Chuckanut Formation
Encyclopedia
The Chuckanut Formation in northwestern Washington (named after the Chuckanut Mountains
, near Bellingham
), its extension in southwestern British Columbia (the Huntingdon Formation), and various related formations in central Washington (including the Swauk, Roslyn, Manastash, and Chumstick) are fluvial sedimentary formations of Eocene
age, deposited from about 54 Ma (millions of years ago) to around 42 to 34 Ma. The nature of the deposits and included plant fossils indicate a low-lying coastal plain with a subtropical climate; the nature of the sediments indicates metamorphic sources in northeastern Washington.
was correlated with the Chuckanut, but the Nanaimo Group is now known to be earliar (Upper Cretaceous). The principal outcrops of the Chuckanut Formation (marked CK on the map) are in the vicinity of Bellingham
, with other outcrops as far south as the Darrington—Devils Mountain Fault Zone
. The Swauk, Roslyn, Chumstick, and Manastash Formations (SW and MA) are on the east side of the Cascade Range and south of Mount Stuart
(in the vicinity of Roslyn, Washington
); the offset between these and the Chuckanut/Huntingdon is evidence of large-scale (about 110 km) strike-slip motion on the Straight Creek Fault
, starting at 48 Ma. Other related formations (such as the Puget Group and Raging River Formation) occur east and south of Seattle. Other sedimentary formations of similar age and environment occur throughout southwestern Washington and western Oregon. Various sedimentary formations underlying Puget Sound and the eastern Olympic Peninsula (such as the Crescent Formation) are of similar age, but petrographically distinct, and appear to have different sources.
massif and probably from uplifted metamorphic sources in northeastern Washington (this is well before the rise of the Cascade Range), and distributed by rivers across a low-lying coastal plain starting about 54 Ma. These were laid over a metamorphic suite of rocks, those under the Chuckanut now known as the Shuksan, and its correlate under the Swuak known as the Easton. Near Vancouver
parts of the Huntingdon Formation lie disconformably on parts of the Cretaceous Nanaimo Group.
Deposition of the Chuckanut continued as convergence of the Crecscent Terrane (Olympic Peninsula) initiated strike-slip motion on the Straight Creek Fault
(48 Ma), displacing much of the original formation to the north. Continued depositon across the Straight Creek Fault formed the Raging River and Puget Group formations east of Seattle; the former is partly marine, indicating it was probably a large delta, and locating the Eocene coast line. Deposition is believed to have largely ended in the late Eococene (around 42 Ma?) when regional uplift diverted the rivers supplying the sediments, but some deposition may have continued, supplied from local sources.
estimated a total thickness of 6,000 m (about 20,000 ft), which would make the Chuckanut Formation one of the thickest nonmarine sedimentary sequences in North America. But more recent work suggest that, at least in parts, it may be only 2,500 m thick.
shell was recovered from the formation at Clark Point in 1960. The specimen was held in the private collection of the finders until 1981 when it was examined at Western Washington University
and identified as an indeterminate member of the Testudinoidea
superfamily
. Reexamination of the fossil in 2000 showed specimen to belong to the Trionychidae
family of soft shelled turtles.
Eocene
fossil trackway
s are found in the Chuckanut Formation, composed of both bird
s and animals, including mammal
s and some turtle
tracks. It is thought that the Chuckanut Formation shoreline was of riverine environments combined with a large scale "bedding plane" of material deposition. Four deposition or track sites are known.
Chuckanut Mountains
The Chuckanut Mountains , or Chuckanuts, are located on the northern Washington state coast of Puget Sound, just south of Bellingham, Washington. Being a part of the Cascade Range, they are the only place where the Cascades come west down to meet the sea...
, near Bellingham
Bellingham
- Places :Australia:* Bellingham, Tasmania, coastal hamlet in Northern TasmaniaEngland:* Bellingham, London, neighbourhood and electoral ward in the London Borough of Lewisham* Bellingham, Northumberland, villageUnited States:* Bellingham, Washington...
), its extension in southwestern British Columbia (the Huntingdon Formation), and various related formations in central Washington (including the Swauk, Roslyn, Manastash, and Chumstick) are fluvial sedimentary formations of Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
age, deposited from about 54 Ma (millions of years ago) to around 42 to 34 Ma. The nature of the deposits and included plant fossils indicate a low-lying coastal plain with a subtropical climate; the nature of the sediments indicates metamorphic sources in northeastern Washington.
Location
The original Chuckanut/Huntingdon/Swauk formation appears to have been deposited as a single unit in a large basin, and subsequently separated by faulting. The original extent of the formation is unknown, parts having been uplifted and eroded away, and the current extents largely covered by volcanic and glacial deposits. Early work suggested that the marine Nanaimo Group on Vancouver IslandVancouver Island
Vancouver Island is a large island in British Columbia, Canada. It is one of several North American locations named after George Vancouver, the British Royal Navy officer who explored the Pacific Northwest coast of North America between 1791 and 1794...
was correlated with the Chuckanut, but the Nanaimo Group is now known to be earliar (Upper Cretaceous). The principal outcrops of the Chuckanut Formation (marked CK on the map) are in the vicinity of Bellingham
Bellingham
- Places :Australia:* Bellingham, Tasmania, coastal hamlet in Northern TasmaniaEngland:* Bellingham, London, neighbourhood and electoral ward in the London Borough of Lewisham* Bellingham, Northumberland, villageUnited States:* Bellingham, Washington...
, with other outcrops as far south as the Darrington—Devils Mountain Fault Zone
Straight Creek Fault
The Straight Creek Fault is the principal north-south strike-slip fault in the state of Washington, with a minimum of 90 kilometers of right-lateral offset, and a major geological structure in the North Cascade mountains, where it separates the pre-Tertiary igneous and metamorphic rocks of the...
. The Swauk, Roslyn, Chumstick, and Manastash Formations (SW and MA) are on the east side of the Cascade Range and south of Mount Stuart
Mount Stuart
Mount Stuart is a mountain in the Cascade Range, in the U.S. state of Washington. It is the second highest non-volcanic peak in the state, after Bonanza Peak and tenth-highest overall...
(in the vicinity of Roslyn, Washington
Roslyn, Washington
Roslyn is a city in Kittitas County, Washington, United States. The population was 893 at the 2010 census.-Geography:Roslyn is located at...
); the offset between these and the Chuckanut/Huntingdon is evidence of large-scale (about 110 km) strike-slip motion on the Straight Creek Fault
Straight Creek Fault
The Straight Creek Fault is the principal north-south strike-slip fault in the state of Washington, with a minimum of 90 kilometers of right-lateral offset, and a major geological structure in the North Cascade mountains, where it separates the pre-Tertiary igneous and metamorphic rocks of the...
, starting at 48 Ma. Other related formations (such as the Puget Group and Raging River Formation) occur east and south of Seattle. Other sedimentary formations of similar age and environment occur throughout southwestern Washington and western Oregon. Various sedimentary formations underlying Puget Sound and the eastern Olympic Peninsula (such as the Crescent Formation) are of similar age, but petrographically distinct, and appear to have different sources.
Geology
The Chuckanut and related formations "are all composed predominately of fine- to medium-grained sandstones with lesser amounts of interbedded shale, conglomerate, and coal." The sandstones consist of sand eroded from the Mount StuartMount Stuart
Mount Stuart is a mountain in the Cascade Range, in the U.S. state of Washington. It is the second highest non-volcanic peak in the state, after Bonanza Peak and tenth-highest overall...
massif and probably from uplifted metamorphic sources in northeastern Washington (this is well before the rise of the Cascade Range), and distributed by rivers across a low-lying coastal plain starting about 54 Ma. These were laid over a metamorphic suite of rocks, those under the Chuckanut now known as the Shuksan, and its correlate under the Swuak known as the Easton. Near Vancouver
Vancouver
Vancouver is a coastal seaport city on the mainland of British Columbia, Canada. It is the hub of Greater Vancouver, which, with over 2.3 million residents, is the third most populous metropolitan area in the country,...
parts of the Huntingdon Formation lie disconformably on parts of the Cretaceous Nanaimo Group.
Deposition of the Chuckanut continued as convergence of the Crecscent Terrane (Olympic Peninsula) initiated strike-slip motion on the Straight Creek Fault
Straight Creek Fault
The Straight Creek Fault is the principal north-south strike-slip fault in the state of Washington, with a minimum of 90 kilometers of right-lateral offset, and a major geological structure in the North Cascade mountains, where it separates the pre-Tertiary igneous and metamorphic rocks of the...
(48 Ma), displacing much of the original formation to the north. Continued depositon across the Straight Creek Fault formed the Raging River and Puget Group formations east of Seattle; the former is partly marine, indicating it was probably a large delta, and locating the Eocene coast line. Deposition is believed to have largely ended in the late Eococene (around 42 Ma?) when regional uplift diverted the rivers supplying the sediments, but some deposition may have continued, supplied from local sources.
estimated a total thickness of 6,000 m (about 20,000 ft), which would make the Chuckanut Formation one of the thickest nonmarine sedimentary sequences in North America. But more recent work suggest that, at least in parts, it may be only 2,500 m thick.
Fossils
Various plant and animal fossils have been found in the Chuckanut Formation. A fossil turtleTurtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
shell was recovered from the formation at Clark Point in 1960. The specimen was held in the private collection of the finders until 1981 when it was examined at Western Washington University
Western Washington University
Western Washington University is one of six state-funded, four-year universities of higher education in the U.S. state of Washington. It is located in Bellingham and offers bachelor's and master's degrees.-History:...
and identified as an indeterminate member of the Testudinoidea
Testudinoidea
Testudinoidea is a superfamily within the suborder Cryptodira of the order Testudines. It includes the families of pond turtles ; Asian turtles ; the Big-headed turtle and tortoises ....
superfamily
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
. Reexamination of the fossil in 2000 showed specimen to belong to the Trionychidae
Trionychidae
Trionychidae is a taxonomic family which comprises a number of turtle genera commonly known as softshells. They are also sometimes called pancake turtles. Softshells consist of some of the world's largest fresh water turtles, though many can adapt to living in highly brackish areas. Members of this...
family of soft shelled turtles.
Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
fossil trackway
Fossil trackway
A fossil trackway is a type of trace fossil, a trackway made by an organism. Many fossil trackways were made by dinosaurs, early tetrapods, and other quadrupeds and bipeds on land...
s are found in the Chuckanut Formation, composed of both bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s and animals, including mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s and some turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
tracks. It is thought that the Chuckanut Formation shoreline was of riverine environments combined with a large scale "bedding plane" of material deposition. Four deposition or track sites are known.