OVERVIEW OF GEOLOGIC EVENTS
(chronostratigraphy after Gradstein et al., 2004)
Late Proterozoic -- pre-Middle Devonian
Passive margin (Cordilleran miogeocline) followed rifting along Western North America
locally 10+ km sedimentary rocks in miogeocline, much thinner on craton to east
Middle - Late Devonian (397-359 Ma)
Antler arc approached and collided 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.
Mississippian (359 - 318 Ma)
Reorganization of western North American plate-tectonic setting
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
Peri-Gondwanan terranes near SE NAM on leading edge of Gondwanan plate
Initial collision of Africa and Peri-Gondwanan terranes with NAM in Chester (~325 Ma); Ouachita orogeny well underway by close of Mississippian
Major collision with Africa ~320 Ma near Miss-Penn boundary
Pennsylvanian (318 - 299 Ma )
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
Cratonic basins and uplifts of Greater Ancestral Rocky Mountains (GARM) develop; note that GARM features somewhat non-synchronous across region
Cyclic sedimentation reflects Gondwanan glacial cycles
Appalachian-Ouachitan systems near climax
Western peri-Gondwanan terranes close on W Texas to initiate Marathon orogeny
Permian (299 251 Ma)
Western peri-Gondwanan terranes collide to form Marathon orogeny
Major fluvial and eolian deposition across GARM region continued cyclicity
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
Major global marine lowstand late in Permian; extensive salts deposited on craton
Triassic (251-200 Ma)
Lowstand continues
Continued tightening of segments of McCloud arc
Waning Ancestral Rockies
Early Cordilleran arc built on reorganized W NAM margin in Middle Triassic (~240 Ma) continental to south, marine to north
Caborca translated to SE to near current position
Triassic continental deposits onlap and overlap uplifts of GARM; highlands on Uncompahgre and Front Range elements persisted into Late Jurassic