Bedrock and surficial geology of the Maritime Provinces

The oldest rocks in the Maritimes belong to the Blair River Complex, a small pocket of Proterozoic rocks located in the northwestern edge of Cape Breton Island, Nova Scotia. These rocks include high-grade metamorphic gneiss, schist, amphibolite and associated granitoid intrusions associated with the Grenville Orogeny. The rocks of the Grenville Orogen represent the southeastern margin of the Canadian Shield, and were accreted or welded onto the Canadian Shield about 1 billion years ago during the formation of the paleo-supercontinent of Rodinia. One continent that resulted from the breakup of Rodinia was Laurentia, the original mp;lt;"coremp;gt;" of the North America, surrounded by oceans including Iapetus. During the Ordovician to early Carboniferous interval, several Early Paleozoic and older terranes were accreted to Laurentia in the Appalachian Orogen. From west to east these include several terranes related to the Iapetus Ocean, Ganderia, Avalonia, and Meguma. Today, remains of the Orogen and its constituent terranes extend from Newfoundland through Nova Scotia, Prince Edward Island, and New Brunswick, along the eastern seaboard of the United States to Florida. They also connect across the Atlantic Ocean with the Caledonian Orogen of Greenland, northwestern British Isles and Scandinavia. Ganderia consists dominantly of Precambrian and Cambrian sedimentary and volcanic rock assemblages. The accretion of Ganderia onto Laurentia occurred approximately 430 million years ago and resulted in the closure of the Iapetus Ocean. Rocks associated with Ganderia occur today in central New Brunswick, western Prince Edward Island and western Cape Breton Island. The accretion of the Avalon Terrane onto the southern margin of Ganderia occurred approximately 400 million years ago. Volcanic rocks of Avalonia are located along the southern margin of New Brunswick, as well as northern mainland Nova Scotia and the eastern half of Cape Breton Island. The final Appalachian terrane to accrete was Meguma, the most outboard terrane in the Canadian Appalachian orogen and found onshore only in southern Nova Scotia. The Meguma Terrane accreted to Avalonia approximately 390 million years ago and consists of Cambro-Ordovician metasediments. Meguma rocks display many similarities to rocks currently found in northern Africa (Morocco). Major structures formed during the accretion of the Appalachian terranes include the Caledonia Fault Zone that separates Ganderia from Avalonia in southern New Brunswick and the Cobequid-Chedabucto Fault Zone that separates the Meguma to the south from the Avalonia to the north. Magmatism occurred in association with the accretion of terranes and Appalachian mountain building. One example, the South Mountain Batholith, is the largest exposed intrusion in the Appalachian Orogen, and is associated with the closure of the Rheic Ocean, which separated Meguma from Gondwana, about 380 million years ago. As collisions that created the Appalachian Orogen ended, a complex series of fault-bounded basins and uplands developed called the Maritimes Basin. The subbasins (generally called basins) of the Maritimes include the Moncton Basin, Stellarton Basin and the Sydney Basin. Uplands included the Caledonia Highlands, Cobequid Highlands, Antigonish Highlands and the Cape Breton Highlands. During latest Devonian and earliest Carboniferous time, the basins were filled with Horton Group sediments sourced from the eroding upland ranges by large, extensive river systems and lakes. The basins were subsequently inundated by transgressive and regressive cycles associated with the Windsor Sea beginning approximately 340 million years ago. Deposition of Windsor Group carbonates, evaporates and siliciclastic sedimentary rocks occurred during this much drier climatic period. Approximately 325 million years ago (late Carboniferous) the Windsor Seas regressed for the last time, the climate became relatively wetter and the Maritimes were once again subjected to large terrestrial rivers (and floodplains) that resulted in the deposition of thick siliciclastic sedimentary rocks of the Mabou and Cumberland groups until about 305 million years ago. During this roughly 20 million year time period, lush vegetation associated with aerially extensive rainforests and swamps were the precursor to the significant coal deposits (Sydney, Springhill, Stellarton) of the Maritime Provinces. During the Permian, approximately 250 to 290 million years ago, the climate changed once again but this time included some very dry conditions to form the distinct red rocks of Prince Edward Island and northern mainland Nova Scotia. Approximately 230 million years ago Pangea started to rift apart and about 200 million years ago the pieces began to drift apart. In Nova Scotia, the drifting is indirectly heralded by a major volcanic event that resulted in the formation of the North Mountain basalt around what is today the Bay of Fundy (which coincidently forms the northern margin of the Annapolis Valley) as well as basalt exposures at Five Islands, Wasson Bluff and Partridge Island along the north shore of Cobequid Bay, Nova Scotia, and Grand Manan Island, New Brunswick. The drifting created the Atlantic Ocean, whose margins became the locus of deep sedimentary basins subsequently in-filled with siliciclastic sediments. Deposition of thin deposits of red sandstones and mudstones immediately post-date eruption and deposition of the basalt. On onshore Nova Scotia for the remaining 200 million years until the present, there is very little evidence preserved in the rock record of much activity except for the development of some sand and mud deposits associated with rivers and lakes approximately 100 125 million years ago during the early Cretaceous. Most of the surficial glacial deposits and associated landforms throughout the Maritimes were formed during Wisconsinan glaciation (Pleistocene) in the last 100 000 years which includes the mp;lt;"recentmp;gt;" Holocene. Several local ice centers, collectively referred to as the Appalachian Glacier Complex, were sufficiently large enough to withhold advancement of the continental Laurentide ice sheet. Throughout the Wisconsian, the ice centers were very dynamic which resulted in a very complex ice flow history for the Maritime Provinces. Reconstruction of the ice flow history of the Maritimes has established a link between ice flow patterns onshore and ice margin terminal moraines offshore. The oldest observed Wisconsinan ice flow indicators are associated with the Caledonia Phase occurring approximately 70 000 to 65 000 years ago. Ice flow was towards the east and southeast likely emanating from the Notre Dame Mountains Ice Divide. The Escuminac Phase occurred approximately 24 000 to 20 000 years ago and resulted in south and southwest flow associated with the east-west trending Escuminac Ice Divide situated in central northern New Brunswick extending to the north of Prince Edward Island. Ice flow to the north of the divide was characterized by ice streams into the Bay of Chaleurs and into the Gulf of St. Lawrence. The Scotian Phase occurred approximately 20 000 to 17 000 years ago and was characterized by the mobile Scotian Ice Divide situated over mainland Nova Scotia and the Central Northern Maine Ice Divide along the margin of western New Brunswick. In Nova Scotia, this resulted in complex ice flow movement to the north and south as well as southwesterly flow associated with ice streaming into the Bay of Fundy. For New Brunswick, flow was dominantly to the east-northeast during this time period. Final deglaciation commenced approximately 15 000 years ago with the Chignecto Phase. During this time, glacial ice was likely centered over Prince Edward Island with another smaller ice divide (Fundy Highlands Ice Divide) located in New Brunswick along the northern margin of the bay of Fundy. Remnant ice was thinning and beginning to retreat back from the Scotia Shelf and along the margins of the Bay of Fundy. Ice-dammed lakes likely existed in the St. John River Valley in New Brunswick and Glacial Lake Shubenacadie in Nova Scotia. The Collins Pond Phase, however, was the final phase of glacier formation and likely involved expansion of local ice centers in response to a short-lived period of climatic cooling lasting approximately 1000 years during the Younger Dryas Chronozone around 11 000 years ago. Since the Younger Dryas, ice continued to recede and the Maritimes have been ice free for several thousand years. Various multiple-flow directional indicators, the result of shifting ice centers, have been mapped and are evidence that the Maritimes was characterized by a relatively complex ice flow history. The complex ice flow history of the Maritime Provinces has, locally, resulted in superimposed till sheets including palimpsest landforms. The surficial geology of the Maritime Provinces is highly variable and includes large areas of variable thick ground moraine and associated streamlined landforms, glaciofluvial deposits (outwash fans and deltas, valley trains, kames and eskers) as well as glaciolacustrine and glaciomarine deposits. Post glacial (Holocene) sediments include alluvial, colluvial, organic and marine deposits. Enrichment of elements reflecting the bedrock geology is characteristic of many of the surficial deposits throughout the Maritimes. These elements are commonly enriched in soil down ice from their bedrock sources (including zones of mineralized bedrock); the result of mechanical dispersal (erosion, transportation and deposition) by advancing glacial ice. Glacial dispersal distances vary but are commonly hundredmp;gt;'s of meters to several kilometres down-ice from source. The diversity of the Maritime bedrock and surficial geology has yielded a wide array of mineral resources that have been exploited for centuries. Archaeological evidence to support this include clay pots, agate and sla

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