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41-476: The Campanian was an age when a worldwide sea level rise covered many coastal areas. The morphology of some of these areas has been preserved: it is an unconformity beneath a cover of marine sedimentary rocks . The Campanian was introduced in scientific literature by Henri Coquand in 1857. It is named after the French village of Champagne in the department of Charente-Maritime . The original type locality

82-405: A change from carbonates to shale only, or a transgression from sandstone to shale, and so on. Lateral changes in facies are also important; a well-marked transgression sequence in an area where an epeiric sea was deep may be only partial farther away, where the water was shallow. One should consider such factors when interpreting a specific sedimentary column. Bering land bridge Beringia

123-464: A land bridge from c.  30,000  – c.  11,000  YBP, followed by a Holocene sea-level rise that reopened the strait. Post-glacial rebound has continued to raise some sections of the coast. During the last glacial period , enough of the Earth's water became frozen in the great ice sheets covering North America and Europe to cause a drop in sea levels . For thousands of years

164-480: A rich diversity of grasses and herbs. There were patches of shrub tundra with isolated refugia of larch ( Larix ) and spruce ( Picea ) forests with birch ( Betula ) and alder ( Alnus ) trees. It has been proposed that the largest and most diverse megafaunal community residing in Beringia at this time could only have been sustained in a highly diverse and productive environment. Analysis at Chukotka on

205-574: Is 30% less than in the upper Campanian. Marine transgression A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling with water or decreasing in capacity. Transgressions and regressions may be caused by tectonic events such as orogenies , severe climate change such as ice ages or isostatic adjustments following removal of ice or sediment load. During

246-616: Is defined as the place in the stratigraphic column where the ammonite Pachydiscus neubergicus first appears. The Campanian can be subdivided into Lower, Middle and Upper Subages. In the western interior of the United States, the base of the Middle Campanian is defined as the first occurrence of the ammonite Baculites obtusus (80.97 Ma) and the base of the Upper Campanian defined as the first occurrence of

287-991: Is defined today as the land and maritime area bounded on the west by the Lena River in Russia ; on the east by the Mackenzie River in Canada ; on the north by 72° north latitude in the Chukchi Sea ; and on the south by the tip of the Kamchatka Peninsula . It includes the Chukchi Sea , the Bering Sea , the Bering Strait , the Chukchi and Kamchatka Peninsulas in Russia as well as Alaska in

328-709: The Anadyr River ), and Arctodus simus , American badger , American kiang -like equids, Bootherium and Camelops in North America, with the existence of Homotherium being disputed in Late Pleistocene Siberia. The lack of mastodon and Megalonyx has been attributed to their inhabitation of Alaska and the Yukon being limited to interglacials. However, ground sloth eDNA has potentially been recovered from Siberia. The peopling of

369-666: The Arctic Ocean . The opposite of transgression is regression in which the sea level falls relative to the land and exposes former sea bottom. During the Pleistocene Ice Age , so much water was removed from the oceans and stored on land as year-round glaciers that the ocean regressed 120 m, which exposed the Bering land bridge between Alaska and Asia. Sedimentary facies changes may indicate transgressions and regressions and are often easily identified because of

410-584: The Cretaceous , seafloor spreading created a relatively shallow Atlantic basin at the expense of a deeper Pacific basin. That reduced the world's ocean basin capacity and caused a rise in sea level worldwide. As a result of the sea level rise, the oceans transgressed completely across the central portion of North America and created the Western Interior Seaway from the Gulf of Mexico to

451-611: The Last Glacial Maximum , when ice sheets began advancing from 33,000   YBP and reached their maximum limits 26,500   YBP. Deglaciation commenced in the Northern Hemisphere approximately 19,000   YBP and in Antarctica approximately 14,500 years   YBP, which is consistent with evidence that glacial meltwater was the primary source for an abrupt rise in sea level 14,500   YBP and

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492-786: The United States and the Yukon in Canada . The area includes land lying on the North American Plate and Siberian land east of the Chersky Range . At various times, it formed a land bridge referred to as the Bering land bridge , that was up to 1,000 km (620 mi) wide at its greatest extent and which covered an area as large as British Columbia and Alberta together, totaling about 1.6 million km (620,000 sq mi), allowing biological dispersal to occur between Asia and North America. Today,

533-496: The "Campanian Explosion". However, it is not yet clear if the event is artificial, i.e. the low number of genera in the lower Campanian can be caused by a lower preservation chance for fossils in deposits of that age. The generally warm climates and large continental area covered in shallow sea during the Campanian probably favoured the dinosaurs. In the following Maastrichtian stage, the number of North American dinosaur genera found

574-790: The Americas began when Paleolithic hunter-gatherers ( Paleo-Indians ) entered North America from the North Asian Mammoth steppe via the Beringia land bridge , which had formed between northeastern Siberia and western Alaska due to the lowering of sea level during the Last Glacial Maximum (26,000 to 19,000 years ago). These populations expanded south of the Laurentide Ice Sheet and spread rapidly southward, occupying both North and South America by 12,000 to 14,000 years ago. The earliest populations in

615-634: The Americas sometime after 16,500 years Before Present (YBP). This would have occurred as the American glaciers blocking the way southward melted, but before the bridge was covered by the sea about 11,000 YBP. The term Beringia was coined by the Swedish botanist Eric Hultén in 1937, from the Danish-born Russian explorer Vitus Bering . During the ice ages, Beringia, like most of Siberia and all of North and Northeast China ,

656-491: The Americas, before roughly 10,000 years ago, are known as Paleo-Indians . Indigenous peoples of the Americas have been linked to Siberian populations by proposed linguistic factors , the distribution of blood types , and in genetic composition as reflected by molecular data, such as DNA . Around 3,000 years ago, the progenitors of the Yupik peoples settled along both sides of the straits. The governments of Russia and

697-494: The Last Glacial Maximum. This was followed by a single population of modern wolves expanding out of their Beringia refuge to repopulate the wolf's former range, replacing the remaining Late Pleistocene wolf populations across Eurasia and North America. The extinct pine species Pinus matthewsii has been described from Pliocene sediments in the Yukon areas of the refugium. The existence of fauna endemic to

738-523: The Siberian edge of the land bridge indicated that from c.  57,000  – c.  15,000  YBP (MIS 3 to MIS 2) the environment was wetter and colder than the steppe–tundra to the east and west, with warming in parts of Beringia from c.  15,000  YBP. These changes provided the most likely explanation for mammal migrations after c.  15,000  YBP, as the warming provided increased forage for browsers and mixed feeders. At

779-818: The United States announced a plan to formally establish "a transboundary area of shared Beringian heritage". Among other things this agreement would establish close ties between the Bering Land Bridge National Preserve and the Cape Krusenstern National Monument in the United States and Beringia National Park in Russia. Biogeographical evidence demonstrates previous connections between North America and Asia. Similar dinosaur fossils occur both in Asia and in North America . The dinosaur Saurolophus

820-610: The Yukon where it was blocked by the Wisconsin glaciation . Therefore, the flora and fauna of Beringia were more related to those of Eurasia rather than North America. Beringia received more moisture and intermittent maritime cloud cover from the north Pacific Ocean than the rest of the Mammoth steppe, including the dry environments on either side of it. This moisture supported a shrub-tundra habitat that provided an ecological refugium for plants and animals. In East Beringia 35,000 YBP,

861-596: The Yukon. In the driest and coldest periods of the Late Pleistocene, and possibly during the entire Pleistocene, moisture occurred along a north–south gradient with the south receiving the most cloud cover and moisture due to the air-flow from the North Pacific. In the Late Pleistocene, Beringia was a mosaic of biological communities. Commencing from c.  57,000  YBP ( MIS 3), steppe–tundra vegetation dominated large parts of Beringia with

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902-478: The ammonite Didymoceras nebrascense (76.27 Ma). In the Tethys domain , the Campanian encompasses six ammonite biozones . They are, from young to old: During the Campanian age, a radiation among dinosaur species occurred. In North America, for example, the number of known dinosaur genera rises from four at the base of the Campanian to forty-eight in the upper part. This development is sometimes referred to as

943-666: The beginning of the Holocene , some mesic habitat -adapted species left the refugium and spread westward into what had become tundra-vegetated northern Asia and eastward into northern North America. The latest emergence of the land bridge was c.  70,000 years ago. However, from c.  24,000  – c.  13,000  YBP the Laurentide Ice Sheet fused with the Cordilleran Ice Sheet , which blocked gene flow between Beringia (and Eurasia) and continental North America. The Yukon corridor opened between

984-520: The bridge was finally inundated around 11,000 YBP. The fossil evidence from many continents points to the extinction of large animals, termed Pleistocene megafauna , near the end of the last glaciation. During the Ice Age a vast, cold and dry Mammoth steppe stretched from the arctic islands southwards to China, and from Spain eastwards across Eurasia and over the Bering land bridge into Alaska and

1025-421: The climate was warmer and wetter. The environmental conditions were not homogenous in Beringia. Recent stable isotope studies of woolly mammoth bone collagen demonstrate that western Beringia ( Siberia ) was colder and drier than eastern Beringia ( Alaska and Yukon ), which was more ecologically diverse. Grey wolves suffered a species-wide population bottleneck (reduction) approximately 25,000 YBP during

1066-614: The dry beds of the English Channel and North Sea , and the dry bed of the South China Sea linked Sumatra , Java , and Borneo to Indochina . The last glacial period , commonly referred to as the "Ice Age", spanned 125,000 –14,500   YBP and was the most recent glacial period within the current ice age , which occurred during the last years of the Pleistocene era. The Ice Age reached its peak during

1107-594: The globe. Today, the average water depth of the Bering Strait is 40–50 m (130–160 ft); therefore the land bridge opened when the sea level dropped more than 50 m (160 ft) below the current level. A reconstruction of the sea-level history of the region indicated that a seaway existed from c.  135,000  – c.  70,000  YBP, a land bridge from c.  70,000  – c.  60,000  YBP, an intermittent connection from c.  60,000  – c.  30,000  YBP,

1148-574: The ice mass balance, leading to global sea-level fluctuations were viewed as the cause of the Bering land bridge. In 1937, Eric Hultén proposed that around the Aleutians and the Bering Strait region were tundra plants that had originally dispersed from a now-submerged plain between Alaska and Chukotka, which he named Beringia after Vitus Bering who had sailed into the strait in 1728. The American arctic geologist David Hopkins redefined Beringia to include portions of Alaska and Northeast Asia. Beringia

1189-536: The northern arctic areas experienced temperatures 1.5 °C (2.7 °F) degrees warmer than today but the southern sub-Arctic regions were 2 °C (4 °F) degrees cooler. During the LGM 22,000 YBP the average summer temperature was 3–5 °C (5–9 °F) degrees cooler than today, with variations of 2.9 °C (5.2 °F) degrees cooler on the Seward Peninsula to 7.5 °C (13.5 °F) cooler in

1230-416: The oldest to the youngest rocks. A regression will feature the opposite pattern, with offshore facies changing to nearshore ones. The strata represent regressions less clearly, as their upper layers are often marked by an erosional unconformity . These are both idealized scenarios; in practice identifying transgression or regressions can be more complicated. For instance, a regression may be indicated by

1271-539: The only land that is visible from the central part of the Bering land bridge are the Diomede Islands , the Pribilof Islands of St. Paul and St. George, St. Lawrence Island , St. Matthew Island , and King Island . It is believed that a small human population of at most a few thousand arrived in Beringia from eastern Siberia during the Last Glacial Maximum before expanding into the settlement of

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1312-686: The origin of these wolves in eastern Beringia during the Middle Pleistocene . Fossil evidence also indicates an exchange of primates and plants between North America and Asia around 55.8 million years ago. 20 million years ago, evidence in North America shows the last natural interchange of mammalian species. Some, like the ancient saber-toothed cats , have a recurring geographical range: Europe, Africa, Asia, and North America. The pattern of bidirectional flow of biota has been asymmetric, with more plants, animals, and fungi generally migrating from Asia to North America than vice versa throughout

1353-468: The receding ice sheets c.  13,000  YBP, and this once again allowed gene flow between Eurasia and continental North America until the land bridge was finally closed by rising sea levels c.  10,000  YBP. During the Holocene, many mesic-adapted species left the refugium and spread eastward and westward, while at the same time the forest-adapted species spread with the forests up from

1394-495: The respective Siberian and North American portions of Beringia has led to the 'Beringian Gap' hypothesis, wherein an unconfirmed geographic factor blocked migration across the land bridge when it emerged. Beringia did not block the movement of most dry steppe-adapted large species such as saiga antelope, woolly mammoth, and caballid horses. Notable restricted fauna include the woolly rhino in Siberia (which went no further east than

1435-479: The sea floors of many interglacial shallow seas were exposed, including those of the Bering Strait , the Chukchi Sea to the north, and the Bering Sea to the south. Other land bridges around the world have emerged and disappeared in the same way. Around 14,000 years ago, mainland Australia was linked to both New Guinea and Tasmania , the British Isles became an extension of continental Europe via

1476-607: The south. The arid-adapted species were reduced to minor habitats or became extinct. Beringia constantly transformed its ecosystem as the changing climate affected the environment, determining which plants and animals were able to survive. The land mass could be a barrier as well as a bridge: during colder periods, glaciers advanced and precipitation levels dropped. During warmer intervals, clouds, rain and snow altered soils and drainage patterns. Fossil remains show that spruce , birch and poplar once grew beyond their northernmost range today, indicating that there were periods when

1517-484: The unique conditions required to deposit each type of sediment . For instance, coarse-grained clastics like sand are usually deposited in nearshore, high-energy environments; fine-grained sediments however, such as silt and carbonate muds, are deposited farther offshore, in deeper, lower energy waters. Thus, a transgression reveals itself in the sedimentary column when there is a change from nearshore facies (such as sandstone ) to offshore ones (such as marl ), from

1558-590: Was a series of outcrops near the village of Aubeterre-sur-Dronne in the same region. The base of the Campanian Stage is defined as a place in the stratigraphic column where the extinction of crinoid species Marsupites testudinarius is located. A GSSP was ratified for the base of the Campanian in October 2022, having been placed in Bottaccione, Gubbio , Italy . The top of the Campanian stage

1599-512: Was found in both Mongolia and western North America. Relatives of Troodon , Triceratops , and Tyrannosaurus rex all came from Asia. The earliest Canis lupus specimen was a fossil tooth discovered at Old Crow, Yukon , Canada. The specimen was found in sediment dated 1 million YBP, however the geological attribution of this sediment is questioned. Slightly younger specimens were discovered at Cripple Creek Sump, Fairbanks , Alaska, in strata dated 810,000 YBP. Both discoveries point to

1640-586: Was later regarded as extending from the Verkhoyansk Mountains in the west to the Mackenzie River in the east. The distribution of plants in the genera Erythranthe and Pinus are good examples of this, as very similar genera members are found in Asia and the Americas. During the Pleistocene epoch, global cooling led periodically to the expansion of glaciers and the lowering of sea levels. This created land connections in various regions around

1681-461: Was not glaciated because snowfall was very light . The remains of Late Pleistocene mammals that had been discovered on the Aleutians and islands in the Bering Sea at the close of the nineteenth century indicated that a past land connection might lie beneath the shallow waters between Alaska and Chukotka . The underlying mechanism was first thought to be tectonics, but by 1930 changes in

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