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.

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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


Anh Tran

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Faculty Mentor: Prof. Matthew E. Kirby

Geology (B.Sc.), 2015, Department of Geological Sciences

2357 W Moro Pl. Anaheim CA, 92801

[email protected]

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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

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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).

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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

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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.

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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.

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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.

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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

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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.

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Figure 2. 1894 historical coastal Wetland of Los Angeles and Orange County

(U.S fish and wildlife

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Figure 3. Location of freshwater swale and bolsa chica flood channel (U.S Fish

and Wildlife)

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Figure 4. Changes in Seal Beach’s wetland 1873 to 1976 (U.S Fish and Wildlife)

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Figure 5. Mapped located of the Palos verdes fault, work base on Dr. Robert

Francis (CSU Long Beach Department of Geological Sciences).

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Figure 6. Large 1cm plus shell fragments found in core SBPCTC-1B

Figure 7. Sediment core of SBPCTC-2A

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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

Anh Tran Thesis

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