Tyrrell Sea
Encyclopedia
The Tyrrell Sea, named for Canadian
geologist
Joseph Tyrrell
, is another name for prehistoric Hudson Bay
, namely as it existed during the retreat of the Laurentide Ice Sheet
.
Roughly 8,000 years BP
, the Laurentide Ice Sheet thinned and split into two lobes, one centered over Quebec
-Labrador
, the other over Keewatin
. This drained Glacial Lake Ojibway
, a massive proglacial lake
south of the ice sheet, leading to the formation of the early Tyrrell Sea. The weight of the ice had isostatically
depressed the surface as much as 270-280 m below its current level, making the Tyrrell Sea much larger than modern Hudson Bay. Indeed, in some places the shoreline was 100 to 250 km farther inland than at present. It was at its largest at roughly 7,000 years BP.
Isostatic uplift proceeded rapidly after the retreat of the ice, as much as .09 m per year, causing the margins of the sea to regress quickly towards its present margins. The rate of uplift decreased with time however, and in any event was nearly matched by sea-level rise from the melting ice sheets. When the Tyrrell Sea "became" Hudson Bay is difficult to define, as Hudson Bay is still shrinking from isostatic rebound.
Cañada
The Spanish word cañada means glen; it is etymologically unrelated to Canada, which is derived from an Iroquois word meaning "village" or "settlement" and generally refers to the country in North America...
geologist
Geologist
A geologist is a scientist who studies the solid and liquid matter that constitutes the Earth as well as the processes and history that has shaped it. Geologists usually engage in studying geology. Geologists, studying more of an applied science than a theoretical one, must approach Geology using...
Joseph Tyrrell
Joseph Tyrrell
Joseph Burr Tyrrell was a Canadian geologist, cartographer, and mining consultant. He discovered dinosaur bones in Alberta's Badlands and coal around Drumheller in 1884....
, is another name for prehistoric Hudson Bay
Hudson Bay
Hudson Bay , sometimes called Hudson's Bay, is a large body of saltwater in northeastern Canada. It drains a very large area, about , that includes parts of Ontario, Quebec, Saskatchewan, Alberta, most of Manitoba, southeastern Nunavut, as well as parts of North Dakota, South Dakota, Minnesota,...
, namely as it existed during the retreat of the Laurentide Ice Sheet
Laurentide ice sheet
The Laurentide Ice Sheet was a massive sheet of ice that covered hundreds of thousands of square miles, including most of Canada and a large portion of the northern United States, multiple times during Quaternary glacial epochs. It last covered most of northern North America between c. 95,000 and...
.
Roughly 8,000 years BP
Before Present
Before Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use AD 1950 as the origin of the age scale, reflecting the fact that radiocarbon...
, the Laurentide Ice Sheet thinned and split into two lobes, one centered over Quebec
Quebec
Quebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....
-Labrador
Labrador
Labrador is the distinct, northerly region of the Canadian province of Newfoundland and Labrador. It comprises the mainland portion of the province, separated from the island of Newfoundland by the Strait of Belle Isle...
, the other over Keewatin
Keewatin
-Places:United States* Keewatin, Minnesota, USA, a cityCanada* Keewatin, Ontario, a town amalgamated with the towns of Kenora and Jaffray Melick to form Kenora* District of Keewatin, Northwest Territories* Keewatin Region...
. This drained Glacial Lake Ojibway
Glacial Lake Ojibway
Glacial Lake Ojibway was a prehistoric lake in what is now Northern Ontario and Quebec in Canada. Ojibway was the last of the great proglacial lakes of the last ice age. Comparable in size to Lake Agassiz , and north of the Great Lakes, it was at its greatest extent c. 8,500 years BP.Lake Ojibway...
, a massive proglacial lake
Proglacial lake
In geology, a proglacial lake is a lake formed either by the damming action of a moraine or ice dam during the retreat of a melting glacier, or by meltwater trapped against an ice sheet due to isostatic depression of the crust around the ice...
south of the ice sheet, leading to the formation of the early Tyrrell Sea. The weight of the ice had isostatically
Isostasy
Isostasy is a term used in geology to refer to the state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density. This concept is invoked to explain how different topographic...
depressed the surface as much as 270-280 m below its current level, making the Tyrrell Sea much larger than modern Hudson Bay. Indeed, in some places the shoreline was 100 to 250 km farther inland than at present. It was at its largest at roughly 7,000 years BP.
Isostatic uplift proceeded rapidly after the retreat of the ice, as much as .09 m per year, causing the margins of the sea to regress quickly towards its present margins. The rate of uplift decreased with time however, and in any event was nearly matched by sea-level rise from the melting ice sheets. When the Tyrrell Sea "became" Hudson Bay is difficult to define, as Hudson Bay is still shrinking from isostatic rebound.