Or  search
Oran  search
SNNo longer a valid term for GeoRef. Valid 1978-1981. As of 1982, see Oran region for the department of French Algeria. As of 1993, see Oran Algeria for the department.
Oran Algeria  search
BTAfrica
 .North Africa
 ..Algeria
 ...Oran Algeria
NTDescartes Algeria
SNDepartment. NW coast. Before 1993, also search Oran region.
Oran region  search
SNNo longer a valid term for GeoRef. Used as large department of French Algeria. As of 1993, see Algeria for departments.
Orange County California  search
BTUnited States
 .California
 ..Orange County California
NTSanta Ana California
RTSan Jacinto Fault
 San Pedro Bay
 Newport Bay
 Santa Ana Mountains
 Santa Ana River
SNS California.
Orange County Florida  search
BTUnited States
 .Florida
 ..Orange County Florida
SNCentral Florida.
Orange County Indiana  search
BTIndiana
 .Orange County Indiana
SNS Indiana.
Orange County New York  search
BTUnited States
 .New York
 ..Orange County New York
NTPort Jervis New York
SNSE New York.
Orange County North Carolina  search
BTUnited States
 .North Carolina
 ..Orange County North Carolina
SNN central North Carolina.
Orange County Texas  search
BTUnited States
 .Texas
 ..Orange County Texas
RTSabine Lake
SNSE Texas.
Orange County Vermont  search
BTUnited States
 .Vermont
 ..Orange County Vermont
SNCentral and E Vermont.
Orange County Virginia  search
BTUnited States
 .Virginia
 ..Orange County Virginia
SNN central Virginia.
Orange Free State South Africa  search
USEFree State South Africa
orange material  search
RTMoon
Orange River  search
BTAfrica
 .Southern Africa
 ..Orange River
RTNamibia
 Cape Province region
 Northern Cape Province South Africa
 Eastern Cape Province South Africa
 Free State South Africa
 Lesotho
SNRises in the Drakensberg Range in Lesotho and flows W into the Pacific Ocean. Indexed with Namibia, Lesotho and provinces of South Africa.
Orangeburg County South Carolina  search
BTUnited States
 .South Carolina
 ..Orangeburg County South Carolina
Orava Valley  search
BTEurope
 .Central Europe
 ..Slovakia
 ...Orava Valley
SNRiver valley in N Slovakia. Also search Orava.
orbicular texture  search
BTtextures
 .orbicular texture
RTspherulites
SNBefore 1978, search orbicular AND texture.
orbit  search
USEorbits
orbital forcing  search
UFclimatic orbital forcing
 Milankovitch forcing
RTsedimentation
 climate
 paleoclimatology
 paleo-oceanography
 climate effects
 climatic controls
 cyclic processes
 periodicity
 Milankovitch theory
SNAlso search Milankovitch theory if applicable. Added to Thesaurus in 1998.
orbital motion  search
USEorbits
orbital observations  search
RTobservations
 orbits
 remote sensing
 satellite methods
SNBefore 1978, search observations AND orbital.
Orbitoidacea  search
BTInvertebrata
 .Protista
 ..Foraminifera
 ...Rotaliina
 ....Orbitoidacea
NTAmphistegina
 Asterocyclina
 Cibicides
 Discocyclina
 Lepidocyclina
 Nephrolepidina
 Orbitoididae
RTmicrofossils
SNIndexed with microfossils if applicable.
Orbitoidae  search
USEOrbitoididae
Orbitoididae  search
BTInvertebrata
 .Protista
 ..Foraminifera
 ...Rotaliina
 ....Orbitoidacea
 .....Orbitoididae
UFOrbitoidae
RTmicrofossils
SNIndexed with microfossils if applicable.
Orbitolina  search
BTInvertebrata
 .Protista
 ..Foraminifera
 ...Textulariina
 ....Lituolacea
 .....Orbitolinidae
 ......Orbitolina
RTmicrofossils
SNGenus. Indexed with microfossils if applicable.
Orbitolinidae  search
BTInvertebrata
 .Protista
 ..Foraminifera
 ...Textulariina
 ....Lituolacea
 .....Orbitolinidae
NTOrbitolina
RTmicrofossils
SNFamily. Indexed with microfossils if applicable.
orbits  search
UForbit
 orbital motion
 planetary orbits
RTmotions
 planetology
 extraterrestrial geology
 satellite methods
 orbital observations
Orbulina  search
BTInvertebrata
 .Protista
 ..Foraminifera
 ...Rotaliina
 ....Globigerinacea
 .....Globigerinidae
 ......Orbulina
NTOrbulina universa
RTmicrofossils
SNGenus. Indexed with microfossils if applicable.
Orbulina universa  search
BTInvertebrata
 .Protista
 ..Foraminifera
 ...Rotaliina
 ....Globigerinacea
 .....Globigerinidae
 ......Orbulina
 .......Orbulina universa
RTmicrofossils
SNSpecies. Indexed with microfossils if applicable.
Orca Basin  search
BTAtlantic Ocean
 .North Atlantic
 ..Gulf of Mexico
 ...Orca Basin
RTDSDP Site 618
SNDepression on the continental slope of the N central Gulf of Mexico, containing brines. Added to Thesaurus in 1981.
Orca Group  search
BTChronostratigraphic Units
 .Phanerozoic
 ..Cenozoic
 ...Paleogene
 ....Orca Group
RTPaleocene
 Eocene
 Alaska
SNS central Alaska. Indexed with ages as applicable. Added to Thesaurus in 1989.
Orcadian Basin  search
BTAtlantic Ocean
 .North Atlantic
 ..North Sea
 ...Orcadian Basin
RTScotland
 Orkney Islands
SNOffshore NE Scotland, in the North Sea. Added to Thesaurus in 1989.
order-disorder  search
RTamorphous materials
 bonding
 crystal chemistry
 substitution
ordinary chondrites  search
BTmeteorites
 .stony meteorites
 ..chondrites
 ...ordinary chondrites
RTenstatite chondrites
 carbonaceous chondrites
SNAdded to Thesaurus in 1985.
Ordos Basin  search
BTAsia
 .Far East
 ..China
 ...Ordos Basin
UFEerduosi Basin
 Erduos Basin
RTInner Mongolia China
 Shanxi China
 Gansu China
 Ningxia China
 Shaanxi China
SNNE central China. Before 1995, also search Eerduos Basin. Added to Thesaurus in 1989.
Ordovician  search
BTChronostratigraphic Units
 .Phanerozoic
 ..Paleozoic
 ...Ordovician
NTLower Ordovician
 Middle Ordovician
 Upper Ordovician
 Antelope Valley Limestone
 Bala
 Betts Cove Ophiolite
 Borrowdale Volcanic Series
 Buchans Group
 Catoche Formation
 Chickamauga Group
 Clays Ferry Formation
 Davidsville Group
 Ely Springs Dolomite
 Eureka Quartzite
 Gander Lake Group
 Gull River Formation
 Ledbetter Slate
 Lushs Bight Group
 Martinsburg Formation
 Meguma Group
 Montoya Group
 Pogonip Group
 Shap Granite
 Skiddaw Slates
 Tetagouche Group
 Valmy Formation
 Vinini Formation
 Viola Limestone
 Viruan
 Womble Shale
RTBowers Supergroup
 Ellis Bay Formation
 Berwick Formation
 Merrimack Group
 Collier Shale
 Cow Head Group
 Delamerian Orogeny
 Elberton Granite
 Henderson Gneiss
 New York City Group
 Hanson Creek Formation
 Lincolnshire Limestone
 Kittery Formation
 Penobscot Formati
SNAfter the Cambrian, before the Silurian.
Ordubad Azerbaijan  search
BTEurope
 .Azerbaijan
 ..Nakhichevan Azerbaijan
 ...Ordubad Azerbaijan
SNCity in Nakhichevan Autonomous Soviet Socialist Republic (W enclave of Azerbaijan). This term has multiple hierarchies.
ore bodies  search
UFbodies, ore
RTmineral deposits, genesis
 metal ores
 blind deposits
 chimneys
 size
ore deposits  search
SNAs of 1981, no longer a valid term for GeoRef. Before 1981, included use for all papers on metal commodities. Was sometimes used in combination with origin (i.e. ore deposits, origin). Now use metal ores; mineral deposits, genesis; mineral resources or sp
ore exploration  search
USEmineral exploration
ore finding  search
SNNot a valid index term for GeoRef. See mineral exploration.
ore grade  search
RTcutoff grade
 economic geology
 evaluation
 grade
 metal ores
 mineral economics
 mineral exploration
 production
 productive capacity
 reserves
 tonnage
SNAdded to Thesaurus in 1985.
ore guides  search
UFguides, ore
RTmetal ores
 mineral exploration
 gossan
ore microscopy  search
UFmicroscopy, ore
 mineragraphy
RTmetal ores
 microscope methods
 mineralogy
 optical mineralogy
 universal stage
ore minerals  search
RTeconomic geology
 metal ores
 metals
 minerals
 ore-forming fluids
 platinum minerals
 uranium minerals
ore of sedimentation  search
USEplacers
ore reflectivity  search
RTmetal ores
 mineral deposits, genesis
 reflectance
SNBefore 1982, reflectivity was used for this term. Added to Thesaurus in 1982.
ore rolls  search
USEroll-type deposits
ore sources  search
SNAs of 1981, no longer a valid term for GeoRef. See mineral deposits, genesis.
ore transport  search
SNNo longer a valid term for GeoRef. As of 1995, see mineral deposits, genesis for specific natural processes and controls involved, e.g. epigene processes, ore-forming fluids. Before 1978, ore deposits AND transport was used.
ore-forming fluids  search
UFfluids, ore-forming
RTmineral deposits, genesis
 hydrothermal alteration
 mineralization
 ore minerals
SNBefore 1981, also search mineralizers; hydrothermal solutions; hydrothermal fluids.
Oread Limestone  search
BTChronostratigraphic Units
 .Phanerozoic
 ..Paleozoic
 ...Carboniferous
 ....Pennsylvanian
 .....Upper Pennsylvanian
 ......Virgilian
 .......Oread Limestone
RTIowa
 Missouri
 Oklahoma
 Nebraska
 Kansas
 Shawnee Group
 Plattsmouth Limestone Member
SNIn Shawnee Group. Includes Toronto Limestone, Snyderville Shale, Leavenworth Limestone, Heebner Shale, Plattsmouth Limestone, Heumader Shale, Kereford Limestone members. SW Iowa, E Kansas, NW Missouri, SE Nebraska, and N Oklahoma.
orebodies, hidden  search
USEblind deposits
Orebro Sweden  search
BTEurope
 .Western Europe
 ..Scandinavia
 ...Sweden
 ....Orebro Sweden
NTStripa region
UFOerebro Sweden
RTBergslagen
SNCounty and city in S central Sweden.
Oregon  search
BTUnited States
 .Oregon
NTBaker County Oregon
 Benton County Oregon
 Brothers fault zone
 Clackamas County Oregon
 Clatsop County Oregon
 Columbia County Oregon
 Coos County Oregon
 Crook County Oregon
 Curry County Oregon
 Deschutes County Oregon
 Douglas County Oregon
 Gilliam County Oregon
 Grant County Oregon
 Harney County Oregon
 Hood River County Oregon
 Jackson County Oregon
 Jefferson County Oregon
 Josephine County Oregon
 Klamath County Oregon
 Lake County Oregon
 Lane County Oregon
 Lincoln County Oregon
 Linn County Oregon
 Malheur County Oregon
 Marion County Oregon
 Morrow County Oregon
 Mount Hood
 Multnomah County Oregon
 Polk County Oregon
 Rogue River
 Sherman County Oregon
 Tillamook County Oregon
 Umatilla County Oregon
 Union County Oregon
 Wallowa County Oregon
 Wallowa Mountains
 Wasco County Oregon
 Washington County Oregon
 Wheeler County Oregon
 Willamette River
 Willamette Valley
 Yamhill County Oregon
RTAstoria
Oregon County Missouri  search
BTUnited States
 .Missouri
 ..Oregon County Missouri
Orenburg Russian Federation  search
BTCommonwealth of Independent States
 .Russian Federation
 ..Orenburg Russian Federation
BTEurope
 .Orenburg Russian Federation
NTBlyava
 Orsk Russian Federation
 Romashkino Field
 Sakmara Russian Federation
UFChkalov Russian Federation
RTUral region
 Sakmara Zone
SNOblast and city in the Southern Urals in European Russian Federation. Before 1993, also search Chkalov Russian Republic. This term has multiple hierarchies. Indexed with Europe if applicable.
Orense City Spain  search
BTEurope
 .Southern Europe
 ..Iberian Peninsula
 ...Spain
 ....Galicia Spain
 .....Orense Spain
 ......Orense City Spain
SNRefers to only the city in NW Spain. Before 1993, also search Orense Spain.
Orense Spain  search
BTEurope
 .Southern Europe
 ..Iberian Peninsula
 ...Spain
 ....Galicia Spain
 .....Orense Spain
NTOrense City Spain
SNRefers only to the province in NW Spain. From 1981-1992, also search Orense Province and Spain. For the city, see Orense City Spain.
ores  search
SNNot a valid term for GeoRef. Use specific commodity terms (see list C) or mineral resources or mineral deposits, genesis.
ores in sedimentary rocks  search
SNA valid term through 1973. Use sedimentary rocks or sedimentation in conjunction with the individual ore (list C).
ores, polymetallic  search
USEpolymetallic ores
Oresund  search
BTAtlantic Ocean
 .North Atlantic
 ..Oresund
RTBaltic Sea
 Sweden
 Denmark
 Kattegat
SNStrait connecting the Kattegat with the Baltic Sea. Indexed with Kattegat and/or Baltic Sea as applicable.
organic  search
SNA valid term through 1977. As of 1998, use organic compounds if applicable.
organic acids  search
BTorganic compounds
 .organic acids
NTamino acids
 carboxylic acids
 fatty acids
 fulvic acids
 humic acids
RTacids
 DNA
 inorganic acids
 RNA
 ketones
SNMay be used for groups of several organic acids or when more specific term is not known. Added to Thesaurus in 1981.
organic carbon  search
BTcarbon
 .organic carbon
RTorganic compounds
 total organic carbon
 carbon cycle
SNAlso search organic compounds AND carbon.
organic compounds  search
NTacetate
 alcohols
 carbohydrates
 chlorophenols
 dioxins
 esters
 fullerenes
 halogenated hydrocarbons
 humates
 hydrocarbons
 isoprenoids
 ketones
 lignin
 organic acids
 peptides
 phenols
 pigments
 proteins
 sapropel
 sporopollenin
 steroids
 total organic carbon
 volatile organic compounds
RTanthraxolite
 asphalt
 biochemistry
 biomarkers
 bitumens
 carbon
 carbonaceous composition
 caustobiolith
 chelation
 chitin
 clathrates
 coal
 color alteration index
 complexing
 compounds
 creosote
 crude oil
 epimerization
 gas sands
 gasoline
 gilsonite
 grahamite
 humic
SNCompounds may be naturally occurring or manufactured. For economic deposits, use petroleum, coal or other appropriate commodity terms in list C. For minerals, use organic minerals. See sedimentary rocks or sediments for discussions of their organic compos
organic materials  search
SNNo longer a valid term for GeoRef. Was used for discussions of naturally occurring organic materials before 1998. Now use organic compounds. For economic deposits, use petroleum, coal or other appropriate commodity terms in list C. For minerals, search or
organic minerals  search
NTamber
 ozocerite
RTgilsonite
 grahamite
 organic compounds
 porphyrins
organic mound  search
USEbioherms
organic nitrogen  search
BTnitrogen
 .organic nitrogen
RTorganic compounds
SNAlso search organic compounds AND nitrogen.
organic residues  search
SNNo longer a valid term for GeoRef. As of 1998, see sediments or sedimentary rocks. From 1978-1997, this term was used in hierarchies with both sediments and sedimentary rocks. From 1981-1992, macerals was used as a narrower term. Before 1981, organic sedi
organic sediments  search
SNAs of 1981, no longer a valid term for GeoRef. Use sediments. Term was introduced in 1976.
organic sulfur  search
BTsulfur
 .organic sulfur
RTorganic compounds
SNBefore 1998, also search organic compounds AND sulfur. Added to Thesaurus in 1993.
organisms  search
USEbiota
organization  search
RTacademic institutions
 associations
 government agencies
 museums
 survey organizations
 symposia
organo-metallic complexes  search
USEorgano-metallics
organo-metallic compounds  search
USEorgano-metallics
organo-metallics  search
UForgano-metallic complexes
 organo-metallic compounds
RTgeochemistry
 organic compounds
 porphyrins
 ligands
 methylmercury
SNAdded to Thesaurus in 1981.
Orgon III  search
RTAtlantic Ocean
 expeditions
 marine geology
 marine sediments
 oceanography
SNOceanographic expedition. Added to Thesaurus in 1985.
Orgueil Meteorite  search
BTmeteorites
 .stony meteorites
 ..chondrites
 ...carbonaceous chondrites
 ....Orgueil Meteorite
UFMontauban Meteorite
RTFrance
 Tarn-et-Garonne France
SNBefore 1981, also search Montauban AND meteorites; Orgueil AND meteorites. Added to Thesaurus in 1981.
orientation  search
RTdip
 discordant folds
 drag folds
 fabric
 faults
 folds
 horizontal orientation
 inclined folds
 linear orientation
 lineation
 nappes
 navigation
 oblique orientation
 overturned folds
 petrofabrics
 plunging folds
 preferred orientation
 recumbent folds
 schistosity
 str
SNIncludes use as attitude of fold elements with respect to external coordinates.
Oriente  search
SNNo longer a valid term for GeoRef. See Santiago de Cuba.
Oriente Cuba  search
USESantiago de Cuba
origin  search
SNA valid index term through 1977 used in combination with life. Before 1971, was used sometimes used alone or in combination with ore deposits or mineral deposits (i.e. ore deposits, origin; mineral deposits, origin). Also see provenance or genesis or pedo
Orin  search
Orinoco Basin  search
USEOrinoco River basin
Orinoco Belt  search
BTSouth America
 .Venezuela
 ..Orinoco Belt
RTCerro Negro
SNPetroliferous region in Venezuela. Added to Thesaurus in 1989.
Orinoco Delta  search
BTSouth America
 .Venezuela
 ..Orinoco Delta
UFOrinoco River delta
RTOrinoco River
SNOn Atlantic Ocean in Delta Amacuro Territory, NE Venezuela. Added to Thesaurus in 1989.
Orinoco River  search
BTSouth America
 .Orinoco River
RTColombia
 Venezuela
 Amazonas Brazil
 Amazonas Colombia
 Amazonas Venezuela
 Anzoategui Venezuela
 Bolivar Venezuela
 Orinoco River basin
 Guarico Venezuela
 Monagas Venezuela
 Orinoco Delta
SNRises in the Serra Parima of S Venezuela, flows W across Amazonas, then flows N along the Colombia-Venezuela border, turns E in central Venezuela and empties through a wide delta into the Atlantic Ocean. Also search Orinoco. Indexed with countries as appl
Orinoco River basin  search
BTSouth America
 .Orinoco River basin
UFOrinoco Basin
RTColombia
 Venezuela
 Orinoco River
 Llanos
SNDrainage basin of the Orinoco River. Indexed with countries as applicable. Added to Thesaurus in 1989.
Orinoco River delta  search
USEOrinoco Delta
Oriskany Sandstone  search
BTChronostratigraphic Units
 .Phanerozoic
 ..Paleozoic
 ...Devonian
 ....Lower Devonian
 .....Oriskany Sandstone
RTVirginia
 Pennsylvania
 New York
 Maryland
 West Virginia
SNComprises Shriver Chert, and Ridgeley Sandstone Member. W Maryland, New York, Pennsylvania, Western Virginia and E West Virginia.
Orissa India  search
BTAsia
 .Indian Peninsula
 ..India
 ...Orissa India
NTBalasore India
 Bolangir India
 Cuttack India
 Dhenkanal India
 Keonjhar India
 Koraput India
 Mayurbhanj India
 Sambalpur India
 Talchir
 Talchir coal field
RTDeccan Plateau
 Singhbhum Granite
 Singhbhum shear zone
 Gangpur Series
 Kamthi Formation
 Mahanadi Valley
 Rampur coal field
 Talchir Series
SNState on the Bay of Bengal in E India.
Orivesi Finland  search
BTEurope
 .Western Europe
 ..Scandinavia
 ...Finland
 ....Western Finland Province
 .....Orivesi Finland
SNTown, SW central Finland. Before 1998, may also have been used for an administrative region.
Orizaba, Pico de  search
USEPico de Orizaba
Orkney Islands  search
BTEurope
 .Western Europe
 ..United Kingdom
 ...Great Britain
 ....Scotland
 .....Orkney Islands
UFOrkney region Scotland
RTAtlantic Ocean Islands
 South Orkney Islands
 Orcadian Basin
SNArchipelago off NE coast of Scotland.
Orkney region Scotland  search
USEOrkney Islands
Orleans County New York  search
BTUnited States
 .New York
 ..Orleans County New York
Orleans County Vermont  search
BTUnited States
 .Vermont
 ..Orleans County Vermont
Orleans France  search
BTEurope
 .Western Europe
 ..France
 ...Loiret France
 ....Orleans France
SNCity in N central France.
Orleans Parish Louisiana  search
BTUnited States
 .Louisiana
 ..Orleans Parish Louisiana
NTNew Orleans Louisiana
SNSE Louisiana, coextensive with New Orleans.
Orlov Russian Federation  search
BTCommonwealth of Independent States
 .Russian Federation
 ..Orlov Russian Federation
RTVyatka Russian Federation
SNOld name for city of Khalturin just W of Vyatka in Vyatka Oblast of European Russian Federation. May occur in other locations. Before 1993, Orlov Russian Republic was also used. Indexed with oblast as applicable.
ornamental materials  search
RTCarrara Marble
 ceramic materials
 clays
 construction materials
 granite deposits
 jadeite
 limestone deposits
 marble deposits
 materials
 rhodonite
SNMay be used as a commodity term with terms such as granite deposits, limestone deposits, marble deposits and construction materials. Added to Thesaurus in 1982.
ornamentation  search
RTpaleontology
 shells
Orne France  search
BTEurope
 .Western Europe
 ..France
 ...Orne France
NTMortagne France
RTNormandy
 Eure Valley
SNDepartment in NW France.
Ornithischia  search
BTChordata
 .Vertebrata
 ..Tetrapoda
 ...Reptilia
 ....Diapsida
 .....Archosauria
 ......Ornithischia
BTChordata
 .Vertebrata
 ..Tetrapoda
 ...Reptilia
 ....dinosaurs
 .....Ornithischia
NTAnkylosauria
 Ceratopsia
 Ornithopoda
 Stegosaurus
SNOrder. This term has multiple hierarchies.
Ornithopoda  search
BTChordata
 .Vertebrata
 ..Tetrapoda
 ...Reptilia
 ....Diapsida
 .....Archosauria
 ......Ornithischia
 .......Ornithopoda
NTHadrosauridae
SNThis term has multiple hierarchies.
ORNL  search
USEOak Ridge National Laboratory
oroclines  search
BTorogenic belts
 .oroclines
RTtectonics
 plate tectonics
SNOrogenic belts that curve sharply, possibly due to horizontal bending of the crust. Added to Thesaurus in 1989.
Orocopia Schist  search
BTChronostratigraphic Units
 .Phanerozoic
 ..Mesozoic
 ...Orocopia Schist
RTCalifornia
 Arizona
SNS California and SW Arizona. Added to Thesaurus in 1989.
orogenesis  search
USEorogeny
orogenic belts  search
NToroclines
RTclastic wedges
 fold and thrust belts
 fold belts
 foreland basins
 forelands
 geosynclines
 intracontinental belts
 mobile belts
 orogeny
 tectonics
SNAdded to Thesaurus in 1981.
orogeny  search
UForogenesis
 tectogenesis
RTabsolute age
 Acadian Phase
 Antler Orogeny
 Alice Springs Orogeny
 Alleghany Orogeny
 Alpine Orogeny
 Andean Orogeny
 Appalachian Phase
 Cadomian Orogeny
 Assyntic Orogeny
 Asturian Orogeny
 Avalonian Orogeny
 back-arc basins
 Baikalian Phase
 Caledonian Orogeny
 Cimme
SNUsed for discussions of either individual orogenies or detailed general treatments on several orogenies. Before 1974, also search mountain building. Before 1981, also search diastrophism if applicable.
Orogrande Basin  search
BTUnited States
 .Orogrande Basin
RTNew Mexico
 Texas
 Sierra County New Mexico
 Dona Ana County New Mexico
 El Paso County Texas
 Hudspeth County Texas
 Otero County New Mexico
 Socorro County New Mexico
 Lincoln County New Mexico
SNPetroleum-producing region in S New Mexico and W Texas. Indexed with states and counties as applicable. Added to Thesaurus in 1989.
Oronto Group  search
BTChronostratigraphic Units
 .Precambrian
 ..Proterozoic
 ...Oronto Group
RTWisconsin
 Minnesota
 Michigan
 Freda Sandstone
 Nonesuch Shale
SNKeweenawan. Includes Freda Sandstone. Added to Thesaurus in 1989.
Orosei  search
BTMediterranean Sea
 .West Mediterranean
 ..Tyrrhenian Sea
 ...Orosei
RTSardinia Italy
SNGulf of Tyrrhenian Sea. As of 1993, see Orosei Italy for the village.
Orosei Italy  search
BTEurope
 .Southern Europe
 ..Italy
 ...Sardinia Italy
 ....Orosei Italy
SNVillage in Sardinia.
Orosian  search
BTChronostratigraphic Units
 .Precambrian
 ..Proterozoic
 ...Paleoproterozoic
 ....Orosian
Oroville California  search
BTUnited States
 .California
 ..Butte County California
 ...Oroville California
SNCity in N California. Site of August, 1975 earthquake.
Oroville Dam  search
BTUnited States
 .California
 ..Butte County California
 ...Oroville Dam
RTFeather River
SNEarth fill dam on Feather River which forms Oroville Reservoir in Butte County of N central California. Also search (Oroville Reservoir OR reservoirs OR dams) AND Oroville California.
Oroville earthquake 1975  search
BTearthquakes
 .Oroville earthquake 1975
RTCalifornia
 Butte County California
SNButte County, N California. Added to Thesaurus in 1989.
Orozco fracture zone  search
BTPacific Ocean
 .North Pacific
 ..Northeast Pacific
 ...Orozco fracture zone
RTEast Pacific Rise
SNEast Pacific Rise, E Pacific. This term has multiple hierarchies. Added to Thesaurus in 1989.
orpiment  search
BTsulfides
 .orpiment
UFyellow arsenic
Orr Formation  search
BTChronostratigraphic Units
 .Phanerozoic
 ..Paleozoic
 ...Cambrian
 ....Upper Cambrian
 .....Orr Formation
RTUtah
SNW Utah. Added to Thesaurus in 1985.
Orsha Belarus  search
BTEurope
 .Belarus
 ..Orsha Belarus
SNCity in Vitebsk Oblast in N Belarus. This term has multiple hierarchies.
Orsk Russian Federation  search
BTCommonwealth of Independent States
 .Russian Federation
 ..Orenburg Russian Federation
 ...Orsk Russian Federation
SNCity in Orenburg Oblast in Southern Urals near the Kazakh border. Before 1993, Orsk Russian Republic was also used. This term has multiple hierarchies.
Ortega Group  search
BTChronostratigraphic Units
 .Precambrian
 ..Proterozoic
 ...Ortega Group
RTNew Mexico
SNN New Mexico. Added to Thesaurus in 1989.
Orthida  search
BTInvertebrata
 .Brachiopoda
 ..Articulata
 ...Orthida
NTEnteletacea
orthite  search
USEallanite
ortho-amphibolite  search
USEorthoamphibolite
orthoamphibole  search
BTsilicates
 .chain silicates
 ..amphibole group
 ...orthoamphibole
NTanthophyllite
 gedrite
 holmquistite
orthoamphibolite  search
BTmetamorphic rocks
 .amphibolites
 ..orthoamphibolite
UFortho-amphibolite
orthoclase  search
BTsilicates
 .framework silicates
 ..feldspar group
 ...alkali feldspar
 ....orthoclase
RTadularia
 K-feldspar
 anorthoclase
 sanidine
orthoenstatite  search
USEenstatite
orthogneiss  search
BTmetamorphic rocks
 .gneisses
 ..orthogneiss
SNAdded to Thesaurus in 1981.
Orthoptera  search
BTInvertebrata
 .Arthropoda
 ..Mandibulata
 ...Insecta
 ....Pterygota
 .....Neoptera
 ......Exopterygota
 .......Orthoptera
RTOrthopteroida
SNOrder. Also search Orthopteroida if applicable.
Orthopteroida  search
BTInvertebrata
 .Arthropoda
 ..Mandibulata
 ...Insecta
 ....Pterygota
 .....Neoptera
 ......Orthopteroida
RTOrthoptera
SNAlso search Orthoptera if applicable.
orthopyroxene  search
BTsilicates
 .chain silicates
 ..pyroxene group
 ...orthopyroxene
NTenstatite
 hypersthene
 protoenstatite
RTorthopyroxenite
orthopyroxenite  search
BTigneous rocks
 .plutonic rocks
 ..ultramafics
 ...orthopyroxenite
RTwebsterite
 pyroxenite
 orthopyroxene
orthoquartzite  search
BTsedimentary rocks
 .clastic rocks
 ..orthoquartzite
UForthoquartzitic sandstone
 sedimentary quartzite
RTsandstone
 terrigenous materials
 ferruginous quartzite
 quartzites
 quartz arenite
orthoquartzitic sandstone  search
USEorthoquartzite
orthorhombic  search
USEorthorhombic system
orthorhombic system  search
BTcrystal systems
 .orthorhombic system
UForthorhombic
RTcrystallography
SNAdded to Thesaurus in 1985.
orthosilicates  search
BTsilicates
 .orthosilicates
NTbritholite
 ellenbergerite
 nesosilicates
 sorosilicates
SNSorosilicates and nesosilicates.
Orulgan Mountains  search
BTCommonwealth of Independent States
 .Russian Federation
 ..Yakutia Russian Federation
 ...Orulgan Mountains
SNExtend N and S, E of Lena River in N central Russian Federation. Before 1978, also search Orulgan. This term has multiple hierarchies.
Oruro Bolivia  search
BTSouth America
 .Bolivia
 ..Oruro Bolivia
SNDepartment and city in W Bolivia on the Chilean border.