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26-556: The Broome Sandstone , formerly known as the Broome Beds , is an Early Cretaceous geologic formation found in Western Australia , and formerly considered part of Dampier Group . Fossil sauropod tracks, belonging to an unknown ichnotaxon, and stegosaur tracks belonging to the ichnogenus and species Garbina roeorum have been reported from the formation since the 1990s. Early Cretaceous Proposals for

52-488: A generally humid climate. However, evidence from the growth rings of petrified wood indicates that the humidity and water supply dropped regularly. This shows that the wet, humid conditions were punctuated by dry seasons, in which the environment became more arid. Evidence from the study of oxygen isotopes has shown that the average yearly temperature during this time period was 10 degrees celsius (50 degrees Fahrenheit ), significantly colder than once thought. This indicates

78-467: A temperate climate with unusually cold winters for the generally warm Mesozoic era, possibly due to northern China's high latitude during this time. A study by Wu et al. (2013) concluded that orbital forcing , which is the effect on climate caused by shifts in the tilt of the Earth's axis and by the shape of the Earth's orbit, contributed to the climate fluctuations of this formation. The Yixian Formation

104-735: Is a geological formation in Jinzhou , Liaoning , People's Republic of China , that spans the Barremian stage of the Early Cretaceous. It is known for its exquisitely preserved fossils , and is mainly composed of basalts interspersed with siliciclastic sediments. The potential importance of the Yixian Formation was initially recognized during the time the Empire of Japan occupied China's Rehe ("Jehol") Province after

130-788: Is now considered to have been deposited in the Barremian , some 125.8–124.1 mya. The Yixian Formation forms the lowest part of the Jehol group , defined by Gu (1962 and 1983) as a group of geological formations including the Jehol Coal-bearing Beds, the Jehol Oil Shale Beds, and the Jehol Volcanic Rocks. The Yixian Formation is preceded by the older Daohugou Beds , of uncertain Jurassic or Early Cretaceous age, which are sometimes considered part of

156-401: Is well known for its great diversity of well-preserved specimens and its feathered dinosaurs, such as the large tyrannosauroid Yutyrannus , the therizinosaur Beipiaosaurus , and various small birds, along with a selection of other dinosaurs, such as the iguanodontian Bolong , the sauropod Dongbeititan and the ceratopsian Psittacosaurus . Other biota included the troodontid Mei ,

182-728: The Chaomidianzi Formation , with a type locality at the village of Sihetun, approximately 25 km south of Beipiao City. However, this classification has fallen out of favor, and the Chaomidianzi Formation is disused as a synonym for the Jianshangou Bed of the Yixian Formation. The Dabeigou Formation in Fengning, Hebei Province may immediately precede the Yixian, or it may be equivalent to

208-622: The Defense of the Great Wall in 1933. Many Japanese scientists had noticed fossil remains of extinct fish and reptiles, possibly the champsosaurs . These initial fossil discoveries made by Japanese scientists vanished once World War II ended in 1945. By 1949, when administration of the area passed to the Chinese Communist Party and its leader Mao Zedong , the fossils of Yixian were studied only by Chinese scientists. It

234-460: The Jehol Biota , mainly based on changes in invertebrate diversity. In the Yixian, ostracods (seed shrimp) had diversified considerably, despite a very low diversity in the earlier Dabeigou Formation . Other major invertebrate groups in the Yixian include clam shrimp and insects . Insects, as a group, experienced their largest diversification of the entire Mesozoic era in the Yixian. On

260-599: The Late Jurassic continued to persist. Angiosperms (flowering plants) appeared for the first time during the Early Cretaceous; Archaefructaceae , one of the oldest fossil families (124.6 Ma) was found in the Yixian Formation , China. This time also saw the evolution of the first members of the Neornithes (modern birds). Sinodelphys , a 125 Ma-old boreosphenidan mammal found in

286-865: The Panthalassic Ocean the Pacific Plate continued to grow; the Arctic Alaska-Chukotka terrane formed the Bering Strait. Continued rifting opened new basins in the Indian Ocean, separating India, Antarctica, and Australia. By 110 Ma the Mid-Atlantic Ridge reached south into the Proto-Caribbean and South Atlantic, effectively separating South America from Africa, and continued rifting in

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312-647: The Prudhoe Bay Oil Field has been interpreted as being sourced from the Triassic Shublik Formation shale and carbonate, Lower Cretaceous highly radioactive zone shale, and Lower Jurassic Kingak Shale . [REDACTED] Geology portal [REDACTED] Palaeontology portal Yixian Formation The Yixian Formation ( simplified Chinese : 义县组 ; traditional Chinese : 義縣組 ; pinyin : Yìxiàn zǔ ; formerly transcribed as Yihsien Formation )

338-542: The Jehol group. The Yixian Formation (including the synonymous Jingangshan, Tuhulu, Jianchang, Lower Volcanic and Volcanic Rock formations) is followed stratigraphically by the slightly younger Jiufotang Formation and the Fuxin Formation . Chiappe et al. argued in 1999 that the oldest beds of the Yixian (those bearing a fauna dominated by confuciusornithid birds ) were best separated as a distinct formation, called

364-602: The South Pacific at c. 120 Ma, is by far the largest LIP in Earth's history. The Ontong Java Plateau today covers an area of 1,860,000 km . In the Indian Ocean another LIP began to form at c. 120 Ma, the Kerguelen Plateau – Broken Ridge , together covering 2,300,000 km . Another LIP on the Liaodong Peninsula , China, c.  131–117 Ma, lasted for 10 million years. It

390-510: The Yixian Formation, China, is one of the oldest mammal fossils found. The fossil location indicates early mammals began to diversify from Asia during the Early Cretaceous. Sinodelphys was more closely related to metatherians (marsupials) than eutherians (placentals) and had feet adapted for climbing trees. Steropodon is the oldest monotreme (egg-lying mammal) discovered. It lived in Gondwana (now Australia) at 105 Ma. Oil in

416-562: The Yixian. Five species of flowering plant were present (three of Archaefructus , one of Archaeamphora and one of Hyrcantha (formerly Sinocarpus ), as were a variety of horsetails that closely resembled modern species. It is possible that increasing animal and plant diversity were linked. The Yixian is characterized by extensive forests, dominated by trees such as ginkgoes , conifers , cycads , and seed fern trees. Ground cover plants included lycopods , horsetails, ferns , and primitive flowering plants, which were rare compared to

442-706: The banks of Newfoundland and to connect to the Canada Basin in the Arctic Ocean. With the opening of the Labrador Sea , Greenland became a separate tectonic plate and Laurentia became North America . The Proto-Caribbean Sea continued to grow and the Paraná-Etendeka LIP began to break Africa into three pieces. The Falkland Plateau broke off from southern Africa at 132 Ma and Madagascar ceased to move independently c. 120 Ma. In

468-590: The dominant species. The Yixian preserves the first Jehol dinosaurs and pterosaurs (which have not been found in the older Dabeigou Formation), and the first major radiation of birds (only one bird species is known from the Dabeigou). The Yixian also preserves the largest (and only) mammal radiation so far known from the Jehol group. Most vertebrates showed a tendency to climb trees or become arboreal , including many tree-dwelling birds, and climbing mammals and lizards. Plant life reached its Jehol biota peak in

494-630: The exact age of the Barremian–Aptian boundary ranged from 126 to 117 Ma until recently (as of 2019), but based on drillholes in Svalbard the defining early Aptian Oceanic Anoxic Event 1a (OAE1a) was carbon isotope dated to 123.1±0.3 Ma, limiting the possible range for the boundary to c. 122–121 Ma. There is a possible link between this anoxic event and a series of Early Cretaceous large igneous provinces (LIP). The Ontong Java - Manihiki - Hikurangi large igneous province, emplaced in

520-514: The fast diversification of life forms present in the Yixian ecosystem. With the diversity of plant life in the Yixian well known, including examples of a variety of petrified wood and growth rings, and with the help of chemical analysis, scientists have been able to determine the climate of the formation. The Yixian flora was dominated by conifers closely related to modern species that are found mainly in subtropical and temperate upland forests. The presence of ferns, cycads, and horsetails indicates

546-610: The northern end completed the longitudinal extent of the Atlantic. In Panthalassa the Ontong-Java Mega-LIP resulted in the formation of new tectonic plates and in the Indian Ocean the Kerguelen LIP began to push India northward. During this time many new types of dinosaur appeared or came into prominence, including ceratopsians , spinosaurids , carcharodontosaurids and coelurosaurs , while survivors from

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572-474: The oldest Yixian beds. The Yixian also overlies the Tuchengzi Formation in places. The Yixian Formation is informally divided into several subunits and the stratigraphy remains controversial so a conservative list is give here, from most recent to oldest: (ages when available from Zhong et al. , 2021 ) The Yixian Formation represents the second of three major faunal phases that characterize

598-437: The other hand, some invertebrate groups, such as bivalves and gastropods (snails and slugs), were numerous but low in diversity, being mainly represented by one or two dominant species ( Arguniella in the case of the bivalves). Studies of vertebrates have shown support for the division of the Jehol into phases, and the diversity of fish in the Yixian was distinct from older and younger formations, with Lycoptera as

624-412: The others. This plant life grew around a series of freshwater lakes , provided with abundant minerals thanks to periodic volcanic eruptions . Volcanic activity, along with periodic wildfires , and noxious gasses released from the lake bottoms caused the ecosystem to be continually destroyed and regrown. This, along with the wide diversity of habitats in the surrounding region, may have contributed to

650-497: Was not until the 1990s when remarkable fossils of birds and other non-avian dinosaurs were excavated. Since 1996, a number of dinosaur fossils that have revolutionized knowledge of these animals have been found at Yixian; among them are the first known non- avian theropods with feathers . For some time, the formation was believed to be from the Late Jurassic – Early Cretaceous boundary, some 145 mya (million years ago). Radiometric dating has since resolved it to be younger; it

676-801: Was the result of the subduction of the Kula and Pacific plates, which was probably caused by a superplume . During the opening of the South Atlantic the Paraná–Etendeka LIP produced 1.5 million km of basalts and rhyolites , beginning 133 Ma and lasting for a million years. The opening of the Central Atlantic continued as the Mid-Atlantic Ridge spread north to separate the Iberian Peninsula from

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