Lea Park Formation
Encyclopedia
The Lea Park Formation is a stratigraphical
unit of Late Cretaceous
age
in the Western Canadian Sedimentary Basin
, Canada
.
It takes the name from the settlement of Lea Park, Alberta
, located north-west of Lloydminster
on the banks of the North Saskatchewan River
. It was first defined in an outcrop on the river banks, located in section
15-11-54-3W4M by J.A. Allan in 1918. The early campanian
age was determined from its foraminifera
and mollusks found in the formation.
with minor siltstone
.
Calcite
veins and ironstone
concretions, as well as bentonite
beds are found throughout the formation.
and extends eastwards through north-eastern Alberta
and north-western Saskatchewan
.
and conformably overlies the First White Speckled Shale of the Colorado Group
.
It is equivalent to Judith River Formation
, Clagett Formation
and Eagle Formation
in northern Montana
, and is replaced by the Belly River Formation, Pakowki Formation
and Milk River Formation
in southern Alberta
. In eastern Saskatchewan
and in Manitoba
it is equivalent to the Gammon Ferruginous Member, Pembina Member and lower Millwood Member of the Pierre Shale
. The Lower Lea Park correlates with the Puskwaskau Formation in north-western Alberta, and the entire formation is equivalent to part of the Wapiabi Formation in the northern Canadian Rockies
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
unit of Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
age
Geochronology
Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this, and schemes of classification and terminology have been proposed...
in the Western Canadian Sedimentary Basin
Western Canadian Sedimentary Basin
The Western Canadian Sedimentary Basin is a vast sedimentary basin underlying of Western Canada including southwestern Manitoba, southern Saskatchewan, Alberta, northeastern British Columbia and the southwest corner of the Northwest Territories. It consists of a massive wedge of sedimentary rock...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
.
It takes the name from the settlement of Lea Park, Alberta
Lea Park, Alberta
Lea Park is an unincorporated community in Alberta, Canada. It is located in east-central Alberta, between Lloydminster and Bonnyville.The community was established on the banks of the North Saskatchewan River at its confluence with the Vermilion River, at an elevation of...
, located north-west of Lloydminster
Lloydminster
Lloydminster is a Canadian city which has the unusual geographic distinction of straddling the provincial border between Alberta and Saskatchewan...
on the banks of the North Saskatchewan River
North Saskatchewan River
The North Saskatchewan River is a glacier-fed river that flows east from the Canadian Rockies to central Saskatchewan. It is one of two major rivers that join to make up the Saskatchewan River....
. It was first defined in an outcrop on the river banks, located in section
Alberta Township System
The Alberta Township System is a land surveying system used in the Canadian province of Alberta and other parts of western Canada.-History and background:...
15-11-54-3W4M by J.A. Allan in 1918. The early campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
age was determined from its foraminifera
Foraminifera
The Foraminifera , or forams for short, are a large group of amoeboid protists which are among the commonest plankton species. They have reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net...
and mollusks found in the formation.
Lithology
The Lea Park Formation is composed of dark shaleShale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
with minor siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
.
Calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
veins and ironstone
Ironstone
Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical repacement, that contains a substantial proportion of an iron compound from which iron either can be or once was smelted commercially. This term is customarily restricted to hard coarsely...
concretions, as well as bentonite
Bentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...
beds are found throughout the formation.
Distribution
The Lea Park Formation reaches a maximum depth of 270 metres (885.8 ft) in its eastern reaches. I occurs in the sub-surface in west-central AlbertaCentral Alberta
Central Alberta is a region located in the Canadian province of Alberta.Central Alberta is the most densely populated rural area in the province...
and extends eastwards through north-eastern Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
and north-western Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....
.
Relationship to other units
The Lea Park Formation is conformably overlain (and laterally replaced )by the Judith River FormationJudith River Formation
The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the upper Cretaceous, between 80 and 75 million years ago, corresponding to the "Judithian" land vertebrate age...
and conformably overlies the First White Speckled Shale of the Colorado Group
Colorado Group
The Colorado Group, also called the Colorado shale, is a stratigraphical unit of Cretaceous age in the Western Canadian Sedimentary Basin.It was first described in the Rocky Mountains front ranges of Colorado by A. Hague and S.E...
.
It is equivalent to Judith River Formation
Judith River Formation
The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the upper Cretaceous, between 80 and 75 million years ago, corresponding to the "Judithian" land vertebrate age...
, Clagett Formation
Claggett Shale
The Claggett Shale is a geological formation in Montana whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-Vertebrate paleofauna:...
and Eagle Formation
Eagle Sandstone
The Eagle Sandstone is a geological formation in Montana whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-References:...
in northern Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
, and is replaced by the Belly River Formation, Pakowki Formation
Pakowki Formation
The Pakowki Formation is a stratigraphical unit of Campanian age in the Western Canadian Sedimentary Basin.It takes the name from Pakowki Lake, and was first described in outcrop along the Pakowki Coulee by D.B. Dowling in 1916.-Lithology:...
and Milk River Formation
Milk River Formation
The Milk River Formation is a near- shore to terrestrial sedimentary unit deposited during the Late Cretaceous in southern Alberta...
in southern Alberta
Southern Alberta
Southern Alberta is a region located in the Canadian province of Alberta. As of the year 2004, the region's population was approximately 272,017. The primary cities are Lethbridge and Medicine Hat...
. In eastern Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....
and in Manitoba
Manitoba
Manitoba is a Canadian prairie province with an area of . The province has over 110,000 lakes and has a largely continental climate because of its flat topography. Agriculture, mostly concentrated in the fertile southern and western parts of the province, is vital to the province's economy; other...
it is equivalent to the Gammon Ferruginous Member, Pembina Member and lower Millwood Member of the Pierre Shale
Pierre Shale
The Pierre Shale is a geologic formation or series in the Upper Cretaceous which occurs east of the Rocky Mountains in the Great Plains, from North Dakota to New Mexico....
. The Lower Lea Park correlates with the Puskwaskau Formation in north-western Alberta, and the entire formation is equivalent to part of the Wapiabi Formation in the northern Canadian Rockies
Canadian Rockies
The Canadian Rockies comprise the Canadian segment of the North American Rocky Mountains range. They are the eastern part of the Canadian Cordillera, extending from the Interior Plains of Alberta to the Rocky Mountain Trench of British Columbia. The southern end borders Idaho and Montana of the USA...