Geology of Western Oregon

1
Geology of Western Oregon
Steve Matthes U.S. Department of Energy National
Energy Technology Laboratory Albany, Oregon
2
1. Introduction to Oregon Geology
3
Cartoon by Sidney Harris
4
Oregons Geographic Regions Correspond to
Oregons Geology
USGS Geological Map of Oregon Various colors
represent surface rock of varying types and ages.
5
Metasequoia Oregons State Fossil
Sun Stone Oregons State Gemstone
Thunderegg Oregons State Rock
6
Oregons Oldest Surface Rocks (more than 50MYA)
Paleozoic sedimentary rock (frequently
metamorphosed) (300MYA)
Old Cenozoic marine basalt and andesite (50 MYA)
Mezozoic granitic rocks (150 MYA)
Permian and Triassic sedimentary and volcanic
rocks (250 200 MYA)
Mezozoic sedimentary and volcanic rocks
Eocene and Oligocene marine sediments (50MYA)
Mezozoic sedimentary and volcanic rocks
Permian and Triassic sedimentary and volcanic
rocks (250 200 MYA)
Mezozoic granitic rocks (150 MYA)
7
Paleozoic sedimentary rock (frequently
metamorphosed) (300MYA)
Eocene
Pennsylvanian
Oligocene
Triassic
Mississippian
Permian and Triassic sedimentary and volcanic
rocks (250 200 MYA)
Eocene
Mezozoic sedimentary and volcanic rocks
Eocene and Oligocene marine sediments (50MYA)
Mezozoic sedimentary and volcanic rocks
Permian and Triassic sedimentary and volcanic
rocks (250 200 MYA)
Cretaceous
Jurassic
Jurassic
8
Most surface rocks in Oregon are younger than 25
million years
Oldest Oregon Rocks 360 MYA rocks from the
Mississippian epoch of the Paleozoic era.
9
High Cascades andesite and basalt (less than 10
MYA)
Columbia River Basalts (20 MYA)
Oregons Youngest Surface Rocks (less than
50MYA)
Miocene marine sediment (5 MYA)
Recent basalt and andesite (less than 1 MYA)
Recent alluvial deposits including deposits from
Missoula Floods (15,000 YA or younger)
Western Cascades andesite and basalt (25 MYA)
Older Cenozoic non-marine sedimentary rock-
ash-flow tuffs, banded rhyolite (20-5 MYA)
Recent alluvial lake deposits and pumice (1 MYA
or younger)
Younger Cenozoic ( less than 5 MYA)
10
Miocene marine sediment (5 MYA)
Recent alluvial deposits including deposits from
Missoula Floods (15,000 YA or younger)
Older Cenozoic non-marine sedimentary rock-
ash-flow tuffs, banded rhyolite (20-5 MYA)
Recent alluvial lake deposits and pumice (1 MYA
or younger)
Younger Cenozoic ( less than 5 MYA)
11
High Cascades andesite and basalt (less than 10
MYA)
Columbia River Basalts (20 MYA)
Miocene marine sediment (5 MYA)
Paleozoic sedimentary rock (frequently
metamorphosed) (300MYA)
Old Cenozoic marine basalt and andesite (50 MYA)
Recent basalt and andesite (less than 1 MYA)
Mezozoic granitic rocks (150 MYA)
Recent alluvial deposits including deposits from
Missoula Floods (15,000 YA or younger)
Permian and Triassic sedimentary and volcanic
rocks (250 200 MYA)
Western Cascades andesite and basalt (25 MYA)
Mezozoic sedimentary and volcanic rocks
Eocene and Oligocene marine sediments (50MYA)
Older Cenozoic non-marine sedimentary rock-
ash-flow tuffs, banded rhyolite (20-5 MYA)
Mezozoic sedimentary and volcanic rocks
Recent alluvial lake deposits and pumice (1 MYA
or younger)
Permian and Triassic sedimentary and volcanic
rocks (250 200 MYA)
Mezozoic granitic rocks (150 MYA)
Younger Cenozoic ( less than 5 MYA)
12
Cartoon by Sidney Harris
13
(No Transcript)
14
Corvallis, Oregon
Siletz River volcanics Ancient undersea
volcanoes uplifted by collision of tectonic plates
Corvallis Fault
15
Corvallis
16
(No Transcript)
17
2. How geologists figure out the geologic past.
18
How do geologists know what the earths geologic
history looks like?

• Wells from oil and gas exploration- rocks from
  drill core (geologic column)
• Water wells
• Type of rock (igneous, sedimentary)
• Fossils
• Chemical composition of rocks
• Dating Methods (radioactive decay,
  dendrochronology, ice cores, varves, coral
  clocks)
• Plate tectonics

19
CORE SAMPLES
20
Tertiary Ft. Union Fm .....................100
feet Cretaceous Greenhorn Fm ..................
...4910 feet Cretaceous Mowry Fm................
...... 5370 feet Cretaceous Inyan Kara
Fm.....................5790 feet Jurassic
Rierdon Fm..........................6690 feet
Triassic Spearfish Fm........................732
5 feet Permian Opeche Fm.......................
....7740 feet Pennsylvanian Amsden
Fm........................7990 feet
Pennsylvanian Tyler Fm........................824
5 feet Mississippian Otter Fm..................
....8440 feet Mississippian Kibbey
Lm......................8780 feet Mississippian
Charles Fm......................8945 feet
Mississippian Mission Canyon Fm............9775
feet Mississippian Lodgepole Fm..................
..10255 feet Devonian Bakken Fm..................
.........11085 feet Devonian Birdbear
Fm.........................11340 feet Devonian
Duperow Fm.........................11422 feet
Devonian Souris River Fm....................11832
feet Devonian Dawson Bay Fm....................
....12089 feet Devonian Prairie
Fm.........................12180 feet Devonian
Winnipegosis Grp.....................12310 feet
Silurian Interlake Fm........................125
39 feet Ordovician Stonewall Fm................
.....13250 feet Ordovician Red River
Dolomite...............13630 feet Ordovician
Winnipeg Grp.....................14210 feet
Ordovician Black Island Fm..................14355
feet Cambrian Deadwood Fm......................
....14445 feet Precambrian.......................
...........14945 feet
Complete Geologic Column in North Dakota-
discovered by an oil exploration well drilled
15,000 feet deep!
21
Places where the complete geologic column has
been found
22
Radioactive Dating
Only 0.01 of the potassium in a rock is K-40!
23
(No Transcript)
24
Periodic Table of the Elements
Select an element
(
)
Internet link
Potassium 40 (K) has 19 protons and 21 neutrons.
It is radioactive and decays to Argon 40 (Ar)
which has 18 protons and 22 neutrons.
25
Potassium Argon (K-Ar) Dating

• 1250 Million year half-life (works well for
  mica, amphibole, K-feldspar, volcanic rocks older
  than 30 million years)
• Works best in granitic rocks where the various
  mineral crystals are large enough for processing.
• Based on assumption that Ar will not be present
  in the crystal structure when the rock forms
  (good assumption- Ar is Very rare in the crust)

26
(No Transcript)
27
Plate Tectonics
The earths crust consists of a patchwork of
solid plates floating on the mantle. These
plates are constantly in motion, colliding and
rearranging. The drawings at left show how the
plates have moved over the last 225 million years.
28
Cartoon by Sidney Harris
29
Age of Ocean Crust
Old crust
New crust
30
(No Transcript)
31
Quiz
1. 250 million years ago , the continents were
all connected together in a super continent
called______________.
1. Answer Pangea
32
3. Plate tectonics
33
(No Transcript)
34
New Crust forms here
Plates may Slide by each other. Transform
Plates may Separate. Divergent
Plates may Collide with each other. Convergent
e.g. San Andreas Fault)
(e.g. Juan de Fuca ridge)
35
Oceanic plate
New crust is created at the ocean ridge. The
seafloor spreading pushes the ocean plate into
the continental plate
Volcanoes form near the collision between two
plates
36
Subduction
uplift
uplift
Upwelling
This is where volcanoes form
37
A closer look at subduction
38
What causes the two plates to collide?
Ocean Ridge
Magma
Seafloor Spreading
When hot rock gets close to the surface of the
ocean crust it may liquefy because of reduced
pressure. The liquefied rock solidifies on
exposure to the seawater. Solidified rock expands
forcing the oceanic crust apart at the ridge. The
process repeats resulting in seafloor spreading.
39
Plates are constantly in motion in relation to
each other. Average plate speed is 5 cm per year.
Southern California coast is on the Pacific Plate
and is moving to the NW.
40
California South of San Francisco to Baja
California
41
Quiz
5. 100 million years from now, parts of
California will be an island off of
_______________.
5. Answer Alaska
42
Cartoon by Sidney Harris
43
3. Oregons geologic history Emphasis on
Corvallis.
44
200 million years ago (ya)
Wallowas
Pacific Ocean
Blue
Subduction zone
Continental shelf
Old continent
Klamath
45
100 million ya
(Tropical)
Subduction zone
Volcanoes caused by collision of Pacific Plate
with North American Plate
46
Quiz
2. The ____________ zone is where the oceanic
plate is forced under the continental plate.
2. Answer Subduction
47
50 million ya
(Tropical)
Undersea volcanoes erupt formation of Siletz
River Volcanics (54 million ya)
48
Marys Peak was an undersea volcano 54 million
years ago!
49
Pillow lava on Mauna Loa, Hawaii
Pillow lava at Axial Seamount
Pillow Basalt forms when lava is cooled quickly
underwater. Pillow basalt is evidence that an
area once was underwater.
Pillow Basalt on Marys Peak 2000 feet above
sea level!
50

Pillow Lava on Vineyard Mountain
51
The Earth was several degrees warmer in the
Eocene (50 million years ago)
Today
52
(subtropical)
35 million ya
Subduction zone
53
(No Transcript)
54
(temperate)
25 million ya
Western Cascades erupt
Subduction zone
Siletz Volcanics covered with thick layer of
ocean and river sediments
55
(No Transcript)
56
Western Cascades
High Cascades
Santiam Pass
Tombstone Pass
57
(No Transcript)
58
FLOOD BASALTS
20 million ya
Subduction zone
59
(No Transcript)
60
(No Transcript)
61
Flood Basalts on the Columbia River
62
17 million ya
Coast range had not yet uplifted. This region was
a relatively flat plain.
Old Columbia river channel
Yaquina Head
63

Remnants of Flood Basalt flow that filled the
Columbia River channel and forced the river to
the north.
64
The lava forming Yaquina Head originated in
Central Washington!!
65
10 million ya
Subduction zone
Oregon Coast is near present location. Area west
of the Western Cascades is a broad coastal plain.
Siletz volcanics are covered with sedimentary
rock. As coastal plain is uplifted, sedimentary
rock erodes away.
66
(No Transcript)
67
12,000 ya
Missoula floods
Subduction zone
Sedimentary rock has eroded away exposing older
Siletz river volcanics
High cascades erupt
68
(No Transcript)
69
Cartoon by Sidney Harris
70
Flood waters were 200 feet deep in the Willamette
Valley! Icebergs floated boulders from Canada,
Idaho, and Montana into the valley and deposited
them on hillsides.
71
(No Transcript)
72
(No Transcript)
73
Glacial Erratics near McMinnville
74
Erratic rocks rafted into the Willamette Valley
on icebergs from the melting ice sheet. Erratic
rocks came from Washington, Idaho, Montana , and
Canada. Flood waters were as deep as 122 meters
and extended to Eugene. The famous Willamette
meteorite found in Oregon City is an erratic!!
75
Significant end-of-ice-age floods occurred at the
start of each interglacial period.
We are in a period of cyclic glaciation with
glacial maximum occuring every 100,000 years.
76
Cartoon by Sidney Harris
77
today
Subduction zone
High cascades erupt