|
|
|
|
Maastrichtian
|
| |
|
| |
The Maastrichtian is the last stage of the Cretaceous period, and therefore of the Mesozoic era. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma (million years ago). The Maastrichtian Stage was preceded by the Campanian Stage and succeeded by the Danian Stage of the Paleogene Period. The Maastrichtian is named after the Dutch city Maastricht, where many fossils from the period—most notably those of the mosasaur—were discovered.
At the end of this period, there was a mass extinction commonly referred to as the Cretaceous-Tertiary extinction event (or K/T).
Discussion
Ask a question about 'Maastrichtian' Start a new discussion about 'Maastrichtian' Answer questions from other users |
Encyclopedia
The Maastrichtian is the last stage of the Cretaceous period, and therefore of the Mesozoic era. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma (million years ago). The Maastrichtian Stage was preceded by the Campanian Stage and succeeded by the Danian Stage of the Paleogene Period. The Maastrichtian is named after the Dutch city Maastricht, where many fossils from the period—most notably those of the mosasaur—were discovered.
At the end of this period, there was a mass extinction commonly referred to as the Cretaceous-Tertiary extinction event (or K/T). At this extinction event, many commonly recognized groups such as non-avian dinosaurs, plesiosaurs and mosasaurs, as well as many other lesser known groups, died out.
Geography
Maastrichtian Aged Geologic Formations
Geologic formations with strata dating back to the Maastrichtian stage come from a variety of locations, particularly in Asia and western North America.
The following are summaries of the characteristics of specific Maastrichtian aged formations. More information can be found at those formations' respective main articles.
The Bearpaw Formation, also called the Bearpaw Shale, is a sedimentary rock formation found in northwestern North America. It is exposed in the U.S. state of Montana, as well as the Canadian provinces of Alberta and Saskatchewan, east of the Rocky Mountains. It overlies the older Two Medicine, Judith River and Dinosaur Park Formations, and is in turn overlain by the Horseshoe Canyon Formation in Canada and the Fox Hills Sandstone in Montana. To the east and south it blends into the Pierre Shale.
A marine formation composed mostly of shale, it represents the last major expansion of the Western Interior Seaway before it completely receded from northwestern North America by the end of the Cretaceous Period. It is famous for its well-preserved ammonite fossils. Other fossils found in this formation include many types of shellfish, bony fish, sharks, rays, birds, and marine reptiles like mosasaurs, plesiosaurs and sea turtles. The occasional dinosaur remains have also been discovered, presumably from carcasses washed out to sea.
The Berivotra Formation is an Upper Cretaceous (Maastrichtian) sedimentary rock marine formation found in Madagascar, that is contemporary to the terrestrial Maevarano Formation.
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The Hell Creek Formation occurs in badlands of eastern Montana and portions of North Dakota, South Dakota, and Wyoming. In Montana, the Hell Creek Formation overlies the Fox Hills Formation and is the uppermost formation of the Cretaceous period.
It is a series of fresh and brackish-water clays, mudstones, and sandstones deposited during the Maastrichtian, the last part of the Cretaceous period, by fluvial activity in fluctuating river channels and deltas and very occasional peaty swamp deposits along the low-lying eastern continental margin fronting the late Cretaceous Western Interior Seaway. The climate was mild. The famous iridium-enriched K-T boundary, which separates the Cretaceous from the Cenozoic, occurs as a discontinuous but distinct thin marker bedding within the Formation, near its uppermost strata.
The Horseshoe Canyon Formation is part of the Edmonton Series and is up to 230 m in depth. It is Late Campanian to Early Maastrichtian in age (Edmontonian Land Mammal Age) and is composed of mudstone, sandstone, and carbonaceous shales. There are a variety of environments, which have yielded a diversity of fossil material. The Horseshoe Canyon Formation outcrops extensively in the area of Drumheller, Alberta, as well as further north along the Red Deer River near Trochu, and also in the city of Edmonton.
The Lameta Formation is a sedimentary rock formation found in Madhya Pradesh, Gujarat, and Maharashtra, India. It is of Maastrichtian age (Upper Cretaceous), and is notable for its dinosaur fossils. Many dubious names have been created for isolated bones, but several genera of dinosaurs from these rocks are well-supported, including the titanosaur sauropod Isisaurus and the abelisaurs Indosaurus, Indosuchus, Laevisuchus, and Rajasaurus.
The Maevarano Formation is an Upper Cretaceous sedimentary rock formation found in the Mahajanga Province of northwestern Madagascar. It is most likely Maastrichtian in age, and records a seasonal, semiarid environment with rivers that had greatly varying discharges. Notable animal fossils recovered include the theropod dinosaur Majungasaurus and the early birds Rahonavis and Vorona, and the titanosaurian sauropod Rapetosaurus.
The Sarir Field was discovered in southern Cyrenaica during 1961 and is considered to be the largest oil field in Libya, with estimated oil reserves of . Sarir is operated by the Arabian Gulf Oil Company (AGOCO), a subsidiary of the state-owned National Oil Corporation (NOC).
The Sarir stratigraphic column generally resembles succession patterns throughout the Sirte Basin, with some variations. In the early regressive phase, basal sandstones were deposited on a Precambrian basement of igneous and metamorphic rocks. Sandstones are dated on angiosperm pollen as younger than Albian, probably from the Late Cretaceous. After a lengthy hiatus, represented by unconformity and sandstone erosion, a transgressive sequence of red, green, and purple Anhydrite shales was laid. Variegated bed remnants occur in crestal sections of many northern structures, such as in wells B-1-65 and C-1-80.
Above the transgressive sequence are Late Cretaceous shales with tight, micritic carbonate, marking the top of the Mesozoic. These shales thicken into troughs, providing the field's sole source rock. The youngest fauna are Maastrichtian, with an apparent disconformity between the Late Cretaceous and Paleocene, marked by high levels of gamma radiation on logs.
Uncertain Formations
The following formations dating is somewhat uncertain, but very likely are of Maastrichtian age.
The Barun Goyot Formation, dating from the Late Cretaceous Period, is located within and is widely represented in the Gobi Desert basin, in the Ömnögovi Province of Mongolia.
It was previously known as the "Lower Nemegt Beds", occurring beneath the Nemegt Formation and above the Djadokhta Formation. It is approximately in thickness and was laid down roughly 80-71 mya, making it uncertain whether it should be classed as Campanian or Maastrichtian, although the latter is less likely. The Barun Goyot Formation preserves an environment of sand dunes, created from wind-eroded rocks (aeolian dunes).
The Nemegt Formation is a Late Cretaceous sedimentary formation in the Gobi Desert of Mongolia. It overlies, and in some places interdigitates with, the Barun Goyot Formation. It consists of river channel sediments and contains fossils of fish, turtles, crocodilians, birds and a diverse fauna of dinosaurs. The climate was wetter than when the preceding formations were deposited; there seems to have existed at least some degree of forest cover.
The absolute age of the Nemegt Formation is unknown but it is thought to be Maastrichtian or maybe late Campanian in age, very roughly some 76-65 million years old. The presence of Saurolophus, a taxon also known from the Horseshoe Canyon Formation of Alberta, may indicate an Early Maastrichtian age, about 70 million years old.
Vertebrate Fauna
See Main Article: Flora and fauna of the Maastrichtian stage.
Birds
Several lineages of modern birds existed, though many were of lineages that differed profoundly from their relatives of today and thus are not their ancestors, but became extinct in the Cenozoic. For example, Vegavis iaai indicates that at least four lineages of Anseriformes were distinct: Anhimidae, Anatidae, Anseranatidae and Presbyornithidae (and possibly Dromornithidae), and that there was at least one Galliformes lineage too, and apparently the Gastornithiformes were also distinct. It is also highly likely that there was at least one, and probably several, lineages of Charadriiformes, that penguins were about to split from their closest relatives or had already done so, and that if the Metaves are a valid group they would presumably have been distinct too. Also, paleognaths were of course long distinct from neognaths.
Flora
See Main Article: Flora and fauna of the Maastrichtian stage.
|
| |
|
|
