The Early Cretaceous ( geochronological name) or the Lower Cretaceous ( chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous . It is usually considered to stretch from 145 Ma to 100.5 Ma.
21-648: The Blairmore Group , originally named the Blairmore Formation , is a geologic unit of Early Cretaceous age in the Western Canada Sedimentary Basin that is present in southwestern Alberta and southeastern British Columbia . It is subdivided into four formations : Cadomin Formation , Gladstone , Beaver Mines and Ma Butte , all of which are defined by type sections, most of which contain plant fossils . In some areas
42-749: A clear west to east thinning. In the northwest, thicknesses of 400 to 600 m (1312 to 1968 ft) are common in the foothills. The Blairmore Group unconformably overlies the Kootenay Group and is gradationally overlain by the Crowsnest Formation or, where the Crowsnest Formation is absent, is disconformably overlain by the Alberta Group . It is equivalent to the Luscar Group north of the Clearwater River and to
63-592: A small portion. The marine mudstone Moosebar Member of the Malcolm Creek Formation , which is restricted to the region north of Waiparous Creek (51°20'N), is overlain by the notable sandstone-dominated Torrens Member and the coal-bearing Grande Cache Member . Mudstone to very fine-grained sandstone, as well as layers of conglomerate and coarser sandstone, make up the Ma Butte Formation. The Beaver Mines and Ma Butte formations in
84-651: 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 was the result of the subduction of
105-405: Is normally a very durable, siliceous pebble conglomerate. A sequence of interbedded, highly variable-proportioned grey mudstone to sandstone layers makes up the bottom portion of the underlying Gladstone Formation. Sandstones, whose grain size rarely exceeds fine, frequently show a noticeable upward decline in grain size. Dark grey, argillaceous limestone and fossiliferous calcareous shale make up
126-660: 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
147-811: 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 the banks of Newfoundland and to connect to
168-666: 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
189-778: The Mannville Group in the plains to the east. In northwestern Montana the Cut Bank Sandstone correlates with the Cadomin Formation; the lower Kootenai Formation, including the Draney Limestone with the Beaver Mines Formation; and the lower Blackleaf Formation with the Ma Butte Formation. The Blairmore Group is a westward-thickening clastic wedge of clastic sediments derived from the erosion of newly uplifted mountains to
210-534: The Mountain Park Formation , where greenish grey predominates in more southerly areas and is increasingly prominent higher, grey prevails to the north. In the Smoky River region, the uppermost part of the formation, the proportion of the section with a conspicuously greenish tint is restricted to a subtle shade of greenish-grey as it declines northward. The Blairmore Group is subdivided into
231-804: 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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#1732783735658252-675: 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 Clearwater River (Alberta) Too Many Requests If you report this error to the Wikimedia System Administrators, please include
273-554: The Blairmore contains significant reservoirs of natural gas. The Blairmore group includes the conglomerate and quartzose sandstones of the Cadomin Formation at the base, and grades to sandstone, siltstone , mudstone , and limestone in the overlying formations. The Cadomin Formation has beds of quartzose sandstone and, in some sections, especially in the eastern foothills, is totally quartzose sandstone. It
294-659: The Clearwater River, which were originally assigned to the Blairmore Group, differ in that they contain major coal deposits and they have therefore been reassigned to the Luscar Group . The Blairmore Group has a maximum thickness of about 2,000 m (6,560 ft). The Ma Butte portion has a thickness of 635 m (2,080 ft) The Fernie Basin's maximum reported thickness is estimated to be 2,000 m (6,560 ft). The easternmost foothills have reported thicknesses of roughly 300 m (980 ft), indicating
315-577: 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
336-471: 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 the South Pacific at c. 120 Ma,
357-647: The following formations from top to base: Some early workers included the Crowsnest Formation , which overlies the Ma Butte Formation, at the top of the Blairmore Group, but that practice has been abandoned. The name Blairmore Group is applicable in the foothills and mountains of southwestern Alberta and southeastern British Columbia, from the Canada–United States border northward to the Clearwater River . The equivalent strata north of
378-610: 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
399-412: The top Gladstone Formation. Limestone deposits are few or nonexistent north of the Clearwater River (52°N). Both the Beaver Mines Formation in the south and the Mountain Park Formation in the north are made up of interbedded mudstone to very fine-grained sandstone with minor but noticeable thicker and coarser sandstone units that have abrupt bases and fining upward grain size. Conglomerate beds make up
420-470: The upper part of the group also include minor beds of bentonite and tuff . In the type area, tuffaceous mudstones are widespread in the top portion of the formation, but they vanish to the northwest along the foothills. North of the Clearwater River, the structure is completely missing. Various shades of red and green, frequently speckled south of the Bow River , are particularly prevalent. Except in
441-711: The west. The sediments were transported eastward by river systems and deposited in a variety of braided stream , river channel , floodplain , and coastal plain environments along the western edge of the Western Interior Seaway . Its formations include a variety of plant fossils, trace fossils , bivalves , and microfossils . Early Cretaceous Proposals for 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
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