Post on 21-Aug-2020
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