Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Geology 307-310 (2012):40-57, doi:10.1016/j.margeo.2012.03.001.
Description:
Details of the internal architecture and local geochronology of Plum Island, the longest barrier in the Gulf of Maine, has refined our understanding of barrier island formation in paraglacial settings. Ground-penetrating radar and shallow-seismic profiles coupled with sediment cores and radiocarbon dates provide an 8000-year evolutionary history of this barrier system in response to changes in sediment sources and supply rates as well as variability in the rate of sea-level change. The barrier sequence overlies tills of Wisconsinan and Illinoian glaciations as well as late Pleistocene glaciomarine clay deposited during the post-glacial sea-level highstand at approximately 17 ka. Holocene sediment began accumulating at the site of Plum Island at 7–8 ka, in the form of coarse fluvial channel-lag deposits related to the 50-m wide erosional channel of the Parker River that carved into underlying glaciomarine deposits during a lower stand of sea level. Plum Island had first developed in its modern location by ca. 3.6 ka through onshore migration and vertical accretion of reworked regressive and lowstand deposits. The prevalence of southerly, seaward-dipping layers indicates that greater than 60% of the barrier lithosome developed in its modern location through southerly spit progradation, consistent with a dominantly longshore transport system driven by northeast storms. Thinner sequences of northerly, landward-dipping clinoforms represent the northern recurve of the prograding spit. A 5–6-m thick inlet-fill sequence was identified overlying the lower stand fluvial deposit; its stratigraphy captures events of channel migration, ebb-delta breaching, onshore bar migration, channel shoaling and inlet infilling associated with the migration and eventual closing of the inlet. This inlet had a maximum cross-sectional area of 2800 m2 and was active around 3.5–3.6 ka. Discovery of this inlet suggests that the tidal prism was once larger than at present. Bay infilling, driven by the import of sediment into the backbarrier environment through tidal inlets, as well as minor sediment contribution from local rivers, led to a vast reduction in the bay tidal prism. This study demonstrates that, prior to about 3 ka, Plum Island and its associated marshes, tidal flats, and inlets were in a paraglacial environment; that is, their main source of sediment was derived from the erosion and reworking of glaciogenic deposits. Since that time, Plum Island has been in a state of dynamic equilibrium with its non-glacial sediment sources and therefore can be largely considered to be in a stable, “post-paraglacial” state. This study is furthermore the first in the Gulf of Maine to show that spit accretion and inlet processes were the dominant mechanisms in barrier island formation and thus serves as a foundation for future investigations of barrier development in response to backbarrier infilling.
Description:
This study was funded by the Minerals Management Service (now the “Bureau of Ocean Energy Manegement, Regulation and Enforcement”), the USGS Eastern Geology and Paleoclimate Science Center, the USGS National Cooperative Geologic Mapping Program (State Map), a Geological Society of America (GSA) Student Research Grant, the American Association of Petroleum Geologists (AAPG) Grants-in-Aid program, and the Boston University 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 (NSF) Graduate Research Fellowship.
Keywords:
Inlet processes
;
Inlet-fill sequence
;
Spit accretion
;
Barrier-island formation
;
Paraglacial
;
Ground-penetrating radar
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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