Birth of the Lower Colorado River


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  • Birth of the Lower Colorado River

    1. 1. The Birth of the Lower Colorado River P. Kyle House, Nevada Bureau of Mines and Geology, University of Nevada, Reno
    2. 3. <ul><ul><li>Mio-Pliocene strata near Laughlin, NV support cascading lake-spillover mode of intergration </li></ul></ul><ul><ul><li>Two episodes of lacustrine deposition separated by a divide-breaching flood </li></ul></ul><ul><ul><ul><li>First lake episode in Cottonwood Valley </li></ul></ul></ul><ul><ul><ul><li>Major flood in Mohave Valley </li></ul></ul></ul><ul><ul><ul><li>Second lake episode in both valleys </li></ul></ul></ul><ul><ul><li>Sediment-laden LCR fills valleys in early Pliocene </li></ul></ul><ul><ul><li>Timing consistent with evidence for integration upstream </li></ul></ul>
    3. 4. <ul><ul><li>Inception linked to downstream-directed processes </li></ul></ul><ul><ul><ul><li>Common to rivers in extensional terranes </li></ul></ul></ul><ul><ul><li>The Bouse Formation is a lacustrine deposit </li></ul></ul><ul><ul><ul><li>Not marine / not uplift datum </li></ul></ul></ul><ul><ul><li>Valleys were filled, not carved, by the Colorado R </li></ul></ul><ul><ul><ul><li>Headward erosion concept untenable </li></ul></ul></ul><ul><ul><li>Events linked in time to Grand Canyon incision </li></ul></ul><ul><ul><ul><li>If you dig a big hole… </li></ul></ul></ul>
    4. 5. <ul><li>Antecedence? </li></ul><ul><li>Headward Erosion? </li></ul><ul><li>Spilling Lakes? </li></ul>
    5. 6. <ul><li>‘ Classic’ Integration Paradigm </li></ul><ul><ul><li>Integration driven by headward erosion from the subsiding Gulf of California into the Colorado Plateau </li></ul></ul><ul><li>New (rediscovered) Integration Hypothesis </li></ul><ul><ul><li>Integration via a series of cascading failures of a chain of freshwater to moderately saline lakes, eventually spilling into the developing Gulf </li></ul></ul><ul><ul><li>Proposed by Blackwelder in 1932. </li></ul></ul>
    6. 7. What model best explains its distribution? Uplifted sea level datum? Stable lake level datum in series?
    7. 8. <ul><li>Northward ‘younging’ marine carbonate succeeded by southward prograding River delta </li></ul><ul><ul><li>Marine incursion occurs owing to subsidence associated with rifting in Gulf of California </li></ul></ul><ul><ul><li>Colorado River integrated by headward erosion and stream capture </li></ul></ul><ul><ul><li>Bouse Formation represents sea-level datum subsequently subject to rapid uplift </li></ul></ul><ul><ul><li>Marine regression linked to progradation of Colorado River sediment wedge and delta </li></ul></ul>
    8. 9. <ul><li>Bouse deposits have non-marine geochemical fingerprint </li></ul><ul><li>Geologically short interval of integration (with new data) </li></ul><ul><li>Major LCR aggradation pulse immediately post-dates Bouse </li></ul><ul><li>Existing constraints obviate upstream ‘younging’ </li></ul><ul><li>Stratigraphy analogous to upstream records deemed ‘non-marine’ </li></ul><ul><li>Principal (only?) geological support for marine model is paleontological </li></ul>
    9. 10. <ul><li>Estuarine interpretation supported only by paleontology </li></ul><ul><ul><li>Fresh, brackish, and marine water species from Parker south </li></ul></ul><ul><ul><li>Freshwater only farther north </li></ul></ul><ul><li>Linked to rifting in Gulf of Calif. </li></ul><ul><ul><li>Restricted to LCR area more or less </li></ul></ul><ul><ul><li>Narrow belt of subsidence without contemporaneous faulting </li></ul></ul><ul><ul><li>Relatively brief incursion </li></ul></ul>
    10. 11. <ul><li>Base-level fall drives upstream incision </li></ul><ul><ul><li>Implies some integrated drainage system along LCR </li></ul></ul><ul><ul><li>Headward erosion carves valleys and leads to capture of Colorado River in Grand Canyon region </li></ul></ul><ul><ul><li>Progradation of fluvial sediment drives estuary to south </li></ul></ul><ul><li>Trough rebounds and then some in Pliocene-Quaternary </li></ul><ul><ul><li>Young regional uplift in LCR tied to Colorado Plateau </li></ul></ul>
    11. 12. <ul><li>Simplest Explanation </li></ul><ul><ul><li>The LCR formed via downstream-cascading lake spillover </li></ul></ul><ul><ul><ul><li>Downstream-directed </li></ul></ul></ul><ul><ul><ul><li>Canyon cutting restricted to divides </li></ul></ul></ul><ul><ul><ul><li>No / minimal uplift </li></ul></ul></ul><ul><li>Alternative Paradigm </li></ul><ul><ul><li>LCR formed via headward erosion from the head of the Gulf of California to the Colorado Plateau </li></ul></ul><ul><ul><ul><li>Upstream-directed </li></ul></ul></ul><ul><ul><ul><li>Early, deep incision throughout system </li></ul></ul></ul><ul><ul><ul><li>More than 550 m uplift </li></ul></ul></ul><ul><ul><ul><li>By-passes graded tributaries to incise bedrock divides </li></ul></ul></ul>
    12. 13. Study Area—Cottonwood and Mohave Valleys Pyramid hills paleodivide Black Mountains (Arizona) Newberry Mountains (Arizona) Mohave Valley Cottonwood Valley
    13. 14. <ul><li>Local basin fill—Fanglomerates and axial alluvium </li></ul><ul><li>Transition to axial drainage—Newberry gravel </li></ul><ul><li>Flood from divide breach—Pyramid gravel </li></ul><ul><li>Lake—Bouse Formation (marl, mud, sand, gravel) </li></ul><ul><li>Early through-going river—Panda gravel </li></ul><ul><li>Massive aggradation—Bullhead alluvium </li></ul><ul><li>Deep incision </li></ul>
    14. 15. <ul><li>Qc : Young river sediment </li></ul><ul><li>Qf : Young fan gravel </li></ul><ul><li>QTf : Old fan gravel </li></ul><ul><li>Tfb2 : Ancient fan gravel </li></ul><ul><li>Tvn : Nomlaki ash (3.3 Ma) </li></ul><ul><li>Tvln : lower Nomlaki ash (4 Ma) </li></ul><ul><li>Tcb : Bullhead alluvium </li></ul><ul><li>Tbms : Bouse mud and sand </li></ul><ul><li>Tbl : Bouse marl (limestone) </li></ul><ul><li>Tpg : Pyramid gravel </li></ul><ul><li>Tng : Newberry gravel </li></ul><ul><li>Tfb1 : Ancient fan gravel </li></ul><ul><li>Tvw : Wolverine Ck tuff (5.6 Ma) </li></ul><ul><li>Tfn : Ancient Fanglomerate </li></ul>Key Strata
    15. 16. Paleochannels portend significant change in local drainage
    16. 17. <ul><li>Monomictic cobble-boulder conglomerate </li></ul><ul><li>Occupies/exploits early axial paleochannels </li></ul><ul><li>Multi-phased, crudely to moderately well stratified </li></ul><ul><li>Overlain by the Bouse marl </li></ul>~30 m Fanglomerate Pyramid gravel
    17. 18. <ul><ul><li>Conspicuous local source </li></ul></ul><ul><ul><li>High-energy deposition </li></ul></ul><ul><ul><li>Clear-water divide failure </li></ul></ul>Pyramid Gravel Outcrop area of granite One of the largest boulders, 5 mi from likely source Boulder Bell
    18. 19. Flat-lying marl unconformably overlain by river gravel in central Mohave Valley
    19. 20. <ul><li>Overlies the Pyramid gravel flood deposit </li></ul><ul><li>Limestone, siltstone, and sandstone </li></ul><ul><li>Overlies paleo-landscape from 640’ to ~1800 ft </li></ul>Mohave Valley: Bouse Formation
    20. 21. <ul><li>Unconformably overlies the transitional sequence </li></ul><ul><li>Compositionally immature paleochannel fill 60 ft above modern river </li></ul><ul><ul><li>Lithologic diversity increases upsection </li></ul></ul><ul><li>Complex fluvial deposit buried pre-existing, deep valleys previously filled with Bouse lake </li></ul><ul><li>Net thickness of approximately 800 ft </li></ul>
    21. 22. <ul><li>Net thickness of ~800 feet </li></ul><ul><li>Predominantly gravel and sand with minor mud </li></ul><ul><li>Elaborately structured river deposit </li></ul>Fanglomerate 80 ft above Modern river Panda Gravel—fluvially reworked Newberry fanglomerate mixed with exotics Mohave Valley: Bullhead alluvium
    22. 23. Pyramid gravel (Tpg) Newberry gravel (Tng) Fanglomerate (Tfn) Bouse marl (Tbo) Panda gravel (Tcbl) The Transitional Section
    23. 24. <ul><li>MOHAVE VALLEY EXAMPLE </li></ul><ul><li>COTTONWOOD VALLEY EXAMPLE </li></ul>Tephra Fan gravel Tephra Distal fan gravel River gravel
    24. 25. <ul><li>Local basin fill /shallow lake—Lost Cabin beds </li></ul><ul><li>Erosional Unconformity </li></ul><ul><li>Deep lake—Bouse Formation </li></ul><ul><li>Early through-going river—Panda gravel (lower Bullhead) </li></ul><ul><li>Massive aggradation—Bullhead alluvium </li></ul><ul><li>Deep incision </li></ul>
    25. 26. <ul><li>Qc : Young river sediment </li></ul><ul><li>Qf : Young fan gravel </li></ul><ul><li>QTf : Old fan gravel </li></ul><ul><li>Tfb2 : Ancient fan gravel </li></ul><ul><li>Tcb : Bullhead alluvium </li></ul><ul><li>Tbms : Bouse mud and sand </li></ul><ul><li>Tbl : Bouse marl (limestone) </li></ul><ul><li>Tfb1 : Ancient fan gravel </li></ul><ul><li>Tvw : Wolverine Ck tuff (5.6 Ma) </li></ul><ul><li>Tlcf : Fine Lost Cabin beds </li></ul><ul><li>Tlcc : Coarse Lost Cabin beds </li></ul><ul><li>Tfn : Ancient Fanglomerate </li></ul><ul><li>Tft : Tilted fanglomerate </li></ul>
    26. 27. <ul><li>Interbedded tributary gravels from the Newberry and Black Mountains </li></ul>
    27. 28. <ul><li>Culmination of basin fill in late Miocene </li></ul><ul><li>Stratigraphic equivalent of Muddy Creek Fm </li></ul><ul><li>Precursor deposit to river integration </li></ul>Cottonwood Valley: Lost Cabin beds
    28. 29. Lost Cabin beds Fanglomerate Tuff bed
    29. 30. <ul><li>Marl interbeds in Lost Cabin sediments </li></ul><ul><li>Unconformity in Tlc filled with interbedded gravel, mud, and marl overlain by beach gravel </li></ul><ul><li>Evidence for two lakes </li></ul>Cottonwood Valley: Lost Cabin beds and Bouse formation
    30. 31. <ul><li>Classic draping contact </li></ul>Mud Mud Marl marl Karl Mohave Valley: Bouse Formation
    31. 32. Cottonwood Valley: Bouse formation
    32. 33. Mud Mud Marl Phil fill Mohave Valley: Bouse Formation
    33. 34. Mud Mud Marl Cottonwood Valley: Lost Cabin beds and Bouse formation
    34. 35. <ul><li>Low-lying deltaic sediments </li></ul><ul><li>Interbedded mud and sand </li></ul><ul><li>Thick clastic package overlies marl </li></ul>Mud Mud Marl Mohave Valley: Bouse Formation
    35. 36. Tfn Tfn Tcb ~720 ft a.s.l. Source area of Tfn
    36. 38. <ul><li>Pre-integration valley fill package in Cottonwood Valley </li></ul><ul><li>Stratigraphic equivalent to the Muddy Creek Formation </li></ul><ul><li>Distinctive basal, marginal, and axial facies </li></ul>Disconformity Lost Cabin beds (Tlc) Flat-bedded mudstone and sandstone Fanglomerate of the Black Mountains (Tfb) not a unicorn
    37. 39. Tlc Tbl Tbl Tfb with Tbl ribbons QTa Shallow lake above Pyramid Divide deposits Tlc(?) Divide is breached, and deeper lake dammed at Topock floods both valleys and deposits Tbl Lake reaches 1800’ in both valleys
    38. 40. Tbl Tlc Newberry Mts Tbl Qtrk QTfb
    39. 41. Cottonwood Valley Mohave Valley Bullhead alluvium Bouse Fm. Bouse Fm. Pyramid gravel Lost Cabin beds Fan gravel Fanglomerate Fan gravel Fanglomerate Transitional sequence Fanglom Bullhead alluvium Fanglom 3.3 Ma 3.6 - 4.2 Ma 5.51 Ma unconformity unconformity
    40. 42. Bouse Beach Facies: Gravel Gravel deposit Sandstone onlap
    41. 43. Bouse Beach Facies: Gravel, Sand, and Marl Low angle, tabular cross-beds dipping toward valley axis
    42. 44. Cross-stratified clean sand and reworked fanglomerate at 1840 ft, Lost Cabin Wash
    43. 45. Wave-sorted / reworked fanglomerate on bedrock. Newberry piedmont, 1840 ft / 560 m
    44. 46. <ul><li>Max elevation of Bouse sediment </li></ul><ul><li>Late Miocene axis of Cottonwood Valley </li></ul><ul><li>Max elevation of LCR alluvium </li></ul><ul><li>Late Miocene Mohave Valley axis </li></ul><ul><li>Holocene floodplain </li></ul>
    45. 47. A N 20 miles / 35 km 560 m 560 m 533 m 544 m
    46. 48. Marl
    47. 49. Pyramid Hills
    48. 50. Sea level 330 m 555 m Modified from Spencer et al., 2008
    49. 51. Detail: in situ tufa bench Tufa ‘reef’ in saddle 1460 ft Tufa and beach gravel 1400-1460’ Dead Mountains
    50. 52. <ul><ul><li>LCR inception linked to downstream-directed processes </li></ul></ul><ul><ul><ul><li>Quiescent deposition follows flood from upstream </li></ul></ul></ul><ul><ul><li>Late Miocene valleys were FILLED, not carved by early LCR </li></ul></ul><ul><ul><ul><ul><li>Inconsistent with headward erosion concept </li></ul></ul></ul></ul><ul><ul><li>New age-controls compress time frame for river integration </li></ul></ul><ul><ul><ul><li>Links massive aggradation with canyon enlargement </li></ul></ul></ul><ul><ul><li>Regional stratigraphic link among pre-river basin fill units </li></ul></ul><ul><ul><ul><li>Change preceded the arrival of the Colorado River </li></ul></ul></ul>
    51. 54. <ul><li>Immediately overlies upstream-derived catastrophic flood deposit </li></ul><ul><ul><li>Coincident marine incursion and flooding from upstream? </li></ul></ul><ul><li>Stratigraphic consequence of river integration via lake failure inferred from geochemical studies </li></ul><ul><ul><li>Spencer and Patchett (1997); Poulson and John (2003) </li></ul></ul><ul><li>Bouse in a similar context below Parker Dam (Buising, 1988) </li></ul><ul><ul><li>Inter-bedded with intricately bedded fluvial gravels </li></ul></ul><ul><ul><li>Far-traveled detritus in sand fraction </li></ul></ul>
    52. 55. <ul><li>Upper Lost Cabin beds contain interbedded marl </li></ul><ul><li>Base of thick marl and mud unit fills erosional niche in upper Lost Cabin bed section </li></ul>
    53. 56. Quaternary river gravel Bouse marl Cross-bedded local gravel with marl interbeds Marl interbedded with downstream-directed fluvial gravel
    54. 57. Lake Bidahochi fills as upper Colorado Drainage extends to south (~6-7 Ma) Lake overtops (undercuts?) ‘Coconino’ divide and spills down Grand Canyon Sequential filling of lakes in Western Lake Mead Area (6-5.6 Ma) Lake overtops ‘Black Canyon’ divide and spills into Cottonwood Basin (6-5.6 Ma) Lake overtops ‘Pyramid’ divide and fills Mohave and Cottonwood Valleys (~5.6 Ma) Lake overtops ‘Topock’ divide and fills Chemehuevi Valley Lake overtops ‘Buckskin’ divide and fills Parker-Cibola Valley Lake overtops ‘Chocolate’ divide and LCR reaches developing Gulf of California Study area
    55. 59. <ul><li>Birth of LCR in study area began with divide failure and flood </li></ul><ul><li>Pre-river valley geometry similar to modern </li></ul><ul><li>Bouse formation is non-marine (not an uplift datum) </li></ul><ul><li>Interval of Bouse deposition relatively short </li></ul><ul><li>Mohave Valley Transitional Sequence parallels changes in Western Grand Canyon / Lake Mead Basin </li></ul><ul><li>Major fluvial backfilling driven by integration </li></ul>
    56. 60. Pyramid Hills Paleodivide Newberry Mountains Black Mountains Bullhead City Laughlin Davis Dam N Black Mtns Dead Mtns 10 km Cottonwood Valley Mohave Valley
    57. 61. minimum Newberry fan extent based on modern outcrops Newberry Fans Newberry Fans
    58. 62. 1 m Bouse Lost Cabin beds Fanglomerate Wave-worked gravel
    59. 63. Fanglomerate deposition in Mohave Valley concurrent with deposition of the Lost Cabin Beds in Cottonwood Valley Pre-Bouse fanglomerate exposed at late Miocene valley axis near level of modern river 5.5 Ma tephra Geologist Bouse marl Fanglomerate
    60. 64. Terminal Basin Lost Cabin Beds Bouse phase 1 Bouse phase 2 Divide Failure Pyramid Gravel Lake Drainage LCR, full-blown Bullhead Alluvium
    61. 65. <ul><li>1. Rio Grande </li></ul><ul><li>2. Central AZ Rivers </li></ul><ul><li>3. Lower Colorado </li></ul><ul><li>4. W. Great Basin </li></ul><ul><li>5. N. Great Basin </li></ul><ul><li>6. Bonneville Basin </li></ul><ul><li>7. Snake River </li></ul>
    62. 66. <ul><li>Phil Pearthree </li></ul><ul><li>Jim Faulds </li></ul><ul><li>Keith Howard </li></ul><ul><li>John Bell </li></ul><ul><li>Mike Perkins </li></ul><ul><li>Amy Brock </li></ul><ul><li>Andrei Sarna-Wojcicki </li></ul><ul><li>Jon Spencer </li></ul><ul><li>Sue Beard </li></ul><ul><li>Brenda Buck </li></ul><ul><li>Dave Miller </li></ul><ul><li>Richard Hereford </li></ul><ul><li>Daniel Malmon </li></ul>