| Maastrichtian | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| 72.2 ± 0.2 – 66.0Ma | |||||||||
 Opening of the western Indian Ocean in the Maastrichtian | |||||||||
| Chronology | |||||||||
| |||||||||
| Etymology | |||||||||
| Name formality | Formal | ||||||||
| Usage information | |||||||||
| Celestial body | Earth | ||||||||
| Regional usage | Global (ICS) | ||||||||
| Time scale(s) used | ICS Time Scale | ||||||||
| Definition | |||||||||
| Chronological unit | Age | ||||||||
| Stratigraphic unit | Stage | ||||||||
| Time span formality | Formal | ||||||||
| Lower boundary definition | Mean of 12 biostratigraphic criteria | ||||||||
| Lower boundary GSSP | Grande Carrière quarry,Landes,France 43°40′46″N1°06′48″W / 43.6795°N 1.1133°W /43.6795; -1.1133 | ||||||||
| Lower GSSP ratified | February 2001[2] | ||||||||
| Upper boundary definition | Iridium enriched layer associated with a major meteorite impact and subsequentK-Pg extinction event. | ||||||||
| Upper boundary GSSP | El Kef Section,El Kef,Tunisia 36°09′13″N8°38′55″E / 36.1537°N 8.6486°E /36.1537; 8.6486 | ||||||||
| Upper GSSP ratified | 1991 | ||||||||
TheMaastrichtian (/mɑːˈstrɪktiən/mahss-TRIK-tee-ən) is, in theInternational Commission on Stratigraphy (ICS)geologic timescale, the latestage (uppermoststage) of theLate CretaceousEpoch orUpper CretaceousSeries, theCretaceousPeriod orSystem, and of theMesozoicEra orErathem. It spanned the interval from72.2 to 66 million years ago. The Maastrichtian was preceded by theCampanian and succeeded by theDanian (part of thePaleogene andPaleocene).[3] It is named after the city ofMaastricht, the capital and largest city of theLimburg province in theNetherlands.
TheCretaceous–Paleogene extinction event (formerly known as the Cretaceous–Tertiary extinction event)[a] occurred at the end of this age.[3] In thismass extinction, many commonly recognized groups such as non-aviandinosaurs,pterosaurs,plesiosaurs andmosasaurs, as well as many other lesser-known groups, died out. The cause of the extinction is most commonly linked toan asteroid about 10 to 15 kilometres (6.2 to 9.3 mi) wide[4][5] colliding with Earth, ending the Cretaceous.
The Maastrichtian was introduced into scientific literature byBelgian geologistAndré Hubert Dumont in 1849, after studyingrock strata of theChalk Group close to theDutch city ofMaastricht. These strata are now classified as theMaastricht Formation – both theformation and stage derive their names from the city.[6] The Maastricht Formation is known for its fossils from this age, most notably those of the giantsea reptileMosasaurus, which in turn derives its name from the nearby riverMaas (mosa being Latin for the river Maas).[7][8]
The base of the Maastrichtian Stage is at the first appearance ofammonite speciesPachydiscus neubergicus. At the original type locality near Maastricht, the stratigraphic record was later found to be incomplete. A reference profile for the base was then appointed in a section along theArdour river calledGrande Carrière, close to the village ofTercis-les-Bains in southwesternFrance.[2][9] The top of the Maastrichtian Stage is defined to be at theiridium anomaly at theCretaceous–Paleogene boundary (K–Pg boundary), which is also characterised by theextinction of many groups of life.[10]
The Maastrichtian is commonly subdivided into two substages (Upper and Lower) and three ammonitebiozones. The biozones are (from young to old):[11]
The Maastrichtian is roughly coeval with theLancianNorth American Land Mammal Age.
The breakup ofPangaea was nearly complete in the Maastrichtian, with Australia beginning to break away from Antarctica and Madagascar breaking away from India. However, Arabia had not yet rifted away from Africa. North America was separated from Europe by rift basins, but sea floor spreading had not yet commenced between the two continents.[12]
The Pacific Plate was rapidly growing in size as the surrounding oceanic plates were consumed bysubduction, and the Pacific-Izanagi Ridge was rapidly approaching Asia.[13]
Eruption of theDeccan Trapslarge igneous province began during the Maastrichtian, at around 67 million years ago. This is thought to be a consequence of India drifting over theRéunion hotspot.[14]
During the Maastrichtian, the global climate began to shift from the warm and humid climate of the Mesozoic to the colder and more arid climate of the Cenozoic.[14] Variation of climate with latitude also became greater. This was likely caused by a major reorganization of oceanic circulation that took place at the boundary between the early and late Maastrichtian. This reorganization was triggered by the breach of tectonic barriers in the South Atlantic, permitting deep ocean water to begin circulating from the nascent North Atlantic to the south. This initiatedthermohaline circulation similar to that of the modern oceans. At the same time, theLaramide orogeny drained theWestern Interior Seaway of North America, further contributing to global cooling.[15] Nonetheless, the latest Maastrichtian featured a sharp, pronounced warming,[16][17] which was caused by the activity of the Deccan Traps.[18]
South-central Alaska had a mean annual temperature of 7.42 ± 1.2 °C, a warm monthly mean temperature of 17.08 ± 1.6 °C, and a cold monthly mean temperature of − 2.31 ± 1.9 °C.[19][20]
Dinosaurs remained the dominant large terrestrial animals throughout the Maastrichtian, though mammals with internal organs similar to modern mammals were also present. Bothammonites andpterosaurs were in serious decline during the Maastrichtian.[21]
Several archaic clades of birds, such asEnantiornithes,Ichthyornithes, andHesperornithes, persisted to the latest Maastrichtian but became extinct during the Cretaceous-Paleogene extinction event.[22]
Traditionally, pterosaur faunas of the Maastrichtian were assumed to be dominated byazhdarchids, with other pterosaur groups having become extinct earlier on. However, more recent findings suggest a fairly composite pterosaur diversity: at least six ("Nyctosaurus"lamegoi, a Mexican humerus, a Jordan humerus and several taxa from Morocco)nyctosaurs date to this period, as do a fewpteranodontids, andNavajodactylus, tentatively assigned to Azhdarchidae, lacks any synapomorphies of the group.[23][24] This seems to underscore a higher diversity of terminal Cretaceous pterosaurs than previously thought.[25][26][27]
The radiation ofangiosperms (flowering plants) was well under way in the Maastrichtian. From 50% to 80% of allgenera of land plants were angiosperms, thoughgymnosperms andferns still covered larger areas of the land surface.[28]
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