Laramidia was an island continent that existed during the Late Cretaceous period (99.6–66 Ma ), when the Western Interior Seaway split the continent of North America in two. In the Mesozoic era, Laramidia was an island land mass separated from Appalachia to the east by the Western Interior Seaway. The seaway eventually shrank, split across the Dakotas , and retreated toward the Gulf of Mexico and the Hudson Bay . The masses joined, forming the continent of North America.
27-543: Laramidia is named after the Laramide orogeny . The name was coined by J. David Archibald in 1996. Laramidia stretched from modern-day Alaska to Mexico . The area is rich in dinosaur fossils. Tyrannosaurs , dromaeosaurids , troodontids , hadrosaurs , ceratopsians (including Kosmoceratops and Utahceratops ), pachycephalosaurs , and titanosaur sauropods are some of the dinosaur groups that lived on this landmass. A strong latitudinal climatic gradient existed on
54-429: A more steeply rising cone (33°-40°), because of the higher viscosity of the emitted material, and eruptions are more violent and less frequent than for shield volcanoes. Examples include Vesuvius , Kilimanjaro , Mount Fuji , Mount Shasta , Mount Hood and Mount Rainier . When plates collide or undergo subduction (that is, ride one over another), the plates tend to buckle and fold , forming mountains. Most of
81-588: A pattern of compressive uplifts and basins, with most of the deformation confined to block edges. Twelve kilometers of structural relief between basins and adjacent uplifts is not uncommon. The basins contain several thousand meters of Paleozoic and Mesozoic sedimentary rocks that predate the Laramide orogeny. As much as 5,000 meters (16,000 ft) of Cretaceous and Cenozoic sediments filled these orogenically-defined basins. Deformed Paleocene and Eocene deposits record continuing orogenic activity. During
108-475: A plate to split apart, it does so such that a center block drops down relative to its flanking blocks. An example is the Sierra Nevada range, where delamination created a block 650 km long and 80 km wide that consists of many individual portions tipped gently west, with east facing slips rising abruptly to produce the highest mountain front in the continental United States. Another example
135-457: Is caused by horizontal compression acting on a thin to thick crust transition zone (as are all passive margins). Hotspots are supplied by a magma source in the Earth's mantle called a mantle plume . Although originally attributed to a melting of subducted oceanic crust, recent evidence belies this connection. The mechanism for plume formation remains a research topic. Several movements of
162-591: Is the Rila – Rhodope massif in Bulgaria , including the well defined horsts of Belasitsa (linear horst), Rila mountain (vaulted domed shaped horst) and Pirin mountain —a horst forming a massive anticline situated between the complex graben valleys of the Struma and Mesta rivers. Unlike orogenic mountains there is no widely accepted geophysical model that explains elevated passive continental margins such as
189-461: The Bighorn , Powder River , and Wind River being the largest. Topographically, the basin floors resemble the surface of the western Great Plains, except for vistas of surrounding mountains. At most boundaries, Paleozoic through Paleogene units dip steeply into the basins off uplifted blocks cored by Precambrian rocks. The eroded steeply dipping units form hogbacks and flatirons . Many of
216-503: The Earth's crust ( tectonic plates ). Folding , faulting , volcanic activity , igneous intrusion and metamorphism can all be parts of the orogenic process of mountain building. The formation of mountains is not necessarily related to the geological structures found on it. From the late 18th century until its replacement by plate tectonics in the 1960s, geosyncline theory was used to explain much mountain-building. The understanding of specific landscape features in terms of
243-528: The North American Plate . Most hypotheses propose that oceanic crust was undergoing flat-slab subduction , that is, subduction at a shallow angle. As a consequence, no magmatism occurred in the central west of the continent, and the underlying oceanic lithosphere actually caused drag on the root of the overlying continental lithosphere. One cause for shallow subduction may have been an increased rate of plate convergence. Another proposed cause
270-611: The Scandinavian Mountains , eastern Greenland , the Brazilian Highlands , or Australia's Great Dividing Range . Different elevated passive continental margins most likely share the same mechanism of uplift. This mechanism is possibly related to far-field stresses in Earth's lithosphere . According to this view elevated passive margins can be likened to giant anticlinal lithospheric folds, where folding
297-601: The Laramide orogeny, basin floors and mountain summits were much closer to sea level than today. After the seas retreated from the Rocky Mountain region, floodplains , swamps , and vast lakes developed in the basins. Drainage systems imposed at that time persist today. Since the Oligocene , episodic epeirogenic uplift gradually raised the entire region, including the Great Plains, to present elevations. Most of
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#1732765723202324-603: The Pacific band in the Indonesian Archipelago. The most important types of volcanic mountain are composite cones or stratovolcanoes and shield volcanoes . A shield volcano has a gently sloping cone because of the low viscosity of the emitted material, primarily basalt . Mauna Loa is the classic example, with a slope of 4°-6°. (The relation between slope and viscosity falls under the topic of angle of repose . ) A composite volcano or stratovolcano has
351-610: The boundaries are thrust or reverse faults . Although other boundaries appear to be monoclinal flexures , faulting is suspected at depth. Most bounding faults show evidence of at least two episodes of Laramide ( Late Cretaceous and Eocene ) movement, suggesting both thrust and strike-slip types of displacement. According to paleontologist Thomas M. Lehman, the Laramide orogeny triggered "the most dramatic event that affected Late Cretaceous dinosaur communities in North America prior to their extinction." This turnover event saw
378-662: The drag that it caused was a broad belt of mountains, some of which were the progenitors of the Rocky Mountains . Part of the proto-Rocky Mountains would be later modified by extension to become the Basin and Range Province . The Laramide orogeny produced intermontane structural basins and adjacent mountain blocks by means of deformation. This style of deformation is typical of continental plates adjacent to convergent margins of long duration that have not sustained continent/continent collisions. This tectonic setting produces
405-660: The easternmost extent of the mountain-building represented by the Black Hills of South Dakota . The phenomenon is named for the Laramie Mountains of eastern Wyoming . The Laramide orogeny is sometimes confused with the Sevier orogeny , which partially overlapped in time and space. The orogeny is commonly attributed to events off the west coast of North America, where the Kula and Farallon Plates were sliding under
432-553: The former Appalachian continent. In western North America, during the Cretaceous, the dominant theropods were the tyrannosaurs , huge predatory dinosaurs with proportionately large heads built for tearing flesh from their prey. In Laramidia, there were the theropods of Tyrannosaurinae such as Tyrannosaurus rex , Nanuqsaurus hoglundi , Daspletosaurus , Teratophoneus , and theropods of Albertosaurinae such as Albertosaurus and Gorgosaurus , all being included under
459-751: The giant club tail of their western relatives . They were scarce in Laramidia by the late Cretaceous, existing only in specialized forms like Edmontonia and Panoplosaurus while nodosaurs were thriving in Appalachia. [REDACTED] Africa [REDACTED] Antarctica [REDACTED] Asia [REDACTED] Australia [REDACTED] Europe [REDACTED] North America [REDACTED] South America [REDACTED] Afro-Eurasia [REDACTED] Americas [REDACTED] Eurasia [REDACTED] Oceania Laramide orogeny The Laramide orogeny
486-644: The landmass in the final 15 million years of the Cretaceous, helping drive regional provincialism of dinosaur faunas. Vertebrate fossils have been found in the region from Alaska to Coahuila . From the Turonian age of the Late Cretaceous to the very beginning of the Paleocene , Laramidia was separated from Appalachia to the east. As a result, the fauna evolved differently on each land mass over that time. Geological conditions were generally favorable for
513-599: The major continental mountain ranges are associated with thrusting and folding or orogenesis . Examples are the Balkan Mountains , the Jura and the Zagros mountains. When a fault block is raised or tilted, a block mountain can result. Higher blocks are called horsts , and troughs are called grabens . A spreading apart of the surface causes tensional forces. When the tensional forces are strong enough to cause
540-555: The modern topography is the result of Pliocene and Pleistocene events, including additional uplift, glaciation of the high country, and denudation and dissection of older Cenozoic surfaces in the basin by fluvial processes. In the United States, these distinctive intermontane basins occur principally in the central Rocky Mountains from Colorado and Utah ( Uinta Basin ) to Montana and are best developed in Wyoming , with
567-586: The plate boundaries, which erupt and form mountains. A volcanic arc system is a series of volcanoes that form near a subduction zone where the crust of a sinking oceanic plate melts and drags water down with the subducting crust. Most volcanoes occur in a band encircling the Pacific Ocean (the Pacific Ring of Fire ), and in another that extends from the Mediterranean across Asia to join
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#1732765723202594-480: The preservation of fossils in Laramidia, making the western United States one of the most productive fossil regions in the world. Less is known about Appalachian biodiversity in the Cretaceous as few fossiliferous deposits exist in the region today and half of the fossil beds in Appalachia were destroyed during the Pleistocene ice age . However, fossil beds which haven't been discovered yet could exist in areas of
621-433: The replacement of specialized and highly ornamented centrosaurine and lambeosaurines by more basal upland dinosaurs in the south, while northern biomes became dominated by Triceratops with a greatly reduced hadrosaur community. Mountain building Mountain formation refers to the geological processes that underlie the formation of mountains . These processes are associated with large-scale movements of
648-563: The same family of Tyrannosauridae , although not all are contemporary. Another common group of North American dinosaurs were the hadrosaurs , the so-called "duck-billed" dinosaurs. The fossil record shows a staggering variety of hadrosaur forms in Laramidia. Other differences in genera appear between the island land masses. Sauropods roamed Laramidia during the Cretaceous after apparently dying out in Appalachia. Nodosaurs , though, appear to have been more plentiful in Appalachia. Nodosaurs were large, herbivorous armored dinosaurs which lacked
675-429: The underlying tectonic processes is called tectonic geomorphology , and the study of geologically young or ongoing processes is called neotectonics . There are five main types of mountains: volcanic , fold , plateau , fault-block , and dome . A more detailed classification useful on a local scale predates plate tectonics and adds to these categories. Movements of tectonic plates create volcanoes along
702-582: Was a time period of mountain building in western North America , which started in the Late Cretaceous , 80 to 70 million years ago, and ended 55 to 35 million years ago. The exact duration and ages of beginning and end of the orogeny are in dispute. The Laramide orogeny occurred in a series of pulses, with quiescent phases intervening. The major feature that was created by this orogeny was deep-seated, thick-skinned deformation , with evidence of this orogeny found from Canada to northern Mexico , with
729-644: Was subduction of thickened oceanic crust. Magmatism associated with subduction occurred not near the plate edges (as in the volcanic arc of the Andes , for example), but far to the east, along the Colorado Mineral Belt . Geologists call such a lack of volcanic activity near a subduction zone a magmatic gap . This particular gap may have occurred because the subducted slab was in contact with relatively cool continental lithosphere, not hotter asthenosphere . One result of shallow angle of subduction and
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