Metamorphosed Silurian brachiopods from New Hampshire

Abstract

Generically identifiable Silurian brachiopods from rocks of the staurolite and sillimanite zones of regional metamorphism have been found at a number of localities in the Clough Formation of west-central New Hampshire. They include representatives of 19 brachiopod genera, 1 gastropod, 1 trilobite, and 1 pelmatozoan. The fossils occur as two faunas. The first, characterized by Stricklandia lens cf. S. lens ultima, is probably of C4 to C5 or C6 age; the second, characterized by Eocoelia hemisphaerica, is of C3 to C5 age. Paleogeographically these New Hampshire fossils demonstrate that during late Llandovery time Appalachia was quite narrow, even if allowance is made for subsequent deformation. The present distance from Utica, New York (where marine beds of Clinton age occur to the west and nonmarine beds to the east), to the Connecticut River valley (where the widely distributed Clough Formation contains marine fossils of late Llandovery age) is about 140 miles. The northern and southern bounds of Appalachia are not well delimited for this time interval. The northern limit may have been an area east of Lake Temiscouata, Quebec, and the southern limit an area in northwestern Georgia. Thus Appalachia during this time is reconstructed as a narrow, elongate island or archipelago extending from Quebec to Georgia. A brachiopod (Howellella sp.) from the Shaw Mountain Formation of eastern Vermont indicates an age of C3 to early Gedinnian for that unit. The brachiopods of Ludlow age from the type Fitch Formation of northern New Hampshire are redescribed.