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Preliminary description of sediments from north Cascadia forearc lakes: cryptic sequences contain evidence of a seismogenic influence Ann E. Morey, Chris Goldfinger and Steve Galer

College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR. morey@coas.oregonstate.edu

College of Earth, Ocean and Atmospheric Sciences

Vivanite - an indicator of disturbance in Leland Lake?

ABSTRACT:

CORE LOCATIONS

Beaver

Seattle

Lake Washington

Sawyer Juan de Fuca M9907-12PC/TC M9907-11PC/TC

Point Mag. Susc.

0

Here we describe the characteristics of lake sediments we recently acquired along a transect from just west of the Olympic Peninsula to the Cascade foothills at the latitude of Seattle, Washington. Density (from computed tomography and gamma-ray attenuation) and magnetic susceptibility data and imagery for the kettle lake cores were compared to each other and to the physical properties from cores containing a record of Cascadia offshore seismoturbidites. Preliminary correlations show strong similarities over the past ~8,000 years when anchoring the records in time with a tephra layer we interpret to be the Mazama tephra (MA) based on published data from nearby lakes. Why do the lake and offshore sedimentary records correlate? There are no graded turbidite deposits visible in the cores, only very subtle differences in texture and color associated with the correlative layers (other than the Mazama tephra). We are in the process of describing and analyzing the sediment from these cores in an attempt to understand why these sedimentary records from such different depositional environments have similar patterns in their physical properties through time.

Leland Tarboo Hall

Leland Lake

Jefferson Co., WA Gamma Density

(no calibration; density increases to the left) 0 CT 1.80 1.84 image

(SI units)

50

CT Density (gray scale)

200

0

Vivianite: a blue hydrous iron phosphate mineral requiring specific geochemical and redox conditions to form.

We present our first results from multiple cores from two kettle lakes, Leland Lake and Tarboo Lake. These lakes are depressions in permeable glacial till that formed when blocks of glacial ice melted, and lake levels during modern times are primarily an expression of the water table. Tarboo Lake (0.09 km2, 17.7 m deep, and 195 m MSL) is perched relative to local terrain with little overland flow, whereas Leland Lake (0.41 km2, 6.1 m deep, and 58 m MSL) is fed by local streams, including a couple of seasonal streams to the west sourced from the foothills of the Olympic Mountains. Sediment properties of these cores are similar, however the average sedimentation rate at Tarboo Lake is about half that of Leland Lake, likely a reflection of the much smaller watershed at this site. Smear slides show that in general the sediment is dominated by diatoms and very fine organic matter, with a smaller percentage of clastics. Layers that correlate to the offshore seismoturbidite record are slightly stiffer and lighter in color than sediment above and below, and contain a higher percentage of clastics. The percentage of clastics in both the denser layers and the background sediment is highest near the base of the cores, and decreases through time to the top of the core. This may be a result of the depletion of clastics in the watershed, much of which is likely to have resulted from sedimentation within a proglacial lake that formed in this area during the latest Pleistocene as the Puget Lobe retreated. Periodic thin layers of vivianite (a blue hydrous Fe (II) phosphate mineral) are observed in Leland Lake cores and are associated with the denser layers. Overturn in deep lakes has been identified as a possible mechanism that could result in the formation of vivianite, however this is not a possible mechanism in Leland Lake which is likely wind-mixed throughout the year because it is so shallow. Would strong shaking entrain sediment into the water column causing flocculation, stripping the water column of primary producers? We will explore this, and other possibilities as we continue to learn about the sedimentary history and the influence of great earthquakes in these unique lake settings.

100

(Fe3(PO4)2.8H2O)

200

300

LLJ-7D 89.75 cm RC

no vivianite

PRELIMINARY CORRELATIONS

CORING

400

A possible mechanism for the formation of vivianite at Leland Lake:

Preferred correlation Forearc Lakes

W

Marine Core Juan de Fuca (JDF) Channel

Overlapping drives were collected using a modfied Livinstone piston corer to create a continuous composite core for each site. Cores were CT scanned with a Toshiba Aquillon 64 slice system (voxel resolution 0.5 mm) prior to splitting, then we aquired point and loop magnetics, gamma density. AMS radiocarbon ages are from the Woods Hole NOSAMS facility and were acquired from fragile terrestrial plant material (leaves, buds, etc.) extracted from sediment thought to not be reworked material. Thus far we have 7 radiocarbon ages which are in stratigraphic order and bracket the Mazama tephra.

Leland Lake, Jefferson Co. WA

M9907-11TC (g/cm3)

Our preliminary results suggest that a number of disturbance events are found in the lake cores across the transect. The Mazama Ash is found in all lakes, and with the exception of Tarboo Lake is found at 6-8 m depth Tarboo Lake is perched relative to the other lakes and has a smaller watershed. We suggest that only two possible sources are likely to be common across the region: a climate signal, and earthquakes. To test the commonality of the signal, we compare the stratigraphy and geophysical signatures between lakes, and to the seismoturbidite record in Juan de Fuca Channel (JDF).

470 (390-550)

870 (770-990) 1210 (1090-1330)

T1

1.2

(SI; loop sensor)

80

Gamma Density

CT density (grayscale) 0

100

200

1.80

300

1.82

LSK-3

JDF Comparison

(bad units - no calibration)

1.84

0

0

100

200

(bad units - no calibration)

1.82

300

0

1.85

T5 T6

3070 (2920-3190)

T7

Disturbance event deposits are not visible in the cores, but rather are “cryptic” features which are obvious features in the CT imagery and physical properties of the cores.

RGB CT imagery imagery

gamma density

We observe a surprising correspondence between the two lakes shown, and to the JDF CT density grayscale trace. The nature of the disturbance events is not known with certainty, and the description of what constitutes an “event” is also highly uncertain. The 14C data are equivocal at this stage as well, with several good fits to the earthquake record, and several very poor fits.

Composition: CT density

400

500

Disturbance event deposit: typical setting with high clastic input. NOT FROM THESE LAKES.

Mag. Susc. (point sensor)

We tentitively conclude that the disturbance events in these lakes are most likely a result of strong shaking during great earthquakes, although there is most definitely an influence from climate (i.e. precipitation). We show tentative correlation ties of several events to illustrate the possible linkage. More radocarbon ages are expected over the next few weeks.

Low density, low magnetic susceptibility = diatoms and fine organics

High density, high magnetic susceptibility = higher percentage and particle size of clastics

3500 (3340-3680)

Probable reversed age

T9

4820 (4660-4970)

T10

5690 (5530-5740)

T11

200

200

0

T13

7550 (7430-7670)

T14

LSK-3G

LLJ-7G 6090 (5990-6210) cal BP

600

Probable reversed age

600

4630 (4530-4650) cal BP

6860 (6790-6950) cal BP 25

2

MA

800

La ke

organic matter

MAZAMA ASH

800

Vivianite

LLJ-7I 97.5 cm RC vivianite

PO4

phosphates

clays

800

Le la

Is the thick tephra we observe in the lake sediments from the eruption of Mt. Mazama?

Mt. St. Helens (published data)

modified from Slomp et al., 2013

900

Further burial and lithification

900

LLJ-7J 74 cm RC vivianite

LLJ-7J 90 cm RC vivianite

900

Disturbance events in kettle lakes may not be “traditional” turbidites; are they formed by a different mechanism? Traditional mechanism:

Possible alternative mechanism:

Larger lakes (lake Washington) have normal turbidites. Is the sediment source internal or external to the lake?

Lakes with little clastic input, small or non-existent side wall failures, and no submarine channel system such as may be with the kettle lakes in study area??

Maybe both: Destabilization of sediments within the lake may lead to both turbidites and a rapid flocculation settling. External sediment may enter the lake later when storms wash in

Glacier Peak (published data)

(Zdanowicz et al., 1999)

Mt. Mazama (published data) New Mazama data (6 samples) LSK-1G - 2051.5cm

10

Glacier Peak

GEOLOGY: Mazama

10

Mazama tephra TLJ-1C - 1728.5cm layer from Lake Sawyer, WA

first

underwater failures

LSK-31 - 2538cm

underwater failures

?

LLJ-7I - 1409cm

delta

landslide

EQ!

Second landslide

EQ!

30

EQ! Sediment containing glacial silt and clay is disturbed from lake floor and margin during shaking. The glacial clay stays in the water column during shaking and mixes with fine organic matter.

St. Helens

(climactic)

Fe2O3

Fe(II)-P Fe2+

700

Probable good age

Probable good Stratigraphic correlation is to T14 offshore age which matches timing of airfall Mazama. T13 is the first turbidite to carry Mazama Ash, ~450 years later.

Tabor et al., 2011

Leland Lake is located along the Leland Spillway, which drained a proglacial lake that covered this area as the Puget Lobe retreated.

vivianite

MA

(Fe3(PO4)2.8H2O)

Fe oxide & P

CH4

Probable good age

We analyzed tthe thick tephra we assume is the result of the Mazama eruption found at most of our sites using Electron Microprobe (EMP) analysis to verify this assumption. A ternary plot below show the ash to be consistent with the Mazama climactic event, and distinct from Glacier Peak and St. Helens sources.

The lakes in this poster are kettle lakes, which are an expression of the water table in a depression formed after buried or partially buried stagnant glacial ice melts.

organic matter

LLJ-7H 80 cm RC

5. Vivianite

Reduced sulfate enters porewater and migrates upward; phosphate is released.

700

LLJ-7H

TEPHRA ANALYSIS:

nd

(anaerobic reduction of methane)

700

FeS and FeS2

H2S

4.

no vivianite

LLJ-7H 48.5 cm RC

PO4

SMT

3. SULFATE REMOVAL:

500

LLJ-7G 81 cm RC

Fe oxide & P

SO4

*Asterisk indicates Benthic age

LSK-3E

40

Sediments organic matter

7298 (7220-7377) Hemipelagic age & est. 2σ range

3230 (3170-3260) cal BP

LLJ-7I

K2O

Sulfate-Methane transition zone is raised

400

8270 (8190-8350) cal BP

Climactic eruption of Mt. Mazama: 7627 ± 150 cal yr BP

2.

Key to Marine Age Data:

CASC 11: 7298 (7220-7377) Sample #: 14C age & 2σ range, erosion corr.

Probable good age

no vivianite

vivianite

Juan de Fuca CT density (grayscale)

CASC 11: 7298 (7220-7377) Sample #: 14C age & 2σ range

500

LLJ-7F 84.5-85 cm RC

LLJ-7G 47 cm RC

600

7

45

500

Water Column

of organic matter

Core break

Mazama Ash: white text equals % ash

300 300

% MA 50

T12 7080 (6970-7190)

1. Rapid accumulation

Radiocarbon sample location

Lake core CT density (grayscale)

Probable reversed age

Fe, Mn oxides

Gamma Density (g/cm3)

100

4180 (4020-4310)

clays

300

Low-resolution magnetic susc. (SI)

LLJ-7D 2860 (2790-2950) cal BP

T8

3440 (3280-3610)

200

Tentative correlations

400

“Cryptic” Sequences

Modified Livingtone corer; platform courtesy of Dan Gavin, UO.

100

Mazama Ash; first occurrence in a turbidite for marine core M9907-11TC

100

100

LLJ-7B 1080 (1050-1180) cal BP

T4

2500 (2340-2600)

CT density (grayscale) 0

Explanation

T2 T3

1580 (1460-1720)*

LLJ-7F 18.5-19 cm RC

no vivianite

organic matter

JDF Comparison

Gamma Density

CT density (grayscale) 0

LLJ-7E 65-65.5 cm RC vivianite

Reduced sulfate availability as a result of anaerobic oxidation of methane (example from the Bothnian Sea)

E

Lake Sawyer, King Co. WA

LLJ-7

Magnetic Susceptibility 0

Gamma Density 1.8

270 (180-360)

Vivianite

CaO

EQ!

EQ!

Flocculation of clay particles and organic matter create heavier clumps, which fall out of the water column. These layers are higher in % clastics.

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IGCP Poster 2014  

Poster prepared for the International Geoscience Programme (IGCP) Project 588 “Preparing for Coastal Change”

IGCP Poster 2014  

Poster prepared for the International Geoscience Programme (IGCP) Project 588 “Preparing for Coastal Change”

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