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34-786: The Straight Cliffs Formation was deposited in a marginal marine basin system along the western edge of the Cretaceous Western Interior Seaway . It is bounded below by the Tropic Shale and above by the Wahweap Formation . A variety of fossil species have been found within the Straight Cliffs including ammonites , mollusks , foraminifera , ostracods , sharks , fish , amphibians , turtles , lizards , crocodyliforms , dinosaurs , and mammals . The Straight Cliffs Formation overlies

68-909: A margin of land temporarily rose above the water along the ancestral Transcontinental Arch , each time rejoining the separated, divergent land populations, allowing a temporary mixing of newer species before again separating the populations. At its largest, the Western Interior Seaway stretched from the Rockies east to the Appalachian Mountains , some 1,000 km (620 mi) wide. At its deepest, it may have been only 800 or 900 metres (2,600 or 3,000 ft) deep, shallow in terms of seas. Two great continental watersheds drained into it from east and west, diluting its waters and bringing resources in eroded silt that formed shifting delta systems along its low-lying coasts. There

102-466: Is Monument Rocks , an exposed chalk formation towering 70 feet (21 m) over the surrounding range land. The Western Interior Seaway is believed to have behaved similarly to a giant estuary in terms of water mass transport. Riverine inputs exited the seaway as coastal jets, while correspondingly drawing in water from the Tethys in the south and Boreal waters from the north. During the late Cretaceous,

136-610: Is 24 – 331 feet thick and increases in thickness in the northern corner of the plateau. The top of the formation is distinguished by the Calico Bed, a braided fluvial unit, named for its white and orange coloring. The Calico Bed is a useful marker bed as it is present across the Kaiparowits Plateau and is easily distinguished in outcrop. The Smoky Hollow was deposited in non-marine environments, including lagoonal, coastal plain, and fluvial settings. The John Henry Member

170-487: Is latest Turonian to early Campanian in age. The stratigraphy of the formation was initially studied for its coal resources and has more recently been studied as an analog for petroleum reservoirs . Consequently, the stratigraphy of the Straight Cliffs has been analyzed in detail. The Straight Cliffs Formation was deposited in the Kaiparowits Basin of the Western Interior Seaway. The basin received sediment from

204-535: Is mainly composed of yellow to brown medium-grained cross stratified sandstone. The Straight Cliffs Formation was deposited in a variety of sub- environments that varied through time as the relative sea level of the Western Interior Seaway changed. The most basal member, the Tibbet Canyon, was deposited on the edge of the Greenhorn Seaway. The Tibbet Canyon preserves the shoreface sands deposited as

238-768: Is primarily fluvial and consequently only water worn fragments of turtle and crocodyliforms have been recovered. Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway , the Niobraran Sea , the North American Inland Sea , the Western Interior Sea and sometimes nicknamed "Hell's Aquarium" ) was a large inland sea that split the continent of North America into two landmasses for 34 million years. The ancient sea, which existed from

272-421: Is the thickest of the four members of the Straight Cliffs. It contains strata that ranges from fluvial to marine. The lithologies seen include gray shales, siltstones, sandstones, carbonaceous shales, occasional coals and shell has beds. It ranges in thickness from 200 – 500 meters. The A – F sandstone intervals have been studied in detail on the eastern margin of the plateau and can be correlated to fluvial units in

306-505: Is well exposed in the southwestern and central parts of the Kaiparowits Plateau. The type locality of the Tibbet Canyon Member is near the mouth of Tibbet Canyon. It is about 70–185 ft thick and composed of yellow and gray very fine to medium sandstone. The base of the unit is transitional into the underlying Tropic Shale, and the top of the member is marked by the contact with overlying mudstones and carbonaceous shales of

340-750: The Arctic Ocean transgressed south over western North America; this formed the Mowry Sea, so named for the Mowry Shale , an organic-rich rock formation . In the south, the Gulf of Mexico was originally an extension of the Tethys Ocean . In time, the southern embayment merged with the Mowry Sea in the late Cretaceous, forming a completed seaway, creating isolated environments for land animals and plants. Relative sea levels fell multiple times , as

374-559: The Prionocyclus hyatti ammonite zone. A variety of invertebrate fossils have been found in the John Henry Member including the ammonite Baculites codyensis and the bivalve Endocostea baltica . Analysis of foraminifera and ostracods has helped refine depositional environment interpretations for a variety of shallow marine sub-environments such as lagoons, bays, and estuaries Vertebrate fossils have been found throughout

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408-809: The Calico Bed from the underlying shales and the Drip Tank Member from the top of the John Henry Member. In addition they describe two minor sequence boundaries, one within the Tibbet Canyon Member while the other above the A-sandstone within the John Henry Member. Work done by Allen and Johnson (2010a, b, 2011) in the Rogers Canyon area reassessed some of the interpretations made by Shanley and McCabe (1991) and found multiple retrogradationally stacked parasequences creating overall transgressive-regressive cycles. The Tibbet Canyon Member consists of shallow- marine, shoreface, and estuarine deposits. It

442-791: The Cenomanian-Turonian Tropic Shale Formation and underlies the Campanian Wahweap Formation. It preserves fluvial and marginal marine strata from the Kaiparowits Basin of the Cretaceous Western Interior Seaway. The formation is primarily composed of sandstone and has lesser amounts of siltstones , mudstones , coals , and conglomerates . It is the partial lateral equivalent of the Mancos Shale formation further east. The Straight Cliffs Formation

476-713: The Dakotas and retreated south towards the Gulf of Mexico . This shrunken and final regressive phase is sometimes called the Pierre Seaway . During the early Paleocene , parts of the Western Interior Seaway still occupied areas of the Mississippi Embayment , submerging the site of present-day Memphis . Later transgression, however, was associated with the Cenozoic Tejas sequence , rather than with

510-413: The John Henry Member preserves ancient river systems which were carrying sediment into the basin from the uplifting Mogollon highlands and Sevier fold – thrust belt. On the eastern side of the Kaiparowits Plateau the John Henry Member preserves interfingered marine and coastal deposits. Careful analysis of the stacking patterns within these beds suggests that the seaway was receding during the bottom third of

544-421: The John Henry Member. Sea level was rising and flooding the land during the middle portion of John Henry Member deposition. Finally, the sea level fell again during the final phase of deposition. A sequence boundary separates the Drip Tank Member from the underlying John Henry Member. This means that the strata of the uppermost John Henry Member were subaerially exposed and eroded before Drip Tank deposition. After

578-866: The Mogollon highlands, the Sevier fold-thrust and the Cordilleran volcanic arc. The Mogollon highlands were mountains in central Arizona. The Sevier fold-thrust belt was a mountain range forming to the west of the Kaiparowits while the Cordilleran volcanic arc was further west in California. Although the Straight Cliffs Fm was deposited in an ancient basin it is preserved in a modern physiographic plateau. The Kaiparowits Plateau covers 3,600 km2 and preserves strata located roughly 120 km east of

612-557: The Smoky Hollow Member. The member is interpreted as beach and shallow marine deposits. As a whole, it is regressive and represents the withdrawal of the Tropic Sea. The Smoky Hollow Member ranges from coal-bearing coastal plain strata to braided river strata. It is moderately well exposed along the southern margin of the plateau; however, it is often covered along the eastern Straight Cliffs escarpment. The Smoky Hollow

646-557: The Straight Cliffs Formation and are often preserved in large shell hash beds in marginal marine parts of the section. Only the Tibbet Canyon and John Henry members are known to contain marine invertebrate fauna because the Smoky Hollow and Drip Tank Member were deposited in terrestrial settings. The Tibbet Canyon Member was initially dated based a middle Turonian index fossil Inoceramus howelli which indicates

680-698: The Straight Cliffs Formation. The fossils from the Straight Cliffs Formation document a diverse assemblage of therian mammals. The Tibbet Canyon Member contains sharks’ teeth from marine deposits rare mammal fossils from deltaic deposits. Recovered fossils include sharks, rays, lepisosteid fishes, crocodyliforms, and fragmentary marsupial mammal teeth. The Smoky Hollow Member also contains a variety of sharks, amphibians, reptiles, snakes, crocodyliforms, and dinosaurs. The member also contains multituberculate and marsupial mammals. The John Henry Member contains more brackish and marine fauna, as well as mammals and other terrestrial species which are less common. The Drip Tank Member

714-587: The Western Interior Seaway went through multiple periods of anoxia , when the bottom water was devoid of oxygen and the water column was stratified. At the end of the Cretaceous, continued Laramide uplift hoisted the sandbanks (sandstone) and muddy brackish lagoons (shale), thick sequences of silt and sandstone still seen today as the Laramie Formation , while low-lying basins between them gradually subsided. The Western Interior Seaway divided across

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748-478: The early Late Cretaceous (100 Ma ) to the earliest Paleocene (66 Ma), connected the Gulf of Mexico to the Arctic Ocean . The two land masses it created were Laramidia to the west and Appalachia to the east. At its largest extent, it was 2,500 feet (760 m) deep, 600 miles (970 km) wide and over 2,000 miles (3,200 km) long. By the late Cretaceous, Eurasia and the Americas had separated along

782-412: The flightless Hesperornis that had stout legs for swimming through water and tiny wings used for marine steering rather than flight; and the tern-like Ichthyornis , an early avian with a toothy beak. Ichthyornis shared the sky with large pterosaurs such as Nyctosaurus and Pteranodon . Pteranodon fossils are very common; it was probably a major participant in the surface ecosystem, though it

816-402: The leading edge of the thrust front at the time of deposition. First analyzed for its coal content, the Straight Cliffs Formation was assessed by Gregory and Moore (1931) and later by Peterson (1969a, 1969b) and Vaninetti (1979). The formation has four members in ascending order, the Tibbet Canyon Member, the Smoky Hollow Member, the John Henry Member and the Drip Tank Member. The lithostratigraphy

850-399: The massive 4-to-5-metre (13 to 16 ft) long Xiphactinus , larger than any modern bony fish . Other sea life included invertebrates such as mollusks , ammonites , squid-like belemnites , and plankton including coccolithophores that secreted the chalky platelets that give the Cretaceous its name, foraminiferans and radiolarians . The seaway was home to early birds, including

884-416: The period of erosion river systems swept over the Kaiparowits Plateau and deposited the braided fluvial sheet deposits sands of the Drip Tank Member. The most diverse and abundant fossils found in the Straight Cliffs Formation are invertebrate fauna. The fauna observed include oysters, ammonites, inoceramids, bivalves, ostracods and foraminifera. Oysters are one of the most common invertebrate fossils found in

918-484: The previous event responsible for the seaway. The Western Interior Seaway was a shallow sea, filled with abundant marine life. Interior seaway denizens included predatory marine reptiles such as plesiosaurs , and mosasaurs . Other marine life included sharks such as Squalicorax , Cretoxyrhina , and the giant shellfish-eating Ptychodus mortoni (believed to be 10 metres (33 ft) long); and advanced bony fish including Pachyrhizodus , Enchodus , and

952-403: The seaway. Many species can easily fit in the palm of the hand, while some like Inoceramus (Haploscapha) grandis could be well over a meter in diameter. Entire schools of fish sometimes sought shelter within the shell of the giant Platyceramus . The shells of the genus are known for being composed of prismatic calcitic crystals that grew perpendicular to the surface, and fossils often retain

986-409: The shoreline built out into the basin and the seaway retreated. The Smoky Hollow Member preserves fluvial and lagoonal deposits. It was deposited at a time when sea level was relatively low and the shoreline was east of the Kaiparowits Plateau. The John Henry Member records fluctuations in the sea level. It contains interfingered marine and terrestrial deposits. In the southwestern region of the plateau

1020-454: The south Atlantic, and subduction on the west coast of the Americas had commenced, resulting in the Laramide orogeny , the early phase of growth of the modern Rocky Mountains . The Western Interior Seaway may be seen as a downwarping of the continental crust ahead of the growing Laramide/Rockies mountain chain. The earliest phase of the seaway began in the mid-Cretaceous when an arm of

1054-526: The southwest and coastal plain coals in the center of the plateau. The overlying Drip Tank Member consists of a coarse-grained fluvial facies thought to reflect a braided river environment. The base of the member often creates a bench at the top of the plateau. The upper contact of the Drip Tank grades into the Wahweap Formation creating sloped interval. The Drip Tank is 141 – 523 feet thick and

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1088-452: Was first examined by Peterson, who broke the John Henry Member into seven sandstone intervals (A-F) and three coal zones. Shanley and McCabe (1991) outlined sequence boundaries and systems tracts for the plateau based on the facies seen on the southern and eastern sides of the plateau. The formation is thought to represent the final transgression of the Tropic Sea. Shanley and McCabe (1991) described two major sequence boundaries, which separate

1122-481: Was found in only the southern reaches of the seaway. Inoceramids (oyster-like bivalve molluscs) were well-adapted to life in the oxygen-poor bottom mud of the seaway. These left abundant fossils in the Kiowa , Greenhorn , Niobrara , Mancos , and Pierre formations. There is great variety in the shells and the many distinct species have been dated and can be used to identify specific beds in those rock formations of

1156-547: Was little sedimentation on the eastern shores of the seaway; the western boundary, however, consisted of a thick clastic wedge eroded eastward from the Sevier orogenic belt . The western shore was thus highly variable, depending on variations in sea level and sediment supply. Widespread carbonate deposition suggests that the seaway was warm and tropical, with abundant calcareous planktonic algae . Remnants of these deposits are found in northwest Kansas. A prominent example

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