LAURENTIAN MARGIN DEPOSITS

Donald Kenney (donaldkenney@gmail.com)
Last Update: Thu Sep 1 07:38:39 2016



Introduction

Sometime around 600,000,000 years ago the huge paleocontinent of Rodinia started to break up. Eventually, an ocean called Iapetus Ocean opened up between paleo-North America (Laurentia) and paleo-Africa (Gondwanaland). Sometime around 500,000,000 years ago, the Iapetus started to close.

Still working from Northeast to Southwest across North America, the next set of terranes we encounter after those of the Iapetus seafloor are those that were originally deposited along the margin of ancient North America -- the Paleocontinent of Laurentia. These rocks were pushed into their present positions during the Ordovician as volcanic island arcs in the closing Iapetus Sea plowed into Laurentia pushing portions of the sea bottom in front of them.

The distinction between these rocks and those of Laurentia proper is often somewhat hazy. The rocks of these regions tend to be fault delimited slices and sometimes overturned folds -- often extending many tens of kilometers along the axis parallel to the Laurentian boundary, but much narrower perpendicular to that axis. The problem is that the rocks along the margin of Laurentia were sometimes crumpled and or moved a bit as the sea bottom to their East was pushed up into the basin to their East. In many cases, it's very hard to tell how far blocks were moved. Pragmatics require a boundary somewhere. I have chosen mine roughly along the line where most rocks to the East and South have been transported and most rocks to the North and West are probably more or less in place.

Somewhat more precisely, I have defined the Laurentian margin region for my purposes as follows: The Southern/Eastern boundary follows the Baia Verte Fault line in Newfoundland, then a line about 50km South of the South bank of the Saint Lawrence River in New Brunswick and Quebec. In Western New England, it is the first major (unnamed) thrust East of the Oak Hill-Hinesburg thrust structure which runs down the West side of the Green Mountains. South of New York City, it is the Western margin of the Piedmont region in the Mid Atlantic and Southern States. On the North and West sides I consider the zone to end somewhere in the strait between Labrador and Newfoundland, and then to swing West including the Saint Lawrence South shore exposures of New Brunswick and Quebec, but not the large Islands in the St Lawrence like Anticosti Island. In the vicinity of Quebec City, the Margin rocks overlap onto the North Shore of the St Lawrence. West of Quebec City, the limit then follows Logan's/Emmons' line West to the Richileu River. It then swings South down the Richileu River, the East Shore of Lake Champlain, the East side of the Hudson River and then swings Southwest generally including the first (Blue Mountain) ridge of the Appalachians along the line where Early Paleozoic marine sediments from the East have been thrust over generally younger Paleozoic rocks. In the Carolinas, Alabama and Georgia the western boundary moves further West into the Appalachians.

Largely my dividing line coincides closely with classical divisions like Logan's Line in Canada and Emmons' Line in the US.

Terminology

Almost all of the rocks I am discussing have been transported from where they were originally deposited. That doesn't mean that the structures are always small. Indeed many are county sized or larger. A few terms that I use and/or will inevitably be found while researching sites:

The Rocks

I have somewhat arbitrarily divided the Laurentian Margin rocks into six terranes


APPALACHIAN MARGIN TERRANE

Rocks

These are shallow water Precambrian, Cambrian, Ordovician, and possibly a few Silurian rocks pushed into place prior to the formation of the Appalachian Mountains. The Western boundary is somewhat obscure. Unlike regions further North there seems to be extensive faulting and slicing in the Laurentian platform deposits West of the rocks pushed into place during the early part of Iapetus closure. The slicing results in repetition of Early Paleozoic formations as one moves from East and West. My inclination is to put the Appalachian Margin boundary at the most westerly rock sequences containing deep water/continental slope sediments and/or Iapetus seafloor volcanic rocks in the basement rocks. I believe that boundary is on the East side of the first major Appalachian Ridge (Blue Mountain) in Pennsylvania and moves westward over the mountain as one moves further South through Maryland, Virginia, the Carolinas and into Georgia.

I could well have parts of this all wrong.

Formations

Age North and West South and East Principle Rock Types
Silurian, Middle ???
Silurian, Lower Tuscarora Sandstones
Ordovician,Upper Juniata Sandstones and shales
Ordovician,Upper Oswego Sandstones
Ordovician,Middle Martinsburg Shales
Ordovician,Middle Chambersburg Limestones
Ordovician,Middle New Market,Row Park Limestones
Ordovician,Lower Beekmantown Pinesburg Station Limestones
Ordovician,Lower Rockdale Run Limestones
Ordovician,Lower Stonehenge Limestones
Cambrian,Upper Conococheague Limestones
Cambrian,Middle Kinzers,Ledger,Elbrooke Brooke Shales and Limestones
Cambrian,Lower-Middle Kinzers Waynesboro Shales and Limestones
Cambrian,Lower Vintage Tomstown Shales and Limestones
Cambrian,Lower Antietam quartizes
Cambrian,Lower Harpers quartizes
Cambrian,Lower Weaverton-Loudun quartizes
Ediacaran? Catoctin quartizes and conglomerates
Ediacaran? Swift Run quartizes and conglomerates
Ediacaran? {Flattop} Metamorphic rocks
Ediacaran? {Montezuma} Metamorphic rocks
Ediacaran? {Linville} Metamorphic rocks
bold=fossiliferous italic=calcareous ()=largely volcanic {} = intrusives,deep sea metamorphics

TACONIC TERRANE

Rocks

Continental slope deposits thrust over Ordovician continental sediments from the vicinity of Fairhaven, Vermont South to Poughkeepsie, New York. The rocks consist mostly of slates with minor limestones, conglomerates, sandstones, etc. There are many commercial slate quarries. The Taconic Terrane has been thrust over native Laurentian rocks to the West and also over rocks of the Champlain Trust plate to its Northwest. On the East side of the terrane, rocks of the Hinesburg Thrust have been pushed over the Taconic rocks.

The Lower Cambrian beds contain a distinctive Elliptocephala asaphoides fauna typically in limestones or limestone conglomerates. Some younger beds contain graptolites

Formations

AGE FORMATIONS ROCK TYPES
Middle Ordovician Austin Glen greywacke (granitic sandstone)
Middle Ordovician Mt Merino Chert and Shale
Middle Ordovician Pawlet interbedded black slate and greywacke
Middle Ordovician Mount Hamilton (Indian River) maroon,red,light green slates
Lower Ordovician Mount Hamilton (Poultney) Green to grey slates
Lower to Upper Cambrian Mount Hamilton (Hatch Hill - White Creek) Black slate with ribbon limestones
Lower Cambrian Mount Hamilton (Hatch Hill - Boomoseen) Sooty black slate above limestone
Lower Cambrian Mount Hamilton (Middle Granville Slate) maroon,grey,green slates
Lower Cambrian Mount Hamilton (Browns Pond) Gray to Black slates, limestones, quartzites
Lower Cambrian Bull (Mettawee) Purple and green slate, mudstone, and phyllite
Lower Cambrian Bull (North Brittain conglomerate) intraformational limestone-pebble, slate-matrix conglomerate
Lower Cambrian Bull (Mudd Pond) A thin but persistent orthoquartzite
Lower Cambrian Bull (Zion Hill) A discontinuous graywacke or sub-graywacke unit ranging from a pebble conglomerate to a mudstone
Lower Cambrian Bull (Bomoseen) massive, olive-drab, medium-grained graywacke
Lower Cambrian Bull (Nassau,Truthville)
Lower Cambrian Biddie Knob purple and green slate and phyllite with minor beds of limestone and quartzite
bold=fossiliferous italic=calcareous ()=largely volcanic {} = intrusives,deep sea metamorphics

The Taconic sequence has been studied extensively now that plate tectonics explains its nature which was quite baffling to older geologists. Analysis is difficult due to the many thrust faults and the large number of lithologically similar slate formations that are difficult or impossible to distinguish from each other where the intervening beds are missing. Formation nomenclature is undergoing frequent revision.


CHAMPLAIN THRUST TERRANE (NORTHERN BASIN)

Rocks

Rocks deposited in what appears to be a basin that developed in the Lower Cambrian. There is a substantial facies change along the line of US2 and the LaMoille River between shallow water sandstones/carbonates to the South and deeper water siltstones/sandstones with minor carbonates to the North The Champlain Thrust Block has clearly been pushed into place from the East. The thrust fault which places Lower Cambrian rocks of the thrust plate over Ordovician rocks is exposed at several locations along the East shore of Lake Champlain. On the East, the Champlain plate is bounded by the rocks of the Hinesbug-Oak Hill Thrust. To the South basin rocks appear as thin slates along the line of US2 and thicken rapidly to the North displacing the sandstones and dolomites of the platform to the south with finer grained and less calcareous sediments. In the North, a thrust fault within the plate reveals Upper Cambrian Gorge formation dolomites thrust over Ordovician Morses Line slates.

Fossils include occasional Ollenelus fauna fossils in the Cheshire and Dunham formations. A more diverse and abundant Lower and Middle Cambrian fauna in the Parker formation and Upper Cambrian/Lowest Ordovician fossils in the Gorge and Highgate formations

Formations

CHAMPLAIN THRUST PLATE NORTH OF LaMOILLE RIVER

AGE FORMATIONS ROCK TYPES
Ordovician Morses Line Black slates
Upper Cambrian Gorge Sandy Dolomite, black shales
Middle Cambrian Parker-Skeels Corner slates, shales
Lower Cambrian Parker-Skeels Corner slates, shales
Lower Cambrian Dunham Dolomite, some limestones
Lower Cambrian Cheshire Grey Quartzite
bold=fossiliferous italic=calcareous ()=largely volcanic {} = intrusives,deep sea metamorphics

CHAMPLAIN THRUST TERRANE (SOUTHERN PLATFORM)

Rocks

Rocks deposited in what appears to be a shallow water environment South of a basin that developed in the Lower Cambrian. There is a substantial facies change along the line of US2 and the LaMoille River between shallow water sandstones/carbonates to the South and deeper water siltstones/sandstones with minor carbonates to the North. To the West, the platform rocks end at the eastern shore of Lake Champlain. There is a classic exposure on the bike trail North of Burlington of Lower Cambrian Dunham Dolomite thrust over Middle Ordovician black shales.

Fossils include occasional Ollenelus fauna fossils in the Monkton, Cheshire, and Dunham formations. A few fossils are found in the younger formations, which appear to be somewhat altered versions of the rock sequence found in place in Eastern Laurentia. The Middle Ordovician limestones (Black River,Chazy,etc are present here, but are altered to marble and have different names. For the most part the rocks have been altered extensively and most fossils have been destroyed. Most of the classic Vermont marble quarries are in these altered limestones between Shelburne and Rutland.

Formations

CHAMPLAIN THRUST PLATE SOUTH OF LaMOILLE RIVER

AGE FORMATIONS ROCK TYPES
Ordovician several formations -- Chipman, Beldens, Weybridge, Burchards,etc Marbles (altered versions of Bridport,Chazy, Black River, etc
Upper Cambrian Sandy Dolomites, Quartzites
Middle Cambrian Winooski Dolomite
Lower Cambrian Monkton| red and varicolored quartzites
Lower Cambrian Dunham Dolomite, some limestones
Lower Cambrian Cheshire Grey Quartzite
bold=fossiliferous italic=calcareous ()=largely volcanic {} = intrusives,deep sea metamorphics

HINESBURG THRUST TERRANE

Rocks

These rocks are part of a huge overturned fold that extends along the Westernmost edge of the Green Mountains from Quebec to Northern Connecticut. The oldest rocks appear to be billion year old "Grenville" sediments of the North American core. Most sediments deposited on floor of the Iapetus Sea as it opened. The youngest rocks appear to be shallow water and beachfront sediments deposited during the Lower Cambrian. Older, pre-plate tectonic, literature indicates that the Dunham Dolomite and other rocks of the Champlain Thrust Terrane are in place above the Cheshire, but that is very likely an inferred relationship rather than an observed relationship.

The relationship of the shallow water Hinesburg Thrust rocks to the continental slope rocks of the Taconic Terrane that they are thrust over on their West is unclear.

Because the structure is an overturned fold, the formations are upside down in places with younger rocks lying under older rocks.

Fossils -- tracks and a very few body fossils are found in the youngest formations -- Lower Cambrian Cheshire quartzite and underlying Fairfield Pond Phyllite. The condition of the rocks varies from place to place. Only slightly altered in some places, melted and quite distorted in others.

Formations

AGE FORMATIONS ROCK TYPES
Lower Cambrian Cheshire - Gilman quartzites
Ediacaran?-Lower Cambrian? Fairfield Pond - Gilman silicified siltstones with quartz stringers
Ediacaran? several thin laterally variable formations slates-limestone
Ediacaran? Pinnacle Greywacke ((granitic sandstone))
Ediacaran? (Tibbet Hill) Underwater Lavas
bold=fossiliferous italic=calcareous ()=largely volcanic {} = intrusives,deep sea metamorphics

ST LAWRENCE TERRANE

Rocks

I have been unable to locate much material describing the sedimentary rocks exposed along the hundreds of kilometers on the South shore of the St Lawrence River East of the Richileu River other than those on the Gaspe Peninsula and those exposed opposite Quebec City. At a guess, they consist of two sequences. To the North are Cambrian and Ordovician rocks -- possibly continental shelf deposits similar to those of the Taconic Terrane. Thrust over them from the South are Ordovician, Silurian, and Devonian marine sediments that are (possibly?) an extension of the similar sequence in the Connecticut River Valley. Both of these sequences are only slightly altered, especially in the Gaspe region of Eastern Quebec.

Quebec Formations

Carboniferous Maritime Cover Terrane
Devonian, Upper Escuminac sandstone,shale
Devonian, Upper Fleurant Conglomerate
Devonian, Middle Touladi limestone
Devonian, Middle Mountain Wharf,Famine Conglomerate,limestone,shale
Devonian, Middle Malbaie Conglomerate,sandstone
Devonian, Lower Battery Point
Devonian, Lower York River Sandstone
Silurian Cabano
Point aux Trembles
Silurian, Upper West Point
Sayabec/La Vieille
Ordovician-Silurian White Head carbonates
Ordovician? Arsenault, Garin, Pabos
Ordovician Chloridrome,Magog Black Shale
Ordovician,Lower Riviere Ouelle
Cambrian,Upper Grosses-Roches Formation
Cambrian,Lower
bold=fossiliferous italic=calcareous ()=largely volcanic {} = intrusives,deep sea metamorphics

New Brunswick Formations

New Brunswick

Age Humber(?) and Dunnage Formations
Carboniferous Maritime Cover Terrane
Devonian Gaspe Sandstone
Gaspe
Escuminac
Fleurant
Pirate Cove
Devonian La garde
Silurian Gascons,IndianPoint,Roncelles
Sayabant
Val-Brillant
Awantjish,Burnt Jam Brook,Sources
White Head
Ordovician Pabos
Garin
older [Iapetus Sea Floor Terranes IAPETUS.HTM ]
bold=fossiliferous italic=calcareous ()=largely volcanic {} = intrusives,deep sea metamorphics

HUMBER TERRANE

Rocks

The rocks of Western Newfoundland seem to be broken into two slices -- a Western slice consisting of local (autocthonous) rocks and an Eastern slice of alien (allocthonous) rocks that were pushed over the local rocks during the Ordovician Taconic Orogeny.

Formations

Western Slice
Devonian-Carboniferous Maritime Cover Terrane
Silurian-Devonian Clam Bank
Ordovician,Upper Long Point (Lourdes)
Inthrust granitic rocks
Ordovician,Middle Goose Tickle Shales
Ordovician,Middle Table Point Limestones
Ordovician,Lower Aguathuna Limestones
Ordovician,Lower Catouche Limestones
Ordovician,Lower Boat Harbour,Barbace Cove Limestones
Ordovician,Lower Watts Bight Limestones
Cambrian,Upper Berry Head Dolostones,Limestones
Cambrian,Middle-Upper Point Jardin Dolostones,Limestones,Shales
Cambrian, Lower Hawkes Bay Sandstones
Cambrian, Lower Forteau Shales
Cambrian, Lower Brandore Sandstones
bold=fossiliferous italic=calcareous ()=largely volcanic {} = intrusives,deep sea metamorphics
Eastern Slice
Devonian-Carboniferous Maritime Cover Terrane
Silurian-Devonian Clam Bank
Ordovician,Upper Long Point (Lourdes)
Ordovician, Lower Cow Head shales
Lower Head sandstones
Ordovician, Lower Maiden Point sandstones
Cambrian, Upper Maiden Point - Cooks Brook/Middle Arm Point/Eagle Island conglomerate,shale,limestone
Cambrian, Lower Maiden Point - Blow Me Down Brook/Summerside/Irishtown sandstones,shales
bold=fossiliferous italic=calcareous ()=largely volcanic {} = intrusives,deep sea metamorphics

Formations in US largely based on American Association of Petroleum Geologists Geological Highway Maps


Localities

No recommended localities. Although fossils are quite diverse and are much more common than in the collapsed Iapetus Seafloor region to the East, nowhere other than possibly the Perce region in Quebec's Gaspe peninsula fossils really abundant. Mostly, the outcrops of the Atlantic margin seem to be best suited to local collectors who can make multiple visits in order to scope out the sites and specific outcrops.

Devonian outcrops at Miguasha National Park on the Restigouche River across from Dalhousie, NB. Have yielded a wide variety of Devonian fishes. There is an interpretive center. Collecting is forbidden.

Maps and Figures

Geologic Maps


Newfoundland Island Map http://www.nr.gov.nl.ca/mines&en/geosurvey/maps/nf.pdf Detailed maps http://www.nr.gov.nl.ca/mines&en/geosurvey/maps/nl/


New Brunswick Province map http://www2.gnb.ca/content/gnb/biling/en.html


Quebec -- So far, I have not located a province scale bedrock geology map of Quebec

Gaspe Peninsula Geology http://ebookbrowse.com/marcil-j-gaspe-basin-pdf-d17372744


Vermont State map http://www.anr.state.vt.us/DEC/geo/centmap.htm


Massachusetts State map (simplified) http://geology.about.com/library/bl/maps/blmassachusettsmap.htm State map http://www.geo.umass.edu/stategeologist/frame_maps.htm


Connecticut State maps http://web.archive.org/web/20120306154657/http://www.wesleyan.edu/ctgeology/images/CtGeoMap_big.jpg

State maps https://web.archive.org/web/20050911162123/http://tmsc.org/geology/bedrock/


New York Generalized Bedrock Geology of NY

Overview of NY Geology


New Jersey Simplified map of NJ

Index to online geology maps of New Jersey


Pennsylvania Simplified map of PA

Digital Geologic map of Pennsylvania


Maryland Geologic Map


Virginia


North Carolina Generalized map

Access to detailed maps


South Carolina


Georgia High Resolution map


Alabama


Formations

See Rocks


References


Copyright 2006-2012 Donald Kenney (Donald.Kenney@GMail.com). Unless otherwise stated, permission is hereby granted to use any materials on these pages under the Creative Commons License V2.5.

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