birth of the lower colorado river
TRANSCRIPT
The Birth of the Lower Colorado River
P. Kyle House, Nevada Bureau of Mines and Geology, University of Nevada, Reno
Mio-Pliocene strata near Laughlin, NV support cascading lake-spillover mode of intergration
Two episodes of lacustrine deposition separated by a divide-breaching flood
First lake episode in Cottonwood Valley
Major flood in Mohave Valley
Second lake episode in both valleys
Sediment-laden LCR fills valleys in early Pliocene
Timing consistent with evidence for integration upstream
Inception linked to downstream-directed processes Common to rivers in extensional terranes
The Bouse Formation is a lacustrine deposit Not marine / not uplift datum
Valleys were filled, not carved, by the Colorado R Headward erosion concept untenable
Events linked in time to Grand Canyon incision If you dig a big hole…
Antecedence?
Headward Erosion?
Spilling Lakes?
‘Classic’ Integration Paradigm Integration driven by headward erosion from the
subsiding Gulf of California into the Colorado Plateau
New (rediscovered) Integration Hypothesis
Integration via a series of cascading failures of a chain of
freshwater to moderately saline lakes, eventually spilling
into the developing Gulf
Proposed by Blackwelder in 1932.
What model best explains its distribution?
Uplifted sea level datum?
Stable lake level datum in series?
Northward ‘younging’ marine carbonate succeeded by southward prograding River delta Marine incursion occurs owing to subsidence
associated with rifting in Gulf of California Colorado River integrated by headward erosion
and stream capture Bouse Formation represents sea-level datum
subsequently subject to rapid uplift Marine regression linked to progradation of
Colorado River sediment wedge and delta
Bouse deposits have non-marine geochemical fingerprint
Geologically short interval of integration (with new data)
Major LCR aggradation pulse immediately post-dates Bouse
Existing constraints obviate upstream ‘younging’
Stratigraphy analogous to upstream records deemed ‘non-
marine’
Principal (only?) geological support for marine model is
paleontological
Estuarine interpretation supported only by paleontology Fresh, brackish, and marine water species from Parker south Freshwater only farther north
Linked to rifting in Gulf of Calif. Restricted to LCR area more or less Narrow belt of subsidence without contemporaneous faulting Relatively brief incursion
Base-level fall drives upstream incision Implies some integrated drainage system along LCR Headward erosion carves valleys and leads to capture of
Colorado River in Grand Canyon region Progradation of fluvial sediment drives estuary to south
Trough rebounds and then some in Pliocene-Quaternary Young regional uplift in LCR tied to Colorado Plateau
Simplest Explanation The LCR formed via downstream-cascading lake
spillover Downstream-directed Canyon cutting restricted to divides No / minimal uplift
Alternative Paradigm LCR formed via headward erosion from the head
of the Gulf of California to the Colorado Plateau Upstream-directed Early, deep incision throughout system More than 550 m uplift By-passes graded tributaries to incise bedrock divides
Study Area—Cottonwood and Mohave Valleys
Pyramid hillsPyramid hillspaleodividepaleodivide
Black Mountains (Arizona)
Black Mountains (Arizona)
Newberry Mountains
Newberry Mountains (Arizona)(Arizona)
Mohave ValleyMohave ValleyCottonwood Cottonwood ValleyValley
Local basin fill—Fanglomerates and axial
alluvium
Transition to axial drainage—Newberry gravel
Flood from divide breach—Pyramid gravel
Lake—Bouse Formation (marl, mud, sand,
gravel)
Early through-going river—Panda gravel
Massive aggradation—Bullhead alluvium
Deep incision
Qc: Young river sediment
Qf: Young fan gravel
QTf: Old fan gravel
Tfb2: Ancient fan gravel
Tvn: Nomlaki ash (3.3 Ma)
Tvln: lower Nomlaki ash (4
Ma)
Tcb: Bullhead alluvium
Tbms: Bouse mud and sand
Tbl: Bouse marl (limestone)
Tpg: Pyramid gravel
Tng: Newberry gravel
Tfb1: Ancient fan gravel
Tvw: Wolverine Ck tuff (5.6
Ma)
Tfn: Ancient Fanglomerate
Key Strata
Paleochannels portend significant change in local drainagePaleochannels portend significant change in local drainage
Monomictic cobble-boulder conglomerate Occupies/exploits early axial paleochannels Multi-phased, crudely to moderately well stratified Overlain by the Bouse marl
~3
0 m
~3
0 m
FanglomerateFanglomerate
Pyramid Pyramid gravelgravel
Conspicuous local source
High-energy deposition Clear-water divide
failure
Pyramid Pyramid GravelGravel
Outcrop area of granite
One of the largest boulders, 5 mi from likely source
BoulderBell
Flat-lying marl unconformably overlain by river gravel in central Mohave Valley
Overlies the Pyramid gravel flood deposit
Limestone, siltstone, and sandstone
Overlies paleo-landscape from 640’ to ~1800 ft
Mohave Valley:Bouse Formation
Unconformably overlies the transitional sequence
Compositionally immature paleochannel fill 60 ft above modern river Lithologic diversity increases upsection
Complex fluvial deposit buried pre-existing, deep valleys previously filled with Bouse lake
Net thickness of approximately 800 ft
Net thickness of ~800 feet
Predominantly gravel and sand with minor mud
Elaborately structured river deposit
FanglomerateFanglomerate
80 ft above80 ft aboveModern riverModern river
Panda Gravel—fluvially reworked Newberry fanglomerate mixed with exotics
Mohave Valley:Bullhead alluvium
Pyramid gravel Pyramid gravel (Tpg)(Tpg)
Newberry gravelNewberry gravel(Tng)
Fanglomerate (Tfn)
Bouse marl Bouse marl (Tbo)(Tbo)
Panda gravel Panda gravel (Tcbl)(Tcbl)
The Transitional Section
TephraTephra
Fan gravel
TephraTephra
Distal fan gravel
River gravel
MOHAVE VALLEY EXAMPLE
COTTONWOOD VALLEY EXAMPLE
Local basin fill /shallow lake—Lost Cabin beds
Erosional Unconformity
Deep lake—Bouse Formation
Early through-going river—Panda gravel (lower
Bullhead)
Massive aggradation—Bullhead alluvium
Deep incision
Qc: Young river sediment
Qf: Young fan gravel
QTf: Old fan gravel
Tfb2: Ancient fan gravel
Tcb: Bullhead alluvium
Tbms: Bouse mud and sand
Tbl: Bouse marl (limestone)
Tfb1: Ancient fan gravel
Tvw: Wolverine Ck tuff (5.6
Ma)
Tlcf: Fine Lost Cabin beds
Tlcc: Coarse Lost Cabin beds
Tfn: Ancient Fanglomerate
Tft: Tilted fanglomerate
Interbedded tributary gravels from the Newberry and Black Mountains
Culmination of basin fill in late Miocene
Stratigraphic equivalent of Muddy Creek Fm
Precursor deposit to river integration
Cottonwood Valley: Lost Cabin beds
Marl interbeds in Lost Cabin sediments
Unconformity in Tlc filled with interbedded gravel, mud, and marl overlain by beach gravel
Evidence for two lakes
Cottonwood Valley: Lost Cabin beds and Bouse formation
Classic draping contact
Mud
Mud
MarlMarl
marlmarl
KarlKarl
Mohave Valley:Bouse Formation
Cottonwood Valley: Bouse formation
Mud
Mud
MarlMarl
PhilPhil
fillfill
Mohave Valley:Bouse Formation
Mud
Mud
MarlMarl
Cottonwood Valley: Lost Cabin beds and Bouse formation
Low-lying deltaic sediments
Interbedded mud and sand
Thick clastic package overlies marl
Mud
Mud
MarlMarl
Mohave Valley:Bouse Formation
TfnTfn TfnTfn
TcbTcb
~720 ft a.s.l.
Source area of TfnSource area of Tfn
Pre-integration valley fill package in Cottonwood Valley
Stratigraphic equivalent to the Muddy Creek Formation
Distinctive basal, marginal, and axial facies
Lost Cabin beds (Tlc) Lost Cabin beds (Tlc) Flat-bedded mudstone and sandstoneFlat-bedded mudstone and sandstone
Fanglomerate of the Black Mountains (Tfb)
not a unicorn
TlcTlcTblTbl
TblTbl
Tfb with Tbl ribbonsTfb with Tbl ribbons
QTaQTa
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
TblTbl
TlcTlc
Newberry Mts
TblTbl
QtrkQtrk
QTfbQTfb
Cottonwood Valley Mohave ValleyT
ran
siti
on
alse
qu
ence
unconformity
unconformity
Bouse Beach Facies: Gravel
Gravel depositGravel deposit
Sandstone onlap
Bouse Beach Facies: Gravel, Sand, and Marl
Low angle, tabular cross-beds dipping toward valley axis
Cross-stratified clean sand and reworked fanglomerate at 1840 ft, Lost Cabin Wash
Wave-sorted / reworked fanglomerate on bedrock. Newberry piedmont, 1840 ft / 560 m
Max elevation of
Bouse sediment
Late Miocene axis
of Cottonwood
Valley
Max elevation of
LCR alluvium
Late Miocene
Mohave Valley axis
Holocene floodplain
AA
N
20 miles /
35 km
560 m560 m
560 m560 m
533 m533 m
544 m544 m
Marl
Pyramid Hills
Sea levelSea level
330 m330 m
555 m555 m
Modified from Spencer et al., 2008
Tufa ‘reef’ in Tufa ‘reef’ in saddle 1460 ftsaddle 1460 ft
Tufa and beach Tufa and beach gravel gravel 1400-1460’1400-1460’
Dead MountainsDead Mountains
Detail: in situ tufa bench
LCR inception linked to downstream-directed processes
Quiescent deposition follows flood from upstream
Late Miocene valleys were FILLED, not carved by early LCR
Inconsistent with headward erosion concept
New age-controls compress time frame for river
integration
Links massive aggradation with canyon enlargement
Regional stratigraphic link among pre-river basin fill units
Change preceded the arrival of the Colorado River
Immediately overlies upstream-derived catastrophic flood deposit Coincident marine incursion and flooding from
upstream? Stratigraphic consequence of river integration
via lake failure inferred from geochemical studies Spencer and Patchett (1997); Poulson and John (2003)
Bouse in a similar context below Parker Dam (Buising, 1988) Inter-bedded with intricately bedded fluvial gravels Far-traveled detritus in sand fraction
Upper Lost Cabin beds contain interbedded marl
Base of thick marl and mud unit fills erosional niche in upper Lost Cabin bed section
Quaternary river gravelQuaternary river gravel
Bouse marlBouse marl
Cross-bedded local gravel with marl interbedsCross-bedded local gravel with marl interbeds
Marl interbedded with downstream-directed fluvial gravel
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
Birth of LCR in study area began with divide failure and flood
Pre-river valley geometry similar to modern
Bouse formation is non-marine (not an uplift datum)
Interval of Bouse deposition relatively short
Mohave Valley Transitional Sequence parallels changes in
Western Grand Canyon / Lake Mead Basin
Major fluvial backfilling driven by integration
Pyramid Hills Paleodivide
Newberry Mountains
Black Mountains
Bullhead CityLaughlin
Davis Davis DamDam
N
Black Mtns
Dead Dead MtnsMtns
10 km
CottonwoodValley
MohaveValley
minimum Newberry fan extent based on modern outcrops
Newberry Fans
Newberry FansNewberry FansNewberry Fans
Wave-worked gravelWave-worked gravel
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
Terminal BasinTerminal Basin Lost Cabin BedsLost Cabin Beds
Bouse phase 1Bouse phase 1
Bouse phase 2Bouse phase 2
Divide FailureDivide Failure
Pyramid GravelPyramid GravelLake DrainageLake Drainage LCR, full-blownLCR, full-blown
Bullhead AlluviumBullhead Alluvium
1. Rio Grande
2. Central AZ Rivers
3. Lower Colorado
4. W. Great Basin
5. N. Great Basin
6. Bonneville Basin
7. Snake River
Phil PearthreeJim Faulds Keith HowardJohn BellMike PerkinsAmy BrockAndrei Sarna-WojcickiJon SpencerSue BeardBrenda BuckDave MillerRichard HerefordDaniel Malmon