SE GSA 2011

Barrier Evolution in Response to Inlet Closure: An Example from a Paraglacial Barrier System

Christopher Hein and Duncan FitzGerald Geological Society of America Southeastern Section Meeting 24 March 2011

In Tribute to Bill Cleary

Study Site: Plum Island, MA

Merrimack River

Gulf of Maine

Plum Island Essex Inlet

N 0

2 km

Cape Ann

Massachusetts Post-Glacial Sea Level History

Modified from Oldale et al., 1993, Quat. Res.

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 50 100 -5

150 200

0

50 m

Spit Platform

250

-10

• Deltaic and braid plain sediments deposited during regression • Reworked onshore during transgression as sand shoals (12-4 ka) • Shallow shoals are pinned to glacial deposits • Vertical accretion: 30% Spit elongation: 60% Inlet fill processes: 10%

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

Depth (m)

TWT (nS)

1 MHW

Spit Progradation

Evolution of Plum Island Barrier System

Evolution of Plum Island Barrier System

0

MHW

100 150

-4

200 250

-8

Depth (m)

TWT (nS)

50

1

Evolution of Plum Island Barrier System

Inlet Base 14C Date: 3.3 cal ka BP

Topic: Barrier Island Response to Tidal Inlets 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

Stratigraphic Database Merrimack River

Stratigraphic Data Sources:

N

0

2 km

• McIntire & Morgan, 1963, LSU Technical Report • USGS Water Supply Paper, 1963 • McCormick, 1968, Ph.D. Thesis • Hartwell, 1970, ONR Report • Rhodes, 1971, USACE Technical Memo

Parker River

• Anderson-Nichols, 1987, unpub. cores Rowley River

• Som, 1990, MS Thesis • Mass. State Boring Data

Parker River Inlet Castle Neck

• Hein et al., cores

Topographic / Bathymetric Data Sources: • US Coast & Geodetic Survey Hydrographic Survey Soundings (19531954) • Mass GIS DTM Files (2003)

Plum Island Stratigraphy 0 Median Grain Size Mean Grain Size

Barrier

Depth (m)

5

10

Backbarrier 15

20

Glaciomarine Clay (Presumpscot) 0

5

Grain Size (ÎŚ)

10

Well Sorted

Poorly Sorted

Sorting

Very Poorly Sorted

Plum Island Stratigraphy: Backbarrier Sediments N 2 km

3m+ Elevation with respect to MLW (m)

0

-15 m

Merrimack River Parker River Rowley River Ipswich River

Plum Island Stratigraphy: Backbarrier Base N 2 km

3m Elevation with respect to MLW (m)

0

-15 m (-)

Merrimack River Parker River Rowley River Ipswich River

Backbarrier Sediment Thickness N 2 km

18 m Thickness of Backbarrier Sediments (m)

0

Paleo-Parker Inlet

0m

NET VOLUME: 8.5 x 108 m3

Northern Massachusetts Calibrated Sea Level Curve

Base of inlet sequence: 3.3 ka

Backbarrier Backstripping If Mo-BBo=0; BB1=BBar*T1 If Mo-BBo>3; BB1=BBo If Mo-BBo<3; (T1-(Mo- BBo)*Mar)*BBar Mo: modern marsh level M1: marsh level at time T1 BBo: modern backbarrier sediment BBo: backbarrier sediment at T1 BBar: mean BB sed acc rate (0.28 cm/yr) Mar: mean marsh acc rate (0.12 cm/yr)

Volume Sediment Removed: 660 x 106 (Âą 60 x 106) m3 Backbarrier at 3.3 ka

Tidal Prism: 155 x 106 (Âą 11 x 106) m3

Merrimack Inlet X-C Area: 1900 TP: 25 x 106 m3

m2

Combined Modern Inlets: Combined TP: 88 x 106 m3 Combined X-C Area: 6700 m2

Parker Inlet X-C Area: 3100 m2 TP: 40 x 106 m3

Essex Inlet

Backbarrier: Tidal Prism: 155 x 106 m3 Equivalent Inlet X-C Area: 13,100 m2

X-C Area: 1700 m2 TP: 23 x 106 m3

Residual: Tidal Prism: 67 x 106 m3 Equivalent Inlet X-C Area: 5300 m2

Paleo-Plum Island Inlet 1 MHW

0

100 150

-4

Depth (m)

TWT (nS)

50

200 -8

250 0

1

100

200

1300

300

m2

-7

-11 400

50 m

-15

Depth (m)

TWT (nS)

-3

Conclusions • Sediment Sources: paraglacial offshore & fluvial • Plum Island Barrier Evolution: onshore migration, vertical accretion, spit elongation, inlet closure, & progradation • Influence of Backbarrier Infilling: delivery of sediment to backbarrier crucial driving process behind barrier evolution: Transgressive Sediment Input Backbarrier Infilling Tidal Prism Reduction Inlet Closure • The Problem: 1300 m2 << 5300 m2

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), Britt Argow (Wellesley College) Parker River National Wildlife Refuge Staff