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