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34-664: The Portezuelo Formation is a geologic formation of Late Cretaceous ( Late Turonian to Early Coniacian ) age, outcropping in the Mendoza , Río Negro and Neuquén provinces of Argentina . It is the fourth-oldest formation in the Neuquén Group and the older of the two formations in the Río Neuquén Subgroup. Formerly, that subgroup was treated as a formation, and the Portezuelo Formation

68-463: A dry-summer humid continental climate ( Köppen Dsb ), bordering on a dry-summer subalpine climate ( Köppen Dsc ). Most of the plateau is within the 6b USDA Hardiness Zone (-5°F to 0°F), with the highest elevations in the 6a zone (-10°F to -5°F). There is no weather station at the summit, but this climate table contains interpolated data for an area around the summit. Dry Park is a Remote Automated Weather Station located 6 miles northwest of

102-589: A topographic prominence of 3,580 feet (1,090 m), and a topographic isolation of 70.44 miles (113.36 km). The plateau is bounded on the south by the Grand Canyon of the Colorado River, the elevation in this southern area of the plateau varies from 8,800 feet (2,700 m) to slightly less than 6,000 feet (1,800 m). The most extensive platform of the plateau is the Esplanade, which

136-611: A geologic formation goes back to the beginnings of modern scientific geology. The term was used by Abraham Gottlob Werner in his theory of the origin of the Earth, which was developed over the period from 1774 to his death in 1817. The concept became increasingly formalized over time and is now codified in such works as the North American Stratigraphic Code and its counterparts in other regions. Geologic maps showing where various formations are exposed at

170-440: A great increase in numbers during the early decades of the 20th century. One estimate put the population as high as 100,000 deer inhabiting the range in 1924. Again, there was no systematic survey to support this estimate, which may have been exaggerated to twice the actual number. Shortly after that time, however, the deer population did begin to decline from over-browsing . By the mid-1920s, many deer were starving to death. After

204-402: A heated legal dispute between the federal government and the state of Arizona, hunting was once more permitted, to reduce the deer's numbers. Hunters were able to kill only a small fraction of the starving deer. The range itself was damaged, and its carrying capacity was greatly reduced. Once ecologists began to study the area and reflect on the changes that had occurred there, they began to use

238-542: A newly designated formation could not be named the Kaibab Formation, since the Kaibab Limestone is already established as a formation name. The first use of a name has precedence over all others, as does the first name applied to a particular formation. As with other stratigraphic units, the formal designation of a formation includes a stratotype which is usually a type section . A type section

272-617: A permanent natural or artificial feature of the geographic area in which they were first described. The name consists of the geographic name plus either "Formation" or a descriptive name. Examples include the Morrison Formation , named for the town of Morrison, Colorado , and the Kaibab Limestone , named after the Kaibab Plateau of Arizona. The names must not duplicate previous formation names, so, for example,

306-449: Is not a valid lithological basis for defining a formation. The contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region. Formations must be able to be delineated at the scale of geologic mapping normally practiced in the region; the thickness of formations may range from less than a meter to several thousand meters. Geologic formations are typically named after

340-533: Is also used informally to describe the odd shapes (forms) that rocks acquire through erosional or depositional processes. Such a formation is abandoned when it is no longer affected by the geologic agent that produced it. Some well-known cave formations include stalactites and stalagmites . Kaibab Plateau The Kaibab Plateau is a plateau almost entirely in Coconino County, Arizona (but extending slightly north into Kane County , Utah ) in

374-557: Is available. The average carrying capacity of the land was unknown, in part because this concept was not widely used by naturalists at the time. Years later, Aldo Leopold estimated that the capacity had been about 30,000 deer. The idea in 1906 was simply to protect and expand the herd, so on November 28, President Theodore Roosevelt created the Grand Canyon National Game Preserve. Overgrazing by herds of sheep, cattle, and horses had taken place on

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408-531: Is called "Sand Rocks" by local cowboys. This area was formed as a result from weathering of the Hermit shale, which left a hard layer of Permian sandstone exposed. This red sandstone is one of the outstanding features of the plateau. The plateau's western boundary is the Kanab Creek Canyon which high perpendicular walls form a natural barrier to the movement of most animals. The northwestern boundary of

442-560: Is central to the geologic discipline of stratigraphy , and the formation is the fundamental unit of stratigraphy. Formations may be combined into groups of strata or divided into members . Members differ from formations in that they need not be mappable at the same scale as formations, though they must be lithologically distinctive where present. The definition and recognition of formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata . Formations were at first described as

476-455: Is ideally a good exposure of the formation that shows its entire thickness. If the formation is nowhere entirely exposed, or if it shows considerably lateral variation, additional reference sections may be defined. Long-established formations dating to before the modern codification of stratigraphy, or which lack tabular form (such as volcanic formations), may substitute a type locality for a type section as their stratotype. The geologist defining

510-519: The Colorado River form the plateau's eastern and western boundaries, and tiers of uplifted cliffs define the northern edges of the landform . Winter snowfall is often heavy (sometimes exceeding 17 feet [5.2 m]), and this creates opportunities for backcountry Nordic skiing and snow camping. This broad feature is heavily forested with aspen , spruce - fir , ponderosa pine , and pinyon-juniper woodland , and stands in sharp contrast to

544-692: The Southwestern United States . The high plain is also known as the Buckskin Mountain , Buckskin Plateau , and Kaibab Mountain . The plateau, part of the larger Colorado Plateau , is bordered on the south by the Grand Canyon and reaches an elevation of 9,200 feet (2,800 m). The plateau is divided between Kaibab National Forest and the "North Rim" portion of Grand Canyon National Park . Tributary canyons of

578-574: The Kaibab Plateau High Point, at an elevation of 8706 ft (2654 m). At the beginning of the 20th century, the Kaibab Plateau was witness to an interesting experiment in what some might call population engineering. The plateau's pre-1905 population of mule deer was estimated to be around 4,000. This number was never confirmed by any kind of count or survey, and has become an accepted number mainly because no other estimate

612-483: The Kaibab deer as a simple lesson about how the removal of the deer's natural predators , which had been done in the interest of preserving the deer population, had allowed the deer to over-reproduce, and quickly overwhelm the plateau's resources. Some ecologists suggested that the situation highlighted the importance of keeping a population in balance with its environment's carrying capacity. The more meaningful lesson of

646-499: The Kaibab suggests that human efforts to protect wildlife and preserve wild areas must be balanced with ecological complexity and social priorities that are difficult to predict. Changes take place, sometimes rapidly, but their effects linger for decades. Today, the Arizona Game Commission manages the area, controlling the numbers of deer as well as predators, and issues hunting permits to keep the deer in balance with

680-450: The Portezuelo Formation. There are also occasional cemented claystone deposits, as well as numerous paleosols (fossil soils). The formation varies between 95 and 130 metres (312 and 427 ft) thick throughout its range. Many dinosaur fossils have recently been described from this formation, as well as remains of several other types of animals : Geologic formation A formation must be large enough that it can be mapped at

714-432: The area was probably due to a period of severe overbrowsing by a large population of deer. This, they write, is consistent with the original assessment of the rapid rise in deer population as a result of persistent predator control. Their contribution of original research is a refreshing addition to the ongoing discussion of predator-prey interactions on the Kaibab. [Binkley, Dan, et al., 2006. "Was Aldo Leopold right about

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748-665: The arid lowlands encircling it. The cool forests of the plateau are home to the Kaibab squirrel , which is endemic to the region. Other fauna includes deer , turkey , cougar , and bobcat . The Kaibab deer are particularly important because of the changes in their population during the early 1900s. This particular fluctuation is a great example of population engineering and the effects humans can have on nature. The Kaibab Plateau consists of approximately 1,152 square miles (2,980 km ) which are above 6,000 feet (1,800 m). The highest point has an elevation of 9,200 feet (2,800 m),

782-474: The deer Caughley's opinion led to confusion by teachers and scientists over what to include and teach in ecology and biology classes, therefore this story stopped being used as an example of prey and predator population dynamics. This is important to the development of scientific studies because it shows that events—like the Kaibab deer controversy—do not have a definitive start and beginning but include other opinions and approaches which teachers use to showcase

816-550: The essential geologic time markers, based on their relative ages and the law of superposition . The divisions of the geological time scale were described and put in chronological order by the geologists and stratigraphers of the 18th and 19th centuries. Geologic formations can be usefully defined for sedimentary rock layers, low-grade metamorphic rocks , and volcanic rocks . Intrusive igneous rocks and highly metamorphosed rocks are generally not considered to be formations, but are described instead as lithodemes . "Formation"

850-522: The formation is expected to describe the stratotype in sufficient detail that other geologists can unequivocally recognize the formation. Although formations should not be defined by any criteria other than primary lithology, it is often useful to define biostratigraphic units on paleontological criteria, chronostratigraphic units on the age of the rocks, and chemostratigraphic units on geochemical criteria, and these are included in stratigraphic codes. The concept of formally defined layers or strata

884-614: The plateau is marked by a fault line north of the Snake Gulch which is approximately sixteen miles to the east of the Kanab Creek. The eastern boundary is marked by the so-called Houserock Valley, which is a marble platform caused by a monoclinical fold, which strata dips down 2,000 to 3,000 feet. The climate of the Kaibab Plateau consists of rain and thunderstorms in late summer during the summer monsoon season, snow, heavy at times, in winter, and drier weather in early summer. There

918-710: The plateau since the 1880s. During that time, many predators were also killed by ranchers and bounty hunters. By the time Roosevelt established the game preserve, ranchers had moved most domestic livestock elsewhere. The primary change brought by the creation of the game preserve was to ban deer hunting. Government efforts, led by the United States Forest Service , began to protect the deer's numbers by killing off their natural predators once again; to this end, between 1907 and 1939, 816 mountain lions , 20 wolves , 7388 coyotes and over 500 bobcats were reportedly killed. The deer population experienced

952-416: The range. Although the story of the Kaibab deer rose to fame in the 1920s due to their sudden increase and decrease in population, the story can also be used to demonstrate the way in which scientific studies and ideas about history can help educate current students. The first interpretation of the deer story as demonstrated in textbooks was that predator control had destroyed the deer's population growth. It

986-425: The richness of controversy. In the summers of 2002 and 2003, forest ecologist Dan Binkley and associates undertook a careful analysis of the age structure of aspen stands on the Kaibab. Their work shows that few aspen sprouted successfully on the plateau in the 1920s. They ruled out browsing by domestic livestock or exceptionally dry conditions as causes of that change and concluded that the age structure of aspen in

1020-643: The surface are fundamental to such fields as structural geology , allowing geologists to infer the tectonic history of a region or predict likely locations for buried mineral resources. The boundaries of a formation are chosen to give it the greatest practical lithological consistency. Formations should not be defined by any criteria other than lithology. The lithology of a formation includes characteristics such as chemical and mineralogical composition, texture, color, primary depositional structures , fossils regarded as rock-forming particles, or other organic materials such as coal or kerogen . The taxonomy of fossils

1054-432: The surface or traced in the subsurface. Formations are otherwise not defined by the thickness of their rock strata, which can vary widely. They are usually, but not universally, tabular in form. They may consist of a single lithology (rock type), or of alternating beds of two or more lithologies, or even a heterogeneous mixture of lithologies, so long as this distinguishes them from adjacent bodies of rock. The concept of

Portezuelo Formation - Misplaced Pages Continue

1088-510: Was an average annual precipitation of 26.57 inches (67.5 cm) for the period 1925 to 1936. During winter, snow is heavy and often accumulates at a depth of 8–10 feet (2.4–3.0 m). June is the driest month of the year, followed by May and early July. Storms occur several times each week until early September. The highest portions of the plateau are usually touched by snow, and snowstorms usually occur between May and September. The Kaibab Plateau High Point, 9,213 ft (2,808 m), has

1122-794: Was known as the Portezuelo Member . The type locality of the Portezuelo Formation is the mountain range known as Sierra del Portezuelo in Neuquén Province. This formation conformably overlies the Lisandro Formation of the Río Limay Subgroup. In the top layers it grades into the Plottier Formation , the younger formation within the Río Neuquén Subgroup. Sandstones and siltstones , probably deposited under fluvial conditions, make up

1156-524: Was thought that initially the high number of deer predators were obtruding the growth of the deer's population, therefore rules were put in place in order to minimize the predator population and allow the deer to increase their population size. However, as scientific studies continued, ecologist Graeme Caughley suggested that predator control alone could not have caused the Kaibab irruption, but rather factors like climate, grazing by other animals, and preservation policies actually had more significant impacts on

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