Bertie Formation

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Bertie Group
Stratigraphic range: Pridoli (Cayugan/Ulsterian)
~422.9–416.0 Ma
TypeGeological group
Unit ofCayugan Series
Sub-unitsAkron, Cobleskill, Fiddlers Green, Fort Hill, Moran Corner, Scajaquada, Williamsville, Oatka, Oxbow formations
UnderliesBois Blanc Formation
OverliesSalina Group
ThicknessUp to 495 ft (151 m)
Coordinates42°54′N 78°54′W / 42.9°N 78.9°W / 42.9; -78.9Coordinates: 42°54′N 78°54′W / 42.9°N 78.9°W / 42.9; -78.9
Approximate paleocoordinates30°18′S 40°48′W / 30.3°S 40.8°W / -30.3; -40.8
New York
Country Canada
 United States
ExtentAppalachian Basin
Type section
Named forBertie, Ontario
Named byChapman
Year defined1864
Bertie Formation is located in the United States
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation (the United States)
Bertie Formation is located in New York
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation
Bertie Formation (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 and Ulsterian age in the local chronologies) 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, 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 groups 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]

Geographic extent[edit]

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 Groupfrom 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]


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

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
Eurypterids Acutiramus macrophthalmus Fiddlers Green
20201231 Acutiramus macrophthalmus.png
Buffalopterus pustulosus Williamsville
The Eurypterida of New York plate 23.jpg
Carcinosoma scorpionis Oxbow Dolomite
Carcinosoma scorpioides 2.png
Clarkeipterus testudineus Fiddlers Green
The Eurypterida of New York plate 57.jpg
Dolichopterus herkimerensis Fiddlers Green
The Eurypterida of New York plate 40.jpg
D. jewetti Fiddlers Green [24]
D. macrocheirus Williamsville [20][21]
D. siluriceps Fiddlers Green
Erieopterus pustulosus Fiddlers Green [25]
Eurypterus dekayi Williamsville
Eurypterus dekayi Exhibit Museum of Natural History.JPG
E. laculatus Fiddlers Green [27]
E. lacustris Williamsville
E. remipes Williamsville
Eurypterus remipes (fossil sea scorption) Silurian; New York State.jpg
Eusarcana scorpionis Williamsville [20]
Pterygotus cobbi Williamsville [20]
P. cummingsi Fiddlers Green
Pterygotus, sea scorpion, Silurian, Fiddlers Green Formation, Phelps Member, Lang's Quarry, Herkimer County, New York, USA - Houston Museum of Natural Science - DSC01993.JPG
P. grandis Fiddlers Green [25]
P. juvensis Fiddlers Green [25]
P. macrophthalmus Fiddlers Green
Erettopterus sp. Fiddlers Green
Erettopterus osiliensis.jpg
Rhinocarcinosoma sp. Williamsville
Planaterga Bunaia woodwardi Fiddlers Green [25]
Limuloides eriensis Fiddlers Green [25]
Pseudoniscus clarkei, P. roosevelti Fiddlers Green
20200921 Pseudoniscus roosevelti.png
Arachnids Palaeophonus osborni Fiddlers Green
Scorpiones - Palaeophonus nuncius.JPG
Proscorpius osborni Fiddlers Green
The Eurypterida of New York plate 88.jpg
Machaeridians Lepidocoleus reinhardi Fiddlers Green [25]
Graptolites Climacograptus ultimus Fiddlers Green [25]
Palaeodictyota buffaloensis Fiddlers Green [25]
Ascograptus sp. Fiddlers Green [25]
Orthograptus sp. Fiddlers Green [25]
Crustaceans Ceratiocaris aculeatus, C. maccoyana Fiddlers Green [25]
Emmelezoe minuta Fiddlers Green [25]
Gonatocaris sp. Williamsville [20]
Cephalopods Dawsonoceras oconnellae Fiddlers Green [25]
Gomphoceras ruedemanni Fiddlers Green
Gomphoceras characters.PNG
Mitroceras gebhardi Fiddlers Green [25]
Pristeroceras timidum Fiddlers Green [25]
Trochoceras cf. anderdonense Fiddlers Green [25]
Orthoceras sp. Fiddlers Green
Orthoceras BW.jpg
Phragmoceras sp. Fiddlers Green [25]
Gastropods Loxonema bertiense Fiddlers Green [25]
Mesocoelia gregaria Fiddlers Green [25]
Platyceras (Platyostoma) sp. Fiddlers Green [25]
Bivalves "Hercynella" buffaloensis Fiddlers Green [25]
Modiolopsis dubius Fiddlers Green [25]
Goniophora sp. Fiddlers Green [25]
Nuculites sp. Fiddlers Green [25]
Rhytimya sp. Fiddlers Green [25]
Ostracods Eukloedenella umbilicata Fiddlers Green [25]
Leperditia alta, L. scalaris Fiddlers Green [25]
Zygobeyrichia cf. regina Fiddlers Green [25]
Polychaeta Serpulites sp. Fiddlers Green [25]
Spirorbis sp. Fiddlers Green [25]
Rhynchonellata Camarotoechia cf. andrewsi Fiddlers Green [25]
Reticularia (Prosserella) modestoidea Fiddlers Green [25]
Howellella eriensis Fiddlers Green [25]
Whitfieldella sulcata Fiddlers Green [25]
Delthyris sp. Fiddlers Green [25]
Edrioasteroidea Pyrgocystis batheri Fiddlers Green [25]
Strophomenata Schuchertella sp. Fiddlers Green [25]
Bryozoans Hernodia sp. Fiddlers Green [25]
Reptaria sp. Fiddlers Green [25]
Stigmatella sp. Fiddlers Green [25]
Lingulata Lingula semina, L. subtrigona Fiddlers Green [25]
Orbiculoidea cf. numulus Fiddlers Green [25]
Scyphozoa Metaconularia perglabra Fiddlers Green [25]
Anthozoa Aulocystis sp. Fiddlers Green [25]
?Ceratopora sp. Fiddlers Green [25]
Stromatoporoidea Stromatopora constellata Fiddlers Green [25]
Dasycladophyceae Medusaegraptus graminiformis Fiddlers Green [25]
Flora Inocaulis lesqueureuxi Williamsville [31]
Cooksonia sp. Williamsville
Cooksonia sp. - MUSE.jpg
Hostinella silurica Fiddlers Green [33]
Cyanobacteria Morania bertiensis Fiddlers Green [25]
Calithamnopsis silurica Fiddlers Green [25]


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

Interpretations of depositional environments[edit]

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.[34] 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).[35] Zones of stromatolites and thrombolites (non-laminated algal mounds) occur in several formations in the Bertie Group,[36] along with numerous desiccation cracks.[35] 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.[37]

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][38]

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.[29] Alternating hypersaline and brackish estuarine conditions have been recorded in the group.[14] The dolomitization of the group most probably was not primary.[39]

See also[edit]


  1. ^ "National Geologic Map Database".
  2. ^ Ridgemount Quarry South at
  3. ^ a b c d Vrazo et al., 2017, p.5
  4. ^ Sun et al., 2014, p.7
  5. ^ Vrazo et al., 2014, p.431
  6. ^ Edwards et al., 2004, p.399
  7. ^ Hewitt, 1972, p.19
  8. ^ a b Armstrong & Dodge, 2007, p.8
  9. ^ Hewitt, 1972, p.10
  10. ^ Swezey, 2002
  11. ^ Rickard, 1969, p.4
  12. ^ Hewitt, 1972, p.11
  13. ^ Rickard, 1969, p.5
  14. ^ a b c d Burrow & Rudkin, 2014, p.1
  15. ^ Lau, 2009, p.10
  16. ^ Vrazo et al., 2016, p.53
  17. ^ Vrazo et al., 2016, p.58
  18. ^ Burrow & Rudkin, 2014, p.2
  19. ^ Eurypterid-Associated Biota of the Fiddlers Green Member, Herkimer Co., New York at
  20. ^ a b c d e f g h i Eurypterid-Associated Biota of the Williamsville Member, Buffalo, New York at
  21. ^ a b c d Lau, 2009, p.22
  22. ^ Heard's Gypsum Quarry at
  23. ^ a b Cranes Corners at
  24. ^ Jerusalem Hill at
  25. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc Bertie at
  26. ^ a b c d Lau, 2009, p.21
  27. ^ Eurypterids of the Fiddlers Green Member, Morganville, New York at
  28. ^ Lau, 2009, p.20
  29. ^ a b Forge Hollow, Waterville at
  30. ^ Passage Gulf at
  31. ^ Edwards et al., 2004, p.405
  32. ^ Edwards et al., 2004, p.401
  33. ^ Bertie Formation at
  34. ^ Ettensohn, 2008, p.107
  35. ^ a b Vrazo et al., 2016, p.49
  36. ^ Brett et al., 1999, p.10
  37. ^ Ettensohn, 2008, p.136
  38. ^ Lau, 2009, p.24
  39. ^ Vrazo et al., 2016, p.56


External links[edit]