The Evolution of Foreland Basins Megan Mueller Field Geology Summer 2020 2. Paleozoic Review 2 Generalized History of W. North America Basin & Range Extension, CRBG Pangea Passive margin Laramide Orogeny (miogeocline) Western Interior Seaway Rodinia Sevier Orogeny (and Nevadaplano) Onset of FTB Building (?) Columbia/ Nuna Begin subduction (?) - chaotic organization - passive margin (Slide Mtn basin) 3 Pennsylvanian-Permian • What type of margin? • Sediment transport direction? • Lithology and depositional environments? • Sediment composition? 4 Analog: Namibia • Quadrant: aeolian dunes • Phosphoria: passive margin, epicontinental shallow sea 5 Early Triassic • Chaotic margin • Lithology? • Depositional environment? 6 3. North American Foreland Basin 7 North American Foreland Basin • Major tectonic regions • Magmatic arcs, accreted terranes • Sevier thrust belts • Sevier foreland basin system • Laramide intra-foreland uplifts & basins DeCelles, 2004 AJS 8 North American Foreland Basin • > 1000 km wide, 6000 km long • >100 Myr lifespan • Foreland basin system evolved in response to crust and mantle processes • Late Jurassic to Eocene deposition DeCelles, 2004 AJS 9 Triassic Dinwoody Fm PC: Marli Miller PC: Megan Mueller 10 Triassic to Mid Jurassic • Little topography -> open to Pacific • marine deposition • Triassic Dinwoody Fm • shallow marine shale and limestone • Begin to set-up thrust belt • Foreland system migrates east images by Ron Blakey, Northern Arizona University DeCelles, 2004 AJS 11 Fuentes et al. 2011 12 PC: Maddie Hille Morrison Formation Montana: ~158-152 Ma PC: Megan Mueller What is lithology and depositional environment? 13 14 Late Jurassic (155-142) • Orogenic loading from FTB • Subsidence driven by loading • Eastward migration of magmatism • Low angle subduction or partial delamination • Extension in SW • Obliquity of NW-SE convergence • Rift basin? • Morrison Fm: non-marine shale and sandstone, limestone, conglomerate, paleosols 15 DeCelles, 2004 AJS Morrison Fm Debate • Fluvial, lacustrine • Paleotopography controls thickness • Major unconformity at top Setting and subsidence mechanism? • Foredeep • Does not thicken to W • Not flexural subsidence from FTB • Backbulge • Where is foredeep? Eroded in K. • Metamorphic grade supports thick overburden (foredeep) existed • Dynamic subsidence • Unconformity too far inboard • Slab foundering? Mezcalera or Farallon? • Wavelengths of subsidence debated 16 DeCelles, 2004 AJS PC: Maddie Hille PC: Maddie Hille PC: Adam Woods What is lithology and depositional environment? 17 DeCelles, 2004 AJS Aptian • Sevier Orogeny • East migrating • Classic flexural foreland basin • Flexural loading • Peak FTB • All 4 depozones preserved • Minimal magmatism 18 Skagit River 19 Neuquen, Argentina Kootenai: river channels, floodplain, limestone lakes 20 Western Interior Seaway (shaded) Albian • Blackleaf Fm PC: Adam Woods What is lithology and depositional environment? 21 DeCelles, 2004 AJS Early Cretaceous to Albian • Marine transgressions & regressions • Western Interior Seaway • Kootenai Fm. and Flood Mbr.: paleosols, lacustrine limestones, fluvial and floodplain • Chert, coarse- to fine-grained deposition, thick sed. units • Vaughn Mbr.: shallow marine deposition records transgression 22 DeCelles, 2004 AJS Coniacian (~89-85) • Chaotic subsidence pattern further east • Dynamic subsidence dominates • Asymmetric subsidence pattern in west; symmetric in east • Demise of well-organized foreland system 23 Campanian to Eocene (83-40 Ma) • Laramide intraforeland uplifts • Basement-involved thrusts along paleo-weaknesses • Partitioned basins • Local flexural subsidence • Eastward migration of magmatism and deformation • Interpretation: flat slab subduction DeCelles, 2004 AJS Dumitru 1991 24 Western Interior Seaway peak transgression ~92 Ma Blum & Pecha, 2014 Lockshin et al. 2017 25 NA Foreland Basin Summary • Triassic – Mid-Jurassic: marine deposition, connected to Pacific Ocean • Late Jurassic: orogenic loading, dynamic subsidence from Farallon subduction • Non-marine deposition • Sevier Orogeny • Classic foreland basin system • Fold and thrust belt building • Marine deposition from Western Interior Seaway • Coniacian (89-85) • not well-defined foredeep, dynamic subsidence dominates • ~80 Ma to Eocene: Laramide orogeny • Deformation front migrates east due to flab slab subduction • Local subsidence • Partitioned basins 26 Conclusions • Depositional environments and sedimentary provenance that we see in the field is evidence for all these events! • Sedimentary record preserved in foreland basins document the evolution of orogenies • Stratigraphy is an excellent tool to reconstruct basin history and thus tectonic evolution at the regional scale • Knowledge of basin tectonic evolution helps us to better interpret long-term changes in depositional systems Figures modified from DeCelles 2004 AJS Western Interior Seaway (shaded) Seaway Interior Western.