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. 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 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).
Description The type locality for the Bertie Group is Ridgemount Quarry,Ridgemount Quarry South at Fossilworks.org located west of Fort Erie on the Niagara Peninsula of Bertie, Ontario, west of Buffalo, New York, after which the group is named.Sun et al., 2014, p.7 The first author who recognized the group as a separate stratigraphic unit was Chapman in 1884.Vrazo et al., 2017, p.5 In more recent years, the unit has been elevated to group status.Vrazo et al., 2014, p.431Edwards et al., 2004, p.399
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.Hewitt, 1972, p.19 The group consists of medium- to massive-bedded aphanitic brown to grey, laminated, bituminous and burrowed dolomites,Armstrong & Dodge, 2007, p.8 with minor thin-bedded shaly dolomites.Hewitt, 1972, p.10
Along the outcrop area between Fort Erie and Hagersville, the thickness varies from . It thickens to 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.
Stratigraphy The Bertie Group is the uppermost unit in the Cayugan Series and forms part of the Tippecanoe II sequence.Swezey, 2002 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.Rickard, 1969, p.4 The group is in Ontario conformably overlain by the Middle Devonian Bois Blanc Formation.Hewitt, 1972, p.11
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. In Pennsylvania, the Bertie Group is time-equivalent with the Keyser Formation.Rickard, 1969, p.5
Paleobiota
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 (sea scorpions) since collecting began in earnest in the mid-20th century.Lau, 2009, p.10Vrazo et al., 2016, p.53 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.Vrazo et al., 2016, p.58
Arthropods GenusSpeciesMember/FormationNotesImageAcutiramus A. macrophthalmus Fiddlers Green Phelps Member/Ellicott Creek Breccia Williamsville A. cummingsi Williamsville Buffalopterus B. pustulosus Williamsville Fiddlers Green Phelps Member/Ellicott Creek Breccia BunaiaB. woodwardi WilliamsvilleA Offacolid Chelicerate.CarcinosomaC. scorpionis WilliamsvilleRenamed as CruinnopterusCeratiocarisC. acuminata WilliamsvilleC. maccoyanus UnknownC. praecedens UnknownCruinnopterus C. scorpionis Williamsville A Carcinosomatid Eurypterid originally described under the genus Carcinosoma. Clarkeipterus C. testudineus Fiddlers Green Phelps Member/Ellicott Creek Breccia Williamsville A Dolichopterid Eurypterid originally described as Dolichopterus? testudineus DiploaspisD. praecursor Fiddlers Green Phelps MemberA Chasmataspidid Chelicerate.Dolichopterus D. herkimerensis Fiddlers Green Moran Corner A Dolichopterid originally referred to D.? testudineus from Cranes Corners. D. jewetti Fiddlers Green Ellicott Creek Breccia/Phelps Member A Dolichopterid Eurypterid. D. macrocheirus Williamsville A Dolichopterid Eurypterid. D. siluriceps Fiddlers GreenWilliamsville Considered a Junior Synonym of C. macrocheirus D. sp Moran Corner Akron/Cobleskil Williamsville Ellicott Creek Breccia/PhelpsEmmelezoeE. minnuta UnknownEmmelezoe has been regarded as a junior synonym of Ceratiocaris.Erieopterus E. pustulosus Eurypterus E. dekayi Williamsville Moran Corner E. laculatus Cobleskill E. lacustris Williamsville Moran Corner Akron/Cobleskill Fiddlers Green Phelps Member/Ellicott Creek Breccia E. remipes Fiddlers Green Phelps Member/Ellicott Creek Breccia Vernon Member Eusarcana E. scorpionis Williamsville GonatocarisG. sp.Limuloides?L. eriensis Williamsville likely a Bunodid but its fragmentary nature makes generic identification difficult.Naraoia N. bertiensis WilliamsvilleN. cf. bertiensis Fiddlers Green Phelps MemberProscorpiusP. osborni Fiddlers Green Phelps Member/Ellicott Creek BrecciaPseudoniscusP. clarkei Fiddlers GreenP. roosevelti UnknownPterygotus P. cobbi Williamsville Fiddlers Green Phelps Member/Ellicott Creek Breccia Falkirk? P. juvensis Fiddlers GreenReinterpreted as juveniles of A. macrophthalmusErettopterus E. sp. Fiddlers Green E. grandis Fiddlers Green Rhinocarcinosoma R. sp. Williamsville OstracodsEukloedenella umbilicataFiddlers GreenLeperditia alta, L. scalarisFiddlers GreenZygobeyrichia cf. reginaFiddlers Green
Acanthodians Genus Species Member/Formation Notes Image Nerepisacanthus N. denisoni Williamsville The only vertebrate found in the Bertie GroupBurrow & Rudkin, 2014, p.2
Annelids Group Fossils Member/Formation Notes Image Machaeridians Lepidocoleus reinhardi Fiddlers Green Serpulitessp.
Molluscs GenusSpeciesMember/FormationNotesImage Dawsonoceras D. oconnellae Fiddlers Green Gomphoceras Gomphoceras ruedemanni Fiddlers Green Mitroceras M. gebhardi Fiddlers Green Pristeroceras P. timidum Unknown (Buffalo, NY) Trochoceras T. cf. anderdonense Fiddlers Green Orthoceras O. sp. Fiddlers Green O. vicinusUnknownPhragmoceras Phragmoceras sp. Fiddlers Green LoxonemaLoxonema bertienseFiddlers GreenMesocoelia gregariaFiddlers GreenPlatyceras (Platyostoma) sp.Fiddlers GreenHercynella"H." buffaloensisFiddlers GreenModiolopsis dubiusFiddlers GreenGoniophora sp.Fiddlers GreenNuculites sp.Fiddlers GreenRhytimyaR. buffaloensisFiddlers Green
Cnidarians GenusSpeciesMember/FormationNotesImage Bertratis B. ciurcae Fiddlers Green Phelps Member Williamsville
Pterobranchs Group Fossils Member/Formation Notes Climacograptus C. ultimus Unknown (Buffalo, NY) Bertie at Fossilworks.orgPalaeodictyota P. buffaloensis Fiddlers Green Ascograptus A. sp. Fiddlers Green Orthograptus O. sp. Unknown Rotaciurca R. superbus Williamsville
Polychaeta Serpulites sp. Fiddlers Green Spirorbis sp. Fiddlers Green Rhynchonellata Camarotoechia cf. andrewsi Fiddlers Green Reticularia (Prosserella) modestoidea Fiddlers Green Howellella eriensis Fiddlers Green Whitfieldella sulcata Fiddlers Green Delthyris Delthyris sp. Fiddlers Green Delthyris eriensis Edrioasteroidea Pyrgocystis batheri Fiddlers Green Strophomenata Schuchertella sp. Fiddlers Green Bryozoans Hernodia sp. Fiddlers Green Reptaria sp. Fiddlers Green Stigmatella sp. Fiddlers Green Lingulata Lingula semina, L. subtrigona Fiddlers Green Orbiculoidea cf. numulus Fiddlers Green Orbiculoidea bertiensis Scyphozoa Metaconularia perglabraUnknown (Buffalo, NY) Anthozoa Aulocystis sp. Fiddlers Green ?Ceratopora sp. Fiddlers Green Stromatoporoidea Stromatopora constellata Fiddlers Green
Flora GenusSpeciesMember/FormationNotesImageCooksoniaCooksonia cf. hemisphaericaFiddlers Green Phelps Member Cooksonia sp. Williamsville Fiddlers Green Phelps Member HostinellaH. siluricaH. sp.Williamsville Fiddlers Green Phelps MemberInocaulisI. lesqueureuxi WilliamsvilleDasycladophyceaeMedusaegraptus graminiformisFiddlers Green Morania M. bertiensis Unknown Calithamnopsis silurica Fiddlers Green
Age The Bertie Formation is late Silurian (Pridoli, or Cayugan in the local chronologies).
Interpretations of depositional environments
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.Ettensohn, 2008, p.107 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 .Vrazo et al., 2016, p.49 Zones of stromatolites and thrombolites (non-laminated algal mounds) occur in several formations in the Bertie Group,Brett et al., 1999, p.10 along with numerous desiccation cracks. 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.Ettensohn, 2008, p.136
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.Burrow & Rudkin, 2014, p.1Lau, 2009, p.24
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, and the evaporites and casts of halite pseudomorphs, with sides of up to , suggest the environment was far from normal marine; hypersalinity must have prevailed throughout most of the depositional history of the group.Forge Hollow, Waterville at Fossilworks.org Alternating hypersaline and brackish estuarine conditions have been recorded in the group. The dolomitization of the group most probably was not primary.Vrazo et al., 2016, p.56
See also
List of fossiliferous stratigraphic units in New York List of fossiliferous stratigraphic units in Ontario Tonoloway Formation, contemporaneous formation of Pennsylvania, Maryland, Virginia and West Virginia Tymochtee Dolomite, contemporaneous dolomite formation of Ohio Catavi Formation, contemporaneous fossiliferous formation of Bolivia Peel Sound Formation, contemporaneous fossiliferous formation of Nunavut, Canada Stony Mountain Formation, Late Ordovician Lagerstätte of Manitoba, Canada