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