The Maltese archipelago, situated between Sicily and Tunisia, was created through the uplift of sedimentary rocks. 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.[3] The isle of Lampedusa is made up of an identical structure on the southwest side of this rift.
Nature of the sub-soilEdit
The rocks are exclusively sedimentary. There is a lot of limestone, which has contributed to the construction of the ancient buildings of the island. These rocks come from marine deposits (essentially from lagoons) dating from between 25 and 5 million years ago.[4]
Dingli cliffs showing stratification in the Lower Coralline Limestone
OligoceneEdit
Lower Coralline Limestone FormationEdit
Hardground at the top of the Lower Coralline Limestone Formation with limestone clasts and fossils of the echinoidScutella subrotunda and bivalves
The oldest exposed rock layer of Malta is the Lower Coralline Limestone Formation (Maltese: Żonqor), which is of Chattian age (~28–23 million years old) with a maximum thickness of 162 m.[1] The unit is exposed on the lower parts of cliffs in the south-west of the archipelago such as at Dingli, and also along rifts, particularly near Mosta and Naxxar. 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.[6] 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.
The Globigerina Limestone (Maltese: Franka) is a soft, gold-coloured limestone of Aquitanian to Langhian age (~23–14 million years old), ranging in thickness from 23 m to 207 m.[1] It contains many fossils, especially those of the foraminiferaGlobigerina 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.[6]
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. This rock has also been exported, and was used in the construction of the government palace of Corfu.[4] The Maltese Lower Globigerina Limestone has been designated by the International Union of Geological Sciences as a Global Heritage Stone Resource.[7]
Gardjola Tower at Senglea, built from Globigerina Limestone
.
Blue Clay FormationEdit
Blue Clay Formation exposed in the cliffs at the northern end of Ġnejna Bay overlying yellow-weathering Upper Globigerina Limestone
The Blue Clay (Maltese: Tafal) is a blue-gray mudstone of Langhian 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.[1] 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 aquifers. Water is extracted through wells or escapes through occasional springs when the topsoil has been eroded.[8]
Greensand FormationEdit
The Greensand (Maltese: Ġebla s-Safra) is a glauconite-bearing sandstone of Tortonian age (~10–7 million years old).[1] 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 FormationEdit
Cliffs of Upper Coralline Limestone Formation on islands at the western end of Comino
The top layer, the Upper Coralline Limestone (Maltese: Qawwi ta' Fuq), is the youngest formation of Messinian age (~7–5 million years old) and is around 140 m thick.[1] It is mainly present on the islands of Malta, Comino 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.
FaultsEdit
SW-dipping minor fault on the southwest coast of Malta, near the Blue Grotto
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 18.5 kilometres (11.5 mi) long.[1][8]
Overall, the islands of the archipelago are tilted towards the northeast, with cliffs on the southwest coast and descending gradients towards the northeast.
Blouet, Brian (1989). The Story of Malta. Progress Press Publication.
Catalano, Raimondo. "CENNI SUL MEDITERRANEO MARINO". Siripro (in Italian). Retrieved 26 January 2015.
Courtin, Jean (1995). "Malte préhistorique, une île de Pâques méditerranéenne?". In Villain-Gandossi, Christiane (ed.). Le Carrefour Maltais. Edisud. ISBN2-85744-801-5.
Galea, Pauline (2007). Seismic history of the Maltese islands and considerations on seismic risk. pp. 725–740. {{cite book}}: |website= ignored (help)
Samut Tagliaferro, John (1991). Malta, its Archeology and History. Casa Editrice Perseus. ISBN978-8872807040.
Sultana, Joe; Falzon, Victor. Wildlife of the Maltese Islands. Environment Protection Department.
geology, malta, consists, sequence, sedimentary, rocks, late, oligocene, late, miocene, through, extensional, faults, pliocene, cliffs, upper, globogerina, limestone, formation, Ħofra, kbira, near, marsaxlokk, contents, tectonics, formation, islands, nature, s. 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 faults of Pliocene age 1 Cliffs of Upper Globogerina Limestone Formation at Il Ħofra l Kbira near Marsaxlokk Contents 1 Tectonics 2 Formation of the islands 3 Nature of the sub soil 4 The geological strata 4 1 Oligocene 4 1 1 Lower Coralline Limestone Formation 4 2 Miocene 4 2 1 Globigerina Limestone Formation 4 2 2 Blue Clay Formation 4 2 3 Greensand Formation 4 2 4 Upper Coralline Limestone Formation 5 Faults 6 Recent geological history 7 ReferencesTectonics EditThe 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 The islands lie around 200 km to the south of the subduction boundary between the African Plate and the Eurasian Plate The platform is crossed by a rift zone formed of three grabens 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 2 Formation of the islands EditThe Maltese archipelago situated between Sicily and Tunisia was created through the uplift of sedimentary rocks 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 3 The isle of Lampedusa is made up of an identical structure on the southwest side of this rift Nature of the sub soil EditThe rocks are exclusively sedimentary There is a lot of limestone which has contributed to the construction of the ancient buildings of the island These rocks come from marine deposits essentially from lagoons dating from between 25 and 5 million years ago 4 The geological strata EditThe stratigraphy of the Maltese islands consists of five geological formations ranging in age from late Oligocene to late Miocene 1 5 nbsp Dingli cliffs showing stratification in the Lower Coralline LimestoneOligocene Edit Lower Coralline Limestone Formation Edit nbsp Hardground at the top of the Lower Coralline Limestone Formation with limestone clasts and fossils of the echinoid Scutella subrotunda and bivalvesThe oldest exposed rock layer of Malta is the Lower Coralline Limestone Formation Maltese Zonqor which is of Chattian age 28 23 million years old with a maximum thickness of 162 m 1 The unit is exposed on the lower parts of cliffs in the south west of the archipelago such as at Dingli and also along rifts particularly near Mosta and Naxxar 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 6 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 Edit Globigerina Limestone Formation Edit nbsp Limestone wall showing honeycomb weatheringThe Globigerina Limestone Maltese Franka is a soft gold coloured limestone of Aquitanian to Langhian age 23 14 million years old ranging in thickness from 23 m to 207 m 1 It contains many fossils especially those of the foraminifera Globigerina 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 6 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 This rock has also been exported and was used in the construction of the government palace of Corfu 4 The Maltese Lower Globigerina Limestone has been designated by the International Union of Geological Sciences as a Global Heritage Stone Resource 7 nbsp Gardjola Tower at Senglea built from Globigerina Limestone Blue Clay Formation Edit nbsp Blue Clay Formation exposed in the cliffs at the northern end of Ġnejna Bay overlying yellow weathering Upper Globigerina LimestoneThe Blue Clay Maltese Tafal is a blue gray mudstone of Langhian 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 1 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 aquifers Water is extracted through wells or escapes through occasional springs when the topsoil has been eroded 8 Greensand Formation Edit The Greensand Maltese Ġebla s Safra is a glauconite bearing sandstone of Tortonian age 10 7 million years old 1 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 Edit nbsp Cliffs of Upper Coralline Limestone Formation on islands at the western end of CominoThe top layer the Upper Coralline Limestone Maltese Qawwi ta Fuq is the youngest formation of Messinian age 7 5 million years old and is around 140 m thick 1 It is mainly present on the islands of Malta Comino 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 Edit nbsp SW dipping minor fault on the southwest coast of Malta near the Blue GrottoThe 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 18 5 kilometres 11 5 mi long 1 8 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 EditThe 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 by which animals have been able to cross as evinced by the presence of island dwarfism Maltese dwarf hippopotamus and dwarf elephant fossils 9 as well as island gigantism fossils of the Maltese Giant Dormouse Leithia melitensis References Edit a b c d e f g h Continental Shelf Department Geological Map of the Maltese Islands Government of Malta Retrieved 2018 02 22 Galea P pp 725 740 Catalano R a b Samut Tagliaferro John Sultana J et al a b Dart C J Bosence D W J McClay K R 1993 Stratigraphy and structure of the Maltese graben system Journal of the Geological Society 150 6 1153 1166 doi 10 1144 gsjgs 150 6 1153 S2CID 131447222 Designation of GHSR IUGS Subcommission Heritage Stones Retrieved 24 February 2019 a b Blouet B Courtin J Blouet Brian 1989 The Story of Malta Progress Press Publication Catalano Raimondo CENNI SUL MEDITERRANEO MARINO Siripro in Italian Retrieved 26 January 2015 Courtin Jean 1995 Malte prehistorique une ile de Paques mediterraneenne In Villain Gandossi Christiane ed Le Carrefour Maltais Edisud ISBN 2 85744 801 5 Galea Pauline 2007 Seismic history of the Maltese islands and considerations on seismic risk pp 725 740 a href Template Cite book html title Template Cite book cite book a website ignored help Samut Tagliaferro John 1991 Malta its Archeology and History Casa Editrice Perseus ISBN 978 8872807040 Sultana Joe Falzon Victor Wildlife of the Maltese Islands Environment Protection Department Portals nbsp Geology nbsp Malta Retrieved from https en wikipedia org w index php title Geology of Malta amp oldid 1144597471 Faults, wikipedia, wiki, book, books, library,
