The Geological Society of Maine Short Course

The Geology of Maine

October 15, 2003

Filene Room - Pettigrew Building, Bates College

Moderator - Walter Anderson, former State Geologist

Presentation Summaries

Ordovician through Devonian Paleogeography, Tectonic Setting, Volcanism and Sedimentary Environments, Northern Maine

Stephen Pollock, Ph.D., Department of Geosciences, University of Southern Maine

Various paleogeographic maps such as those shown at www.scotese.com illustrate eastern North America lying south of the equator from the Ordovician through the Devonian.  These same maps illustrate that the eastern margin of North America was northeast trending during this interval of time.

Applications of plate tectonics to New England geology began in the late 1960’s.  Since then numerous workers have recognized New England and Maine to be a collage of accreted terranes.  While accretion occurred throughout much of the lower Paleozoic, the Ordovician was a particularly important time for terrane accretion in northern New England, and Maine in particular.   E-an Zen (1983) was one of the first to apply the “terrane” concept to Maine geology.  Currently, the region encompassed by northern Maine and eastern Quebec is considered to have three basement terranes.  Ancestral North America is commonly referred to as Laurentia.  East of the Laurentian margin are the Boundary Mountain, Gander and composite Avalon terranes respectively.

 

Lineaments or tectonic features associated with the terrane borders are the Baie Verte Brompton Line (BBL), which separates Laurentia and the composite Dunnage terrane, and the Red Indian Line (RIL), which separates the Dunnage and Gander terrane.  Timing of accretion of the Gander and Dunnage terranes is currently considered to have occurred during the late Early Ordovician and early Middle Ordovician.  Somewhat later in the Ordovician the composited Gander and Dunnage terranes accreted to the eastern Laurentian margin.

Melanges and fragmented ophiolites discontinuously crop out in the vicinity of the BBL and RIL.  Fossils recovered from the melanges and rock which overlie the melanges are rare.  These fossils suggest that the melanges are not the same age everywhere along the strike of the units.  Also, the melanges vary in internal structure and composition.  The eastern melanges are almost everywhere tectonically formed and contain inclusions of metabasalt or are underlain by metabasalts.  The western melange belt is associated with ophiolite in the eastern townships in Quebec.  Mapping in northern Maine has not demonstrated an association with metabasalts.

A magmatic arc formed in the vicinity of the Dunnage - Gander terrane boundary beginning in the Middle Ordovician.  Volcanic activity of this arc ceased in Late Ordovician.  Sedimentation patterns demonstrate that much of the Middle Ordovician and early Late Ordovician was in “deep” water basins.  Most sedimentary units are flysch sequences containing metasandstone and slate of variable proportion and character.   By latest Ordovician (Ashgill) a shallow water sequence of sandstone and red slate was deposited to the west and a deeper water sequence to the east.

Silurian history is complex.  Units tend to be highly variable and local.  For the purposes of this talk, the Silurian is divided into:  a) the Rangely sequence in southwestern Maine, b) the central Maine slate belt; c) the eastern Aroostook County sequence; d) the central interior of northern Maine and e) the Frontenac Formation of western Maine.  Here we concentrate on the central interior of northern Maine.  The volcanic rocks are dominantly basaltic in composition.  Eruption occurred primarily in both shallow water and subaerial environments.  Sedimentation occurred in shallow water.  Sediments include limestones, and a variety of clastics that range from mudstone through conglomerate.  Evidence of the intertidal environment is locally preserved.  Volcanism and shallow water sedimentation locally span the Silurian - Devonian boundary.

 

The Early Devonian is marked by the development and infilling of a major northeast trending foreland basin.  Within the foreland basin is a complex assemblage of slate and metasandstone generally referred to as the Seboomook Group.  The Seboomook Group is, in general, understudied.  However, the unit has been subdivided into a number of units that have been both formally and informally named.  Along the eastern margin of this deeper water assemblage are a number of discontinuous sandstone bodies.  These sandstones represent a well-documented delta complex.  Sediments of both the Seboomook Group and deltaic sandstones were derived from the present day southeast.  Associated with the sandstones are eruptive rocks assigned to the Traveler and Kineo rhyolites.  These units and their equivalents have been referred to as the Piscataquis volcanic belt.  Overlying these early Devonian rocks are the “post-orogenic” Mapleton Sandstone and Trout Valley Formation of early Middle Devonian age.

The Coastal Maine Magmatic Province – utilizing “fossil” magma chambers to elucidate magma chamber processes

David Gibson, Associate Professor of Geology, University of Maine at Farmington

The granitic rocks of coastal Maine have long been used as building stone across the USA. In fact at one time over 40 quarries were active on the island of Vinalhaven alone. Nowadays there are only a few quarries operating but the granites of coastal Maine remain fascinating to many of us interested in what happens in magma chambers.

The term Coastal Maine Magmatic Province (or CMMP) was first used by Hogan and Sinha (1989) although previous workers especially Chapman (1962) had examined what he termed the Bays-of-Maine igneous complex. The CMMP contains over 100 intrusions, which range in age from Silurian to Devonian and in composition from gabbroic to granitic.  Hogan and Sinha subdivided these intrusions into 4 groups based on the level of interaction between coeval mafic and felsic magmas. Developing this theme further Wiebe and co-workers (1993, 1997) introduced the term MASLI (standing for Mafic and Silicic Layered Intrusions) to denote those plutons where mafic magma had periodically invaded crystallizing felsic chambers. This produced spectacular field relations with pillow structures akin to pillow lavas, hybrid rocks of intermediate composition and numerous disequilibrium textures such as quartz ocelli and rapakivi feldspars. MASLI are recognized in the older Silurian intrusions, which have also been tilted to reveal cross sections from their base to volcanic carapaces.

Our recent research has focused on the younger granitic phase of magmatism within the CMMP. In particular we have examined the Mt. Waldo and Deer Isle granites (both ~ 370My) and compared their field relationships, petrography, mineral and whole-rock chemistry to the Vinalhaven complex – a known MASLI style pluton. We see extensive evidence at many levels that mafic magma was also involved in the crystallization of these granites. Of note are the variable nature of the plagioclase compositions, the range of magmatic enclaves, disequilibrium textures and linear geochmical trends. These younger plutons may in fact be “cryptic” MASLI even though there is no direct field evidence of magma hybrization at the present erosion level. It would appear therefore that within the CMMP there was a long-lived supply of mafic magma that fueled these dynamic magma chambers.

References:

Chapman, C.A. (1962). Bays-of-Maine igneous complex. GSA Bulletin, v. 73, p. 883 – 888.

Hogan, J.P. and Sinha, A.K. (1989). Compositional variation of plutonism in the coastal Maine magmatic province: Mode of origin and tectonic setting. In, Tucker and Marvinney (eds), Studies in Maine Geology, v. 4; Igneous and Metamorphic Geology, p. 1 – 35.

Wiebe, R. A. (1993). Basaltic injections into floored silicic magma chambers. Eos, v. 74, p. 1 – 3.  

The Odyssey of New England’s Bedrock

Douglas Reusch, Ph.D., Natural Sciences Department, University of Maine at Farmington; reusch@maine.edu

Appalachian bedrock significantly influences the shape of New England’s landscape and hence the flow of water over and through it. It supplies nutrients to the biosphere and valuable mineral resources. Last but hardly least, it is an intellectual treasure chest of information about past biologic, climatic, and tectonic change.

The Appalachian mountain belt borders the Atlantic Ocean, a relatively young feature formed by the break-up of Pangea 200 million years ago. Its rocks record the life cycle of the Atlantic’s predecessor, the Iapetus Ocean, between 600 and 300 million years ago. A poster (32” ´ 39” portrait) is being developed for the purpose of conveying the tectonic evolution of this valuable “local” resource to a layperson audience, especially K-16 educators. On the tectonic map of New England and block diagrams, types of materials are indicated by patterns, explained in a tutorial at the base of the poster; age is shown by hue (older units are higher frequency); and position is shown by lightness (higher paleolatitudes are lighter).

One method for elucidating the tectonic evolution of a mountain belt is to identify boundaries between sharply contrasting strata of the same age (especially contrasts in fauna, flora, and paleolatitude).  Several of these major facies, or terrane boundaries, have been defined in Canada (van Staal, Dewey, Mac Niocaill, & McKerrow, 1998) and extrapolated into New England:

During latest Precambrian time, the Newfoundland promontory of Laurentia may have dovetailed with the western South American reentrant. Following rifting, a passive margin developed on the eastern margin of Laurentia. The Avalon terrane was a stable platform but the leading Gondwanan terrane, Ganderia (central New England) became the locus of arc volcanism above a southeast-dipping subduction zone during the Cambrian. In Newfoundland, a back-arc basin developed, and a major ophiolite sheet was thrust southeast over the passive margin (Gander Group) during the Penobscot orogeny. The Ellsworth terrane, made of Cambrian oceanic rocks, now sits on top of the southeastern margin of Ganderia.

During Ordovician time, the eastern margin of Laurentia experienced a Taiwan or New Guinea-type arc-continent collision. Following aborted subduction of the passive margin, a new outboard subduction zone was initiated beneath Laurentia. In this framework, the Rangeley sequence is in a forearc position. To the south, the leading Gondwanan crust became the locus of arc volcanism (Popologan and Bronson Hill [?]) with formation of a major back arc basin (Exploits-Tetagouche-Casco Bay) that split Ganderia in half.

During Late Ordovician through Early Silurian time, this back-arc basin closed via northwest-dipping subduction, which brought together the active (NW) and passive (SE) margins of the basin along the Dog Bay Line. Silurian sediments were deposited unconformably in the northwest (Ripogenus Dam) and the southeast (Ames Knob; Oak Bay) prior to subaerial volcanism. The Coastal Magmatic Belt formed above the northwest-subducting Avalon plate, and the arrival of Avalonia and/or Meguma caused the Acadian orogeny. A retro-arc clastic wedge propagated from central to northern Maine, culminating in the Catskill Delta. Middle Paleozoic plutonism followed and was widespread.

During the Late Paleozoic, plutonism persisted (Sebago) and sedimentation was controlled by dextral strike-slip faults. During the Mesozoic, hot spot magmatism (White Mountains) and extensional tectonics accompanied the rifting of Pangea and beginning of the Atlantic cycle.

For more information:

Websites

www.scotese.com

References

 Barr, S.M. et al., 2001. The Last Billion Years: A Geological History of the Maritime Provinces of Canada, Atlantic Geoscience Society Special Publication No. 15, 212 p.

Origin and Evolution of Maine’s Mountains

Chris Gerbi, Ph.D. candidate, Department of Earth Sciences, Bryand Global Sciences Center, University of Maine, Orono, ME 04469; gerbi@umit.maine.edu

Maine’s present-day topography is the product of competing erosional and tectonic processes that have operated over the past 500 million years.  The tectonic processes thickened the crust, to approximately 50 km, in a series of small collisions, probably building a series of narrow mountain ranges.  Although narrow, each of these ranges could have been high, much like the highest peaks in Papua-New Guinea rise more than 5000 m out of the Pacific Ocean.  The accretionary collisions progressively widened the Appalachians, but never produced an orogen comparable, in either average elevation or width, to the Himalayas.  The main Appalachian spine was probably at its highest during the late Devonian, approximately 350 million years ago.  Another mountain range lay over the Casco Bay belt, located in a line roughly connecting Bath and Belfast.  This range would have been built somewhere in the middle of the ocean, before the amalgamated microcontinent accreted to North America.  Today’s mountains exist because differential erosion wore down the thick crust faster in some places than in others, producing valleys and ridges.  Erosion over the past 350 million years has removed approximately 16 km of rock, with most of the erosion taking place long ago soon after the crust was thickened.  The state’s present-day relief is only 1600 m, so most of the thickened crust had to be eroded before the modern shape of the mountains emerged.  Although rivers eroded most of the material and produced the gross distribution of peaks, ice played a role in creating some of the characteristic mountain landforms we see today.

For more information:

Websites

There isn’t really anything I’ve found online that directly addresses Maine’s mountains, but a couple of good general plate tectonics site are:

http://pubs.usgs.gov/publications//text/dynamic.html

http://www.scotese.com/

References

*Bradley, D.C., Tucker, R.D., Lux, D.R., Harris, A.G., and McGregor, D.C., 2000, Migration of the Acadian orogen and foreland basin across the northern Appalachians of Maine and adjacent areas. U.S.G.S. Professional Paper 1624. http://geopubs.wr.usgs.gov/prof-paper/pp1624/

*Keary, P., and Vine, F.J., 1996, Global Tectonics 2^nd ed., Blackwell Scientific, London.

*Moores, E.M., and Twiss, R.J., 1995, Tectonics, W.H. Freeman, New York.

*van Staal, C.R., Dewey, J.F., MacNiocaill, C., and McKerrow, W.S., 1998, The Cambrian –Silurian tectonic evolution of the northern Appalachians and British Caledonides: history of a complex, west and southwest pacific-type segment of Ipetus, In: Blundell, D.J., & Scott, A.C., (eds.) Lyell: the Past is the Key to the Present. Geological Society of London Special Publications, v. 143, p, 199-242.

The History of Metamorphism in Maine

Rachel Beane, Ph.D., Assistant Professor of Geology, Bowdoin College, 6800 College Station, Brunswick, ME 04011; rbeane@bowdoin.edu

The prevalent mountain building and plutonism of Maine’s geologic history transformed much of the state’s original sedimentary layers and volcanics into metamorphic rocks.  The shale, sandstone, carbonate, basalt and other rocks of Precambrian to Early Paleozoic age are now schist, quartzite, marble, amphibolite and gneiss as a result of being buried kilometers under mountains and heated by underground igneous intrusions.

The metamorphic history of Maine is complex.  Metamorphic reactions are a function of a number of conditions including pressure, temperature, fluid flow and the original rock type.  A single unified history cannot explain all the metamorphism observed in Maine’s rocks.  For example, the mineralogy of altered basalts and peridotites of north-central Maine suggests low-temperature sea-floor metamorphism, while rocks of the Chain Lakes massif were recrystallized at very high temperatures then almost entirely retrograded, and some granite along the Norumbega Fault Zone was ground to fine-grained mylonite during intense shearing.

Stepping away from the details, however, a metamorphic pattern emerges for the state of Maine. Low-temperature, low-pressure conditions dominated metamorphism in the northern two-thirds of Maine.  The metamorphic grade increases southward.  In the south, regional high-temperature, low-pressure metamorphism is associated with Devonian mountain building – the Acadian orogeny.  During this collisional event between pre-North America and a microcontinent, sediments and volcanics were buried at mid-crustal depths, heated, and metamorphosed.   Igneous activity during and after the Acadian orogeny provided heat for the regional metamorphism, and for some of the local high-temperature contact metamorphic aureoles.

For more information:

Websites

Digital Library for Earth System Education (collection of educational resources): www.dlese.org

Maine Geological Survey (Bedrock Geology of Maine – summary and photos): http://www.state.me.us/doc/nrimc/mgs/bedrock/bedrock.htm

Metamorphic Rocks (comprehensive introduction to metamorphic rocks by L. Fichter, James Madison University): http://csmres.jmu.edu/geollab/Fichter/MetaRx/index.html

References

*Guidotti, C.V., 1989, Metamorphism in Maine: An overview, in Tucker, R.D., and Marvinney, R.G. (editors), Studies in Maine Geology, v. 3: Igneous and Metamorphic Geology: Maine Geological Survey, p. 1-17.

*Hussey, A.M., and Berry, H.N., 2002.  Bedrock Geology of the Bath 1:100, 000 Map Sheet, Coastal Maine, Maine Geological Survey, Bulletin 42, 50 pp.

*Marvinney, R.G., and Thompson, W.B., 2000, A geologic history of Maine, in King, V.T. (editor), Mineralogy of Maine: Volume 2 – Mining history, gems, and geology: Maine Geological Survey, p. 1-8. (also at http://www.state.me.us/doc/nrimc/pubedinf/factsht/bedrock/megeol.htm)

*Spear, F. 1993. Metamorphic phase equilibria and pressure-temperature-time paths. Monograph 1. Mineralogical Society of America, Washington, D.C.

Maine’s Fossil Record

Lisa Churchill-Dickson, M.S., C.G., President, Geological Society of Maine, 7 Penley Street, Augusta, ME 04330; paleo@gwi.net

There is a rich diversity of life preserved in Maine’s rocks and sediments.  Some of Maine’s fossils date from nearly 545 million years ago.  Others are much younger, recording conditions as the glacier retreated approximately 12,000 years ago.  While most of the deposits are marine, there are some terrestrial ones, including the world-renown Trout Valley Formation from which the State Fossil, Pertica quadrifaria, comes.

Maine has a significant Paleozoic record that dates from the Cambrian through the Devonian.  It preserves a fauna and flora that were living along a tectonically active margin and subject to extreme and frequent ecological perturbations. This setting contrasts markedly with contemporaneous, inland areas such as New York and Cincinnati and there is good reason to expect differences not only in the taxonomic composition of the different biotas, but also within their community structures and possibly even within their evolutionary histories as well. 

The accretion of other landmasses to Maine throughout the Paleozoic created a patchwork of fossil communities hailing from disparate geographies and climates. However, there is a significant gap in Maine’s fossil record following that time, ranging from the Carboniferous through the Pliocene (approximately 360 million years ago to 1 million years ago).  This represents missing material rather than an actual absence of organisms from Maine. Following the Devonian, Maine transitioned from a marine-dominated setting to a fully terrestrial one.  Because terrestrial environments are more prone to erosion than marine ones, the potential for fossil preservation within them is likewise reduced. Also, any post-Devonian remains that may have been deposited in Maine were later eroded during the glacial events of the Pleistocene. Nonetheless, there is still a small chance that a fossiliferous remnant from the Late Paleozoic, Mesozoic or Early Cenozoic may have survived somewhere in Maine. 

For more information:

Websites

University of California’s Museum of Paleontology (great site for basic paleo and history of life): www.ucmp.berkeley.edu

Paleontological Research Institute (online collections, teaching resources): www.priweb.org

Maine Geological Survey (Maine fossils – summary and photos): www.state.me.us/doc/nrimc/pubedinf/factsht/paleo

References

*Benton, M. J. and Harper, D. A. T. 1997. Basic Palaeontology. Addison Wesley Longman, Ltd.

*Boardman, R. S., Cheetham, A. H., and Rowell, A. J. (eds) 1987. Fossil Invertebrates.  Blackwell Science.

*Churchill-Dickson, L. 2004. Maine’s Fossil Record: The Paleozoic.  Maine Geological Survey.

*Fortey, R. A. 1998. Life: A Natural History of The First Four Billion Years of Life on Earth.  Knopf, Inc.

*Gensel, P. G. and Edwards, D. (eds) 2001. Plants Invade the Land. Columbia University Press.

*Gould, S. J. (ed.) 1993.  The Book of Life: an Illustrated History of the Evolution of Life on Earth.  Norton and Co.  

An Overview of the Geomorphology of Maine

Joseph T. Kelley, Ph.D., Department of Earth Sciences, University of Maine, Orono, Maine 04469

The overall landscape of Maine is one resulting from a long period of erosion. Following mountain building in the middle Devonian, there is a record of terrestrial, clastic sediment accumulation in the late Devonian and Carboniferous in high-relief settings. The post-Acadian unconformity of Perry Formation sandstones and conglomerates over the Red Beach granite has long been recognized as demarking the end of mountain building and the start of mountain destruction in Maine. There are no Permian-age rocks in the region, but uplift must have accompanied the formation of the Atlantic Ocean in the early Mesozoic. Today, failed rift basins containing red sandstones and conglomerates, along with basalt flows are the only record from that time. Some basins in the Gulf of Maine and the nearby Bay of Fundy basin are left from that time. There is speculation that the many diabase dikes, so visible along our coast, were feeders to massive basalt flows, but if so, those flows are completely eroded from Maine. Likely uplift associated with late Mesozoic intrusions in southern Maine was associated with deep erosion into rocks of the Appalachian Mountains. Rare occurrences of Cenozoic sediment in Rockland, Maine, Brandon, VT, Nova Scotia and the Gulf of Maine suggest that Maine may have once possessed a cover of Coastal Plain sediment analogous to areas south of New York City, but Quaternary glaciations removed most traces of this material. Although isolated outcrops of “rotten stone” are recognized as a soil that formed prior to the last glaciation, most direct evidence of pre-glacial landscapes was  removed by glacial erosion in the Quaternary.

Many geologists have written on the landscapes of Maine (Thornbury, 1965), with most early work focused on episodes of downwasting to a flat terrain (peneplanation). Around the time that a new bedrock map was in preparation and new topographic maps were appearing, Toppan (1935) defined the major geomorphic provinces of the state. The Coastal Lowlands traverse the state from southwest to northeast, and from the present coast to about 30 km inland. This area averages less than 30 m in elevation, with a few distinct monadnocks like Mt Agamenticus. Paralleling this province, the Central Uplands averages 150 m in elevation, with a sharp border on the west with the Moosehead Plateau. The Moosehead Plateau averages 300 m in elevation, and waterfalls are common on the abrupt contact with the Coastal Upland. The Aroostook Valley province forms the relatively low-relief, northeast corner of the state and is an area averaging 130 m in elevation.  Denny (1980) subsequently carved out eastern Maine as the New Brunswick Highlands in recognition of the greater topographic relief from the Camden Hills through Mt Desert Island and northeast into Canada.

Although Toppan found no obvious relationship between rock type and physiographic subdivision, Hansen and Caldwell (1989) and Caldwell (1998) demonstrate the strong association between rock type and elevation.  Generally slates are easily eroded and form lowlands throughout the state; volcanic rocks, granophyre, quartzites and hornfels form high areas. Granite forms both the highest (Mt Katahdin) and lowest  (Sebago Lake bottom) points in Maine owing to variations in its texture and association with difficult-to-erode adjacent hornfels rocks. Many lakes are located over plutonic rocks, and rivers generally avoid such bodies.

Curiously, most Maine rivers run against the northeast structural grain of the regional rocks and many have wondered why streams are not deeply downcut into northeast-trending slatey rocks. Glacial derangement of rivers is one possible explanation, and is most evident in the coastal regions where glacial-marine mud (Marsh Stream, Penobscot River) and glacial outwash (Brunswick sand plain, Kennebec River) fill many pre-glacial valleys. The upper reaches of some rivers are deeply eroded, such as the Androscoggin River near Bethel, but many ancient river channels are now occupied by lakes and glacial fill.

Maine’s coast was subdivided on the basis of bedrock geology by Kelley (1987), with the relative abundance of coastal environments controlled by rock structure and glacial deposits. The Arcuate Embayments, south of Portland, are characterized by sand beaches, the Indented Shoreline from Portland to Penobscot Bay, is most associated with salt marshes and mud flats, the Island-Bay coast from Penobscot Bay to Cutler contains mostly coarse-grained tidal flats and the Cliffed Shoreline from Cutler to the Canadian border possesses the largest proportion of bedrock along the shore. Recent work offshore (Kelley et al., 1998) shows that these compartments continue with modification underwater.  Sandy seafloor is found mostly in the south; muddy areas dominate the seafloor off the Indented Shoreline, gravel bottom is most common off the Island-Bay coast and Cliffed Shoreline. Numerous valley systems cut into bedrock emerge from all Maine embayments. Their origin may be a combination of pre-glacial fluvial erosion, glacial scour or sub-glacial meltwater downcutting.

For more information:

References

*Caldwell, D.W., 1998, The Roadside Geology of Maine, Mountain Press Publishing Company, Missoula, MT, 317 p.

*Denny, C.S., 1980, Geomorphology of New England, U.S. Geological Survey Professional Paper 1208, 18 p.

*Hansen, L., and Caldwell, D.W., 1989, The lithologic and structural controls on the geomorphology of the mountainous areas in north-central Maine. In Robert Tucker and Robert Marvinney,  (eds.) Studies in Maine Geology,  p. 147-160.

*Kelley, J.T., 1987, An Inventory of Environments and Classification of Maine's Estuarine Coastline. In A Treatise on Glaciated Coastlines, P. Rosen and D. FitzGerald (eds.), Academic Press, San Diego, CA; p. 151-176.

*Kelley, J.T., Barnhardt, W.A., Belknap, D.F., Dickson, S.M., and Kelley, A.R., 1998, The Seafloor revealed: The geology of Maine's inner continental shelf.  A report to the Regional Marine Research Program, Maine Geological Survey Open-file Report 98-6, 55 p.

*Toppan,  F.W., 1935, The Physiography of Maine. Journal of Geology, v. 43, p. 76-87.

*Thornbury, W. D., 1965, Regional geomorphology of the United States. John Wiley and Sons, Inc., 609 p.

The Glacial History of Maine

Julia Daly, Department of Natural Science, University of Maine, Farmington;dalyj@maine.edu

Maine has a rich and diverse assemblage of deposits and bedrock features resulting from glaciation during the Quaternary period.  During the last glacial maximum (LGM), ice from the Laurentide ice sheet advanced across Maine from the northwest and terminated at the southeastern margin of the Gulf of Maine.  The advance of this ice sheet scoured the bedrock surface of Maine, removing most of the unconsolidated material from the surface and sculpting the underlying bedrock.  Erosional features associated with glaciation include striated and polished bedrock surfaces, roche moutonees, and cirques.  Following this period of erosion, till was deposited unconformably on many bedrock surfaces.  The thickness, form, and depositional mode of this till vary with location, but it is all interpreted to be material deposited directly from the ice.

The LGM came to an abrupt end, and by 14,000 years ago the front of the Laurentide ice sheet roughly paralleled the present shoreline.  As the ice sheet retreated, it constructed numerous moraines in the southern and eastern areas of the state.  The front of the ice sheet continued to retreat to the northwest.  During the LGM, the mass of overlying ice depressed the crust, and the front of the ice sheet retreated faster than the crust could rebound.  While the crust was still depressed, the southern and eastern parts of Maine were flooded, and the ice sheet would have been calving into this marine embayment.  Numerous deltas and widespread glacio-marine deposits record this brief submergence.  In northern and western Maine, deglaciation is associated with deposition of outwash material, eskers, and other stratified drift.

Investigation of the local glacial history by students affords the opportunity to meet the state Learning Results.  Fossils associated with the glacio-marine deposits address themes of biologic change.  Striated outcrops can be rich sites for acquiring data to synthesize and interpret.  Local outcrops of till or unusual erratics are excellent opportunities for identifying and classifying different types of bedrock.  Projects such as these all help students to learn techniques of field work and scientific inquiry.

For more information:

Websites

Maine Geological Survey: www.state.me.us/doc/nrimc/mgs/mgs.htm; see the fantastic Geologic Site of the Month pages for information about local glacial features, as well as the glacial geology section for an overview of Maine’s glacial history

NOAA Paleoclimatic data center: www.ngdc.noaa.gov/paleo/paleo.html

Satellite images (including glaciated areas): http://visibleearth.nasa.gov

References

*Borns, H. W. et al. (eds) 1985.  Late Pleistocene history of northeastern New England and adjacent Quebec.  Geological Society of America Special Paper 197.

*Thompson, W. B. and Borns, H. W. 1985.  Surficial geologic map of Maine: Maine Geological Survey, Augusta; scale: 1:500,000.

*Weddle, T. K. and Retelle, M. J. (eds.) 2001.  Deglacial history and relative sea-level changes, northern New England and adjacent Canada.  Geological Society of America Special Paper 351, 292 p.

*Numerous surficial geologic maps are also available from the survey at the 1:24,000 scale.

Geoarchaeology: Investigating the Link Between People and Landscapes in Maine

Alice Kelley, Department of Earth Sciences, University of Maine, Orono, Maine 04469; akelley@maine.edu

Archaeology is the study of past human behavior through the study of cultural remains. Geology is the investigation of earth processes and materials.  Geoarchaeolgy combines these two disciplines by using geological techniques to address archaeological questions relating to resources, travel, and occupation locations of past human inhabitants.  Although geologists and archaeologists have a long-standing record of professional cooperation, geoarchaeology, or archaeological geology, did not became a recognized subdiscipline of each field until the 1970’s.  At this time archaeological interest at sites formally expanded beyond artifact description and cultural history, and began to consider the linkage between people and their environment.

Geoarchaeology can be divided into three, complimentary, subheadings: materials analysis, landscape reconstruction, and archaeological prospection.  The pre-European inhabitants of Northern New England used lithic, or rock, resources extensively to produce a wide range of tools, weapons, and domestic objects.  Geological analysis of these materials can identify the material used, provide clues to production technology, and sometimes locate the source of distinctive rock types, suggesting travel and/or trade networks.  Climate change, human intervention, and on-going geological processes have dramatically shaped the Northern New England landscape through time.  Geoarchaeologists use standard sedimentological and surficial mapping techniques, combined with paleoenvironmental information, to describe the landscape as it was seen by past occupants.  Because landscapes change through time, and human needs and perceptions also change through time, archaeological sites may not be readily apparent to modern researchers.  However, by combining a geological understanding of landscape dynamics with an archaeological recognition of human patterns of behavior and land use, the locations of sites can be predicted, either for preservation or investigation.

Geoarchaeology helps to set the stage in the interpretation of past human behavior by providing the landscape context in which people lived and traveled, as well as providing information about the resources used by the region’s past inhabitants.

For more information:

References

*Principles of Geoarchaeology: A North American Perspective  by Michael R. Waters,

*Geoarchaeology: The Earth-Science Approach to Archaeological Interpretation by Christopher L. Hill, George Robert Rapp, George, Jr. Rapp

History of Sea Level Change in Maine

Maine’s coast and coastal lowlands have been strongly affected by sea-level changes over the past 14,000 (radiocarbon) years.  Retreat of the latest Laurentide ice sheet revealed a land depressed more than 100 m below the sea, resulting in marine transgression and deposition of glaciomarine sediments as far north as Millinocket and Bingham. Evidence for the ultimate height comes from emerged shorelines and deltas, and is dated from marine fossils.  After ice retreat the land rebounded isostatically, resulting in a relative fall of sea level to a lowstand 60-65 m deep on the inner shelf 10,500 yrs B.P.  Lowstand shorelines and deltas record this phase.  Subsequent slowing of the rate of rebound and overtaking by the rise in eustatic sea level due to global melting of ice resulting in local relative sea-level rise at a generally decreasing rate to present. Marine shells and peat recovered from the inner shelf by coring allow dating of this rise.

Sea-level rise over the past 5000 years is known in considerable detail from cores through salt marshes, recovering fossil high-marsh peats that indicate sea level within decimeters, dated to a century or so precision.  Besides the fossil plants, preserved foraminifera microfossils provide a highly detailed record of marsh zonation with respect to paleo-tidal levels.  Transects of cores provide a history of sea-level rise, migration of shorelines, transgression of the marsh onto the adjacent upland, migrating tidal creeks, and minor fluctuations in rates of change possible related to changing climates.

Study of sea-level change is critical for understanding the history of coastal systems.  Knowledge of past rates of sea-level and coastline change allows extrapolation of changes expected in the future, especially with expected acceleration of sea-level rise with warming climate.   

For more information:

Websites

University of Maine’s Department of Earth Sciences: www.geology.um.maine.edu/marine

Maine Geological Survey’s marine web site: www.state.me.us/doc/nrimc/mgs/marine/marine.htm

References

*Barnhardt, W.A., Gehrels, W.R., Belknap, D.F. and Kelley, J.T., 1995, Late Quaternary relative sea-level change in the western Gulf of Maine: evidence for a migrating glacial forebulge: Geology, v. 23, p. 317-320.

*Kelley, J.T., Gehrels, W.R. and Belknap, D.F., 1995, Late Holocene relative sea-level rise and the geologic development of tidal marshes at Wells, Maine, U.S.A., Journal of Coastal Research, v. 11,  p. 136-153.

*Gehrels, W.R., Belknap, D.F. and Kelley, J.T., 1996, Integrated high-precision analyses of Holocene relative sea-level changes along the coast of Maine: Geological Society of America Bulletin, v. 108, p. 1073-1088.

*Gehrels, W.R., Belknap, D.F., Black, S. and Newnham, R.M., 2002, Rapid Sea-level rise in the Gulf of Maine, USA, since AD1800: The Holocene, v. 12, p. 383-389.  1 July, 2002.

*Kelley, J.T., Dickson, S.M., Belknap, D.F. and Stuckenrath, R., Jr., 1992, Sea-level change and the introduction of late Quaternary sed­iment to the southern Maine inner continental shelf: In: C.H. Fletcher and J.F. Wehmiller, eds., Quaternary Coastal Systems of the United States, Marine and Lacustrine Systems: IGCP Project #274/SEPM Spec. Pub. 48, p. 23-34.

Coastal Geology

Stephen M. Dickson, Ph.D., C.G., State Marine Geologist, Maine Geological Survey,

22 State House Station, Augusta, ME 04333-0022; stephen.m.dickson@maine.gov

The coast of Maine has 5600 kilometers (3480 miles) of tidally influenced shoreline and is the third longest in the United States.  There are about 3500 islands included in the shoreline length.  State submerged lands extend from the low tide line a distance 5.56 kilometers (three nautical miles) offshore.  The seafloor below the Territorial Sea is some 1080 square kilometers (2800 square miles) or about 9% of the land area of the State of Maine.

The geology of Maine’s inner continental shelf is a complex mosaic of bedrock exposures (41%), muddy basins (39%), gravel plains (12%), and sandy areas (8%).  Rocky seafloor is dominant in water depths less than 50 meters.  Muddy seafloor is dominant below 50 meters.  Gravel is a minor bottom type at all depths, but is most common in the 10 to 30 meter depth range.  Sandy seafloor is rare but present at all depths to 100 meters; sand is only slightly more abundant in water less than 30 meters deep.

The stratigraphy of sediments layered over the bedrock is spatially variable on the seafloor and in shoreline depositional environments.  Due to the fall and subsequent rise of sea level, most marine sedimentary sequences in water shallower than 60 meters are incomplete, condensed sections with considerable textural variability compared to the more continuous record of deep basin marine mud deposition below 60 meters.  On the shallow inner continental shelf, bedrock is often mantled with glacial till and then glaciomarine mud.  A gravel lag deposit and regressive coastal sand sometimes overlie the glacial sediments.  Nonmarine sediments such as lake gyttja, freshwater peat, and a soil horizon may underlie modern marine mud and salt marsh peat and/or modern shoreface sand and gravel deposits.

Coastal sedimentation and erosion are strongly influenced by tidal currents and waves.  Tides along the Maine coast are semidiurnal (two highs and two lows a day) and range from 5.6 meters (18.4 feet) in Eastport to 2.6 meters (8.7 feet) in Kittery.  The tidal range increases with the new and full moon phases to create spring tides that are 10 to 15% larger than the mean range.  Seasonality in wave heights results in relatively calm conditions in July and August and stormy conditions in the winter.  Buoys off the coast record wave heights as high as 7 meters (23 feet) in winter storms.

Maine’s intertidal area is not accurately known but is approximately 590 square km (145,000 acres) based on MGS maps.  Mud flats (44%), bedrock ledge exposures (25%), and salt marshes (14%) account for over 80% of the intertidal geologic environments.  Mixed grain size flats (7%), sand flats (5%), boulder flats (3%), and sand beaches (2%) are minor components of the intertidal zone. 

Sediment bluffs with a relief of a meter or more are present along about 50% of the Maine shoreline.  Coastal bluffs are composed of glaciomarine mud, sand, and till and are found above all of the intertidal environments.  Marine erosion, freshwater runoff, and groundwater sapping result in chronic bluff erosion and land loss.  Sediment eroded from bluffs has been reworked in the intertidal zone to form Holocene mudflats, salt marshes, and some beaches.  Clay bluffs with 3 meters (20 feet) of relief of more may experience landslides and subsequent adjustment to the shoreline for decades.

About 2% of the Maine shoreline (120 km or 75 miles) has beaches.  About half of this distance is composed of sandy beaches and the other half is composed of coarser gravel and boulder beaches.  There are over 200 gravel pocket barrier beaches that front salt marshes and estuarine channels.  Most large sandy beaches occur along the southern coast between Kittery and Cape Elizabeth, south of Portland.  A few kilometers of sandy beaches also occur in midcoast Maine near the mouth of the Kennebec River.  Large salt marshes are common behind in the back barrier environment of sandy beaches.

Coastal sand dunes are relatively rare (less than 12 square km or 3000 acres statewide) and subject to rapid erosion and sedimentation during coastal flooding from storms and overwash by waves.  Wind modifies dune morphology all year and contributes to the elevation of the frontal dune ridge.  Many beaches are subject to longshore drift within littoral cells framed by bedrock headlands or tidal inlets.  Currents, waves, coastal engineering, and channel dredging affect beach erosion and accretion patterns and coastal sand budgets.  In the last 50 to 150 years human activity along beaches and adjacent tidal inlets has dramatically altered coastal processes and accelerated shoreline change in many locations. 

For more information:

Websites

Maine Geological Survey – Marine Geology (with local links) http://www.maine.gov/doc/nrimc/mgs/marine/marine.htm

NOAA – Coastal Services Center

http://www.csc.noaa.gov/

US Army Corps of Engineers – Coastal Hydraulics Laboratory

http://chl.wes.army.mil/

US Geological Survey – Coastal and Marine Geology Program

http://marine.usgs.gov/

References

*Carter, R. W. G., 1988.  Coastal Environments.  Academic Press, 617 p. 

*FitzGerald, D. M. and P. S. Rosen, 1987.  Glaciated Coasts.  Academic Press, 364 p.

*Kelley, J. T., W. A. Barnhardt, D. F. Belknap, S. M. Dickson, and A. R. Kelley, 1998.  The Seafloor Revealed – The Geology of the Northwestern Gulf of Maine Inner Continental Shelf.  Maine Geological Survey, 55 p.

*Kelley, J. T., A. R. Kelley, and O. H. Pilkey, Sr., 1989.  Living with the Coast of Maine.  Duke University Press, 174 p.  Available from the Maine Geological Survey.  

The application of geological principles can guide our use of resources in remediation of existing environmental problems and in planning for the future. 

A case study is presented in which an early attempt at recycling resulted in the deposition of lead in a residential neighborhood.  The remediation of the site required the use of soils derived from glacial tills, volcanic ash, and beach sands.  As a result of the remediation, a dangerous site in a residential area became a park with ball fields and walking trails.

In addition, geologic principles are being used to provide new methods for disposal of wastewater and to provide green sources of energy.  New research is showing the efficacy of disposal of wastewater from municipalities and commercial facilities as spray and as snow, removing ove