Thompson, Armentrout and Blackwell, 5/2019

Rocky Johnson

PacWest Drone Services

Tectonic History of Coos Bay Basin

and its’ Relationship to Cenozoic Tectonics in the Pacific Northwest

A Preliminary Report of Ongoing Research

Laird Thompson, Utah State University

John Armentrout, University of Oregon

Dave Blackwell, University of Oregon

Thompson, Armentrout and Blackwell, 5/2019

‘Siletzia’ Accreted a “Large Igneous Province”

Siletzia Time-Rock Diagram

Wells et al. (2014)

Aeromagnetic Map

Coos

Bay

Basin

Thompson, Armentrout and Blackwell, 5/2019

Topics

Basin Setting

Structural Observations

Deformation Phases

Emerging Regional Pattern

Ongoing Research

Thompson, Armentrout and Blackwell, 5/2019

Coos Bay Basin

Cape

Arago

North

Bend

Basal Contact of Coaledo

Fm. from Newton (1980)

Base Coaledo

Fault

Relative

Accommodation

30

50

40

0

20

10

Bastendorff

1000m’

Tunnel Point

250m

Sacchi Beach

600m

Empire

500m

Tarheel

300m+?

Coaledo

2000m

Terraces

FormationsMillion

Years

Deformational

Phases

Extension

Extension

Contraction

Contraction

Contraction

‘Collision’KilometersMiles

0 6 12

630

Thompson, Armentrout and Blackwell, 5/2019

Stratigraphic Record

Umpqua Gp.

Miocene Beds

(Tarheel fm.)

Coos

Bay

Siletzia

Terraces

Empire Formation

Tunnel Point Sdst.

Sacchi Beach Beds

Coaledo Formation

Bastendorff Fm.

Modified 5/23/18 from McDougall (2008)

Empire Formation

Cape

Blanco

Terraces

Miocene Beds

Eocene Shale

Ma

0

5

15

25

20

30

35

60

65

55

40

45

50

10

Umpqua Gp.

Newport

Basin

Siletzia

Terraces

Depoe Bay BasaltCape Foulweather B

Yamhill

Formation

Yachats Basalt

Tyee Formation

Alsea Formation

Yaquina

Fm.

Astoria Formation

Tillamook Vol.

Cenozoic Time Scale

Approximates the detail from Armentrout et al. (1983)

Adjusted appropriately for the modified 2008 Time Scale

Baldwin

Armentrout

Addicott

Baldwin

Armentrout

Addicott

Snavely

Lander

Niem Wells

Rau

Willapa

Hills

Siletzia

Grande Ronde

B

Frenchmen Sp. B

Terraces

Cowlitz Formation

McIntosh Fm.

Astoria Formation

Lincoln Creek

Formation

Goble Vol.

Cowlitz Formation

Troutdale Formation

Astoria

Basin

Siletzia

Grande Ronde

B

Frenchmen Sp. B

Terraces

Astoria Formation

Oswald West

Formation

Pittsburg Bluff

Keasey Formation

Tillamook Vol.

Yamhill Fm. ?

Cowlitz Formation

Troutdale Formation

51

48

16

13

5

Ma

Troutdale Formation

Thompson, Armentrout and Blackwell, 5/2019

Topics

Basin Setting

Structural Observations

Deformation Phases

Emerging Regional Pattern

Ongoing Research

Thompson, Armentrout and Blackwell, 5/2019

Deformation Observations: Multiple Scales

Deformation BandsDisequilibrium Compaction

Abutting Relationships

Fault Kinematics

Thompson, Armentrout and Blackwell, 5/2019

Primary Observation Sites

Cape Arago

Gregory Pt.

Fivemile Pt.

Sacchi Beach

Fossil Point

Yoakum Point

Lighthouse Beach

Gregory Point

Sunset Bay

Shore Acres

North Cove

Cape Arago

South Cove

Sacchi Beach

Seven Devils Fault

Fivemile Point

Coos Head

Lidar Image

N

KilometersMiles

0 2 4

210

Southernmost Siletzia

Accretionary

Boundary

Coos Head

So

uth

Slo

ug

h

Thompson, Armentrout and Blackwell, 5/2019

Goggle Maps

Shoreface Sandstone Cycles

Bedding

Major Offset

Primary Faults

Secondary Faulting

1

Deformation Observations: Multiple Scales

3

3

1

1

12

2

2

2

Strawberry Point

Sunset

Bay

Pacific Ocean

Dogami File

Lidar

North Shore Sunset

Bay

Deformation “Phases”

Miocene

Eo-Oligocene

1000 50Meters

N

N

Thompson, Armentrout and Blackwell, 5/2019

Topics

Basin Setting

Structural Observations

Deformation Phases

Emerging Regional Pattern

Ongoing Research

Thompson, Armentrout and Blackwell, 5/2019

Timing of Deformational “Phases” and Orientations

Google Maps

The Coaledo records three phases of deformation:

Each subsequent phase modifies the previous.

Sunset Bay

Deformation “Phases”

Pliocene

Miocene

Eo-OligoceneMeters

0 100 200

N

Late ‘Overprint’

Modifications

Thompson, Armentrout and Blackwell, 5/2019

Upper Plate Deformation

Phase 1

< 45-38 Ma

Post-Tunnel

Point

Progressive Clockwise Rotation

55-51 Ma

Siletzia

Accretion

Phase 3

< 5(?) Ma

Post-Empire

Phase 4

< 200 ka

Uplift

Paleo-Stress

Orientationσ1

40o-56o

Folding

25o

Folding

5o-12o

Folding

Phase 2

< 14(?) Ma

Post-Tarheel

Paleomagnetic Rotation

Under Re-study

Thompson, Armentrout and Blackwell, 5/2019

Lighthouse Beach Outcrop

Lighthouse Beach Outcrop

Lighthouse Beach Thrust

• Within the Upper Coaledo Formation

• Post-Tarheel Event (≤15 Ma)

• Slip-surface traced

through 3 coves and at

points 1.2 km apart

Thompson, Armentrout and Blackwell, 5/2019

Post Empire (<5 Ma) Deformation

Slip Elements

Non-Orthogonal Joints

Shear Patterns

Apparent Coeval SHmax

Deformation “Phases”

Modern

Pliocene

N-S

N55E

Borehole Breakout

Niem et al., 2006

Thompson, Armentrout and Blackwell, 5/2019

Topics

Basin Setting

Deformation Phases

Tectonic “Phases”

Emerging Regional Pattern

Ongoing Research

Thompson, Armentrout and Blackwell, 5/2019

Stratigraphic and Structural Interpretations

Siletzia Terrain Accretion

51-49 Ma

Folding

25 Degrees

40 – 56

Degrees

5-12

Degrees

Deformational

Phases

Extension

Extension

Contraction

Contraction

Contractio

n

‘Collision’

30

50

40

0

20

10

FormationsMillion

Years

Change in plate motions

generates oblique extension

along coast with intrusion of

Tillamook Volcanics and

extension of Tualatin Basin

San Andreas plate boundary

change generates Juan de Fuca

plate fragmentation and

contraction along coast, and

folding of S. Slough Syncline

Coupling of upper and lower

plate deformation

Likely post-CRB deformation with

dextral oblique shortening

Upper plate Shmax based on

borehole breakout

Bastendorff

1000m’

Tunnel Point

250m

Sacchi Beach

600m

Empire

500m

Tarheel

300m+?

Coaledo

2000m

Terraces

3,800+m

10’sm+

500m+

300m+

Shmax

Vector

Thompson, Armentrout and Blackwell, 5/2019

Topics

Basin Setting

Deformation Phases

Tectonic “Phases”

Emerging Regional Pattern

Ongoing Research

Thompson, Armentrout and Blackwell, 5/2019

Ongoing Research

Paleogeography:

Paleoclimate (Palynomorphs, Marine Biofacies)

Sandstone Mineralogy

Zircon Age Clusters

Tectonics:

Basin Scale Structure, including subsurface

Balanced Cross Sections

Paleomagnetic Rotation History – Refined and Expanded

Stratigraphy:

Lateral Facies Correlation – Drone-Image Refinement

Depositional Environments, including integrated biofacies:

(Forams, Mollusks, Elasmobranchs, Palynomorphs)

Geochronology:

Ar/Ar on Tuffs and Pb/Ur on Zircons

Paleomagnetic Reversals – Expanded Section

Micropaleontology - Updated

Thompson, Armentrout and Blackwell, 5/2019

Coaledo Team: Cross Discipline Integration

J.Jackson

D.Blackwell

J.Armentrout

Structure/Stratigraphy

L.Thompson S.Bogue

Magnetostratigraphy

N.BlackwellR.Weldon

Drone Pilot

R.JohnsonS.PappajohnA.Niem

Coal Subbasin

Field Safety

T.Armentrout

T.Demchuk

A.BarbatoS.WarnyB.Welton

C.Hickman

PaleontologyK.McDougall

Sedimentology/PaleogeographyS.Cooke

M.DarinB.Dorsey

Thompson, Armentrout and Blackwell, 5/2019

Thank You

Shore Acres State Park, Coos Bay, Oregon Photo from S. Taylor, Western Oregon