Bertie Formation
Stratigraphic range: Pridoli (Cayugan Series) ~422.9–416.0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological group
Unit of	Cayugan Series
Sub-units	Falkirk (dolomite), Scajaquada (shale) and Williamsville (dolomite) - Western New York Fiddlers Green (dolomite), Forge Hollow (shale) and Oxbow (dolomite) - Central New York
Underlies	Bois Blanc Formation, Hederberg Group , Bass Islands Group
Overlies	Salina Group
Thickness	Up to 495 ft (151 m)
Lithology
Primary	Dolomite, Shale
Other	Shale
Location
Coordinates	42°54′N 78°54′W / 42.9°N 78.9°W / 42.9; -78.9
Approximate paleocoordinates	30°18′S 40°48′W / 30.3°S 40.8°W / -30.3; -40.8
Region	Ontario New York
Country	Canada  United States
Extent	Appalachian Basin
Type section
Named for	Bertie, Ontario
Named by	Chapman
Year defined	1864
Bertie Formation (the United States) Show map of the United States Bertie Formation (New York) Show map of New York

The Bertie Group or Bertie Limestone, also referred to as the Bertie Dolomite and the Bertie Formation, is an upper Silurian (Pridoli, or Cayugan) geologic group and Lagerstätte in southern Ontario, Canada, and western New York State, United States. Details of the type locality and of stratigraphic nomenclature for this unit as used by the U.S. Geological Survey are available on-line at the National Geologic Map Database.^[1] The formation comprises dolomites, limestones and shales and reaches a thickness of 495 feet (151 m) in the subsurface, while in outcrop the group can be 60 feet (18 m) thick.

The group represents the uppermost unit of the Cayugan Series and the youngest Silurian unit in Ontario. The group overlies the Salina Group and is conformably overlain by the Devonian Bois Blanc Formation in Ontario and Onondaga Limestone in New York.

Two formations within the Bertie Group, the Fiddler's Green and Williamsville, are considered Konservat-Lagerstätten; geologic units that contain a unique and typically soft-bodied fauna. These formations have produced thousands of Silurian eurypterids (sea scorpions) as well as early scorpion Proscorpius osborni, xiphosurans, primitive fossil flora, the planktonic cephalodiscid Rotaciurca superbus and the fish Nerepisacanthus denisoni. The excellent preservation of the many eurypterids and other taxa was the possibly result of periodic hypersaline and anoxic conditions owing to the group's position within a shallow inland sea (the Appalachian basin).

The type locality for the Bertie Group is Ridgemount Quarry,^[2] located west of Fort Erie on the Niagara Peninsula of Bertie, Ontario, 6 miles (9.7 km) west of Buffalo, New York,^[3] after which the group is named.^[4] The first author who recognized the group as a separate stratigraphic unit was Chapman in 1884.^[3] In more recent years, the unit has been elevated to group status.^[5][6]

The Bertie Group forms the bedrock in a narrow band extending from Fort Erie, west of Buffalo, New York, through Hagersville, New Hamburg, Harriston, and Walkerton to Southampton on Lake Huron.^[7] The group consists of medium- to massive-bedded aphanitic brown to grey, laminated, bituminous and burrowed dolomites,^[8] with minor thin-bedded shaly dolomites.^[9]

Along the outcrop area between Fort Erie and Hagersville, the thickness varies from 35 to 60 feet (11 to 18 m). It thickens to 495 feet (151 m) in the subsurface. Sanford (1969) used the term Bertie Group from Fort Erie to the vicinity of Hagersville and the term Bass Islands Formation north and west of Hagersville. The group is correlated with the Bass Islands Formation of Michigan. Bertie Group dolomite is quarried for crushed stone at Fort Erie, Port Colborne, Dunnville, Cayuga, and Hagersville.

The Bertie Group is the uppermost unit in the Cayugan Series and forms part of the Tippecanoe II sequence.^[10] At its type locality, the group is subdivided into several formations.^[3] In central New York, the Group is subdivided into the Fiddlers Green Dolomite, Forge Hollow Shale, and Oxbow Dolomite members, from oldest to youngest.^[3] Here, the Bertie Group is overlain by the Honeoye and Chrysler formations. In New York, the Onondaga Limestone overlies the Bertie Group.^[11] The group is in Ontario conformably overlain by the Middle Devonian Bois Blanc Formation.^[12]

Laterally, the group is equivalent to the Bass Islands Formation and is mapped as a combined stratigraphic unit. Haynes and Parkins (1992) reported that the Bertie Group is progressively cut by the Bass Islands Formation from Dunnville to Hagersville.^[8] In Pennsylvania, the Bertie Group is time-equivalent with the Keyser Formation.^[13]

The Bertie Group Fiddler's Green and Williamsville formations are considered Konservat-Lagerstätten;^[14] units characterized by rare and typically soft-bodied fauna. These formations have produced thousands of fossil eurypterids (sea scorpions) since collecting began in earnest in the mid-20th century.^[15][16] Other fossils from the unit include early scorpion Proscorpius osborni, early flora, and a fossil fish; Nerepisacanthus denisoni. The excellent preservation of the many eurypterids possibly was the result of periodic hypersaline and anoxic conditions.^[17]

Group	Fossils	Member	Image	Notes
Fish	Nerepisacanthus denisoni	Williamsville		[18]
Eurypterids	Acutiramus macrophthalmus	Fiddlers Green Williamsville		[19][20]
	A. cummingsi	Fiddlers Green		[21]
	Buffalopterus pustulosus	Williamsville		[20][22]
	Carcinosoma scorpionis	Oxbow Dolomite		[23]
	Clarkeipterus testudineus	Fiddlers Green		[22][24]
	Dolichopterus herkimerensis	Fiddlers Green		[22][24]
	D. jewetti	Fiddlers Green		[25]
	D. macrocheirus	Williamsville		[20][22]
	D. siluriceps	Fiddlers Green Williamsville		[20][21]
	Erieopterus pustulosus	Fiddlers Green		[21]
	Eurypterus dekayi	Williamsville		[20][26]
	E. laculatus	Fiddlers Green		[27]
	E. lacustris	Williamsville		[26]
	E. remipes	Williamsville		[20][26]
	Eusarcana scorpionis	Williamsville		[20]
	Pterygotus cobbi	Williamsville		[20]
	P. juvensis	Fiddlers Green		[21]
	Erettopterus sp.	Fiddlers Green		[21]
	E. grandis	Fiddlers Green		[21]
	Rhinocarcinosoma sp.	Williamsville		[26]
Chasmataspidid	Diploaspis praecursor	Fiddlers Green		[28]
Planaterga	Bunaia woodwardi	Fiddlers Green		[21]
	Limuloides eriensis	Fiddlers Green		[21]
	Pseudoniscus clarkei, P. roosevelti	Fiddlers Green		[21]
Arachnids	Proscorpius osborni	Fiddlers Green		[29]
Artiopod	Naraoia bertiensis	Williamsville		[30]
Machaeridians	Lepidocoleus reinhardi	Fiddlers Green		[21]
Graptolites	Climacograptus ultimus	Fiddlers Green		[21]
	Palaeodictyota buffaloensis	Fiddlers Green		[21]
	Ascograptus sp.	Fiddlers Green		[21]
	Orthograptus sp.	Fiddlers Green		[21]
Non-graptolite Pterobranch	Rotaciurca superbus	Williamsville		[31]
Crustaceans	Ceratiocaris acuminata, C. maccoyanus, C. praecedens	Williamsville		[32]
	Emmelezoe minuta	Fiddlers Green		[21]
	Gonatocaris sp.	Williamsville		[20]
Cephalopods	Dawsonoceras oconnellae	Fiddlers Green		[21]
	Gomphoceras ruedemanni	Fiddlers Green		[21]
	Mitroceras gebhardi	Fiddlers Green		[21]
	Pristeroceras timidum	Fiddlers Green		[21]
	Trochoceras cf. anderdonense	Fiddlers Green		[21]
	Orthoceras sp.	Fiddlers Green		[21]
	Phragmoceras sp.	Fiddlers Green		[21]
Gastropods	Loxonema bertiense	Fiddlers Green		[21]
	Mesocoelia gregaria	Fiddlers Green		[21]
	Platyceras (Platyostoma) sp.	Fiddlers Green		[21]
Bivalves	"Hercynella" buffaloensis	Fiddlers Green		[21]
	Modiolopsis dubius	Fiddlers Green		[21]
	Goniophora sp.	Fiddlers Green		[21]
	Nuculites sp.	Fiddlers Green		[21]
	Rhytimya sp.	Fiddlers Green		[21]
Ostracods	Eukloedenella umbilicata	Fiddlers Green		[21]
	Leperditia alta, L. scalaris	Fiddlers Green		[21]
	Zygobeyrichia cf. regina	Fiddlers Green		[21]
Polychaeta	Serpulites sp.	Fiddlers Green		[21]
	Spirorbis sp.	Fiddlers Green		[21]
Rhynchonellata	Camarotoechia cf. andrewsi	Fiddlers Green		[21]
	Reticularia (Prosserella) modestoidea	Fiddlers Green		[21]
	Howellella eriensis	Fiddlers Green		[21]
	Whitfieldella sulcata	Fiddlers Green		[21]
	Delthyris sp.	Fiddlers Green		[21]
Edrioasteroidea	Pyrgocystis batheri	Fiddlers Green		[21]
Strophomenata	Schuchertella sp.	Fiddlers Green		[21]
Bryozoans	Hernodia sp.	Fiddlers Green		[21]
	Reptaria sp.	Fiddlers Green		[21]
	Stigmatella sp.	Fiddlers Green		[21]
Lingulata	Lingula semina, L. subtrigona	Fiddlers Green		[21]
	Orbiculoidea cf. numulus	Fiddlers Green		[21]
Scyphozoa	Metaconularia perglabra	Fiddlers Green		[21]
Hydrozoa	Bertratis ciurcae	Williamsville Fiddlers Green		[33]
Anthozoa	Aulocystis sp.	Fiddlers Green		[21]
	?Ceratopora sp.	Fiddlers Green		[21]
Stromatoporoidea	Stromatopora constellata	Fiddlers Green		[21]
Dasycladophyceae	Medusaegraptus graminiformis	Fiddlers Green		[21]
Flora	Inocaulis lesqueureuxi	Williamsville		[34]
	Cooksonia sp.	Williamsville		[35]
	Hostinella silurica	Fiddlers Green		[36]
Cyanobacteria	Morania bertiensis	Fiddlers Green		[21]
	Calithamnopsis silurica	Fiddlers Green		[21]

The Bertie Formation is late Silurian (Pridoli, or Cayugan in the local chronologies).

The Appalachian Foreland basin was formed during the Alleghanian orogeny in the Early to Middle Ordovician. The period of mountain building led to the closure of the Iapetus and Rheic Oceans. Due to tectonic loading, the foreland basin developed in the present-day area north of the Appalachian Mountains.^[37] The late Silurian climate was arid and warm; this, and the restricted and shallow nature of the inland basin, resulted in the deposition of evaporites in the Salina Group, ranging in thickness from 120 to 800 metres (390 to 2,620 ft).^[38] Zones of stromatolites and thrombolites (non-laminated algal mounds) occur in several formations in the Bertie Group,^[39] along with numerous desiccation cracks.^[38] During the Hercynian orogeny in the Devonian, many of the Silurian sediments were eroded to the south in the Appalachians, while north of the mountains the Silurian units were preserved.^[40]

The sediments of the Bertie Group were deposited on the paleosouthern side of the subsiding Algonquin Arch, flanking the northern rim of the Appalachian foreland basin of Laurentia.^[14][41]

The Bertie Group was deposited in a hypersaline marine environment. The stratigraphic sections and the fossil content suggest that the group was deposited in a near-shore marine to lagoonal setting,^[14] and the evaporites and casts of halite pseudomorphs, with sides of up to 30 centimetres (12 in), suggest the environment was far from normal marine; hypersalinity must have prevailed throughout most of the depositional history of the group.^[42] Alternating hypersaline and brackish estuarine conditions have been recorded in the group.^[14] The dolomitization of the group most probably was not primary.^[43]

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• Brett, Carlton E.; Goodman, William M.; Loduca, Steven T.; Tetreaul, Denis (1999), Silurian-Early Devonian sequence stratigraphy, events, and paleoenvironments of western New York and Ontario, Canada (PDF), NYSGA, pp. 1–58, retrieved 2019-03-23
• Burrow, Carole J.; Rudkin, David (2014), "Oldest Near-Complete Acanthodian: The First Vertebrate from the Silurian Bertie Formation Konservat-Lagersta¨tte, Ontario", PLoS ONE, 9 (8): 1–7, Bibcode:2014PLoSO...9j4171B, doi:10.1371/journal.pone.0104171, PMC 4122448, PMID 25093877
• Edwards, D.; Banks, H.P.; Ciurca, S.J.; Laub, R.S. (2004), "New Silurian cooksonias from dolostones of north-eastern North America", Botanical Journal of the Linnean Society, 146 (4): 399–413, doi:10.1111/j.1095-8339.2004.00332.x
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• Hewitt, D.H (1972), Paleozoic Geology of Southern Ontario (PDF), Ontario Division of Mines, pp. 1–19, retrieved 2019-03-23
• Lau, Kimberly (2009), Paleoecology and Paleobiogeography of the New York Appalachian Basin Eurypterids (BSc. thesis) (PDF), Yale University, pp. 1–48, S2CID 14229267, archived from the original (PDF) on 2018-02-28, retrieved 2019-03-23 Archived 2018-02-28 at the Wayback Machine
• Rickard, Lawrence V (1969), Stratigraphy of the Upper Silurian Salina Group New York, Pennsylvania, Ohio, Ontario (PDF), New York State Museum and Science Service, pp. 1–77, retrieved 2019-03-23
• Sun, S.; Brunton, F.R.; Jin, J. (2014), Sequence Stratigraphic Architecture and Bedrock Aquifers of Upper Silurian to Middle Devonian Strata, Southwestern Ontario, Ontario Geological Survey, Open File Report 6300, pp. 1–15, retrieved 2019-03-23
• Swezey, Christopher S (2002), Regional Stratigraphy and Petroleum Systems of the Appalachian Basin, North America (PDF), USGS, p. 1, retrieved 2019-03-23
• Treesh, Michael (1972), Sedimentology and Stratigraphy of the Salina Group (upper Silurian) in East-central New York (PDF), Rensselaer Polytechnic Institute, pp. 1–26, retrieved 2019-03-23
• Vrazo, Matthew B.; Brett, Carlton E.; Ciurca Jr, Samuel J. (2016), "Buried or brined? Eurypterids and evaporites in the Silurian Appalachian basin" (PDF), Palaeogeography, Palaeoclimatology, Palaeoecology, 444: 48–59, Bibcode:2016PPP...444...48V, doi:10.1016/j.palaeo.2015.12.011, retrieved 2019-03-23
• Vrazo, Matthew B.; Trop, Jeffrey M.; Brett, Carlton E. (2014), "A new eurypterid Lagerstätte from the Upper Silurian of Pennsylvania" (PDF), PALAIOS, 29 (8): 431–448, Bibcode:2014Palai..29..431V, doi:10.2110/palo.2014.003, S2CID 30066085, archived from the original (PDF) on 2019-03-09, retrieved 2019-03-23

• The Eurypterida of New York/Volume 1
• The Eurypterida of New York/Volume 2