Print this pageAbstract: Intertidal and Subtidal Stromatolites in Lockport Formation (Middle Silurian) of New York State
Stromatolites are exposed in the laterally contiguous Oak Orchard, Sconondoa, and Ilion Members of the Lockport Formation from Niagara Falls to Utica, New York, a distance of about 200 mi (320 km).
Stromatolites in the Oak Orchard Member near Niagara Falls are present as large mounds and mound complexes up to 13 ft (4 m) thick and extend laterally as much as 290 ft (88 m). A single mound complex is formed from coalesced circular to ellipsoidal domes as large as 15 ft (4.5 m) wide and 4 ft (1.3 m) high. Terminal ends of some mound complexes show algal laminations curving sharply downward, bending back under the mounds with thin-bedded dolomite butting up against the curved end indicating that the mounds stood at least 4 ft (1.3 m) above the sediment surface. Internally the mounds reveal laminated columnar structures alternating between close-linked hemispheroids and discrete hemispheroids that appear ellipsoidal in plan view. Similar stromatolite mounds are forming now from collo orm algal mats in shallow, subtidal areas of Shark Bay, Australia.
Most stromatolites in the Sconondoa and Ilion Members between Rochester and Utica are in the form of stratiform sheets, elongate ridge-rill structures (up to 3 ft or 1 m wide), and discrete elliptical and circular columns (up to 6 in. or 150 cm high). Similar stromatolites, classed as smooth-mat types, are common in the lower intertidal zone of Shark Bay, Australia.
Close similarity of Lockport stromatolites to those forming in Australia, the lack of associated fossil fauna, and the presence of mud cracks and oolites, all suggest that this part of the formation was deposited in a broad, shallow, shelf lagoon (in the west) and intertidal flat (in the east). Water circulation was restricted and salinity was too high for normal marine fauna.
AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA