Bertie Formation
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. The formation comprises dolomites, limestones and shales and reaches a thickness of in the subsurface, while in outcrop the group can be 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 "Proscorpius osborni", the oldest known scorpion, 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).
Q62412
upper Silurian
LOC
Q1062563
Pridoli
Concept
None
Cayugan
UNK
None
Ulsterian
UNK
Q824979
group
Concept
Q2122699
Lagerstätte
LOC
Q1134814
dolomites
Concept
Q23757
limestone
Concept
Q751300
shale
Concept
Q531953
outcrop
Concept
Q18353693
Salina Group
LOC
Q30640024
Bois Blanc Formation
LOC
Q7094487
Onondaga Limestone
LOC
Q2122699
Konservat-Lagerstätten
LOC
Q19436
eurypterid
Concept
Q45305797
Proscorpius osborni
Concept
Q152
fish
Concept
Q6996068
Nerepisacanthus denisoni
MISC
Q568324
anoxic
Concept
Q5535417
Appalachian basin
LOC
Q85746704
Bertie Formation
UNK
part of