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The Role of Backbarrier Infilling in the Formation of Barrier Island Systems

Christopher Hein and Duncan FitzGerald Coastal Sediments 2011 3 May 2011


Backbarriers & The “Doomsday Scenario”

(FitzGerald et al., 2006, Journal of Coastal Research)


Study Site: Plum Island, MA

Merrimack River

Gulf of Maine

Plum Island Parker River Inlet

N 0

2 km

Cape Ann


Massachusetts Post-Glacial Sea Level History

(Modified from Oldale et al., 1993, Quaternary Research)


Paraglacial Sediment Inputs

(FitzGerald et al., 1993)


Data Collection

N 0

2 km

• 20 km of ground-penetrating radar, 100 & 200 MHz antenna (blue lines) • 7 vibracores, max. 4 m depth (green dots) • 12 Geoprobe cores, max. 15 m (red dots) • 11 auger drill cores, max. 38 m (yellow dots)


Evolution of Plum Island Barrier System 0

0

5 200 10

300

400 15

Channel Fill

5 cm

Channel Weathered Lag Gm

Unweathered Gm

Depth (m)

TWT (nS)

100


Evolution of Plum Island Barrier System


Evolution of Plum Island Barrier System

1

0

MHW

100 150

-4

200 250

3.6 ka -8

Depth (m)

TWT (nS)

50


Northern Massachusetts Calibrated Sea Level Curve

Base of inlet sequence: 3.6 ka


Evolution of Plum Island Barrier System

(Hein et al., in review, Marine Geology)


Research Question 30-50% of barrier length in wave dominated settings (Moslow and Tye, 1985)

Scientific Question: how does a change in tidal fluxes affect island development? Essex Inlet, MA

FitzGerald et al., in press


Research Question

O’Brien Relationship: Jarrett Curve Paleo-Parker Inlet Inlet Fill Sequence Area: 2800 m2 Equivalent Tidal Prism: 36 x 106 m3

(Jarrett, 1976, USACE Report)


Research Question

TP ~ 32 x 106 m3*

TP >> 32 x 106 m3

(* - Vallino and Hopkinson, 1998, Estuarine, Coastal and Shelf Science)


Stratigraphic Database Barrier Sands Merrimack River

N

0

2 km

Marsh / Peat Tidal Flat

Parker River Rowley River

Parker River Inlet Castle Neck

Backbarrier Sands

Glaciomarine Clay

Till / Bedrock Data: 6 grad theses & 4 govt data sets


Plum Island Stratigraphy: Surface N 156 cores + known elevation points 2 km

3m+ Elevation with respect to MLW (m)

0

-15 m

Plum Island Sound drainage basin

Points tied to MSL


Plum Island Stratigraphy: Backbarrier Sediment Surface N 2 km

3m+ Elevation with respect to MLW (m)

0

156 cores penetrate to backbarrier sediment

-15 m

Backbarrier: strip off marsh, barrier sands, modern organics, etc


Plum Island Stratigraphy: Backbarrier Base N 2 km

3m+ Elevation with respect to MLW (m)

0

63 cores penetrate to backbarrier base

-15 m

Backbarrier Base: basal freshwater peat, glaciomarine clay, till, bedrock Volume of Backbarrier Sediment: 290 x 106 m3


Backbarrier Backstripping If P > 3.6, then B = Bo If P = 0, then B = Bo-(T1*Br) If 3.6 > P > 0, then B = Bo-([T1-(P/Pr)]*Br)

N 2 km

3m+ Elevation with respect to MLW (m)

0

P: marsh / peat thickness (m) T1: time in past B: marsh level at time T1 Bo: modern backbarrier sediment elevation Br: backbarrier sediment accretion rate (0.25 cm/yr) Pr: mean marsh accretion rate (0.1 cm/yr) 3.6: maximum marsh thickness in 3600 yrs

-15 m

T1: 3600 yrs BP


Results N 2 km

3m+ Elevation with respect to MLW (m)

0

Volume Sediment Removed: 225 x 106 m3

-15 m

Backbarrier Tidal Prism: 45 x 106 m3 (140% modern) Modern Parker River Inlet: X-C Area: 3000 m2 TP: 32 x 106 m3


Results

Backstripping Tidal Prism: 45 x 106 m3 3600 Parker River Inlet: Cross-Sectional Area: 1300 m2 Tidal Prism: 18 x 106 m3 Max Paleo-Parker Tidal Prism: 37 x 106 m3 Residual Backbarrier Tidal Prism: ~10 x 106 m3


Implications: Backbarriers & The “Doomsday Scenario”

(FitzGerald et al et al., 2008, Annual Reviews of Earth Science)


Acknowledgements Funding: NSF Graduate Research Fellowship Program, US Minerals Management Service, GSA Graduate Student Research Grant, AAPG Student Grant, AGU Tilford Field Studies Scholarship Field / Lab Assistants: Byron Stone (USGS), Emily Carruthers, (WHOI), Mary Ellison (U. of New Orleans), Nicholas Cohn, Jeff Grey (USGS), Allen Gontz (Umass Boston) Parker River National Wildlife Refuge Staff

Coastal Sediments 2011 Presentation  

Hein and FitzGerald Coastal Sediments 2011 Presentation on Plum Island Formation and Backstripping

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