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Transcript of Anh Tran Thesis
Examine modern and paleo tidal channel deposits from Seal Beach: Insight to Paleotsunami Studies.
By
Anh Tran
Geology (B.Sc.): August 2015
California State University, Fullerton
Department of Geological Sciences
Faculty Advisor: Matthew E. Kirby, Ph.D.
1
Examine modern and paleo tidal channel deposits from Seal Beach: Insight to Paleotsunami Studies.
By Anh Tran
A Thesis Submitted in Partial Fulfillment of Requirements for the Degree of Bachelor of Science at
California State University, Fullerton
Approved, Thesis Committee
___________________________ Dr. Matthew E. Kirby
Assistant Professor of Geology Thesis Advisor
Fullerton, CA
April 04, 2015
Examine modern and paleo tidal channel deposits from Seal Beach: Insight to Paleotsunami Studies.
Anh Tran
2
Faculty Mentor: Prof. Matthew E. Kirby
Geology (B.Sc.), 2015, Department of Geological Sciences
2357 W Moro Pl. Anaheim CA, 92801
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1.0 ABSTRACT
Off shore fault and submarine landslides can produce tsunamis in
southern California. Sediment cores taken from the Seal Beach wetlands contain
shell hash layers that are potential paleotsunami units (Creager, 2014).
However, an alternative explanation is that the shell hash layers found in the
wetland cores reflect lag deposits associated with a relict tidal channel. To
assess whether or not the wetland shell hash layers are or are not relict tidal
channel lag deposits, we examine two tidal channel sediment cores SBPCTC-1B
and SBPCTC-2A from Seal Beach. Both cores contain typical fine to silty sands
with occasional plant roots and leaf debris. They contain very few shells or shell
fragments. Notably, they contain no shell hash layers. These results suggest that
the shell hash layers in the Seal Beach wetland cores discussed by Creager
(2014) are not relict tidal channel lag deposits. Consequently, it is possible that
the wetland shell hash layers are tsunamigenic.
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2.0 Table of Contents
LIST OF FIGURES AND TABLE ………………………………………………..……5
INTRODUCTION ………………………………………………………………….……6
BACKGROUND ……………………………………………………………………….. 7
QUESTION AND HYPHOTHESIS ………………………………………..….….… 12
MATERIALS AND METHODS ………………………………………………………13
RESULTS …………………………………………………………………………...…14
CONCLUSIONS AND DISCUSSION…..……………………………………………16
ACKNOWLEDGEMENT ……………………………………………………………...18
REFERENCES ……………..…………………………………………………………19
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3.0 LIST OF FIGURES AND TABLE
Figure 1. Google Earth image of core SBPCTC14-2A and SBPCTC-14B……. 22
Figure 2. 1894 historical coastal Wetland of Los Angeles and Orange County . 23
Figure 3. Location of freshwater swale and bolsa chica flood channel ………... 24
Figure 4. Seal Beach’s wetland 1873 to 1976 …………………………..………... 25
Figure 5. Mapped located of the Palos verdes fault ………………………...…… 26
Figure 6. Large 1cm plus shell fragments found in core SBPCTC-1B ……….... 27
Figure 7. Sediment core of SBPCTC-2A ………………………………………….. 27
Figure 8. CHI and Core description of SBPCTC-1B………….……………………28
Figure 9. CHI and Core description of SBPCTC-2A ……..………………………. 28
Figure 10. Comparison of core SBPCTC-1B and core SBPCTC-2A………….... 29
Table 1. Core Location ……………………………………………...………………. 29
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4.0 INTRODUCTION
Purpose
Shell hash layers were found in Seal Beach wetland cores (Creager,
2014). Shell hash deposits are indicative of tsunami deposits particularly if they
are laterally extensive (Donato et al., 2008). However tidal channels often
migrate through time, resulting in relict tidal channels that are now buried
beneath wetland environments. It is hypothesized that tidal channels are
associated with the deposition of shell hash layers. The purpose of this study is
to identify and describe sediments from modern tidal channels in Seal Beach to
see if any shell hash layers (aka shell lag deposits) are observed. Cores are
used to examine both modern and paleo tidal channel sediment types. This study
will help to refute or confirm that shell hash layers found in wetland sediment are
actually relict tidal channel shell lag deposits. The locations of these cores can be
seen in Table 1.
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5.0 BACKGROUND
Coastal Wetland significance
Coastal Wetlands and Their Significance in Paleotsunami Research
Coastal Wetlands are useful environment to study past depositional events due
to their often-excellent preservation potential. Coastal wetlands often encompass
an intermediate position between coastal beaches and its adjoining river system.
Coastal wetland receives their sediment as suspended loads associated with
tidal processes that mobilize, suspend and transport fine sediment. This
sediment is then captured by the vegetation causing deposition; consequently,
wetland environments contain the finest sediment associated with coastal
environments (Pethick, 1984; Christiansen at el., 2000). This special environment
makes coastal wetlands ideal for capturing and preserving paleotsunami
deposits.
Shell deposits
Shell deposits are often considered diagnostic paleotsunami indicators for
coastal environment (Donato et al. 2008; Rhodes et al., 2011; Reinhardt et al.,
2012). Past studies have shown that tsunamigenic shell hash layers are
characterized by thick (5-25 cm), laterally extensive beds (> 1km2), out of place
shells, and/or fragmented shells (Donato et al. 2008). Tsunami events transport
and rework shelly material resulting in fragmented pieces (Reinhardt et al.,
2012). The lateral extent of shell bed is use to differentiate tsunami deposits
from storm deposits, as both events have the energy to remobilize shell deposits.
The major difference is that tsunami shell hash layers are laterally more
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extensive. Coarse grain sand, mud clasts and cobbles can also be found with
shell deposits and can be use as signatures in deposits where allochthonous
bivalves are not abundant or absent (Donato et al. 2008; Reinhardt et al., 2012).
Seal Beach Wetland
Historically, Seal Beach wetlands receive its freshwater source from
riverine systems and run off, perhaps associated with the San Gabriel and the
Santa Ana River systems at times. Today, neither the San Gabriel River nor the
Santa Ana River flow into the Seal Beach wetlands (U.S U.S Fish and Wildlife,
2011). Anaheim Creek also provided freshwater to the wetlands but now it has
insignificant, possibly due to agricultural use and land modification (Figure 2). To
the south of the wetland is the Bolsa Chica storm channel; it connects the
Westminster, Anaheim Barber City, and Stanton storm channels into one, which
today travel around the wetland and empty into Anaheim Bay (Figure 3).
Construction of these channels cut off potential storm runoff into the wetland that
would normally occur during rainstorms. The only freshwater sources today are
two small swales but they are insignificant in contributing to the freshwater input
and to the accretion of sediment in the wetland (Figure 3). The Seal Beach
wetland exhibits two high tides and two low tides, with high tides being up to +7.2
feet above mean level and low tide is being up to -1.7 below (U.S Fish and
Wildlife, 2011). Today, the wetland is covered in vegetation and a variety of
organisms including bivalves and gastropods. It also is characterized by a high-
salinity environment and receives its sediment from the ocean and from the
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accumulation of organic detritus. Accretion rate is estimated by the U.S Fish and
Wildlife at 2mm per year (U.S Fish and Wildlife, 2011).
Tidal Channel
Tidal channel can be seen as system where marine water flows into the
wetland supplying it with nutrients, sediments and mixing with the incoming
freshwater and its nutrients and sediments (Mallin, M. , & Lewitus, A., 2004;
Christiansen et al. 2000). Tidal inlets are characterize by trough cross bedding,
horizontal lamination, ripple beds, flaser and wavy bed consisting of fine sand
/silty clay (Moslow et al.,1985). Burrows, and shell deposits are common since
many organism uses tidal channels as home (Moslow et al.,1985). Tidal channel
compositions are influenced in part by incoming freshwater fluvial system, tides
and wave action (Mallin et al., 2004). In Seal Beach, there are no fluvial
influences into the wetland today and the tidal channels are fed entirely by the
ocean. However, before significant human modification of the southern
California coast, Seal Beach wetlands were – at times – connected to fluvial
systems that contributed sediment, nutrients, and freshwater. Consequently, we
examine not only the modern tidal channel sediments but paleo tidal channel
sediments by coring down into the modern tidal channel. California’s coastal
environment are usually rocky with steep shorelines, this reduces the influence of
tidal channels on the coastal system and also their frequency of occurrence
(Mallin et al., 2004). According to the U.S Fish and Wildlife, Seal Beach wetland
tidal channels consist of organic rich, silty sand. Figure 4 show the extent of
change in the tidal channel from 1873 to 1976, note the freshwater system that
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once fed into this tidal channel. Comparing Figure 4 and Figure 1 can give view
an idea of how the core environment of tidal channel has changed over the
century.
Tsunami Sources
Faults that cut across the San Pedro Shelf have historically resulted in
moderate strength earthquakes; M 5.2 in 1979 and M 5.0 in 1989 (Fisher et al.,
2004; Figure 5). Although no large earthquakes have occurred since, it is
speculated to have a potential to unleash an M 7 earthquake (Fisher et al.,
2004). The latest record of submarine slope failure in the San Pedro shelf is
about 7500 years old; the submarine landslide is about 4.5 km long and
deposited over 0.34 km2 of material into the southwest basin (Bohannon et al.,
2004). This slope failure was estimated to generate 8-12 m high tsunami and
was probably caused by a 7.0 M or greater earthquake (Bohannon et al., 2004).
Submarine landslides are major tsunami generators. The 1964 Alaskan Port
Valdez earthquake is the prime example of how destructive these landslides can
be as tsunamigenic forces. The massive 9.2 earthquake cause a 4,000 feet long
by 600 feet wide mass of land to slump into port Valdez causing a reported 40
feet high wave that destroy the town of “old” Valdez town (Parsons et al., 2014).
The tsunami extended 550 m landward covering the area up to 5.5 m depth
(Parsons et al., 2014). The fault also generated enough energy to send tsunami
reaching Crescent City in northern California, killing 11 people and causing $15
million worth of damage (Uslu et al., 2007). The Aleutian megathrust subduction
zone, which was responsible for the Valdez tsunami, is the biggest non-local
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potential tsunami source for southern California. The Aleutian megathrust is
active and had earthquakes greater then M. 8 in the past; M. 9.1 1957, M. 9.2 in
1964, M. 8.7 1965, M (Lander et al., 1993). Other potentials source includes
Japan’s highly active subduction trench and the Hawaiian Island, but large
earthquakes from these area rarely results in significant damage in the pacific
west coast.
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6.0 QUESTION
It is possible that shell hash deposits found in the wetland cores are
actually relict tidal channel shell lag deposits? To answer this question, we
examined two tidal channel cores taken from Seal Beach to investigate the
sedimentology of the modern and paleo tidal inlets and to look for shell lag
deposits. If no shell lag deposits are found in the tidal inlet cores matching the
description of the shell hash deposits found in the wetland cores (Creager, 2014),
it raises the possibility that the wetland shell hash layers are tsunamigenic.
7.0 HYPHOTHESIS
Shell hash layer found in Wetlands are not relict tidal channel lag deposits.
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8.0 MATERIALS AND METHODS
Cores SBPCTC14-1B and SBPCTC14-2A were described visually
following standard core description protocol (http://lrc.geo.umn.edu/laccore/).
Most importantly cores were thoroughly examined for any shell deposits. These
cores were then digitally photographed. Each core was sampled for 2 g of wet
sediment weight at 1 cm contiguous intervals using a stainless steel spatula; the
samples will be placed into 8 cm3 plastic cubes. These labeled plastic cubes
were placed into a Bartington MS2 magnetic susceptibility meter to measure the
mass magnetic susceptibility. These measurements, for the most part are taken
on the same day sediments were sampled to avoid oxidation of the magnetic
minerals, but time restraints made temporary storage at 34°F necessary. Each
cube was individually weighted with and without the sediments inside. Entering
the weighted cube minus the same empty cube give us total sediment mass.
Magnetic susceptibility would then be normalized base on weight of sediments.
Core SBPCTC-1B was examined over two days beginning 8/25/2014 and
finished on 8/28/2014; core SBPCTC-2A was also examined over two days
beginning on 9/03/2014 and finishing on 9/18/2014.
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9.0 RESULTS
Visual examination reveals that both tidal inlet sediment cores contain two
types of sediment compositions including grey sandy, organic rich sediment and
a very fine silty sand roughly 20-30% mud, with some evidence of thin bedding
(Figure 6&7). Overall these sediment cores exhibit very slight coarsening with
increasing depth but no obvious abrupt grain size changes. Both cores give off a
sulfurous smell and contain abundant micas, these micas often form dark bands
of the laminae. Core SBPCTC14-1B contains some shelly material at 70 cm with
some organic root like materials between 0.5 cm to 1 cm in length (Figure 6).
Shells found are fragmented and ranged from 0.2 cm up to 0.5 cm. Core
SBPCTC14-2A contains some shell fragments at 47 cm but not abundant like in
core SBPCTC14-1B. Small 2 mm – 3 mm Bivalve’s shell fragments are
dispersed throughout both cores. Core SBPCTC14-2A contains much more
organic root-like materials concentrated at 10-22 cm and 39-52 cm. These
organic materials range from decaying roots to grass like material, probably from
the common Cord grass or Pickleweed species growing in the marshland. Core
SBPCTC14-2A contains laminations below 48cm with dark bands containing
biotite/muscovite and other dark colored sediments, sediment below this marker
are also lighter in color (Figure 7). Sediment below 48cm in core SBPCTC14-2A
also appears to have flaser bedding or hummocky cross stratification. CHI value
for both cores where different in both cores and did not match (Figure 10). Core
SBPCTC14-1B CHI values were invariable and did not show significant changes
(Figure 8). Core SBPCTC-2A CHI values exhibit greater CHI change over depth
15
with a peak value of 7.0 at 46.5 cm, CHI value then decrease to 0.9 at 52.5 cm
where it remained low to the core bottom (Figure 9). This rapid decrease in MS
denotes the beginning of the laminated sediment (Figure 9).
16
10.0 DISCUSION AND CONCLUSION
Visual examination showed no evidences of shell lag deposit resembling
“shell hash” deposit describe in the wetland core by Creager (2014). In the tidal
inlet core, small < 3 cm isolated fragmented clusters with 3-4 shells exist; this is
very different than that found in the wetland cores (Figure 6). Shells and their
fragments were not found with any coarser grain sediment or cobbles. CHI
values also do not change significantly over the length of the core taken, except
in the last 48 cm of SBPCTC14-2A. CHI values do not change within the shelly
layers or in conjunction with shells fragments. For these following reasons I
conclude that shell hash deposits found in previous wetland cores at Seal Beach
(Creager, 2014) do not represent relict tidal channel shelly lag deposits.
No age model
No radiocarbon dates were measured on the tidal channel shell material.
Future research should date the shells in the tidal channel cores for comparison
to the ages from the shell hash units in the wetland cores. Faulting occurs in this
wetland and dates will make correlating tidal channel cores with wetland cores
easier. In addition, similar ages between the tidal inlet and wetland core shell
materials may help determine their origin as either relict tidal channel lag
deposits or paleotsunami.
Zone of accumulation
Another alternative is that shell lag accumulation zones might exist in
different parts of a tidal channel, perhaps in narrower channels where tide energy
is higher and fine sediment is winnowed away. Future work should consider
17
extracting sediment cores from other Seal Beach tidal channels, particularly
channels that have existed since the 1873–1976 A.D. map (Figure 4).
In-situ Shell deposits
Bivalves are abundant in the wetland, thus it is possible that shell deposits
found in previous wetland core (Creager 2014) are in-situ shell deposits
associated with ambient wetland deposition. Thick vegetation in the wetlands
prevents the bivalves from being swept away by tidal currents. To investigate
this scenario, modern studies of shell fragmentation in the wetland should be
explored to see how much bivalve shells have been reworked, remobilize, and
fragmented.
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11.0 ACKNOWLEDGEMENT
This projected was funded by Kirby Paleoclimatology and Paleostunami
Laboratory (KPPL). Special thanks to Dr. Kirby and Robert Leeper for guiding
me through the process.
19
12.0 REFERENCES
Rhodes, B. P., Kirby, M. E., Jankaew, K., & Choowong, M. (2011). Evidence for a
mid-Holocene tsunami deposit along the Andaman coast of Thailand
preserved in a mangrove environment. Marine Geology, 282(3), 255-
267.
Creager O. D. (2014). Searching for Prehistoric Earthquakes and Tsunamis at
the Seal Beach Wetlands, Seal Beach, CA. Dimension journal of
mathematics and sciences. CSUF Department of Geology.
Bohannon, R. , & Gardner, J. (2004). Submarine landslides of san pedro
escarpment, southwest of long beach, california. Marine Geology, 203(3),
261-268.
Christiansen, T. , Wiberg, P. , & Milligan, T. (2000). Flow and sediment transport
on a tidal salt marsh surface. Estuarine, Coastal and Shelf Science, 50(3),
315-331.
Donato, S. V., et al. (2008) Identifying tsunami deposits using bivalve shell
taphonomy. Geology, (36.3): 199-202.
20
Fisher, M. A., Normark, W. R., Langenheim, V. E., Calvert, A. J., & Sliter, R.
(2004). The Offshore Palos Verdes Fault Zone near San Pedro, Southern
California. Bulletin of the Seismological Society of America, 94(2), 506-
530.
Lander, J. F., Lockridge, P. A., & Kozuch, M. J. (1993). Tsunamis affecting the
west coast of the United States, 1806-1992 (No. 29). US Dept. of
Commerce, National Oceanic and Atmospheric Administration, National
Environmental sdf Satellite, Data, and Information Service, National
Geophysical Data Center.
Mallin, M. , & Lewitus, A. (2004). The importance of tidal creek ecosystems.
Journal of Experimental Marine Biology and Ecology, 298(2), 145-149.
Normark, W. , McGann, M. , & Sliter, R. (2004) Age of palos verdes submarine
debris avalanche, southern California. Marine Geology, 203(3): 247-259.
Moslow, T. F., & Tye, R. S. (1985). Recognition and characterization of Holocene
tidal inlet sequences. Marine Geology, 63(1), 129-151.
Oceanic and Atmospheric Administration, National Environmental Satellite, Data,
and Information Service, National Geophysical Data Center.
21
Parsons, T. , Geist, E. , Ryan, H. , Lee, H. , Haeussler, P. , et al. (2014). Source
and progression of a submarine landslide and tsunami: The 1964 great
Alaska earthquake at valdez. Journal of Geophysical Research: Solid
Earth, 119(11), 8502-8516.
Pethick, J.S. (1984). An introduction to coastal geomorphology. United States:
Edward Arnold Publishers,Baltimore, MD.
Reinhardt, E. G., Pilarczyk, J., & Brown, A. (2012). Probable tsunami origin for a
shell and sand sheet from marine ponds on Anegada, British Virgin
Islands.Natural hazards, 63(1), 101-117.
Robert L. Wesson1 , Arthur D. Frankel1 , Charles S. Mueller1 , and Stephen C.
Harmsen1 (1999). Probabilistic Seismic Hazard Maps of Alaska. U.S.
Geological Survey Open-File Report 99- 36
U.S. Fish and Wildlife Service. 2011. Draft Comprehensive Conservation Plan/
Environmental Assessment March 2011. U. S. Fish and Wildlife Service
Pacific Southwest Region Sacramento, CA.
Uslu, B., J. C. Borrero, L. A. Dengler, and C. E. Synolakis (2007), Tsunami
inundation at Crescent City, California generated by earthquakes along
22
the Cascadia Subduction Zone, Geophys. Res. Lett., 34, L20601,
doi:10.1029/2007GL030188.
Figure 1. Google Earth image of core SBPCTC14-2A and SBPCTC-14B.
23
Figure 2. 1894 historical coastal Wetland of Los Angeles and Orange County
(U.S fish and wildlife
24
Figure 3. Location of freshwater swale and bolsa chica flood channel (U.S Fish
and Wildlife)
25
Figure 4. Changes in Seal Beach’s wetland 1873 to 1976 (U.S Fish and Wildlife)
26
Figure 5. Mapped located of the Palos verdes fault, work base on Dr. Robert
Francis (CSU Long Beach Department of Geological Sciences).
27
Figure 6. Large 1cm plus shell fragments found in core SBPCTC-1B
Figure 7. Sediment core of SBPCTC-2A
28
Figure 8. Core description of SBPCTC-1B
Figure 9. MS and Core description of SBPCTC-2A
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0
10
20
30
40
50
60
70
80
90
0.0 2.0 4.0 6.0 8.0
1B
2A
Figure 10. Comparison of core SBPCTC-1B and core SBPCTC-2A. The X Axis
indicates M.S values while the Y axes indicate Depth (cm).
Core Latitude Longitude Length
SBPCTC14-1B
33°44'26.66"N 118° 4'58.80"W longitude
78 cm
SBPCTC14-2A
33°44'37.36"N latitude
118° 5'0.73"W 74 cm
Table 1. Core location and length