Redefining the model of barrier island formation along a paraglacial coast: Plum Island, Massachusetts 11
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Emily Emily A. A. Carruthers Carruthers ,, Christopher Christopher J. J. Hein Hein ,, Duncan Duncan M. M. FitzGerald FitzGerald ,, Byron Byron D. D. Stone Stone ,, Mary Mary S. S. Ellison Ellison 11
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11Department of Earth Sciences, Boston University, Boston, MA 02215; 22US Geological Survey, Reston, VA 20192 Department of Earth Sciences, Boston University, Boston, MA 02215; US Geological Survey, Reston, VA 20192
• Sands become pinned to glacial deposits; Barrier sequence up to 15 m thick; Base of barrier: BP 3505 +/- 145 cal
• Parker River forms 8 to 10 m deep channel through proto-Plum Island, offshore of modern Plum Island
Marsh
High Intertidal
Subtidal Sand Shoal
Channel
Ebb Tidal Delta Front
5
150
6 7 8
200
A
5m 250
STAGE II: SOUTHERLY MIGRATION OF PARKER INLET Long Shore Current
deflected to the south
Migrating sand shoals
• Short, stubby, sections of
proto-Plum Island elongate through spit migration (GPR A)
Park er R iver Cha nne l
Parker River ebb tidal delta
1 km
iver Cha nn
el
Small southern inlet
-50 0
J
2
4
50
2 3
100
4 150
5
8
Truncation
B
200 5m
• Ebb tidal delta breaching occurs
Approximate Depth (meters)
Laurentide Ice Sheet
6 8 9 10 11 12 13 AGE (103 yr B.P.)
establishment of marsh decreases bay tidal prism: smaller inlets close; Parker Inlet narrows and deepens prism at Parker River, ebb flow from the Parker River is deflected south due to vertical growth of shoals and tidal flats
50 m Ground Penetrating Radar (GPR) profile taken NW to SE along the section of Plum Island highlighted in orange in figure to the left. Each red-blue couple represents a single subsurface reflector. Dashed lines indicate locations of cores (Red: Geoprobe core; Green: Vibracore; Yellow: auger drill core). Colored boxes refer to GPR sections shown in “Ground Penetrating Radar Interpretation” below (Yellow: Profile A; Red: Profile B; Green: Profile C; Green: Profile D). GPR profiles in following section are shown in grayscale with key reflectors highlighted.
250
GPR data were post-processed using GSSI’s RADAN software package and analyzed in ArcMap. Auger cores were logged on site and samples analyzed in the lab using standard sieve techniques and a laser diffraction particle size analyzer. Vibracore and Geoprobe cores were analyzed in the lab.
0
1 50
2 3
100
4 150
5 6 7 8
200
C
5m 250
Long Shore Current
Spit progradation closing inlet
• Parker Inlet narrows and shoals as it continues to close due to reduced tidal flux
• Dominant longshore transport
causes limited southerly spit accretion and migration of 1 to 2 m deep Parker Inlet
0
1 50
2 3
100
4
Inlet Filling
5
150
6 7 8
200
D
5m
STAGE V: RAPID SPIT PROGRADATION
• Parker Inlet closes completely after a short southerly excursion
progrades to the south (GPR C), overtopping smaller inlet fill sequences (GPR D)
• Backbarrier shoal and marsh Backbarrier infilling
establish an equilibrium with slowly rising sea level
STAGE VI: BARRIER ISLAND STABILIZATION PRESENT:
• Plum Island has aggradated due to continued supply of sand from the Merrimack River via longshore sediment transport
• Parker River joins with Rowley and Ipswich Rivers in Plum Island Sound, forming one inlet stabilized between two drumlins
250
Long Shore Current
CONCLUSIONS:
• Extensive lengths of Plum Island lithosome are formed through processes of inlet migration and spit progradation
• GPR transects reveal that evolution of Plum Island involved inlets narrowing and closure due to backbarrier infilling resulting in a reduction in the bay tidal prism
Spit progradation over intertidal sediment
South East West Dashed Prevalent nondominant dip
250
Arrows represent dominant GPR reflector dip orientation. Note that primary dip direction is to south; northern and southern GPR sections show only shallow data due to salt water intrusion.
ACKNOWLEDGMENTS
This study was funded by the Minerals Management Service (MMS), the United States Geological Survey (USGS), and the Undergraduate Research Opportunities Program (UROP). Additionally, E. Carruthers was funded in part by the Clare Booth Luce Summer Research Fellowship and C. Hein was funded by the National Science Foundation Graduate Research Fellowship. The authors would also like to acknowledge Dr. Susana Costas, Mr. Jeff Grey, and Mr. Nicholas Cohn for their assistance both in the field and in the lab.
REFERENCES
BOOTHROYD, J.C., and FITZGERALD, D.M., 1989, Coastal Geology of the Merrimack Embayment, SE New Hampshire, NE Massachusetts, Field Trip Guide: SEPM Eastern Section Field Trip, 2-4 June, 1989.
FITZGERALD, D.M., ROSEN, P.S., and VAN HETEREN, S., 1994. New England Barriers, In: DAVIS, R.A. (ed.), Geology of Holocene Barrier Island Systems, Berlin, Germany: Springer-Verlag, pp. 305-394.
to present day mouth of Parker River was once the site of an 8 to 10-m deep tidal inlet (Parker Inlet)
HEIN, C.J., FITZGERALD, D.M, and BARNHARDT, W., 2007, Holocene reworking of a sand sheet in the Merrimack Embayment, Western Gulf of Maine, Journal of Coastal Research, SI 50, 2007.
• The site of the Parker Inlet shows
evidence of complex inlet channel migration and infilling processes. The channel-fill units are overlain by upper spit accretion facies representing the last vestige of tidal prism exiting the former inlet.
KEY North
FITZGERALD, D., and VAN HETEREN, S., 1999, Classification of paraglacial barrier systems: coastal New England, U.S.A., Sedimentology, v. 46, p. 10831108.
• The center of Plum Island, adjacent
• Plum Island spit rapidly
towards present inlet mouth
Collapsed ETD
7
0
• Parker River flows south
Parker River captures southern stream
200
GPR and core locations. Blue line: GPR transects; Orange Line: GPR transect of interest; Red Circle: Geoprobe core; Green Circle: Vibracore; Yellow Circle: auger drill core
from marine and riverine sediment and saltmarsh peat production
Ebb tidal delta breach
6
14
• Additional backbarrier filling
Long Shore Current
150
5
During 2007-08, 11 km of Ground Penetrating Radar (GPR) were collected along both north-south (shore parallel) and east-west (shore-normal) transects. These data encompass the full length of Plum Island. Several coring devices were used to ground truth these data. Seven vibracores provide detailed stratigraphy in the top 4 m of the island sequence. A Geoprobe Model 54DT direct push machine was used to collect nine continuous core samples that retained fine stratigraphy to a maximum depth of 15 m. Finally, samples were collected from eleven cores penetrating as deep as 38 m using a truck-mounted B2 auger drill rig.
STAGE IV: CLOSURE OF PARKER INLET
STAGE III: EBB DELTA BREACHING
4
8
0
1
7
100
M
15 kya: Sea level (SL) highstand 12 kya: Relative sea level lowstand 11.5 - 8 kya: Rapid transgression 8 kya - Present: Continued SL rise
0
6
3
HIGHLIGHTS OF SEA LEVEL CURVE:
0
• Coincident with decreasing tidal Row ley R
ALTITUDE (m)
Cape Ann
• Gradual filling of backbarrier and
• Landward sand transport
through tidal inlets coupled with sediment discharge from Ipswich, Rowley and Parker Rivers begin filling backbarrier as sea level continues to rise slowly
Ipswich River
at Parker Inlet; inlet deflected to the north, truncating southward prograding spit and platform (GPR B)
• Parker River ebb tidal delta
I
Approximate Depth (meters)
Silt / Clay
4
induce southerly long shore sand transport
Evolutionary Diagram Key Low Intertidal
Medium Sand
Very Fine / Fine Sand
100
• Dominant northeast storms Present Day Plum Island
Barrier Sediment
Coarse / Very Coarse Sand
50
3
I
GROUND PENETRATING RADAR INTERPRETATION
1 2
P
-20
-60
Approximate Depth (meters)
intertidal shoals
Core Log Key
Approximate Depth (meters)
• Sand migrates onshore as overwash barriers and subtidal and
Shallow Channel Fill
-10
P P P H P P
L
50
2
Approximate Depth (nanoseconds)
lowstand periods are reworked during transgression
Spit Platform
0
0
-30
Rowley River
• Rowley River: Watershed Area = 36 km2 Annual Discharge = N/A (tidal) • Ipswich River: Watershed Area = 402 km 2 Annual Discharge = 0.056 km3
0
10
P H M J L P Portland I Isles of Shoals
0
1
Approximate Depth (nanoseconds)
• Deltaic and braid plain sediments deposited during regression and
Deep Cut / Fill
Wood
X
Ice-contact delta Plum Island Hampton Marsh Merrimack paleodelta Jeffreys Ledge Lynn
-40
Rivers of the Plum Island Backbarrier:
Spit Sequence
Saltwater peat Shell
Approximate Depth (nanoseconds)
10000-3500 BP:
Parker River
• Dominant long shore sediment transport to the south
GPR Key
Freshwater peat
20
Plum Island
• Influenced by strong northeast winter storms
Explanation
30
Merrimack River
• Island within the longest continuous barrier chain in the Gulf of Maine
• Merrimack River: Watershed Area = 12,885 km2 Annual Discharge = 6.24 km3 • Parker River: Watershed Area = 167 km2 Annual Discharge = 0.033 km3
40
Great Boar’s Head
• Merrimack Embayment: mixed-energy and tide dominated
Approximate Depth (nanoseconds)
STAGE I: TRANGRESSIVE MIGRATION OF SAND SHOALS
• Plum Island located between Cape Ann (MA) and Great Boar’s Head (NH)
0
Approximate Depth (nanoseconds)
A geophysical and sedimentological study of Plum Island in northern Massachusetts has refined our understanding of barrier formation in northern New England. Previous studies suggest various sources of sediment for building the Plum Island and adjacent barrier system, including erosion of drumlin sediments, sand discharged from the Merrimack River, and the Holocene reworking of lowstand deltaic sediments and braid plain deposits. Although identifying different sediment sources, all models agree that the island evolved through the process of vertical accretion. Analysis of sediment from vibracores, deep (~36 m) drill auger cores and Geoprobe cores along the barrier show a generally coarsening upward sequence from the fine mud of the Presumpscot formation though fluvial deposits and into the barrier island sequence. Occasionally, impenetrable shallow till is encountered that may represent buried drumlins, onto which Plum Island became pinned during its formation. Sediment core and Ground Penetrating Radar (GPR) data suggest that the barrier lithosome ranges in thickness from 5 to 15 m and is composed of pervasive southerly dipping layers along the southern 2/3 of the island’s length. These layers are interpreted as spit (thickness: 4-6 m) and inlet fill sands (thickness: 6 to > 8 m). These southerly dipping layers are frequently underlain by thinner sequences of northerly dipping GPR reflectors that represent the northern recurve of the southerly prograding spit. The predominant southerly dipping reflectors are consistent with dominantly southerly longshore transport system driven by northeast storms. Although previous studies have shown that existing barriers are commonly reworked by tidal inlet migration, this is the first study in New England to show that spit accretion and inlet migration were dominant processes in the formation of the barrier.
MASSACHUSETTS SEA-LEVEL CURVE
DATA COLLECTION AND RESULTS
Approximate Depth (meters)
STUDY AREA
ABSTRACT
McINTIRE, W.G., and MORGAN, J.P., 1964, Recent geomorphic History of Plum Island, Massachusetts and Adjacent Coasts, in: Morgan, J.p., ed., Louisiana State University Studies, Coastal Studies Series, no. 8, Baton Rouge: LSU Press RHODES, E.G., 1973, Pleistocene - Holocene Sediments Interpreted by Seismic Refraction and Wash-bore Sampling, Plum Island-Castle Neck Massachusetts: U.S. Army Crop of Engineers, Coastal Engineering Research Technical Memorandum., no.40, p.75. Drumlins
STONE, B.D., STONE, J.R., and MCWEENEY, L.J., 2004. Where the glacier met the sea: Late Quaternary geology of the northeast coast of Massachusetts from Cape Ann to Salisbury, In: HANDSON, L. (ed.), Proceedings of the New England Intercollegiate Geological Conference, Salem, Massachusetts, B-3, pp. 25