Bertie Formation

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, 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 (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. At its type locality, the group is subdivided into several formations. 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 (1992) reported that the Bertie Group is progressively cut by the Bass Islands Formation from Dunnville to Hagersville. == Fossils ==

The Bertie Group Fiddler's Green and Williamsville formations are considered Konservat-Lagerstätten; 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. == 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. 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 . Zones of stromatolites and thrombolites (non-laminated algal mounds) occur in several formations in the Bertie Group, along with numerous desiccation cracks. 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. 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, Alternating hypersaline and brackish estuarine conditions have been recorded in the group. == See also ==