Great Bay Reserve, New Hampshire

Great Bay Reserve, New Hampshire

Geology

The region surrounding the Great Bay is included in the Seaboard Lowland section of the New England Province. The most recent glaciation of the area ended in the Wisconsin stage of the Pleistocene epoch (10,000 to 20,000 yrs. B.P.) The glaciation proceeded through the area in a southeasterly direction, resulting in the orientation of the many drumlins in the area. Substantial amounts of glacial till were deposited as the glacier receded.

Bedrock surrounding Great and Little bays is primarily metamorphic, consisting of dark gray slate of the Kittery formation visible as outcrops along the northern and western shores and in the Pierce Point area of Greenland. The Eliot formation, also dark-gray slate, can be seen along the shores of Stratham and Newington. A fold in the Eliot formation, the Great Bay syncline, passes through Newington to Thomas Point, under Great Bay, then into Stratham near Bracketts Point.

Immediately to the north and West of Great and Little bays, a granite intrusion of Exeter diorite comprising the Exeter pluton (i.e. part of the Hillsboro plutonic series) is present. Large outcrops of the slate described above serve as an important source of stable substratum for macroalgal attachment and contribute to the shingle beach common around Great Bay.

Crustal depression in New Hampshire from glacial weight was on the order of 12.2 m (40 ft.) After glacial melt, crustal rebound occurred and is complete today. However, the uplift was not uniform throughout the region and Great and Little bays represent a sag along the surface. The low-lying area was filled by rising sea level from glacial melting. Thus, the Great Bay estuary is representative of a drowned-river valley. Present sea level was reached approximately 3,000 to 5,000 years ago.

Soil Types

Marshes bordering streams such as the Squamscott River and the Crommett and Lubberland Creeks are generally sulfihemists. The fringing marshes, common around the bay, also have sulfihemist soils of varying thicknesses and overlaying a variety of substrata. The sulfihemist soil type has slow internal drainage, a very high water table and contains high amounts of organic matter and sulfitic minerals.