Bertie Formation

The Bertie Formation, also called Bertie Limestone and Bertie Dolomite, formerly named as Bertie Group, is a Late Silurian (Pridoli, or Cayugan and Ulsterian in the local chronologies) geologic formation and Lagerstätte in southern Ontario, Canada and western New York State, United States. The formation comprises dolomites, limestones and shales and reaches a thickness of 495 feet (151 m) in the subsurface, while in outcrop the formation can be 60 feet (18 m) thick.

Bertie Formation
Stratigraphic range: Pridoli (Cayugan/Ulsterian)
~422.9–416.0 Ma
TypeGeological formation
Unit ofSalina Group
Sub-unitsFiddlers Green, Scajacagua, Akron, Williamsville & Oxbow Dolomite Members
UnderliesBois Blanc Formation
OverliesCamillus Formation
ThicknessUp to 495 ft (151 m)
Lithology
PrimaryDolomite
OtherShale
Location
Coordinates42.9°N 78.9°W / 42.9; -78.9
Approximate paleocoordinates30.3°S 40.8°W / -30.3; -40.8
RegionOntario
New York
Country Canada
 United States
ExtentAppalachian Basin
Type section
Named forBertie, Ontario
Named byChapman
Year defined1864
Bertie Formation (the United States)
Bertie Formation (New York)

The formation represents the uppermost unit of the Salina Group and the youngest Silurian formation in Ontario. The formation overlies the Camillus Formation and is in Ontario conformably overlain by the Bois Blanc Formation and in New York by the Onondaga Limestone, both dating to the Devonian.

The Bertie Formation is considered a Konservat-Lagerstätte; a formation renowned for the preservation of a unique fauna. The formation has provided many fossils of Silurian eurypterids (sea scorpions) and Proscorpius osborni, the oldest known scorpion, as well as primitive fossil flora and the fish Nerepisacanthus denisoni. The excellent preservation of the many eurypterids possibly was the result of periodic hypersaline and anoxic conditions.

Description

The type locality for the Bertie Formation is in the Ridgemount Quarry,[1] located west of Fort Erie on the Niagara Peninsula of Bertie, Ontario, 6 miles (9.7 km) west of Buffalo, New York,[2] after which the formation is named.[3] The first author who recognized the formation as a separate stratigraphic unit was Chapman in 1884.[2] In older literature and other authors maintain this definition,[4][5] the formation was named Bertie Group.[6]

Geographic extent

The Bertie Formation 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 formation 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 Formation from Fort Erie to the vicinity of Hagersville and the term Bass Islands Formation north and west of Hagersville. The formation is correlated with the Bass Islands Formation of Michigan. The Bertie Dolomite is quarried for crushed stone at Fort Erie, Port Colborne, Dunnville, Cayuga, and Hagersville. It is the uppermost formation of the Silurian System in Ontario,[9] dating to the Pridoli epoch, or in the local chronology Cayugan or Murderian.[10]

Stratigraphy

The Bertie Formation is the uppermost unit of the Salina Group and forms part of the Tippecanoe II sequence.[11] At its type locality, the formation is subdivided into the Falkirk Dolomite, Scajaquada Shale, and Williamsville Dolomite members.[2] In central New York, the formation is subdivided into the Fiddlers Green Dolomite, Forge Hollow Shale, and Oxbow Dolomite members, from oldest to youngest.[2] Here, the Bertie Formation is overlain by the Cobleskill Dolomite,[12] also named Akron Member.[13] In New York, the Onondaga Limestone overlies the Bertie Formation.[14] The formation is in Ontario conformably overlain by the Middle Devonian Bois Blanc Formation.[15]

Laterally, the formation is equivalent to the Bass Islands Formation and is mapped as a combined stratigraphic unit. Haynes and Parkins (1992) reported that the Bertie Formation is progressively cut by the Bass Islands Formation from Dunnville to Hagersville.[8] In Pennsylvania, the formation is time-equivalent with the Keyser Formation.[16]

Fossils
Many Eurypterus fossils were found in the formation
The fish Nerepisacanthus denisoni is the only vertebrate found in the Bertie Formation

The Bertie Formation is considered a Konservat-Lagerstätte;[17] a formation characterized by a rich and well-conserved fauna. The formation has provided more than 800 fossil eurypterids (sea scorpions).[18][19] Of just Eurypterus lacustris almost 600 specimens were found in the Williamsville Member.[20] Other fossils from the formation are Proscorpius osborni, the oldest known scorpion, flora and a fossil fish; Nerepisacanthus denisoni. The excellent preservation of the many eurypterids possibly was the result of periodic hypersaline and anoxic conditions.[21]

GroupFossilsMemberImageNotes
FishNerepisacanthus denisoniWilliamsville
[10]
EurypteridsAcutiramus macrophthalmusFiddlers Green
Williamsville
[22][23]
Buffalopterus pustulosusWilliamsville
[23][24]
Carcinosoma scorpionisOxbow Dolomite
[25]
Clarkeipterus testudineusFiddlers Green
[24][26]
Dolichopterus herkimerensisFiddlers Green
[24][26]
D. jewettiFiddlers Green[27]
D. macrocheirusWilliamsville[23][24]
D. siluricepsFiddlers Green
Williamsville		[23][28]
Erieopterus pustulosusFiddlers Green[28]
Eurypterus dekayiWilliamsville
[23][20]
E. laculatusFiddlers Green[29]
E. lacustrisWilliamsville
[20]
E. remipesWilliamsville
[23][20]
Eusarcana scorpionisWilliamsville[23]
Pterygotus cobbiWilliamsville[23]
P. cummingsiFiddlers Green
[28]
P. grandisFiddlers Green[28]
P. juvensisFiddlers Green[28]
P. macrophthalmusFiddlers Green
Williamsville		[30]
Erettopterus sp.Fiddlers Green
[28]
Rhinocarcinosoma sp.Williamsville
[20]
PlanatergaBunaia woodwardiFiddlers Green[28]
Limuloides eriensisFiddlers Green[28]
Pseudoniscus clarkei, P. rooseveltiFiddlers Green[28]
ArachnidsPalaeophonus osborniFiddlers Green
[31]
Proscorpius osborniFiddlers Green
[32]
MachaeridiansLepidocoleus reinhardiFiddlers Green[28]
GraptolitesClimacograptus ultimusFiddlers Green[28]
Palaeodictyota buffaloensisFiddlers Green[28]
Ascograptus sp.Fiddlers Green[28]
Orthograptus sp.Fiddlers Green[28]
CrustaceansCeratiocaris aculeatus, C. maccoyanaFiddlers Green[28]
Emmelezoe minutaFiddlers Green[28]
Gonatocaris sp.Williamsville[23]
CephalopodsDawsonoceras oconnellaeFiddlers Green[28]
Gomphoceras ruedemanniFiddlers Green
[28]
Mitroceras gebhardiFiddlers Green[28]
Pristeroceras timidumFiddlers Green[28]
Trochoceras cf. anderdonenseFiddlers Green[28]
Orthoceras sp.Fiddlers Green
[28]
Phragmoceras sp.Fiddlers Green[28]
GastropodsLoxonema bertienseFiddlers Green[28]
Mesocoelia gregariaFiddlers Green[28]
Platyceras (Platyostoma) sp.Fiddlers Green[28]
Bivalves"Hercynella" buffaloensisFiddlers Green[28]
Modiolopsis dubiusFiddlers Green[28]
Goniophora sp.Fiddlers Green[28]
Nuculites sp.Fiddlers Green[28]
Rhytimya sp.Fiddlers Green[28]
OstracodsEukloedenella umbilicataFiddlers Green[28]
Leperditia alta, L. scalarisFiddlers Green[28]
Zygobeyrichia cf. reginaFiddlers Green[28]
PolychaetaSerpulites sp.Fiddlers Green[28]
Spirorbis sp.Fiddlers Green[28]
RhynchonellataCamarotoechia cf. andrewsiFiddlers Green[28]
Reticularia (Prosserella) modestoideaFiddlers Green[28]
Howellella eriensisFiddlers Green[28]
Whitfieldella sulcataFiddlers Green[28]
Delthyris sp.Fiddlers Green[28]
EdrioasteroideaPyrgocystis batheriFiddlers Green[28]
StrophomenataSchuchertella sp.Fiddlers Green[28]
BryozoansHernodia sp.Fiddlers Green[28]
Reptaria sp.Fiddlers Green[28]
Stigmatella sp.Fiddlers Green[28]
LingulataLingula semina, L. subtrigonaFiddlers Green[28]
Orbiculoidea cf. numulusFiddlers Green[28]
ScyphozoaMetaconularia perglabraFiddlers Green[28]
AnthozoaAulocystis sp.Fiddlers Green[28]
?Ceratopora sp.Fiddlers Green[28]
StromatoporoideaStromatopora constellataFiddlers Green[28]
DasycladophyceaeMedusaegraptus graminiformisFiddlers Green[28]
FloraInocaulis lesqueureuxiWilliamsville[33]
Cooksonia sp.Williamsville
[34]
Hostinella siluricaFiddlers Green[35]
CyanobacteriaMorania bertiensisFiddlers Green[28]
Calithamnopsis siluricaFiddlers Green[28]

Age
Early Silurian (440 Ma)
Early Devonian (400 Ma)

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

Interpretations of depositional environments
See also: Geology of the Appalachians

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.[36] The Late Silurian was represented by the deposition of evaporites, underlying the Bertie Formation in the Salina Group, ranging in thickness from 120 to 800 metres (390 to 2,620 ft). The evaporites and related dolomites and limestones were deposited in a warm, arid climate shallow water restricted basin.[37] Zones of stromatolites and thrombolites (non-laminated algal mounds) occur at several horizons in the Fiddlers Green member of the formation,[38] as well as desiccation cracks exist in the Bertie Formation.[37] 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.[39]

The sediments of the Bertie Formation were deposited on the paleosouthern side of the subsiding Algonquin Arch, flanking the northern rim of the Appalachian foreland basin of Laurentia.[17][40]

The Bertie Formation was deposited in a hypersaline marine environment. The stratigraphic sections and the fossil content suggest that the formation was deposited in a near-shore marine to lagoonal setting,[17] 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 formation.[31] Alternating hypersaline and brackish estuarine conditions have been recorded in the formation.[17] The dolomitization of the formation most probably was not primary.[41]

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See also

References
  1. Ridgemount Quarry South at Fossilworks.org
  2. Rickard, 1969, p.15
  3. Sun et al., 2014, p.7
  4. Vrazo et al., 2014, p.431
  5. Edwards et al., 2004, p.399
  6. Bertie Group at Fossilworks.org
  7. Hewitt, 1972, p.19
  8. Armstrong & Dodge, 2007, p.8
  9. Hewitt, 1972, p.10
  10. Burrow & Rudkin, 2014, p.2
  11. Swezey, 2002
  12. Treesh, 1972, p.10
  13. Lau, 2009, p.12
  14. Rickard, 1969, p.4
  15. Hewitt, 1972, p.11
  16. Rickard, 1969, p.5
  17. Burrow & Rudkin, 2014, p.1
  18. Lau, 2009, p.10
  19. Vrazo et al., 2016, p.53
  20. Lau, 2009, p.21
  21. Vrazo et al., 2016, p.58
  22. Eurypterid-Associated Biota of the Fiddlers Green Member, Herkimer Co., New York at Fossilworks.org
  23. Eurypterid-Associated Biota of the Williamsville Member, Buffalo, New York at Fossilworks.org
  24. Lau, 2009, p.22
  25. Heard's Gypsum Quarry at Fossilworks.org
  26. Cranes Corners at Fossilworks.org
  27. Jerusalem Hill at Fossilworks.org
  28. Bertie at Fossilworks.org
  29. Eurypterids of the Fiddlers Green Member, Morganville, New York at Fossilworks.org
  30. Lau, 2009, p.20
  31. Forge Hollow, Waterville at Fossilworks.org
  32. Passage Gulf at Fossilworks.org
  33. Edwards et al., 2004, p.405
  34. Edwards et al., 2004, p.401
  35. Bertie Formation at Fossilworks.org
  36. Ettensohn, 2008, p.107
  37. Vrazo et al., 2016, p.49
  38. Brett et al., 1999, p.10
  39. Ettensohn, 2008, p.136
  40. Lau, 2009, p.24
  41. Vrazo et al., 2016, p.56

Bibliography
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