The Cretaceous (, ), derived from the Latin "creta" (chalk), usually abbreviated K for its German translation ''Kreide'' (chalk), is a geologic period and system from circa }} to }} million years (Ma) ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the Cenozoic era. It is the youngest period of the Mesozoic era, and at 80 million years long, the longest period of the Phanerozoic Eon. The end of the Cretaceous defines the boundary between the Mesozoic and Cenozoic eras. In many languages this period is known as "chalk period".

The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels and creating numerous shallow inland seas. These oceans and seas were populated with now extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. At the same time, new groups of mammals and birds, as well as flowering plants, appeared. The Cretaceous ended with a large mass extinction, the Cretaceous–Paleogene extinction event, in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out.

Geology

Research history

The Cretaceous as a separate period was first defined by a Belgian geologist Jean d'Omalius d'Halloy in 1822, using strata in the Paris Basin and named for the extensive beds of chalk (calcium carbonate deposited by the shells of marine invertebrates, principally coccoliths), found in the upper Cretaceous of western Europe. The name Cretaceous was derived from Latin ''creta'', meaning ''chalk''. The name of the island Crete has the same origin.

Stratigraphic subdivisions

The Cretaceous is divided into Early and Late Cretaceous epochs or Lower and Upper Cretaceous series. In older literature the Cretaceous is sometimes divided into three series: Neocomian (lower/early), Gallic (middle) and Senonian (upper/late). A subdivision in eleven stages, all originating from European stratigraphy, is now used worldwide. In many parts of the world, alternative local subdivisions are still in use.

As with other older geologic periods, the rock beds of the Cretaceous are well identified but the exact ages of the system's top and base are uncertain by a few million years. No great extinction or burst of diversity separates the Cretaceous from the Jurassic. However, the top of the system is sharply defined, being placed at an iridium-rich layer found worldwide that is believed to be associated with the Chicxulub impact crater in Yucatan and the Gulf of Mexico. This layer has been tightly dated at 65.5 Ma.

Rock formations

The high eustatic sea level and warm climate of the Cretaceous meant a large area of the continents was covered by warm shallow seas. The Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the Cretaceous system consists for a major part of marine limestone, a rock type that is formed under warm, shallow marine circumstances. Due to the high sea level there was extensive accommodation space for sedimentation so that thick deposits could form. Because of the relatively young age and great thickness of the system, Cretaceous rocks crop out in many areas worldwide.

Chalk is a rock type characteristic for (but not restricted to) the Cretaceous. It consists of coccoliths, microscopically small calcite skeletons of coccolithophores, a type of algae that prospered in the Cretaceous seas.

In northwestern Europe, chalk deposits from the Upper Cretaceous are characteristic for the Chalk Group, which forms the white cliffs of Dover on the south coast of England and similar cliffs on the French Normandian coast. The group is found in England, northern France, the low countries, northern Germany, Denmark and in the subsurface of the southern part of the North Sea. Chalk is not easily consolidated and the Chalk Group still consists of loose sediments in many places. The group also has other limestones and arenites. Among the fossils it contains are sea urchins, belemnites, ammonites and sea reptiles such as ''Mosasaurus''.

In southern Europe, the Cretaceous is usually a marine system consisting of competent limestone beds or incompetent marls. Because the Alpine mountain chains did not yet exist in the Cretaceous, these deposits formed on the southern edge of the European continental shelf, at the margin of the Tethys Ocean.

Stagnation of deep sea currents in middle Cretaceous times caused anoxic conditions in the sea water. In many places around the world, dark anoxic shales were formed during this interval. These shales are an important source rock for oil and gas, for example in the subsurface of the North Sea.

Paleogeography

During the Cretaceous, the late-Paleozoic-to-early-Mesozoic supercontinent of Pangaea completed its tectonic breakup into present day continents, although their positions were substantially different at the time. As the Atlantic Ocean widened, the convergent-margin orogenies that had begun during the Jurassic continued in the North American Cordillera, as the Nevadan orogeny was followed by the Sevier and Laramide orogenies.

Though Gondwana was still intact in the beginning of the Cretaceous, it broke up as South America, Antarctica and Australia rifted away from Africa (though India and Madagascar remained attached to each other); thus, the South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Sea continued to narrow. Broad shallow seas advanced across central North America (the Western Interior Seaway) and Europe, then receded late in the period, leaving thick marine deposits sandwiched between coal beds. At the peak of the Cretaceous transgression, one-third of Earth's present land area was submerged.

The Cretaceous is justly famous for its chalk; indeed, more chalk formed in the Cretaceous than in any other period in the Phanerozoic. Mid-ocean ridge activity—or rather, the circulation of seawater through the enlarged ridges—enriched the oceans in calcium; this made the oceans more saturated, as well as increased the bioavailability of the element for calcareous nanoplankton. These widespread carbonates and other sedimentary deposits make the Cretaceous rock record especially fine. Famous formations from North America include the rich marine fossils of Kansas's Smoky Hill Chalk Member and the terrestrial fauna of the late Cretaceous Hell Creek Formation. Other important Cretaceous exposures occur in Europe (e.g., the Weald) and China (the Yixian Formation). In the area that is now India, massive lava beds called the Deccan Traps were erupted in the very late Cretaceous and early Paleocene.

Climate

The Berriasian epoch showed a cooling trend that had been seen in the last epoch of the Jurassic. There is evidence that snowfalls were common in the higher latitudes and the tropics became wetter than during the Triassic and Jurassic. Glaciation was however restricted to alpine glaciers on some high-latitude mountains, though seasonal snow may have existed farther south. Rafting by ice of stones into marine environments occurred during much of the Cretaceous but evidence of deposition directly from glaciers is limited to the Early Cretaceous of the Eromanga Basin in southern Australia.

After the end of the Berriasian, however, temperatures increased again, and these conditions were almost constant until the end of the period. This trend was due to intense volcanic activity which produced large quantities of carbon dioxide. The production of large quantities of magma, variously attributed to mantle plumes or to extensional tectonics, further pushed sea levels up, so that large areas of the continental crust were covered with shallow seas. The Tethys Sea connecting the tropical oceans east to west also helped in warming the global climate. Warm-adapted plant fossils are known from localities as far north as Alaska and Greenland, while dinosaur fossils have been found within 15 degrees of the Cretaceous south pole.

A very gentle temperature gradient from the equator to the poles meant weaker global winds, contributing to less upwelling and more stagnant oceans than today. This is evidenced by widespread black shale deposition and frequent anoxic events. Sediment cores show that tropical sea surface temperatures may have briefly been as warm as 42 °C (107 °F), 17 °C (63 °F) warmer than at present, and that they averaged around 37 °C (99 °F). Meanwhile deep ocean temperatures were as much as 15 to 20 °C (59 to 68 °F) higher than today's.

Life

Flora

Flowering plants (angiosperms) spread during this period, although they did not become predominant until the Campanian stage near the end of the epoch. Their evolution was aided by the appearance of bees; in fact angiosperms and insects are a good example of coevolution. The first representatives of many leafy trees, including figs, planes and magnolias, appeared in the Cretaceous. At the same time, some earlier Mesozoic gymnosperms like Conifers continued to thrive; pehuéns (Monkey Puzzle trees, ''Araucaria'') and other conifers being notably plentiful and widespread. Some fern orders such as Gleicheniales appeared as early in the fossil record as the Cretaceous, and achieved an early broad distribution. Gymnosperm taxa like Bennettitales died out before the end of the period.

Terrestrial fauna

On land, mammals were a small and still relatively minor component of the fauna. Early marsupial mammals evolved in the Early Cretaceous, with true placentals emerging in the Late Cretaceous period. The fauna was dominated by archosaurian reptiles, especially dinosaurs, which were at their most diverse stage. Pterosaurs were common in the early and middle Cretaceous, but as the Cretaceous proceeded they faced growing competition from the adaptive radiation of birds, and by the end of the period only two highly specialized families remained.

The Liaoning lagerstätte (Chaomidianzi formation) in China provides a glimpse of life in the Early Cretaceous, where preserved remains of numerous types of small dinosaurs, birds, and mammals have been found. The coelurosaur dinosaurs found there represent types of the group Maniraptora, which is transitional between dinosaurs and birds, and are notable for the presence of hair-like feathers.

During the Cretaceous, insects began to diversify, and the oldest known ants, termites and some lepidopterans, akin to butterflies and moths, appeared. Aphids, grasshoppers, and gall wasps appeared.

Marine fauna

In the seas, rays, modern sharks and teleosts became common. Marine reptiles included ichthyosaurs in the early and middle of the Cretaceous, becoming extinct during the late Cretaceous, plesiosaurs throughout the entire period, and mosasaurs appearing in the Late Cretaceous.

''Baculites'', an ammonite genus with a straight shell, flourished in the seas along with reef-building rudist clams. The Hesperornithiformes were flightless, marine diving birds that swam like grebes. Globotruncanid Foraminifera and echinoderms such as sea urchins and starfish (sea stars) thrived. The first radiation of the diatoms (generally siliceous, rather than calcareous) in the oceans occurred during the Cretaceous; freshwater diatoms did not appear until the Miocene. The Cretaceous was also an important interval in the evolution of bioerosion, the production of borings and scrapings in rocks, hardgrounds and shells (Taylor and Wilson, 2003).

Extinction

There was a progressive decline in biodiversity during the Maastrichtian stage of the Cretaceous period prior to the suggested ecological crisis induced by events at the K–T boundary. Furthermore, biodiversity required a substantial amount of time to recover from the K–T event, despite the probable existence of an abundance of vacant ecological niches.

Despite the severity of this boundary event, there was significant variability in the rate of extinction between and within different clades. Species which depended on photosynthesis declined or became extinct because of the reduction in solar energy reaching the Earth's surface due to atmospheric particles blocking the sunlight. As is the case today, photosynthesizing organisms, such as phytoplankton and land plants, formed the primary part of the food chain in the late Cretaceous. Evidence suggests that herbivorous animals, which depended on plants and plankton as their food, died out as their food sources became scarce; consequently, top predators such as ''Tyrannosaurus rex'' also perished.

Coccolithophorids and molluscs, including ammonites, rudists, freshwater snails and mussels, as well as organisms whose food chain included these shell builders, became extinct or suffered heavy losses. For example, it is thought that ammonites were the principal food of mosasaurs, a group of giant marine reptiles that became extinct at the boundary.

Omnivores, insectivores and carrion-eaters survived the extinction event, perhaps because of the increased availability of their food sources. At the end of the Cretaceous there seem to have been no purely herbivorous or carnivorous mammals. Mammals and birds which survived the extinction fed on insects, larvae, worms, and snails, which in turn fed on dead plant and animal matter. Scientists theorise that these organisms survived the collapse of plant-based food chains because they fed on detritus.

In stream communities, few groups of animals became extinct. Stream communities rely less on food from living plants and more on detritus that washes in from land. This particular ecological niche buffered them from extinction. Similar, but more complex patterns have been found in the oceans. Extinction was more severe among animals living in the water column, than among animals living on or in the sea floor. Animals in the water column are almost entirely dependent on primary production from living phytoplankton, while animals living on or in the ocean floor feed on detritus or can switch to detritus feeding.

The largest air-breathing survivors of the event, crocodilians and champsosaurs, were semi-aquatic and had access to detritus. Modern crocodilians can live as scavengers and can survive for months without food and go into hibernation when conditions are unfavourable, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms or fragments of organisms for their first few years. These characteristics have been linked to crocodilian survival at the end of the Cretaceous.

See also

Chalk Formation

List of fossil sites ''(with link directory)''

South Polar dinosaurs

Western Interior Seaway

Cretaceous Thermal Maximum

Notes

References

Neal L Larson, Steven D Jorgensen, Robert A Farrar and Peter L Larson. ''Ammonites and the other Cephalopods of the Pierre Seaway''. Geoscience Press, 1997.

Ogg, Jim; June, 2004, ''Overview of Global Boundary Stratotype Sections and Points (GSSP's)'' http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006.

Ovechkina, M.N. and Alekseev, A.S. 2005. Quantitative changes of calcareous nannoflora in the Saratov region (Russian Platform) during the late Maastrichtian warming event. ''Journal of Iberian Geology'' 31 (1): 149–165. PDF

—detailed coverage of various aspects of the evolutionary history of the insects.

Skinner, Brian J., and Stephen C. Porter. ''The Dynamic Earth: An Introduction to Physical Geology''. 3rd ed. New York: John Wiley & Sons, Inc., 1995. ISBN 0-471-60618-9}

Stanley, Steven M. ''Earth System History''. New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6

Taylor, P.D. and Wilson, M.A., 2003. Palaeoecology and evolution of marine hard substrate communities. Earth-Science Reviews 62: 1–103.

External links

UCMP Berkeley Cretaceous page

Bioerosion website at The College of Wooster

Cretaceous Microfossils: 180+ images of Foraminifera

Category:Mesozoic

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name	Ron Jarzombek
background	non_vocal_instrumentalist
origin	San Antonio, Texas, United States
instrument	Guitar
genre	Progressive metal, heavy metal, thrash metal, technical death metal
years active	1984–present
associated acts	Blotted Science, Terrestrial Exiled, Spastic Ink, WatchTower, S.A.Slayer, Gordian Knot, Marty Friedman, Happy Kitties
website	RonJarzombek.com }}

Ron Jarzombek is an American guitarist best known for his work with Austin, Texas progressive metal trailblazers WatchTower, '90s madcap trio, Spastic Ink, technical extreme metal band Blotted Science, featuring Cannibal Corpse bassist Alex Webster and Obscura drummer Hannes Grossmann, and most recently Terrestrial Exiled, an all-star instrumental quartet, featuring Spastic Ink bassist Pete Perez and Obscura members Christian Muenzner and Hannes Grossmann.

Jarzombek has also guested with a number of artists ranging from fellow guitarists Marty Friedman and Jeff Loomis to death metal outfits Obscura and Odious Mortem, and collaborated with Cynic off-shoot Gordian Knot as well as Lamb of God drummer Chris Adler. He also teaches guitar in San Antonio, Texas.

Influence

Ron has been hailed as one of the most influential progressive metal guitarists and has been called ''"the Godfather of Technical Metal."'' He has been cited as an influence by numerous players, particularly from the burgeoning technical death metal scene, most prominently Muhammed Suiçmez of Necrophagist. Ron is also featured in the 2009 book ''The 100 Greatest Metal Guitarists'' by British author Joel McIver who calls Jarzombek ''"the most underrated axemonger ever”.'' Decibel Magazine remarked, ''"Ron Jarzombek should be a friggin’ legend by now"'' in its review of Blotted Science's ''The Machinations of Dementia''.

Soundtrack work

Ron wrote several exclusive pieces for Atlanta, GA-based Morley Arts Productions, a small animation company. These include the intro to a proposed science fiction short film titled Magnatania and bits featured on the Morley Arts 2005 demo reel which starts off with 'See and It's Sharp' by Spastic Ink. Another unreleased piece utilized was the Vai-esque Martians Marchin', originally meant to be a 'soundtrack for' a lithograph called ''House of Stairs'' by M.C. Escher. In 2004, the animated 15-minute space mini-epic Time Ace, produced by Morley Arts and featuring two of Jarzombek's compositions, was awarded 'Best Animation' by a jury of film industry professionals in clickflick.tv's online film festival.

Family

Ron is the youngest of three musical brothers, Ralph, a keyboard player, and drummer Bobby Jarzombek, with whom he formed a short-lived project named Happy Kitties in the mid 1980's and collaborated with more extensively in Spastic Ink in the 1990s.

Equipment

Jarzombek plays custom-made guitars he builds himself, the reason being that ''"I am rather selective when it comes to guitars. For me, it's easier to build a guitar totally from scratch than to buy something off the shelf and customize it. The necks are taken off of guitars that I come across at local music stores."''

Discography

Albums:

(2011) Blotted Science - ''The Animation of Entomology'' (''EclecticElectric'')

(2009) Ron Jarzombek (solo) - ''PHHHP! Plus'' (''EclecticElectric'')

(2007) Blotted Science - ''The Machinations of Dementia'' (''EclecticElectric''; released by ''Marquee/Avalon'' in Japan in 2011)

(2007) Marty Friedman - ''Exhibit A - Live In Europe'' (''Avex Entertainment''; released by ''Mascot Records'' in 2008)

(2004) Spastic Ink - ''Ink Compatible'' (''EclecticElectric / Marquee Avalon'')

(2002) Ron Jarzombek (solo) - ''Solitarily Speaking Of Theoretical Confinement'' (''Mr. Kitty'')

(2002) WatchTower - ''Demonstrations in Chaos'' (archives release) (''Monster Records'')

(1998) Gordian Knot - ''Gordian Knot'' (''Sensory'')

(1998) Ron Jarzombek (solo) - ''PHHHP!'' (''Mr. Kitty'')

(1997) Spastic Ink - ''Ink Complete'' (''Dream Circle'', re-released by ''EclecticElectric'' in 2000'')

(1989) WatchTower - ''Control And Resistance'' (''Noise Records'')

(1988) S.A.Slayer - ''Go For The Throat'' (''Under Den Linden'')

Singles:

(2011) Terrestrial Exiled - ''Duodecimal Levorotation'' (digital release)

(2010) WatchTower - ''The Size of Matter'' (digital release)

Compilations & guest appearances:

(2010) Ray Riendeau - ''Atmospheres'' (guest guitar solo on "A Search For Lifeforms") (''Groove Theory Records'')

(2009) Obscura - ''Cosmogenesis'' (guest guitar solo on "Cosmogenesis") (''Relapse Records'')

(2008) Jeff Loomis - ''Zero Order Phase'' (guest guitar solo on "Jato Unit") (''Century Media'')

(2008) The Fractured Dimension - ''Towards the Mysterium'' (guest guitar solo on "Towards the Mysterium") (''Independent'')

(2007) Odious Mortem - ''Cryptic Implosion'' (guest guitar solo on "Collapse Of Recreation") (''Willowtip Records'')

(2006) Various Artists - ''Drum Nation Vol.3'' (''Magna Carta'') w/ Chris Adler

(2006) Loch Vostok - ''Destruction Time Again!'' (guest guitar solo on "Talk") (''Escapi Music'')

(1999) Various Artists - ''A Tribute To Accept Vol.1'' (''Nuclear Blast'') w/ WatchTower

(1998) Various Artists - ''The Music Of Raymond Scott'' (''Esotericity'')

(1996) Various Artists - ''12 Years In Noise: Metal & Beyond'' [2-CD] (''Noise Records'') w/ WatchTower

(1989) Various Artists - ''Doomsday News 2'' (''Noise Records'') w/ WatchTower

Videos & DVDs:

(2007) Marty Friedman - ''Exhibit B - Live In Japan'' (''Avex Entertainment'')

(2006) Chris Adler / Jason Bittner - ''Live At Modern Drummer Festival 2005'' (Hudson Music)+

(2005) Bobby Jarzombek - ''Performance & Technique'' (''Warner Bros. Publications'')+

(1990) Various Artists - ''Doomsday News - The Video Compilation Volume 2'' (''Noise Records'') w/ WatchTower

''+ NOTE: Ron is not seen but rather heard as the guitarist and co-writer of some of the music on these DVDs!''

External links

Ron Jarzombek website

Ron Jarzombek YouTube channel

Ron Jarzombek MySpace page

Ron Jarzombek Facebook page

2010 interview with Ron Jarzombek on Prog Sphere

References

Category:People from San Antonio, Texas Category:American heavy metal guitarists Category:Living people Category:Year of birth missing (living people)

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