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 million years ago to around 34 million years ago . 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.
14-396: 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 Island
28-521: Is a geologic group in both British Columbia and Washington state . It preserves fossils dating back to the Cretaceous period . This article about a specific stratigraphic formation in Canada is a stub . You can help Misplaced Pages by expanding it . This article related to the Cretaceous period is a stub . You can help Misplaced Pages by expanding it . This British Columbia -related article
42-474: Is a stub . You can help Misplaced Pages by expanding it . Group (geology) In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form a group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into supergroups . Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying
56-571: The Glenwoody Formation , other strata (particularly in the lower part of the group) remain undivided into formations. Some well known groups of northwestern Europe have in the past also been used as units for chronostratigraphy and geochronology . These are the Rotliegend and Zechstein (both of Permian age); Buntsandstein , Muschelkalk , and Keuper ( Triassic in age); Lias , Dogger , and Malm ( Jurassic in age) groups. Because of
70-820: The Wingate Sandstone , the Moenave Formation , the Kayenta Formation , and the Navajo Sandstone . Each of the formations can be distinguished from its neighbor by its lithology , but all were deposited in the same vast erg . Not all these formations are present in all areas where the Glen Canyon Group is present. Another example of a group is the Vadito Group of northern New Mexico . Although many of its strata have been divided into formations, such as
84-613: The Chuckanut Formation. A fossil turtle 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 the specimen belongs to the Trionychidae family of soft shelled turtles. In 2023,
98-702: The Chuckanut continued as convergence of the Crescent Terrane (Olympic Peninsula) initiated strike-slip motion on the Straight Creek Fault (48 Ma), displacing much of the original formation to the north. Continued deposition 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
112-693: The Eocene coast line. Deposition is believed to have largely ended in the late Eocene (around 42 Ma?) when regional uplift diverted the rivers supplying the sediments, but some deposition may have continued, supplied from local sources. Johnson (1984) estimated a total thickness of 6,000 metres (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 metres (8,200 ft) thick. Various plant and animal fossils have been found in
126-592: The eastern Olympic Peninsula (such as the Crescent Formation ) are of similar age, but petrographically distinct, and appear to have different sources. The Chuckanut and related formations "are all composed predominantly of fine- to medium-grained sandstones with lesser amounts of interbedded shale, conglomerate, and coal." The sandstones consist of sand eroded from the Mount Stuart massif and probably from uplifted metamorphic sources in northeastern Washington (this
140-481: The first articulated fossil fish was identified from the formation, which was a fragmented specimen of Phareodus . Eocene fossil trackways are found in the Chuckanut Formation, composed of birds , mammals , 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. Nanaimo Group The Nanaimo Group
154-460: The stratigraphy of large regions. Geologists exploring a new area have sometimes defined groups when they believe the strata within the groups can be divided into formations during subsequent investigations of the area. It is possible for only some of the strata making up a group to be divided into formations. An example of a group is the Glen Canyon Group , which includes (in ascending order)
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#1732852830520168-622: 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
182-666: Was correlated with the Chuckanut, but the Nanaimo Group is now known to be earlier ( 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
196-748: Was 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 Swauk known as the Easton. Near Vancouver parts of the Huntingdon Formation lie disconformably on parts of the Cretaceous Nanaimo Group. Deposition of
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