Geologic Overview of Southern
California Coastal Areas
 Continental
Mark Bordelon
Irvine Valley College
March 2012
Margin
 Coastal & Offshore Faulting
 Geology of Offshore Islands
 Orange County Coastal Geology
 Sediment & Sedimentary Rock
 Long Shore Currents and Coastal Cells
 Depositional vs. Erosional Coastlines
 Geology of San Onofre
 Landslide and tsunami hazards
 Geology of Dana Point area
Subduction of the Farallon Plate 100 m.y. ago
Continental Margins
Where land meets the ocean

Margins
near plate
boundaries
are
―active.‖
Fig.

Margins far
from plate
boundaries
are
―passive.‖
Physiographic Provinces of S. Calif.
http://scamp.wr.usgs.gov/scgeo
Rotation of Transverse Ranges
Fritsche and Behl, 2008
Extension creates basins 20-30 m.y. ago
Up block
Up block
Basin
Offshore Faulting
Newport-Inglewood Fault Zone
Huntington Beach Oil Field (1920s)
Offshore Islands – N. Channel Islands

Four northern Channel Islands are an
extension of the Santa Monica Mts.
•
•
•
San Miguel, Santa Rosa, Santa Cruz &
Anacapa Islands
Geology consists of Miocene volcanic rocks:
pillow basalts, lava flows, tuff
Islands were isolated from one another
12-10 y.b.p. when sea level rose
Pygmy Mammoth on Santa Rosa Island



Radiocarbon date = 13,000 years old
Lower sea level
created one large
island, 5 miles
from mainland
Isolated when
sea level rose
12,000 y.b.p.
http://www.nps.gov/chis/pygmy.htm
Channel Islands
National Marine
Sanctuary
http://www.cinms.nos.noaa.gov/
Offshore Islands – S. Channel
Islands
•
•
•
Southern islands include Catalina, San
Clemente, Santa Barbara and San Nicolas
Islands
Remnants of up-faulted blocks
Marine Terraces well-developed on San
Clemente Island
Marine Terraces – San Clemente Island
25 terraces
2.8 m.y. oldest
580 m high
Catalina Island
•
Catalina Island has extensive outcrops of
Catalina Schist on northern portion of
island
•
Represents blueschist metamorphism which is
typical of subduction zones.
Subduction Metamorphism

Subduction creates the unique blueschist
facies.
A
low geothermal gradient—low T, high P.
 Blueschist minerals
 Glaucophane
 Lawsonite
Lawsonite Blueschist
Geologic Time Scale
OC Coastal
Geology
represented by
Neogene
sedimentary
and igneous
rocks
Geologic Map of Orange County
Sediment vs. Sedimentary Rock


Drilling into the bottom of a coastal area, we encounter:
 Soft mud and loose sand, silt, pebbles, and shells.
Then:
 Similar materials that are more solidified. Then:
 Fragments of solid rock.
 Cemented sand and silt.
 Cemented shells.
Transition from loose sediment into cemented
sedimentary rock.
 This change occurs as burial depth increases.
Classes of Sedimentary Rock
 Clastic—loose
rock fragments (clasts)
cemented together.
 Biochemical—cemented shells of organisms.
 Chemical—minerals that crystallize directly
from water.
Clasti
c
Biochemica
l
Chemical
Beach
•
•
Active Zone of sediment transportation
Beach lies between:
•
•
Erosional area above water level
Depositional area below water level
Coastal Zones
Waves Erode
platform
Summer vs. Winter Beach Profile
Sand Budgets
•
•
•
Estimates of sand gains (inputs) and losses
(outputs) to a beach
Beach profile studies
Inputs:
•
•
•
•
Rivers (Los Angeles, San Gabriel, Santa Ana)
Cliff erosion
Onshore transport of sediment by LSC
Outputs:
•
•
Offshore transport of sediment by LSC
Submarine Canyons
Newport Beach Harbor
Where does
the sand go?
Longshore Drift
Longshore Current and Beach Drift
View from Huntington Beach to the south
Oblique View of Submarine Canyons
Oblique View of Newport Submarine Canyon
Coastal Cells in S. Calif.
5 major coastal cells within 200 miles
Coastal Cell Model
Depositional vs. Erosional Coasts
•
Depositional Coasts
•
•
•
•
Rate of accumulation exceeds erosion
LSC slowed, sand deposits
Features: spits, deltas, barrier islands
Erosional Coasts
•
•
•
Strong wave activity; erosion rates high
Rate of erosion depends on
• Local geology
• Degree of wave exposure
• Tidal range
Features: Cliffs, sea stacks, wave-cut platforms
Erosional
Shoreline
Features
(Exposure to wave
energy high; no
slowing of LSC)
Sea Arches
Sea Stacksisolated rock
remnants
Marine Terraces
Elevated wave-cut
platforms
Wave-cut Platforms
Emergent & Submergent Coasts

Emergent Coastlines



Result from uplift and/or sea level drop
Features: marine terraces
Submergent Coastlines


Result from downdrop and/or sea level rise
Features: estuaries
Geologic Map of San Onofre Area
Cristianitos Fault at San Onofre
Stratigraphic Cross-Section at SONGS Area
Onshore & Offshore Marine
Terraces – San Onofre Area
Rotational Landslides in coastal cliffs
Wave notched cliff
Translational Landslides in coastal areas
Tsunami Risk at SONGs



Honshu Earthquake 3/2011
Magnitude 9.0 (USGS)
Depth 19.9 mile
http://neic.usgs.gov/neis/eq_depot/2011/eq_110311_c0001xgp/neic
_c0001xgp_l.html


Most earthquake damage is due to ground
shaking.
Tsunamis also can significant damage in
coastal areas.
 December 26, 2004—Indian Ocean
tsunami.
 March 11, 2011—eastern coast of Japan.
Fukushima power plant damage

The Fukushima nuclear power plant was damaged.
 Water breached the seawalls placed to protect
the plant.
 Hydrogen explosions destroyed the reactor
buildings.
Megathrust earthquakes
Dana Point Harbor
Capistrano Formation at Dana
Point Harbor
Capistrano Formation at Dana
Point Harbor
Capistrano Formation at Dana
Point Harbor
Submarine Canyons
Turbidite Deposits
http://eqdoc.home.netcom.com/salt2.html
Dana Cove Fault near Cannons Restaurant
at Dana Pt. Harbor
Laguna Beach at Heisler Park
Volcanic dikes cutting through
sedimentary rocks
Sedimentary rock with tafoni
weathering at Heisler Park