Bedrock Geology of the Bath 1:100,000 Map Sheet, Coastal Maine

Pemaquid Point
Bucksport Formation at Pemaquid Point


This report, a companion to the Bedrock Geology of the Bath 1:100,000 Quadrangle, Maine (Hussey and Marvinney, 2002, which hereafter is referred to as the "Bath map sheet"), describes the bedrock geology of the highly indented south-central coast of Maine (Figure 1). Throughout much of the area bedrock outcrops are abundant, providing superior control in mapping the variety of metasedimentary, metavolcanic, and intrusive rocks that underlie the area. The purpose of this report is to describe the lithology of metamorphic and intrusive rock units, and to discuss the structure, metamorphism, age relations, and economic resources of this part of the southern Maine coast.

The metasedimentary and metavolcanic rocks represent seven lithotectonic sequences: the Central Maine, Falmouth-Brunswick, Casco Bay, East Harpswell, Fredericton, Benner Hill, and Megunticook sequences (Figure 2 and Figure 3). Most sequences are separated by faults from the other sequences, so stratigraphic relationships among sequences are uncertain. The Central Maine sequence in central Maine preserves rocks of Late Ordovician to Early Devonian age, but only Late Ordovician to Early Silurian rocks are exposed here, in the very northwestern corner of the map area. The Falmouth-Brunswick sequence and Casco Bay Group are of probable Middle to Late Ordovician age. The East Harpswell Group is of Late Ordovician-Early Silurian age. The Fredericton sequence is probably Early Silurian. The Benner Hill sequence is Middle to perhaps Late Ordovician. Rocks of the Megunticook sequence are Late Cambrian to Early Ordovician in age. These stratified rocks have been intruded by syn-tectonic to post-tectonic granite, quartz diorite, gabbro, granitic pegmatite, and a variety of small plutons, some Silurian but most of probable Devonian age, and by numerous undeformed and unmetamorphosed Mesozoic basalt and diabase dikes.

stratigraphic diagram
Figure 2
tectono-stratigraphic sequences
Figure 3

Introduction   Central Maine sequence   Falmouth-Brunswick sequence   Casco Bay Group   East Harpswell Group   Fredericton sequence   Megunticook sequence   Benner Hill sequence   Sequence uncertain   Correlations   Intrusives   Structure   Metamorphism   Timing   Minerals   Acknowledgements   References  

Last updated on February 1, 2008