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HEIN AND STONE

A5-1

ICE, WATER, AND WIND: A SOURCE-TO-SINK VIEW OF THE GLACIAL, PARAGLACIAL AND COASTAL SEDIMENTS AND PROCESSES THAT HAVE SHAPED NORTHEASTERN MASSACHUSETTS by Christopher J. Hein1, Virginia Institute of Marine Science, College of William and Mary, P.O. Box 1346, Gloucester Point, VA 23062 Byron D. Stone2, Eastern Geology and Paleoclimate Science Center, U.S. Geological Survey, 101 Pitkin St., East Hartford, CT 06108 Email addresses: 1hein@vims.edu, 2bdstone@usgs.gov

INTRODUCTION Modern geologic maps have revealed the detailed extent of glacial, proglacial-meltwater, paraglacial, and postglacial deposits across the Merrimack Embayment area of northeastern Massachusetts (Sammel, 1963; Oldale, 1964; Cuppels, 1969; Stone et al., 2006; Hein et al., 2013). Recent offshore mapping studies have located critical evidence of submerged coastal features, which track the level and age of the late Wisconsinan postglacial marine regression and latest transgression (Oldale and Wommack, 1987; Oldale et al., 1993; Barnhardt et al., 2009; Hein et al., 2012, 2013, 2014). This trip will focus on the glacial, proglacial, paraglacial, and postglacial coastal deposits associated with the regressive and transgressive marine cycles following the retreat of the Laurentide Ice Sheet from northeastern Massachusetts. Relative sea level during deglaciation of this region reached a maximum of about 31 m above the present level. Glacial, fluvial and coastal processes resulted in the shaping of drumlins, deposition of glacial deltas and draped glaciomarine clay, and development of regressive shoreline features and fluvial terraces, all of which dominate the modern onshore landscape. Many of these deposits have been mapped continuously across the modern shoreline (Hein et. al., 2013) and into the submerged environment offshore of the barrier islands. Detailed mapping and stratigraphic analysis extend beyond the 13,000-year-old lowstand shoreline located 45 m below modern mean sea level (MSL). Reworking of these glacial and post-glacial sedimentary deposits by coastal processes during the most recent and ongoing marine transgression has culminated in construction of the massive barriers, beaches, marshes and dunes of the modern coastal zone. This trip will trace the shoreline from its highstand position at Haverhill, Massachusetts, down the Merrimack River valley, and out to Plum Island, tracking the various processes and deposits responsible for building the modern landscape. We will discuss how Quaternary glacial and marine geologists can come together to map continuous surficial geology across the modern shoreline.

PHYSICAL SETTING Physiography of the lower Merrimack Valley / Merrimack Embayment This field trip covers a region in the lower Merrimack River valley downstream from Haverhill, Massachusetts, to its mouth in the area known as the Merrimack Embayment, which extends from Cape Ann to north of the New Hampshire state line (Figs. 1, 2, 3). The Merrimack River basin, 13,000 km2 in area, heads in the White Mountains of New Hampshire and extends 180 km to the ocean (Fig. 2a). It drains areas dominated by granitic plutons and other crystalline rocks that have been eroded to produce quartzose, sandy glacial deposits (Fig. 2b). The lower part of the river flows through coarse, sandy glacial deltas that formed along the retreating ice front in the glaciomarine highstand sea and in subsequent glacial lakes up valley (Stone et al., 2006). In its coastal reach, the Merrimack largely flows over till and bedrock before draining into a mixed-energy, tide-dominated, inlet-influenced (FitzGerald and van Heteren, 1999) embayment in the western Gulf of Maine. The Merrimack Embayment coastal barrier system consists of a 34-km long series of barriers, tidal inlets, estuaries and backbarrier sand flats, channels and marshes (Fig. 3). This is the longest such barrier system in the Gulf of Maine. Individual barriers (Seabrook Beach, Salisbury Beach, Plum Island, Castle Neck and Coffins Beach) are 2–13 km long, generally less than 1 km wide and are backed primarily by marsh and tidal creeks that typically expand to small bays near inlets (Smith and FitzGerald, 1994). Barriers contain abundant, vegetated parabolic dunes that reach as much as 20 m in elevation. These are best developed along central and southern Plum Island and Castle Neck, reflecting abundant quartz sand associated with high rates of longshore transport.

NEIGC 2014 Hein & Stone Field Trip Guide  

Field trip guide to the lower Merrimack River Valley and Plum Island by Christopher Hein and Byron Stone. This field trip was part of the 10...

NEIGC 2014 Hein & Stone Field Trip Guide  

Field trip guide to the lower Merrimack River Valley and Plum Island by Christopher Hein and Byron Stone. This field trip was part of the 10...

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