birth of the lower colorado river

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