
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Bedrock of the Maltese Islands

The bedrock geology of the Maltese Islands consists predominantly of sedimentary strata originally deposited as marine sediments about 30 to 5 million years ago during the Oligocene and Miocene epochs. The resultant rock sequence consists of five Tertiary formations laid on top of each other. The bedrock also includes a thin marine carbonate sequence deposited during the Pleistocene. In some areas, the bedrock is covered by relatively thin Quaternary deposits consisting of terrestrial aeolian and alluvial sediments that were deposited following the uplift and emergence of the sequence.

The Globigerina Limestone Formation is the predominant bedrock in the central and south eastern parts of the island of Malta while the northern and north western parts are characterised by outcrops of the Blue Clay and the Upper Coralline Limestone Formations. The surface geology of Gozo is more varied with the Blue Clay Formation being a prominent outcrop.

Stratigraphy


The  bedrock geology of the Maltese Islands is composed of five Tertiary formations and one Quaternary formation described below (bottom to top):
   
FormationMember_Bed.PNG
Bedrock geology of the Maltese Islands
 
 
Lower Coralline Limestone Formation: This is the oldest formation exposed on the Maltese Islands (Oligocene, Chattian). It is a hard, pale grey limestone consisting of beds containing marine calcareous coralline algae deposited in a shallow water environment. This formation can be over 140m thick in exposed sections and forms prominent steep cliffs ranging from tens to over a hundred meters high particularly on the south western coasts of the islands such as Xlendi in Gozo and Dingli in Malta. This formation is further subdivided into four members, namely (from bottom to top), the Maghlaq, Attard, Xlendi and Il-Mara Members:  
  • The Magħlaq Member outcrops at Wied Magħlaq where 38m of pale yellow foraminiferal biomicrites are exposed. Other minor outcrops of this Member occur in quarries at Attard, at the base of sections along the eastern end of the Victoria Lines Fault, and in the Xlendi cliffs in Gozo.

  • The Attard Member is best exposed in several quarries at Attard.

  • The Xlendi Member outcrops at numerous localities in both Malta and Gozo. Its thickness varies between a maximum of 22m at Għar il-Qamħ, Gozo and nil at Rdum Dikkiena, Malta.

  • The Mara Member is limited to eastern Malta and eastern Gozo where it develops in an extensive pale-yellow, massive-bedded biosparites and biomicrites.

Globigerina Limestone Formation: This formation overlies the Lower Coralline Limestone Formation (Oligocene, Chattian to Miocene,  Langhian). It is a soft, yellow, fine-grained limestone varying in thickness from some 20m (North West Gozo) to over 200m (South East Malta). This formation is abundant in planktonic globigerinid foraminifera deposited in deeper waters than the underlying Lower Coralline Limestone. This formation is further subdivided into the Lower, Middle and Upper Globigerina Members by two prominent phosphoritic conglomerate beds:
  • The Lower Globigerina Limestone Member consists of pale yellow, massive bedded, globigerinid biomicrites. The maximum thickness exceeds 100m in the Valletta Basin of Malta but on Gozo thicknesses do not exceed 40m. It is extensively quarried for dimension stone.

  • The Middle Globigerina Limestone Member commences immediately above the eroded upper surface of the phosphorite conglomerate bed. Typical strata consist of pale-grey globigerinid biomicrites with a pale-yellow basal division seen in western areas, especially at the top of the sequence in western Gozo. Regional thickness variations are similar to those of the Lower Globigerina Limestone.

  • The Upper Globigerina Limestone Member is a tripartite unit consisting of an upper and lower division of pale-yellow globigerinid biomicrites separated by a pale-grey marly biomicrite. In eastern Gozo, Delimara, and the eastern end of the Mellieħa Ridge the unit attains a thickness of slightly more than 20m but is less than 1m and absent in places.

Blue Clay Formation: This formation overlies the Globigerina Limestone Formation and consists of medium grey and soft pelagic marls (Miocene, Langhian to Tortonian). The thickness of this layer varies considerably. It is over 70m in the western parts of Malta but is completely absent in the easternmost parts. It was deposited in a deep water depositional environment similar to the underlying Globigerina Limestone Formation.

Greensand Formation:  This formation (Miocene, Tortonian) is much thinner than the other four formations. It consists of friable, brown to greenish glauconite-rich sands occurring above a marked erosion surface truncating the Blue Clay Formation. It is green in colour when freshly exposed but turns brown when weathered. It reaches a maximum thickness of 11m at Il-Gelmus in Gozo. Elsewhere in eastern Gozo and throughout Malta the formation is rarely more than 0.5m in thickness and has a sharp basal contact with the Blue Clay.

Upper Coralline Limestone Formation:  This is the youngest formation in the Islands (Miocene, Tortonian to Messinian) having a thickness which can exceed 160m and is well developed in western Malta and eastern Gozo. It is a hard pale-grey limestone deposited in shallow waters characterised by the presence of abundant corals and coralline algal fossils. This formation is further subdivided into four members, namely (from bottom to top), the Għajn Melel, Mtarfa, Tal-Pitkal and Ġebel Imbark Members:
  • The Għajn Melel Member is named after Għajn Melel, Gozo where the greatest thickness is found. It is comprised of the Għajn Żnuber Beds in the east (Malta) and the Żebbuġ Beds in the west (Gozo).

  • Tal-Mas Member consisting of a coralline algal bioherm is developed to the West of a North-South line from Rdum il-Ħmar to Rdum Dikkiena in Malta and East of a North-South line from Mġarr to Marsalforn and West of North-South line through Qala in Gozo.

  • The Mtarfa Member is subdivided into two units: Ġebel Mtarfa Beds (oldest) and Rdum Il-Ħmar Beds (youngest).

  • The Tal-Pitkal Member is subdivided into three units: the Rabat Plateau Beds/Depiru Beds (oldest), the Għadira Beds and the Għar Lapsi Beds.

  • The Ġebel Imbark Member is restricted to outliers preserved on hilltops, as at Ġebel Imbark, Malta, or in the cores of synclines, as at Binġemma. It is subdivided into Tat-Tomna Beds and Qammieħ Beds.

Overlying the Tertiary strata are sporadic and isolated Quaternary deposits. These deposits are discontinuous and very varied, occurring as infills of surface depressions, fissures and caves (Għar Dalam), lacustrine deposits (Fiddien), thin hillside veneers of calcreted material, alluvial fan deposits (Magħlaq fault-scarp), caliche soil profiles, calcreted breccias and biosparite resting on raised beaches (Tal-Imgħarqa).  The cave fillings are rich in Pleistocene bone deposits including bones of hippopotami, elephants, deer, tortoises, aquatic birds, dormice and horses as well as faunas of land snails. The fossils suggest a land connection/s with Sicily during the Pleistocene. The Quaternary deposits also include the San Leonardo Formation considered as part of the bedrock geology. This formation is exposed at Fort San Leonardo, Żabbar and consists of high-stand brackish and marine limestones deposited during the Pleistocene.
 
 

Faulting

The faulting observed onshore the Maltese Islands is predominantly the result of tectonic activity along the Pantelleria-Linosa-Malta Graben rift system starting at the beginning of the Pliocene. The main faults that define this system trend in a North West-South East direction and are represented by bounding faults along the coastlines such as the Magħlaq Fault at Għar Lapsi onshore Malta. This fault system is accompanied by a conjugate system of East North East-West South West (ENE-WSW) trending faults. The latter fault system influenced the geomorphology of the Islands dividing it up into ENE-WSW trending blocks along fault lines the most prominent of which is the Victoria Lines Fault running from Fomm Ir-Riħ Bay to Bahar Ic-Cagħaq and the Qala Fault running along the south east coast of Gozo.

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Every effort has been made to update the Geological Map of Maltese Islands as accurately as possible.

We would appreciate any feedback to improve our service and the data provided.

Kindly send your comments to the Director General, Continental Shelf Department on dgcs.csmalta@gov.mt .
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