million d o

i years r a Stratified Rocks Intrusive Igneous Rocks r Simplified Bedrock Geologic e

E P ago

c (Sedimentary, volcanic, and metamorphic rocks) Fort Kent i Mesozoic - Small intrusions Map of Maine o in southwest. Mostly syenite z

o and related intrusive rocks s

e with some associated

DEPARTMENT OF CONSERVATION M 248 volcanic rocks.

Maine Geological Survey n a i m r e P

Carboniferous - Large

290

Modified from Osberg, P. H., s granite and small gabbro u o

Hussey, A. M., II, and Boone, G. M., r intrusions in southwest. e f i

Bedrock Geologic Map of Maine, n

Presque o b r

1985, Maine Geological Survey Isle a C

Late Devonian-Carboniferous -

354

Unmetamorphosed terrestrial

Digital cartography by conglomerate and sandstone. n c a i i Devonian - Granite,

Marc Loiselle n Devonian - Marine sandstone and slate in o o

z granodiorite, and gabbro v northern and central Maine. Gneiss Silurian-Devonian - Marine e o throughout state. e D and schist in southwest. l sandstone and slate in east Ordovician-Devonian -

a

Robert G. Marvinney grading to gneiss and P n 417 Silurian - Limy marine shale in north Ordovician-Silurian - Mixed volcanic rocks a i schist in southwest. State Geologist r grading to lime-bearing gneiss and schist Marine sandstone and in north. Silurian - Mostly granite in u l i in southwest. Volcanic rocks in southeast. Some volcanic rocks slate in east grading coastal Maine, gabbro in east. S

443 in central coast. to gneiss and schist n a 2002 i Ordovician - Volcanic and related in southwest.

c Ordovician - Granite, quartz i sedimentary rocks in north and west. v Cambrian-Ordovician - syenite, diorite, and gabbro o

d Gneiss, schist, and marble along central Houlton r Mostly volcanic rocks in north and west.

O coast.

and related sedimentary 490

n rocks in north and east. Precambrian(?)-Ordovician - a

Mt. Katahdin i r Cambrian - Volcanic and related Schist, marble, and Wide range of volcanic and b Cambrian - Gabbro and

m sedimentary rocks in north. Volcanic gneiss in central coast. marine sedimentary rocks that a related rocks in northwest.

C rocks in central coast. have been metamorphosed to 543 gneiss and schist. n a i

r Precambrian - Gneiss and breccia A b in northwest. Limestone, marble, Millinocket m sandstone, slate, and volcanic a

c rocks in central coast. e r P Greenville ? Generalized geologic cross section Calais A B 0 km

Rangeley Eastport 15 km Bangor Geologic cross section enlarged 1.6x the geologic map; no vertical exaggeration. A and B mark the endpoints of the section on the map at left. Machias Generalized regional metamorphic zones Generalized Northern Appalachian geology

New Brunswick Unmetamorphosed Younger basins Augusta Mount Desert Weakly metamorphosed Late Ordovician-Devonian n si Island a sedimentary basins Low-grade metamorphism B y lle Coastal volcanic belt Quebec Va ut tic Cambrian-Ordovician volcanic arc increasing metamorphism ec nn o Composite Avalon microcontinent B C Ordovician oceanic crust and Cambrian Penobscot Bay in Highly metamorphosed s. as tn B rocks of the Penobscottian and e M in Maine Taconic events ry a a d M Intrusive igneous rocks Vermont n l Ordovician oceanic crust and related u a o tr B n rocks of the Taconic event Portland e Casco Bay C Cambrian-Ordovician continental shelf-rise sequence New Precambrian Chain Lakes rocks Hampshire Fault Precambrian North American basement (Laurentia)

Massachusetts Modified from Guidotti, C. V., in Osberg and others, Modified from Robinson and others, 1985, Bedrock Geologic Map of Maine: 1998, Paleozoic orogens in New England, USA: Kittery Maine Geological Survey. GFF, v. 120, p. 119-148. A Summary of the Geologic History of Maine

Maine’s bedrock records more than half a billion years of geologic history. Over this period References of time, geologic processes such as erosion and sedimentation, mountain-building, deformation (folding and faulting), metamorphism, and igneous activity produced the complex pattern of Berry, H. N., IV, and Osberg, P. H., 1989, A stratigraphic synthesis of eastern Maine and western bedrock geology that we see today. The large geologic wall map of the state by Osberg and others New Brunswick, in Tucker, R. D., and Marvinney, R. G. (editors), Studies in Maine (1985) shows hundreds of bedrock formations and igneous intrusions distinguished on the basis geology: Volume 2 - structure and stratigraphy: Maine Geological Survey, p. 1-32. of age and rock type. On this simplified map, these rocks have been grouped into units of similar Marvinney, R. G., and Thompson, W. B., 2000, A geologic history of Maine, in King, V. T. geologic age. The theory of plate tectonics describes the interactions of large, mobile, semi-rigid (editor), Mineralogy of Maine: Volume 2 - Mining history, gems, and geology: Maine plates that comprise Earth’s crust. The movement of these plates is responsible for Maine's Geological Survey, p. 1-8. complex geology. Where plates collide, mountains are built. Volcanic island arcs form where Osberg, P. H., Hussey, A. M., II, and Boone, G. M., 1985, Bedrock geologic map of Maine: one section of oceanic crust slides beneath another. Furthermore, mountain ranges such as the Maine Geological Survey, scale 1:500,000. Appalachian Mountains are often composed of multiple, small plate fragments, both continental Osberg, P. H., 1978, Synthesis of the geology of the northeast Appalachians, U.S.A., in Schenk, and oceanic in composition, which are distinctive and have had separate histories. While ongoing P. E., and Tosier, E. T. (editors), Appalachian-Caledonide orogen: Geological Survey of research continues to refine the nature and exact boundaries, it is generally accepted that the Canada, Paper 78-13, p. 137-167. geology of Maine is composed of a mosaic of such terranes (e.g. Osberg, 1978; Zen, 1983; Berry Palmer, A. R., and Geissman, J. (compilers), 1999, Geologic time scale: Geological Society of and Osberg, 1989; Robinson and others, 1998; Tucker and others, 2001). These were once widely America. scattered microplates in Iapetus, an ocean which preceded the modern Atlantic Ocean. The Tucker, R. D., and McKerrow, W. S., 1995, Early Paleozoic chronology: A review in light of new geologic history recorded in Maine’s bedrock spans several major cycles of deposition, U-Pb zircon ages from Newfoundland and Britain: Canadian Journal of Earth Science, v. deformation, and igneous activity related to plate tectonic movements. The simplified chart 32, p. 368-379. below recounts the histories of the various terranes that were later to become Maine’s bedrock. In Tucker, R. D., Osberg, P. H., and Berry, H. N. IV, 2001, The geology of a part of Acadia and the the chart, while the terranes have separate histories, they are shown in separate blocks. Laurentia nature of the Acadian orogeny across central and eastern Maine: American Journal of refers to the ancient eastern margin of North America. The Iapetus terranes comprise a composite Science, v. 301, p. 205-260. island arc, formed in Iapetus, that collided with Laurentia during the Ordovician Period. Avalon Robinson, P., Tucker, R. D., Bradley, D., Berry, H. N., IV, and Osberg, P. H., 1998, Paleozoic is a microplate which collided with early North America in the Devonian to form eastern North orogens in New England, USA: GFF, v. 120, p. 119-148. America as we know it today. Refer to the inset map of the northern Appalachians on the reverse Zen, E-an, 1983, Exotic terranes in the New England Appalachians - limits, candidates, and dates: side for the distribution of these terranes today. For a more detailed discussion of these events, a speculative essay, in Hatcher, R. D., Williams, H., and Zietz, I. (editors), Contributions to see Marvinney and Thompson (2000). This chart is best read from the bottom to the top (from the the tectonics and geophysics of mountain chains: Geological Society of America, Memoir oldest to the youngest events). 158, p. 55-81.

Geo logic Time Age* MAINE AND VICINITY

Ceno zoic Era Present - 66 Continued uplift and erosion of the Northern Appalachian Mountains. Stress release during uplift and erosion produces numerous fractures in the bedrock. Erosion by glacial ice shapes the landscape. Maine became ice-free about 11,000 years ago.

Mesozioc Era 66 - 248 Late Mesozoic: Continued widening of the Atlantic Ocean. Limited igneous activity (southern Maine). Limited faulting and fracturing. Early Mesozoic: Pangea breaks up. Combined Europe and Africa rift away from North America, opening the modern Atlantic Ocean. Faulting and fracturing of existing bedrock. Intrusive and volcanic activity; intrusion of basalt dikes (promi nent in southwestern coastal Maine). c i

o Per mian 248 - 290 Continued uplift and erosion of the Northern Appalachian Mountains gradu ally bring deep rocks to ward the surface. North America drifted north of the equa - z

o tor. e a l r a E P Car bon if er ous 290 - 354

e Intrusion of Sebago granite. Last regional metamorphism and deformation. Deposition of sandstone and related sedimentary rocks, only remnants of which t

a remain in eastern Maine. All Earth's crustal plates were joined as one conti nent, Pan gea. L De vo nian 354 - 417 Late Devonian: Sedimentary rocks deposited in northern and eastern Maine following the last major mountain-building event. Mid dle and Late Devo nian: Mountain build ing (called the Aca dian event by ge olo gists) – Ma jor de for mation of the Earth's crust caused by col li sion of the mi cro con ti nent of Ava lon with early North America. Assem bly of the varied terranes of eastern and coastal Maine and the Central Maine ba sin. Many sig - nifi cant faults de velop dur ing this pe riod. Burial of sedi ments in southwest ern Maine to depths greater than 9 miles trans forms them into meta morphic rock. Fi nal de vel op ment of an ces tral North ern Ap pa la chian Moun tains. Rocks at depth melt, pro duc ing wide spread ig ne ous ac tiv ity dur ing and af ter mountain- building epi sode. All of this oc curred while the east ern mar gin of early North America re mained south of the equa tor. a r

E Early Devonian: Youngest sediments deposited in major basins as precursor to major mountain-building event.

c i o z o e l a P

e l

d EARLY NORTH AMERICA AVALON d i

M Si lu rian 417 - 443 Limited rifting apart of North American continental margin formed small marine seas. Considerable deformation in the Avalon composite terrane Deposition in the Connecticut Valley basin of northwestern Maine. Deposition of large due to microplate collisions that formed the composite quantities of sediment in central Maine as the Ava lon ter rane ap proached, clos ing Ia pe tus. terrane. Continued deposition of sediments and increased Much sedi ment comes from the young mountains formed when Lau ren tia and the Iapetus volcanic activity. Some explosive volcanism related to ter ranes col lided in the Ordovician. Early North America is situ ated well south of the equa - crustal extension and intrusion now exposed in eastern tor at this time. coastal Maine. Intrusion of Silurian granite bodies in what is now central and eastern coastal Maine.

Or do vi cian 443 - 490 Late Ordovician: Additional sediment deposition following deformation and uplift. Late Ordovician: Beginning of events that preceded the Mid dle Or do vi cian: Moun tain build ing (called the Taconic event by ge olo gists) – De for - collision of the Avalon composite terrane with Laurentia. mation, up lift, and ig ne ous ac tiv ity re lated to the col li sion of sev eral(?) off shore vol canic is- Early and Middle Ordovician: Continued deposition of land ter ranes with Laurentia. This was part of an Or do vi cian island arc de vel oped in Iapetus. sediments and minor volcanic ac tiv ity produced rocks of Remnants of this arc are pres ent in the Boundary Mountains. the composite terrane called Avalon. The volcanic activity was related to tectonic events that assembled this composite terrane before its collision with Laurentia. The composite Avalon was located a considerable distance south of the edge of Laurentia at this time. a

r LAURENTIA IAPETUS TERRANES E

c i

o Deposition of limestone and shale on the Early Ordovician: Continued deposition z o

e continental shelf of Lauren tia. Lau rentia of sediments and volcanic activity. l a

P was lo cated much closer to the equa tor than

y Cam brian 490 - 543 Late Cambrian: Mountain building Sedimentation and significant volcanic activity produced l North America is to day, al lowing for ac cu - r

a (called the Penobscottian event by rocks of the composite Avalon terrane which was

E mula tion of large vol umes of warm-water lime stone. The limestone and shale is now geologists) – Episode of deformation and separated from Laurentia by a portion of the Iapetus ex posed just south of Que bec City, in west - metamorphism of rocks now found in Ocean. These rocks are now part of the Penobscot Bay ern Ver mont, and in east ern New York northwestern to north-central Maine area and eastern coastal Maine. Ava lon was situ ated in the state. attributed to microplate collision within southern hemi sphere, much far ther south than Lau ren tia ancestral Iapetus Ocean. and accu mu lated far less limestone. Early to Late Cambrian: Deposition of sediments and volcanic activity produced rocks now exposed in uplift features in north-central and northern Maine.

Pre cam brian 543 - 650(?) The edge of the ances tral North American As the ancestral supercontinent rifted, the Deposition of limestone and other marine sediments

a (most recent con ti nent, Lau ren tia, shed eroded material Iapetus Ocean opened and widened. eroded from an ancient microcontinent bor der ing Iapetus. r E part) into the adjacent widening ocean. These Sedimentary material from eroding Approximately 650 million year old episode of c i

o sedi ments be gan to ac cu mu late on the con - continents was deposited in this ocean. metamorphism and pegmatite intrusion in unknown z o

r ti nen tal shelf. geologic setting (now northern Penobscot Bay). e t o r P

e t Pre cam brian > 650 Events prior to approximately 650 million years ago are essentially unknown. Rocks over a billion years old may be present in the units of the Chain Lakes in a L northwestern Maine. North American (Lau ren tian) basement rocks had been formed by about 1.1 billion years ago. Break-up of a supercontinent which included North America occurred around this time resulting in the opening of an ocean called Ia pe tus, prede ces sor of the mod ern At lan tic.

* Age in mil lions of years be fore pres ent. The calibra tion (in years) of the geo logic time scale is Produced by the Maine Geological Survey, 22 State House Station, Augusta, Maine 04333. con tinu ally under re vi sion. The ages listed in this column are taken from Pal mer and Geissman Call 207-287-2801 for information. Web address: www.maine.gov/doc/nrimc/mgs/mgs.htm (1999) and Tucker and McKer row (1995).