A REVIEW OF COASTAL MAINE STRATIGRAPHY

At this symposium in his honor, I offer to Father Jim a review of coastal Maine stratigraphy to affirm his belief that spending time with rocks is a good way to learn from the Earth, and to confess that Maine geology continues to hold mysteries beyond our understanding. The work of many geologists is summarized.

The following stratigraphic columns are used, from east to west. (1) coastal volcanics, (2) Ellsworth, (3) Islesboro, (4) Rockport, (5) St. Croix, (6) Benner Hill, (7) Fredericton, (8) Casco Bay, (9) East Harpswell, (10) Falmouth-Brunswick, (11) central Maine, (12) Merrimack, and (13) Shapleigh.

I. Progress since the 1985 State map: (1) may lack Devonian strata entirely; includes coeval volcanic-plutonic complexes; sub-Bar Harbor unconformity at West Gouldsboro. (2) Ellsworth is Cambrian; Lamoine Granite Gneiss carries Ellsworth foliation; Castine unconformity is within the Cambrian. (5) Battie may = Matthews Lake; Jam Brook is fault-related; Clarry Hill schist is west of Sennebec Pond fault. (6) Formations are defined; Prison Farm in thrust contact. (7) Appleton Ridge = Digdeguash. (8) is M. Ord. (9) is Late Ord, exposed in window through Boothbay thrust. (10) is separate from 8. (11) Hutchins Corner Fm defined, may rest on 10; Waterville/Vassalboro thrust on Sangerville. (12) is Sil., may rest on 8; may be partly equivalent to 11. (13) equivalent to Rangeley sequence; east-bounding thrust in question.

II. Remaining questions (for me): (1) Relationship to 2? (2) Deer Isle ultramafic? Calderwood Fm? (3) Islesboro Fm age? (4) Ogier Point = Islesboro? Rockport ls congl = Ashburn? (5) Rhyolites at Owls Head? Origin of Battie congl? (6) Pillow basalts at Friendship? (7) Cross River Fm? (8) Sheepscot Pond Gn? Passagassawakeag Gn? Kingdom Bog mem. of Scarboro? (9) Relationship to 7? (10) Mt. Ararat Fm? (11) Relationship to 10? Vassalboro vs. Hutchins Corner SW of Augusta? Rocks near Sebago pluton, in Standish? (12) Berwick Fm? (13) Relationship to 11?

Assignment of these sections to various terranes by workers from away remains unsatisfying because of so many loose ends and mis-matched stratigraphy. Diagnostic Avalon faunas (Acado-Baltic) lie to the east. Celtic faunas lie to the northwest. A peri-Gondwanan origin in eastern Iapetus seems likely, with accretion by late Silurian and significant modification by Devonian thrusting.