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41-420: The Snow Hill Island Formation is an Early Maastrichtian geologic formation found on James Ross Island , James Ross Island group , Antarctica . Remains of a paravian theropod Imperobator antarcticus have been recovered from it, as well as the elasmarian ornithopods Trinisaura santamartaensis , "Biscoveosaurus" and Morrosaurus antarcticus , the ankylosaurian Antarctopelta oliveroi , and

82-516: A few pteranodontids , and Navajodactylus , tentatively assigned to Azhdarchidae, lacks any synapomorphies of the group. This seems to underscore a higher diversity of terminal Cretaceous pterosaurs than previously thought. The radiation of angiosperms (flowering plants) was well under way in the Maastrichtian. From 50% to 80% of all genera of land plants were angiosperms, though gymnosperms and ferns still covered larger areas of

123-669: A large slowing of the rate of counterclockwise rotation of Africa. The close correlations between the plate motions suggest that they were both driven by the force of the Réunion plume. When comparing the Na 8 , Fe 8 , and Si 8 contents of the Deccan to other major igneous provinces, the Deccan appears to have undergone the greatest degree of melting suggesting a deep plume origin. Olivine appears to have fractionated at near- Moho depths with additional fractionation of gabbro ~6 km below

164-532: A volume of about 1,000,000 cubic kilometres (200,000 cu mi). Originally, the Deccan Traps may have covered about 1,500,000 square kilometres (600,000 sq mi), with a correspondingly larger original volume. This volume overlies the Archean age Indian Shield , which is likely the lithology the province passed through during eruption. The province is commonly divided into four subprovinces:

205-478: A warm monthly mean temperature of 17.08 ± 1.6 °C, and a cold monthly mean temperature of − 2.31 ± 1.9 °C. Dinosaurs remained the dominant large terrestrial animals throughout the Maastrichtian, though mammals with internal organs similar to modern mammals were also present. Both ammonites and pterosaurs were in serious decline during the Maastrichtian. Several archaic clades of birds, such as Enantiornithes , Ichthyornithes , and Hesperornithes , persisted to

246-563: Is postulated that the Deccan Traps eruption was associated with a deep mantle plume . High He/ He ratios of the main pulse of the eruption are often seen in magmas with mantle plume origin. The area of long-term eruption (the hotspot ), known as the Réunion hotspot , is suspected of both causing the Deccan Traps eruption and opening the rift that separated the Mascarene Plateau from India. Regional crustal thinning supports

287-611: The Chalk Group close to the Dutch city of Maastricht . These strata are now classified as the Maastricht Formation – both formation and stage derive their names from the city. The Maastricht Formation is known for its fossils from this age, most notably those of the giant sea reptile Mosasaurus , which in turn derives its name from the nearby river Maas ( mosa being Latin for the river Maas). The base of

328-494: The Chicxulub impact was the primary cause of the extinction. While some scholars suggest that the eruptions may have been a contributing factor in the extinctions, others suggest that the role of the Deccan Traps in the extinction may have been negligible or even partially negated the effects of the impact. The Deccan Traps are thought to have been produced in major part by the still active Réunion hotspot , responsible for

369-584: The Cenozoic. 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 initiated thermohaline circulation similar to that of

410-581: The Chicxulub event" found in the gills of fish fossils and embedded in amber , an iridium -rich top layer that is considered another signature of the event, and an atypical lack of evidence for scavenging perhaps suggesting that there were few survivors. The exact mechanism of the site's destruction has been debated as either an impact-caused tsunami or lake and river seiche activity triggered by post-impact earthquakes, though there has yet been no firm conclusion upon which researchers have settled. Within

451-534: The Deccan Traps at least 95% of the lavas are tholeiitic basalts . Major mineral constituents are olivine , pyroxenes , and plagioclase , as well as certain Fe-Ti-rich oxides. These magmas are <7% MgO. Many of these minerals are observed however, as highly altered forms. Other rock types present include: alkali basalt , nephelinite , lamprophyre , and carbonatite . Mantle xenoliths have been described from Kachchh (northwestern India) and elsewhere in

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492-496: The Indian tectonic plate and the eruptive history of the Deccan traps show strong correlations. Based on data from marine magnetic profiles, a pulse of unusually rapid plate motion began at the same time as the first pulse of Deccan flood basalts, which is dated at 67 million years ago. The spreading rate rapidly increased and reached a maximum at the same time as the peak basaltic eruptions. The spreading rate then dropped off, with

533-528: The Maastrichtian Stage is at the first appearance of ammonite species Pachydiscus 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 the Ardour river called Grande Carrière , close to the village of Tercis-les-Bains in southwestern France . The top of

574-618: The Maastrichtian Stage is defined to be at the iridium anomaly at the Cretaceous–Paleogene boundary (K–Pg boundary), which is also characterised by the extinction of many groups of life. The Maastrichtian is commonly subdivided into two substages (Upper and Lower) and three ammonite biozones . The biozones are (from young to old): The Maastrichtian is roughly coeval with the Lancian North American Land Mammal Age . The breakup of Pangaea

615-599: The Pacific-Izanagi Ridge was rapidly approaching Asia. Eruption of the Deccan Traps large igneous province began during the Maastrichtian, at around 67 million years ago. This is thought to be a consequence of India drifting over the Réunion hotspot . 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

656-539: The beds of fossils that have been found between layers of lava. Particularly well known species include the frog Oxyglossus pusillus (Owen) of the Eocene of India and the toothed frog Indobatrachus , an early lineage of modern frogs, which is now placed in the Australian family Myobatrachidae . The Infratrappean Beds (Lameta Formation) and Intertrappean Beds also contain fossil freshwater molluscs . It

697-534: The creation of the modern Mascarene Islands in the Indian Ocean. The term trap has been used in geology since 1785–1795 for such rock formations . It is derived from the Swedish word for stairs ( trapp ) and refers to the step-like hills forming the landscape of the region. The name Deccan has Sanskrit origins meaning "southern". The Deccan Traps began forming 66.25  million years ago , at

738-468: The current consensus among the scientific community is that the extinction was primarily triggered by the Chicxulub impact event in North America, which would have produced a sunlight-blocking dust cloud that killed much of the plant life and reduced global temperature (this cooling is called an impact winter ). A 2014 study suggested the extinction may have been caused by both the volcanism and

779-414: The decrease occurring around 63 million years ago, by which time the main phase of Deccan volcanism ended. This correlation is seen as driven by plume dynamics. The motions of the Indian and African plates have also been shown to be coupled, the common element being the position of these plates relative to the location of the Réunion plume head. The onset of accelerated motion of India coincides with

820-581: The destruction from the impact alone, however. In a March 2019 article in the Proceedings of the National Academy of Sciences , an international team of twelve scientists revealed the contents of the Tanis fossil site discovered near Bowman, North Dakota , that appeared to show a devastating mass destruction of an ancient lake and its inhabitants at the time of the Chicxulub impact. In the paper,

861-535: The end of the Cretaceous period, although it is possible that some of the oldest material may underlie younger material. The bulk of the volcanic eruption occurred at the Western Ghats between 66 and 65 million years ago when lava began to extrude through fissures in the crust known as fissure eruptions. Determining the exact age for Deccan rock is difficult due to a number of limitations, one being that

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902-571: The end of this age. In this mass extinction , many commonly recognized groups such as non-avian dinosaurs , plesiosaurs and mosasaurs , as well as many other lesser-known groups, died out. The cause of the extinction is most commonly linked to an asteroid about 10 to 15 kilometres (6.2 to 9.3 mi) wide colliding with Earth, ending the Cretaceous. The Maastrichtian was introduced into scientific literature by Belgian geologist André Hubert Dumont in 1849, after studying rock strata of

943-513: The gases released during the formation of the Deccan Traps played a major role in the Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary or K–T extinction). It has been theorized that sudden cooling due to sulfurous volcanic gases released by the formation of the traps and toxic gas emissions may have contributed significantly to the K–Pg mass extinction. However,

984-618: The group reports that the geology of the site is strewn with fossilized trees and remains of fish and other animals. The lead researcher, Robert A. DePalma of the University of Kansas , was quoted in the New York Times as stating that "You would be blind to miss the carcasses sticking out... It is impossible to miss when you see the outcrop". Evidence correlating this find to the Chicxulub impact included tektites bearing "the unique chemical signature of other tektites associated with

1025-418: The impact event. This was followed by a similar study in 2015, both of which consider the hypothesis that the impact exacerbated or induced the Deccan volcanism, since the events occurred approximately at antipodes . A 2020 study questioned the idea that the Deccan Traps were a contributory factor at all, suggesting that the Deccan Traps eruptions may have even partially negated the climatic change induced by

1066-401: The impact. A major criticism of the Deccan Traps as the primary cause of the extinctions is that the extinction event appears to be globally geologically instantaneous and simultaneous in both marine and terrestrial environments, as would be expected from an impact cause, rather than staggered as would be expected from an LIP cause. A more recent discovery appears to demonstrate the scope of

1107-454: The land surface. Deccan Traps The Deccan Traps are a large igneous province of west-central India (17–24°N, 73–74°E). They are one of the largest volcanic features on Earth, taking the form of a large shield volcano . They consist of many layers of solidified flood basalt that together are more than about 2,000 metres (6,600 ft) thick, cover an area of about 500,000 square kilometres (200,000 sq mi), and have

1148-554: The latest Maastrichtian but became extinct during the Cretaceous-Paleogene extinction event. Traditionally, pterosaur faunas of the Maastrichtian were assumed to be dominated by azhdarchids , 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

1189-675: The main Deccan, the Malwa Plateau , the Mandla Lobe, and the Saurashtran Plateau. The eruptions occurred over a 600–800,000 year time period between around 66.3 to 65.6 million years ago, spanning the Cretaceous–Paleogene boundary . While some authors have suggested that the eruptions were the primary cause of the Cretaceous–Paleogene mass extinction event , which dates to around 66.05 million years ago, this has been strongly disputed, with many authors suggesting that

1230-545: The modern oceans. At the same time, the Laramide orogeny drained the Western Interior Seaway of North America, further contributing to global cooling. Nonetheless, the latest Maastrichtian featured a sharp, pronounced warming, which was caused by the activity of the Deccan Traps. Northern Alaska's mean annual temperature was 6.3 °C. South-central Alaska had a mean annual temperature of 7.42 ± 1.2 °C,

1271-411: The overall flow volume. It can be difficult, however, to locate the largest dikes as they are often located towards the west coast and are therefore believed to currently reside under water. Although the Deccan Traps began erupting well before the impact , in a 2015 study it was proposed based on argon–argon dating that the impact may have caused an increase in permeability that allowed magma to reach

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1312-502: The sequence of events in Deccan extrusion, it is now more widely accepted that these horizons relate more closely to paleo topography and distance from the eruption site. The release of volcanic gases , particularly sulfur dioxide , during the formation of the traps may have contributed to climate change . An average drop in temperature of about 2 °C (3.6 °F) was recorded during this period. Because of its magnitude, some scientists (notably Gerta Keller ) have speculated that

1353-649: The shark Notidanodon sp. Alongside these described genera are also the remains of indeterminate elasmosaurids , lithostrotian titanosaurs and an indeterminate pterosaur . In the Herbert Sound Member of the Snow Hill Island Formation, bivalves, ammonites , and fish were found. Maastrichtian The Cretaceous–Paleogene extinction event (formerly known as the Cretaceous– Tertiary extinction event) occurred at

1394-465: The size of modern India . The Deccan Traps region was reduced to its current size by erosion and plate tectonics; the present area of directly observable lava flows is around 500,000 km (200,000 sq mi). The Deccan Traps are segmented into three stratigraphic units: the Upper, Middle, and Lower traps. While it was previously interpreted that these groups represented their own key points in

1435-465: The suggestion as being "convenient interpretations based on superficial and cursory observations." A geological structure that exists in the sea floor off the west coast of India has been suggested as a possible impact crater, in this context called the Shiva crater . It was also dated approximately 66 million years ago, potentially matching the Deccan traps. The researchers claiming that this feature

1476-461: The surface and produced the most voluminous flows, accounting for around 70% of the volume. The combination of the asteroid impact and the resulting increase in eruptive volume may have been responsible for the mass extinctions that occurred at the time that separates the Cretaceous and Paleogene periods, known as the K–Pg boundary . However this proposal has been questioned by other authors, who describe

1517-470: The surface. Features such as widespread faulting , frequent diking events, high heat flux, and positive gravity anomalies suggest that the extrusive phase of the Deccan Traps is associated with the existence of a triple junction which may have existed during the Late Cretaceous, having been caused by a deep mantle plume. Not all of these diking events are attributed to large-scale contributions to

1558-484: The theory of this rifting event and likely encouraged the rise of the plume in this area. Seafloor spreading at the boundary between the Indian and African Plates subsequently pushed India north over the plume, which now lies under Réunion island in the Indian Ocean , southwest of India. The mantle plume model has, however, been challenged. Data continues to emerge that supports the plume model. The motion of

1599-491: The transition between eruption events may have lasted only a few thousand years and the resolution of dating methods isn't sufficient to pinpoint these events. In this way, determining the rate of magma emplacement is also difficult to constrain. This series of eruptions may have lasted for less than 30,000 years. The original area covered by the lava flows is estimated to have been as large as 1.5 million km (0.58 million sq mi), approximately half

1640-436: The western Deccan and contain spinel lherzolite and pyroxenite constituents. While the Deccan traps have been categorized in many different ways including the three different stratigraphic groups, geochemically the province can be split into as many as eleven different formations. Many of the petrologic differences in these units are a product of varying degrees of crustal contamination. The Deccan Traps are famous for

1681-438: 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. The Pacific Plate was rapidly growing in size as the surrounding oceanic plates were consumed by subduction , and

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