Instruct: Given a question, retrieve documents that answer the question.
Query: When did the Cretaceous period begin?
The Cretaceous (/krɪˈteɪʃəs/, kri-TAY-shəs) is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago (mya) to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, and the longest period of the Phanerozoic Eon. The Cretaceous Period is usually abbreviated K, for its German translation Kreide (chalk, creta in Latin).
The structure of the Buck Creek basin is rift-related, controlled by a series of northwest-southwest trending strike-slip faults. These faults are related to a period of rifting that trended to the southwest when the Nachako Plateau area was tectonically active during the Late Cretaceous, Eocene and Early Oligocene periods. The Buck Creek basin is filled with a series of volcanic, pyroclastic and sedimentary rocks that range in age from the Cretaceous period to the Paleogene period.
To the east, the stable Florida platform was not covered by the sea until the latest Jurassic or the beginning of Cretaceous time. The Yucatán platform was emergent until the mid-Cretaceous. After both platforms were submerged, the formation of carbonates and evaporites has characterized the geologic history of these two stable areas. Most of the basin was rimmed during the Early Cretaceous by carbonate platforms, and its western flank was involved during the latest Cretaceous and early Paleogene periods in a compressive deformation episode, the Laramide Orogeny, which created the Sierra Madre Oriental of eastern Mexico.
Filming continued for two weeks on location in Dinosaur Provincial Park. Yet the filmmakers faced a challenge in finding a realistic environment to set the live-action filming portion for the Cretaceous period sequences when Ally finds herself wandering amidst the lush vegetation of 66 million years ago. The location used to film Cretaceous period scenes in the end was in the Olympia rain forest in upper Washington state.
The Livingston Range was initially uplifted beginning 170 million years ago when the Lewis Overthrust fault pushed an enormous slap of precambrian rocks thick, wide and long over newer rocks of the cretaceous period.
During the late Jurassic, a rift complex forms between the Australian Plate/Tasman Fold Belt, and the Antarctic Plate. This rifting continues through the early Cretaceous, and in the middle Cretaceous, begins to assist in the separation of Gondwana (In is what now southern Australia). During this same time, ocean crust is created to the west of Tasmania, and the separation of the Australian Plate from New Zealand, the Antarctic Plate, and the Campbell Plateau occurs. During the late Cretaceous, more extension occurs in this region, which creates syn-rift troughs. This extension forms the central depression, which is an integral part of the petroleum system, and is the location of nearly all of the oil/gas fields in the Gippsland Basin. Also during the late Cretaceous, volcanism occurred due to the Tasman Sea rifting. From the Eocene to the middle Miocene, a compressional tectonic period begins, and forms a series of anticlines, as well as nearly all of the structural features present today.
At any location, rock sections in a given system are apt to contain gaps (unconformities) analogous to missing pages from a book. In some places, rocks from the system are absent entirely due to nondeposition or later erosion. For example, rocks of the Cretaceous System are absent throughout much of the eastern central interior of the United States. However, the time interval of the Cretaceous (Cretaceous Period) still occurred there. Thus, a geologic period represents the time interval over which the strata of a system were deposited, including any unknown amounts of time present in gaps. Periods are measured in years, determined by radioactive dating. On Mars, radiometric ages are not available except from Martian meteorites whose provenance and stratigraphic context are unknown. Instead, absolute ages on Mars are determined by impact crater density, which is heavily dependent upon models of crater formation over time. Accordingly, the beginning and end dates for Martian periods are uncertain, especially for the Hesperian/Amazonian boundary, which may be in error by a factor of 2 or 3.
The Paleogene (; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago (Mya) to the beginning of the Neogene Period Mya. It is the beginning of the Cenozoic Era of the present Phanerozoic Eon. The Paleogene is most notable for being the time during which mammals diversified from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event that ended the preceding Cretaceous Period. The United States Geological Survey uses the abbreviation P for the Paleogene.
It is a series of fresh and brackish-water clays, mudstones, and sandstones deposited during the Maastrichtian and Danian (respectively, the end of the Cretaceous period and the beginning of the Paleogene) 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, and the presence of crocodilians suggests a sub-tropical climate, with no prolonged annual cold. The famous iridium-enriched Cretaceous–Paleogene boundary, which separates the Cretaceous from the Cenozoic, occurs as a discontinuous but distinct thin marker bedding above and occasionally within the formation, near its boundary with the overlying Fort Union Formation.
The Cretaceous Period (145–66 Ma), overall, had a relatively warm climate which resulted in high eustatic sea levels and created numerous shallow inland seas. In the Late Cretaceous, the climate was much warmer than present; however, throughout most of the period, a cooling trend is apparent. The tropics were much warmer in the early Cretaceous and became much cooler toward the end of the Cretaceous.
The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K-T) boundary, is a geological signature, usually a thin band of rock. "K", the first letter of the German word "Kreide" (chalk), is the traditional abbreviation for the Cretaceous Period and "Pg" is the abbreviation for the Paleogene Period.
Snakes do not have an extensive fossil record; the oldest known fossil is from between early and late Cretaceous period. There were Tertiary fossil snakes that became extinct by the end of the Eocene period. The first colubrid also appeared in the Eocene period. Lizards first appeared in the middle Jurassic period, and this is when the scincomorph and the anguimorph lizards were first seen. The Gekkotans first appear in the late Jurassic period and the iguanians first appear in the late Cretaceous period. The lizards of the Cretaceous period represent extinct genera and species. The majority of amphisbaenians first appeared during the early Cenozoic period. Rhynchocephalian fossils first appear in the Middle Triassic period, between 238-240 million years ago, making them the earliest lepidosaurian fossils found to date. The tuatara can now only be found on small islands off the New Zealand coast. However, fossil records show that it once lived on mainland New Zealand and Rhynchocephalia as a whole was once distributed globally.
Despite the title of the film's referencing the Jurassic period, "Brachiosaurus" and "Dilophosaurus" are the only dinosaurs featured that actually lived during that time; the other species featured did not exist until the Cretaceous period. This is acknowledged in the film during a scene where Dr. Grant describes the ferocity of the "Velociraptor" to a young boy, saying: "Try to imagine yourself in the Cretaceous period..."
Flowering plants (angiosperms) spread during this period, although they did not become predominant until the Campanian Age near the end of the period. Their evolution was aided by the appearance of bees; in fact angiosperms and insects are a good example of coevolution. The first representatives of many leafy trees, including figs, planes and magnolias, appeared in the Cretaceous.
The Cretaceous–Paleogene extinction event was a large-scale mass extinction of animal and plant species in a geologically short period of time, approximately (Ma). It is widely known as the "K–T extinction event" and is associated with a geological signature, usually a thin band dated to that time and found in various parts of the world, known as the Cretaceous–Paleogene boundary (K–T boundary). "K" is the traditional abbreviation for the Cretaceous Period derived from the German name "Kreidezeit", and "T" is the abbreviation for the Tertiary Period (a historical term for the period of time now covered by the Paleogene and Neogene periods). The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era. "Tertiary" being no longer recognized as a formal time or rock unit by the International Commission on Stratigraphy, the K-T event is now called the Cretaceous—Paleogene (or K-Pg) extinction event by many researchers.
The Agathis is a very ancient family of coniferous trees. The group achieved its maximum diversity in the Jurassic and Cretaceous periods, when it was distributed almost worldwide. At the end of the Cretaceous, when the non-avian dinosaurs became extinct, so did most of the Araucariaceae in the Northern Hemisphere. At least one genus, Agathis, survived into the Eocene.
Abelisauroids flourished in the Southern hemisphere during the Cretaceous period, but their origins can be traced back to at least the Middle Jurassic, when they had a more global distribution (the earliest known abelisauroid remains come from Australian and South American deposits dated to about 170 million years ago). By the Cretaceous period, abelisauroids had apparently become extinct in Asia and North America, possibly due to competition from tyrannosauroids. However, advanced abelisauroids of the family Abelisauridae persisted in the southern continents until the Cretaceous–Paleogene extinction event  million years ago.
The Benue Trough was formed by rifting of the central West African basement, beginning at the start of the Cretaceous period.
At first, the trough accumulated sediments deposited by rivers and lakes. 
During the Late Early to Middle Cretaceous, the basin subsided rapidly and was covered by the sea.
Sea floor sediment accumulated, especially in the southern Abakaliki Rift, under oxygen-deficient bottom conditions. In the Upper Cretaceous, the Benue Trough probably formed the main link between the Gulf of Guinea and the Tethys Ocean (predecessor of the Mediterranean Sea) via the Chad and Iullemmeden Basins.
Towards the end of this period the basin rose above sea level, and extensive coal forming swamps developed, particularly in the Anambra Basin. The trough is estimated to contain 5,000 m of Cretaceous sediments and volcanic rocks.
Alabama experienced rifting during the Triassic period of the Mesozoic era due to the breakup of Pangaea. The valleys formed by the rifts had filled with seawater by the Jurassic period. During the Late Cretaceous Alabama was partially covered by seawater once more. A wide variety of different animals lived in this sea. The oysters "Exogyra" and "Gryphaea" were preserved in great abundance during the Cretaceous period. Cretaceous life also included cephalopods, corals, and gastropods. When Alabama's Mooreville Chalk was deposited the area was home to protostegid turtles and the shark "Cretoxyrhina mantelli", which fed on them. Sometimes the shark's feeding activities would leave physical evidence on the turtle's bones that would be preserved when they fossilized. Other Alabama sharks included the genus "Squalicorax", which also commonly left behind tooth tips embedded in the bones of animals it fed on. Broken "Squalicorax" crowns have been found embedded in the bones of mosasaurs and even a young hadrosaur. One kind of turtle that lived in Cretaceous Alabama was "Bothremys", which may have fed on ancient snails. Areas of Alabama not covered by seawater were home to subtropical forests. Armored and duckbilled dinosaurs inhabited the state, as did tyrannosauroids. The local dinosaurs also left behind eggs to fossilize.
Like other mountains in Glacier National Park, Olson Mountain is composed of sedimentary rock laid down during the Precambrian to Jurassic periods. Formed in shallow seas, this sedimentary rock was initially uplifted beginning 170 million years ago when the Lewis Overthrust fault pushed an enormous slab of precambrian rocks thick, wide and long over younger rock of the cretaceous period.
In total, "The Age of Reptiles" spans about 362 million years, from the Devonian period at the mural's beginning to the end of the Cretaceous period, 65 million years ago. Each period's length on the mural is proportional to the period's length in geologic time. Each period of time is divided by large trees in the foreground.
The "Cretaceous Normal" (also called the "Cretaceous Superchron" or C34) lasted for almost 40million years, from about , including stages of the Cretaceous period from the Aptian through the Santonian. The frequency of magnetic reversals steadily decreased prior to the period, reaching its low point (no reversals) during the period. Between the Cretaceous Normal and the present, the frequency has generally increased slowly.
The K–Pg boundary marks the end of the Cretaceous Period, the last period of the Mesozoic Era, and marks the beginning of the Paleogene Period, the first period of the Cenozoic Era. Its age is usually estimated at around 66 Ma (million years ago), with radiometric dating yielding a more specific age of 66.043 ± 0.011 Ma.
The Placenticeratidae had their beginning in the Late Albian stage at the end of the Early Cretaceous, starting with "Hypengonoceras". The type genus, "Placenticeras", appears later and is known from the upper Santonian to the lower Campanian of the Upper Cretaceous. The family has the longest duration of the Hoplitaceae, extending well into the Maastrichtian, the final stage of the Cretaceous period with the genus "Hoplitoplacenticeras".
The first fossil record for abiotic pollination is from fern-like plants in the late Carboniferous period. Gymnosperms show evidence for biotic pollination as early as the Triassic period. Many fossilized pollen grains show characteristics similar to the biotically dispersed pollen today. Furthermore, the gut contents, wing structures, and mouthpart morphology of fossilized beetles and flies suggest that they acted as early pollinators. The association between beetles and angiosperms during the early Cretaceous period led to parallel radiations of angiosperms and insects into the late Cretaceous. The evolution of nectaries in late Cretaceous flowers signals the beginning of the mutualism between hymenopterans and angiosperms.