OVERVIEW OF GEOLOGIC EVENTS  (chronostratigraphy after Gradstein et al., 2004)

All directions given relative to present coordinates; in general, events listed by period from east to west

Late Proterozoic (600 - 542 Ma)

• Passive margins followed rifting along Eastern, Southern, and Western North America
• Like many rifted margins, partially rifted blocks of NAM probably stranded off coasts (eg. Madagascar)
• PreCordilleran and Taconian terranes much farther traveled
• Iapetus Ocean to S and E, Panthalassa Ocean to N and W

 

Cambrian (542 - 488 Ma)

• Complex transgressive patterns of sedimentation onto NAM
• Early patterns of convergence in N Iapetus Ocean marked by Finnmarkian and Grampian orogenies
• West-facing Taconic arc and microcontinents (previously rifted NAM fragments?) close on eastern NAM
• Transcontinental arch forms positive, though not necessarily continuous NE-SW ridge
• Silisiclastic sedimentation dominates lower parts of most Cambrian sections
• Begin long-lived carbonate deposition late in period

Ordovician (488 - 444 Ma

• General continued patterns of Late Cambrian sedimentation – carbonates
• Major continent-wide Early Ordovician unconformity
• Taconic terranes approach and collide to generate Taconic orogeny
• Avalonia closes with Baltica
• Iapetus Ocean narrows in N
• Early convergent events begin in Arctic
• Continued passive margin along western NAM

Silurian (444 - 416 Ma)

• Iapetus Ocean closes as Baltica-Avalonia collides with NAM – Scandian and Acadian phases of Calledonian orogeny
• Uplands and mountains rim Eastern NAM
• Widespread carbonate deposition across interior NAM
• Complex string of microcontinents rifted from Gondwana (Hun superterrane) to SE of NAM and Baltica
• Continued passive margin on Western NAM as Antler arc terrane approaches

Devonian (416 - 359 Ma)

• Suturing of Baltica and NAM form Calledonian-Acadian Mountains and megacontinent of Laurussia
• Collisional phase followed by left-lateral transform motion between Greenland and Baltica
• Collisions with string-like Hunic terranes close central and southern Iapetus – Rheic Ocean separates Laurussia from Gondwana
• Major orogeny in Arctic as arcs and fragments of Siberia collide with northern Canada – greater Ellsmerian orogeny
• Antler arc approaches and collides with Cordilleran miogeocline
• Distal passive margin deepwater deposits thrust eastward over coeval carbonate shelf deposits as the Roberts Mountain Allocthon (RMA). The arc itself collided with partly rifted fragments off Western North America; the largest blocks became the nucleus for the Quesnell and Stikine terranes, which were accreted to NAM in the Mesozoic
• Widespread cratonic deposits thin and locally absent across Transcontinental arch
• Major global plate reorganization
• Continued widespread carbonate deposition except in foreland basins adjacent to orogenic belts where thick silisiclastics form

Mississippian (359 - 318 Ma) 

• NAM and Gondwana approach and close Rheic ocean
• Initial contact at promontories of Africa and Eastern US  -- Lakawanna phase of Alleghenian orogeny -- initial collision of Africa and Peri-Gondwanan terranes with NAM in Chester ~325 Ma);
• Major collision with Africa ~320 Ma near Miss-Penn boundary
• Considerable transform motions along Hun superterrane shorten and stack elements (eg Iberia)
• Western fragments of Hun superterrane collide with Southern US to form Ouachita orogeny --  well underway by close of Mississippian
• Widespread and dominant carbonate deposition across much of NAM except adjacent to orogenic areas
• RMA and Quesnell and Stikine terranes became the leading edge of NAM along an east-dipping subduction zone as the early phases of the Cordilleran margin evolved
• Back arc spreading and transform processes transported Stikine outboard of Quesnell to eventually form a double east-dipping arc complex (McCloud arc).  The Havallah backarc basin formed between Quesnell and Nam
• Cratonic NAM shelf sediments formed throughout the interval but none of the basins that would dominate the Late Paleozoic were evident yet

Pennsylvanian (318 - 299 Ma )

• Western Pangaean collision as Gondwana sutures with Eastern US -- Appalachian-Ouachitan systems near climax
• Extensive foreland basins form in both Old and New Worlds
• Juxtaposition of Hun superterrane along Southern Europe
• East of Southern Europe, Tethyian Ocean separates Gondwana from Asia
• Cratonic basins and uplifts of Greater Ancestral Rocky Mountains (GARM) develop; GARM features somewhat non-synchronous across region and generally young to west
• Dramatic change in sedimentation from carbonate to silisiclastic; carbonate sedimentation continues in some basins
• Early phases of aeolian sedimentation in parts of Western NAM
• Cyclic sedimentation obvious in all sedimentary facies reflects Gondwanan glacial cycles
• General drying across Western Pangaea – thick salt deposits in Western Interior
• Western peri-Gondwanan terranes close on W Texas to initiate Marathon orogeny
• Transform truncation of W NAM – Caborca block moved SE as S McCloud arc (Stikine) drifted NW; Quesnell fragment McCloud arc separated from NAM by backarc Havallah basin

Permian (299 – 251 Ma)

• Assembly of Western Pangaea complete
• Only remnants of Permian deposits in Eastern NAM
• Widespread Aeolian and fluvial redbed deposition across Western Interior and North Sea region; thick carbonate deposition in basins – complex lateral and vertical facies changes – continued cyclicity
• Major global marine lowstand late in Permian; extensive salts deposited on craton from Nebraska to Texas and across Northern Europe
• Western peri-Gondwanan terranes collide to form Marathon orogeny
• Continued reorganization of McCloud arc and closure of Havallah basin as Quesnell collapses towards W NAM
• Collapsing McCloud arc initiates Sonoman orogeny
• McCloud arc reorganizes during Sonoman orogeny; Cache Creek interarc mélange between Stikine and Quesnell
• Obduction of “Tethyian” limestone plateaus along W NAM – McCloud Limestone formed on these terranes

Triassic (251 - 200 Ma) 

• Rifting and basaltic magmatism along East Coast signals early stages of break-up of Western Pangaea
• Lowstand continues
• Waning Ancestral Rockies
• Triassic continental deposits onlap and overlap uplifts of GARM; highlands on Uncompahgre and Front Range elements persisted into Late Jurassic
• Continental Divide ran from Eastern Canada to Northern Mexico – Triassic and Early Jurassic rivers headed in Continental Divide
• Mc Cloud arc fragmented and collapsed against North America resulting in Sonoman orogeny
• Caborca terrane moved SE along truncated continental margin
•  Diverse suite of fore arc and inter arc deposits, fringing arcs, and trench deposits built between and west of Mc Cloud arc elements as Cordilleran subduction pattern initiated
• Early Cordilleran arc built on reorganized W NAM margin in Middle Triassic (~240 Ma) – continental to south, marine to north
• Wrangell terrane looms well off shore in Pacific Ocean

Jurassic (200 - 146 Ma)

• Atlantic Ocean opens from Maritime Canada into Gulf of Mexico – Yucatan rifts and drifts S as Gulf opens
• Pangaean mountains including Appalachians mostly worn down by erosion
• Marine deposition between massifs of Western Europe
• Widespread Aeolian deposition across Western Interior formed greatest aeolian deposits in rock record
• Western Interior seaway established in Middle Jurassic
• Morrison fluvial interval blankest Western Interior in Late Jurassic
• Cordilleran arc and associated terranes and deposits built on or accreted to western North America including Bridge River, North Cascades, western parts of Eastern Oregon terranes, and western terranes of Klamaths and Sierras
• Older Mesozoic back arc basins closed as Cordilleran region continues collapse against continent
• Cordilleran arc was continental to south and marine to north
• Wrangell and Guerrero terranes converged towards North America -- initial collision between southern Wrangellia and Cordilleran margin at approximately the latitude of Klamaths and Sierras; fringing arcs built off collision zone
• Ophiolites obducted in collision zone and in inter arc region between Cordilleran arc and fringing arcs
• Major Cordilleran arc magmatism in Middle Jurassic
• Probable foreland basin in Utah and thrusting in Nevada mark early phase of Nevadan (Elko) orogeny; much of eastern Cordillera was positive at this time
• Rift basin in southwestern North America related to opening Gulf of Mexico
• Major plate reorganization in Late Jurassic -- change in relative plate motion (to sinistral) of Farallon Plate with respect to North America causes Wrangellia to begin moving southward
• Complex series of events at SW margin of North America in Late Jurassic: Chortis and related terranes shift SE as Atlantic and Proto-Caribbean expand; transform fault and oblique rift systems developed along waning continental arc (Mc Coy-Bisbee; Mojave-Sonoran megashear); intra arc and inter arc flysch basins formed (Orocopia-Rand); mélange formed farther outboard (early Franciscan)

Cretaceous (146 - 65 Ma)

   Early

• Rapid spreading of Atlantic Ocean  -- aulocogens formed at numerous triple junctions along opening Atlantic
• Western Interior seaway reestablished
• Early Sevier thrust belt and foreland basin formed
• Guerrero collided -- subduction zone rebuilt on west face
• South-moving Wrangellia captured North Cascades, Tyaughton-Methow, and adjacent terranes to form Baja BC
• Guerrero collision and southward drift of Baja BC caused much of Intermontane terrane (Stikine and Quesnell) to move northward via tectonic escape
• Great Valley fore arc basin and Franciscan subduction complex built on reorganized Cordilleran margin
• Nutzotin Ocean remained open between Wrangellia and Canada
• North Slope terrane rotated CCW as Canadian basin opened – North Slope terrane moves to south and E Siberian terranes move west

   Late

• Atlantic now mature ocean
• Caribbean sea begins to open as South America pulls away from NAM – first subduction event in Atlantic
• Silisiclastic sedimentation along N and W margins of Gulf of Mexico
• Marine highstands cause expanded Western Interior seaway – NAM landmass bifurcated
• Arctic Amerasian basin fully opened
• Foreland basin deposits form complex transgressive-regressive cycles on W side of seaway -- foreland basin shifted locus of subsidence southward
• Cordilleran arc renewed with large plutonic events (Penninsular, Sierra Nevada, Idaho; Coast Range complex built on Baja BC
• South-moving Baja BC approached maximum S position – a moderate translation is shown on these maps
• Nutzotin Ocean almost closed as N Wrangellia sutures with NW NAM
• Chugach seafloor fans fed by uplifts in Coast Range plutonic complex
• Great Valley and Franciscan complexes continued to build in fore arc
• Rotated North Slope terrane collided with Yukon-Tanana and related terranes
• Sevier orogeny continued and foreland basin expanded eastward
• Plate reorganization as Kula separated from Farallon Plate; dextral transpression with north America; Kula-Farallon plate boundary began movement northward along coast (dextral motion)
• Baja BC transported northward after 85 Ma, probably along migrating triple junction
• Active plutonic activity in Sierra-Idaho-Penninsular (100-85 Ma) followed by strong decline and null in arc activity (80-40 Ma)
• Andean-style arc established from Central America to Alaska
• Extraterrestrial impact forms depression in NW Yucatan at 65 Ma

Paleogene (65 – 23 Ma)

• Passive margin along Atlantic and Gulf Coast
• Greenland rifts from NAM; rotation along N margin generates fold and fault belt in E Arctic region – Eurekan orogeny
• North Atlantic and E Arctic oceans open
• Eastward expansion of Caribbean Plate
• Deposition of extensive wedges of sediment into Gulf of Mexico as detritus from Rocky Mountains reaches area
• Farallon Plate underwent shallow subduction -- strong Sevier thrusting and expansion NE of foreland basin followed by foreland uplifts (Laramide orogeny)
• Rocky Mountain foreland uplift, deformation, and shallow-subduction-related magmatism; interior sedimentation mostly restricted to Rocky Mountain foreland basins (Uinta, Green River, etc) early, then sedimentation spilled onto High Plains
• S Colorado Plateau high and dissected ~ 25 Ma (Plateau uplift?) as coarse conglomerate deposited along S margin
• Several episodes of planation and exhumation of Rocky Mountains
• Triple junction and Baja BC migrated rapidly northward
• Inboard terranes (Quesnell, Stikine) also translate to north
• Arc activity continued on Baja BC and across W Mexico but waned across Idaho-Sierra Nevada
• Fore arc sedimentation (Franciscan-Great Valley and similar units) continued into Plaeocene along Cordilleran margin
• Uplift of Coast Range plutonic complex generated deep-sea fan deposits (Chugach flysch) onto ocean floor

• Many terranes approach their present latitude with respect to North America by 50 – 40 Ma
• Olympic terrane accreted ~ 50 Ma
• California borderlans active – basins inboard fill with thick marine and continental deposits
• Mendocino Fracture Zone on East Pacific Rise intercepts NAM ~ 40 Ma – transform margin follows

Neogene (23 – 0 Ma)

• Spreading ceases in Labrador Sea – all spreading now occurs on Mid-Atlantic Ridge
• Passive margin along Atlantic and Gulf coasts continues
• Caribbean expands well into Atlantic as Antilles arc migrates eastward
• Large deltaic and coastal plain depo systems in Gulf – extensive slumping and landslides along NW margin
• Colorado Plateau high -- relative undissected until last 5 – 7 million years
• Complex erosion and exhumation continues in Rocky Mountains
• Basin and Range orogeny: early (30 – 15 Ma) extension along large detachment faults; late (10 – 0 Ma) normal high-angle faulting; extensive basaltic magmatism in Basin and Range and on S, W, and E margins of Colorado Plateau
• Expansion of transform Pacific margin throughout Neogene – subduction continues N and S of transform margin
• Continues N translation of terranes towards Alaska
• Complex transfer (plate capture) of parts of W NAM onto Pacific Plate as San Andreas Fault and earlier similar faults generate right lateral transform motion
• Opening of Gulf of California +/- 5 Ma allowed integration of Colorado River system by complex stream capture and canyon cutting and erosion of Colorado Plateau and Rocky Mountains
• Pleistocene glaciation greatly affected sea level and erosional and depositional patterns across NAM