Bertie Formation


The Bertie Group or Bertie Limestone, also referred to as the Bertie Dolomite and the Bertie Formation, is an upper Silurian 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 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.

Description

The type locality for the Bertie Group is Ridgemount Quarry, located west of Fort Erie on the Niagara Peninsula of Bertie, Ontario, west of Buffalo, New York, after which the group is named. The first author who recognized the group as a separate stratigraphic unit was Chapman in 1884. In more recent years, the unit has been elevated to group status.

Geographic extent

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. The group consists of medium- to massive-bedded aphanitic brown to grey, laminated, bituminous and burrowed dolomites, with minor thin-bedded shaly dolomites.
Along the outcrop area between Fort Erie and Hagersville, the thickness varies from. It thickens to in the subsurface. Sanford 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.

Stratigraphy

The Bertie Group is the uppermost unit in the Cayugan Series and forms part of the Tippecanoe II sequence. At its type locality, the group is subdivided into several formations. In central New York, the Group is subdivided into the Fiddlers Green Dolomite, Forge Hollow Shale, and Oxbow Dolomite members, from oldest to youngest. Here, the Bertie Group is overlain by the Honeoye and Chrysler formations. In New York, the Onondaga Limestone overlies the Bertie Group. The group is in Ontario conformably overlain by the Middle Devonian Bois Blanc Formation.
Laterally, the group is equivalent to the Bass Islands Formation and is mapped as a combined stratigraphic unit. Haynes and Parkins reported that the
Bertie Group is progressively cut by the Bass Islands Formation from Dunnville to Hagersville. In Pennsylvania, the Bertie Group is time-equivalent with the Keyser Formation.

Fossils

The Bertie Group Fiddler's Green and Williamsville formations are considered Konservat-Lagerstätten; units characterized by rare and typically soft-bodied fauna. These formations have produced thousands of fossil eurypterids since collecting began in earnest in the mid-20th century. 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.
GroupFossilsMemberImageNotes
FishNerepisacanthus denisoniWilliamsville
EurypteridsAcutiramus macrophthalmusFiddlers Green
Williamsville
EurypteridsA. cummingsiFiddlers Green
EurypteridsBuffalopterus pustulosusWilliamsville
EurypteridsCarcinosoma scorpionisOxbow Dolomite
EurypteridsClarkeipterus testudineusFiddlers Green
EurypteridsDolichopterus herkimerensisFiddlers Green
EurypteridsD. jewettiFiddlers Green
EurypteridsD. macrocheirusWilliamsville
EurypteridsD. siluricepsFiddlers Green
Williamsville
EurypteridsErieopterus pustulosusFiddlers Green
EurypteridsEurypterus dekayiWilliamsville
EurypteridsE. laculatusFiddlers Green
EurypteridsE. lacustrisWilliamsville
EurypteridsE. remipesWilliamsville
EurypteridsEusarcana scorpionisWilliamsville
EurypteridsPterygotus cobbiWilliamsville
EurypteridsP. juvensisFiddlers Green
EurypteridsErettopterus sp.Fiddlers Green
EurypteridsE. grandisFiddlers Green
EurypteridsRhinocarcinosoma sp.Williamsville
ChasmataspididDiploaspis praecursorFiddlers Green
PlanatergaBunaia woodwardiFiddlers Green
PlanatergaLimuloides eriensisFiddlers Green
PlanatergaPseudoniscus clarkei, P. rooseveltiFiddlers Green
ArachnidsProscorpius osborniFiddlers Green
ArtiopodNaraoia bertiensisWilliamsville
MachaeridiansLepidocoleus reinhardiFiddlers Green
GraptolitesClimacograptus ultimusFiddlers Green
GraptolitesPalaeodictyota buffaloensisFiddlers Green
GraptolitesAscograptus sp.Fiddlers Green
GraptolitesOrthograptus sp.Fiddlers Green
Non-graptolite PterobranchRotaciurca superbusWilliamsville
CrustaceansCeratiocaris acuminata, C. maccoyanus, C. praecedensWilliamsville
CrustaceansEmmelezoe minutaFiddlers Green
CrustaceansGonatocaris sp.Williamsville
CephalopodsDawsonoceras oconnellaeFiddlers Green
CephalopodsGomphoceras ruedemanniFiddlers Green
CephalopodsMitroceras gebhardiFiddlers Green
CephalopodsPristeroceras timidumFiddlers Green
CephalopodsTrochoceras cf. anderdonenseFiddlers Green
CephalopodsOrthoceras sp.Fiddlers Green
CephalopodsPhragmoceras sp.Fiddlers Green
GastropodsLoxonema bertienseFiddlers Green
GastropodsMesocoelia gregariaFiddlers Green
GastropodsPlatyceras sp.Fiddlers Green
Bivalves"Hercynella" buffaloensisFiddlers Green
BivalvesModiolopsis dubiusFiddlers Green
BivalvesGoniophora sp.Fiddlers Green
BivalvesNuculites sp.Fiddlers Green
BivalvesRhytimya sp.Fiddlers Green
OstracodsEukloedenella umbilicataFiddlers Green
OstracodsLeperditia alta, L. scalarisFiddlers Green
OstracodsZygobeyrichia cf. reginaFiddlers Green
PolychaetaSerpulites sp.Fiddlers Green
PolychaetaSpirorbis sp.Fiddlers Green
RhynchonellataCamarotoechia cf. andrewsiFiddlers Green
RhynchonellataReticularia modestoideaFiddlers Green
RhynchonellataHowellella eriensisFiddlers Green
RhynchonellataWhitfieldella sulcataFiddlers Green
RhynchonellataDelthyris sp.Fiddlers Green
EdrioasteroideaPyrgocystis batheriFiddlers Green
StrophomenataSchuchertella sp.Fiddlers Green
BryozoansHernodia sp.Fiddlers Green
BryozoansReptaria sp.Fiddlers Green
BryozoansStigmatella sp.Fiddlers Green
LingulataLingula semina, L. subtrigonaFiddlers Green
LingulataOrbiculoidea cf. numulusFiddlers Green
ScyphozoaMetaconularia perglabraFiddlers Green
HydrozoaBertratis ciurcaeWilliamsville
Fiddlers Green
AnthozoaAulocystis sp.Fiddlers Green
Anthozoa?Ceratopora sp.Fiddlers Green
StromatoporoideaStromatopora constellataFiddlers Green
DasycladophyceaeMedusaegraptus graminiformisFiddlers Green
FloraInocaulis lesqueureuxiWilliamsville
FloraCooksonia sp.Williamsville
FloraHostinella siluricaFiddlers Green
CyanobacteriaMorania bertiensisFiddlers Green
CyanobacteriaCalithamnopsis siluricaFiddlers Green