Geology of the Capitol Reef area 1114005 213290561 2008-05-18T18:13:43Z NE2 1757249 Cleaning up, mostly per [[WP:USSH]], Replaced: [[Utah State Route 24]] → [[Utah State Route 24|State Route 24]] using [[Project:AutoWikiBrowser|AWB]] [[Image:Waterpocket Fold from above Capitol Reef Scenic Drive.jpeg|thumb|300px|The [[Waterpocket Fold]] is the major geographic feature in the area of the park. This view is from above Capitol Reef Scenic Drive looking back at the west face of the broken and eroded fold.]] The exposed '''geology of the Capitol Reef area''' presents a record of mostly [[Mesozoic]]-aged sedimentation in an area of [[North America]] in and around [[Capitol Reef National Park]]. Nearly 10,000&nbsp;[[foot (unit of length)|feet]] (3,000&nbsp;[[metres|m]]) of sedimentary strata are found in the Capitol Reef area, representing nearly 200 million years of geologic history of the south-central part of the U.S. state of [[Utah]]. These rocks range in age from [[Permian]] (as old as 270 million years old) to [[Cretaceous]] (as young as 80 million years old.)<ref>NPS, "Capitol Reef"</ref> Rock layers in the area reveal ancient climates as varied as [[river]]s and [[swamp]]s ([[Chinle Formation]]), Sahara-like deserts ([[Navajo Sandstone]]), and shallow ocean ([[Mancos Shale]]). The area's first known sediments were laid down as a shallow sea invaded the land in the Permian. At first [[sandstone]] was deposited but [[limestone]] followed as the sea deepened. After the sea retreated in the [[Triassic]], streams deposited [[silt]] before the area was [[Tectonic uplift|uplifted]] and underwent [[erosion]]. [[Conglomerate (geology)|Conglomerate]] followed by logs, sand, mud and wind-transported [[volcanic ash]] were later added. Mid to Late [[Triassic]] time saw increasing aridity, during which vast amounts of sandstone were laid down along with some deposits from slow-moving [[stream]]s. As another sea started to return it periodically flooded the area and left [[evaporite]] deposits. [[Bar (landform)|Barrier islands]], sand bars and later, [[tidal flat]]s, contributed sand for sandstone, followed by cobbles for conglomerate and mud for shale. The sea retreated, leaving streams, [[lake]]s and swampy plains to become the resting place for sediments. Another sea, the [[Western Interior Seaway]], returned in the Cretaceous and left more sandstone and shale only to disappear in the early [[Cenozoic]]. From 70 to 50 million years ago the [[Laramide orogeny]], a major mountain building event in western North America, created the [[Rocky Mountains]] to the east. The uplift possibly acted on a buried [[fault (geology)|fault]] to form the area's [[Waterpocket Fold]]. More recent uplift of the entire [[Colorado Plateau]] and the resulting erosion has exposed this fold at the surface only within the last 15 to 20 million years. [[Ice age]]s in the [[Pleistocene]] increased the rate of [[Precipitation (meteorology)|precipitation]] and erosion. The cracked upper parts of the Waterpocket Fold were especially affected and the fold itself was exposed and dissected. [[Image:Capitolreef strat.jpg|250px|thumb|Stratigraphic section (USGS), [[media:Geologic cross section of Capitol Reef NP.png|Geologic cross section (NPS)]]]] ==Primary deposition of sediments== '''Some important concepts:''' A ''[[formation (geology)|formation]]'' is a formally named and defined [[geologic unit]] with unique characteristics. Those characteristics were created during a largely unbroken period of time and result from the specific depositional environment the formation was laid down in. A ''[[member (geology)|member]]'' is a minor unit in a formation and a ''bed'' is a distinct subunit of a member. ''[[Group (geology)|Group]]s'' are sets of formations that are related in significant ways such as, for example, all being deposited during a dry period that lasted millions of years or as the result of an ocean periodically flooding the same area over millions of years. The various kinds of ''[[unconformity|unconformities]]'' are gaps in the geologic record. Such gaps can be due to a prolonged absence of deposition or due to subsequent erosion that removes previously deposited rock units. The following sections are ordered from oldest to youngest rock units in order to create a [[geologic time scale|geologic history]] of events. This is the opposite order one would see in an actual cross section of the sediments due to the fact that newer rock units are deposited on top of older ones per the [[law of superposition]]. ===Cutler and Kaibab formations (Permian)=== [[Image:Pangaea continents.png|thumb|The blue ocean surrounding the supercontinent [[Pangaea]] is [[Panthalassa]].]] In early [[Permian]] time, [[Utah]] was on a [[continental shelf]] that was occasionally covered by a shallow arm of the [[Panthalassa Ocean]].<ref>Stokes, 1988, page 95, paragraph 3</ref> That part of [[Laurasia]] was on a [[passive continental margin]] not unlike the current west coast of equatorial [[Africa]]. The resultant [[formation (geology)|formation]]s are part of the approximately 290 to 250 million year old [[Cutler Formation]]<ref name="Morris96Tec">Morris et al, 2003, page 96, Tectonics and Geologic History"</ref> (called a [[group (geology)|group]] locally)<ref>'Cutler Formation' is the accepted usage by the USGS while 'Cutler Group' is preferred by the Utah Geological Survey, according to the [http://ngmdb.usgs.gov/Geolex/NewUnits/unit_7824.html GEOLEX database entry for 'Cutler']. Accessed 18 March 2006</ref> Utah was nearly on the [[Paleocene|paleoequator]] while the first [[member (geology)|member]]s of the Cutler Formation were deposited but it had migrated nearly to 10° north latitude by around 275 million years ago.<ref name="Morris96Tec" /> The Cutler records sedimentation during this time and is composed of four members (oldest to youngest): *Elephant Canyon (locally buried), *Cedar Mesa Sandstone, *Organ Rock Shale (locally missing), and the *White Rim Sandstone. Only the two [[sandstone]] members of the Cutler Formation, the Cedar Mesa and White Rim, are exposed in the park but they can't be easily distinguished from each other and are thus often treated as a single stratigraphic unit there.<ref>Morris et al, 2003, page 86, "Culter Group", paragraph 1</ref> The White Rim and Cedar Mesa are composed of fossilized cross-bedded [[sand dune]]s that were likely deposited in an arid coastal environment that periodically flooded with [[sea water]]. Sand in these formations are somewhat sorted by size, well-rounded and range from very fine to medium-grained.<ref name="Morris90">Morris et al, 2003, page 90</ref> Good outcrops of the locally 800&nbsp;[[foot (unit of length)|foot]] (240&nbsp;[[metre|m]]) thick Cedar Mesa and 420&nbsp;foot (128&nbsp;m) thick White Rim can be found in the bottom of Sulphur Creek and at the bottom of the [[Circle Cliffs]] outside the park's western border.<ref name="Harris62">Harris et al, 1997, page 62</ref> In other areas the Organ Rock Shale is between the Cedar Mesa and White Rim but it pinches out east of the park. Both the locally buried Elephant Canyon and missing Organ Rock are exposed in nearby [[Canyonlands National Park]] 60&nbsp;[[mile]]s (100&nbsp;[[kilometre|km]]) east (see [[geology of the Canyonlands area]]). Later in Permian time, the [[Kaibab Sea]] invaded the land and laid down a [[Lime (mineral)|lime]]y ooze that later [[lithology|lithified]] to form the locally 0 to 200&nbsp;foot (60&nbsp;m) thick [[Kaibab Limestone]]. This is the same light gray to white formation that rims the [[Grand Canyon]] to the southwest (see [[Geology of the Grand Canyon area]]). The lower parts of the Kaibab were interbedded with sand and silt before its main component, [[limestone]], was converted into [[chert]]-rich [[dolomite]] by the intrusion of [[magnesium]].<ref name="Harris62" /> The formation contains [[fossil]]s of [[invertebrate]]s including [[brachiopod]]s, [[bryozoan]]s, [[crinoid]]s, [[gastropod]]s, and [[pelecypod]]s. Outcrops of the cliff-forming Kaibab in Capitol Reef can only be seen in the deeper canyons located in the westernmost part of the park.<ref>For the whole paragraph except where noted: Morris et al, 2003, page 90, "Kaibab Limestone"</ref> Retreat of the Kaibab Sea by the Mid Permian exposed its seabed to erosion, resulting in 100&nbsp;foot (30&nbsp;m) deep channels and the creation of a gap in the geologic record called an [[unconformity]]. ===Moenkopi Formation (Triassic)=== [[Image:Ripple marks in Moenkopi Formation rock off of Capitol Reef Scenic Drive.jpeg|thumb|Ripple marks in Moenkopi Formation rock]] Local climatic conditions were wetter and more tropical in the Early [[Triassic]] than they were previously. In the Capitol Reef area the resulting [[Moenkopi Formation]] is divided into four [[member (geology)|member]]s (from oldest to youngest): *Black Dragon Member *Sinbad Limestone Member, *Torrey Member, and *Moody Canyon Member. Distinctive exposures of the uppermost Moenkopi are along the lower slopes of the west-facing cliffs of the Waterpocket Fold. Uplift and subsequent partial [[erosion]] of the Moenkopi then created an approximately 6 million year long unconformity that lasted the entire Mid Triassic.<ref name="Morris90" /> [[Image:Moenkopi Formation below Chinle on cliff above Capitol Reef Scenic Drive.jpeg|thumb|left|Moenkopi Formation below Chinle on cliff above Capitol Reef Scenic Drive]] The 50 to 110&nbsp;foot (15 to 34&nbsp;m) thick slope-forming Black Dragon is composed of reddish [[conglomerate (geology)|conglomerate]], sandstone, and siltstone that were likely deposited on a [[coastal plain]] followed by a [[tidal flat]]. [[Chert]] clasts from the underlying Kaibab Limestone make-up part of conglomerates at the member's base while ripple marks and mudcracks are common in its upper parts. Also common in the upper parts of the member are thin interbeds of [[carbonate rock]] with some [[fossil]]s.<ref name="Morris90" /> Later in the early Triassic, fossil-rich to muddy limey ooze with small amounts of [[silt]] and [[sand]] were laid down as a short-lived arm of the ocean covered the region. This created the locally 70 to 140&nbsp;foot (21 to 43&nbsp;m) thick yellowish-colored Sinbad Limestone member of the Moenkopi. Some of the fossils found in this layer include the [[brachiopod]] genus ''[[Lingula (genus)|Lingula]]'' and the [[ammonite]] genus ''[[Meekoceras]]''.<ref name="Morris90" /> A tidal flat briefly returned to the area after the sea retreated. This created the locally 250 to 320&nbsp;foot (76 to 98&nbsp;m) thick reddish-brown to chocolate colored siltstone and fine-grained sandstone of the Moenkopi's Torrey Member.<ref>Morris et al, 2003, page 90 to 91, "Moenkopi Formation"</ref> Some of the finer-grained beds display ripple marks and mudcracks while the sandstone has horizontal and low-angle crossbedding. Small to large fossilized [[fossil trackway|track-way]]s from [[amphibian]]s and [[reptile]]s are found in this layer as well as casts of [[halite]]. The youngest member of the Moenkopi is the 320 to 430&nbsp;foot (98 to 130&nbsp;m) thick Moody Canyon Member. Moody Canyon is informally sub-divided into two units: *a lower slope-forming 200 to 300&nbsp;foot (60 to 90&nbsp;m) thick unit of reddish-brown siltstone and *an upper cliff-forming 120 to 130&nbsp;foot (37 to 40&nbsp;m) thick unit of reddish-orange siltstone. About 30 to 40% of the stone in the upper unit is ripple-laminated while the lower unit is structureless to horizontally laminated.<ref name="WholeMorris91">For the whole paragraph except where noted: Morris et al, 2003, page 91</ref> Good exposures of the ripple-laminated upper unit are found on the lower part of Egyptian Temple. ===Chinle Formation (Triassic)=== [[Image:Chinle Formation showing each member on a cliff above Capitol Reef Scenic Drive.jpeg|thumb|Chinle Formation section showing each member represented in the Capitol Reef area: Monitor Butte Member (m), the two units of the Petrified Forest Member (p) and the Owl Rock Member (o - partially obscured by overlaying Windgate rubble). <small>[[media:Cliffs along Capitol Reef Scenic Drive-2.jpeg|Non-cropped image]]</small>]] A complex, relatively high velocity and likely braided stream system covered most of southern [[Utah]] in the Late Triassic. Various members of the resulting [[Chinle Formation]] are found over much of the [[Colorado Plateaus]]. Logs, sand, mud and wind-transported [[volcanic ash]] from distant eruptions were mixed by streams as they migrated over a subsiding [[basin (geology)|basin]] to form the Chinle. [[Uranium]] [[salt]]s accumulated in this formation in economically extractable quantities and [[petrified wood]] was formed (petrification was probably aided by the presence of volcanic ash).<ref name="Harris62" /> Chinle members represented in the Capitol Reef area are (from oldest to youngest): *Shinarump Member, *Monitor Butte Member, *Petrified Forest Member, and *Owl Rock Member. Together they form the purple and orange rounded slopes and hills that are occasionally above white cliffs along the Waterpocket Fold's west face.<ref name="WholeMorris91" /> Discontinuous beds of sediment were deposited in broad channels eroded into the Moenkopi, creating the locally 0 to 90&nbsp;foot (0 to 27&nbsp;m) thick white to yellowish gray cliff-forming Shinarump Member of the Chinle Formation.<ref name="WholeMorris91" /> The Shinarump is made of low to high-angle cross-stratified and friable fine to coarse-grained [[sandstone]] interbedded with [[conglomerate (geology)|conglomerate]]. Good outcrops of the Shinarump are found near the park's west entrance capping such features as the Egyptian Temple and Chimney Rock while all traces of this member are absent further east. Members above the Shinarump tend to be finer due to the slower speed of the streams that deposited them.<ref name="Harris62" /> A river system then migrated northward and transitioned into either a large [[lake]] or [[marsh]]. As this occurred, [[bentonite]]-rich [[clay]] (formed in part from volcanic ash erupted from nearby [[volcano]]es) and clayey cross-bedded sand with some interbeds and lenses of [[Lime (mineral)|lime]] ooze were laid down. This eventually became the light purplish-gray [[claystone]], sandstone, and [[carbonate rock]] of the Chinle's Monitor Butte Member. Burrows that measure 5 [[inch]]es (13&nbsp;cm) in diameter and 5&nbsp;feet (1.5&nbsp;m) long were excavated by [[lungfish]] into the Monitor Butte.<ref name="WholeMorris91" /> This member easily stands out in the lower to middle slopes of the Waterpocket Fold's west face in such places as The Castle and along the cliff's just north of [[Utah State Route 24|State Route 24]] as it enters the park. [[Image:Closeup of the Owl Rock member above the Capitol Reef Bed.jpg|thumb|left|Closeup of the Owl Rock member above the Capitol Reef Bed. <small>[[media:Cliffs along Capitol Reef Scenic Drive-1.jpeg|Non-cropped image]]</small>]] Very sinuous rivers covered the area in later Triassic time, forming the sediments of the Chinle's Petrified Forest Member. The Petrified Forest is composed of reddish-orange bentonite-rich cross-bedded siltstones and clayey fine-grained [[quartz]] sandstones. The lower part of this member forms [[gully|gullied]] slopes and the upper part forms a resistant cliff called the 'Capitol Reef bed.' [[Carbonate]] nodules along with fossil [[bivalve]]s, [[coprolite]]s, marine [[snail]]s, lungfish toothplates, and [[tetrapod]]s are found in the Petrified Forest Member.<ref name="WholeMorris91" /> Deposition from a series of lakes then dominate the geologic record, resulting in the locally 150 to 200&nbsp;foot (45 to 60&nbsp;m) thick Owl Rock Member of the Chinle. The Owl Rock is made of purple and orange [[mudstone]]s, fine-grained sandstones and [[siltstone]]s with interbedded 1 to 10&nbsp;foot (30 to 300 cm) thick green to mottled pink micritic and knobby [[limestone]].<ref name="WholeMorris91" /> Fossilized desiccation mudcracks that are up to 4 inches (10 cm) wide and 3&nbsp;feet (1&nbsp;m) deep are found at the very top of the Owl Rock (they were later filled with sand from the overlying Windgate Sandstone). Also found in the Owl Rock are trace fossils of cylindrical burrows and fossils of [[ostracode]]s. The Owl Rock erodes into littered slopes and is found directly below the Windgate Sandstone along the Waterpocket Fold's west face. ===Glen Canyon Group (Jurassic)=== [[Image:Wingate Sandstone capping The Castle in Capitol Reef NP.jpg|thumb|Wingate Sandstone capping The Castle. <small>[[media:The Castle from Capitol Reef NP visitors center.jpeg|Non-cropped image]]</small>]] All three formations of the [[Glen Canyon Group]] were laid down in the Mid to Late Triassic during a time of increasing aridity. Slightly clockwise and northward movement of the [[North American Plate]] was bringing the area into a dryer climatic belt. The direction of cross-bedding in Glen Canyon Group sand dunes suggests that prevailing [[wind]]s from the north transported the sand into the region.<ref name="Morris96Tec" /> Outcrops of the Glen Canyon Group's three formations are the most prominently exposed rock layers in the spine of the [[Waterpocket Fold]].<ref name="Harris62" /> Together they reach a thickness of 1,500 to 2,700&nbsp;feet (460 to 820&nbsp;m) in the area and their sandstones are seen in many of the arches, domes and [[slot canyon]]s in Capitol Reef.<ref name="Morris92">Morris et al, 2003, page 92</ref> They are, from oldest (lowest) to youngest (highest); *[[Wingate Sandstone]] *[[Kayenta Formation]] *[[Navajo Sandstone]] Sand dunes migrated back and forth on the shore of the [[Sundance Sea]], creating the 350&nbsp;foot (107&nbsp;m) thick cliff-forming Wingate Sandstone.<ref name="Harris62" /> This formation is composed of orange-colored cross bedded fossilized sand dunes made of fine-grained and well-rounded [[quartz]] sand. Wingate outcrops are found capping the Waterpocket Fold's western escarpment. Prominent examples are easy to see near the Visitor Center in the Fruita Cliffs and in The Castle. [[Image:Double arch in Kayenta Formation in Upper Muley Twist Canyon.jpg|left|thumb|Double arch in Kayenta Formation in Upper Muley Twist Canyon (USGS)]] The climate became more [[humidity|humid]] later in Triassic time. Slow-moving, southwestward flowing braided streams laid down thin-bedded layers of sand, silt, mud and cobbles in channels, across low flood plains and in lakes. Fossilized footprints of [[dinosaur]]s and the [[crocodile]]-like [[tritylodont]]s can be found in this 350&nbsp;foot (107&nbsp;m) thick ledgy-slope forming formation, called the Kayenta.<ref name="Harris62" /> The Kayenta weathers into three units; a lower ledge and middle cliff that are dominated by cross-bedded sandstone and an upper slope that has relatively more [[siltstone]]. It is often difficult to spot the contact between the Windgate and Kayenta due to their similar color and grain size. One place where the contact is easiest to discern is west of State Route 24 along the Fremont River at mile marker 82.<ref name="Morris92" /> [[Image:Capitol Dome in Capitol Reef NP.jpeg|thumb|Capitol Dome is made of Navajo Sandstone]] A massive [[Sahara]]-like [[desert]] geologists call an [[erg (geology)|erg]] then invaded the area, covering it with 800 to 1,100&nbsp;feet (240 to 335&nbsp;m) of accumulated white to tan-colored fossilized sand dunes.<ref name="Morris92" /> The resulting formation, called the Navajo Sandstone, is composed of cross-bedded and very clean sandstone with well-rounded, generally very fine-grained and frosted sand. It reached its greatest thickness, 2,000&nbsp;feet (610&nbsp;m) in what is now [[Zion National Park]] (see [[geology of the Zion and Kolob canyons area]]). The cross-bedded make-up of the Navajo leads to the formation of curvilinear [[canyon]]s and rounded domes such as Capitol Dome and Navajo Dome. In other places it forms massive cliffs and [[monolith]]s. Subsequent erosion leveled the tops of the sand dunes and left them in up to 60&nbsp;foot (18&nbsp;m) thick easy to discern layers.<ref name="Morris92" /> ===San Rafael Group (Jurassic)=== Frequent but short-lived changes in [[sea level]] during the Mid to Late [[Jurassic]] periodically flooded the area with shallow extensions of the ocean.<ref name="Morris92" /> The resulting [[San Rafael Group]] is composed of four formations that were deposited on top of the Glen Canyon Group's regionally-traceable erosion surface. San Rafael Group formations are (from oldest to youngest); *[[Page Sandstone]], *[[Carmel Formation]], *[[Entrada Sandstone]], *[[Curtis Formation]], and *[[Summerville Formation]]. San Rafael formations can be seen on the east-dipping part of the Waterpocket Fold. Climatic conditions were still arid when the locally 0 to 100&nbsp;feet (0 to 30&nbsp;m) thick Page Sandstone was deposited above the reach of high [[tide]] yet near the shore of an advancing sea ([[sabkha]]-like conditions).<ref>For the whole paragraph, except where noted: Morris et al, 2003, pages 92–93</ref> This formation is composed of three members; the *Harris Wash, *Judd Hollow, and the *Thousand Pockets. Together they were laid on top of the Navajo sand dunes as the sea slowly flooded the vast desert. An outcrop of the Judd Hollow Member can be seen from mile marker 86.5 as a red cliff above the Fremont River falls. The cross-bedded sandstone just above the red cliff is an example of the Thousand Pockets Member. In Mid Jurassic time [[gypsum]], [[sand]], and limey [[silt]] were deposited in what may have been a [[graben]] that was periodically covered by [[sea water]] and thus a place where repeated [[flooding]] was followed by [[evaporation]].<ref>Harris et al, 1997, page 63, section 4, paragraph 1</ref> The resulting Carmel Formation is composed of 200 to 1,000&nbsp;feet (60 to 300&nbsp;m) of reddish-brown siltstone, [[mudstone]] and sandstone that alternates with whitish-gray [[gypsum]] and [[fossil]]-rich limestone in a banded pattern. Fossils include marine [[bivalve]]s and [[ammonite]]s.<ref name="Morris94">Morris et al, 2003, page 94</ref> Most of the Carmel has been removed from the Waterpocket Fold's crest but outcrops can be seen capping the Golden Throne and atop various domes in the area. It can also be seen as reddish-brown triangular-shaped spurs called 'flatirons' that form the Waterpocket Fold's eastern rampart. [[Image:Entrada Sandstone capped by Curtis Formation in Cathedral Valley.jpg|left|thumb|Entrada Sandstone capped by Curtis Formation in Cathedral Valley. <small>[[media:Capitol Reef - Cathedral Valley.jpg|Non-cropped image]]</small>]] A near-shore environment dominated by barrier islands, sand bars and tidal flats later returned to the region. The sand and silt deposited created the 400 to 900&nbsp;foot (120 to 275&nbsp;m) thick reddish orange Entrada Sandstone.<ref name="Morris94" /> Distinctive jointing systems in the Entrada lead to the formation of cathedrals and monoliths in Capitol Reef's Cathedral Valley, [[natural arch|arches]] in [[Arches National Park]]<!-- red link (see [[Geology of the Arches area]])--> and 'goblins' (the local name for [[hoodoo (geology)|hoodoo]]s) in nearby [[Goblin Valley State Park]]. Entrada exposures in the southern part of the park are mostly made of flat-bedded siltstones and erode into slopes. Moving north, Entrada exposures increasingly become rich in cross-bedded sandstone and erode into cliffs with fewer and fewer slopes. Fine-grained sand and silt mixed with sandy lime were laid down as sediments on top of the Entrada Sandstone, forming the locally 0 to 175&nbsp;foot (53&nbsp;m) thick erosion-resistant Curtis Formation.<ref name="Morris94" /> A green [[iron]] [[potassium]] [[silicate]] called [[glauconite]] in the Curtis indicates it was deposited in a shallow sea. Outcrops of the light grayish-green Curtis can be seen as a capstone in the northern section of the park while it is locally absent in the southern part. Tidal flat conditions returned as the shallow sea that created the Curtis Formation retreated from land. Thin beds of reddish-brown mudstone alternating with less frequent beds of greenish-gray sandstone and limestone were deposited as sediments, forming the locally 50 to 250&nbsp;foot (15 to 75&nbsp;m) thick Summerville Formation.<ref name="Morris94" /> This formation erodes into ledgy cliffs and slopes and can be seen above Curtis caprock in Cathedral Valley. Fossilized mudcracks and ripple marks are found in the Curtis along with up to 28&nbsp;foot (8.5&nbsp;m) thick [[gypsum]]-rich beds. ===Morrison Formation (Jurassic)=== [[Image:Morrison Formation from near Notom-Bullfrog Road in southern Capitol Reef National Park.jpg|thumb|Morrison Formation from near Notom-Bullfrog Road (USGS)]] Again above [[sea level]], streams laid down mud and sand in their channels, on lakebeds, and in [[swamp]]y plains during the Upper Jurassic. This became the [[Morrison Formation]], which is locally divided into three members (from oldest to youngest); *Tidwell Member, *Salt Wash, and *Brushy Basin. The 50 to 100&nbsp;foot (15 to 30&nbsp;m) thick Tidwell Member is locally difficult to recognize and therefore may or may not be in the area's rocks.<ref name="Morris94" /> Easier to identify and study outcrops elsewhere in southeastern Utah indicate they were deposited in hypersaline [[lagoon]]s. Clay, mud, silt, cross-bedded sand and pebbles were later deposited by meandering [[stream]]s and in [[flood plain]]s, forming the locally 100 to 500&nbsp;foot (30 to 150&nbsp;m) thick Salt Wash Member.<ref name="Morris94" /> Claystone and mudstone beds of this member erode into gray slopes that can exhibit brown, red, yellow, and green colors. Salt Wash sandstone is moderately sorted and fine to medium grained while pebble conglomerate beds are made of [[chert]] with small amounts of [[silica]]-rich limestone. Both bed types erode into ledges and small cliffs. The Salt Wash was locally mined in the 1950s to extract [[uranium]] ore.<ref>Harris et al, 1997, page 64, section 5</ref> The 200 to 350&nbsp;foot (60 to 105&nbsp;m) thick Brushy Basin Member is composed of claystone, mudstone, and siltstone with small amounts of conglomerate and sandstone.<ref name="Morris94" /> Clays in this member are rich in [[smectite]] and thus tend to swell when wet and dry to a crumbled surface that looks a bit like [[popcorn]]. Fossilized [[dinosaur]] bones are abundant in this member in several places located in Utah and western [[Colorado]]. The bones are usually scattered and are thus hard to identify but nearly complete [[skeleton]]s have been found in lake floor and flood-plain clays. Good exposures of the Brushy Basin Member can be seen in the Bentonite Hills. ===Cedar Mountain and Dakota formations (Cretaceous)=== [[Image:Cretaceous seaway.png|right|frame|The Capitol Reef area was on the edge of an epicontinental sea for much of the Cretaceous (USGS)]] Early Cretaceous time brought continental deposition that was dominated by rivers to the area. Sandstones and mudstones accumulated to form the 0 to 166&nbsp;foot (50.5&nbsp;m) thick slope-forming [[Cedar Mountain Formation]]. The 73&nbsp;foot (22&nbsp;m) thick Buckhorn Conglomerate Member thins out north and east of the park and is nearly absent in it, making it difficult to distinguish the underlying Morrison from the somewhat more pastel-colored Cedar Mountain. Fossilized freshwater animals such as [[mollusk]]s and [[ostrapod]]s along with dinosaurs, [[fish scale]]s, [[pollen]] and a genus of fern called ''[[Tempskya]]'' have been found in this formation.<ref>For the whole section, except where noted: Morris et al, 2003, pages 94 to 95</ref> The passive continental margin became active when the [[Faralon Plate]] started to dive below the [[North American Plate]]. Geologists call the resulting mountain-building event the [[Sevier orogeny]]. Compressive forces detached sedimentary units across western Utah and [[Nevada]] from their Precambrian basement rocks and pushed them eastward.<ref name="Morris96Tec" /> The weight of the resulting high [[mountain range]] that formed to the west, lowered much of Utah and allowed the sea to invade. This grew into a vast sea that periodically divided [[North America]] in the [[Cretaceous]] called the [[Western Interior Seaway]]. Non-marine sediments of the approximately 100 to 94 million year old [[Dakota Sandstone]] were deposited on the shore of this seaway early in the Cretaceous.<ref name="Morris97">Morris et al, 2003, page 97</ref> The 0 to 150&nbsp;foot (0 to 45&nbsp;m) thick formation consists of fine-grained tan to brownish-gray colored [[quartz]]-rich sandstone that is interbedded with thin layers of [[carbon]]-rich shale, [[coal]], and conglomerate. [[Petrified wood]] is found in the lower part of the formation while fossilized marine bivalves such as ''[[Corbula]]'' and ''[[Pycnodonte newberryi]]'' are in the upper layers. This fossil progression shows a record of flooding that created the seaway. Dakota erode into small cliffs and hogbacks that can be seen in the southern section of the park.<ref>For the whole section, except where noted: Morris et al, 2003, page 95, "Dakota Sandstone"</ref> ===Mancos Shale and Mesaverde Formation (Cretaceous)=== [[Image:Mancos Shale slopes along the east side of the Strike Valley.jpg|thumb|Mancos Shale slopes along the east side of Strike Valley (USGS)]] Approximately 94 to 85 million years ago, the seaway advanced onto and retreated from land as it laid down the [[Mancos Shale]].<ref name="Morris97" /> The Mancos is composed mostly of [[shale]] but two of its members, the Ferron and Muley Canyon, are sandstone that were laid down when relative sea level temporarily dropped. The five Mancos members from oldest to youngest are: #Tununk Shale, #Ferron Sandstone, #Blue Gate Shale, #Muley Canyon, and #Masuk. Parts of this formation are found in some [[mesa]]s and [[butte]]s in the southernmost part of the park and in [[badland]]s east of the park.<ref>Harris et al, 1997, page 65, section 6, paragraph 2</ref> Open marine conditions created the locally 40 to 720&nbsp;feet (12 to 220&nbsp;m) thick gullied slope-forming Tununk Shale Member. It is made of bluish-gray [[shale]] with interbedded [[mudstone]], fine-grained [[sandstone]] and [[siltstone]]. The Tununk erodes into a slope and is locally fossil-rich.<ref name="Billingsley">Billingsley et al, 1987, page 5</ref> It is most prominently exposed in the Blue Desert immediately southeast of Cathedral Valley and contains [[fossil]]ized examples of [[cephalopod]]s, [[bivalve]]s, and [[fish scale]]s. [[Image:Mancos Shale badlands in Capitol Reef NP.jpg|thumb|left|Mancos Shale badlands]] A wave-dominated [[delta (landform)|delta]] and river system then spread over the area, creating the locally 205 to 385&nbsp;feet (62 to 117&nbsp;m) thick cliff-forming Ferron Sandstone. It is composed of brown fine-grained sandstone along with white cross-bedded sandstone with interbedded [[carbonate]]-rich gray shale.<ref name="Billingsley" /> The marine bivalve ''[[Inoceramus]]'' and [[trace fossil]]s of ''[[Ophiomorpha]]'' are found in the lower part of this member. Ferron Sandstone north of the area contains seams of [[coal]] in its upper part, prompting some [[petroleum]] geologists to study this member to model oil-bearing regions. Open marine conditions returned in the Late [[Cretaceous]], forming the locally 1,200 to 1,500&nbsp;foot (365 to 460&nbsp;m) thick slope-forming Blue Gate Shale. This member is composed of [[bentonite]] rich [[clay]]s, siltstone and some sandstone. It erodes into gullied slopes similar in appearance to the Tununk Shale. The presence of two species of planktonic [[foraminifera]] in the upper Blue Gate, ''[[Clioscaphites vermiformis]]'' and ''[[Clioscaphites choteauenis]]'', was used to date this member. An ancient shoreline once again approached the area, resulting in the formation of the locally 300 to 400&nbsp;feet (90 to 120&nbsp;m) thick Muley Canyon Member. It is composed of evenly-bedded, fine-grained sandstone and [[carbon]]-rich shales. Coal beds are found in the upper parts of this member, indicating continental coastal plain conditions at that time. Alternating layers of shallow marine and non-marine sediments were deposited as the shoreline fluctuated back and forth over the area. These sediments became the locally 650 to 750&nbsp;foot (200 to 230&nbsp;m) thick Masuk Member. The Masuk consists of cliff-forming cross-bedded sandstones and slope-forming yellowish-gray to bluish-gray mudstones with interbedded light gray sandstones. Fossils of bivalves, ceratopsian [[dinosaur]]s, [[crocodile]]s, [[gastropod]]s, and [[turtle]]s have been collected in this member.<ref>For the whole section, except where noted: Morris et al, 2003, page 95, "Mancos Shale"</ref> The Western Interior Seaway was shrinking due to infilling and uplift while the high mountains to the east were being reduced by erosion. Barrier [[beach]]es and [[river delta]]s migrated eastward into the seaway. The resulting 300 to 400&nbsp;foot (90 to 120&nbsp;m) thick [[Mesaverde Formation]] consists of light-brown to dark-gray thick-bedded and cross-stratified sandstone with interbedded dark gray shale and intertongues with the Masuk Member of the overlying Mancos Shale.<ref>For the whole paragraph: Morris et al, 2003, pages 95–96, "Mesaverde Formation" and Billingsley et al, 1987, page 5</ref> Only small remnants are found capping a few mesas in the park's eastern section<!-- red link (see [[geology of the Mesa Verde area]])-->. == Uplift and Cenozoic events == ===Waterpocket Fold, Lake Uinta and volcanism=== [[Image:Waterpocket Fold cross section.JPG|frame|Waterpocket Fold cross section showing eroded part (NPS)<br/><small>[[media:Waterpocket Fold - Looking south from the Strike Valley Overlook.jpg|Photo of the fold looking south from the Strike Valley Overlook (USGS)]]</small>]] The [[Laramide orogeny]] compacted the region from about 70 million to 50 million years ago and in the process created the [[Rocky Mountains]]. Many monoclines (a type of gentle upward [[fold (geology)|fold]] in rock strata) were also formed by the deep compressive forces of the Laramide. One of those [[monocline]]s, called the [[Waterpocket Fold]], is the major geographic feature of the park. The 100&nbsp;mile (160&nbsp;km) long fold has a north-south alignment with a steeply east-dipping side. The rock layers on the west side of the Waterpocket Fold have been lifted more than 7,000&nbsp;feet (2,100&nbsp;m) higher than the layers on the east.<ref>NPS, "Geology", paragraph 1</ref> Thus older rocks are exposed on the western part of the fold and younger rocks on the eastern part. It is possible that this particular fold may have been created where it is due to movement along a [[fault (geology)|fault]] thought to be in the [[Precambrian]] basement rocks hidden well below any exposed formations (some small [[earthquake]]s centered below the fold in 1979&nbsp;may be from such a fault).<ref>Harris et al, 1997, page 65, section 7</ref> Contemporary with the Waterpocket Fold's formation was the development of an intermontane (between mountains) basin in the area. [[Lake Uinta]] filled this basin with stream water derived from the north and south. This large [[lake]] existed from about 58 million until 35 million years ago and is responsible for creating the [[Flagstaff Limestone]] and [[Green River Formation]], which locally reach a thickness of around 200&nbsp;feet (60&nbsp;m). Elsewhere these formations have a combined thickness of over 9,000&nbsp;feet (2,740&nbsp;m).<ref name="Morris97" /> The Flagstaff is a white-colored, fossil rich layer that is composed of limestone, [[tuffa]] and conglomerate that erodes into ledges and slopes.<ref name="Billingsley" /> Compressive forces caused by the Laramide [[orogeny]] were followed by some minor stretching as the crust tried to find a new equilibrium. This created weaknesses in the crust that [[magma]] took advantage of by squeezing toward the surface to create [[composite volcano]]s west of the area some 25 to 20 million years ago.<ref name="Morris97" /> Within the fold, magma intruded through and between formations about 4.6 to 3.7 million years ago to respectively create [[dike (geology)|dike]]s and [[sill (geology)|sill]]s.<ref name="Morris97" /> Small [[basalt]]ic lava flows erupted through fissures at the surface and igneous activity continued sporadically afterwards. Subsequent erosion preferentially removed the softer sedimentary rock that initially entombed the dikes, sills, and volcanic plugs, often leaving them standing in relief.<ref>Harris et al, 1997, page 60, "Igneous Rocks"</ref> Good examples can be seen in South Desert and Cathedral Valley at the northern end of the fold. ===Erosion=== [[Image:Fremont River from near the Gifford Farmhouse in Capitol Reef NP.jpeg|thumb|The Fremont River has been able to keep up with the uplift of the Waterpocket Fold]] Ten to fifteen million years ago the entire region was uplifted several thousand feet (well over a kilometer) by the creation of the [[Colorado Plateau]]s. This time the uplift was more even, leaving the overall orientation of the formations mostly intact. Most of the erosion that carved today's landscape occurred after the uplift of the Colorado Plateau with much of the major canyon cutting probably occurring between 1 and 6 million years ago.<ref>NPS, "Erosion"</ref> Even in this desert climate, water is the erosional agent most responsible for the carving of the landscape. The pull of [[gravity]], in the form of rock falls or rock creep, plays a major role in the shaping of the cliff lines. [[Wind]] is a minor agent of erosion here. The drainage system in the area was rearranged and steepened as the Waterpocket Fold was uplifted. Larger streams, such as the [[Fremont River (Utah)|Fremont River]], were more likely to keep up with the uplift by [[downcutting]] into the Waterpocket Fold faster. Other streams, such as Sand Creek, changed their course by flowing parallel to the fold and cutting into less resistant formations. Yet other streams tried to keep up with the uplift by carving slot [[canyon]]s only to later change course, leaving their canyons literally high and dry.<ref>For the whole paragraph except where noted: Harris et al, 1997, page 66, section 9, paragraph 1</ref> A total of 7,000&nbsp;feet (2,100&nbsp;m) of overlying [[Mesozoic]] and [[Tertiary]] sediment has been removed by erosion in the area.<ref>Morris et al, 2003, page 98, paragraph 1</ref> Wetter and cooler conditions developed during the [[Pleistocene]] epoch and briefly returned via at least two neoglacial episodes ([[little ice age]]s) in the current epoch, the [[Holocene]].<ref>Harris et al, 1997, page 66, section 9</ref> The various rivers and streams in the area were engorged by increased precipitation and with melt-water from mountain [[glacier]]s on the [[Henry Mountains]] to the east and the [[Aquarius Plateau]] to the west of the park.<ref>Hintze, 1973</ref> [[Flash flood]]s, [[mass wasting]] of hillsides, [[Weathering#Freeze-thaw|frost wedging]], and [[landslide]]s all contributed to a significantly faster rate of [[erosion]]. Glaciers plucked 20 to 30 million year old black basaltic boulders from atop [[Boulder Mountain (Utah)|Boulder]] and [[Thousand Lake Mountain]]s that were subsequently deposited over the park area by meltwater streams from the glaciers, rockslides and [[flood]]s.<ref>Harris et al, 1997, page 60, "Igneous Rocks", paragraph 2</ref> ==References== [[Image:Capital Reef satellite image.jpg|right|thumb|The Fremont River crosses the Waterpocket Fold in the upper half of this satellite picture, while the white line of Capitol Reef bisects the lower half.]] ===Works cited=== <div class="references-small"> *[http://geology.utah.gov/maps/geomap/parkmaps/pdf/M-87.pdf Billingsley, G.H., Breed, W.J. and Huntoon, P.W.; 1987; Geologic Map of capitol Reef National Park and vicinity, Utah; Utah Geologic Survey] (viewed 25 March 2006) *Halka Chronic, ''Roadside Geology of Utah'' (Mountain Press; 1990) ISBN 0-87842-228-5 *Ann G. Harris, Esther Tuttle, Sherwood D., Tuttle, ''Geology of National Parks: Fifth Edition'' (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7 *L. F. Hintze, ''Geologic History of Utah'', Brigham Young University Geology Studies, v. 20, Part 3. Provo UT, page 181 *Thomas H. Morris, Vicky Wood Manning, and Scott M. Ritter, "Geology of Capitol Reef National Park, Utah" in ''Geology of Utah's Parks and Monuments'', Douglas A. Sprinkel, Thomas C. Chindsey, Jr., and Paul B. Anderson, Editors (Salt Lake City; Utah Geological Association; 2003) ISBN 1-882054-10-5 *[http://www.nps.gov/care/geology1.htm National Park Service, "Capitol Reef: Geology"] (viewed 25 March 2006) *William Lee Stokes, ''Geology of Utah'' (Salt Lake City; Utah Museum of Natural History; 1988) ISBN 0-940378-05-1 </div> ===Notes=== {{reflist}} ==External links== *[http://www.nps.gov/care/resources/admin%20history/adhi1.htm Administrative History of Capitol Reef National Park: Chapter 1 (NPS.gov)] *[http://geology.utah.gov/maps/geomap/parkmaps/index.htm Geologic Map of capitol Reef National Park and vicinity, Utah; Utah Geologic Survey] *[http://www.nps.gov/care/geology1.htm National Park Service: Capitol Reef Geology] *[http://www2.nature.nps.gov/geology/education/foos/capitol.pdf Geology of Capitol Reef National Park] {{featured article}} [[Category:Geology of Utah]] [[Category:Regional geology of the United States|Capitol Reef]] [[io:Geologio di la areo di Capitol Reef]]